Elucidation of the enhanced ferromagnetic origin in Mn-doped ZnO nanocrystals embedded into a SiO2 matrix

International Nuclear Information System (INIS)

Lee, Sejoon; Lee, Youngmin; Kim, Deukyoung

2013-01-01

The origin of the enhanced room temperature ferromagnetism in Mn-doped ZnO (ZnO:Mn) nanocrystals is investigated. ZnO:Mn nanocrystals, which were fabricated by using a laser irradiation method with a 248-nm KrF excimer laser, exhibited two-times increase in the spontaneous magnetization (∼0.4 emu/cm 3 at 300 K) compared to the ZnO:Mn thin film (∼0.2 emu/cm 3 at 300 K). The increased exchange integral of J 1 /k B = 51.6 K in ZnO:Mn nanocrystals, in comparison with the ZnO:Mn thin film (J 1 /k B = 46.9 K), is indicative of the enhanced ferromagnetic exchange interaction. This is attributed to the large number of acceptor defects in the SiO 2 -capped ZnO:Mn nanocrystals. Namely, the holes bound to the acceptor defects form microscopic bound-magnetic-polarons with Mn ions; hence, long-range ferromagnetic coupling is enhanced. The results suggest that ferromagnetism in ZnO-based dilute magnetic semiconductors can be controlled by modulating the density of native point defects, which can be chemically and thermodynamically modified during the material synthesis or preparation.

Microstructure and magnetic properties of MFe2O4 (M = Co, Ni, and Mn) ferrite nanocrystals prepared using colloid mill and hydrothermal method

Science.gov (United States)

Wang, Wei; Ding, Zui; Zhao, Xiruo; Wu, Sizhu; Li, Feng; Yue, Ming; Liu, J. Ping

2015-05-01

Three kinds of spinel ferrite nanocrystals, MFe2O4 (M = Co, Ni, and Mn), are synthesized using colloid mill and hydrothermal method. During the synthesis process, a rapid mixing and reduction of cations with sodium borohydride (NaBH4) take place in a colloid mill then through a hydrothermal reaction, a slow oxidation and structural transformation of the spinel ferrite nanocrystals occur. The phase purity and crystal lattice parameters are estimated by X-ray diffraction studies. Scanning electron microscopy and transmission electron microscopy images show the morphology and particle size of the as-synthesized ferrite nanocrystals. Raman spectrum reveals active phonon modes at room temperature, and a shifting of the modes implies cation redistribution in the tetrahedral and octahedral sites. Magnetic measurements show that all the obtained samples exhibit higher saturation magnetization (Ms). Meanwhile, experiments demonstrate that the hydrothermal reaction time has significant effects on microstructure, morphologies, and magnetic properties of the as-synthesized ferrite nanocrystals.

Controllable synthesis, magnetic and biocompatible properties of Fe3O4 and α-Fe2O3 nanocrystals

International Nuclear Information System (INIS)

Zhou, Xi; Shi, Yanfeng; Ren, Lei; Bao, Shixiong; Han, Yu; Wu, Shichao; Zhang, Honggang; Zhong, Lubin; Zhang, Qiqing

2012-01-01

Iron oxide nanocrystals (NCs) with a series of well-controlled morphologies (octahedron, rod, wire, cube and plate) and compositions (Fe 3 O 4 and α-Fe 2 O 3 ) were synthesized via a facile hydrothermal process. The morphological and compositional control of various iron oxide NCs was based on the regulations of precursor thermolysis kinetics and surfactants. The obtained samples were characterized by XRD, SEM, TEM, SQUID and cytotoxicity test. These as-prepared iron oxide NCs showed excellent magnetic properties and good biocompatibility, paving the way for their high-efficiency bio-separation and bio-detection applications. - Graphical Abstract: Schematic illustration for the formation of iron oxide NCs (Fe 3 O 4 and α-Fe 2 O 3 ) with different controlled morphologies and compositions. Highlights: ► Iron oxide NCs with a series of well-controlled morphologies (octahedron, rod, wire, cube, and plate) and compositions (Fe 3 O 4 and α-Fe 2 O 3 ) were synthesized via a facile hydrothermal method. ► The mechanism of the morphological and compositional control process is directly related to precursor thermolysis kinetics and surfactants. ► These iron oxide NCs exhibited excellent magnetic response and good biocompatibility, which should have great applications in the cell separation and biodetection.

Tuning the morphology, stability and photocatalytic activity of TiO2 nanocrystal colloids by tungsten doping

International Nuclear Information System (INIS)

Xu, Haiping; Liao, Jianhua; Yuan, Shuai; Zhao, Yin; Zhang, Meihong; Wang, Zhuyi; Shi, Liyi

2014-01-01

Graphical abstract: - Highlights: • W 6+ -doped TiO 2 nanocrystal colloids were prepared by hydrothermal methods. • The properties of TiO 2 nanocrystal colloids can be tuned by tungsten doping. • W 6+ -doped TiO 2 nanocrystal colloids show higher stability and dispersity. • W 6+ -doped TiO 2 nanocrystal colloids show higher photocatalytic activity. - Abstract: The effects of tungsten doping on the morphology, stability and photocatalytic activity of TiO 2 nanocrystal colloids were investigated. The nanostructure, chemical state of Ti, W, O, and the properties of tungsten doped TiO 2 samples were investigated carefully by TEM, XRD, XPS, UV–vis, PL and photocatalytic degradation experiments. And the structure–activity relationship was discussed according to the analysis and measurement results. The analysis results reveal that the morphology, zeta potential and photocatalytic activity of TiO 2 nanocrystals can be easily tuned by changing the tungsten doping concentration. The tungsten doped TiO 2 colloid combines the characters of high dispersity and high photocatalytic activity

Sub-2 nm SnO2 nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties

International Nuclear Information System (INIS)

Zhang Hui; Du Ning; Chen Bindi; Cui Tianfeng; Yang Deren

2008-01-01

A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO 2 nanocrystals, in which NaBH 4 is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO 2 nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO 2 nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO 2 nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO 2 (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO 2 nanocrystals has been preliminary presented

Preparation of Sb2S3 nanocrystals modified TiO2 dendritic structure with nanotubes for hybrid solar cell

Science.gov (United States)

Li, Yingpin; Wei, Yanan; Feng, Kangning; Hao, Yanzhong; Pei, Juan; Sun, Bao

2018-06-01

Array of TiO2 dendritic structure with nanotubes was constructed on transparent conductive fluorine-doped tin oxide glass (FTO) with titanium potassium oxalate as titanium source. Sb2S3 nanocrystals were successfully deposited on the TiO2 substrate via spin-coating method. Furthermore, TiO2/Sb2S3/P3HT/PEDOT:PSS composite film was prepared by successively spin-coating P3HT and PEDOT:PSS on TiO2/Sb2S3. It was demonstrated that the modification of TiO2 dendritic structure with Sb2S3 could enhance the light absorption in the visible region. The champion hybrid solar cell assembled by TiO2/Sb2S3/P3HT/PEDOT:PSS composite film achieved a power conversion efficiency (PCE) of 1.56%.

Colloidal nanocrystal ZnO- and TiO2-modified electrodes sensitized with chlorophyll a and carotenoids: a photoelectrochemical study

International Nuclear Information System (INIS)

Petrella, Andrea; Cosma, Pinalysa; Lucia Curri, M.; Rochira, Sergio; Agostiano, Angela

2011-01-01

Heterostructures formed of films of organic-capped ZnO and TiO 2 nanocrystals (both with the size of ca. 6 nm) and photosynthetic pigments were prepared and characterized. The surface of optically transparent electrodes (Indium Tin Oxide) was modified with nanocrystals and prepared by colloidal synthetic routes. The nanostructured electrodes were sensitized by a mixture of chlorophyll a and carotenoids. The characterization of the hybrid structures, carried out by means of steady-state optical measurements, demonstrated such class of dyes able to extend the photoresponse of the large band-gap semiconductors. The charge-transfer processes between the components of the heterojunction were investigated, and photoelectrochemical measurements taken on the sensitized ZnO and TiO 2 nanocrystals electrodes elucidated the photoactivity of the heterojunctions as a function of the dyes and of the red–ox mediator used in solution. The effect of methyl viologen as different red–ox mediator was also evaluated in order to show its effect on the heterojunction photoactivity. The overall results contributed to describe the photoelectrochemical potential of the investigated heterojunctions, highlighting a higher response of the dye-sensitized ZnO nanocrystals, and then provided the TiO 2 -modified counterparts.

Facile synthesis of ultrafine Co3O4 nanocrystals embedded carbon matrices with specific skeletal structures as efficient non-enzymatic glucose sensors

International Nuclear Information System (INIS)

Li, Mian; Han, Ce; Zhang, Yufan; Bo, Xiangjie; Guo, Liping

2015-01-01

Highlights: • Novel hyperfine Co 3 O 4 nanocrystals decorated porous carbon matrixes. • Facile synthesis without use of any harmful dispersing reagents or surfactants. • High dispersion degree of Co 3 O 4 nanocrystals and excellent e − transport rates. • A large current sensitivity of 955.9 μA cm −2 mM −1 toward glucose. • Excellent anti-interference and stability for glucose detection. - Abstract: A facile, effective, and environmentally friendly method has been adopted for the first time to prepare tiny Co 3 O 4 nanocrystals embedded carbon matrices without using surfactants, harmful organic reagents or extreme conditions. Structural characterizations reveal that the size-controlled Co 3 O 4 nanocrystals are uniformly dispersed on carbon matrices. Electrochemical measurements reveal that Co 3 O 4 -ordered mesoporous carbon (OMC) can more efficiently catalyze glucose oxidation and acquire better detection parameters compared with those for the Co 3 O 4 -macroporous carbon, Co 3 O 4 -reduced graphene oxide, and free Co 3 O 4 nanoparticles (NPs) (such as: the large sensitivity (2597.5 μA cm −2 mM −1 between 0 and 0.8 mM and 955.9 μA cm −2 mM −1 between 0.9 and 7.0 mM), fast response time, wide linear range, good stability, and surpassingly selective capability to electroactive molecules or Cl − ). Such excellent performances are attributed to the synergistic effect of the following three factors: (1) the high catalytic sites provided by the uniformly dispersed and size-controlled Co 3 O 4 nanocrystals embedded on OMC; (2) the excellent reactant transport efficiency caused by the abundant mesoporous structures of OMC matrix: (3) the improved electron transport in high electron transfer rate (confinement of the Co 3 O 4 NPs in nanoscale spaces ensured intimate contact between Co 3 O 4 nanocrystals and the conducting OMC matrix). The superior catalytic activity and selectivity make Co 3 O 4 -OMC very promising for application in direct

Influences of Different Preparation Conditions on Catalytic Activity of Ag2O-Co3O4/γ-Al2O3 for Hydrogenation of Coal Pyrolysis

Directory of Open Access Journals (Sweden)

Lei Zhang

2014-01-01

Full Text Available A series of catalysts of Ag2O-Co3O4/γ-Al2O3 was prepared by equivalent volume impregnation method. The effects of the metal loading, calcination time, and calcination temperatures of Ag and Co, respectively, on the catalytic activity were investigated. The optimum preparing condition of Ag2O-Co3O4/γ-Al2O3 was decided, and then the influence of different preparation conditions on catalytic activity of Ag2O-Co3O4/γ-Al2O3 was analyzed. The results showed the following: (1 at the same preparation condition, when silver loading was 8%, the Ag2O-Co3O4/γ-Al2O3 showed higher catalyst activity, (2 the catalyst activity had obviously improved when the cobalt loading was 8%, while it was weaker at loadings 5% and 10%, (3 the catalyst activity was influenced by different calcination temperatures of silver, but the influences were not marked, (4 the catalyst activity can be influenced by calcination time of silver, (5 different calcination times of cobalt can also influence the catalyst activity of Ag2O-Co3O4/γ-Al2O3, and (6 the best preparation conditions of the Ag2O-Co3O4/γ-Al2O3 were silver loading of 8%, calcination temperature of silver of 450°C, and calcinations time of silver of 4 h, while at the same time the cobalt loading was 8%, the calcination temperature of cobalt was 450°C, and calcination time of cobalt was 4 h.

Nonstoichiometric Zn Ferrite and ZnFe2O4/Fe2O3 Composite Spheres: Preparation, Magnetic Properties, and Chromium Removal

Science.gov (United States)

Hang, Chun-Liang; Yang, Li-Xia; Sun, Chang-Mei; Liang, Ying

2018-03-01

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe2O4/Fe2O3 composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe2O4/Fe2O3 composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe2O4/Fe2O3 composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe2O4/Fe2O3 composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe2O3,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr6+ adsorption property than ZnFe2O4/Fe2O3 composites.

Microstructure and magnetic properties of MFe{sub 2}O{sub 4} (M = Co, Ni, and Mn) ferrite nanocrystals prepared using colloid mill and hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Wang, Wei, E-mail: wangwei@mail.buct.edu.cn; Ding, Zui; Zhao, Xiruo [State Key Laboratory of Chemical Resource Engineering and School of Science, Beijing University of Chemical Technology, Beijing 100029 (China); Beijing Key Laboratory of Environmentally Harmful Chemical Analysis, Beijing University of Chemical Technology, Beijing 100029 (China); Wu, Sizhu [State Key Laboratory of Organic–Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Li, Feng [State Key Laboratory of Chemical Resource Engineering and School of Science, Beijing University of Chemical Technology, Beijing 100029 (China); Yue, Ming [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100022 (China); Liu, J. Ping [Department of Physics, University of Texas at Arlington, Arlington, Texas 76019 (United States)

2015-05-07

Three kinds of spinel ferrite nanocrystals, MFe{sub 2}O{sub 4} (M = Co, Ni, and Mn), are synthesized using colloid mill and hydrothermal method. During the synthesis process, a rapid mixing and reduction of cations with sodium borohydride (NaBH{sub 4}) take place in a colloid mill then through a hydrothermal reaction, a slow oxidation and structural transformation of the spinel ferrite nanocrystals occur. The phase purity and crystal lattice parameters are estimated by X-ray diffraction studies. Scanning electron microscopy and transmission electron microscopy images show the morphology and particle size of the as-synthesized ferrite nanocrystals. Raman spectrum reveals active phonon modes at room temperature, and a shifting of the modes implies cation redistribution in the tetrahedral and octahedral sites. Magnetic measurements show that all the obtained samples exhibit higher saturation magnetization (M{sub s}). Meanwhile, experiments demonstrate that the hydrothermal reaction time has significant effects on microstructure, morphologies, and magnetic properties of the as-synthesized ferrite nanocrystals.

Electrochemically active nanocomposites of Li4Ti5O12 2D nanosheets and SnO2 0D nanocrystals with improved electrode performance

International Nuclear Information System (INIS)

Han, Song Yi; Kim, In Young; Lee, Sang-Hyup; Hwang, Seong-Ju

2012-01-01

Electrochemically active nanocomposites consisting of Li 4 Ti 5 O 12 2D nanosheets and SnO 2 0D nanocrystals are synthesized by the crystal growth of tin dioxide on the surface of 2D nanostructured lithium titanate. According to powder X-ray diffraction and electron microscopic analyses, the rutile-structured SnO 2 nanocrystals are stabilized on the surface of spinel-structured Li 4 Ti 5 O 12 2D nanosheets. The homogeneous hybridization of tin dioxide with lithium titanate is confirmed by elemental mapping analysis. Ti K-edge X-ray absorption near-edge structure and Sn 3d X-ray photoelectron spectroscopy indicate the stabilization of tetravalent titanium ions in the spinel lattice of Li 4 Ti 5 O 12 and the formation of SnO 2 phase with tetravalent Sn oxidation state. The electrochemical measurements clearly demonstrate the promising functionality of the present nanocomposites as anode for lithium secondary batteries. The Li 4 Ti 5 O 12 –SnO 2 nanocomposites show larger discharge capacity and better cyclability than do the uncomposited Li 4 Ti 5 O 12 and SnO 2 phases, indicating the synergistic effect of nanocomposite formation on the electrode performance of Li 4 Ti 5 O 12 and SnO 2 . The present experimental findings underscore the validity of 2D nanostructured lithium titanate as a useful platform for the stabilization of nanocrystalline electrode materials and also for the improvement of their functionality.

Self-assembly of Fe3O4 nanocrystal-clusters into cauliflower-like architectures: Synthesis and characterization

International Nuclear Information System (INIS)

Zhu Luping; Liao Guihong; Bing Naici; Wang Linlin; Xie Hongyong

2011-01-01

Large-scale cauliflower-like Fe 3 O 4 architectures consist of well-assembled magnetite nanocrystal clusters have been synthesized by a simple solvothermal process. The as-synthesized Fe 3 O 4 samples were characterized by XRD, XPS, FT-IR, SEM, TEM, etc. The results show that the samples exhibit cauliflower-like hierarchical microstructures. The influences of synthesis parameters on the morphology of the samples were experimentally investigated. Magnetic properties of the Fe 3 O 4 cauliflower-like hierarchical microstructures have been detected by VSM at room temperature, showing a relatively low saturation magnetization of 65 emu/g and an enhanced coercive force of 247 Oe. - Graphical Abstract: Cauliflower-like Fe 3 O 4 architectures consist of well-assembled magnetite nanocrystal clusters have been synthesized by a simple solvothermal process, using FeCl 3 .6H 2 O and EDA as the starting materials. Highlights: → Cauliflower-like Fe 3 O 4 architectures were successfully prepared by a simple solvothermal route. → The cauliflower-like Fe 3 O 4 architectures have a size in the range of 200-300 nm. → They show a low saturation magnetization of 65 emu/g and an enhanced coercive force of 247 Oe. → These Fe 3 O 4 architectures may have potential applications in catalysis and biological fields.

Nanostructural and magnetic studies of virtually monodispersed NiFe2O4 nanocrystals synthesized by a liquid–solid-solution assisted hydrothermal route

International Nuclear Information System (INIS)

Li Xinghua; Tan Guoguo; Chen Wei; Zhou Baofan; Xue Desheng; Peng Yong; Li, Fashen; Mellors, Nigel J.

2012-01-01

This study presents a comprehensively and systematically structural, chemical and magnetic characterization of ∼9.5 nm virtually monodispersed nickel ferrite (NiFe 2 O 4 ) nanoparticles prepared using a modified liquid–solid-solution (LSS) assisted hydrothermal method. Lattice-resolution scanning transmission electron microscope (STEM) and converged beam electron diffraction pattern (CBED) techniques are adapted to characterize the detailed spatial morphology and crystal structure of individual NiFe 2 O 4 particles at nano scale for the first time. It is found that each NiFe 2 O 4 nanoparticle is single crystal with an fcc structure. The morphology investigation reveals that the prepared NiFe 2 O 4 nanoparticles of which the surfaces are decorated by oleic acid are dispersed individually in hexane. The chemical composition of nickel ferrite nanoparticles is measured to be 1:2 atomic ratio of Ni:Fe, indicating a pure NiFe 2 O 4 composition. Magnetic measurements reveal that the as-synthesized nanocrystals displayed superparamagnetic behavior at room temperature and were ferromagnetic at 10 K. The nanoscale characterization and magnetic investigation of monodispersed NiFe 2 O 4 nanoparticles should be significant for its potential applications in the field of biomedicine and magnetic fluid using them as magnetic materials.

Single-layer and double-layer microwave absorbers based on Co{sub 67}Ni{sub 33} microspheres and Ni{sub 0.6}Zn{sub 0.4}Fe{sub 2}O{sub 4} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Wang, Min [Engineering Technology Research Center of Magnetic Materials of Anhui Province, School of Physics & Materials Science, Anhui University, Hefei 230601 (China); Wang, Zhongzhu, E-mail: wangzz@ahu.edu.cn [Engineering Technology Research Center of Magnetic Materials of Anhui Province, School of Physics & Materials Science, Anhui University, Hefei 230601 (China); Wang, Peihong; Liao, Yanlin [Engineering Technology Research Center of Magnetic Materials of Anhui Province, School of Physics & Materials Science, Anhui University, Hefei 230601 (China); Bi, Hong [School of Chemistry and Chemical Engineering, Anhui University, Hefei 230601 (China)

2017-03-01

Co{sub 67}Ni{sub 33} microspheres and Ni{sub 0.6}Zn{sub 0.4}Fe{sub 2}O{sub 4} nanocrystals were synthesized by hydrothermal method. The complex permeability and complex permittivity of the as-prepared powders dispersing in wax (60 wt% powder) were measured using a vector network analyzer in 2–18 GHz frequency range. The calculated microwave absorption of single-layer and double-layer absorbers based on Co{sub 67}Ni{sub 33} microspheres and Ni{sub 0.6}Zn{sub 0.4}Fe{sub 2}O{sub 4} nanocrystals were analyzed in 2–18 GHz frequency range. The results show that the Ni{sub 0.6}Zn{sub 0.4}Fe{sub 2}O{sub 4}nanocrystals with the relatively low permittivity and Co{sub 67}Ni{sub 33} microspheres with the relatively high dielectric loss and magnetic loss can be used as proper matching layer and excellent absorption layer, respectively. The double-layer absorber with a coating thickness of 2.1 mm exhibits a maximum reflection loss of −43.8 dB as well as a bandwidth (reflection loss less than −10 dB) of 5 GHz. Moreover, their absorption peak and the absorption intensity can be adjusted easily through changing the stacking order and each layer thickness. - Highlights: • Ni-Zn ferrite nanocrystals can use as matching layer in double-layer absorbers. • Co{sub 67}Ni{sub 33} microspheres with high dielectric loss can use as absorption layer. • Double-layer absorbers exhibits an excellent microwave absorption in 2–18 GHz.

Preparation of NiFe binary alloy nanocrystals for nonvolatile memory applications

Institute of Scientific and Technical Information of China (English)

无

2010-01-01

In this work,an idea which applies binary alloy nanocrystal floating gate to nonvolatile memory application was introduced.The relationship between binary alloy’s work function and its composition was discussed theoretically.A nanocrystal floating gate structure with NiFe nanocrystals embedded in SiO2 dielectric layers was fabricated by magnetron sputtering.The micro-structure and composition deviation of the prepared NiFe nanocrystals were also investigated by TEM and EDS.

Paramagnetic behavior of Co doped TiO{sub 2} nanocrystals controlled by self-purification mechanism

Energy Technology Data Exchange (ETDEWEB)

Anitha, B. [Centre for Nanoscience and Nanotechnology, University of Kerala, Kariavattom, Thiruvananthapuram 695 581 (India); Khadar, M. Abdul, E-mail: mabdulkhadar@rediffmail.com [Centre for Nanoscience and Nanotechnology, University of Kerala, Kariavattom, Thiruvananthapuram 695 581 (India); Banerjee, Alok [UGC-DAE Consortium for Scientific Research (CSR), Khandwa Road, Indore 452 001 (India)

2016-07-15

Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO{sub 2} doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO{sub 2} along with weak intensity peaks of Co{sub 3}O{sub 4} for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO{sub 2} matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO{sub 2} nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co{sup 2+} ions and an increased presence of Co{sub 3}O{sub 4} phase near the surface of the TiO{sub 2} nanocrystals due to self-purification mechanism. - Graphical abstract: Variation of the intensity ratios of XRD peaks as a function of atomic ratio of Co. Inset: variation of structure factor for (101) reflection as a function of atomic ratio of Co. Display Omitted - Highlights: • Co doped TiO{sub 2} nanocrystals were synthesized by peroxide gel method. • HRTEM images showed Co doped TiO{sub 2} nanocrystals to be rod-like. • EPR spectra showed +2 oxidation states for Co in the samples. • Co doped TiO{sub 2} nanocrystals showed paramagnetic behavior.

Unusual broadening of the NIR luminescence of Er{sup 3+}-doped Nb{sub 2}O{sub 5} nanocrystals embedded in silica host: Preparation and their structural and spectroscopic study for photonics applications

Energy Technology Data Exchange (ETDEWEB)

Aquino, Felipe Thomaz; Pereira, Rafael R. [Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, CEP 14040-901 Ribeirão Preto, SP (Brazil); Ferrari, Jefferson Luis [Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, CEP 14040-901 Ribeirão Preto, SP (Brazil); Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João Del Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, 36301-160 São João Del Rei, MG (Brazil); Ribeiro, Sidney José Lima [Laboratório de Materiais Fotônicos, Instituto de Química, UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Ferrier, Alban; Goldner, Philippe [Chimie-Paristech, Laboratoire de Chimie de la Matière Condensée de Paris, CNRS-UMR 7574, UPMC Univ Paris 06, 11 Rue Pierre et Marie Curie, 75005 Paris (France); and others

2014-10-15

This paper reports on the preparation of novel sol-gel erbium-doped SiO{sub 2}-based nanocomposites embedded with Nb{sub 2}O{sub 5} nanocrystals fabricated using a bottom-up method and describes their structural, morphological, and luminescence characterization. To prepare the glass ceramics, we synthesized xerogels containing Si/Nb molar ratios of 90:10 up to 50:50 at room temperature, followed by annealing at 900, 1000, or 1100 °C for 10 h. We identified crystallization accompanying host densification in all the nanocomposites with orthorhombic (T-phase) or monoclinic (M-phase) Nb{sub 2}O{sub 5} nanocrystals dispersed in the amorphous SiO{sub 2} phase, depending on the niobium content and annealing temperature. A high-intensity broadband emission in the near-infrared region assigned to the {sup 4}I{sub 13/2} → {sup 4}I{sub 15/2} transition of the Er{sup 3+} ions was registered for all the nanocomposites. The shape and the bandwidth changed with the Nb{sub 2}O{sub 5} crystalline phase, with values achieving up to 81 nm. Er{sup 3+} ions were located mainly in Nb{sub 2}O{sub 5}-rich regions, and the complex structure of the different Nb{sub 2}O{sub 5} polymorphs accounted for the broadening in the emission spectra. The materials containing the T-phase, displayed higher luminescence intensity, longer {sup 4}I{sub 13/2} lifetime and broader bandwidth. In conclusion, these nanostructured materials are potential candidates for photonic applications like optical amplifiers and WDM devices operating in the S, C, and L telecommunication bands. - Highlights: • Rare earth doped Nb{sub 2}O{sub 5} nanocrystals prepared from a bottom-up approach. • Unusual broadband NIR emission in glass ceramic system. • Structural features tuning the luminescence properties. • Potential as optical amplifiers and WDM devices. • Photonic devices operating in the S, C, and L telecommunication.

Design of a novel dual Z-scheme photocatalytic system composited of Ag{sub 2}O modified Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets

Energy Technology Data Exchange (ETDEWEB)

Li, Mengyan; Liu, Hui, E-mail: liuhui@sust.edu.cn; Liu, Tingting; Qin, Yangxiao

2017-02-15

A novel dual Z-scheme photocatalytic system composited of Ag{sub 2}O nanocrystals modified Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets were successfully fabricated. In which, the Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets have been firstly prepared by a simple hydrothermal method, subsequently the as-prepared products were modified with Ag{sub 2}O nanocrystals through a sonochemical depositing process in order to build a novel dual Z-scheme photocatalytic system. The samples were carefully characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflectance spectra (UV–vis DRS), and Brunauer-Emmett-Teller (BET). The photocatalytic activity toward degradation of Rhodamine B (Rh B) aqueous solution under stimulated solar light was investigated. The experimental results showed this new dual Z-scheme photocatalytic system possess an enhanced photocatalytic degradation activity compared to that similar surface heterojunction photocatalysts composed of Ti{sup 3+} self doped TiO{sub 2} nanocrystals with individual exposed (001) and (101) facets. This novel photocatalytic system presents a high charge-separation efficiency and strong redox ability. This study will help us to better understand the photocatalytic mechanism of semiconductor photocatalysts with exposed different facets, and provide a new insight into the design and fabrication of advanced photocatalytic materials. - Highlights: •A novel dual Z-scheme system was built by Ag{sub 2}O and facet exposed TiO{sub 2} nanocrystals. •The individual TiO{sub 2} nanocrystals exposed (001) and (101) facets respectively. •Ag{sub 2}O coupled with Ti{sup 3+} self doped TiO{sub 2} nanocrystals through a sonochemical process. •The as-prepared sample possesses a super photocatalytic activity.

Semiconductor nanocrystals formed in SiO2 by ion implantation

International Nuclear Information System (INIS)

Zhu, J.G.; White, C.W.; Budai, J.D.; Withrow, S.P.; Chen, Y.

1994-11-01

Nanocrystals of group IV (Si, Ge and SiGe), III-V (GaAs), and II-VI (CdSe) semiconductor materials have been fabricated inside SiO 2 by ion implantation and subsequent thermal annealing. The microstructure of these nanocrystalline semiconductor materials has been studied by transmission electron microscopy (TEM). The nanocrystals form in near-spherical shape with random crystal orientations in amorphous SiO 2 . Extensive studies on the nanocrystal size distributions have been carried out for the Ge nanocrystals by changing the implantation doses and the annealing temperatures. Remarkable roughening of the nanocrystals occurs when the annealing temperature is raised over the melting temperature of the implanted semiconductor material. Strong red photoluminescence peaked around 1.67 eV has been achieved in samples with Si nanocrystals in SiO 2

Effect of calcination temperature on the H{sub 2}O{sub 2} decomposition activity of nano-crystalline Co{sub 3}O{sub 4} prepared by combustion method

Energy Technology Data Exchange (ETDEWEB)

Makhlouf, M.Th. [Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut (Egypt); Abu-Zied, B.M., E-mail: babuzied@aun.edu.eg [Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut (Egypt); Mansoure, T.H. [Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut (Egypt)

2013-06-01

Cobalt oxide nano-particles were prepared by combustion method using urea as a combustion fuel. The effects of calcination temperature, 350–1000 °C, on the physicochemical, surface and catalytic properties of the prepared Co{sub 3}O{sub 4} nano-particles were studied. The products were characterized by thermal analyses (TGA and DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. Textural features of the obtained catalysts were investigated using nitrogen adsorption at −196 °C. X-ray diffraction confirmed that the resulting oxide was pure single-crystalline Co{sub 3}O{sub 4} nano-particles. Transmission electron microscopy indicating that, the crystallite size of Co{sub 3}O{sub 4} nano-crystals was in the range of 8–34 nm. The catalytic activities of prepared nano-crystalline Co{sub 3}O{sub 4} catalysts were tested for H{sub 2}O{sub 2} decomposition at 35–50 °C temperature range. Experimental results revealed that, the catalytic decomposition of H{sub 2}O{sub 2} decreases with increasing the calcination temperature. This was correlated with the observed particle size increase accompanying the calcination temperature rise.

Facile synthesis of ultrafine Co{sub 3}O{sub 4} nanocrystals embedded carbon matrices with specific skeletal structures as efficient non-enzymatic glucose sensors

Energy Technology Data Exchange (ETDEWEB)

Li, Mian; Han, Ce; Zhang, Yufan; Bo, Xiangjie, E-mail: baoxj133@nenu.edu.cn; Guo, Liping, E-mail: guolp078@nenu.edu.cn

2015-02-25

Highlights: • Novel hyperfine Co{sub 3}O{sub 4} nanocrystals decorated porous carbon matrixes. • Facile synthesis without use of any harmful dispersing reagents or surfactants. • High dispersion degree of Co{sub 3}O{sub 4} nanocrystals and excellent e{sup −} transport rates. • A large current sensitivity of 955.9 μA cm{sup −2} mM{sup −1} toward glucose. • Excellent anti-interference and stability for glucose detection. - Abstract: A facile, effective, and environmentally friendly method has been adopted for the first time to prepare tiny Co{sub 3}O{sub 4} nanocrystals embedded carbon matrices without using surfactants, harmful organic reagents or extreme conditions. Structural characterizations reveal that the size-controlled Co{sub 3}O{sub 4} nanocrystals are uniformly dispersed on carbon matrices. Electrochemical measurements reveal that Co{sub 3}O{sub 4}-ordered mesoporous carbon (OMC) can more efficiently catalyze glucose oxidation and acquire better detection parameters compared with those for the Co{sub 3}O{sub 4}-macroporous carbon, Co{sub 3}O{sub 4}-reduced graphene oxide, and free Co{sub 3}O{sub 4} nanoparticles (NPs) (such as: the large sensitivity (2597.5 μA cm{sup −2} mM{sup −1} between 0 and 0.8 mM and 955.9 μA cm{sup −2} mM{sup −1} between 0.9 and 7.0 mM), fast response time, wide linear range, good stability, and surpassingly selective capability to electroactive molecules or Cl{sup −}). Such excellent performances are attributed to the synergistic effect of the following three factors: (1) the high catalytic sites provided by the uniformly dispersed and size-controlled Co{sub 3}O{sub 4} nanocrystals embedded on OMC; (2) the excellent reactant transport efficiency caused by the abundant mesoporous structures of OMC matrix: (3) the improved electron transport in high electron transfer rate (confinement of the Co{sub 3}O{sub 4} NPs in nanoscale spaces ensured intimate contact between Co{sub 3}O{sub 4} nanocrystals and the

Influence of TiO2 Nanocrystals Fabricating Dye-Sensitized Solar Cell on the Absorption Spectra of N719 Sensitizer

Directory of Open Access Journals (Sweden)

Puhong Wen

2012-01-01

Full Text Available The absorption spectra of N719 sensitizer anchored on the films prepared by TiO2 nanocrystals with different morphology and size were investigated for improving the performance of dye-sensitized solar cell (DSC. We find that the morphology and size of TiO2 nanocrystals can affect the UV-vis and FT-IR spectra of the sensitizer anchored on their surfaces. In particular, the low-energy metal-to-ligand charge-transfer transitions (MLCT band in the visible absorption spectra of N719 is strongly affected, and locations of these MLCT bands revealed larger differences. The results indicate that there is a red shift of MLCT band in the spectra obtained by using TiO2 nanocrystals with long morphology and large size compared to that in solution. And it produced a larger red-shift on the MLCT band after TiO2 nanocrystals with small size mixed with some long nanocrystals. Accordingly, the utilization rate to visible light is increased. This is a reason why the DSC prepared by using such film as a photoelectrode has better performance than before mixing.

Preparation and structural, optical, magnetic, and electrical characterization of Mn{sup 2+}/Co{sup 2+}/Cu{sup 2+} doped hematite nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Srikrishna Ramya, S.I., E-mail: ramyaskr@gmail.com; Mahadevan, C.K.

2014-03-15

Pure and Mn{sup 2+} / Co{sup 2+} / Cu{sup 2+} doped (1 and 2 at.%) spherical hematite (α-Fe{sub 2}O{sub 3})nanocrystals have been synthesized by a simple solvothermal method using a domestic microwave oven. XRD measurements confirm that all the seven nanocrystals prepared consist of nanocrystalline hematite phase without any other phases. The energy dispersive X-ray and Fourier transform infrared spectral analyses confirm the phase purity of the nanocrystals prepared. TEM analysis shows the average particle sizes within the range 33–51 nm. Optical absorption measurements indicate that all the three dopants enhance the optical transmittance and reflectance. A red shift is observed in the bandgap energy values estimated from optical absorption and reflectance spectra. Results of magnetic measurements made at room temperature using a vibrating sample magnetometer indicate significant changes in the magnetic properties (coercivity, retentivity and saturationmagnetization) due to doping. Results of magnetic measurements indicate significant changes in the magnetic properties. Results of AC electrical measurements made at various temperatures in the range 40–130 °C and frequencies in the range 100 Hz –1 MHz indicate low dielectric constants and AC electrical conductivities and consequently show the occurrence of nanoconfined states. -- Graphical abstract: The indexed X-ray diffraction (XRD) patterns of all the seven nanocrystals indicate the rhombohedral structure of hematite (JCPDS card No.13-0534). No impurity phase like oxides of Mn or Co or Cu was detected above equipment limit. The average crystallite (grain) sizes estimated using the Scherrer's formula. Highlights: • Pure and Mn/Co/Cu-doped hematite nanocrystals have been prepared. • The method adopted for the preparation is simple, economical and scalable. • Prepared nanocrystals are spherical in shape with good crystallinity and phase purity. • Mn/Co/Cu-doping enhances the optical

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

Science.gov (United States)

Wang, Guangshuo; Ma, Yingying; Li, Meixia; Cui, Guohua; Che, Hongwei; Mu, Jingbo; Zhang, Xiaoliang; Tong, Yu; Dong, Xufeng

2017-01-01

In this study, magnesium ferrite (MgFe2O4) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe2O4 nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe2O4 nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe2O4 nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe2O4 nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.

Surface structure of alpha-Fe sub 2 O sub 3 nanocrystal observed by O K-edge X-ray absorption spectroscopy

CERN Document Server

Zhang, J; Ibrahim, K; Abbas, M I; Ju, X

2003-01-01

X-ray absorption near edge structure (XANES) spectra is used as a probe of surface structure of alpha-Fe sub 2 O sub 3 nanocrystal, prepared by sol-gel method. We present O K-edge XANES of alpha-Fe sub 2 O sub 3 in nanocrystal and bulk by total electron yield at the photoemission station of Beijing Synchrotron Radiation Facility. The spectrum of alpha-Fe sub 2 O sub 3 shows a splitting of the pre-edge structure, which is interpreted as two subsets of Fe 3d t sub 2 sub g and e sub g orbitals in oxygen octahedral (O sub h) crystal field, and is also sensitive to long-range order effects. However, no distinguishable splitting of the pre-edge peak of nanocrystal alpha-Fe sub 2 O sub 3 is observed. This suggests that there exists the distorted octahedral coordination around Fe sites and also the long-range disorder due to the surface as compared with bulk alpha-Fe sub 2 O sub 3.

Preparation, characterization and catalytic effects of copper oxalate nanocrystals

International Nuclear Information System (INIS)

Singh, Gurdip; Kapoor, Inder Pal Singh; Dubey, Reena; Srivastava, Pratibha

2012-01-01

Graphical abstract: Prepared copper oxalate nanocrystals were characterized by FE-SEM and bright field TEM micrographs. Its catalytic activity was evaluated on the thermal decomposition of ammonium perchlorate using TG and TG-DSC techniques. Highlights: ► Preparation of nanocrystals (∼9.0 nm) of copper oxalate using Cu(NO 3 ) 2 ·2H 2 O, oxalic acid and acetone under thermal conditions. ► Method is simple and novel. ► Characterization using XRD, SEM, TEM, HRTEM and ED pattern. ► Catalytic activity of copper oxalate nanocrystals on AP thermal decomposition using thermal techniques (TG, TG-DSC and ignition delay). ► Kinetics of thermal decomposition of AP + CONs using isoconversional and model fitting kinetic approaches. - Abstract: Recent work has described the preparation and characterization of copper oxalate nanocrystals (CONs). It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and electron diffraction pattern (ED). The catalytic activity of CONs on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellants (CSPs) has been done by thermogravimetry (TG), differential scanning calorimetry (DSC) and ignition delay measurements. Burning rate of CSPs was also found to be enhanced in presence of copper oxalate nanocrystals. Kinetics of thermal decomposition of AP with and without CONs has also been investigated. The model free (isoconversional) and model-fitting kinetic approaches have been applied to data for isothermal TG decomposition.

Highly efficient solid-state synthesis of carbon-encapsulated ultrafine MoO{sub 2} nanocrystals as high rate lithium-ion battery anode

Energy Technology Data Exchange (ETDEWEB)

Liu, Boyang, E-mail: byliu@shmtu.edu.cn [Shanghai Maritime University, College of Ocean Science and Engineering (China); Shao, Yingfeng, E-mail: shaoyf@lnm.imech.ac.cn [Chinese Academy of Sciences, State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics (China); Zhang, Yuliang, E-mail: ylzhang@shmtu.edu.cn; Zhang, Fuhua, E-mail: fhzhang@shmtu.edu.cn; Zhong, Ning, E-mail: ningzhong@shmtu.edu.cn [Shanghai Maritime University, College of Ocean Science and Engineering (China); Li, Wenge, E-mail: wgli@shmtu.edu.cn [Shanghai Maritime University, Merchant Marine College (China)

2016-12-15

A simple and highly efficient method is developed for the one-step in situ preparation of carbon-encapsulated MoO{sub 2} nanocrystals (MoO{sub 2}@C) with core-shell structure for high-performance lithium-ion battery anode. The synthesis is depending on the solid-state reaction of cyclopentadienylmolybdenum tricarbonyl dimer with ammonium persulfate in an autoclave at 200 °C for 30 min. The large amount of heat generated during the explosive reaction cleaves the cyclopentadiene ligands into small carbon fragments, which form carbon shell after oxidative dehydrogenation coating on the MoO{sub 2} nanocrystals, resulting in the formation of core-shell structure. The MoO{sub 2} nanocrystals have an equiaxial morphology with an ultrafine diameter of 2–8 nm, and the median size is 4.9 nm. Hundreds of MoO{sub 2} nanocrystals are encapsulated together by the worm-like carbon shell, which is amorphous and about 3–5 nm in thickness. The content of MoO{sub 2} nanocrystals in the nanocomposite is about 69.3 wt.%. The MoO{sub 2}@C anode shows stable cyclability and retains a high reversible capacity of 443 mAh g{sup −1} after 50 cycles at a current density of 3 A g{sup −1}, owing to the effective protection of carbon shell.

Novel green synthetic strategy to prepare ZnO nanocrystals using rambutan (Nephelium lappaceum L.) peel extract and its antibacterial applications.

Science.gov (United States)

Yuvakkumar, R; Suresh, J; Nathanael, A Joseph; Sundrarajan, M; Hong, S I

2014-08-01

In the present investigation, we report a sustainable novel green synthetic strategy to synthesis zinc oxide nanocrystals. This is the first report on sustainable biosynthesis of zinc oxide nanocrystals employing Nephelium lappaceum L., peel extract as a natural ligation agent. Green synthesis of zinc oxide nanocrystals was carried out via zinc-ellagate complex formation using rambutan peel wastes. The successful formation of zinc oxide nanocrystals was confirmed employing standard characterisation studies. A possible mechanism for the formation of ZnO nanocrystals with rambutan peel extract was also proposed. The prepared ZnO nanocrystals were coated on the cotton fabric and their antibacterial activity were analyzed. ZnO nanocrystals coated cotton showed good antibacterial activity towards Escherichia coli (E. coli), gram negative bacteria and Staphylococcus aureus (S. aureus), gram positive bacteria. Copyright © 2014 Elsevier B.V. All rights reserved.

Solvothermal synthesis of size-tunable ZnFe{sub 2}O{sub 4} colloidal nanocrystal assemblies and their electrocatalytic activity towards hydrogen peroxide

Energy Technology Data Exchange (ETDEWEB)

Liu, Ruirui, E-mail: liurui1114@outlook.com; Lv, Meng, E-mail: lm199133@126.com; Wang, Qianbin, E-mail: material_wqb@163.com; Li, Hongliang, E-mail: lhl@qdu.edu.cn; Guo, Peizhi, E-mail: pzguo@qdu.edu.cn; Zhao, X.S., E-mail: chezxs@qdu.edu.cn

2017-02-15

Three ZnFe{sub 2}O{sub 4} colloidal nanocrystal assemblies (CNAs), namely CNA1, CNA2 and CNA3, have been synthesized solvothermally with the size of 560 nm, 460 nm and 330 nm and are formed by the self-assembly of primary nanocrystals with the crystallite sizes of 19.2 nm, 15.5 nm and 21.8 nm, respectively. It was found that CNA2 performed superparamagnetic behavior with a saturation magnetization value of 36.9 emu g{sup −1} while either CNA1 or CNA3 exhibited weak ferromagnetic with a small hysteresis loop and large saturation magnetization. Electrochemical sensing measurements toward the reduction of hydrogen peroxide showed that the peak currents of the CNAs in cyclic voltammograms showed a linear relationship with the concentration of hydrogen peroxide in the experimental conditions and the peak potentials were increased with the order of CNA3, CNA2 and CNA1. The formation mechanism of ZnFe{sub 2}O{sub 4} CNAs had been discussed based on the experimental data. The magnetism and electrocatalysis of the ZnFe{sub 2}O{sub 4} CNAs were supposed to be dependent on the size of primary nanoparticles and the structure of the CNAs. - Highlights: • Size-tunable ZnFe{sub 2}O{sub 4} colloidal nanocrystal assemblies were synthesized solvothermally. • Magnetic properties of ZnFe{sub 2}O{sub 4} assemblies are depended on the size and self-assembly of primary nanoparticles. • Electrocatalytic activity of ZnFe{sub 2}O{sub 4} assemblies is determined by their structure.

Strong blue emission from ZnO nanocrystals synthesized in acetone-based solvent

International Nuclear Information System (INIS)

Efafi, B.; Majles Ara, M.H.; Mousavi, S.S.

2016-01-01

In this research, ZnO nanocrystals were synthesized by an improved sol–gel method. UV–vis, FTIR and photoluminescence spectra of the ZnO solution synthesized by this route indicated different properties compared to the other preparation methods. It was observed from FTIR that the sol (prepared using acetone) with the low concentration contains a noticeable amount of the Zn–O bond. The PL spectrum with a strong blue emission confirmed that these nanocrystals are good candidate for use in applications where a monochromatic emission is required. To the best of our knowledge, monochromatic emission ZnO devices have been fabricated through high technology instruments but this paper introduces a simple method for preparation of ZnO with the high intensity blue peak. The size and morphology of ZnO nanocrystals have been studied using FESEM. The nanocrystal size was estimated about 70 nm which was in good agreement with XRD data. - Highlights: • Preparation of ZnO nanocrystals through a novel method by the use of acetone as the solvent. • Observation of the strong blue emission peak from the ZnO prepared solution. • Reduction of green emission in the synthesized sample compared to the other methods of preparation.

Strong blue emission from ZnO nanocrystals synthesized in acetone-based solvent

Energy Technology Data Exchange (ETDEWEB)

Efafi, B. [NanoPhotonics Lab., Physics Department, Kharazmi University, Tehran (Iran, Islamic Republic of); Departments of Physics, Iran University of Science & Technology, Tehran (Iran, Islamic Republic of); Majles Ara, M.H., E-mail: majlesara@gmail.com [NanoPhotonics Lab., Physics Department, Kharazmi University, Tehran (Iran, Islamic Republic of); Mousavi, S.S. [NanoPhotonics Lab., Physics Department, Kharazmi University, Tehran (Iran, Islamic Republic of)

2016-10-15

In this research, ZnO nanocrystals were synthesized by an improved sol–gel method. UV–vis, FTIR and photoluminescence spectra of the ZnO solution synthesized by this route indicated different properties compared to the other preparation methods. It was observed from FTIR that the sol (prepared using acetone) with the low concentration contains a noticeable amount of the Zn–O bond. The PL spectrum with a strong blue emission confirmed that these nanocrystals are good candidate for use in applications where a monochromatic emission is required. To the best of our knowledge, monochromatic emission ZnO devices have been fabricated through high technology instruments but this paper introduces a simple method for preparation of ZnO with the high intensity blue peak. The size and morphology of ZnO nanocrystals have been studied using FESEM. The nanocrystal size was estimated about 70 nm which was in good agreement with XRD data. - Highlights: • Preparation of ZnO nanocrystals through a novel method by the use of acetone as the solvent. • Observation of the strong blue emission peak from the ZnO prepared solution. • Reduction of green emission in the synthesized sample compared to the other methods of preparation.

Preparation of CNC-dispersed Fe3O4 nanoparticles and their application in conductive paper.

Science.gov (United States)

Liu, Kai; Nasrallah, Joseph; Chen, Lihui; Huang, Liulian; Ni, Yonghao

2015-08-01

Well-dispersed Fe3O4 nanoparticles (NPs) were synthesized by a co-precipitation method in the presence of cellulose nano-crystals (CNC) as the template. The thus prepared Fe3O4 NPs were then used as a coating agent for the preparation of conductive paper. Fourier transform infrared spectroscopy (FTIR) results revealed that the Fe3O4 NPs were immobilized on the CNC through interactions between the hydroxyl groups of CNC and Fe3O4. Scanning transmission electron microscopy (STEM) images showed that the Fe3O4 NPs prepared in the presence of CNC can be dispersed in the CNC network, while the Fe3O4 NPs prepared in the absence of CNC tended to aggregate in aqueous solutions. The conductivity of the Fe3O4 NPs coated paper can reach to 0.0269 S/m at the coating amount of 14.75 g/m(2) Fe3O4/CNC nanocomposites. Therefore, the thus obtained coated paper can be potentially used as anti-static packaging material in the packaging field. Copyright © 2015 Elsevier Ltd. All rights reserved.

Ultra-small Fe3O4 nanocrystals decorated on 2D graphene nanosheets with excellent cycling stability as anode materials for lithium ion batteries

International Nuclear Information System (INIS)

Ren, Manman; Yang, Mingzhi; Liu, Weiliang; Li, Mei; Su, Liwei; Qiao, Congde; Wu, Xianbin; Ma, Houyi

2016-01-01

Graphical abstract: Ultra-small Fe 3 O 4 nanocrystals decorated on 2D graphene nanosheets with excellent cycling stability as anode materials for lithium ion batteries Manman Ren, Mingzhi Yang, Weiliang Liu, Mei Li, Liwei Su, Congde Qiao, Xianbin Wu, Houyi Ma Ultra-small Fe 3 O 4 nanocrystals/graphene nanosheets composites demonstrate excellent long-term cycling stability at high-rate. - Abstract: Ultra-small Fe 3 O 4 nanocrystals (NCs)/garphene nanosheets (GNSs) composites have been synthesized through a facile gel-like film (GF) assisted method in this work. Fe 3 O 4 NCs with particle size ∼10 nm homogeneously dispersed on 2D GNSs. Profiting from the ultra-small Fe 3 O 4 NCs and GNSs, the composites demonstrate superior long-term and high-rate performance as anode materials for lithium ion batteries. Even at the current density of 5 A g −1 , the reversible capacity still maintains 323.4 mAh g −1 after 700 cycles. This work might enlighten us on exploring preferable strategies to develop advanced metal oxides NCs/GNSs composites anode materials for lithium ion batteries or other energy storage devices.

Electrical and Plasmonic Properties of Ligand-Free Sn(4+) -Doped In2 O3 (ITO) Nanocrystals.

Science.gov (United States)

Jagadeeswararao, Metikoti; Pal, Somnath; Nag, Angshuman; Sarma, D D

2016-03-03

Sn(4+) -doped In2 O3 (ITO) is a benchmark transparent conducting oxide material. We prepared ligand-free but colloidal ITO (8 nm, 10 % Sn(4+) ) nanocrystals (NCs) by using a post-synthesis surface-modification reaction. (CH3 )3 OBF4 removes the native oleylamine ligand from NC surfaces to give ligand-free, positively charged NCs that form a colloidal dispersion in polar solvents. Both oleylamine-capped and ligand-free ITO NCs exhibit intense absorption peaks, due to localized surface plasmon resonance (LSPR) at around λ=1950 nm. Compared with oleylamine-capped NCs, the electrical resistivity of ligand-free ITO NCs is lower by an order of magnitude (≈35 mΩ cm(-1) ). Resistivity over a wide range of temperatures can be consistently described as a composite of metallic ITO grains embedded in an insulating matrix by using a simple equivalent circuit, which provides an insight into the conduction mechanism in these systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acetone sensors based on TiO{sub 2} nanocrystals modified with tungsten oxide species

Energy Technology Data Exchange (ETDEWEB)

Epifani, Mauro, E-mail: mauro.epifani@le.imm.cnr.it [Consiglio Nazionale delle Ricerche – Istituto per la Microelettronica e Microsistemi (CNR-IMM), via Monteroni c/o Campus Universitario, I-73100, Lecce (Italy); Comini, Elisabetta [SENSOR Lab, Department of Information Engineering, Brescia University and CNR-INO, via Valotti, 9, 25133 Brescia (Italy); Díaz, Raül [Electrochemical Processes Unit, IMDEA Energy Institute, Avda. Ramón de la Sagra, 3 28935 Móstoles (Spain); Genç, Aziz [Metallurgy and Materials Engineering Department, Faculty of Engineering, Bartin University, 74100, Bartin (Turkey); Andreu, Teresa [Catalonia Institute for Energy Research- (IREC), Jardíns de les Dones de Negre, 1, E-08930 Sant Adrià del Besos, Barcelona, CAT (Spain); Siciliano, Pietro [Consiglio Nazionale delle Ricerche – Istituto per la Microelettronica e Microsistemi (CNR-IMM), via Monteroni c/o Campus Universitario, I-73100, Lecce (Italy); Morante, Joan R. [Catalonia Institute for Energy Research- (IREC), Jardíns de les Dones de Negre, 1, E-08930 Sant Adrià del Besos, Barcelona, CAT (Spain); Departament d' Electrònica, Universitat de Barcelona, C./ Martí i Franquès 1, E-08028 Barcelona (Spain)

2016-04-25

TiO{sub 2} nanocrystals were prepared by sol–gel/solvothermal processing and modified by the addition of W precursor before the solvothermal step. The W: Ti nominal atomic ratio (R{sub W}) was fixed to 0.16 and 0.64. Surface modification of TiO{sub 2} occurred for R{sub W} = 0.16 while for R{sub W} = 0.64 nanocomposites with WO{sub 3} nanocrystals were obtained after heat-treatment at 500 °C. Pure TiO{sub 2} proved to be very poorly performing in acetone sensing in all the operating conditions. Instead, the addition of both W concentrations largely enhanced the sensor response. It ranged over two orders of magnitude of conductance variation for all the tested concentrations at as low as 200 °C operating temperature. The results showed that it is possible to enhance the performance of an otherwise almost inactive oxide like TiO{sub 2} by proper combination with another more active oxide like WO{sub 3}. - Highlights: • Sensing architecture are synthesized, combining WO{sub 3} and of TiO{sub 2} nanocrystals. • Surface layers of W oxides or heterojunctions of TiO{sub 2} and WO{sub 3} are obtained. • Simple TiO{sub 2} surface modification by W oxides boosts the TiO{sub 2} acetone response. • High responses even at 200 °C show catalytic effect of WO{sub 3} addition.

Influence of La doping and synthesis method on the properties of CoFe{sub 2}O{sub 4} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Mansour, S.F. [Physics Department, Faculty of Science, Zagazig University, Zagazig (Egypt); Hemeda, O.M. [Physics Department, Faculty of Science, Tanta University, Tanta (Egypt); El-Dek, S.I., E-mail: didi5550000@gmail.com [Materials Science and Nanotechnology Department, Faculty of Post Graduate Studies for Advanced Sciences (PSAS), Beni-Suef University, Beni-Suef (Egypt); Salem, B.I. [Physics Department, Faculty of Science, Tanta University, Tanta (Egypt)

2016-12-15

Nanocrystals of La doped CoFe{sub 2}O{sub 4} were synthesized using three different techniques: flash autocombustion, citrate–nitrate and the standard ceramic technique. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the obtained nanocrystals. All samples were crystallized in a spinel structure with cubic symmetry. The decrease in the lattice constant was endorsed to the large difference in ionic radii of both La{sup +3} (1.216 Å) and Fe (0.65 Å) in 6-f coordination. The citrate method displayed superior M{sub s} values amongst all techniques. The coercivity was found to exhibit largest values for the citrate method and then the flash while smallest values are associated with ceramic technique. - Highlights: • CoLa{sub x}Fe{sub 2−x}O{sub 4} nanocrystals crystallized in spinel cubic structure using 3 techniques. • The decrease in the lattice constant is due to the difference in ionic radius of La{sup +3} and Fe{sup 3+}. • The citrate method exhibit largest values of M{sub s} amongst all techniques. • Coercivity exhibits largest values for citrate and then flash, smallest for ceramic technique.

Nanocrystal in Er3+-doped SiO2-ZrO2 Planar Waveguide with Yb3+ Sensitizer

International Nuclear Information System (INIS)

Razaki, N. Iznie; Jais, U. Sarah; Abd-Rahman, M. Kamil; Bhaktha, S. N. B.; Chiasera, A.; Ferrari, M.

2010-01-01

Higher doping of Er 3+ in glass ceramic waveguides would cause concentration and pair-induced quenching which lead to inhomogeneous line-width of luminescence spectrum thus reduce output intensity. Concentration quenching can be overcome by introducing ZrO 2 in the glass matrix while co-doping with Yb 3+ which acts as sensitizer would improve the excitation efficiency of Er 3+ . In this study, SiO 2 -ZrO 2 planar waveguides having composition in mol percent of 70SiO 2 -30ZrO 2 doped with Er 3+ and co-doped with Yb 3+ , were prepared via sol-gel route. Narrower and shaper peaks of PL and XRD shows the formation of nanocrystals. Intensity is increase with addition amount of Yb 3+ shows sensitizing effect on Er 3+ .

Structural characteristics and gasification reactivity of chars prepared from K{sub 2}CO{sub 3} mixed HyperCoals and coals

Energy Technology Data Exchange (ETDEWEB)

Atul Sharma; Hiroyuki Kawashima; Ikuo Saito; Toshimasa Takanohashi [National Institute of Advanced Industrial Science and Technology, Ibaraki (Japan). Advanced Fuel Group

2009-04-15

HyperCoal is a clean coal with mineral matter content <0.05 wt %. Oaky Creek (C = 82%), and Pasir (C = 68%) coals were subjected to solvent extraction method to prepare Oaky Creek HyperCoal, and Pasir HyperCoal. Experiments were carried out to compare the gasification reactivity of HyperCoals and parent raw coals with 20, 40, 50 and 60% K{sub 2}CO{sub 3} as a catalyst at 600, 650, 700, and 775{sup o}C with steam. Gasification rates of coals and HyperCoals were strongly influenced by the temperature and catalyst loading. Catalytic steam gasification of HyperCoal chars was found to be chemical reaction controlled in the 600-700{sup o}C temperature range for all catalyst loadings. Gasification rates of HyperCoal chars were found to be always higher than parent coals at any given temperature for all catalyst loadings. However, X-ray diffraction results showed that the microstructures of chars prepared from coals and HyperCoals were similar. Results from nuclear magnetic resonance spectroscopy show no significant difference between the chemical compositions of the chars. Significant differences were observed from scanning electron microscopy images, which showed that the chars from HyperCoals had coral-reef like structures whereas dense chars were observed for coals. 26 refs., 8 figs., 2 tabs.

Effect of surface ethoxy groups on photoactivity of TiO2 nanocrystals

International Nuclear Information System (INIS)

Tian Lihong; Deng Kejian; Ye Liqun; Zan Lin

2011-01-01

TiO 2 nanocrystals modified by ethoxy groups were prepared by a facile nonhydrolytic solvothermal method and characterized by XRD, TEM, TG-DTA and XPS, which showed an enhanced visible-light photocatalytic activity on the degradation of Rhodamine B compared with TiO 2 modified by benzyloxy groups and the 'naked' TiO 2 . The adsorption and degradation pathway of Rhodamine B on TiO 2 modified by ethoxy groups were also investigated. The zeta-potential (ζ) results showed that the TiO 2 modified by ethoxy groups had high negative surface charge, which incited the positive -N(Et) 2 group of RhB absorbing on the TiO 2 surface and preferably led the N-dealkylation pathway under visible light irradiation.

CoFe2O4-SiO2 Composites: Preparation and Magnetodielectric Properties

Directory of Open Access Journals (Sweden)

T. Ramesh

2016-01-01

Full Text Available Cobalt ferrite (CoFe2O4 and silica (SiO2 nanopowders have been prepared by the microwave hydrothermal (M-H method using metal nitrates as precursors of CoFe2O4 and tetraethyl orthosilicate as a precursor of SiO2. The synthesized powders were characterized by XRD and FESEM. The (100-x (CoFe2O4 + xSiO2 (where x = 0%, 10%, 20%, and 30% composites with different weight percentages have been prepared using ball mill method. The composite samples were sintered at 800°C/60 min using the microwave sintering method and then their structural and morphological studies were investigated using X-ray diffraction (XRD, Fourier transformation infrared (FTIR spectra, and scanning electron microscopy (SEM, respectively. The effect of SiO2 content on the magnetic and electrical properties of CoFe2O4/SiO2 nanocomposites has been studied via the magnetic hysteresis loops, complex permeability, permittivity spectra, and DC resistivity measurements. The synthesized nanocomposites with adjustable grain sizes and controllable magnetic properties make the applicability of cobalt ferrite even more versatile.

Nanocrystals of a new complex perovskite dielectric Ba{sub 2}TmSbO{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Nair, V.M. [Department of Physics, University College, Trivandrum 695034, Kerala (India); Jose, R., E-mail: rjose@ump.edu.my [Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang, 26300 Kuantan (Malaysia); Anil Kumar, G.M. [Noritake Co Ltd, 300 Higashiyama, Miyoshi, Aichi 470-0293 (Japan); Yusoff, Mashitah M. [Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang, 26300 Kuantan (Malaysia); Wariar, P.R.S. [Department of Physics, University College, Trivandrum 695034, Kerala (India)

2012-01-25

Highlights: Black-Right-Pointing-Pointer A new material, Ba{sub 2}TmSbO{sub 6}, has been synthesized as nanocrystals for the first time. Black-Right-Pointing-Pointer A combustion process, characterized by a one-pot procedure, was adopted to synthesize Ba{sub 2}TmSbO{sub 6} as nanocrystals. Black-Right-Pointing-Pointer Crystal structure and dielectric properties of the Ba{sub 2}TmSbO{sub 6} have been studied and compared with similar materials. - Abstract: Nanocrystals of a new complex perovskites ceramic oxide, barium thulium antimony oxide - Ba{sub 2}TmSbO{sub 6}, were synthesized using a single step auto-ignition combustion process. The combustion product was single phase and composed of aggregates of nanocrystals of sizes in the range 20-50 nm. Ba{sub 2}TmSbO{sub 6} crystallized in cubic perovskite structure with lattice parameter, a = 8.4101 Angstrom-Sign . The polycrystalline fluffy combustion product was sintered to high density ({approx}97%) at {approx}1450 Degree-Sign C for 4 h. Resistivity of the sintered specimen was {approx}5 M{Omega}/cm. The Ba{sub 2}TmSbO{sub 6} has dielectric constant ({epsilon} Prime ) and dielectric loss (tan {delta}) of 17 and {approx}10{sup -4} at 5 MHz; the new material would probably be developed as a low-loss dielectric material.

Selective detection of Fe2+ by combination of CePO4:Tb3+ nanocrystal-H2O2 hybrid system with synchronous fluorescence scan technique.

Science.gov (United States)

Chen, Hongqi; Ren, Jicun

2012-04-21

A new method for quenching kinetic discrimination of Fe(2+) and Fe(3+), and sensitive detection of trace amount of Fe(2+) was developed by using synchronous fluorescence scan technique. The principle of this assay is based on the quenching kinetic discrimination of Fe(2+) and Fe(3+) in CePO(4):Tb(3+) nanocrytals-H(2)O(2) hybrid system and the Fenton reaction between Fe(2+) and H(2)O(2). Stable, water-soluble and well-dispersible CePO(4):Tb(3+) nanocrystals were synthesized in aqueous solutions, and characterized by transmission electron microscopy (TEM) and electron diffraction spectroscopy (EDS). We found that both Fe(2+) and Fe(3+) could quench the synchronous fluorescence of CePO(4):Tb(3+) nanocrytals-H(2)O(2) system, but their quenching kinetics velocities were quite different. In the presence of Fe(3+), the synchronous fluorescent intensity was unchanged after only one minute, but in the presence of Fe(2+), the synchronous fluorescent intensity decreased slowly until 28 min later. The Fenton reaction between Fe(2+) and H(2)O(2) resulted in hydroxyl radicals which effectively quenched the synchronous fluorescence of the CePO(4):Tb(3+) nanocrystals due to the oxidation of Ce(3+) into Ce(4+) by hydroxyl radicals. Under optimum conditions, the linear range for Fe(2+) is 3 nM-2 μM, and the limit of detection is 2.0 nM. The method was used to analyze water samples.

Synthesis and characterization of MgO nanocrystals for biosensing applications

Energy Technology Data Exchange (ETDEWEB)

Li, Hongji [Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry & Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Li, Mingji, E-mail: limingji@163.com [Tianjin Key Laboratory of Film Electronic and Communication Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300384 (China); Qiu, Guojun [Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry & Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Li, Cuiping; Qu, Changqing; Yang, Baohe [Tianjin Key Laboratory of Film Electronic and Communication Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300384 (China)

2015-05-25

Highlights: • MgO nanocrystals were prepared using DC arc plasma jet CVD method. • The growth time does not exceed 10 min in process of the synthesis. • The samples were found to consist of cubic MgO nanobelts and nanosheets. • Nanocrystals contain contacts, rough edges, vacancies, and doping defects. • The samples exhibited excellent electrochemical biosensing properties. - Abstract: MgO nanocrystals were prepared using a simple direct current arc plasma jet chemical vapor deposition method. Magnesium nitrate was used as source material and Mo film was used as a substrate and catalyst. The high-temperature plasma produced ensured rapid synthesis of the MgO nanocrystals. The as-prepared nanocrystals were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, Fourier transform infrared spectrometry, ultraviolet–visible spectrophotometry, and photoluminescence measurements. The as-synthesized samples were found to consist of cubic MgO nanobelts and nanosheets with large surface areas and low coordination oxide ions, and contained numerous contacts, rough edges, vacancies, and doping defects. The nanostructures exhibited excellent electrochemical sensing properties with high-sensing sensitivity toward ascorbic acid. Their high electrocatalytic activity was attributed to the effect of defects and the surface electron transfer ability of the one-dimensional MgO nanobelts.

Three-dimensional mesoporous graphene aerogel-supported SnO2 nanocrystals for high-performance NO2 gas sensing at low temperature.

Science.gov (United States)

Li, Lei; He, Shuijian; Liu, Minmin; Zhang, Chunmei; Chen, Wei

2015-02-03

A facile and cost-efficient hydrothermal and lyophilization two-step strategy has been developed to prepare three-dimensional (3D) SnO2/rGO composites as NO2 gas sensor. In the present study, two different metal salt precursors (Sn(2+) and Sn(4+)) were used to prepare the 3D porous composites. It was found that the products prepared from different tin salts exhibited different sensing performance for NO2 detection. The scanning electron microscopy and transmission electron microscopy characterizations clearly show the macroporous 3D hybrids, nanoporous structure of reduce graphene oxide (rGO), and the supported SnO2 nanocrystals with an average size of 2-7 nm. The specific surface area and porosity properties of the 3D mesoporous composites were analyzed by Braunauer-Emmett-Teller method. The results showed that the SnO2/rGO composite synthesized from Sn(4+) precursor (SnO2/rGO-4) has large surface area (441.9 m(2)/g), which is beneficial for its application as a gas sensing material. The gas sensing platform fabricated from the SnO2/rGO-4 composite exhibited a good linearity for NO2 detection, and the limit of detection was calculated to be as low as about 2 ppm at low temperature. The present work demonstrates that the 3D mesoporous SnO2/rGO composites with extremely large surface area and stable nanostructure are excellent candidate materials for gas sensing.

Efficient photocatalytic reductive dechlorination of 4-chlorophenol to phenol on {0 0 1}/{1 0 1} facets co-exposed TiO_2 nanocrystals

International Nuclear Information System (INIS)

Jiang, Guodong; Wei, Meng; Yuan, Songdong; Chang, Qing

2016-01-01

Graphical abstract: - Highlights: • 4-Chlorophenol is dechlorinated over {0 0 1}/{1 0 1} co-exposed TiO_2 nanocrystals. • Photo-electrons are accumulated on {1 0 1} facets due to surface heterojunction. • Fluorine will trap photoelectrons to depress the dechlorination performance. • Sufficient isopropanol promotes the dechlorination activity and selectivity. - Abstract: 4-chlorophenol could be efficiently photoreductively dechlorinated over anatase TiO_2 nanocrystals with co-exposed {0 0 1} and {1 0 1} facets, which were synthesized and further characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Although fluorine could adsorb on {0 0 1} facets to decrease their surface energy, enabling TiO_2 to expose high energy {0 0 1} facets, the surface bonded fluorine might depress the photoreductive dechlorination efficiency of 4-chlorophenol, attributed to the electron trapping role of surface ≡Ti−F groups. Due to the formation of a surface heterojunction between {1 0 1} and {0 0 1} facets in a single TiO_2 nanocrystal, electrons and holes were spontaneously self-separated and selectively migrate to {1 0 1} and {0 0 1} facets, respectively. Electron trapping experiments demonstrated that photogenerated electrons are the responsible for the reductive dechlorinaton of 4-chlorophenol to phenol. To avoid the oxidative degradation of 4-chlorophenol by holes and ensure sufficient electrons to reductively dechlorinate the substrate, moderate scavengers were required in the reaction system and dissolved oxygen, which might deplete electron on TiO_2, also should be removed. With the optimal scavengers, the conversion efficiency of 4-chlorophenol (4-CP) achieved 97.5% and the selectivity for phenol was 92.5%, which were much higher than that of commercial TiO_2 P25.

Size-tunable phosphorescence in colloidal metastable gamma-Ga2O3 nanocrystals.

Science.gov (United States)

Wang, Ting; Farvid, Shokouh S; Abulikemu, Mutalifu; Radovanovic, Pavle V

2010-07-14

We report a colloidal synthesis of gallium oxide (Ga(2)O(3)) nanocrystals having metastable cubic crystal structure (gamma phase) and uniform size distribution. Using the synthesized nanocrystal size series we demonstrate for the first time a size-tunable photoluminescence in Ga(2)O(3) from ultraviolet to blue, with the emission shifting to lower energies with increasing nanocrystal size. The observed photoluminescence is dominated by defect-based donor-acceptor pair recombination and has a lifetime of several milliseconds. Importantly, the decay of this phosphorescence is also size dependent. The phosphorescence energy and the decay rate increase with decreasing nanocrystal size, owing to a reduced donor-acceptor separation. These results allow for a rational and predictable tuning of the optical properties of this technologically important material and demonstrate the possibility of manipulating the localized defect interactions via nanocrystal size. Furthermore, the same defect states, particularly donors, are also implicated in electrical conductivity rendering monodispersed Ga(2)O(3) nanocrystals a promising material for multifunctional optoelectronic structures and devices.

Fabrication and Thermophysical Properties of La(2-x)Zr(2-y)O7 Nanocrystal by a Sol-Gel Method.

Science.gov (United States)

Li, Hui; Che, Ping; Zhao, Ziqiang; Liu, Shixiang; Li, Wenjun

2016-03-01

Non-Stoichiometric La2Zr2O7 (La(2-x)Zr(2-y)O7) Nanocrystal was synthesized by a simple sol-gel method. The crystalline structure, oxygen vacancy concentration, thermal expansion coefficient, as well as the fracture toughness of as-prepared materials were charactered by XRD, TG-DSC, PL spectra, dilatometer, and electronic universal testing machine respectively. The crystal structure of La2Zr2O7 is of the cubic type while lattice parameter increases with the deviatation of Zr4+ and La3+ from Stoichiometric La2Zr2O7 increasing. The average linear thermal expansion coefficient of non-stoichiometric La2Zr2O7 is obviously bigger than that of La2Zr2O7 in the temperature range between 150 degrees C and 950 degrees C. The fracture toughness of La(2-x)Zr(2-y)O7 increases with x and y increasing up to x = 0.3 and y = 0.25.

CuO and Co3O4 Nanoparticles: Synthesis, Characterizations, and Raman Spectroscopy

Directory of Open Access Journals (Sweden)

M. Rashad

2013-01-01

Full Text Available Copper oxide and cobalt oxide (CuO, Co3O4 nanocrystals (NCs have been successfully prepared in a short time using microwave irradiation without any postannealing treatment. Both kinds of nanocrystals (NCs have been prepared using copper nitrate and cobalt nitrate as the starting materials and distilled water as the solvent. The resulted powders of nanocrystals (NCs were characterized by X-ray diffraction (XRD, transmission electron microscopy (TEM, scanning electron microscopy (SEM, and atomic force microscopy (AFM measurements. The obtained results confirm the presence of the both of oxides nanopowders produced during chemical precipitation using microwave irradiation. A strong emission under UV excitation is obtained from the prepared CuO and Co3O4 nanoparticles. The results show that the nanoparticles have high dispersion and narrow size distribution. The line scans of atomic force microscopy (AFM images of the nanocrystals (NCs sprayed on GaAs substrates confirm the results of both X-ray diffraction and transmission electron microscopy. Furthermore, vibrational studies have been carried out using Raman spectroscopic technique. Specific Raman peaks have been observed in the CuO and Co3O4 nanostructures, and the full width at half maximum (FWHM of the peaks indicates a small particle size of the nanocrystals.

Pair Distribution Function Analysis of ZrO2 Nanocrystals and Insights in the Formation of ZrO2-YBa2Cu3O7 Nanocomposites

Directory of Open Access Journals (Sweden)

Hannes Rijckaert

2018-06-01

Full Text Available The formation of superconducting nanocomposites from preformed nanocrystals is still not well understood. Here, we examine the case of ZrO2 nanocrystals in a YBa2Cu3O7−x matrix. First we analyzed the preformed ZrO2 nanocrystals via atomic pair distribution function analysis and found that the nanocrystals have a distorted tetragonal crystal structure. Second, we investigated the influence of various surface ligands attached to the ZrO2 nanocrystals on the distribution of metal ions in the pyrolyzed matrix via secondary ion mass spectroscopy technique. The choice of stabilizing ligand is crucial in order to obtain good superconducting nanocomposite films with vortex pinning. Short, carboxylate based ligands lead to poor superconducting properties due to the inhomogeneity of metal content in the pyrolyzed matrix. Counter-intuitively, a phosphonate ligand with long chains does not disturb the growth of YBa2Cu3O7−x. Even more surprisingly, bisphosphonate polymeric ligands provide good colloidal stability in solution but do not prevent coagulation in the final film, resulting in poor pinning. These results thus shed light on the various stages of the superconducting nanocomposite formation.

Dopant concentration dependent magnetism of Cu-doped TiO{sub 2} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Anitha, B.; Khadar, M. Abdul, E-mail: mabdulkhadar@rediffmail.com [University of Kerala, Centre for Nanoscience and Nanotechnology (India)

2016-06-15

Undoped and Cu-doped nanocrystals of TiO{sub 2} having the size range of 8–11 nm were synthesized by peroxide gel method. XRD analysis using Rietveld refinement confirmed anatase phase with a small percentage of rutile content for undoped TiO{sub 2} nanocrystals while a pure anatase phase with preferential growth along [004] direction was observed for nanocrystals of Cu-doped TiO{sub 2}. Variation in the intensity ratios of the XRD peaks of the doped samples compared to that of the undoped sample offered an evidence for the substitutional incorporation of Cu ions in the TiO{sub 2} lattice. The preferential growth of the nanocrystals along the [004] direction was verified using HRTEM analysis. Cu doping extended the optical absorption edge of TiO{sub 2} nanocrystals to the visible spectral region and caused a blue shift and broadening of the E{sub g} (1) Raman active mode of anatase TiO{sub 2}. Undoped TiO{sub 2} sample showed a weak ferromagnetism superimposed on a diamagnetic background while Cu-doped TiO{sub 2} samples exhibited a weak ferromagnetism in the low-field region with a paramagnetic component in the high-field region. The magnetic moment exhibited by the doped samples is interpreted as the resultant of a weak ferromagnetic moment in the low-field region arising from the presence of defects near the surface of TiO{sub 2} nanoparticles or from the interaction of the substituted Cu ions with the oxygen vacancies, and the paramagnetic contribution from the increased Cu dopant concentration near the surface of the particles arising from self-purification mechanism.

Microwave synthesis of high-quality and uniform 4 nm ZnFe2O4 nanocrystals for application in energy storage and nanomagnetics

Directory of Open Access Journals (Sweden)

Christian Suchomski

2016-09-01

Full Text Available Magnetic nanocrystals with a narrow size distribution hold promise for many applications in different areas ranging from biomedicine to electronics and energy storage. Herein, the microwave-assisted sol–gel synthesis and thorough characterization of size-monodisperse zinc ferrite nanoparticles of spherical shape is reported. X-ray diffraction, 57Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy all show that the material is both chemically and phase-pure and adopts a partially inverted spinel structure with Fe3+ ions residing on tetrahedral and octahedral sites according to (Zn0.32Fe0.68tet[Zn0.68Fe1.32]octO4±δ. Electron microscopy and direct-current magnetometry confirm the size uniformity of the nanocrystals, while frequency-dependent alternating-current magnetic susceptibility measurements indicate the presence of a superspin glass state with a freezing temperature of about 22 K. Furthermore, as demonstrated by galvanostatic charge–discharge tests and ex situ X-ray absorption near edge structure spectroscopy, the as-prepared zinc ferrite nanocrystals can be used as a high-capacity anode material for Li-ion batteries, showing little capacity fade – after activation – over hundreds of cycles. Overall, in addition to the good material characteristics, it is remarkable that the microwave-based synthetic route is simple, easily reproducible and scalable.

Optical properties and thermal stability of germanium oxide (GeO2) nanocrystals with α-quartz structure

International Nuclear Information System (INIS)

Ramana, C.V.; Carbajal-Franco, G.; Vemuri, R.S.; Troitskaia, I.B.; Gromilov, S.A.; Atuchin, V.V.

2010-01-01

Germanium dioxide (GeO 2 ) crystals were prepared by a chemical precipitation method at a relatively low-temperature (100 o C). The grown crystals were characterized by studying their microstructure, optical properties and thermal stability. The results indicate that the grown GeO 2 crystals exhibit α-quartz type crystal structure. The lattice parameters obtained from XRD were a = 4.987(4) A and c = 5.652(5) A. Electron microscopy analysis indicates a high structural quality of GeO 2 crystals grown using the present approach. Optical absorption measurements indicate a direct bandgap of 5.72 eV without any additional bands arising from localized or defect states. Thermogravimetric measurements indicate the temperature stability of the grown GeO 2 nanocrystals. Microscopic analysis coupled with energy dispersive X-ray spectroscopy of the GeO 2 crystals with α-quartz type crystal structure indicates their stability in chemical composition up to a temperature of 400 deg. C. The surface morphology of GeO 2 crystals, however, found to be changing with the increase in temperature.

Efficient photocatalytic reductive dechlorination of 4-chlorophenol to phenol on {0 0 1}/{1 0 1} facets co-exposed TiO{sub 2} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Jiang, Guodong; Wei, Meng; Yuan, Songdong [College of Chemistry and chemical engineering, Hubei Collaborative Innovation Center for High Efficient Utilization of Solar Energy, Hubei University of Technology, Wuhan 430068 (China); Chang, Qing, E-mail: changqinghust@163.com [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, College of Resources and Environmental Science, South-Central University for Nationalities, Wuhan 430074 (China)

2016-01-30

Graphical abstract: - Highlights: • 4-Chlorophenol is dechlorinated over {0 0 1}/{1 0 1} co-exposed TiO{sub 2} nanocrystals. • Photo-electrons are accumulated on {1 0 1} facets due to surface heterojunction. • Fluorine will trap photoelectrons to depress the dechlorination performance. • Sufficient isopropanol promotes the dechlorination activity and selectivity. - Abstract: 4-chlorophenol could be efficiently photoreductively dechlorinated over anatase TiO{sub 2} nanocrystals with co-exposed {0 0 1} and {1 0 1} facets, which were synthesized and further characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Although fluorine could adsorb on {0 0 1} facets to decrease their surface energy, enabling TiO{sub 2} to expose high energy {0 0 1} facets, the surface bonded fluorine might depress the photoreductive dechlorination efficiency of 4-chlorophenol, attributed to the electron trapping role of surface ≡Ti−F groups. Due to the formation of a surface heterojunction between {1 0 1} and {0 0 1} facets in a single TiO{sub 2} nanocrystal, electrons and holes were spontaneously self-separated and selectively migrate to {1 0 1} and {0 0 1} facets, respectively. Electron trapping experiments demonstrated that photogenerated electrons are the responsible for the reductive dechlorinaton of 4-chlorophenol to phenol. To avoid the oxidative degradation of 4-chlorophenol by holes and ensure sufficient electrons to reductively dechlorinate the substrate, moderate scavengers were required in the reaction system and dissolved oxygen, which might deplete electron on TiO{sub 2}, also should be removed. With the optimal scavengers, the conversion efficiency of 4-chlorophenol (4-CP) achieved 97.5% and the selectivity for phenol was 92.5%, which were much higher than that of commercial TiO{sub 2} P25.

Effect of structural evolution of ZnO/HfO2 nanocrystals on Eu2+/Eu3+ emission in glass-ceramic waveguides for photonic applications.

Science.gov (United States)

Ghosh, Subhabrata; Bhaktha B N, Shivakiran

2018-06-01

Eu-doped 70SiO 2 -23HfO 2 -7ZnO (mol%) glass-ceramic waveguides have been fabricated by sol-gel method as a function of heat-treatment temperatures for on-chip blue-light emitting source applications. Structural evolution of spherical ZnO and spherical as well as rod-like HfO 2 nanocrystalline structures have been observed with heat-treatments at different temperatures. Initially, in the as-prepared samples at 900 ◦ C, both, Eu 2+ as well as Eu 3+ ions are found to be present in the ternary matrix. With controlled heat-treatments of up to 1000 ◦ C for 2 h, local environment of Eu-ions become more crystalline in nature and the reduction of Eu 3+ to Eu 2+ takes place in such ZnO/HfO 2 crystalline environments. In these ternary glass-ceramic waveguides, heat-treated at higher temperatures, the blue-light emission characteristic, which is the signature of 4f 6 5d [Formula: see text] 4f 7 energy level transition of Eu 2+ ions is found to be greatly enhanced. The as-prepared glass-ceramic waveguides exhibit a propagation loss of 0.4 ± 0.2 dB cm -1 at 632.8 nm. Though the propagation losses increase with the growth of nanocrystals, the added functionalities achieved in the optimally heat-treated Eu-doped 70SiO 2 -23HfO 2 -7ZnO (mol%) waveguides, make them a viable functional optical material for the fabrication of on-chip blue-light emitting sources for integrated optic applications.

Effect of structural evolution of ZnO/HfO2 nanocrystals on Eu2+/Eu3+ emission in glass-ceramic waveguides for photonic applications

Science.gov (United States)

Ghosh, Subhabrata; N, Shivakiran Bhaktha B.

2018-06-01

Eu-doped 70SiO2–23HfO2–7ZnO (mol%) glass-ceramic waveguides have been fabricated by sol-gel method as a function of heat-treatment temperatures for on-chip blue-light emitting source applications. Structural evolution of spherical ZnO and spherical as well as rod-like HfO2 nanocrystalline structures have been observed with heat-treatments at different temperatures. Initially, in the as-prepared samples at 900 ◦C, both, Eu2+ as well as Eu3+ ions are found to be present in the ternary matrix. With controlled heat-treatments of up to 1000 ◦C for 2 h, local environment of Eu-ions become more crystalline in nature and the reduction of Eu3+ to Eu2+ takes place in such ZnO/HfO2 crystalline environments. In these ternary glass-ceramic waveguides, heat-treated at higher temperatures, the blue-light emission characteristic, which is the signature of 4f 65d \\to 4f 7 energy level transition of Eu2+ ions is found to be greatly enhanced. The as-prepared glass-ceramic waveguides exhibit a propagation loss of 0.4 ± 0.2 dB cm‑1 at 632.8 nm. Though the propagation losses increase with the growth of nanocrystals, the added functionalities achieved in the optimally heat-treated Eu-doped 70SiO2–23HfO2–7ZnO (mol%) waveguides, make them a viable functional optical material for the fabrication of on-chip blue-light emitting sources for integrated optic applications.

Pulsed ion-beam induced nucleation and growth of Ge nanocrystals on SiO2

International Nuclear Information System (INIS)

Stepina, N. P.; Dvurechenskii, A. V.; Armbrister, V. A.; Kesler, V. G.; Novikov, P. L.; Gutakovskii, A. K.; Kirienko, V. V.; Smagina, Zh. V.; Groetzschel, R.

2007-01-01

Pulsed low-energy (200 eV) ion-beam induced nucleation during Ge deposition on thin SiO 2 film was used to form dense homogeneous arrays of Ge nanocrystals. The ion-beam action is shown to stimulate the nucleation of Ge nanocrystals when being applied after thin Ge layer deposition. Temperature and flux variation was used to optimize the nanocrystal size and array density required for memory device. Kinetic Monte Carlo simulation shows that ion impacts open an additional channel of atom displacement from a nanocrystal onto SiO 2 surface. This results both in a decrease in the average nanocrystal size and in an increase in nanocrystal density

Raman Spectroscopy of SiO{sub 2}–Na{sub 2}O–Al{sub 2}O{sub 3}–B{sub 2}O{sub 3} glass doped with Nd{sup 3+} and CdS nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Serqueira, E.O.; Dantas, N.O. [Laboratório de Novos Materiais Isolantes e Semicondutores (LNMIS), Instituto de Física, Universidade Federal de Uberlândia, Uberlândia, MG 38400-902 (Brazil); Anjos, V. [Grupo de Espectroscopia de Materiais, Departamento de Física, ICE – UFJF, Campus Universitário, Juiz de Fora, MG 36036-330 (Brazil); Bell, M.J.V., E-mail: mjvbell@yahoo.com.br [Grupo de Espectroscopia de Materiais, Departamento de Física, ICE – UFJF, Campus Universitário, Juiz de Fora, MG 36036-330 (Brazil)

2014-01-05

Highlights: • The formation of CdS nanocrystals in the glassy host is shown by Raman measurements. • Nd{sub 2}O{sub 3} modifies the growth of CdS nanocrystals in the SNAB glass. • Nd{sup 3+} ions are not incorporated inside the semiconductor nanocrystals. -- Abstract: We report the Raman spectroscopic characterization of a SNAB glass system doped with neodymium and CdS nanocrystals and fabricated by the fusion process. Raman spectra revealed CdS nanocrystals in the glass host and bands associated with Si–O vibrational modes with five structural configurations, boroxol modes of B{sub 2}O{sub 3}, Al–O and Cd–S vibrational modes. Additionally, Nd{sub 2}O{sub 3} modifies the growth of CdS nanocrystals in the SNAB glass and Nd{sup 3+} ions are not incorporated inside the semiconductor nanocrystals.

Size-Controlled TiO{sub 2} nanocrystals with exposed {001} and {101} facets strongly linking to graphene oxide via p-Phenylenediamine for efficient photocatalytic degradation of fulvic acids

Energy Technology Data Exchange (ETDEWEB)

Yan, Wen-Yuan; Zhou, Qi [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Chen, Xing, E-mail: xingchen@iim.ac.cn [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Laboratory of Nanomaterials and Environmental Detection, Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031 (China); Yang, Yong [State Key Laboratory of High Performance Ceramics and Superfine Microstructure,Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Zhang, Yong [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Huang, Xing-Jiu [Laboratory of Nanomaterials and Environmental Detection, Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031 (China); Wu, Yu-Cheng, E-mail: ycwu@hfut.edu.cn [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Anhui Key Laboratory of Advanced Functional Materials and Devices, Hefei 230009 (China)

2016-08-15

Highlights: • N-RGO/TiO{sub 2} nanocomposites were prepared via one-step hydrothermal method. • Facets of TiO{sub 2} nanocrystals were modulated with addition of HF. • Sizes of TiO{sub 2} nanocrystals were controlled by the contents of RGO-NH{sub 2.} • Obtained N-RGO/TiO{sub 2} nanocomposites exhibited excellent photocatalytic activity and stability. - Abstract: Photocatalytic degradation is one of the most promising methods for removal of fulvic acids (FA), which is a typical category of natural organic contamination in groundwater. In this paper, TiO{sub 2}/graphene nanocomposites (N-RGO/TiO{sub 2}) were prepared via simple chemical functionalization and one-step hydrothermal method for efficient photodegradation of FA under illumination of a xenon lamp as light source. Here, p-phenylenediamine was used as not only the linkage chemical agent between TiO{sub 2} nanocrystals and graphene, but also the nitrogen dopant for TiO{sub 2} nanocrystals and graphene. During the hydrothermal process, facets of TiO{sub 2} nanocrystals were modulated with addition of HF, and sizes of TiO{sub 2} nanocrystals were controlled by the contents of graphene oxide functionalized with p-phenylenediamine (RGO-NH{sub 2}). The obtained N-RGO/TiO{sub 2} nanocomposites exhibited a much higher photocatalytic activity and stability for degradation of methyl blue (MB) and FA compared with other TiO{sub 2} samples under xenon lamp irradiation. For the third cycle, the 10wt%N-RGO/TiO{sub 2} catalyst maintains high photoactivity (87%) for the degradation of FA, which is much better than the TiO{sub 2}-N/F (61%) in 3 h. This approach supplies a new strategy to design and synthesize metal oxide and graphene oxide nanocomposites with highly efficient photocatalytic performance.

Novel preparation and photocatalytic activity of one-dimensional TiO2 hollow structures

International Nuclear Information System (INIS)

Yu Huogen; Yu Jiaguo; Cheng Bei; Liu Shengwei

2007-01-01

Usually, templated methods include two important steps: the coating of nanocrystals on the surface of the templates and the removal of the templates. In this study, one-dimensional TiO 2 hollow structures, based on the template-directed deposition and then in situ template-sacrificial reaction (or dissolution), were prepared by a one-step template method using vanadium oxide nanobelts as the templates and TiF 4 as the precursor at 60 deg. C. The coating of TiO 2 nanoparticles on the surface of the templates was accompanied with the dissolution of vanadium oxide nanobelts by HF produced during the hydrolysis of TiF 4 in the reaction solution. It was found that the prepared one-dimensional TiO 2 hollow structures with a mesoporous wall were composed of TiO 2 nanoparticles with a diameter of 10-55 nm, resulting in a large specific surface area (77.2 m 2 g -1 ) and high pore volume (0.13 cm 3 g -1 ), and the wall thickness of the TiO 2 hollow structures could be easily controlled by adjusting the precursor concentration of TiF 4 . The photocatalytic activity experiment indicated that the prepared one-dimensional TiO 2 hollow structures, which could be readily separated from a slurry system after photocatalytic reaction, exhibited obvious photocatalytic activity for the photocatalytic degradation of methyl orange aqueous solution

Eu-doped ZnO-HfO2 hybrid nanocrystal-embedded low-loss glass-ceramic waveguides

Science.gov (United States)

Ghosh, Subhabrata; N, Shivakiran Bhaktha B.

2016-03-01

We report on the sol-gel fabrication, using a dip-coating technique, of low-loss Eu-doped 70SiO2 -(30-x) HfO2-xZnO (x = 2, 5, 7 and 10 mol%) ternary glass-ceramic planar waveguides. Transmission electron microscopy and grazing incident x-ray diffraction experiments confirm the controlled growth of hybrid nanocrystals with an average size of 3 nm-25 nm, composed of ZnO encapsulated by a thin layer of nanocrystalline HfO2, with an increase of ZnO concentration from x = 2 mol% to 10 mol% in the SiO2-HfO2 composite matrix. The effect of crystallization on the local environment of Eu ions, doped in the ZnO-HfO2 hybrid nanocrystal-embedded glass-ceramic matrix, is studied using photoluminescence spectra, wherein an intense mixed-valence state (divalent as well as trivalent) emission of Eu ions is observed. The existence of Eu2+ and Eu3+ in the SiO2-HfO2-ZnO ternary matrix is confirmed by x-ray photoelectron spectroscopy. Importantly, the Eu{}2+,3+-doped ternary waveguides exhibit low propagation losses (0.3 ± 0.2 dB cm-1 at 632.8 nm) and optical transparency in the visible region of the electromagnetic spectrum, which makes ZnO-HfO2 nanocrystal-embedded SiO2-HfO2-ZnO waveguides a viable candidate for the development of on-chip, active, integrated optical devices.

Solvothermal synthesis of TiO2 nanocrystals with {001} facets using titanic acid nanobelts for superior photocatalytic activity

Science.gov (United States)

Cao, Yuhui; Zong, Lanlan; Li, Qiuye; Li, Chen; Li, Junli; Yang, Jianjun

2017-01-01

Anatase TiO2 nanocrystals exposed with {001} facets were fabricated by solvothermal strategy in HF-C4H9OH mixed solution, using titanic acid nanobelts (TAN) as a precursor. The shape of TAN is a long flat plane with a high aspect ratio, and F- is easily adsorbed on the surface of the nanobelts, inducing a higher exposure of {001} facet of TiO2 nanoparticles during the structure reorganization. The exposed percentage of {001} facets could vary from 40 to 77% by adjusting the amount of HF. The as-prepared samples were characterized by transmission electron microscopy, N2 adsorption-desorption isotherms, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscope. The photocatalytic measurement showed that TiO2 nanocrystals with 77% {001} facets exhibited much superior photocatalytic activity for photodegradation of methyl orange, methylene blue, and rhodamine B. And what's more, the mineralization rate of methyl orange was as high as 96% within 60 min. The photocatalytic enhancement is due to a large amount of the high energetic {001} facets exposing, the special truncated octahedral morphology and a stronger ability for dyes adsorption.

Solvothermal Synthesis of Hierarchical Colloidal Nanocrystal Assemblies of ZnFe2O4 and Their Application in Water Treatment

Directory of Open Access Journals (Sweden)

Peizhi Guo

2016-09-01

Full Text Available Hierarchical colloidal nanocrystal assemblies (CNAs of ZnFe2O4 have been synthesized controllably by a solvothermal method. Hollow ZnFe2O4 spheres can be formed with the volume ratios of ethylene glycol to ethanol of 1:4 in the starting systems, while solid ZnFe2O4 CNAs are obtained by adjusting the volume proportion of ethylene glycol to ethanol from 1:2 to 2:1. Magnetometric measurement data showed that the ZnFe2O4 CNAs obtained with the volume ratios of 1:2 and 1:1 exhibited weak ferromagnetic behavior with high saturation magnetization values of 60.4 and 60.3 emu·g−1, respectively. However, hollow spheres showed a saturation magnetization value of 52.0 emu·g−1, but the highest coercivity among all the samples. It was found that hollow spheres displayed the best ability to adsorb Congo red dye among all the CNAs. The formation mechanisms of ZnFe2O4 CNAs, as well as the relationship between their structure, crystallite size, and properties were discussed based on the experimental results.

Solvothermal synthesis of TiO{sub 2} nanocrystals with {001} facets using titanic acid nanobelts for superior photocatalytic activity

Energy Technology Data Exchange (ETDEWEB)

Cao, Yuhui; Zong, Lanlan [National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Henan University, Kaifeng, 475004 (China); Li, Qiuye, E-mail: qiuyeli@henu.edu.cn [National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Henan University, Kaifeng, 475004 (China); Collaborative Innovation Center of Nano Functional Materials and Applications of Henan Province, Henan University, Kaifeng, 475004 (China); Li, Chen; Li, Junli [National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Henan University, Kaifeng, 475004 (China); Yang, Jianjun, E-mail: yangjianjun@henu.edu.cn [National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Henan University, Kaifeng, 475004 (China); Collaborative Innovation Center of Nano Functional Materials and Applications of Henan Province, Henan University, Kaifeng, 475004 (China)

2017-01-01

Highlights: • TiO{sub 2} exposed with {001} facets were firstly prepared using TAN as Ti source. • The mineralization rate of MO on sample with 77% {001} facets was as high as 96%. • The superior photocatalytic activity was greatly due to {001} facets exposing. - Abstract: Anatase TiO{sub 2} nanocrystals exposed with {001} facets were fabricated by solvothermal strategy in HF-C{sub 4}H{sub 9}OH mixed solution, using titanic acid nanobelts (TAN) as a precursor. The shape of TAN is a long flat plane with a high aspect ratio, and F{sup −} is easily adsorbed on the surface of the nanobelts, inducing a higher exposure of {001} facet of TiO{sub 2} nanoparticles during the structure reorganization. The exposed percentage of {001} facets could vary from 40 to 77% by adjusting the amount of HF. The as-prepared samples were characterized by transmission electron microscopy, N{sub 2} adsorption-desorption isotherms, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscope. The photocatalytic measurement showed that TiO{sub 2} nanocrystals with 77% {001} facets exhibited much superior photocatalytic activity for photodegradation of methyl orange, methylene blue, and rhodamine B. And what’s more, the mineralization rate of methyl orange was as high as 96% within 60 min. The photocatalytic enhancement is due to a large amount of the high energetic {001} facets exposing, the special truncated octahedral morphology and a stronger ability for dyes adsorption.

TiO{sub 2} colloidal nanocrystals surface modification by V{sub 2}O{sub 5} species: Investigation by {sup 47,49}Ti MAS-NMR and H{sub 2}, CO and NO{sub 2} sensing properties

Energy Technology Data Exchange (ETDEWEB)

Epifani, Mauro, E-mail: mauro.epifani@le.imm.cnr.it [Consiglio Nazionale delle Ricerche—Istituto per la Microelettronica e Microsistemi (CNR–IMM), via Monteroni c/o Campus Universitario, I-73100 Lecce (Italy); Comini, Elisabetta [SENSOR Lab, Department of Information Engineering, Brescia University and CNR-INO, via Valotti 9, 25133 Brescia (Italy); Díaz, Raül [Electrochemical Processes Unit, IMDEA Energy Institute, Avda. Ramón de la Sagra 3, 28935 Móstoles (Spain); Force, Carmen [NMR Unit, Centro de Apoyo Tecnológico, Universidad Rey Juan Carlos, c/Tulipán, s/n, 28933 Móstoles (Spain); Siciliano, Pietro [Consiglio Nazionale delle Ricerche—Istituto per la Microelettronica e Microsistemi (CNR–IMM), via Monteroni c/o Campus Universitario, I-73100 Lecce (Italy); Faglia, Guido [SENSOR Lab, Department of Information Engineering, Brescia University and CNR-INO, via Valotti 9, 25133 Brescia (Italy)

2015-10-01

Highlights: • Novel sensing architecture is presented, made by V{sub 2}O{sub 5} modification of TiO{sub 2} surface. • MAS NMR techniques are a powerful tool for studying the influence of the V{sub 2}O{sub 5} layer. • The V{sub 2}O{sub 5} surface deposition enhanced the adsorption properties with respect to pure TiO{sub 2}. - Abstract: TiO{sub 2} and TiO{sub 2}–V{sub 2}O{sub 5} nanocrystals were prepared by coupling sol–gel and solvothermal methods, followed by heat-treatment at 400 °C, after which the mean nanocrystal size was about 5 nm. The materials were characterized by X-ray diffraction, transmission electron microscopy and solid state nuclear magnetic resonance spectroscopy. It was shown that while the TiO{sub 2} phase was always anatase even after heat-treatment at 500 °C, the presence of the vanadium oxide species enhanced the surface re-configuration of the Ti ions. Hence the coordination environment of surface Ti atoms was drastically changed, by formation of further bonds and imposition of a given local geometry. The final hypothesis was that in pure titania surface rearrangement occurs, leading to the new NMR signal, but this modification was favored in the TiO{sub 2}–V{sub 2}O{sub 5} sample, where the Ti surface atoms were forced into the final configurations by the bonding with V atoms through oxygen. The materials heat-treated at 400 °C were used to process chemoresistive sensors, which were tested to hydrogen, CO and NO{sub 2}, as examples of gases with peculiar sensing mechanisms. The results evidenced that the surface deposition of V{sub 2}O{sub 5} onto the anatase TiO{sub 2} nanocrystals was effective in modifying the adsorption properties of the anatase nanocrystals.

A hierarchical nanostructure consisting of amorphous MnO{sub 2}, Mn{sub 3}O{sub 4} nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors

Energy Technology Data Exchange (ETDEWEB)

Hu, Chi-Chang; Hung, Ching-Yun [Department of Chemical Engineering, National Tsing Hua University, Hsin-Chu 30013 (China); Chang, Kuo-Hsin [Department of Chemical Engineering, National Tsing Hua University, Hsin-Chu 30013 (China); Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621 (China); Yang, Yi-Lin [Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621 (China)

2011-01-15

In this communication, a porous hierarchical nanostructure consisting of amorphous MnO{sub 2} (a-MnO{sub 2}), Mn{sub 3}O{sub 4} nanocrystals, and single-crystalline MnOOH nanowires is designed for the supercapacitor application, which is prepared by a simple two-step electrochemical deposition process. Because of the gradual co-transformation of Mn{sub 3}O{sub 4} nanocrystals and a-MnO{sub 2} nanorods into an amorphous manganese oxide, the cycle stability of a-MnO{sub 2} is obviously enhanced by adding Mn{sub 3}O{sub 4}. This unique ternary oxide nanocomposite with 100-cycle CV activation exhibits excellent capacitive performances, i.e., excellent reversibility, high specific capacitances (470 F g{sup -1} in CaCl{sub 2}), high power property, and outstanding cycle stability. The highly porous microstructures of this composite before and after the 10,000-cycle CV test are examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). (author)

Phase controlled solvothermal synthesis of Cu_2ZnSnS_4, Cu_2ZnSn(S,Se)_4 and Cu_2ZnSnSe_4 Nanocrystals: The effect of Se and S sources on phase purity

International Nuclear Information System (INIS)

Pal, Mou; Mathews, N.R.; Paraguay-Delgado, F.; Mathew, X.

2015-01-01

In this study, we have reported the synthesis of Cu_2ZnSnSe_4 (CZTSe), Cu_2ZnSnS_4 (CZTS) and Cu_2ZnSn(S,Se)_4 (CZTSSe) nanocrystals with tunable band gap and composition obtained by solvothermal method. The crystalline structure, composition, morphology and optical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman scattering, energy dispersive X-ray spectroscopy, transmission electron microscopy and diffuse reflectance (DR) spectroscopy. While the XRD patterns of CZTS and CZTSe nanoparticles prepared with elemental S/Se powder revealed the presence of phase pure nanoparticles, the CZTSSe nanoparticles obtained using a mixture of S and Se, were found to contain many secondary phases under the same synthesis protocol. Formation of impurity phases in CZTSSe sample, can be avoided by using a mixture of 1-dodecanethiol (DT; CH_3(CH_2)_1_1SH)/oleylamine (OLA) instead of S powder and following the same experimental procedure. The incorporation of S in CZTSe nanocrystals prepared in presence of DDT/OLA mixture was confirmed through structural and optical characterizations. The optical properties of the quaternary chalcogenide nanocrystals were found to vary with the chemical composition of the material. - Highlights: • Solvothermal synthesis of CZTS, CZTSSe and CZTSe nanocrystals and discussion on possible formation mechanism. • Use of dodecanethiol/oleylamine mixture to synthesize phase-pure CZTSSe nanocrystals. • Formation of impurity phases can be controlled with proper S and Se sources.

Colloidal Fe-doped ZnO nanocrystals: Facile low temperature synthesis, characterization and properties

Energy Technology Data Exchange (ETDEWEB)

Singhal, A. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)], E-mail: ansing@barc.gov.in; Achary, S.N.; Tyagi, A.K. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Manna, P.K.; Yusuf, S.M. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

2008-09-25

Colloidal Fe-doped ZnO nanocrystals, Zn{sub 1-x}Fe{sub x}O (x = 0.00, 0.05, 0.07 and 0.1) have been prepared by thermal decomposition of metal precursors at 200 deg. C with hexadecylamine (HDA) as solvent and surfactant. The nanocrystals so prepared can be easily dispersed in non-polar solvents like chloroform and toluene. The nanocrystals have been structurally characterized using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). Magnetization measurements on a representative sample, Zn{sub 0.95}Fe{sub 0.05}O using a vibrating sample magnetometer (VSM) reveal that the nanocrystals exhibit a weak ferromagnetic behavior at 300 K. This observation is further confirmed by the electron paramagnetic resonance spectrum of Zn{sub 0.95}Fe{sub 0.05}O nanocrystals, which shows a distinct ferromagnetic resonance signal at room temperature.

Synthesis and photocatalytic CO2 reduction performance of Cu2O/Coal-based carbon nanoparticle composites

Science.gov (United States)

Dedong, Zhang; Maimaiti, Halidan; Awati, Abuduheiremu; Yisilamu, Gunisakezi; Fengchang, Sun; Ming, Wei

2018-05-01

The photocatalytic reduction of CO2 into hydrocarbons provides a promising approach to overcome the challenges of environmental crisis and energy shortage. Here we fabricated a cuprous oxide (Cu2O) based composite photocatalyst consisting of Cu2O/carbon nanoparticles (CNPs). To prepare the CNPs, coal samples from Wucaiwan, Xinjiang, China, were first treated with HNO3, followed by hydrogen peroxide (H2O2) oxidation to strip nanocrystalline carbon from coal. After linking with oxygen-containing group such as hydroxyl, coal-based CNPs with sp2 carbon structure and multilayer graphene lattice structure were synthesized. Subsequently, the CNPs were loaded onto the surface of Cu2O nanoparticles prepared by in-situ reduction of copper chloride (CuCl2·2H2O). The physical properties and chemical structure of the Cu2O/CNPs as well as photocatalytic activity of CO2/H2O reduction into CH3OH were measured. The results demonstrate that the Cu2O/CNPs are composed of spherical particles with diameter of 50 nm and mesoporous structure, which are suitable for CO2 adsorption. Under illumination of visible light, electron-hole pairs are generated in Cu2O. Thanks to the CNPs, the fast recombination of electron-hole pairs is suppressed. The energy gradient formed on the surface of Cu2O/CNPs facilitates the efficient separation of electron-hole pairs for CO2 reduction and H2O oxidation, leading to enhanced photocatalytic activity.

Hot-injection synthesis of Ni-ZnO hybrid nanocrystals with tunable magnetic properties and enhanced photocatalytic activity

Energy Technology Data Exchange (ETDEWEB)

Zeng, Deqian; Qiu, Yulong; Chen, Yuanzhi, E-mail: yuanzhi@xmu.edu.cn; Zhang, Qinfu; Liu, Xiang; Peng, Dong-Liang, E-mail: dlpeng@xmu.edu.cn [Xiamen University, Department of Materials Science and Engineering, Fujian Provincial Key Laboratory of Materials Genome, Collaborative Innovation Center of Chemistry for Energy Materials, College of Materials (China)

2017-04-15

Magnetic metal-semiconductor hybrid nanocrystals containing ferromagnetic Ni and semiconductor ZnO have been prepared via a hot-injection route. The Ni-ZnO hybrid nanocrystals have a flower-like morphology that consists of Ni inner cores and ZnO petal shells. In spite of their large lattice mismatch, ZnO nanocrystals can still grow on faceted Ni nanocrystals to form stable interfaces. The composition of Ni-ZnO hybrid nanocrystals is readily controlled, and the average size of Ni core is tunable from 25 to 50 nm. Room temperature ferromagnetic properties are observed in these hybrid nanocrystals, and tunable magnetic properties also can be achieved by varying the size of Ni core. The as-prepared Ni-ZnO hybrid nanocrystals exhibit enhanced photocatalytic performance under ultraviolet light illumination as compared to pure ZnO nanocrystals. Furthermore, the superior reusability of hybrid nanocrystals for photocatalytic application is achieved by virtue of their magnetic properties. The facile and efficient seed-mediate strategy is particularly attractive to construct hybrid magnetic-semiconducting heterostructures. The as-obtained Ni-ZnO hybrid nanocrystals offer great potential for various applications due to their combined magnetic and semiconducting properties and low-cost earth-abundant availability.

Facile preparation and characterization of ZnCdS nanocrystals for interfacial applications in photovoltaic devices.

Science.gov (United States)

Duan, Chenghao; Luo, Weining; Jiu, Tonggang; Li, Jiangsheng; Wang, Yao; Lu, Fushen

2018-02-15

Recently, ZnCdS nanocrystals (NCs) have attracted intense attention because of their specific optical properties and electrical characteristics. In this paper, a green and facile solution method is reported for the preparation of ZnCdS nanocrystals using dimethylsulfoxide as small molecular ligands. The ZnCdS nanocrystals are used as an interface modification material in the photovoltaic devices. It is found that the modification of ZnCdS on TiO 2 surface not only suppresses the recombination loss of carriers but also reduces the series resistance of TiO 2 /active layer. Consequently, both of the short circuit current (J sc ) and the fill factor (FF) of the solar cells were significantly improved. Power conversion efficiency (PCE) of 7.75% based on TiO 2 /ZnCdS was achieved in contrast to 6.65% of the reference devices based on pure TiO 2 film in organic solar cells. Furthermore, the PCE of perovskite solar cells based on TiO 2 /ZnCdS was observed with 8.3% enhancement compared to that of pure TiO 2 -based ones. Copyright © 2017 Elsevier Inc. All rights reserved.

Controllable synthesis of Co3O4 nanocrystals as efficient catalysts for oxygen reduction reaction

Science.gov (United States)

Li, Baoying; Zhang, Yihe; Du, Ruifeng; Liu, Lei; Yu, Xuelian

2018-03-01

The electrochemical oxygen reduction reaction (ORR) has received great attention due to its importance in fuel cells and metal-air batteries. Here, we present a simple approach to prepare non-noble metal catalyst-Co3O4 nanocrystals (NCs). The particle size and shape were simply controlled by different types and concentrations of metal precursor. Furthermore, different sizes and shapes of Co3O4 NCs are explored as electrocatalysts for ORR, and it has been observed that particles with a similar shape, and smaller particle size led to greater catalytic current densities because of the greater surface area. For particles with a comparable size, the shape or crystalline structure governed the activity of the electrocatalytic reactions. Most importantly, the 9 nm-Co3O4 were demonstrated to act as low-cost catalysts for the ORR with a similar performance to that of Pt catalysts.

Facile synthesis and electrochemical performance of Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} nanocomposite for lithium-ion batteries

Energy Technology Data Exchange (ETDEWEB)

An, Bonan [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Engineering Research Center of Materials and Technology for Electrochemical Energy Storage (Ministry of Education), Guangzhou 510006 (China); Ru, Qiang, E-mail: ruqiang@scnu.edu.cn [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Engineering Research Center of Materials and Technology for Electrochemical Energy Storage (Ministry of Education), Guangzhou 510006 (China); Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Hu, Shejun; Song, Xiong; Li, Juan [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Engineering Research Center of Materials and Technology for Electrochemical Energy Storage (Ministry of Education), Guangzhou 510006 (China)

2014-12-15

Graphical abstract: TEM of Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} composite and the discharge curves of pure Co{sub 3}O{sub 4}, pure Co{sub 2}SnO{sub 4} and Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} composite. - Highlights: • Novel Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} composite has been prepared by simple co-precipitation method. • Small spherical nanocrystals adhering to the surface of large polyhedral particles. • Formation mechanism is relate to solubility of Sn(OH){sub 6}{sup 2−} in high concentration OH{sup −} . • The composite shows better electrochemical performance than Co{sub 2}SnO{sub 4} and Co{sub 3}O{sub 4} - Abstract: A novel dispersed structure Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} composite has been successfully synthesized by a conventional co-precipitation method with certain amount of NaOH concentration. The obtained composite exhibits dispersed structure with small spherical nanocrystals adhering to the surface of large polyhedral particles, which has been studied as an anode material in lithium-ion battery. Galvanostatic charge–discharge and cyclic voltammetry has been conducted to measure the electrochemical properties of the material. The results show that Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} composite demonstrates good reversible capacity of 702.5 mA h g{sup −1} after 50 cycles at a current density of 100 mA h g{sup −1}, much better than that of pure Co{sub 3}O{sub 4} (375.1 mA h g{sup −1}) and pure Co{sub 2}SnO{sub 4} (194.1 mA h g{sup −1}). This material also presents improved rate performance with capacity retention of 71.1% when the current ranges from 100 mA g{sup −1} to 1000 mA g{sup −1}. The excellent electrochemical performance of the as-prepared dispersed structure Co{sub 2}SnO{sub 4}/Co{sub 3}O{sub 4} composite could be attributed to the good dispersibility of nanoparticles which can effectively alleviate the volume expansion and improve the conductivity, thus enhance the cycling stability.

Growth Mechanism and Surface Structure of Ge Nanocrystals Prepared by Thermal Annealing of Cosputtered GeSiO Ternary Precursor

Directory of Open Access Journals (Sweden)

Bo Zhang

2014-01-01

Full Text Available Ge nanocrystals (Ge-ncs embedded in a SiO2 superlattice structure were prepared by magnetron cosputtering and postdeposition annealing. The formation of spherical nanocrystals was confirmed by transmission electron microscopy and their growth process was studied by a combination of spectroscopic techniques. The crystallinity volume fraction of Ge component was found to increase with crystallite size, but its overall low values indicated a coexistence of crystalline and noncrystalline phases. A reduction of Ge-O species was observed in the superlattice during thermal annealing, accompanied by a transition from oxygen-deficient silicon oxide to silicon dioxide. A growth mechanism involving phase separation of Ge suboxides (GeOx was then proposed to explain these findings and supplement the existing growth models for Ge-ncs in SiO2 films. Further analysis of the bonding structure of Ge atoms suggested that Ge-ncs are likely to have a core-shell structure with an amorphous-like surface layer, which is composed of GeSiO ternary complex. The surface layer thickness was extracted to be a few angstroms and equivalent to several atomic layer thicknesses.

Electrospinning direct preparation of SnO2/Fe2O3 heterojunction nanotubes as an efficient visible-light photocatalyst

International Nuclear Information System (INIS)

Zhu, Chengquan; Li, Yuren; Su, Qing; Lu, Bingan; Pan, Jiaqi; Zhang, Jiawang; Xie, Erqing; Lan, Wei

2013-01-01

Highlights: •SnO 2 /Fe 2 O 3 nano-heterojunction-tubes are prepared by a facile electrospinning technique. •The formation mechanism of heterojunction tubes is proposed for self-polymer-templates action. •SnO 2 /Fe 2 O 3 nano-heterojunction-tubes show high photocatalytic activity under visible light irradiation. •The reasons for the high photocatalytic activity are investigated in detail. -- Abstract: Herein SnO 2 /Fe 2 O 3 heterojunction nanotubes are prepared by a facile electrospinning technique. The heterojunction nanotubes with a diameter of about 200 nm uniformly distribute SnO 2 and Fe 2 O 3 nanocrystals and present the obvious interfaces between them, which form perfect SnO 2 /Fe 2 O 3 nano-heterojunctions. A possible mechanism based on self-polymer-templates is proposed to explain the formation of SnO 2 /Fe 2 O 3 heterojunction nanotubes. The heterojunction nanotubes show high photocatalytic activity for the degradation of RhB dye under visible light irradiation. The prepared SnO 2 /Fe 2 O 3 heterojunction nanotubes can also be applied to other fields such as sensor, lithium-ion batteries

Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study.

Science.gov (United States)

Pita, Kantisara; Baudin, Pierre; Vu, Quang Vinh; Aad, Roy; Couteau, Christophe; Lérondel, Gilles

2013-12-06

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix.

Ge nanocrystals formed by furnace annealing of Ge(x)[SiO2](1-x) films: structure and optical properties

Science.gov (United States)

Volodin, V. A.; Cherkov, A. G.; Antonenko, A. Kh; Stoffel, M.; Rinnert, H.; Vergnat, M.

2017-07-01

Ge(x)[SiO2](1-x) (0.1  ⩽  x  ⩽  0.4) films were deposited onto Si(0 0 1) or fused quartz substrates using co-evaporation of both Ge and SiO2 in high vacuum. Germanium nanocrystals were synthesized in the SiO2 matrix by furnace annealing of Ge x [SiO2](1-x) films with x  ⩾  0.2. According to electron microscopy and Raman spectroscopy data, the average size of the nanocrystals depends weakly on the annealing temperature (700, 800, or 900 °C) and on the Ge concentration in the films. Neither amorphous Ge clusters nor Ge nanocrystals were observed in as-deposited and annealed Ge0.1[SiO2]0.9 films. Infrared absorption spectroscopy measurements show that the studied films do not contain a noticeable amount of GeO x clusters. After annealing at 900 °C intermixing of germanium and silicon atoms was still negligible thus preventing the formation of GeSi nanocrystals. For annealed samples, we report the observation of infrared photoluminescence at low temperatures, which can be explained by exciton recombination in Ge nanocrystals. Moreover, we report strong photoluminescence in the visible range at room temperature, which is certainly due to Ge-related defect-induced radiative transitions.

Hydrothermal Synthesis of PbTiO3 Nanocrystals with a pH-Adjusting Agent of Ammonia Solution

Science.gov (United States)

Li, Xinyi; Huang, Zhixiong; Zhang, Lianmeng; Guo, Dongyun

2018-05-01

The PbTiO3 nanocrystals were synthesized by a hydrothermal method, and ammonia solution was firstly used as a pH-adjusting agent. The effect of ammonia concentration on formation and morphologies of PbTiO3 nanocrystals was investigated. At low ammonia concentration (0-2.2 mol/L), no perovskite PbTiO3 phase was formed. When the ammonia concentration was 4.4 mol/L, the rod-like PbTiO3 nanocrystals with highly crystalline were successfully synthesized. As the ammonia concentration further increased to 13.2 mol/L, the flake-like PbTiO3 nanocrystals were formed.

Hydroxyapatite nanocrystals: Simple preparation, characterization and formation mechanism

International Nuclear Information System (INIS)

Mohandes, Fatemeh; Salavati-Niasari, Masoud; Fathi, Mohammadhossein; Fereshteh, Zeinab

2014-01-01

Crystalline hydroxyapatite (HAP) nanoparticles and nanorods have been successfully synthesized via a simple precipitation method. To control the shape and particle size of HAP nanocrystals, coordination ligands derived from 2-hydroxy-1-naphthaldehyde were first prepared, characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ( 1 H-NMR) spectroscopies, and finally applied in the synthesis process of HAP. On the other hand, the HAP nanocrystals were also characterized by several techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to the FE-SEM and TEM micrographs, it was found that the morphology and crystallinity of the HAP powders depended on the coordination mode of the ligands. - Highlights: • HAP nanobundles and nanoparticles have been prepared by a precipitation method. • Morphologies of HAP nanocrystals were controlled by different coordination ligands. • The formation mechanism of hydroxyapatite nanocrystals was also considered

Hydroxyapatite nanocrystals: Simple preparation, characterization and formation mechanism

Energy Technology Data Exchange (ETDEWEB)

Mohandes, Fatemeh [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P. O. Box. 87317-51167, Islamic Republic of Iran (Iran, Islamic Republic of); Salavati-Niasari, Masoud, E-mail: salavati@kashanu.ac.ir [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P. O. Box. 87317-51167, Islamic Republic of Iran (Iran, Islamic Republic of); Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box 87317-51167, Islamic Republic of Iran (Iran, Islamic Republic of); Fathi, Mohammadhossein [Biomaterials Research Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Islamic Republic of Iran (Iran, Islamic Republic of); Dental Materials Research Center, Isfahan University of Medical Sciences, Isfahan, Islamic Republic of Iran (Iran, Islamic Republic of); Fereshteh, Zeinab [Biomaterials Research Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Islamic Republic of Iran (Iran, Islamic Republic of)

2014-12-01

Crystalline hydroxyapatite (HAP) nanoparticles and nanorods have been successfully synthesized via a simple precipitation method. To control the shape and particle size of HAP nanocrystals, coordination ligands derived from 2-hydroxy-1-naphthaldehyde were first prepared, characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ({sup 1}H-NMR) spectroscopies, and finally applied in the synthesis process of HAP. On the other hand, the HAP nanocrystals were also characterized by several techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to the FE-SEM and TEM micrographs, it was found that the morphology and crystallinity of the HAP powders depended on the coordination mode of the ligands. - Highlights: • HAP nanobundles and nanoparticles have been prepared by a precipitation method. • Morphologies of HAP nanocrystals were controlled by different coordination ligands. • The formation mechanism of hydroxyapatite nanocrystals was also considered.

Al2O3 nanocrystals embedded in amorphous Lu2O3 high-k gate dielectric for floating gate memory application

International Nuclear Information System (INIS)

Yuan, C L; Chan, M Y; Lee, P S; Darmawan, P; Setiawan, Y

2007-01-01

The integration of nanoparticles has high potential in technological applications and opens up possibilities of the development of new devices. Compared to the conventional floating gate memory, a structure containing nanocrystals embedded in dielectrics shows high potential to produce a memory with high endurance, low operating voltage, fast write-erase speeds and better immunity to soft errors [S. Tiwari, F. Rana, H. Hanafi et al. 1996 Appl.Phys. Lett. 68, 1377]. A significant improvement on data retention [J. J. Lee, X. Wang et al. 2003 Proceedings of the VLSI Technol. Symposium, p33] can be observed when discrete nanodots are used instead of continuous floating gate as charge storage nodes because local defect related leakage can be reduced efficiently. Furthermore, using a high-k dielectric in place of the conventional SiO2 based dielectric, nanodots flash memory is able to achieve significantly improved programming efficiency and data retention [A. Thean and J. -P. Leburton, 2002 IEEE Potentials 21, 35; D. W. Kim, T. Kim and S. K. Banerjee, 2003 IEEE Trans. Electron Devices 50, 1823]. We have recently successfully developed a method to produce nanodots embedded in high-k gate dielectrics [C. L. Yuan, P. Darmawan, Y. Setiawan and P. S. Lee, 2006 Electrochemical and Solid-State Letters 9, F53; C. L. Yuan, P. Darmawan, Y. Setiawan and P. S. Lee, 2006 Europhys. Lett. 74, 177]. In this paper, we fabricated the memory structure of Al 2 O 3 nanocrystals embedded in amorphous Lu 2 O 3 high k dielectric using pulsed laser ablation. The mean size and density of the Al 2 O 3 nanocrystals are estimated to be about 5 nm and 7x1011 cm -2 , respectively. Good electrical performances in terms of large memory window and good data retention were observed. Our preparation method is simple, fast and economical

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties

Science.gov (United States)

Zeng, Deqian; Gong, Pingyun; Chen, Yuanzhi; Zhang, Qinfu; Xie, Qingshui; Peng, Dong-Liang

2016-06-01

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications

MC3T3-E1 cell response of amorphous phase/TiO{sub 2} nanocrystal composite coating prepared by microarc oxidation on titanium

Energy Technology Data Exchange (ETDEWEB)

Zhou, Rui [Department of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Wei, Daqing, E-mail: daqingwei@hit.edu.cn [Department of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Yang, Haoyue; Feng, Wei [Department of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Cheng, Su [Department of Mechanical Engineering, School of Architecture and Civil Engineering, Harbin University of Science and Technology, Harbin 150001 (China); Li, Baoqiang; Wang, Yaming; Jia, Dechang; Zhou, Yu [Department of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

2014-06-01

Bioactive amorphous phase/TiO{sub 2} nanocrystal (APTN) composite coatings were fabricated by microarc oxidation (MAO) on Ti. The APTN coatings are composed of much amorphous phase with Si, Na, Ca, Ti and O elements and a few TiO{sub 2} nanocrystals. With increasing applied voltage, the micropore density of the APTN coating decreases and the micropore size of the APTN coating increases. The results indicate that less MC3T3-E1 cells attach on the APTN coatings as compared to Ti. However, the APTN coatings greatly enhance the cell proliferation ability and the activity of alkaline phosphatase. The amorphous phase and the concentrations of the released Ca and Si from the APTN coatings during cell culture have significant effects on the cell response. - Highlights: • Amorphous phase/TiO2 nanocrystal (APTN) composite coatings were fabricated. • The MC3T3-E1 cell response of the APTN coatings was evaluated. • The APTN coatings greatly enhanced the cell proliferation ability.

Synthesis and characterization of Fe3O4–TiO2 core-shell nanoparticles

International Nuclear Information System (INIS)

Stefan, M.; Pana, O.; Leostean, C.; Silipas, D.; Bele, C.; Senila, M.; Gautron, E.

2014-01-01

Composite core-shell nanoparticles may have morpho-structural, magnetic, and optical (photoluminescence (PL)) properties different from each of the components considered separately. The properties of Fe 3 O 4 –TiO 2 nanoparticles can be controlled by adjusting the titania amount (shell thinness). Core–shell nanoparticles were prepared by seed mediated growth of semiconductor (TiO 2 ) through a modified sol-gel process onto preformed magnetite (Fe 3 O 4 ) cores resulted from the co-precipitation method. The structure and morphology of samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), and high resolution-TEM respectively. X-ray photoelectron spectroscopy was correlated with ICP-AES. Magnetic measurements, optical absorption spectra, as well as PL spectroscopy indicate the presence of a charge/spin transfer from the conduction band of magnetite into the band gap of titania nanocrystals. The process modifies both Fe 3 O 4 and TiO 2 magnetic and optical properties, respectively.

Elucidation of the enhanced ferromagnetic origin in Mn-doped ZnO nanocrystals embedded into a SiO₂ matrix

Energy Technology Data Exchange (ETDEWEB)

Lee, Sejoon; Lee, Youngmin; Kim, Deukyoung [Dongguk University, Seoul (Korea, Republic of)

2013-01-01

The origin of the enhanced room temperature ferromagnetism in Mn-doped ZnO (ZnO:Mn) nanocrystals is investigated. ZnO:Mn nanocrystals, which were fabricated by using a laser irradiation method with a 248-nm KrF excimer laser, exhibited two-times increase in the spontaneous magnetization (∼0.4 emu/cm³ at 300 K) compared to the ZnO:Mn thin film (∼0.2 emu/cm³ at 300 K). The increased exchange integral of J₁/k{sub B} = 51.6 K in ZnO:Mn nanocrystals, in comparison with the ZnO:Mn thin film (J₁/k{sub B} = 46.9 K), is indicative of the enhanced ferromagnetic exchange interaction. This is attributed to the large number of acceptor defects in the SiO₂-capped ZnO:Mn nanocrystals. Namely, the holes bound to the acceptor defects form microscopic bound-magnetic-polarons with Mn ions; hence, long-range ferromagnetic coupling is enhanced. The results suggest that ferromagnetism in ZnO-based dilute magnetic semiconductors can be controlled by modulating the density of native point defects, which can be chemically and thermodynamically modified during the material synthesis or preparation.

Single crystalline Co3O4: Synthesis and optical properties

International Nuclear Information System (INIS)

Hosny, Nasser Mohammed

2014-01-01

Crystals of Co 3 O 4 have been prepared from thermal decomposition of molecular precursors derived from salicylic acid and cobalt (II) acetate or chloride at 500 °C. A cubic phase Co 3 O 4 micro- and nanocrystals have been obtained. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The images of electron microscopes showed octahedral crystals of Co 3 O 4 . The volume and polarizability of the optimized structures of molecular precursors have been calculated and related to the particle size. The optical band gap of the obtained crystals has been measured. The results indicated two optical band gaps with values 2.65 and 2.95 eV for (E g1 ) (E g2 ), respectively. - Highlights: • Synthesis of Co 3 O 4 nanocrystals by decomposition of cobalt salicylic acid precursor. • Characterization of the isolated nanocrystals by using XRD, SEM and HRTEM. • The optical band gap has been measured

Al2O3-Cact-(CuO, Cr2O3, Co3O4 Adsorbents-Catalysts: Preparation and Characterization

Directory of Open Access Journals (Sweden)

Gitana DABRILAITĖ-KUDŽMIENĖ

2013-03-01

Full Text Available Al2O3-Cact-(CuO, Cr2O3 Co3O4 adsorbents-catalysts were prepared using Al2O3-Cact (alumina gel–activated carbon adsorbent and different amount of CuO, Cr2O3 and Co3O4. The active components were incorporated into wet alumina gel–carbon mixture using different conditions (by sol-gel method and mixing a milled metal oxides. Equilibrium adsorptive capacity measurements of alcohol vapours were carried out in order to determine the influence of preparation conditions on the stability of prepared adsorbents–catalysts. Specific surface area of the prepared adsorbents-catalysts were measured by BET method. It was established that for adsorbent-catalyst produced by sol-gel method SBET = 244.7 m2/g. Surface area SBET = 29.32 m2/g was obtained for adsorbent-catalyst with metal oxides. On the basis of these results it was assumed that active carbon was lost in this adsorbent-catalyst during the preparation process. Sol-gel derived adsorbent–catalyst was tested for the oxidation of methanol vapours. Catalytic oxidation was carried out in fixed-bed reactor. Experimental data indicate that adsorptive capacity of the adsorbent–catalyst is (3.232 – 3.259 mg/m3 CH3OH at relative air humidity is 40 % – 50 %. During a fast heating of CH3OH – saturated adsorbent-catalyst a part of adsorbate is converted to CO2 and H2O. Methanol conversion increases with increasing of adsorbent-catalyst heating rate.DOI: http://dx.doi.org/10.5755/j01.ms.19.1.3832

Structural, optical and magnetic studies of CuFe2O4, MgFe2O4 and ZnFe2O4 nanoparticles prepared by hydrothermal/solvothermal method

Science.gov (United States)

Kurian, Jessyamma; Mathew, M. Jacob

2018-04-01

In this paper we report the structural, optical and magnetic studies of three spinel ferrites namely CuFe2O4, MgFe2O4 and ZnFe2O4 prepared in an autoclave under the same physical conditions but with two different liquid medium and different surfactant. We use water as the medium and trisodium citrate as the surfactant for one method (Hydrothermal method) and ethylene glycol as the medium and poly ethylene glycol as the surfactant for the second method (solvothermal method). The phase identification and structural characterization are done using XRD and morphological studies are carried out by TEM. Cubical and porous spherical morphologies are obtained for hydrothermal and solvothermal process respectively without any impurity phase. The optical studies are carried out using FTIR and UV-Vis reflectance spectra. In order to elucidate the nonlinear optical behaviour of the prepared nanomaterial, open aperture z-scan technique is used. From the fitted z-scan curves nonlinear absorption coefficient and the saturation intensity are determined. The magnetic characterization of the samples is performed at room temperature using vibrating sample magnetometer measurements. The M-H curves obtained are fitted using theoretical equation and the different components of magnetization are determined. Nanoparticles with high saturation magnetization are obtained for MgFe2O4 and ZnFe2O4 prepared under solvothermal reaction. The magnetic hyperfine parameters and the cation distribution of the prepared materials are determined using room temperature Mössbauer spectroscopy. The fitted spectra reveal the difference in the magnetic hyperfine parameters owing to the change in size and morphology.

Facile synthesis of high-temperature (1000 °C) phase-stable rice-like anatase TiO2 nanocrystals

Science.gov (United States)

Lv, Lizhen; Chen, Qirong; Liu, Xiuyun; Wang, Miaomiao; Meng, Xiangfu

2015-05-01

High-temperature phase-stable rice-like anatase TiO2 nanocrystals were synthesized by one-pot solvothermal method using soluble titania xerogel and isopropyl alcohol (IPA) as the precursor and the solvent, respectively. Sample characterization was carried out by powder X-ray diffraction, high-resolution transmission electron microscopy, field emission scanning electron microscope, X-ray photoelectron spectroscopy, and N2 adsorption-desorption isotherms. The results showed that TiO2 nanocrystals had rice-like shapes with an average size of 5 nm in width and 35 nm in length. The BET surface area was 153 m2/g. Unexpectedly, the rice-like TiO2 nanocrystals exhibited high-temperature phase stability, which could remain as pure anatase phase after calcinations at 1000 °C. Growth mechanism investigation revealed that the IPA solvent played a key role in nucleation and growth of rice-like anatase TiO2 nanocrystals. The photodegradation of rhodamine B demonstrated that rice-like anatase TiO2 nanocrystals exhibited enhanced photocatalytic activity under visible light irradiation.

Role of Eu"2"+ on the blue‐green photoluminescence of In_2O_3:Eu"2"+ nanocrystals

International Nuclear Information System (INIS)

Devi, Konsam Reenabati; Meetei, Sanoujam Dhiren; Singh, Shougaijam Dorendrajit

2016-01-01

Blue‐green light emitting undoped and europium doped indium oxide nanocrystal were synthesized by simple precipitation method. X-ray diffraction (XRD) pattern confirmed the cubic phase of undoped and europium doped samples. Further, transmission electron microscopy (TEM), scanning electron microscopy (SEM) , energy dispersive analysis of X-rays (EDAX), Fourier transform infra-red (FT-IR), photoluminescence (PL), electron paramagnetic resonance (EPR) studies were performed to characterise the samples. PL analysis of the samples is the core of the present research. It includes excitation, emission and CIE (Commission Internationale de l’e´ clairage) studies of the samples. On doping europium to In_2O_3 lattice, ln"3"+ site is substituted by Eu"2"+ thereby increasing the concentration of singly ionized oxygen vacancy and hence blue–green emission from the host is found to increase. Further, this increase in blue–green emission after doping may also be attributed to 4f → 5d transitions of Eu"2"+. However, the blue–green PL emission is found to decrease after an optimum dopant concentration (Eu"2"+ = 4%) due to luminescence and size quenching. CIE co-ordinates of the samples are calculated to know colour of light emitted from the samples. It suggests that this blue–green light emitting In_2O_3: Eu"2"+ nanocrystals may find application in lighting such as in generation of white light. - Highlight: • XRD and TEM study confirms the synthesis of cubic doped and europium doped nanocrystals. • EPR study reveals the doped europium is in + 2 oxidation state. • Enhance PL emission intensity of host material due to increase in singly ionized oxygen vacancy and 4f–5d transitions of Eu"2"+ • CIE co-ordinates suggest the blue–green colour of the samples.

Si nanocrystals embedded in SiO2: Optical studies in the vacuum ultraviolet range

DEFF Research Database (Denmark)

Pankratov, V.; Osinniy, Viktor; Kotlov, A.

2011-01-01

done. It is demonstrated that the experimentally determined blueshift of the photoluminescence excitation and absorption spectra is larger than the theoretical predictions. The influence of point defects in the SiO2 matrix on the optical and luminescence properties of the embedded Si nanocrystals...... is discussed. Moreover, it is demonstrated that no energy transfer takes place between the SiO2 and Si nanocrystals when the excitation energy is higher than the band-to-band transition energy in SiO2....

ZnO nanowire-based nano-floating gate memory with Pt nanocrystals embedded in Al2O3 gate oxides

International Nuclear Information System (INIS)

Yeom, Donghyuk; Kang, Jeongmin; Lee, Myoungwon; Jang, Jaewon; Yun, Junggwon; Jeong, Dong-Young; Yoon, Changjoon; Koo, Jamin; Kim, Sangsig

2008-01-01

The memory characteristics of ZnO nanowire-based nano-floating gate memory (NFGM) with Pt nanocrystals acting as the floating gate nodes were investigated in this work. Pt nanocrystals were embedded between Al 2 O 3 tunneling and control oxide layers deposited on ZnO nanowire channels. For a representative ZnO nanowire-based NFGM with embedded Pt nanocrystals, a threshold voltage shift of 3.8 V was observed in its drain current versus gate voltage (I DS -V GS ) measurements for a double sweep of the gate voltage, revealing that the deep effective potential wells built into the nanocrystals provide our NFGM with a large charge storage capacity. Details of the charge storage effect observed in this memory device are discussed in this paper

Improving pure red upconversion emission of Co-doped Y{sub 2}O{sub 3}:Yb{sup 3+}–Er{sup 3+} nanocrystals with a combination of sodium sulfide and surfactant Pluronic-F127

Energy Technology Data Exchange (ETDEWEB)

López-Luke, T., E-mail: tzarara@cio.mx [Centro de Investigaciones en Óptica, A.P. 1-948, León, Gto. 37160, México (Mexico); De la Rosa, E., E-mail: elder@cio.mx [Centro de Investigaciones en Óptica, A.P. 1-948, León, Gto. 37160, México (Mexico); Campos Villalobos, I. [Centro de Investigaciones en Óptica, A.P. 1-948, León, Gto. 37160, México (Mexico); Rodriguez, R.A. [Universidad de Guadalajara, Unidad Lagos, Lagos de Moreno, Jal. 47460, México (Mexico); Ángles-Chávez, C. [Instituto Mexicano del Petróleo, Cd. México, D.F. 07730, México (Mexico); Salas, P. [Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, A.P. 1-1010, Querétaro, Qro. 76000, México (Mexico); Wheeler, Damon A.; Zhang, J.Z. [Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064 (United States)

2014-01-15

Nanocrystals of Y{sub 2}O{sub 3}:Yb{sup 3+}–Er{sup 3+} (2:1 mol% Yb{sup 3+}:Er{sup 3+}) were prepared by a novel precipitation technique using Na{sub 2}S and Pluronic-F127 (PF127) surfactant. Crystal structure, particle size, red emission intensity and fluorescence decay lifetimes were determined using microscopy and spectroscopy techniques. TEM analysis indicates that the average particle size ranged from 40 to 70 nm. The nanocrystals showed a strong red emission band centered at 663 nm after excitation at 970 nm. The upconverted signal intensity was improved 250% with an optimum concentration of Na{sub 2}S (0.48 M) and PF127 (0.1 mM). The improvement was explained in terms of the reduction of surface contaminants as well as the cubic crystalline phase of the parent Y{sub 2}O{sub 3} material. Interestingly, the formation of sulfates (SO{sub 4}{sup 2−}) is faster than that of O–H, which is responsible for quenching the red and green emissions. The results suggest that Na{sub 2}S and PF127 are good candidates for surface passivation, especially when used in conjunction. The preparation of Y{sub 2}O{sub 3}:Yb{sup 3+}–Er{sup 3+} using Na{sub 2}S with strong red emission band was produced at a lower cost than that of other sulfuration processes. -- Highlights: • . • Strong red emission band centered at 663 nm was obtained after excitation at 970 nm. • Yb-Er codoped Y2O3 nanocrystals with average size ranging from 40 to 70 nm. • Improvement of the red emission in Y2O3:Yb-Er nanocrystals by the introduction of sodium sulfide and pluronic. • Passivation of nanocrystal surface with sodium sulfide and pluoronic.

Preparation, characterization and catalytic behavior of hierachically porous CuO/α-Fe2O3/SiO2 composite material for CO and o-DCB oxidation

Institute of Scientific and Technical Information of China (English)

Xiaodong Ma; Xi Feng; Xuan He; Hongwen Guo; Lu Lü

2011-01-01

Hierachically porous (HP) CuO/α-Fe2O3/SiO2 composite material was fabricated by sol-gel method and multi-hydrothermal processes using HP-SiO2 as support.The resulting material was characterized by N2 adsorption-desorption,X-ray diffraction and scanning electron microscopy.The as-prepared CuO/Fe2O3/HP-SiO2 sample,with α-Fe2O3 and CuO nanocrystals,possessed a co-continuous skeleton,through-macroporous and mesoporous structure.Its catalytic behavior for CO and o-DCB oxidation was investigated.The result showed that CuO/Fe2O3/HP-SiO2 catalyst exhibited high catalytic activity for both CO and o-DCB oxidation,indicating its potential application in combined abatement of CO and chlorinated volatile organic compounds.

Depth-selective 2D-ACAR and coincidence Doppler investigation of embedded Au nanocrystals in MgO

International Nuclear Information System (INIS)

Eijt, S.W.H.; Veen, A. van; Falub, C.V.; Schut, H.; Huis, M.A. van; Mijnarends, P.E.

2004-01-01

We present a depth-selective 2D-ACAR and two-detector Doppler broadening study on Au nanocrystals in monocrystalline MgO(100), produced in sub-surface layers by ion implantation and subsequent thermal annealing to temperatures beyond the stability range of vacancy clusters in MgO. In contrast to the case of Li nanocrystals, it was found that positrons do not trap inside the Au nanocrystals, but only in defects at the nanocrystal-to-host interface (attached vacancy clusters). This is interpreted in terms of the positron affinity of Au, MgO and the defects. (orig.)

Depth-selective 2D-ACAR and coincidence Doppler investigation of embedded Au nanocrystals in MgO

Energy Technology Data Exchange (ETDEWEB)

Eijt, S.W.H.; Veen, A. van; Falub, C.V.; Schut, H.; Huis, M.A. van [Interfaculty Reactor Inst., Delft Univ. of Technology, Delft (Netherlands); Mijnarends, P.E. [Interfaculty Reactor Inst., Delft Univ. of Technology, Delft (Netherlands); Dept. of Physics, Northeastern Univ., Boston, MA (United States)

2004-07-01

We present a depth-selective 2D-ACAR and two-detector Doppler broadening study on Au nanocrystals in monocrystalline MgO(100), produced in sub-surface layers by ion implantation and subsequent thermal annealing to temperatures beyond the stability range of vacancy clusters in MgO. In contrast to the case of Li nanocrystals, it was found that positrons do not trap inside the Au nanocrystals, but only in defects at the nanocrystal-to-host interface (attached vacancy clusters). This is interpreted in terms of the positron affinity of Au, MgO and the defects. (orig.)

Single-crystalline MFe(2)O(4) nanotubes/nanorings synthesized by thermal transformation process for biological applications.

Science.gov (United States)

Fan, Hai-Ming; Yi, Jia-Bao; Yang, Yi; Kho, Kiang-Wei; Tan, Hui-Ru; Shen, Ze-Xiang; Ding, Jun; Sun, Xiao-Wei; Olivo, Malini Carolene; Feng, Yuan-Ping

2009-09-22

We report a general thermal transformation approach to synthesize single-crystalline magnetic transition metal oxides nanotubes/nanorings including magnetite Fe(3)O(4), maghematite gamma-Fe(2)O(3), and ferrites MFe(2)O(4) (M = Co, Mn, Ni, Cu) using hematite alpha-Fe(2)O(3) nanotubes/nanorings template. While the straightforward reduction or reduction-oxides process was employed to produce Fe(3)O(4) and gamma-Fe(2)O(3), the alpha-Fe(2)O(3)/M(OH)(2) core/shell nanostructure was used as precursor to prepare MFe(2)O(4) nanotubes via MFe(2)O(4-x) (0 MFe(2)O(4) nanocrystals with tunable size, shape, and composition have exhibited unique magnetic properties. Moreover, they have been demonstrated as a highly effective peroxidase mimic catalysts for laboratory immunoassays or as a universal nanocapsules hybridized with luminescent QDs for magnetic separation and optical probe of lung cancer cells, suggesting that these biocompatible magnetic nanotubes/nanorings have great potential in biomedicine and biomagnetic applications.

Synthesis, Characterization and Properties of CeO2-doped TiO2 Composite Nanocrystals

Directory of Open Access Journals (Sweden)

Oman ZUAS

2013-12-01

Full Text Available Pure TiO2 and CeO2-doped TiO2 (3 % CeO2-97 %TiO2 composite nanocrystals were synthesized via co-precipitation method and characterized using TGA, XRD, FTIR, DR-UV-vis and TEM. The XRD data revealed that the phase structure of the synthesized samples was mainly in pure anatase having crystallite size in the range of 7 nm – 11 nm. Spherical shapes with moderate aggregation of the crystal particles were observed under the TEM observation. The presence of the CeO2 at TiO2 site has not only affected morphologically but also induced the electronic property of the TiO2 by lowering the band gap energy from 3.29 eV (Eg-Ti to 3.15 eV (Eg-CeTi. Performance evaluation of the synthesized samples showed that both samples have a strong adsorption capacity toward Congo red (CR dye in aqueous solution at room temperature experiment, where  the capacity of the CeTi was higher than the Ti sample. Based on DR-UV data, the synthesized samples obtained in this study may also become promising catalysts for photo-assisted removal of synthetic dye in aqueous solution. DOI: http://dx.doi.org/10.5755/j01.ms.19.4.2732

Preparation and characterization of nanocomposites of the carboxymethyl cellulose reinforced with cellulose nanocrystals

International Nuclear Information System (INIS)

Flauzino Neto, Wilson P.; Silverio, Hudson A.; Vieira, Julia G.; Silva, Heden C.; Rosa, Joyce R.; Pasquini, Daniel; Assuncao, Rosana M.N.

2011-01-01

Nanocrystals of cellulose (NCC) isolated from Eucalyptus urograndis Kraft pulp were used to prepare nanocomposites employing carboxymethyl cellulose (CMC) as matrix. The nanocrystals were isolated by hydrolysis with H 2 SO 4 64% solution, for 20 minutes at 45 deg C. The nanocrystals were characterized by X-ray diffraction to evaluate the crystallinity of them. The amount of NCC used in the preparation of nanocomposites varied from 0 to 15%. The nanocomposites were characterized by thermal and mechanical analysis. A large reinforcing effect of NCC on the CMC matrix was observed. With the incorporation of the NCC, the tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and heat resistance to decomposition increased subtle. The improvement in thermo-mechanical properties are attributed to strong interactions between nanoparticles and CMC matrix. (author)

Experimental evidence for self-assembly of CeO2 particles in solution: Formation of single-crystalline porous CeO2 nanocrystals

DEFF Research Database (Denmark)

Tan, Hui Ru; Tan, Joyce Pei Ying; Boothroyd, Chris

2012-01-01

Single-crystalline porous CeO2 nanocrystals, with sizes of ∼20 nm and pore diameters of 1-2 nm, were synthesized successfully using a hydrothermal method. Using electron tomography, we imaged the three-dimensional structure of the pores in the nanocrystals and found that the oriented aggregation ...... energy-loss spectroscopy. The oxygen vacancies might play an important role in oxygen diffusion in the crystals and the catalytic activities of single-crystalline porous CeO 2 structures. © 2011 American Chemical Society....

Mesoporous carbon-coated LiFePO4 nanocrystals co-modified with graphene and Mg2+ doping as superior cathode materials for lithium ion batteries.

Science.gov (United States)

Wang, Bo; Xu, Binghui; Liu, Tiefeng; Liu, Peng; Guo, Chenfeng; Wang, Shuo; Wang, Qiuming; Xiong, Zhigang; Wang, Dianlong; Zhao, X S

2014-01-21

In this work, mesoporous carbon-coated LiFePO4 nanocrystals further co-modified with graphene and Mg(2+) doping (G/LFMP) were synthesized by a modified rheological phase method to improve the speed of lithium storage as well as cycling stability. The mesoporous structure of LiFePO4 nanocrystals was designed and realized by introducing the bead milling technique, which assisted in forming sucrose-pyrolytic carbon nanoparticles as the template for generating mesopores. For comparison purposes, samples modified only with graphene (G/LFP) or Mg(2+) doping (LFMP) as well as pure LiFePO4 (LFP) were also prepared and investigated. Microscopic observation and nitrogen sorption analysis have revealed the mesoporous morphologies of the as-prepared composites. X-ray diffraction (XRD) and Rietveld refinement data demonstrated that the Mg-doped LiFePO4 is a single olivine-type phase and well crystallized with shortened Fe-O and P-O bonds and a lengthened Li-O bond, resulting in an enhanced Li(+) diffusion velocity. Electrochemical properties have also been investigated after assembling coin cells with the as-prepared composites as the cathode active materials. Remarkably, the G/LFMP composite has exhibited the best electrochemical properties, including fast lithium storage performance and excellent cycle stability. That is because the modification of graphene provided active sites for nuclei, restricted the in situ crystallite growth, increased the electronic conductivity and reduced the interface reaction current density, while, Mg(2+) doping improved the intrinsically electronic and ionic transfer properties of LFP crystals. Moreover, in the G/LFMP composite, the graphene component plays the role of "cushion" as it could quickly realize capacity response, buffering the impact to LFMP under the conditions of high-rate charging or discharging, which results in a pre-eminent rate capability and cycling stability.

Single crystalline Co{sub 3}O{sub 4}: Synthesis and optical properties

Energy Technology Data Exchange (ETDEWEB)

Hosny, Nasser Mohammed, E-mail: Nasserh56@yahoo.com

2014-04-01

Crystals of Co{sub 3}O{sub 4} have been prepared from thermal decomposition of molecular precursors derived from salicylic acid and cobalt (II) acetate or chloride at 500 °C. A cubic phase Co{sub 3}O{sub 4} micro- and nanocrystals have been obtained. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The images of electron microscopes showed octahedral crystals of Co{sub 3}O{sub 4}. The volume and polarizability of the optimized structures of molecular precursors have been calculated and related to the particle size. The optical band gap of the obtained crystals has been measured. The results indicated two optical band gaps with values 2.65 and 2.95 eV for (E{sub g1}) (E{sub g2}), respectively. - Highlights: • Synthesis of Co{sub 3}O{sub 4} nanocrystals by decomposition of cobalt salicylic acid precursor. • Characterization of the isolated nanocrystals by using XRD, SEM and HRTEM. • The optical band gap has been measured.

Effect of europium ion concentration on the structural and photoluminescence properties of novel Li2BaZrO4: Eu3+ nanocrystals

Science.gov (United States)

Ahemen, I.; Dejene, F. B.; Kroon, R. E.; Swart, H. C.

2017-12-01

This work reports the influence of Eu3+ ion concentration on the structure and photoluminescence properties of Li2BaZrO4 nanocrystals including its intrinsic quantum efficiency (IQE). Chemical bath method was employed in the synthesis procedure. X-ray diffraction results showed tetragonal phase for Eu3+ ion concentration in the range 1 and 7 mol% and cubic phase at 8 mol%. The presence of barium oxide (BaO) was confirmed from selected area electron diffraction (SAED). The excitation spectra for these phosphors consisted of broad charge transfer (CT) bands due to the combination of Zr4+ - O2- and Eu3+-O2- charge transfer states. Superimposed on the CT band were direct excitation levels of Eu3+ and Ba2+ ions, in the range 320-450 nm. At high Eu3+ ions concentrations, the intensities of CT bands decreased because some of the ions were coordinated with Ba2+ ions. Photoluminescence emissions for all the doped samples at room temperature appeared to be entirely from intraconfigurational Eu3+ emissions and depended both on the site symmetry as well as the ion concentration. The quadrupole-quadrupole multipolar process was found to be solely responsible for the luminescence quenching. The intensity parameters (Ω2 ,Ω4), asymmetry ratio, R0 and the average decay lifetime of the nanocrystals showed dependence on concentration. High internal quantum efficiency (IQE) values were obtained at low Eu3+ ion concentrations, but efficiency decreased with increasing ion concentration. The CIE coordinates values were comparable to existing red phosphors and in combination with the high IQE make this phosphor a good candidate for red light emitting applications.

Memory characteristics of Au nanocrystals embedded in metal-oxide-semiconductor structure by using atomic-layer-deposited Al2O3 as control oxide

International Nuclear Information System (INIS)

Wang, C.-C.; Chiou, Y.-K.; Chang, C.-H.; Tseng, J.-Y.; Wu, L.-J.; Chen, C.-Y.; Wu, T.-B.

2007-01-01

The nonvolatile memory characteristics of metal-oxide-semiconductor (MOS) structures containing Au nanocrystals in the Al 2 O 3 /SiO 2 matrix were studied. In this work, we have demonstrated that the use of Al 2 O 3 as control oxide prepared by atomic-layer-deposition enhances the erase speed of the MOS capacitors. A giant capacitance-voltage hysteresis loop and a very short erase time which is lower than 1 ms can be obtained. Compared with the conventional floating-gate electrically erasable programmable read-only memories, the erase speed was promoted drastically. In addition, very low leakage current and large turn-around voltage resulting from electrons or holes stored in the Au nanocrystals were found in the current-voltage relation of the MOS capacitors

Sequential coating upconversion NaYF{sub 4}:Yb,Tm nanocrystals with SiO{sub 2} and ZnO layers for NIR-driven photocatalytic and antibacterial applications

Energy Technology Data Exchange (ETDEWEB)

Tou, Meijie; Luo, Zhenguo; Bai, Song; Liu, Fangying; Chai, Qunxia; Li, Sheng; Li, Zhengquan, E-mail: zqli@zjnu.edu.cn

2017-01-01

ZnO is one of the most promising materials for both photocatalytic and antibacterial applications, but its wide bandgap requires the excitation of UV light which limits their applications under visible and NIR bands. Herein, we demonstrate a facile approach to synthesize core-shell-shell hybrid nanoparticles consisting of hexagonal NaYF{sub 4}:Yb,Tm, amorphous SiO{sub 2} and wurtzite ZnO. The upconversion nanocrystals are used as the core seeds and sequentially coated with an insulting shell and a semiconductor layer. Such hybrid nanoparticles can efficiently utilize the NIR light through the upconverting process, and display notable photocatalytic performance and antibacterial activity under NIR irradiation. The developed NaYF{sub 4}:Yb,Tm@SiO{sub 2}@ZnO nanoparticles are characterized with TEM, XRD, EDS, XPS and PL spectra, and their working mechanism is also elucidated. - Highlights: • Core-shell NaYF{sub 4}:Yb,Tm@SiO{sub 2}@TiO{sub 2} NPs were synthesized via a sequential coating method. • Hybrid NaYF{sub 4}:Yb,Tm@SiO{sub 2}@TiO{sub 2} NPs show NIR-light enhanced photocatalytic activity. • NIR-driven antibacterial performance has been realized with NaYF{sub 4}:Yb,Tm@SiO{sub 2}@TiO{sub 2} NPs. • Working mechanism of the hybrid photocatalysts as antibacterial agents was proposed.

Synthesis and characterization of Fe{sub 3}O{sub 4}–TiO{sub 2} core-shell nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Stefan, M., E-mail: maria.stefan@itim-cj.ro; Pana, O.; Leostean, C.; Silipas, D. [National Institute for R and D of Isotopic and Molecular Technology, 67–103 Donat St., 400295 Cluj-Napoca (Romania); Bele, C. [University of Agricultural Sciences and Veterinary Medicine, 3-5 Calea Mănăştur, 400372 Cluj-Napoca (Romania); Senila, M. [INCDO-INOE 2000, Research Institute for Analytical Instrumentation, 65 Donat St., 400293 Cluj-Napoca (Romania); Gautron, E. [Institute of Materials Jean Rouxel, 2 rue de la Houssière, P.O. Box 32229, 44322 Nantes Cedex 3 (France)

2014-09-21

Composite core-shell nanoparticles may have morpho-structural, magnetic, and optical (photoluminescence (PL)) properties different from each of the components considered separately. The properties of Fe{sub 3}O{sub 4}–TiO{sub 2} nanoparticles can be controlled by adjusting the titania amount (shell thinness). Core–shell nanoparticles were prepared by seed mediated growth of semiconductor (TiO{sub 2}) through a modified sol-gel process onto preformed magnetite (Fe{sub 3}O{sub 4}) cores resulted from the co-precipitation method. The structure and morphology of samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), and high resolution-TEM respectively. X-ray photoelectron spectroscopy was correlated with ICP-AES. Magnetic measurements, optical absorption spectra, as well as PL spectroscopy indicate the presence of a charge/spin transfer from the conduction band of magnetite into the band gap of titania nanocrystals. The process modifies both Fe{sub 3}O{sub 4} and TiO{sub 2} magnetic and optical properties, respectively.

ZnO nanocrystals on SiO2/Si surfaces thermally cleaned in ultrahigh vacuum and characterized using spectroscopic photoemission and low energy electron microscopy

International Nuclear Information System (INIS)

Ericsson, Leif K. E.; Magnusson, Kjell O.; Zakharov, Alexei A.

2010-01-01

Thermal cleaning in ultrahigh vacuum of ZnO nanocrystals distributed on SiO 2 /Si surfaces has been studied using spectroscopic photoemission and low energy electron microscopy (SPELEEM). This study thus concern weakly bound ZnO nanocrystals covering only 5%-10% of the substrate. Chemical properties, crystallinity, and distribution of nanocrystals are used to correlate images acquired with the different techniques showing excellent correspondence. The nanocrystals are shown to be clean enough after thermal cleaning at 650 deg. C to be imaged by LEEM and x-ray PEEM as well as chemically analyzed by site selective x-ray photoelectron spectroscopy (μ-XPS). μ-XPS shows a sharp Zn 3d peak and resolve differences in O 1s states in oxides. The strong LEEM reflections together with the obtained chemical information indicates that the ZnO nanocrystals were thermally cleaned, but do not indicate any decomposition of the nanocrystals. μ-XPS was also used to determine the thickness of SiO 2 on Si. This article is the first to our knowledge where the versatile technique SPELEEM has been used to characterize ZnO nanocrystals.

Photocatalytic performances and activities of Ag-doped CuFe{sub 2}O{sub 4} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Zhu, Zhengru, E-mail: zhengruzhu@gmail.com [Research Center of Hydrology and Water Source, School of Urban and Environment, Liaoning Normal University, Dalian, 116029 (China); State Key Laboratory of Fine Chemical, Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024 (China); Li, Xinyong; Zhao, Qidong [State Key Laboratory of Fine Chemical, Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian, 116024 (China); Li, Yonghua; Sun, Caizhi; Cao, Yongqiang [Research Center of Hydrology and Water Source, School of Urban and Environment, Liaoning Normal University, Dalian, 116029 (China)

2013-08-01

Graphical abstract: - Highlights: • CuFe{sub 2}O{sub 4} nanocrystals were synthesized by a co-precipitation method. • Ag/CuFe{sub 2}O{sub 4} catalyst was prepared by the wetness impregnation strategy. • The structural properties of Ag/CuFe{sub 2}O{sub 4} were investigated by XRD, TEM, DRS, and XPS techniques. • Ag/CuFe{sub 2}O{sub 4} has higher photocatalytic activity. - Abstract: In this work, CuFe{sub 2}O{sub 4} nanoparticles were synthesized by a chemical co-precipitation route. The Ag/CuFe{sub 2}O{sub 4} catalyst was prepared based on the CuFe{sub 2}O{sub 4} nanoparticles by the incipient wetness impregnation strategy, which showed excellent photoelectric property and catalytic activity. The structural properties of these samples were systematically investigated by X-ray powder diffraction (XRD), transmission electronic microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic degradation of 4-CP by the Ag/CuFe{sub 2}O{sub 4} and CuFe{sub 2}O{sub 4} samples were comparatively studied under xenon lamp irradiation. The results indicate that the Ag/CuFe{sub 2}O{sub 4} sample exhibited the higher efficiency for the degradation of 4-CP.

Desulfurization and oxidation behavior of ultra-fine CaO particles prepared from brown coal; Kattan wo mochiite choseishita CaO chobiryushi no datsuryu tokusei to sanka tokusei

Energy Technology Data Exchange (ETDEWEB)

Benjamin, G.; Roman, M.; Yamazaki, Y.; Abe, H.; Harano, Y.; Takarada, Y. [Gunma University, Gunma (Japan). Faculty of Engineering

1996-10-28

The effect of reaction temperature and oxygen concentration on the desulfurization and oxidation behavior of ion-exchanged brown coal by Ca as new desulfurizing agent was studied. In experiment, Yallourn coal was used for ion- exchange, and limestone produced in Tochigi prefecture was also used for comparative study. Ca-exchanged brown coal was prepared by agitating coal in Ca(OH)2 slurry for 24 hours. The desulfurization behavior of a desulfurizing agent was obtained by measuring H2S and sulfur compounds in outlet gas of a reactor, and the oxidation behavior by measuring SO2 emission in outlet gas after oxidation reaction. As the experimental result, CaO produced from Ca-exchanged brown coal offered the extremely high activity to desulfurization reaction in a temperature range of 850-950{degree}C as compared with limestone. Although the oxidation behavior was dependent on oxidation temperature and oxygen concentration, CaS obtained from Ca-exchanged brown coal was more rapidly converted to CaSO4 than limestone. 3 refs., 8 figs., 2 tabs.

Phase controlled solvothermal synthesis of Cu{sub 2}ZnSnS{sub 4}, Cu{sub 2}ZnSn(S,Se){sub 4} and Cu{sub 2}ZnSnSe{sub 4} Nanocrystals: The effect of Se and S sources on phase purity

Energy Technology Data Exchange (ETDEWEB)

Pal, Mou [Instituto de Energías Renovables, Universidad Nacional Autónoma de México, 62580 Temixco, Morelos (Mexico); Instituto de Física, BUAP, Av. San Claudio y Blvd. 18 Sur Col. San Manuel, Ciudad Universitaria, C.P. 72570, Puebla (Mexico); Mathews, N.R. [Instituto de Energías Renovables, Universidad Nacional Autónoma de México, 62580 Temixco, Morelos (Mexico); Paraguay-Delgado, F. [Departamento de Materiales Nanoestructurados, Centro de Investigación en Materiales Avanzados (CIMAV), Chihuahua (Mexico); Mathew, X., E-mail: xm@ier.unam.mx [Instituto de Energías Renovables, Universidad Nacional Autónoma de México, 62580 Temixco, Morelos (Mexico)

2015-09-15

In this study, we have reported the synthesis of Cu{sub 2}ZnSnSe{sub 4} (CZTSe), Cu{sub 2}ZnSnS{sub 4} (CZTS) and Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) nanocrystals with tunable band gap and composition obtained by solvothermal method. The crystalline structure, composition, morphology and optical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman scattering, energy dispersive X-ray spectroscopy, transmission electron microscopy and diffuse reflectance (DR) spectroscopy. While the XRD patterns of CZTS and CZTSe nanoparticles prepared with elemental S/Se powder revealed the presence of phase pure nanoparticles, the CZTSSe nanoparticles obtained using a mixture of S and Se, were found to contain many secondary phases under the same synthesis protocol. Formation of impurity phases in CZTSSe sample, can be avoided by using a mixture of 1-dodecanethiol (DT; CH{sub 3}(CH{sub 2}){sub 11}SH)/oleylamine (OLA) instead of S powder and following the same experimental procedure. The incorporation of S in CZTSe nanocrystals prepared in presence of DDT/OLA mixture was confirmed through structural and optical characterizations. The optical properties of the quaternary chalcogenide nanocrystals were found to vary with the chemical composition of the material. - Highlights: • Solvothermal synthesis of CZTS, CZTSSe and CZTSe nanocrystals and discussion on possible formation mechanism. • Use of dodecanethiol/oleylamine mixture to synthesize phase-pure CZTSSe nanocrystals. • Formation of impurity phases can be controlled with proper S and Se sources.

Ge nanocrystals embedded in ultrathin Si3N4 multilayers with SiO2 barriers

Science.gov (United States)

Bahariqushchi, R.; Gundogdu, Sinan; Aydinli, A.

2017-04-01

Multilayers of germanium nanocrystals (NCs) embedded in thin films of silicon nitride matrix separated with SiO2 barriers have been fabricated using plasma enhanced chemical vapor deposition (PECVD). SiGeN/SiO2 alternating bilayers have been grown on quartz and Si substrates followed by post annealing in Ar ambient from 600 to 900 °C. High resolution transmission electron microscopy (HRTEM) as well as Raman spectroscopy show good crystallinity of Ge confined to SiGeN layers in samples annealed at 900 °C. Strong compressive stress for SiGeN/SiO2 structures were observed through Raman spectroscopy. Size, as well as NC-NC distance were controlled along the growth direction for multilayer samples by varying the thickness of bilayers. Visible photoluminescence (PL) at 2.3 and 3.1 eV with NC size dependent intensity is observed and possible origin of PL is discussed.

Density functional theory study of atomic and electronic properties of defects in reduced anatase TiO2 nanocrystals

Science.gov (United States)

Morita, Kazuki; Yasuoka, Kenji

2018-03-01

Anatase TiO2 nanocrystals have received considerable attention owing to their promising applications in photocatalysis, photovoltaics, and fuel cells. Although experimental evidence has shown that the performance of nanocrystals can be significantly improved through reduction, the mechanistic basis of this enhancement remains unclear. To shed a light on the chemistry of reduced anatase TiO2 nanocrystals, density functional theory were used to investigate the properties of defects and excess electrons. We demonstrated that oxygen vacancies are stable both on the surface and at the sub-surface of the nanocrystal, while titanium interstitials prefer sub-surface sites. Different defect locations possessed different excess electron structures, which contributed to deep and shallow states in the band gap of the nanocrystals. Furthermore, valence band tailing was observed, resulting in band gap narrowing. The theoretical results presented here deepen our understanding, and show the potential of defects to considerably change the macroscopic properties of anatase TiO2 nanocrystals.

Density functional theory study of atomic and electronic properties of defects in reduced anatase TiO2 nanocrystals

Directory of Open Access Journals (Sweden)

Kazuki Morita

2018-03-01

Full Text Available Anatase TiO2 nanocrystals have received considerable attention owing to their promising applications in photocatalysis, photovoltaics, and fuel cells. Although experimental evidence has shown that the performance of nanocrystals can be significantly improved through reduction, the mechanistic basis of this enhancement remains unclear. To shed a light on the chemistry of reduced anatase TiO2 nanocrystals, density functional theory were used to investigate the properties of defects and excess electrons. We demonstrated that oxygen vacancies are stable both on the surface and at the sub-surface of the nanocrystal, while titanium interstitials prefer sub-surface sites. Different defect locations possessed different excess electron structures, which contributed to deep and shallow states in the band gap of the nanocrystals. Furthermore, valence band tailing was observed, resulting in band gap narrowing. The theoretical results presented here deepen our understanding, and show the potential of defects to considerably change the macroscopic properties of anatase TiO2 nanocrystals.

TiO{sub 2} nanocrystals synthesized by laser pyrolysis for the up-scaling of efficient solid-state dye-sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Melhem, Hussein; Boucharef, Mourad; Di Bin, Catherine; Ratier, Bernard; Boucle, Johann [XLIM UMR 6172 Universite de Limoges/CNRS, Limoges Cedex (France); Simon, Pardis; Leconte, Yann; Herlin-Boime, Nathalie [IRAMIS/SPAM/LFP, CEA-CNRS URA 2453, CEA Saclay, Gif sur Yvette (France); Beouch, Layla; Goubard, Fabrice [Laboratoire de Physico-Chimie des Polymeres et des Interfaces (LPPI), Federation Institut des Materiaux (FD 4122), Universite de Cergy-Pontoise (France)

2011-10-15

A crucial issue regarding emerging nanotechnologies remains the up-scaling of new functional nanostructured materials towards their implementation in high performance applications on a large scale. In this context, we demonstrate high efficiency solid-state dye-sensitized solar cells prepared from new porous TiO{sub 2} photoanodes based on laser pyrolysis nanocrystals. This strategy exploits a reduced number of processing steps as well as non-toxic chemical compounds to demonstrate highly porous TiO{sub 2} films. The possibility to easily tune the TiO{sub 2} nanocrystal physical properties allows us to demonstrate all solid-state dye-sensitized devices based on a commercial benchmark materials (organic indoline dye and molecular hole transporter) presenting state-of-the-art performance comparable with reference devices based on a commercial TiO{sub 2} paste. In particular, a drastic improvement in pore infiltration, which is found to balance a relatively lower surface area compared to the reference electrode, is evidenced using laser-synthesized nanocrystals resulting in an improved short-circuit current density under full sunlight. Transient photovoltage decay measurements suggest that charge recombination kinetics still limit device performance. However, the proposed strategy emphasizes the potentialities of the laser pyrolysis technique for up-scaling nanoporous TiO{sub 2} electrodes for various applications, especially for solar energy conversion. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Mg doping induced high structural quality of sol–gel ZnO nanocrystals: Application in photocatalysis

Energy Technology Data Exchange (ETDEWEB)

Abed, Chayma; Bouzidi, Chaker [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, BP 95, Hammam-Lif 2050 (Tunisia); Elhouichet, Habib, E-mail: Habib.elhouichet@fst.rnu.tn [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, BP 95, Hammam-Lif 2050 (Tunisia); Département de Physique, Faculté des Sciences de Tunis, Université Tunis El Manar, Tunis 2092 (Tunisia); Gelloz, Bernard [Graduate School of Engineering, Nagoya University, 2-24-16 Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Ferid, Mokhtar [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, BP 95, Hammam-Lif 2050 (Tunisia)

2015-09-15

Highlights: • ZnO nancrystals doped with Mg were prepared from sol–gel method. • Structural and optical properties of ZnO:Mg nanocrystals were investigated. • Good crystalline quality of ZnO nanocrystals was reported after Mg doping. • Good photocatalytic activity of Mg doped ZnO nanocrystals was demonstrated under sun light illumination. - Abstract: Undoped and Mg doped ZnO nanocrystals (NCs) ZnO:x%Mg (x = 1, 2, 3, and 5) were synthesized using sol–gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectivity, and photoluminescence (PL). XRD analysis demonstrates that all prepared samples present pure hexagonal wurtzite structure without any Mg related phases. The NCs size varies from 26.82 nm to 42.96 nm with Mg concentrations; it presents an optimal value for 2% of Mg. The Raman spectra are dominated by the E{sub 2high} mode. For highly Mg doping (5%), the occurrence of silent B{sub 1(low)} mode suggested that the Mg ions do substitute at Zn sites in the ZnO lattice The band gap energy was estimated from both Tauc and Urbach methods and found to be 3.39 eV for ZnO:2%Mg. The PL spectra exhibit two emission bands in the UV and visible range. Their evolution with Mg doping reveals the reduction of defect density in ZnO at low Mg doping by filling Zn vacancies. In addition, it was found that further Mg doping, above 2%, improves the photocatalytic activity of ZnO NCs for photodegradation of Rhodamine B (RhB) under sunlight irradiation. The efficient electron–hole separation is the main factor responsible for the enhancement of photocatalytic performance of Mg doped ZnO NCs. Through this work, we show that by varying the Mg contents in ZnO, this material can be a potential candidate for both optoelectronic and photocatalytic applications.

Facile synthesis of high-temperature (1000 °C) phase-stable rice-like anatase TiO{sub 2} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Lv, Lizhen [Capital Normal University, Beijing Key Laboratory for Optical Materials and Photonic Devices, Department of Chemistry (China); Chen, Qirong [Beijing Center for Physical and Chemical Analysis (BCPCA) (China); Liu, Xiuyun; Wang, Miaomiao; Meng, Xiangfu, E-mail: xfmeng@cnu.edu.cn [Capital Normal University, Beijing Key Laboratory for Optical Materials and Photonic Devices, Department of Chemistry (China)

2015-05-15

High-temperature phase-stable rice-like anatase TiO{sub 2} nanocrystals were synthesized by one-pot solvothermal method using soluble titania xerogel and isopropyl alcohol (IPA) as the precursor and the solvent, respectively. Sample characterization was carried out by powder X-ray diffraction, high-resolution transmission electron microscopy, field emission scanning electron microscope, X-ray photoelectron spectroscopy, and N{sub 2} adsorption–desorption isotherms. The results showed that TiO{sub 2} nanocrystals had rice-like shapes with an average size of 5 nm in width and 35 nm in length. The BET surface area was 153 m{sup 2}/g. Unexpectedly, the rice-like TiO{sub 2} nanocrystals exhibited high-temperature phase stability, which could remain as pure anatase phase after calcinations at 1000 °C. Growth mechanism investigation revealed that the IPA solvent played a key role in nucleation and growth of rice-like anatase TiO{sub 2} nanocrystals. The photodegradation of rhodamine B demonstrated that rice-like anatase TiO{sub 2} nanocrystals exhibited enhanced photocatalytic activity under visible light irradiation.

Fundamental absorption edge of NiO nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Sokolov, V.I., E-mail: visokolov@imp.uran.ru [Institute of Metal Physics, Ural Branch of RAS, S. Kovalevskaya Street 18, 620990 Yekaterinburg (Russian Federation); Druzhinin, A.V. [Institute of Metal Physics, Ural Branch of RAS, S. Kovalevskaya Street 18, 620990 Yekaterinburg (Russian Federation); Kim, G.A. [Institute of Organic Synthesis Ural Branch of RAS, S. Kovalevskaya Street 20, 620990 Yekaterinburg (Russian Federation); Gruzdev, N.B.; Yermakov, A.Ye.; Uimin, M.A.; Byzov, I.V.; Shchegoleva, N.N.; Vykhodets, V.B.; Kurennykh, T.E. [Institute of Metal Physics, Ural Branch of RAS, S. Kovalevskaya Street 18, 620990 Yekaterinburg (Russian Federation)

2013-12-01

NiO nanocrystals with the average size of 5, 10 and 25 nm were synthesized by gas-condensation method. The well-defined increase of the optical density D near the fundamental absorption edge of NiO nanocrystals in the range of 3.5–4.0 eV observed after the annealing in air is caused by the oxygen content growth. It is the direct experimental evidence of the fact that p—d charge transfer transitions form the fundamental absorption edge.

Fundamental absorption edge of NiO nanocrystals

International Nuclear Information System (INIS)

Sokolov, V.I.; Druzhinin, A.V.; Kim, G.A.; Gruzdev, N.B.; Yermakov, A.Ye.; Uimin, M.A.; Byzov, I.V.; Shchegoleva, N.N.; Vykhodets, V.B.; Kurennykh, T.E.

2013-01-01

NiO nanocrystals with the average size of 5, 10 and 25 nm were synthesized by gas-condensation method. The well-defined increase of the optical density D near the fundamental absorption edge of NiO nanocrystals in the range of 3.5–4.0 eV observed after the annealing in air is caused by the oxygen content growth. It is the direct experimental evidence of the fact that p—d charge transfer transitions form the fundamental absorption edge

Energy Transfer between Conjugated Colloidal Ga2O3 and CdSe/CdS Core/Shell Nanocrystals for White Light Emitting Applications

Directory of Open Access Journals (Sweden)

Paul C. Stanish

2016-02-01

Full Text Available Developing solid state materials capable of generating homogeneous white light in an energy efficient and resource-sustainable way is central to the design of new and improved devices for various lighting applications. Most currently-used phosphors depend on strategically important rare earth elements, and rely on a multicomponent approach, which produces sub-optimal quality white light. Here, we report the design and preparation of a colloidal white-light emitting nanocrystal conjugate. This conjugate is obtained by linking colloidal Ga2O3 and II–VI nanocrystals in the solution phase with a short bifunctional organic molecule (thioglycolic acid. The two types of nanocrystals are electronically coupled by Förster resonance energy transfer owing to the short separation between Ga2O3 (energy donor and core/shell CdSe/CdS (energy acceptor nanocrystals, and the spectral overlap between the photoluminescence of the donor and the absorption of the acceptor. Using steady state and time-resolved photoluminescence spectroscopies, we quantified the contribution of the energy transfer to the photoluminescence spectral power distribution and the corresponding chromaticity of this nanocrystal conjugate. Quantitative understanding of this new system allows for tuning of the emission color and the design of quasi-single white light emitting inorganic phosphors without the use of rare-earth elements.

Energy Transfer between Conjugated Colloidal Ga2O3 and CdSe/CdS Core/Shell Nanocrystals for White Light Emitting Applications

Science.gov (United States)

Stanish, Paul C.; Radovanovic, Pavle V.

2016-01-01

Developing solid state materials capable of generating homogeneous white light in an energy efficient and resource-sustainable way is central to the design of new and improved devices for various lighting applications. Most currently-used phosphors depend on strategically important rare earth elements, and rely on a multicomponent approach, which produces sub-optimal quality white light. Here, we report the design and preparation of a colloidal white-light emitting nanocrystal conjugate. This conjugate is obtained by linking colloidal Ga2O3 and II–VI nanocrystals in the solution phase with a short bifunctional organic molecule (thioglycolic acid). The two types of nanocrystals are electronically coupled by Förster resonance energy transfer owing to the short separation between Ga2O3 (energy donor) and core/shell CdSe/CdS (energy acceptor) nanocrystals, and the spectral overlap between the photoluminescence of the donor and the absorption of the acceptor. Using steady state and time-resolved photoluminescence spectroscopies, we quantified the contribution of the energy transfer to the photoluminescence spectral power distribution and the corresponding chromaticity of this nanocrystal conjugate. Quantitative understanding of this new system allows for tuning of the emission color and the design of quasi-single white light emitting inorganic phosphors without the use of rare-earth elements. PMID:28344289

Preparation and characterization of Fe3O4/SiO2/Bi2MoO6 composite as magnetically separable photocatalyst

International Nuclear Information System (INIS)

Hou, Xuemei; Tian, Yanlong; Zhang, Xiang; Dou, Shuliang; Pan, Lei; Wang, Wenjia; Li, Yao; Zhao, Jiupeng

2015-01-01

Highlights: • Fe 3 O 4 /SiO 2 /Bi 2 MoO 6 composite was prepared by a hydrothermal method. • The composite has an enhanced visible absorption compared with pure Bi 2 MoO 6 . • The magnetic photocatalyst displayed excellent stability and reusability. • O 2 ·− and · OH play a major role during the photocatalytic process. - Abstract: In this paper, Fe 3 O 4 /SiO 2 /Bi 2 MoO 6 microspheres were prepared by a facile hydrothermal method. The scanning electron microscope (SEM) results revealed that flower-like three dimensional (3D) Bi 2 MoO 6 microspheres were decorated with Fe 3 O 4 /SiO 2 magnetic nanoparticles. The UV–vis diffuse reflection spectra showed extended absorption within the visible light range compared with pure Bi 2 MoO 6 . We evaluated the photocatalytic activities of Fe 3 O 4 /SiO 2 /Bi 2 MoO 6 microspheres on the degradation of Rhodamine B (RhB) under visible light irradiation and found that the obtained composite exhibited higher photocatalytic activity than pure Bi 2 MoO 6 and P25. Moreover, the Fe 3 O 4 /SiO 2 /Bi 2 MoO 6 composite also displayed excellent stability and their photocatalytic activity decreased slightly after reusing 5 cycles. Meanwhile, the composite could be easily separated by applying an external magnetic field. The trapping experiment results suggest that superoxide radical species O 2 ·− and hydroxyl radicals · OH play a major role in Fe 3 O 4 /SiO 2 /Bi 2 MoO 6 system under visible light irradiation. The combination of flower-like three dimensional (3D) Bi 2 MoO 6 microspheres and Fe 3 O 4 /SiO 2 magnetic nanospheres provides a useful strategy for designing multifunctional nanostructure materials with enhanced photocatalytic activities in the potential applications of water purification

Influence of Ti addition on the room temperature ferromagnetism of tin oxide (SnO{sub 2}) nanocrystal

Energy Technology Data Exchange (ETDEWEB)

Sakthiraj, K.; Balachandrakumar, K., E-mail: dkbaldr@gmail.com

2015-12-01

Nano-crystalline Sn{sub 1−x}Ti{sub x}O{sub 2} (x=0.00, 0.02, 0.05 and 0.07) particles were synthesized by the sol–gel method without any surfactant and dispersant material. The X-ray diffraction (XRD) pattern shows the formation of the tetragonal rutile phase structure for the undoped SnO{sub 2} nanoparticle and Ti doping does not alter the structure of undoped tin oxide. Due to quantum confinement effect, a larger optical band gap for as-synthesized materials was found. Vibrating sample magnetometer (VSM) result demonstrates the undoped and 2% Ti doped SnO{sub 2} samples exhibit perfect room temperature ferromagnetism (RTFM) but 5% and 7% of Ti doped samples show a weak ferromagnetism with diamagnetic contribution. The ferromagnetic property of the material was initiated with the help of oxygen vacancy. The amount of oxygen vacancy present in the samples were identified from the photoluminescence spectra and the value of oxygen vacancy decreased with increasing Ti concentration. - Highlights: • Pure Ti doped and undoped SnO{sub 2} nanocrystal were prepared using sol–gel method. • Oxygen vacancy induced RTFM was observed in SnO{sub 2} nanostructures. • Higher amount of ferromagnetism was detected in pristine SnO{sub 2} nanocrystal. • Ferromagnetic property was decreased with increasing Ti concentration. • Redshift of energy band gap was noted with increasing Ti content.

Phase relations in the M2MoO4 - Ag2MoO4 - Hf(MoO4)2 (M=Li, Na) systems

International Nuclear Information System (INIS)

Bazarova, Zh.G.; Bazarov, B.G.; Balsanova, L.V.

2002-01-01

The M 2 MoO 4 - Ag 2 MoO 4 - Hf(MoO 4 ) 2 (M=Li, Na) systems were studied by X-ray diffraction and differential thermal analyses in the subsolidus area (450 - 500 Deg C) for the first time. The formation of the binary compound with the variable composition Li 4-x Hf 1+0.2x (MoO 4 ) 4 (0 ≤ x ≤ 0.6) in the Li 2 MoO 4 - Hf(MoO 4 ) 2 system and the ternary molybdates Li 4 Ag 2 Hf(MoO 4 ) 5 (S 1 ) and Na 2 Ag 2 Hf(MoO 4 ) 4 (S 2 ) was established and the thermal characteristics of the prepared compounds were examined. The new binary molybdate Ag 2 Hf(MoO 4 ) 3 was prepared by the reaction between Ag 2 MoO 4 and Hf(MoO 4 ) 2 [ru

Luminescent nanocrystals in the rare-earth niobate–zirconia system formed via hydrothermal method

International Nuclear Information System (INIS)

Hirano, Masanori; Dozono, Hayato

2013-01-01

Luminescent nanocrystals based on the rare-earth niobates (Ln 3 NbO 7 , Ln=Y, Eu) and zirconia (ZrO 2 ) that were composed of 50 mol% Ln 3 NbO 7 and 50 mol% ZrO 2 , were hydrothermally formed as cubic phase under weakly basic conditions at 240 °C. The lattice parameter of the as-prepared nanoparticles corresponding to the composition of Y 3−x Eu x NbO 7 –4ZrO 2 that was estimated as a single phase of cubic gradually increased as the content of europium x increased. The existence of small absorbance peaks at 395 and 466 nm corresponding to the Eu 3+7 F 0 → 5 L 6 , and 7 F 0 → 5 D 2 excitation transition, respectively, was clearly observed in the diffuse reflectance spectra of the as-prepared samples containing europium. The optical band gap of the as-prepared samples was in the range from 3.5 to 3.7 eV. The photoluminescence spectra of the as-prepared nanocrystals containing europium showed orange and red luminescences with main peaks at 590 and 610 nm, corresponding to 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 transitions of Eu 3+ , respectively, under excitation at 395 nm Xe lamp. The emission intensity corresponding to 5 D 0 → 7 F 2 transition increased as heat-treatment temperature rose from 800 to 1200 °C. - Graphical abstract: This graphical abstract shows the excitation and emission spectra and a transmission electron microscopy image of nanocrystals (with composition based on the rare-earth niobates (Ln 3 NbO 7 , Ln=Y, Eu) and zirconia (ZrO 2 ) that were composed of 50 mol% Ln 3 NbO 7 and 50 mol% ZrO 2 ) formed via hydrothermal route. Display Omitted - Highlights: • Nanocrystals composed of 50 mol% Y 3−x Eu x NbO 7 and 50 mol% ZrO 2 was directly formed. • The nanocrystals were hydrothermally formed under weakly basic conditions at 240 °C. • The Y 3 NbO 7 showed an UV-blue and broad-band emission under excitation at 240 nm. • The emission is originated from the niobate octahedral group [NbO 6 ] 7− . • The nanocrystals showed orange and

InAs nanocrystals on SiO2/Si by molecular beam epitaxy for memory applications

International Nuclear Information System (INIS)

Hocevar, Moiera; Regreny, Philippe; Descamps, Armel; Albertini, David; Saint-Girons, Guillaume; Souifi, Abdelkader; Gendry, Michel; Patriarche, Gilles

2007-01-01

We studied a memory structure based on InAs nanocrystals grown by molecular beam epitaxy directly on thermal SiO 2 on silicon. Both nanocrystal diameter and density can be controlled by growth parameters. Transmission electron microscopy analysis shows high crystallinity and low size dispersion. In an electrical test structure with a 3.5 nm tunnel oxide, we observed that 80% of the initial injected electrons remain stored in the InAs nanocrystals after 3 months and that the retention time for electrons in InAs nanocrystals is four orders of magnitude higher than in silicon nanocrystals

Memory Effect of Metal-Oxide-Silicon Capacitors with Self-Assembly Double-Layer Au Nanocrystals Embedded in Atomic-Layer-Deposited HfO2 Dielectric

International Nuclear Information System (INIS)

Yue, Huang; Hong-Yan, Gou; Qing-Qing, Sun; Shi-Jin, Ding; Wei, Zhang; Shi-Li, Zhang

2009-01-01

We report the chemical self-assembly growth of Au nanocrystals on atomic-layer-deposited HfO 2 films aminosilanized by (3-Aminopropyl)-trimethoxysilane aforehand for memory applications. The resulting Au nanocrystals show a density of about 4 × 10 11 cm −2 and a diameter range of 5–8nm. The metal-oxide-silicon capacitor with double-layer Au nanocrystals embedded in HfO 2 dielectric exhibits a large C – V hysteresis window of 11.9V for ±11 V gate voltage sweeps at 1 MHz, a flat-band voltage shift of 1.5 V after the electrical stress under 7 V for 1 ms, a leakage current density of 2.9 × 10 −8 A/cm −2 at 9 V and room temperature. Compared to single-layer Au nanocrystals, the double-layer Au nanocrystals increase the hysteresis window significantly, and the underlying mechanism is thus discussed

ZnO nanowire-based nano-floating gate memory with Pt nanocrystals embedded in Al{sub 2}O{sub 3} gate oxides

Energy Technology Data Exchange (ETDEWEB)

Yeom, Donghyuk; Kang, Jeongmin; Lee, Myoungwon; Jang, Jaewon; Yun, Junggwon; Jeong, Dong-Young; Yoon, Changjoon; Koo, Jamin; Kim, Sangsig [Department of Electrical Engineering and Institute for Nano Science, Korea University, Seoul 136-701 (Korea, Republic of)], E-mail: sangsig@korea.ac.kr

2008-10-01

The memory characteristics of ZnO nanowire-based nano-floating gate memory (NFGM) with Pt nanocrystals acting as the floating gate nodes were investigated in this work. Pt nanocrystals were embedded between Al{sub 2}O{sub 3} tunneling and control oxide layers deposited on ZnO nanowire channels. For a representative ZnO nanowire-based NFGM with embedded Pt nanocrystals, a threshold voltage shift of 3.8 V was observed in its drain current versus gate voltage (I{sub DS}-V{sub GS}) measurements for a double sweep of the gate voltage, revealing that the deep effective potential wells built into the nanocrystals provide our NFGM with a large charge storage capacity. Details of the charge storage effect observed in this memory device are discussed in this paper.

Preparation and nonlinear optical properties of indium nanocrystals in sodium borosilicate glass by the sol–gel route

International Nuclear Information System (INIS)

Zhong, Jiasong; Xiang, Weidong; Zhao, Haijun; Chen, Zhaoping; Liang, Xiaojuan; Zhao, Wenguang; Chen, Guoxin

2012-01-01

Graphical abstract: The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel methods. And the indium nanocrystals in tetragonal crystal system have formed uniformly in the glass, and the average diameter of indium nanocrystals is about 30 nm. The third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ (3) of the glass are determined to be −4.77 × 10 −16 m 2 /W, 2.67 × 10 −9 m/W, and 2.81 × 10 −10 esu, respectively. Highlights: ► Indium nanocrystals embedded in glass matrix have been prepared by sol–gel route. ► The crystal structure and composition are investigated by XRD and XPS. ► Size and distribution of indium nanocrystals is determined by TEM. ► The third-order optical nonlinearity is investigated by using Z-scan technique. -- Abstract: The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel route. The thermal stability behavior of the stiff gel is investigated by thermogravimetric (TG) and differential thermal (DTA) analysis. The crystal structure of the glass is characterized by X-ray powder diffraction (XRD). Particle composition is determined by X-ray photoelectron spectroscopy (XPS). Size and distribution of the nanocrystals are characterized by transmission electron microscopy (TEM) as well as high-resolution transmission electron microscopy (HRTEM). Results show that the indium nanocrystals in tetragonal crystal structure have formed in glass, and the average diameter is about 30 nm. Further, the glass is measured by Z-scan technique to investigate the nonlinear optical (NLO) properties. The third-order NLO coefficient χ (3) of the glass is determined to be 2.81 × 10 −10 esu. The glass with large third-order NLO coefficient is promising materials for applications in optical devices.

The effect of TiO2 nanocrystal shape on the electrical properties of poly(styrene-b-methyl methacrylate) block copolymer based nanocomposites for solar cell application

International Nuclear Information System (INIS)

Cano, Laida; Gutierrez, Junkal; Di Mauro, A. Evelyn; Curri, M. Lucia; Tercjak, Agnieszka

2015-01-01

Titanium dioxide (TiO 2 ) nanocrystals were synthesized into two shapes, namely spherical and rod-like and used for the fabrication of polystyrene-block-poly(methyl methacrylate) (PSMMA) block copolymer based nanocomposites, which were employed as the active top layer of electro-devices for solar cell application. Electro-devices were designed using nanocomposites with high TiO 2 nanocrystal contents (50-70 wt%) and for comparison as-synthesized TiO 2 nanospheres (TiO 2 NSs) and TiO 2 nanorods (TiO 2 NRs) were also used. The morphology of the electro-devices was studied by atomic force microscopy showing good nanocrystal dispersion. The electrical properties of the devices were investigated by PeakForce tunneling atomic force microscopy and Keithley semiconductor analyzer, which showed higher electrical current values for devices containing TiO 2 NRs in comparison to TiO 2 NSs. Remarkably, the influence of the PSMMA block copolymer on the improvement of the conductivity of the electro-devices was also assessed, demonstrating that the self-assembling ability of block copolymer can be beneficial to improve charge transfer in the fabricated electro-devices, thus representing relevant systems to be potentially developed for photovoltaic applications. Moreover, the absorbance of the prepared electro-devices in solar irradiation range was confirmed by UV–vis spectroscopy characterization.

PPLA-cellulose nanocrystals nanocomposite prepared by in situ polymerization

International Nuclear Information System (INIS)

Paula, Everton L. de; Pereirea, Fabiano V.; Mano, Valdir

2011-01-01

This work reports the preparation and and characterization of a PLLA-cellulose nanocrystals nanocomposite obtained by in situ polymerization. The nanocomposite was prepared by ring opening polymerization of the lactide dimer in the presence of cellulose nanocrystals (CNCs) and the as-obtained materials was characterized using FTIR, DSC, XRD and TGA measurements. The incorporation of cellulose nanocrystals in PLLA using this method improved the thermal stability and increased the crystallinity of PLLA. These results indicate that the incorporation of CNCs by in situ polymerization improve thermal properties and has potential to improve also mechanical properties of this biodegradable polymer. (author)

Hydrothermal synthesis and white light emission of cubic ZrO2:Eu3+ nanocrystals

International Nuclear Information System (INIS)

Meetei, Sanoujam Dhiren; Singh, Shougaijam Dorendrajit

2014-01-01

Highlights: • White light emitting cubic ZrO 2 :Eu 3+ nanocrystal is synthesized by hydrothermal technique. • Eu 3+ is used to stabilize crystalline phase and to get red counterpart of the white light. • Defect emission and Eu 3+ emission combined to give white light. • The white light emitted from this nanocrystal resembles vertical daylight of the Sun. • Lifetime corresponding to red counterpart of the sample is far longer than conventional white light emitters. -- Abstract: Production of white light has been a promising area of luminescence studies. In this work, white light emitting nanocrystals of cubic zirconia doped with Eu 3+ are synthesized by hydrothermal technique. The dopant Eu 3+ is used to stabilize crystalline phase to cubic and at the same time to get red counterpart of the white light. The synthesis procedure is simple and precursor required no further annealing for crystallization. X-ray diffraction patterns show the crystalline phase of ZrO 2 :Eu 3+ to be cubic and it is confirmed by Fourier Transform Infrared spectroscopy. From transmission electron microscopy images, size of the crystals is found to be ∼5 nm. Photoluminescence emission spectrum of the sample, on monitoring excitation at O 2− –Eu 3+ charge transfer state shows broad peak due to O 2− of the zirconia and that of Eu 3+ emission. Commission Internationale de l’éclairage co-ordinate of this nanocrystal (0.32, 0.34) is closed to that of the ideal white light (0.33, 0.33). Correlated color temperature of the white light (5894 K) is within the range of vertical daylight. Lifetime (1.32 ms) corresponding to 5 D 0 energy level of the Eu 3+ is found to be far longer than conventional red counterparts of white light emitters. It suggests that the ZrO 2 :Eu 3+ nanocrystals synthesized by hydrothermal technique may find applications in simulating the vertical daylight of the Sun

Evolution of magnetic states in frustrated diamond lattice antiferromagnetic Co(Al1-xCox)(2)O-4 spinels

DEFF Research Database (Denmark)

Zaharko, O.; Cervellino, A.; Tsurkan, V.

2010-01-01

Using neutron powder diffraction and Monte Carlo simulations we show that a spin-liquid regime emerges at all compositions in the diamond-lattice antiferromagnets Co(Al1−xCox)2O4. This spin-liquid regime induced by frustration due to the second-neighbor exchange coupling J2 is gradually superseded...... by antiferromagnetic collinear long-range order (k=0) at low temperatures. Upon substitution of Al3+ by Co3+ in the octahedral B site the temperature range occupied by the spin-liquid regime narrows and TN increases. To explain the experimental observations we considered magnetic anisotropy D or third......-neighbor exchange coupling J3 as degeneracy-breaking perturbations. We conclude that Co(Al1−xCox)2O4 is below the theoretical critical point J2/J1=1/8, and that magnetic anisotropy assists in selecting a collinear long-range ordered ground state, which becomes more stable with increasing x due to a higher...

Poly(methyl methacrylate) nanocomposites based on TiO{sub 2} nanocrystals: Tailoring material properties towards sensing

Energy Technology Data Exchange (ETDEWEB)

Convertino, A., E-mail: annalisa.convertino@ismn.cnr.i [ISMN-CNR Istituto per lo Studio dei Materiali Nanostrutturati, Via Salaria km. 29.300, 00016 Roma (Italy); Tamborra, M., E-mail: m.tamborra@ba.ipcf.cnr.i [IPCF-CNR Istituto per i Processi Chimici e Fisici, Bari Division, Via Orabona 4, 70126 Bari (Italy); Striccoli, M., E-mail: m.striccoli@ba.ipcf.cnr.i [IPCF-CNR Istituto per i Processi Chimici e Fisici, Bari Division, Via Orabona 4, 70126 Bari (Italy); Leo, G., E-mail: gabriella.leo@ismn.cnr.i [ISMN-CNR Istituto per lo Studio dei Materiali Nanostrutturati, Via Salaria km. 29.300, 00016 Roma (Italy); Agostiano, A., E-mail: a.agostiano@ba.ipcf.cnr.i [IPCF-CNR Istituto per i Processi Chimici e Fisici, Bari Division, Via Orabona 4, 70126 Bari (Italy); Dipartimento di Chimica., Universita di Bari, Via Orabona 4, 70126 Bari (Italy); Curri, M.L., E-mail: lucia.curri@ba.ipcf.cnr.i [IPCF-CNR Istituto per i Processi Chimici e Fisici, Bari Division, Via Orabona 4, 70126 Bari (Italy)

2011-03-31

Nanocomposite materials have been obtained by dispersing organic capped TiO{sub 2} nanocrystals (NCs) with different shape and surface chemistry in poly(methyl methacrylate) (PMMA) as a host medium. Films of the prepared nanocomposites based on TiO{sub 2} NCs have been fabricated by spin coating and morphologically characterized as a function of the preparative conditions. The organic vapor absorption ability of the PMMA/TiO{sub 2} NC based nanocomposites has been then investigated both for spherical and rod-like NCs, and the chemical nature of the coordinating organic molecules has been also varied. The results of the investigation have demonstrated that NC geometry and surface chemistry can modulate the specific absorption characteristics of the modified PMMA in order to absorb different solvent molecules (i.e. acetone, ethanol, propan-2-ol and water). Such features, due to specific interactions between the potential analyte vapors and the functionalized surface of NCs, can effectively be addressed in a controlled and reproducible way, thus offering original opportunities for designing innovative chemical sensors.

Synthesis and Downconversion Emission Property of Yb2O3:Eu3+ Nanosheets and Nanotubes

Directory of Open Access Journals (Sweden)

Chao Qian

2013-01-01

Full Text Available Ytterbium oxide (Yb2O3 nanocrystals with different Eu3+ (1%, 2%, 5%, and 10% doped concentrations were synthesized by a facile hydrothermal method, subsequently by calcination at 700°C. The crystal phase, size, and morphology of prepared samples were characterized by X-ray diffraction (XRD and transmission electron microscopy (TEM. The results show that the as-prepared Yb2O3 nanocrystals with sheet- and tube-like shape have cubic phase structure. The Eu3+ doped Yb2O3 nanocrystals were revealed to have good down conversion (DC property and intensity of the DC luminescence can be modified by Eu3+ contents. In our experiment the 1% Eu3+ doped Yb2O3 nanocrystals showed the strongest DC luminescence among the obtained Yb2O3 nanocrystals.

Raman scattering study of the anharmonic effects in CeO2-y nanocrystals

Science.gov (United States)

Popović, Z. V.; Dohčević-Mitrović, Z.; Cros, A.; Cantarero, A.

2007-12-01

We have studied the temperature dependence of the F2g Raman mode phonon frequency and broadening in CeO2-y nanocrystals. The phonon softening and phonon linewidth are calculated using a model which takes into account the three-and four-phonon anharmonic processes. A detailed comparison of the experimental data with theoretical calculations revealed the predominance of four-phonon anharmonic processes in the temperature dependence of the phonon energy and broadening of the nanocrystals. On the other hand, three-phonon processes dominate the temperature behavior of phonons in polycrystalline samples. The anti-Stokes/Stokes peak intensity ratio was also investigated and found to be smaller for nanosized CeO2 powders than in the bulk counterpart.

Raman scattering study of the anharmonic effects in CeO2-y nanocrystals

International Nuclear Information System (INIS)

Popovic, Z V; Dohcevic-Mitrovic, Z; Cros, A; Cantarero, A

2007-01-01

We have studied the temperature dependence of the F 2g Raman mode phonon frequency and broadening in CeO 2-y nanocrystals. The phonon softening and phonon linewidth are calculated using a model which takes into account the three-and four-phonon anharmonic processes. A detailed comparison of the experimental data with theoretical calculations revealed the predominance of four-phonon anharmonic processes in the temperature dependence of the phonon energy and broadening of the nanocrystals. On the other hand, three-phonon processes dominate the temperature behavior of phonons in polycrystalline samples. The anti-Stokes/Stokes peak intensity ratio was also investigated and found to be smaller for nanosized CeO 2 powders than in the bulk counterpart

Luminescence in colloidal Mn2+-doped semiconductor nanocrystals

International Nuclear Information System (INIS)

Beaulac, Remi; Archer, Paul I.; Gamelin, Daniel R.

2008-01-01

Recent advances in nanocrystal doping chemistries have substantially broadened the variety of photophysical properties that can be observed in colloidal Mn 2+ -doped semiconductor nanocrystals. A brief overview is provided, focusing on Mn 2+ -doped II-VI semiconductor nanocrystals prepared by direct chemical synthesis and capped with coordinating surface ligands. These Mn 2+ -doped semiconductor nanocrystals are organized into three major groups according to the location of various Mn 2+ -related excited states relative to the energy gap of the host semiconductor nanocrystals. The positioning of these excited states gives rise to three distinct relaxation scenarios following photoexcitation. A brief outlook on future research directions is provided. - Graphical abstract: Mn 2+ -doped semiconductor nanocrystals are organized into three major groups according to the location of various Mn 2+ -related excited states relative to the energy gap of the host semiconductor nanocrystals. The positioning of these excited states gives rise to three distinct relaxation scenarios following photoexcitation

Optical properties of transparent Li2O-Ga2O3-SiO2 glass-ceramics embedding Ni-doped nanocrystals

International Nuclear Information System (INIS)

Suzuki, Takenobu; Murugan, Ganapathy Senthil; Ohishi, Yasutake

2005-01-01

Transparent Li 2 O-Ga 2 O 3 -SiO 2 (LGS) glass-ceramics embedding Ni:LiGa 5 O 8 nanocrystals were fabricated. An intense emission centered around 1300 nm with the width of more than 300 nm was observed by 976 nm photoexcitation of the glass-ceramics. The lifetime was more than 900 μs at 5 K and 500 μs at 300 K. The emission could be attributed to the 3 T 2g ( 3 F)→ 3 A 2g ( 3 F) transition of Ni 2+ in distorted octahedral sites in LiGa 5 O 8 . The product of stimulated emission cross section and lifetime for the emission was about 3.7x10 -24 cm 2 s and was a sufficiently practical value

Far-infrared spectroscopic study of CeO2 nanocrystals

Science.gov (United States)

Popović, Z. V.; Grujić-Brojčin, M.; Paunović, N.; Radonjić, M. M.; Araújo, V. D.; Bernardi, M. I. B.; de Lima, M. M.; Cantarero, A.

2015-01-01

We present the far-infrared reflectivity spectra of 5 nm-sized pure and copper-doped Ce1- x Cu x O2- y ( x = 0; 0.01 and 0.10) nanocrystals measured at room temperature in the 50-650 cm-1 spectral range. Reflectivity spectra were analyzed using the factorized form of the dielectric function, which includes the phonon and the free carriers contribution. Four oscillators with TO energies of approximately 135, 280, 370, and 490 cm-1 were included in the fitting procedure. These oscillators represent local maxima of the CeO2 phonon density of states, which is also calculated using the density functional theory. The lowest energy oscillator represents TA(L)/TA(X) phonon states, which become infrared-active E u modes at the L and X points of the Brillouin zone (BZ). The second oscillator originates from TO(Γ) phonon states. The oscillator at 400 cm-1 originates from Raman mode phonon states, which at the L point of BZ also becomes infrared-active E u mode. The last oscillator describes phonons with dominantly LO(Γ) infrared mode character. The appearance of phonon density of states related oscillators, instead of single F 2uinfrared-active mode in the far-infrared reflectivity spectra, is a consequence of the nanosized dimension of the CeO2 particles. The best fit spectra are obtained using the generalized Bruggeman model for inhomogeneous media, which takes into account the nanocrystal volume fraction and the pore shape.

A first-principles study of the electronic and structural properties of Sb and F doped SnO2 nanocrystals

International Nuclear Information System (INIS)

Kim, Minjung; Scott Bobbitt, N.; Marom, Noa; Chelikowsky, James R.

2015-01-01

We examine the electronic properties of Sb and F doped SnO 2 nanocrystals up to 2.4 nm in diameter. A real-space pseudopotential implementation of density functional theory is employed within the local density approximation. We calculate electron binding energies and dopant formation energies as function of nanocrystal size, dopant concentration, and dopant species. Structural changes for different dopant species are also investigated. Our study should provide useful information for the design of transparent conducting oxides at the nanoscale

One-step rapid synthesis of ultrafine γ-Ga2O3 nanocrystals by microwave hydrothermal method in ammonium hydroxide medium

Science.gov (United States)

Cui, Lu; Wang, Hong; Xin, Baifu; Mao, Guijie

2017-10-01

Ultrafine nanocrystals of γ-gallium oxide (γ-Ga2O3) were rapidly synthesized via microwave hydrothermal method at 140 °C, in which Ga(NO3)3 was used as the gallium source and urea was the precipitant. The samples were characterized by X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), transmission electron microscopy (TEM), nitrogen physisorption and photoluminescence spectroscopy (PL). The crystallite size of ultrafine spinel γ-Ga2O3 was in the range from 4 to 5 nm and the optical bandgap was 4.61 eV. To improve the crystallinity, the ultrafine γ-Ga2O3 nanocrystals were calcined at 300-700 °C further. The ultrafine γ-Ga2O3 calcined at 500 °C (calcined-γ-Ga2O3) still remained the metastable γ-phase with relatively high crystallinity and the crystallite size around 5-7 nm. Photocatalytic performances of the synthesized samples were also evaluated by the degradation of rhodamine B (RhB). Results revealed that the ultrafine γ-Ga2O3 and the calcined-γ-Ga2O3 samples exhibited high photocatalytic efficiencies of 68.2 and 90.7%, respectively.

Superheating and supercooling of Ge nanocrystals embedded in SiO2

International Nuclear Information System (INIS)

Xu, Q; Sharp, I D; Yuan, C W; Yi, D O; Liao, C Y; Glaeser, A M; Minor, A M; Beeman, J W; Ridgway, M C; Kluth, P; Iii, J W Ager; Chrzan, D C; Haller, E E

2007-01-01

Free-standing nanocrystals exhibit a size-dependant thermodynamic melting point reduction relative to the bulk melting point that is governed by the surface free energy. The presence of an encapsulating matrix, however, alters the interface free energy of nanocrystals and their thermodynamic melting point can either increase or decrease relative to bulk. Furthermore, kinetic contributions can significantly alter the melting behaviours of embedded nanoscale materials. To study the effect of an encapsulating matrix on the melting behaviour of nanocrystals, we performed in situ electron diffraction measurements on Ge nanocrystals embedded in a silicon dioxide matrix. Ge nanocrystals were formed by multi-energy ion implantation into a 500 nm thick silica thin film on a silicon substrate followed by thermal annealing at 900 deg. C for 1 h. We present results demonstrating that Ge nanocrystals embedded in SiO 2 exhibit a 470 K melting/solidification hysteresis that is approximately symmetric about the bulk melting point. This unique behaviour, which is thought to be impossible for bulk materials, is well described using a classical thermodynamic model that predicts both kinetic supercooling and kinetic superheating. The presence of the silica matrix suppresses surface pre-melting of nanocrystals. Therefore, heterogeneous nucleation of both the liquid phase and the solid phase are required during the heating and cooling cycle. The magnitude of melting hysteresis is governed primarily by the value of the liquid Ge/solid Ge interface free energy, whereas the relative values of the solid Ge/matrix and liquid Ge/matrix interface free energies govern the position of the hysteresis loop in absolute temperature

Study of temperature-dependent charge conduction in silicon-nanocrystal/SiO_2 multilayers

International Nuclear Information System (INIS)

Mavilla, Narasimha Rao; Chavan, Vinayak; Solanki, Chetan Singh; Vasi, Juzer

2016-01-01

Silicon-nanocrystals (Si-NCs) realized by SiO_x _ 8 MV/cm; independent of temperature), while for lower electric fields (5–8 MV/cm) at higher temperatures, the trap-related Generalized Poole–Frenkel (GPF) is dominant. This signified the role of traps in modifying the conduction in bulk ICPCVD SiO_2 films. We then present the conduction in ML samples. For multilayer samples with SiO_2 sublayer thickness of 1.5 nm and 2.5 nm, Direct Tunneling (DT) is observed to be dominant, while for SiO_2 sublayer thickness of 3.5 nm, Space Charge Limited Conduction (SCLC) with exponential trap distribution is found to be the dominant conduction mechanism. This signifies the role of traps in modifying the conduction in Si-NC multilayer samples and SiO_2 sublayer thickness dependence. - Highlights: • Electrical conduction in SiO_2 film & Si-nanocrystal layers (Si-NCs) is reported. • SiO_2/SiO_x multilayer based Si-NCs were realized by Inductively Coupled plasma CVD. • For SiO_2 film, Fowler–Nordheim tunneling & Generalized Poole–Frenkel are observed. • For Si-NCs with thin SiO_2 sublayers (< 2.5 nm) Direct Tunneling is dominant. • For Si-NCs with 3.5 nm SiO_2 sublayers Space Charge Limited Conduction is dominant.

A study of phase and morphology changes occurring as a result of galvanic reactions with FeO nanocrystals

Science.gov (United States)

Onserio, Benard Obae

Recently, iron oxide nanoparticles have attracted great attention from various research groups. This is due to their potential applications in various fields such as biomedicine, environmental remediation, storage media, catalysis, and as anode materials for lithium-ion batteries. The objective of this study is to develop a synthesis of hollow Fe3O4 nanoparticles via galvanic reaction between FeO nanocrystals and oxidizing agents in which a nanoscale Kirkendall effect occurs. The objective is based on prior results in which it was demonstrated that Cu2+ oxidized MnO nanocrystals to yield hollow Mn3O4 nanoparticles. The analogous process starting from FeO is expected to be even more thermodynamically favorable. Despite efforts to obtain FeO nanocrystals, the magnetite Fe3O 4 phase was obtained. With this sample, attempts were made towards galvanic reactions in the presence of Cu2+. The initial result of the reaction of Fe3O4 nanocrystals with Cu2+ was unexpected, and FeO was obtained; however, the result could not be reproduced. Later efforts focused on attempting to understand the galvanic reaction that took place leading to the formation of FeO. Thus reaction of Fe3O 4 with oleylamine, silver (I), and ascorbic acid were studied. Data for the phase and morphological changes of the iron oxides will be presented.

Optical investigation of Tb3+-doped Y2O3 nanocrystals prepared by Pechini-type sol–gel process

International Nuclear Information System (INIS)

Back, M.; Massari, A.; Boffelli, M.; Gonella, F.; Riello, P.; Cristofori, D.; Riccò, R.; Enrichi, F.

2012-01-01

We report an optical study of Tb 3+ -doped Y 2 O 3 nanocrystals synthesized by Pechini-type sol–gel method. The particles are investigated in terms of size and morphology by means of X-ray diffraction and transmission electron microscopy analysis. It is shown how the simple Pechini method allows for the growth of monocrystalline nanoparticles with a volume-weighted average size of about 30 nm. The optical properties of Tb 3+ in the host lattice are studied in terms of PL, PLE, and lifetimes. Moreover, a correlation between the type of decay curves, the emission and excitation bands' shapes, and the site location of the emitting Tb 3+ in the host material Y 2 O 3 is proposed.

NO emission characteristics of superfine pulverized coal combustion in the O2/CO2 atmosphere

International Nuclear Information System (INIS)

Liu, Jiaxun; Gao, Shan; Jiang, Xiumin; Shen, Jun; Zhang, Hai

2014-01-01

Highlights: • Superfine pulverized coal combustion in O 2 /CO 2 atmosphere is a new promising technology. • NO emissions of superfine pulverized coal combustion in O 2 /CO 2 mixture were focused. • Coal particle sizes have significant effects on NO emissions in O 2 /CO 2 combustion. - Abstract: The combination of O 2 /CO 2 combustion and superfine pulverized coal combustion technology can make full use of their respective merits, and solve certain inherent disadvantages of each technology. The technology of superfine pulverized coal combustion in the O 2 /CO 2 atmosphere is easy and feasible to be retrofitted with few reconstructions on the existing devices. It will become a useful and promising method in the future. In this paper, a one-dimensional drop-tube furnace system was adopted to study the NO emission characteristics of superfine pulverized coal combustion in the O 2 /CO 2 atmosphere. The effects of coal particle size, coal quality, furnace temperature, stoichiometric ratio, etc. were analyzed. It is important to note that coal particle sizes have significant influence on NO emissions in the O 2 /CO 2 combustion. For the homogeneous NO reduction, smaller coal particles can inhibit the homogeneous NO formations under fuel-rich combustion conditions, while it becomes disadvantageous for fuel-lean combustion. However, under any conditions, heterogeneous reduction is always more significant for smaller coal particle sizes, which have smoother pore surfaces and simpler pore structures. The results from this fundamental research will provide technical support for better understanding and developing this new combustion process

Sintering of MnCo2O4 coatings prepared by electrophoretic deposition

DEFF Research Database (Denmark)

Bobruk, M.; Molin, Sebastian; Chen, Ming

2018-01-01

Sintering of MnCo2O4 coatings prepared by electrophoretic deposition on steel substrates has been studied in air and in reducing-oxidizing atmosphere. Effect of temperature and pO2 on the resulting coating density was evaluated from scanning electron microscopy images of polished cross sections...

Transparent nanoscale floating gate memory using self-assembled bismuth nanocrystals in Bi(2) Mg(2/3) Nb(4/3) O(7) (BMN) pyrochlore thin films grown at room temperature.

Science.gov (United States)

Jung, Hyun-June; Yoon, Soon-Gil; Hong, Soon-Ku; Lee, Jeong-Yong

2012-07-03

Bismuth nanocrystals for a nanoscale floating gate memory device are self-assembled in Bi(2) Mg(2/3) Nb(4/3) O(7) (BMN) dielectric films grown at room temperature by radio-frequency sputtering. The TEM cross-sectional image shows the "real" structure grown on a Si (001) substrate. The image magnified from the dotted box (red color) in the the cross-sectional image clearly shows bismuth nanoparticles at the interface between the Al(2) O(3) and HfO(2) layer (right image). Nanoparticles approximately 3 nm in size are regularly distributed at the interface. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Colloidal GdVO4:Eu3+@SiO2 nanocrystals for highly selective and sensitive detection of Cu2+ ions

Science.gov (United States)

Liang, Yanjie; Noh, Hyeon Mi; Park, Sung Heum; Choi, Byung Chun; Jeong, Jung Hyun

2018-03-01

Nowadays, in view of health and safety demands, the controlled design of selective and sensitive sensors for Cu2+ detection is of considerable importance. Therefore, we construct herein core-shell colloidal GdVO4:Eu3+@SiO2 nanocrystals (NCs) as optical sensor for the detection of Cu2+, which were synthesized by a facile hydrothermal reaction and encapsulated with a uniform layer of ultrathin silica through a sol-gel strategy. The NCs present strong red emission due to energy transfer from VO43- groups to Eu3+ when exciting with ultraviolet (UV) light. This intense red emission from Eu3+ could be selectively quenched in the presence of Cu2+ in comparison to other metal ions and the limit of detection is as low as 80 nM in aqueous solution. It is revealed that the spectral overlap between the emission band of NCs and the absorption of Cu2+ accounts for this intriguing luminescence behavior. The detection ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA) with the recovery of almost 100% of the original luminescence. The luminescence quenching and recovery processes can be performed repeatedly with good sensing ability. These remarkable performances allow the colloidal GdVO4:Eu3+@SiO2 NCs a promising fluorescence chemosensor for detecting Cu2+ ions in aqueous solution.

Growth of hexagonal NaGdF{sub 4} nanocrystals based on cubic Ln{sup 3+}: CaF{sub 2} precursors and the multi-color upconversion emissions

Energy Technology Data Exchange (ETDEWEB)

Lei, Lei; Chen, Daqin, E-mail: dqchen@fjirsm.ac.cn; Yu, Yunlong; Zhang, Rui; Ling, Hang; Xu, Ju; Huang, Feng; Wang, Yuansheng, E-mail: yswang@fjirsm.ac.cn

2014-04-05

Graphical abstract: We reported a novel hetero-valence cation exchange route to synthesize Ln: NaGdF4 upconversion nanocrystals for the first time. -- Highlights: • The Ln3+: NaGdF4 nanocrystals were synthesized based on the Ln3+: CaF2 precursors. • The microstructures of nanocrystals were characterized. • The multi-color upconversion emissions were easily realized. -- Abstract: Lanthanide-doped upconversion nanomaterials have attracted great attention recently for their potential applications in the fields of bio-label, three-dimensional display, solar cell and so on. In this article, we report a new strategy to prepare hexagonal Ln{sup 3+}:NaGdF{sub 4} upconversion nanocrystals. Unlike the routine way of synthesizing NaGdF{sub 4} nanocrystals through nucleation and growth, the formation of hexagonal NaGdF{sub 4} nanocrystals herein is realized based on the Ln{sup 3+}-doped cubic CaF{sub 2} precursors, following a hetero-valence cation exchange process between Gd{sup 3+}/Na{sup +} and Ca{sup 2+}. Evidently, Ln{sup 3+} dopants in the CaF{sub 2} precursors are retained in the finally formed hexagonal NaGdF{sub 4} nanocrystals and, subsequently, multi-color upconversion emissions are easily realized by simply adjusting the Ln{sup 3+} dopant species and contents in the CaF{sub 2} precursors. This novel hetero-valence cation exchange route may open up a new pathway to synthesize nanomaterials that cannot be fabricated directly.

Nanoindentation Analysis of Elastic/Mechanical Behaviour of Surface of Transparent Glass Ceramics with Fresnoite Ba2TiSi2O8 Nanocrystals

International Nuclear Information System (INIS)

Shinozaki, K; Honma, T; Komatsu, T

2011-01-01

Transparent glass-ceramics containing Ba 2 TiSi 2 O 8 (BTS) nanocrystals with sizes of ∼200 nm were obtained by heat treatment of 40BaO-20TiO 2 -40SiO 2 glass. Their elastic/mechanical properties were evaluated using the cube-resonance method and the Berkovich nanoindentation technique under standard and 'continuous stiffness measurement' (CSM) modes, and the relation between these properties and the volume fraction (f) of BTS nanocrystals was clarified. The glass-ceramics were obtained by 1-h heat treatments at 760-790 deg. C of the precursor glass, resulting in the formation of BTS nanocrystals with f=2.7-54.5%, with a corresponding Young's modulus of 84-107 GPa. The CSM nanoindentation measurements gave an indentation modulus of 90 GPa for the glass and 110 GPa for the glass-ceramic heat-treated at 790 deg. C, for indentation depths of 200-1500 nm. The results suggest that the BTS nanocrystals confer a high resistance to deformation during indenter loading.

Inhomogeneous magnetic phase in Co–Al–O spinel nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Sato, K., E-mail: sato.koichi@nims.go.jp [National Institute for Materials Science, 2-1-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Naka, T., E-mail: naka.takashi@nims.go.jp [National Institute for Materials Science, 2-1-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Nakane, T. [National Institute for Materials Science, 2-1-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Rangappa, D. [International Advanced Research Centre for Powder Metallurgy and New Materials, Balapur PO, Hyderabad 500-005 (India); Takami, S. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Ohara, S. [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Adschiri, T. [WPI, Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan)

2014-01-15

We report on the crystallographic structure and magnetism of 5-nm Co–Al–O spinel nanocrystals synthesized under supercritical hydrothermal conditions. Structural examination using powder X-ray diffraction and chemical analysis showed the composition of the sample to be Co{sub 0.47}Al{sub 2.36}O{sub 4} rather than the stoichiometric composition of CoAl{sub 2}O{sub 4}. The site occupancy of Co on the A-site forming the diamond lattice was 0.47, which is slightly larger than the site percolation limit. Magnetization measurements showed that magnetic clusters emerged below 40 K. At temperatures below 40 K, a Griffiths-phase-like inhomogeneous state appeared in the sample in which magnetic clusters and paramagnetic spins coexisted. The dc-paramagnetic and ac-susceptibilities exhibited an anomaly below 7 K. - Highlights: • The synthesized sample had an Al-rich structure described by Co{sub 0.47}Al{sub 2.36}O{sub 4}. • The site occupancy of Co at the A-site is larger than the site percolation limit of the A-site. • The non-linearity of the magnetization appeared at T<40 K. • The paramagnetic component showed a peak at 7 K. • An inhomogeneous state is established in our Co–Al oxide nanocrystals.

Synthesis and characterization of some metal oxide nanocrystals by microwave irradiation

Energy Technology Data Exchange (ETDEWEB)

Rashad, M.; Gaber, A.; Abdelrahim, M. A.; Abdel-Baset, A. M. [Physics Department, Faculty of Science, Assiut University, 71516 Assiut (Egypt); Moharram, A. H. [Physics Dept., College of Science and Arts, King Abdulaziz Univ., Rabigh 21911 (Saudi Arabia)

2013-12-16

Copper oxide and cobalt oxide (CuO, Co3O4) nanocrystals (NCs) have been successfully prepared in a short time using microwave irradiation. The resulted powders of nanocrystals (NCs) were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) measurements are also studied. Fourier-transform infrared (FT-IR) and UV–visible absorption spectroscopy of both kind of nanoparticels are illustrated. Optical absorption analysis indicated the direct band gap for both kinds of nanocrystals.

Convenient synthesis of magnetically recyclable Fe{sub 3}O{sub 4}@C@CdS photocatalysts by depositing CdS nanocrystals on carbonized ferrocene

Energy Technology Data Exchange (ETDEWEB)

Li, Dan [Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Xie, Jianjian [Department of Materials Physics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Zhang, Yong; Qiao, Ru [Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Li, Sheng [Department of Materials Physics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Li, Zhengquan, E-mail: zqli@zjnu.edu.cn [Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Department of Materials Physics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China)

2015-10-15

Development of magnetic visible-light-driven photocatalysts is desirable to the practical application of photocatalyts for collection and recycling use. Here we present a facile approach to synthesize Fe{sub 3}O{sub 4}@C@CdS magnetic photocatalysts which can avoid multi-step preparation process. Through one-step solvothermal carbonization of ferrocene, the produced carbon-coated Fe{sub 3}O{sub 4} clusters can serve as both magnetic cores and deposition substrates for in situ generating crystalline CdS nanocrystals on them by rapid microwave irradiation. The prepared Fe{sub 3}O{sub 4}@C@CdS nanoparticles exhibit a uniform core–shell structure and display good photocatalytic activity and recyclability in the degradation of organic dyes. These magnetic photocatalysts may find potential application in wastewater treatment for the future environment remedy. - Highlights: • A rapid strategy is presented to obtain multifunctional core–shell nanostructures. • Magnetic visible-light-driven Fe{sub 3}O{sub 4}@C@CdS nanophotocatalysts are synthesized. • Carbonized ferrocene can provide both magnetic cores and good deposition substrate. • Photocatalytic and recyclable properties of Fe{sub 3}O{sub 4}@C@CdS nanoparticles are explored.

Binding SnO2 nanocrystals in nitrogen-doped graphene sheets as anode materials for lithium-ion batteries.

Science.gov (United States)

Zhou, Xiaosi; Wan, Li-Jun; Guo, Yu-Guo

2013-04-18

Hybrid anode materials for Li-ion batteries are fabricated by binding SnO2 nanocrystals (NCs) in nitrogen-doped reduced graphene oxide (N-RGO) sheets by means of an in situ hydrazine monohydrate vapor reduction method. The SnO2NCs in the obtained SnO2NC@N-RGO hybrid material exhibit exceptionally high specific capacity and high rate capability. Bonds formed between graphene and SnO2 nanocrystals limit the aggregation of in situ formed Sn nanoparticles, leading to a stable hybrid anode material with long cycle life. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Control of Electron Transfer from Lead-Salt Nanocrystals to TiO 2

KAUST Repository

Hyun, Byung-Ryool; Bartnik, A. C.; Sun, Liangfeng; Hanrath, Tobias; Wise, F. W.

2011-01-01

The roles of solvent reorganization energy and electronic coupling strength on the transfer of photoexcited electrons from PbS nanocrystals to TiO 2 nanoparticles are investigated. We find that the electron transfer depends only weakly

Integrated coal preparation

International Nuclear Information System (INIS)

Buchanan, D.J.; Jones, T.F.

1992-01-01

Perceptions of quality have changed over the years. The attributes of a certain coal (its rank, slagging propensity, ash content etc) are traditionally referred to as its quality. However, the subject of this paper is quality in a much wider sense: quality as fitness for purpose: and all that such a wide definition entails. British Standard BS 5750 (ISO 9000) Quality Systems defines a systems approach to quality, and includes both the supplier of raw materials and the final customer within this boundary. Coal preparation starts at the production face. The greater the proportion of dirt in run-of-mine product the greater the challenge in satisfying the customer's needs. Significant advances have been made in minimizing mined dirt. For example, the sue of vertical steering on longwall faces improves productivity and quality. Unfortunately modern mining methods produce large quantities of fines, despite efforts to reduce them at the point of production and during transportation to the surface. Coal preparation also produces further fines. It has been estimated that fine coal costs 2.5 times as much to clean as large coal, and the costs of handing wet fine coal product will inflate this estimate. Handling considerations rightly concern our customers and are part of the wider meaning of quality. In this paper the authors address some novel solutions to the challenge posed by fines

The optical and structural properties of graphene nanosheets and tin oxide nanocrystals composite

Science.gov (United States)

Farheen, Parveen, Azra; Azam, Ameer

2018-05-01

A nanocomposite material consisting of metal oxide and reduced graphene oxide was prepared via simple, economic, and effective chemical reduction method. The synthesis strategy was based on the reduction of GO with Sn2+ ion that combines tin oxidation and GO reduction in one step, which provides a simple, low-cost and effective way to prepare graphene nanosheets/SnO2 nanocrystals composites because no additional chemicals were needed. SEM and TEM images shows the uniform distribution of the SnO2 nanocrystals on the Graphene nanosheets (GNs) surface and transmission electron microscope shows an average particle size of 2-4 nm. The mean crystallite size was calculated by Debye Scherrer formula and was found to be about 4.0 nm. Optical analysis was done by using UV-Visible spectroscopy technique and the band gap energy of the GNs/SnO2 nanocomposite was calculated by Tauc relation and came out to be 3.43eV.

Dilute Magnetic Semiconductor Cu2FeSnS4 Nanocrystals with a Novel Zincblende Structure

Directory of Open Access Journals (Sweden)

Xiaolu Liang

2012-01-01

Full Text Available Diluted magnetic semiconductor Cu2FeSnS4 nanocrystals with a novel zincblende structure have been successfully synthesized by a hot-injection approach. Cu+, Fe2+, and Sn4+ ions occupy the same position in the zincblende unit cell, and their occupancy possibilities are 1/2, 1/4, and 1/4, respectively. The nanocrystals were characterized by means of X-ray diffraction (XRD, transmission electron microscopy (TEM, selected area electron diffraction (SAED, energy-dispersive spectroscopy (EDS, and UV-vis-NIR absorption spectroscopy. The nanocrystals have an average size of 7.5 nm and a band gap of 1.1 eV and show a weak ferromagnetic behavior at low temperature.

On formation of silicon nanocrystals under annealing SiO2 layers implanted with Si ions

International Nuclear Information System (INIS)

Kachurin, G.A.; Yanovskaya, S.G.; Volodin, V.A.; Kesler, V.G.; Lejer, A.F.; Ruault, M.-O.

2002-01-01

Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence have been used to study the formation of silicon nanocrystals in SiO 2 implanted with Si ions. Si clusters have been formed at once in the postimplanted layers, providing the excessive Si concentration more ∼ 3 at. %. Si segregation with Si-Si 4 bonds formation is enhanced as following annealing temperature increase, however, the Raman scattering by Si clusters diminishes. The effect is explained by a transformation of the chain-like Si clusters into compact phase nondimensional structures. Segregation of Si nanoprecipitates had ended about 1000 deg C, but the strong photoluminescence typical for Si nanocrystals manifested itself only after 1100 deg C [ru

Far-infrared spectroscopic study of CeO2 nanocrystals

International Nuclear Information System (INIS)

Popović, Z. V.; Grujić-Brojčin, M.; Paunović, N.; Radonjić, M. M.; Araújo, V. D.; Bernardi, M. I. B.; Lima, M. M. de; Cantarero, A.

2015-01-01

We present the far-infrared reflectivity spectra of 5 nm-sized pure and copper-doped Ce 1−x Cu x O 2−y (x = 0; 0.01 and 0.10) nanocrystals measured at room temperature in the 50–650 cm −1 spectral range. Reflectivity spectra were analyzed using the factorized form of the dielectric function, which includes the phonon and the free carriers contribution. Four oscillators with TO energies of approximately 135, 280, 370, and 490 cm −1 were included in the fitting procedure. These oscillators represent local maxima of the CeO 2 phonon density of states, which is also calculated using the density functional theory. The lowest energy oscillator represents TA(L)/TA(X) phonon states, which become infrared-active E u modes at the L and X points of the Brillouin zone (BZ). The second oscillator originates from TO(Γ) phonon states. The oscillator at ∼400 cm −1 originates from Raman mode phonon states, which at the L point of BZ also becomes infrared-active E u mode. The last oscillator describes phonons with dominantly LO(Γ) infrared mode character. The appearance of phonon density of states related oscillators, instead of single F 2u infrared-active mode in the far-infrared reflectivity spectra, is a consequence of the nanosized dimension of the CeO 2 particles. The best fit spectra are obtained using the generalized Bruggeman model for inhomogeneous media, which takes into account the nanocrystal volume fraction and the pore shape

Effect of hydrostatic pressure on photoluminescence spectra from structures with Si nanocrystals fabricated in SiO2 matrix

International Nuclear Information System (INIS)

Zhuravlev, K.S.; Tyschenko, I.E.; Vandyshev, E.N.; Bulytova, N.V.; Misiuk, A.; Rebohle, L.; Skorupa, W.

2002-01-01

The effect of hydrostatic pressure applied at high temperature on photoluminescence of Si-implanted SiO 2 films was studied. A 'blue'-shift of PL spectrum from the SiO 2 films implanted with Si + ions to total dose of 1.2x10 17 cm -2 with increase in hydrostatic pressure was observed. For the films implanted with Si + ions to a total dose of 4.8x10 16 cm -2 high temperature annealing under high hydrostatic pressure (12 kbar) causes a 'red'-shift of photoluminescence spectrum. The 'red' photoluminescence bands are attributed to Si nanocrystals while the 'blue' ones are related to Si nanocrystals of reduced size or chains of silicon atoms or Si-Si defects. A decrease in size of Si nanocluster occurs in result of the pressure-induced decrease in the diffusion of silicon atoms. (author)

A first-principles study of the electronic and structural properties of Sb and F doped SnO{sub 2} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Kim, Minjung; Scott Bobbitt, N. [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Marom, Noa [Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118 (United States); Chelikowsky, James R. [Center for Computational Materials, Institute for Computational Engineering and Sciences, Departments of Physics and Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States)

2015-01-28

We examine the electronic properties of Sb and F doped SnO{sub 2} nanocrystals up to 2.4 nm in diameter. A real-space pseudopotential implementation of density functional theory is employed within the local density approximation. We calculate electron binding energies and dopant formation energies as function of nanocrystal size, dopant concentration, and dopant species. Structural changes for different dopant species are also investigated. Our study should provide useful information for the design of transparent conducting oxides at the nanoscale.

Control of Electron Transfer from Lead-Salt Nanocrystals to TiO 2

KAUST Repository

Hyun, Byung-Ryool

2011-05-11

The roles of solvent reorganization energy and electronic coupling strength on the transfer of photoexcited electrons from PbS nanocrystals to TiO 2 nanoparticles are investigated. We find that the electron transfer depends only weakly on the solvent, in contrast to the strong dependence in the nanocrystal-molecule system. This is ascribed to the larger size of the acceptor in this system, and is accounted for by Marcus theory. The electronic coupling of the PbS and TiO 2 is varied by changing the length, aliphatic and aromatic structure, and anchor groups of the linker molecules. Shorter linker molecules consistently lead to faster electron transfer. Surprisingly, linker molecules of the same length but distinct chemical structures yield similar electron transfer rates. In contrast, the electron transfer rate can vary dramatically with different anchor groups. © 2011 American Chemical Society.

Model for efficient visible emission from Si nanocrystals ion beam synthesized in SiO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Lopez, M. E-mail: mlopez@el.ub.es; Garrido, B.; Bonafos, C.; Perez-Rodriguez, A.; Morante, J.R.; Claverie, A

2001-05-01

The photoluminescence (PL) emission of Si nanocrystals ion beam synthesized in SiO{sub 2} is studied in this work as a function of annealing time and initial Si atomic excess (super-saturation). The optical properties of this system have been correlated with the characteristics of the nanocrystal population. The Si nanocrystals show a wide and very intense PL red/infrared emission. This emission peaks at about 1.7 eV for the low super-saturation range between 1% and 10% and shifts to the infrared for higher super-saturation (20% and 30%). Remarkably, there is a linear increase of PL intensity versus super-saturation in the low range. Moreover, the annealing kinetic studies show a typical behavior of PL intensity with annealing time, with a fast transitory increase that bends over to reach asymptotic saturation. The PL intensity saturation is satisfactorily explained by the Ostwald ripening stage of the nanocrystal population while the transient stage is a consequence of both nanocrystal growth and nanocrystal surface passivation mechanisms acting together. Indeed, electron spin resonance measurements demonstrate that the concentration of P{sub b} centers (Si dangling bonds) at the Si-SiO{sub 2} interface correlates inversely with PL intensity during most of the transient stage.

Role of the interface region on the optoelectronic properties of silicon nanocrystals embedded in SiO2

International Nuclear Information System (INIS)

Daldosso, N.; Dalba, G.; Fornasini, P.; Grisenti, R.; Pavesi, L.; Luppi, M.; Magri, R.; Ossicini, S.; Degoli, E.; Rocca, F.; Boninelli, S.; Priolo, F.; Spinella, C.; Iacona, F.

2003-01-01

Light-emitting silicon nanocrystals embedded in SiO 2 have been investigated by x-ray absorption measurements in total electron and photoluminescence yields, by energy filtered transmission electron microscopy and by ab initio total energy calculations. Both experimental and theoretical results show that the interface between the silicon nanocrystals and the surrounding SiO 2 is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphous stoichiometric SiO 2 . This region plays an active role in the light-emission process

Unconventionally prepared TiO2/g-C3N4 photocatalysts for photocatalytic decomposition of nitrous oxide

Science.gov (United States)

Troppová, Ivana; Šihor, Marcel; Reli, Martin; Ritz, Michal; Praus, Petr; Kočí, Kamila

2018-02-01

The TiO2/g-C3N4 nanocomposites with the various TiO2:g-C3N4 weight ratios from 1:1 to 1:3 were prepared unconventionally by pressurized hot water processing in a flow regime. The parent TiO2 and g-C3N4 was prepared by thermal hydrolysis and thermal annealing, respectively. The nanocomposites as well as parent TiO2 and g-C3N4 were characterized using several complementary characterization methods and investigated in the photocatalytic decomposition of N2O under UVA (λ = 365 nm) irradiation. All the prepared TiO2/g-C3N4 nanocomposites showed higher photocatalytic activity in comparison with the pure g-C3N4 and chiefly pure TiO2. The photocatalytic activity of TiO2/g-C3N4 nanocomposites was decreasing in the following sequence: TiO2/g-C3N4 (1:3) > TiO2/g-C3N4 (1:2) > TiO2/g-C3N4 (1:1). In comparison with the parent TiO2 or g-C3N4, the TiO2/g-C3N4 nanocomposites' photocatalytic capability was significantly enhanced by coupling TiO2 with g-C3N4. The generation of TiO2/g-C3N4 Z-scheme photocatalyst mainly benefited from the effective separation of photoinduced electron-hole pairs and the extended optical absorption range. The TiO2/g-C3N4 (1:3) nanocomposite showed the best photocatalytic behavior in a consequence of the optimal weight ratio of TiO2:g-C3N4 and the lowest band gap energy from all nanocomposites. The N2O conversion in its presence was 70.6% after 20 h of UVA irradiation.

Nanostructured amorphous MnO{sub 2} prepared by reaction of KMnO{sub 4} with triethanolamine

Energy Technology Data Exchange (ETDEWEB)

Yang Yanjing [Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan, Hunan 411105 (China); Liu Enhui, E-mail: liuenhui99@sina.com.c [Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan, Hunan 411105 (China); Li Limin; Huang Zhengzheng; Shen Haijie; Xiang Xiaoxia [Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan, Hunan 411105 (China)

2010-09-03

Amorphous manganese dioxide is prepared by reaction of potassium permanganate with an organic reductant triethanolamine. The effect of heat-treatment temperature is studied on the characteristics of the materials. Power X-ray diffraction (XRD), scanning electron microscope (SEM) and N{sub 2} adsorption and desorption measurements are employed to investigate crystalline structure, surface morphology, the specific surface area and the pore size distribution. It is found that when the annealing temperature reaches up to 400 {sup o}C, the crystalline convert to {alpha}-MnO{sub 2} from amorphous MnO{sub 2}. The electrochemical characteristics of the prepared MnO{sub 2} powder are characterized by means of cyclic voltammetry (CV), experiments in 1.0 mol L{sup -1} Na{sub 2}SO{sub 4} electrolyte. The specific capacitance (SC) value is 251 F g{sup -1} that is obtained from the product annealing at 350 {sup o}C at a CV scan rate of 2 mV s{sup -1}. And charging-discharging measurement reveals the good stability of the prepared material.

Magnetic Pd-Fe{sub 3}O{sub 4} heterodimer nanocrystals as recoverable catalysts for ligand-free hiyama cross-coupling reactions

Energy Technology Data Exchange (ETDEWEB)

Lee, Woong Sup; Byun, Sang Moon; Kwon, Jung Min; Kim, B. Moon [Dept. of Chemistry, College of Natural Sciences, Seoul National University, Seoul (Korea, Republic of)

2016-12-15

Ligand-free Hiyama cross-coupling reaction was achieved through the use of Pd-Fe{sub 3}O{sub 4} heterodimeric nanocrystals (1 mol% in Pd) as recyclable catalysts. The nanocrystal catalysts exhibited good activities accommodating a variety of substrates including aryl bromides and iodides with substituents of varying electronic and steric properties. Furthermore, the nanocrystal catalyst could be conveniently recovered with the aid of an external magnet and recycled five times without the loss of catalytic activity to a considerable degree.

Preparation, Characterization and Thermal Degradation of Polyimide (4-APS/BTDA/SiO2 Composite Films

Directory of Open Access Journals (Sweden)

Arash Dehzangi

2012-04-01

Full Text Available Polyimide/SiO2 composite films were prepared from tetraethoxysilane (TEOS and poly(amic acid (PAA based on aromatic diamine (4-aminophenyl sulfone (4-APS and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA via a sol-gel process in N-methyl-2-pyrrolidinone (NMP. The prepared polyimide/SiO2 composite films were characterized using X-ray diffraction (XRD, Fourier transform infrared spectroscopy (FTIR, scanning electron microscope (SEM and thermogravimetric analysis (TGA. The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA and the formation of SiO2 particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO2 particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO2 composite films were investigated using TGA in N2 atmosphere. The activation energy of the solid-state process was calculated using Flynn–Wall–Ozawa’s method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions.

Preparation of ZnS semiconductor nanocrystals using pulsed laser ablation in aqueous surfactant solutions

International Nuclear Information System (INIS)

Choi, S-H; Sasaki, T; Shimizu, Y; Yoon, J-W; Nichols, W T; Sung, Y-E; Koshizaki, N

2007-01-01

Cubic ZnS semiconductor nanocrystals with the size of 2 to 5 nm were prepared by pulsed laser ablation in aqueous surfactant solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide without any further treatments. The obtained suspensions of the nanocrystals have broad photoluminescence emission from 375 to 600 nm. The abundance and emission intensity of the nanocrystals depend on the concentration of the surfactant in solution

Effects of hydrazine on the solvothermal synthesis of Cu2ZnSnSe4 and Cu2CdSnSe4 nanocrystals for particle-based deposition of films

International Nuclear Information System (INIS)

Chiang, Ming-Hung; Fu, Yaw-Shyan; Shih, Cheng-Hung; Kuo, Chun-Cheng; Guo, Tzung-Fang; Lin, Wen-Tai

2013-01-01

The effects of hydrazine on the synthesis of Cu 2 ZnSnSe 4 (CZTSe) and Cu 2 CdSnSe 4 (CCTSe) nanocrystals in an autoclave as a function of temperature and time were explored. On heating at 190 °C for 24-72 h, pure CZTSe and CCTSe nanocrystals could readily grow in the hydrazine-added solution, while in the hydrazine-free solution the intermediate phases such as ZnSe, Cu 2 Se, and Cu 2 SnSe 3 , and Cu 2 SnSe 3 and CdSe associated with the CZTSe and CCTSe nanocrystals grew, respectively. This result reveals that hydrazine can speed up the synthesis of pure CZTSe and CCTSe nanocrystals via a solvothermal process. The mechanisms for the hydrazine-enhanced growth of CZTSe and CCTSe nanocrystals were discussed. The pure CZTSe and CCTSe nanocrystals were subsequently fabricated to the smooth films by spin coating without further annealing in selenium atmosphere. This processing may be beneficial to the fabrication of the absorber layer for solar cells and thermoelectric devices. - Highlights: • Hydrazine enhances the growth of pure Cu 2 ZnSnSe 4 and Cu 2 CdSnSe 4 nanocrystals. • The nanocrystals can be fabricated to films by spin coating without annealing. • This solvothermal processing is promising for the fabrication of thin film devices

Preparation and properties of poly(vinyl alcohol/chitosan blend bionanocomposites reinforced with cellulose nanocrystals/ZnO-Ag multifunctional nanosized filler

Directory of Open Access Journals (Sweden)

Azizi S

2014-04-01

Full Text Available Susan Azizi,1 Mansor Bin Ahmad,1 Mohd Zobir Hussein,1 Nor Azowa Ibrahim,1 Farideh Namvar2,31Department of Chemistry, Faculty of Science, 2Institute of Tropical Forestry and Forest Products, University Putra Malaysia, Selangor, Malaysia; 3Mashhad Branch, Islamic Azad University, Mashhad, IranAbstract: A series of novel bionanocomposites were cast using different contents of zinc oxide-silver nanoparticles (ZnO-AgNPs stabilized by cellulose nanocrystals (CNC as multifunctional nanosized fillers in poly(vinyl alcohol/chitosan (PVA/Cs matrices. The morphological structure, mechanical properties, ultraviolet-visible absorption, and antimicrobial properties of the prepared films were investigated as a function of their CNC/ZnO-AgNP content and compared with PVA/chitosan/CNC bionanocomposite films. X-ray diffraction and field emission scanning electron microscopic analyses showed that the CNC/ZnO-AgNPs were homogeneously dispersed in the PVA/Cs matrix and the crystallinity increased with increasing nanosized filler content. Compared with pure PVA/Cs, the tensile strength and modulus in the films increased from 0.055 to 0.205 GPa and from 0.395 to 1.20 GPa, respectively. Ultraviolet and visible light can be efficiently absorbed by incorporating ZnO-AgNPs into a PVA/Cs matrix, suggesting that these bionanocomposite films show good visibility and ultraviolet-shielding effects. The bionanocomposite films had excellent antimicrobial properties, killing both Gram-negative Salmonella choleraesuis and Gram-positive Staphylococcus aureus. The enhanced physical properties achieved by incorporating CNC/ZnO-AgNPs could be beneficial in various applications.Keywords: multifunctional nanofiller, bionanocomposite, cellulose nanocrystals, antimicrobial properties, poly(vinyl alcohol/chitosan blend

Raman scattering study of the anharmonic effects in CeO{sub 2-y} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Popovic, Z V [Center for Solid State Physics and New Materials, Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Dohcevic-Mitrovic, Z [Center for Solid State Physics and New Materials, Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Cros, A [Materials Science Institute, University of Valencia, P O Box 22085, E-46071, Valencia (Spain); Cantarero, A [Materials Science Institute, University of Valencia, P O Box 22085, E-46071, Valencia (Spain)

2007-12-12

We have studied the temperature dependence of the F{sub 2g} Raman mode phonon frequency and broadening in CeO{sub 2-y} nanocrystals. The phonon softening and phonon linewidth are calculated using a model which takes into account the three-and four-phonon anharmonic processes. A detailed comparison of the experimental data with theoretical calculations revealed the predominance of four-phonon anharmonic processes in the temperature dependence of the phonon energy and broadening of the nanocrystals. On the other hand, three-phonon processes dominate the temperature behavior of phonons in polycrystalline samples. The anti-Stokes/Stokes peak intensity ratio was also investigated and found to be smaller for nanosized CeO{sub 2} powders than in the bulk counterpart.

Preparation of acid salt M(HPO4)2.nH2 O thin films

International Nuclear Information System (INIS)

Kassem, M.

1998-01-01

The layered crystalline powders of Titanium Phosphate with the formula Ti(HPO 4 ) 2 .nH 2 O (phase α when n=2, phase γ when n=1) were prepared by reaction of titanium three chloride with phosphoric acid under specific thermal conditions. Starting from these powders thin films have been prepared using some methods such as: Thermal evaporation, sol-gel and vapor phase transport. The results of X-ray diffraction and differential thermal deferential analysis show that the temperature plays an important role in the determination of the crystalline phases and the phase transition of the prepared films. (author). 7 refs

Preparation and characterization of chitosan/ZnAl2O4 films

International Nuclear Information System (INIS)

Araujo, P.M.A.G.; Santos, P.T.A.; Rodrigues, P.A.; Costa, A.C.F.M.; Araujo, E.M.

2012-01-01

Chitosan films have been explored for biomedical application, as the chitosan to be, low toxicity, abundant in nature, show affinity for dispersion loads and high mechanical strength. On the other hand, ZnAl 2 O 4 has energy gap of approximately 3.8 eV, which makes it useful for use as photoelectric device ultraviolet. Thus, this work has as objective to prepare films of quitosana/ZnAl 2 O 4 in proportions of 5:1, 5:2, 5:3, 5:4 and evaluate the structural, morphological and thermals characteristics. To this end, ZnAl2O4 first nanoparticles (NPs) was deagglomerated and 325 mesh sieve and added to chitosan diluted in 1% acetic acid, and dried at 60°C. After drying, a solution of 1M sodium hydroxide was added to obtain a film with neutral pH. The films were characterized by XRD, SEM and TG. For all proportions evaluated it was verified the presence of ZnAl 2 O)4 and chitosan phases. By micrographs, it was observed that there was formation of agglomerates of ZnAl 2 O 4 NPs both on the surface of the films, the encapsulated in chitosan. In all samples the ratio 5:4 showed the greatest consistency both in relation to the film surface of the nanoparticles in the chitosan matrix. TG/DTA curves of quitosana/ZnAl 2 O 4 film for all the samples showed that for the concentration of 5:1 to 5:3 occurred three mass loss while for concentration of 5:2 to 5:4 were only two stages decomposition. (author)

Formation of the distributed NiSiGe nanocrystals nonvolatile memory formed by rapidly annealing in N2 and O2 ambient

International Nuclear Information System (INIS)

Hu, Chih-Wei; Chang, Ting-Chang; Tu, Chun-Hao; Chiang, Cheng-Neng; Lin, Chao-Cheng; Chen, Min-Chen; Chang, Chun-Yen; Sze, Simon M.; Tseng, Tseung-Yuen

2010-01-01

In this work, electrical characteristics of the Ge-incorporated Nickel silicide (NiSiGe) nanocrystals memory device formed by the rapidly thermal annealing in N 2 and O 2 ambient have been studied. The trapping layer was deposited by co-sputtering the NiSi 2 and Ge, simultaneously. Transmission electron microscope results indicate that the NiSiGe nanocrystals were formed obviously in both the samples. The memory devices show obvious charge-storage ability under capacitance-voltage measurement. However, it is found that the NiSiGe nanocrystals device formed by annealing in N 2 ambient has smaller memory window and better retention characteristics than in O 2 ambient. Then, related material analyses were used to confirm that the oxidized Ge elements affect the charge-storage sites and the electrical performance of the NCs memory.

Processing of ZnO nanocrystals by solochemical technique

International Nuclear Information System (INIS)

Gusatti, M.; Speckhahn, R.; Silva, L.A.; Rosario, J.A.; Lima, R.B.; Kuhnen, N.C.; Riella, H.G.; Campos, C.E.M.

2009-01-01

In the present work, we report the synthesis of high quality ZnO nanocrystals by solochemical technique. This synthetic strategy has been shown to have advantages over other methods of producing nanostructures in terms of low cost, efficiency, simplicity and uniformity of crystal structure. Zinc chloride solution at room temperature was mixed with sodium hydroxide solution at 50°C to produce ZnO nanocrystals. Transmission electronic microscopy (TEM) and X-ray powder diffraction (XRD) were used to characterize the ZnO nanocrystals obtained. The structure of ZnO was refined by the Rietveld Method from X-ray diffraction data. These methods showed that the product consisted of pure ZnO nanocrystals and has, predominantly, a rod-like morphology. (author)

Water concentration controlled hydrolysis and crystallization in n-octanol to TiO{sub 2} nanocrystals with size below 10 nm

Energy Technology Data Exchange (ETDEWEB)

Wang Meilan [School of Chemical and Biological Science and Engineering, Yantai University, Yantai 264005 (China); He Tao, E-mail: htzy79@yahoo.com.cn [School of Chemical and Biological Science and Engineering, Yantai University, Yantai 264005 (China); Pan Yanfei; Liao Weiping [School of Chemical and Biological Science and Engineering, Yantai University, Yantai 264005 (China); Zhang Shangzhou; Du Wei [School of Environment and Materials Engineering, Yantai University, Yantai 264005 (China)

2011-11-01

Highlights: {yields} Controlled hydrolysis of alkoxide was realized by adjusting water concentration. {yields} Carrying out hydrolysis under different water concentration gave hydrolyzed intermediate with different composition. {yields} A precise size control below 10 nm for anatase TiO{sub 2} nanocrystals was realized. - Abstract: Hydrolysis of tetrabutyl titanate (TBT) and crystallization from hydrolyzed intermediates were carried out in a simple ternary system including n-octanol, TBT and water. Anatase TiO{sub 2} nanocrystals (NCS) were prepared with precise size control below 10 nm. The hydrolysis rate at different water concentration (C{sub water}) was evaluated by measuring the induction time before turbidity changing of the synthetic solution. Fourier transform infrared spectrum (FT-IR) and thermogravimetric/differential thermal analysis (TG/DTA) techniques were applied to make clear the composition of hydrolyzed intermediates obtained at different C{sub water}. Powder X-ray diffraction (XRD) technique was used to track the crystallization process of TiO{sub 2} NCS. Transmission electron microscopy (TEM), XRD, FT-IR and TG/DTA techniques were used to characterize the particular properties of NCS. The C{sub water} controlled mechanism responsible for the slow hydrolysis and crystallization were discussed. Since no other organic capping ligands or rapid injecting techniques were used to limit NCS' growth and the solvent n-octanol can be easily separated and reused, this simple synthetic process is of green chemistry and has application potential in large-scale preparation of inorganic NCS.

Synthesis, characterization, and comparative gas-sensing properties of Fe{sub 2}O{sub 3} prepared from Fe{sub 3}O{sub 4} and Fe{sub 3}O{sub 4}-chitosan

Energy Technology Data Exchange (ETDEWEB)

Cuong, Nguyen Duc [Faculty of Hospitality and Tourism, Hue University, 22 Lam Hoang, Vy Da Ward, Hue City (Viet Nam); College of Sciences, Hue University, 77 Nguyen Hue, Phu Nhuan Ward, Hue City (Viet Nam); International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST), Hanoi (Viet Nam); Hoa, Tran Thai; Khieu, Dinh Quang [College of Sciences, Hue University, 77 Nguyen Hue, Phu Nhuan Ward, Hue City (Viet Nam); Lam, Tran Dai [Institute of Materials Science, Vietnamese Academy of Science and Technology, Hanoi (Viet Nam); Hoa, Nguyen Duc [International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST), Hanoi (Viet Nam); Van Hieu, Nguyen, E-mail: hieu@itims.edu.vn [International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST), Hanoi (Viet Nam)

2012-05-15

Highlights: Black-Right-Pointing-Pointer We have demonstrated a facile method to prepare Fe{sub 3}O{sub 4} nanoparticles and chitosan-coated Fe{sub 3}O{sub 4} nanoparticles. Black-Right-Pointing-Pointer {alpha}-Fe{sub 2}O{sub 3} sensors prepared from those Fe{sub 3}O{sub 4} materials have been investigated and compared. Black-Right-Pointing-Pointer The results show potential application of {alpha}-Fe{sub 2}O{sub 3} for CO sensors in environmental monitoring. - Abstract: In this paper, Fe{sub 3}O{sub 4} and chitosan (CS)-coated Fe{sub 3}O{sub 4} nanoparticles were synthesized via co-precipitation method and subsequent covalent binding of CS onto the surface for functionalization, respectively. Characterization of the crystal structures and morphologies of as-synthesized nanoparticles by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy demonstrated that Fe{sub 3}O{sub 4} had a cubic spinal structure with irregular shapes and average diameters of 10-20 nm. The surface states and magnetic properties of Fe{sub 3}O{sub 4}-CS nanoparticles were characterized by Fourier transform infrared spectra and vibrating sample magnetometry. Results showed that Fe{sub 3}O{sub 4}-CS nanoparticles possessed super-paramagnetic properties, with saturated magnetization up to 60 emu/g. In addition, Fe{sub 3}O{sub 4} and CS-coated Fe{sub 3}O{sub 4} nanoparticles were used in the fabrication of {alpha}-Fe{sub 2}O{sub 3} based gas sensors. Gas sensing measurements revealed that the {alpha}-Fe{sub 2}O{sub 3} gas sensor prepared from Fe{sub 3}O{sub 4}-CS had a better response to H{sub 2}, CO, C{sub 2}H{sub 5}OH, and NH{sub 3} compared with the device prepared from pristine Fe{sub 3}O{sub 4}. Furthermore, the {alpha}-Fe{sub 2}O{sub 3} sensor prepared from Fe{sub 3}O{sub 4}-CS nanoparticles exhibited the highest response to CO among the test gases, suggesting that it has great potential for practical applications in environmental monitoring.

Identification and quantification of oxygen vacancies in CeO{sub 2} nanocrystals and their role in formation of F-centers

Energy Technology Data Exchange (ETDEWEB)

Jaffari, G.Hassnain, E-mail: hassnain@qau.edu.pk [Department of Physics, Quaid-i-Azam University Islamabad (Pakistan); Imran, Ali [Department of Physics, Quaid-i-Azam University Islamabad (Pakistan); Bah, M. [Department of Materials Science and Engineering, University of Delaware, 19716, Newark, DE (United States); Ali, Awais; Bhatti, Arshad S. [Centre for Micro and Nano Devices, Department of Physics, COMSATS Institute of Information Technology, Park Road, Islamabad, 44000 (Pakistan); Qurashi, Umar Saeed [Department of Physics, Quaid-i-Azam University Islamabad (Pakistan); Ismat Shah, S. [Department of Materials Science and Engineering, University of Delaware, 19716, Newark, DE (United States); Department of Physics, University of Delaware, 19716, Newark, DE (United States)

2017-02-28

Highlights: • Detail crystal and electronic structural analysis was employed to quantify oxygen vacancies. • The Raman F{sub 2g} mode shifted towards lower wave number, exhibiting mode softening with broader and asymmetric peak. • Observation of absorption edge revealed presence of 4f band within the band gap. • PL emission studies revealed presence of F-centers with corresponding energy level located below 4f band. • Transitions associated by the F-center are mainly associated with 4f{sup 0} to 4f{sup 1}, F{sup ++} to 4f{sup 1} and 4f{sup 0} to F{sup +}. - Abstract: In this work we present synthesis and extensive characterization of Cerium oxide (CeO{sub 2}) nanocrystals. Comparison between the properties of as-prepared and air annealed nanoparticles has been carried out, with a goal to clearly identify the effect of oxygen vacancies on crystal, electronic and band structure. Detail crystal and electronic structural analysis was employed to quantify oxygen vacancies. Structural analysis confirmed that the formation of single phase cubic Fluorite structure for both as-prepared and annealed samples. Crystal and electronic structural studies confirmed that Ce ions exists in two oxidation states, Ce{sup +3} and Ce{sup +4}. Concentration of oxygen vacancies was larger in as-synthesis nanocrystal. A drastic decrease in oxygen vacancy concentration was observed for the sample annealed in air at 550 °C. For the as-prepared sample, the Raman allowed F{sub 2g} mode shifted towards lower wavenumber, exhibiting mode softening with broader and asymmetric peak. Observation of absorption edge revealed presence of 4f band within the band gap. Absorption with different band edge, confirmed different energy position of 4f level for the sample possessing oxygen vacancies. Blue shift of the band edge for as-prepared sample has been discussed in terms of increase in lattice parameter, formation of Ce{sup +3} ions, quantum confinement effect etc. Photoluminescence emission

Effect of Sb{sub 2}O{sub 3} on the electrical properties of Ba{sub 0.9}Ca{sub 0.1}Zr{sub 0.1}Ti{sub 0.9}O{sub 3} ceramics fabricated using nanocrystals seed

Energy Technology Data Exchange (ETDEWEB)

Parjansri, P. [Rajamangala University of Technology Krungthep, Physics Division, Faculty of Science and Technology, Bangkok (Thailand); Intatha, U. [Mae Fah Luang University, School of Science, Chiang Rai (Thailand); Guo, R.; Bhalla, A.S. [University of Texas at San Antonio, Department of Electrical and Computer Engineering, Faculty of Engineering, San Antonio, TX (United States); Eitssayeam, S. [Chiang Mai University, Department of Physics and Materials Science, Faculty of Science, Chiang Mai (Thailand); Chiang Mai University, Materials Science Research Center, Faculty of Science, Chiang Mai (Thailand)

2016-09-15

This work was to investigate the effects of antimony oxide (Sb{sub 2}O{sub 3}) on the electrical properties of Ba{sub 0.9}Ca{sub 0.1}Zr{sub 0.1}Ti{sub 0.9}O{sub 3} (BCZT) ceramics and was prepared by adding 1 mol% of BCZT nanocrystals. The seed is nanocrystals of BCZT which was synthesized by the molten salt method. The ceramics powders were prepared by the mixed oxide method using BaCO{sub 3}, CaCO{sub 3}, ZrO{sub 2}, TiO{sub 2} as starting materials, and the BCZT seed was added as nanocrystal for induce phase transition. They were doped with x mol% Sb{sub 2}O{sub 3} (x = 0.0-0.5). Results indicated that all samples show pure perovskite phase. The Sb{sub 2}O{sub 3} enhanced the electrical properties of the ceramic systems. Excellent values of a dielectric constant (ε {sub r}) at room temperature (T{sub r}) were 4086 with sample of x = 0.5, and at Curie temperature (T{sub c}) was 15,485 for samples with x = 0.1. The highest remnant polarization (P{sub r}), piezoelectric charge coefficient (d{sub 33}), piezoelectric voltage coefficient (g{sub 33}), electromechanical coefficient for planar mode (k{sub p}) and thickness mode (k{sub t}) values were 6.3 μC/cm{sup 2}, 346 pC/N, 15.6 x 10{sup -3} Vm/N, 42 and 41 %, respectively, which were obtained for the sample of x = 0.2 mol% Sb. (orig.)

Elaboration and characterization of a KCl single crystal doped with nanocrystals of a Sb2O3 semiconductor

International Nuclear Information System (INIS)

Bouhdjer, L.; Addala, S.; Halimi, O.; Boudine, B.; Sebais, M.; Chala, A.

2013-01-01

Undoped and doped KCl single crystals have been successfully elaborated via the Czochralski (Cz) method. The effects of dopant Sb 2 O 3 nanocrystals on structural and optical properties were investigated by a number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) analysis, UV-visible and photoluminescence (PL) spectrophotometers. An XRD pattern of KCl:Sb 2 O 3 reveals that the Sb 2 O 3 nanocrystals are in the well-crystalline orthorhombic phase. The broadening of diffraction peaks indicated the presence of a Sb 2 O 3 semiconductor in the nanometer size regime. The shift of absorption and PL peaks is observed near 334 nm and 360 nm respectively due to the quantum confinement effect in Sb 2 O 3 nanocrystals. Particle sizes calculated from XRD studies agree fairly well with those estimated from optical studies. An SEM image of the surface KCl:Sb 2 O 3 single crystal shows large quasi-spherical of Sb 2 O 3 crystallites scattered on the surface. The elemental analysis from EDAX demonstrates that the KCl:Sb 2 O 3 single crystal is slightly rich in oxygen and a source of excessive quantities of oxygen is discussed. (semiconductor materials)

Quantum-dot light-emitting diodes utilizing CdSe /ZnS nanocrystals embedded in TiO2 thin film

Science.gov (United States)

Kang, Seung-Hee; Kumar, Ch. Kiran; Lee, Zonghoon; Kim, Kyung-Hyun; Huh, Chul; Kim, Eui-Tae

2008-11-01

Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe /ZnS nanocrystals in TiO2 thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO2/QDs /p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO2/QDs /Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.

Very low drift and high sensitivity of nanocrystal-TiO2 sensing membrane on pH-ISFET fabricated by CMOS compatible process

International Nuclear Information System (INIS)

Bunjongpru, W.; Sungthong, A.; Porntheeraphat, S.; Rayanasukha, Y.; Pankiew, A.; Jeamsaksiri, W.; Srisuwan, A.; Chaisriratanakul, W.; Chaowicharat, E.; Klunngien, N.; Hruanun, C.; Poyai, A.; Nukeaw, J.

2013-01-01

High sensitivity and very low drift rate pH sensors are successfully prepared by using nanocrystal-TiO 2 as sensing membrane of ion sensitive field effect transistor (ISFET) device fabricated via CMOS process. This paper describes the physical properties and sensing characteristics of the TiO 2 membrane prepared by annealing Ti and TiN thin films that deposited on SiO 2 /p-Si substrates through reactive DC magnetron sputtering system. The X-ray diffraction, scanning electron microscopy and Auger electron spectroscopy were used to investigate the structural and morphological features of deposited films after they had been subjected to annealing at various temperatures. The experimental results are interpreted in terms of the effects of amorphous-to-crystalline phase transition and subsequent oxidation of the annealed films. The electrolyte–insulator–semiconductor (EIS) device incorporating Ti-O-N membrane that had been obtained by annealing of TiN thin film at 850 °C exhibited a higher sensitivity (57 mV/pH), a higher linearity (1), a lower hysteresis voltage (1 mV in the pH cycle of 7 → 4 → 7 → 10 → 7), and a smaller drift rate (0.246 mV/h) than did those devices prepared at the other annealing temperatures. Furthermore, this pH-sensing device fabrication process is fully compatible with CMOS fabrication process technology.

NdFeO3 nanocrystals under glycine nitrate combustion formation

Science.gov (United States)

Tugova, Ekaterina; Yastrebov, Sergey; Karpov, Oleg; Smith, Roger

2017-06-01

Nanocrystalline perovskite NdFeO3 with the orthorhombic structure was prepared by a glycine nitrate combustion method under different technological conditions. The starting materials Fe(NO3)3 · 9H2O,Nd(NO3)3 · 6H2O in stoichiometric amounts and H2NCH2COOH were used. These quantities were varied by changing the ratio of glycine moles to metal nitrate moles (G/N) in the range between 0.25 and 0.75. The prepared NdFeO3 nanocrystals were characterised by X-ray diffraction (XRD) and electron microscopy. Decomposition of the XRD diffraction profile using Voigt contours was exploited for analysis of the pattern in the area where the most prominent diffraction peak was situated. We demonstrate that Voigt functions reduce to Lorentzians for G / N = 0.75 and 0.55 . A volume-weighted diameter distribution function was derived using the width of the Lorentzians. The log-normal shape of the distribution is discussed in terms of the model, assuming exponential growth of cluster size in the time available for the NdFeO3 nanograin to grow.

UV Photocatalytic Activity for Water Decomposition of SrxBa1−xNb2O6 Nanocrystals with Different Components and Morphologies

Directory of Open Access Journals (Sweden)

Guoqiang Han

2017-01-01

Full Text Available Strontium barium niobate SrxBa1-xNb2O6 (SBN nanocrystals with different components (x=0.2, 0.4, 0.6, and 0.8 were synthesized by Molten Salt Synthesis (MSS method at various reaction temperatures (T = 950°C, 1000°C, 1050°C, and 1100°C. The SBN nanocrystals yielded through flux reactions possess different morphologies and sizes with a length of about ~100 nm~7 μm and a diameter of about ~200~500 nm. The Scanning Electron Microscopy (SEM and X-ray Diffraction (XRD techniques were used to study the compositions, structures, and morphologies of the nanocrystals. The absorption edges of the SBN nanocrystals are at a wavelength region of approximate 390 nm, which corresponds to band-gap energy of ~3.18 eV. The SBN nanocrystals with different sizes display different photocatalytic activity under ultraviolet light in decomposition of water. The SBN60 nanocrystals exhibit stable photocatalytic rates (~100~130 μmol of H2·g−1·h−1 for hydrogen production. The SBN nanocrystals can be a potential material in the application of photocatalysis and micro/nanooptical devices.

Combined coal gasification and Fe{sub 3}O{sub 4}-reduction using high-temperature solar process heat

Energy Technology Data Exchange (ETDEWEB)

Tamaura, Y [Tokyo Inst. of Technology, Tokyo (Japan); Ehrensberger, K; Steinfeld, A [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1997-06-01

The coal/Fe{sub 3}O{sub 4} system was experimentally studied at PSI solar furnace. The reactants were directly exposed to a solar flux irradiation of 3,000 suns (1 sun = 1 kW/m{sup 2}). The combined gasification of coal and reduction of Fe{sub 2}O{sub 3} proceeded rapidly after only one second exposure, suggesting an efficient heat transfer and chemical conversion by direct solar energy absorption at the reaction site. The proposed solar thermochemical process offers the possibility of converting coal to a cleaner fluid fuel with a solar-upgraded calorific value. (author) 2 figs., 8 refs.

Coupling between Ge-nanocrystals and defects in SiO2

International Nuclear Information System (INIS)

Skov Jensen, J.; Franzo, G.; Leervad Petersen, T.P.; Pereira, R.; Chevallier, J.; Christian Petersen, M.; Bech Nielsen, B.; Nylandsted Larsen, A.

2006-01-01

Room temperature photoluminescence (PL) at around 600 nm from magnetron-sputtered SiO 2 films co-doped with Ge is reported. The PL signal is observed in pure SiO 2 , however, its intensity increases significantly in the presence of Ge-nanocrystals (Ge-nc). The PL intensity has been optimized by varying the temperature of heat treatment, type of gas during heat treatment, concentration of Ge in the SiO 2 films, and gas pressure during deposition. Maximum intensity occurs when Ge-nc of around 3.5 nm are present in large concentration in SiO 2 layers deposited at fairly high gas pressure. Based on time resolved PL, and PL measurements after α-particle irradiation or H passivation, we attribute the origin of the PL to a defect in SiO 2 (probably an O deficiency) that is excited through an energy transfer from Ge-nc. There is no direct PL from the Ge-nc; however, there is a strong coupling between excitons created in the Ge-nc and the SiO 2 defect

Photoconductivity of composite structures based on porous SnO2 sensitized with CdSe nanocrystals

International Nuclear Information System (INIS)

Drozdov, K. A.; Kochnev, V. I.; Dobrovolsky, A. A.; Vasiliev, R. B.; Babynina, A. V.; Rumyantseva, M. N.; Gaskov, A. M.; Ryabova, L. I.; Khokhlov, D. R.

2013-01-01

The introduction of CdSe nanocrystals (colloidal quantum dots) into a porous SnO 2 matrix brings about the appearance of photoconductivity in the structures. Sensitization is a consequence of charge exchange between the quantum dots and the matrix. Photoconductivity spectral measurements show that the nanocrystals embedded into the matrix are responsible for the optical activity of the structure. The photoconductivity of the structures sensitized with different-sized quantum dots is studied in the temperature range from 77 to 300 K. It is shown that the maximum photoconductivity is attained by introducing nanocrystals of the minimum size (2.7 nm). The mechanisms of charge-carrier transport in the matrix and the charge-exchange kinetics are discussed.

Highly efficient one-step synthesis of carbon encapsulated nanocrystals by the oxidation of metal π-complexes

Science.gov (United States)

Liu, Boyang; Shao, Yingfeng; Xiang, Xin; Zhang, Fuhua; Yan, Shengchang; Li, Wenge

2017-08-01

Various carbon encapsulated nanocrystals, including MnS and MnO, Cr2O3, MoO2, Fe7S8 and Fe3O4, and ZrO2, are prepared in one step and in situ by a simple and highly efficient synthesis approach. The nanocrystals have an equiaxed morphology and a median size smaller than 30 nm. Tens and hundreds of these nanocrystals are entirely encapsulated by a wormlike amorphous carbon shell. The formation of a core-shell structure depends on the strongly exothermic reaction of metal π-complexes with ammonium persulfate in an autoclave at below 200 °C. During the oxidation process, the generated significant amounts of heat will destroy the molecular structure of the metal π-complex and cleave the ligands into small carbon fragments, which further transform into an amorphous carbon shell. The central metal atoms are oxidized to metal oxide/sulfide nanocrystals. The formation of a core-shell structure is independent of the numbers of ligands and carbon atoms as well as the metal types, implying that any metal π-complex can serve as a precursor and that various carbon encapsulated nanocrystals can be synthesized by this method.

A dual-colored bio-marker made of doped ZnO nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Wu, Y L; Zeng, X T [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, 638075 (Singapore); Fu, S; Kwek, L C [National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, 637616 (Singapore); Tok, A I Y; Boey, F C Y [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Lim, C S [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore)

2008-08-27

Bio-compatible ZnO nanocrystals doped with Co, Cu and Ni cations, surface capped with two types of aminosilanes and titania are synthesized by a soft chemical process. Due to the small particle size (2-5 nm), surface functional groups and the high photoluminescence emissions at the UV and blue-violet wavelength ranges, bio-imaging on human osteosarcoma (Mg-63) cells and histiocytic lymphoma U-937 monocyte cells showed blue emission at the nucleus and bright turquoise emission at the cytoplasm simultaneously. This is the first report on dual-color bio-images labeled by one semiconductor nanocrystal colloidal solution. Bright green emission was detected on mung bean seedlings labeled by all the synthesized ZnO nanocrystals. Cytotoxicity tests showed that the aminosilanes capped nanoparticles are non-toxic. Quantum yields of the nanocrystals varied from 79% to 95%. The results showed the potential of the pure ZnO and Co-doped ZnO nanocrystals for live imaging of both human cells and plant systems.

A novel material Li{sub 2}NiFe{sub 2}O{sub 4}: Preparation and performance as anode of lithium ion battery

Energy Technology Data Exchange (ETDEWEB)

Ding, Keqiang, E-mail: dkeqiang@263.net [College of Chemistry and Materials Science, Hebei Normal University, Shijiazhuang, Hebei, 050024 (China); Zhao, Jing [College of Chemistry and Materials Science, Hebei Normal University, Shijiazhuang, Hebei, 050024 (China); Zhou, Jinming, E-mail: zhoujm@iccas.ac.cn [College of Chemistry and Materials Science, Hebei Normal University, Shijiazhuang, Hebei, 050024 (China); Zhao, Yongbo; Chen, Yuying; Liu, Likun [College of Chemistry and Materials Science, Hebei Normal University, Shijiazhuang, Hebei, 050024 (China); Wang, Li [Institute of Nuclear & New Energy Technology, Beijing Key Lab of Fine Ceramics, Tsinghua University, Beijing, 100084 (China); He, Xiangming, E-mail: hexm@tsinghua.edu.cn [Institute of Nuclear & New Energy Technology, Beijing Key Lab of Fine Ceramics, Tsinghua University, Beijing, 100084 (China); Guo, Zhanhu, E-mail: zguo10@utk.edu [Integrated Composites Laboratory (ICL), Chemical and Biomolecular Engineering Department, University of Tennessee Knoxville, Knoxville, NT, 37996 (United States)

2016-07-01

For the first time, the preparation and characterization of a novel anode material Li{sub 2}NiFe{sub 2}O{sub 4} are reported in this work. The preparation of Li{sub 2}NiFe{sub 2}O{sub 4} is conducted under the air conditions by using a subsection calcination method. The influence of annealing periods on the properties of the resultant materials is thoroughly explored. The characteristics of the materials are mainly examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge tests and electrochemical impedance spectroscopy (EIS). The results of the XRD patterns effectively demonstrate the formation of crystalline Li{sub 2}NiFe{sub 2}O{sub 4}, and the SEM images indicate that particles with octahedron crystal morphology are prepared and the 9 h-annealed sample has the smallest particle size among all the prepared samples. The results of electrochemical measurements reveal that 9 h-calcined sample delivers a high specific capacity of 203 mAh g{sup −1} after 20 cycles at a current density of 100 mA g{sup −1}. The successful preparation of Li{sub 2}NiFe{sub 2}O{sub 4} is believed to be able to trigger the research work concerning the novel group of Li{sub 2}MFe{sub 2}O{sub 4} materials. - Highlights: • A novel anode material Li{sub 2}NiFe{sub 2}O{sub 4} was prepared under the air conditions. • Li{sub 2}NiFe{sub 2}O{sub 4} showed well-defined octahedron crystal morphology. • 9 h-annealed Li{sub 2}NiFe{sub 2}O{sub 4} delivered a capacity of 203 mAh g{sup −1}.

Blue-Emitting Small Silica Particles Incorporating ZnSe-Based Nanocrystals Prepared by Reverse Micelle Method

Directory of Open Access Journals (Sweden)

Masanori Ando

2007-01-01

Full Text Available ZnSe-based nanocrystals (ca. 4-5 nm in diameter emitting in blue region (ca. 445 nm were incorporated in spherical small silica particles (20–40 nm in diameter by a reverse micelle method. During the preparation, alkaline solution was used to deposit the hydrolyzed alkoxide on the surface of nanocrystals. It was crucially important for this solution to include Zn2+ ions and surfactant molecules (thioglycolic acid to preserve the spectral properties of the final silica particles. This is because these substances in the solution prevent the surface of nanocrystals from deterioration by dissolution during processing. The resultant silica particles have an emission efficiency of 16% with maintaining the photoluminescent spectral width and peak wavelength of the initial colloidal solution.

Corroboration of Raman and AFM mapping to study Si nanocrystals embedded in SiO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Rani, Ekta, E-mail: ades.ekta@gmail.com [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Homi Bhabha National Institute, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Ingale, Alka A. [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Homi Bhabha National Institute, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Chaturvedi, A. [Laser Material Processing Division, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Joshi, M.P.; Kukreja, L.M. [Homi Bhabha National Institute, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India); Laser Material Processing Division, Raja Ramanna Centre for Advanced Technology, Indore-452013 (India)

2016-07-05

Raman and atomic force microscopy (AFM) mapping on the same selected area are used to get unique information about the morphology of Si nanocrystals (NCs) embedded in SiO{sub 2}, which is difficult to obtain by any other conventional technique. The sensitivity of Raman spectroscopy to surface/interface and confinement effects in NCs is effectively used to correlate the Raman intensity profile in Raman mapping with the topography obtained from AFM to understand that Si NCs are clustered in i) smaller clusters (∼100 nm) organized closely in two dimensions (2D) and ii) big (∼2 μm) three dimensional (3D) isolated clusters, although the growth is carried out to be multilayer (Si/SiO{sub 2}). Raman mapping performed by varying the focal spot along the depth shows stacking of larger (>∼60 Å) to smaller sizes (<∼40 Å) Si NCs from bottom to top for some clusters. To understand the observed morphologies, further study of specially grown Si–SiO{sub 2} nanocomposites is performed, which suggest formation of smaller Si NCs at the top due to annealing at 800 °C in Si rich SiO{sub 2} and possible existence of thermal gradient in an insulating matrix of SiO{sub 2.} Larger Si NCs are formed in the laser induced plume (plasma) itself. - Graphical abstract: a) Schematic showing the expected stacking of Si NCs obtained from Raman mapping, performed by changing focal spot along the depth, b) top, c) middle and d) bottom region of the cluster. - Highlights: • Methodology is developed to obtain Raman and AFM mapping at same selected area. • To get unique information, difficult to obtain using other conventional techniques. • Clusters (∼100 nm–2 μm) of Si nanocrystals embedded in SiO{sub 2} matrix are formed. • Stacking of Si nanocrystals from bottom to top (10–1 nm) is observed in some clusters. • Stacking of Si nanocrystals is understood as due to annealing and thermal gradient.

Enhanced formation of Ge nanocrystals in Ge : SiO2 layers by swift heavy ions

International Nuclear Information System (INIS)

Antonova, I V; Volodin, V A; Marin, D M; Skuratov, V A; Smagulova, S A; Janse van Vuuren, A; Neethling, J; Jedrzejewski, J; Balberg, I

2012-01-01

In this paper we report the ability of swift heavy Xe ions with an energy of 480 MeV and a fluence of 10 12 cm -2 to enhance the formation of Ge nanocrystals within SiO 2 layers with variable Ge contents. These Ge-SiO 2 films were fabricated by the co-sputtering of Ge and quartz sources which followed various annealing procedures. In particular, we found that the irradiation of the Ge : SiO 2 films with subsequent annealing at 500 °C leads to the formation of a high concentration of nanocrystals (NCs) with a size of 2-5 nm, whereas without irradiation only amorphous inclusions were observed. This effect, as evidenced by Raman spectra, is enhanced by pre-irradiation at 550 °C and post-irradiation annealing at 600 °C, which also leads to the observation of room temperature visible photoluminescence. (paper)

Efeito do teor metálico em catalisadores Co/Al2O3 aplicados à reação de reforma a vapor de etanol Effect of metal load in Co/Al2o3 catalysts for ethanol steam reforming

Directory of Open Access Journals (Sweden)

Rudye K. S. Santos

2005-08-01

Full Text Available The development of cobalt catalysts to produce hydrogen from ethanol is the goal of this investigation. Co/Al2O3 catalysts were prepared by impregnation and characterized by atomic absorption, nitrogen adsorption, X-ray diffraction, Raman spectroscopy, temperature programmed reduction and carbon analysis. The catalysts contained Co3O4 oxide and Co3+ and Co2+ species interacting with alumina. The cobalt load affects the crystal size and the crystalline structure and higher Co loads influence the reaction mechanism, changing the selectivity of the catalysts, decreasing the amount of CO produced and avoiding the formation of products catalyzed by the support. The ethanol conversion was 50-70% with 10-<1% of CO in the hydrogen.

Thin (111) oriented CoFe{sub 2}O{sub 4} and Co{sub 3}O{sub 4} films prepared by decomposition of layered cobaltates

Energy Technology Data Exchange (ETDEWEB)

Buršík, Josef, E-mail: bursik@iic.cas.cz [Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, v.v.i., 250 68 Husinec-Řež 1001 (Czech Republic); Soroka, Miroslav, E-mail: soroka@iic.cas.cz [Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, v.v.i., 250 68 Husinec-Řež 1001 (Czech Republic); Uhrecký, Róbert, E-mail: uhrecky@iic.cas.cz [Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, v.v.i., 250 68 Husinec-Řež 1001 (Czech Republic); Kužel, Radomír, E-mail: kuzel@karlov.mff.cuni.cz [Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 5, 121 16 Praha 2 (Czech Republic); Mika, Filip, E-mail: filip.mika@isibrno.cz [Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 147, 612 64 Brno (Czech Republic); Huber, Štěpán, E-mail: stepan.huber@vscht.cz [University of Chemistry and Technology, Faculty of Chemical Technology, Technická 5, 166 28 Prague 6 (Czech Republic)

2016-07-15

Graphical abstract: Pole figures of NaCoO{sub 2} (left) and of CoFe{sub 2}O{sub 4} (right) films formed through the transformation of O3-type NaCoO{sub 2} phase in consequence of sodium deintercalation occurring at 800 °C. Films were prepared by chemical solution deposition on MgO(111) substrate. - Highlights: • Epitaxial Na(CoFe)O{sub 2} thin films by means of chemical solution deposition were prepared. • Oriented spinel films through transformation of Na(CoFe)O{sub 2} were obtained. • Orientation relation to MgO, SrTiO{sub 3} and Zr(Y)O{sub 2} substrates were determined. • Structural aspects of Na(CoFe)O{sub 2} → CoFe{sub 2}O{sub 4} transformation pathway were elucidated. - Abstract: The formation and structural characterization of highly (111)-oriented Co{sub 3}O{sub 4} and CoFe{sub 2}O{sub 4} films prepared by a novel procedure from 00l-oriented NaCoO{sub 2} and Na(CoFe)O{sub 2} is reported. The Na(CoFe)O{sub 2} films were deposited on MgO, SrTiO{sub 3}, LaAlO{sub 3}, and Zr(Y)O{sub 2} single crystals with (100) and (111) orientations by chemical solution deposition method and crystallized at 700 °C. Subsequently they were transformed into (111)-oriented spinel phase during post-growth annealing at 800–1000 °C. Morphology and structure of the films was investigated by means of scanning electron microscopy and X-ray diffraction. While all spinel films exhibit pronounced out-of-plane orientation irrespective of substrate, the rate of in-plane orientation strongly depend on lattice misfit values. Different epitaxial phenomena ranging from true one-to-one epitaxy to the existence of many-to-one epitaxy involving two or more orientations were determined by full 3D texture analysis.

Highly-crystalline ultrathin Li4Ti5O12 nanosheets decorated with silver nanocrystals as a high-performance anode material for lithium ion batteries

Science.gov (United States)

Xu, G. B.; Li, W.; Yang, L. W.; Wei, X. L.; Ding, J. W.; Zhong, J. X.; Chu, Paul K.

2015-02-01

A novel composite of highly-crystalline ultrathin Li4Ti5O12 (LTO) nanosheets and Ag nanocrystals (denoted as LTO NSs/Ag) as an anode material for Li-ion batteries (LIBs) is prepared by hydrothermal synthesis, post calcination and electroless deposition. The characterizations of structure and morphology reveal that the LTO nanosheets have single-crystal nature with a thickness of about 10 nm and highly dispersed Ag nanocrystals have an average diameter of 5.8 nm. The designed LTO NSs/Ag composite takes advantage of both components, thereby providing large contact area between the electrolyte and electrode, low polarization of voltage difference, high electrical conductivity and lithium ion diffusion coefficient during electrochemical processes. The evaluation of its electrochemical performance demonstrates that the prepared LTO NSs/Ag composite has superior lithium storage performance. More importantly, this unique composite has an ability to deliver high reversible capacities with superlative cyclic capacity retention at different current rates, and exhibit excellent high-rate performance at a current rate as high as 30 C. Our results improve the current performance of LTO based anode material for LIBs.

One dimensional well-aligned CdO nanocrystal by solvothermal method

International Nuclear Information System (INIS)

Kaviyarasu, K.; Manikandan, E.; Paulraj, P.; Mohamed, S.B.; Kennedy, J.

2014-01-01

Graphical abstract: - Highlights: • Cadmium oxide (CdO) emerged as one of the important semiconducting materials. • Iodine concentration increases intensity of the peak around 300 cm −1 becomes stronger. • Surface morphology of these crystals has been modified by varying complexing agent. • Nanofibers structure like CdO crystals first time achieved. • The diameters of these nanofibers range mostly between 40 nm and 70 nm. - Abstract: Cadmium oxide (CdO) is a category of the practical semiconductor metal oxides, which is widely applied in various scientific and industrial fields because of its catalytic, optical, and electrical properties. CdO nanocrystal was successfully synthesized by a virtue of a single source precursor method at mild reaction conditions between cadmium oxide, and element iodine by a solvothermal route. X-ray powder diffraction (XRD), ultraviolet spectroscopy studies (UV–vis), Fourier Transform Infrared analysis (FTIR), scanning electron microscopy (SEM), μ-Raman spectroscopy and cyclic voltammogram (CV) were used to characterize the CdO nanocrystals. The ultra-violet visible absorption peaks of CdO exhibited a large blue shift and the luminescent spectra had a strong and broad emission band centered at 228 nm. The various functional groups present in the CdO nanocrystals were identified by FTIR analysis. Intense PL was also observed with some spectral tuning possibly giving a range of emission photon energies approximately spanning from 2.5 to 3.4 eV. Scanning electron microscopy and μ-Raman microscopy images indicated that the morphology of the product is spherical nanoparticles with an average particle size of 46 nm with standard deviation. The electrochemical response of CdO which is proved the nano-cadmium has high functionality due to the small size and it has higher electrochemical activity without any modifications. The above studies demonstrate the potential for the utilization of cadmium nitrite nanocrystal in visible

Preparation, characterization, and antibacterial activity of NiFe{sub 2}O{sub 4}/PAMA/Ag–TiO{sub 2} nanocomposite

Energy Technology Data Exchange (ETDEWEB)

Allafchian, Alireza, E-mail: Allafchian@cc.iut.ac.ir [Nanotechnology and Advanced Materials Institute, Isfahan University of Technology, Isfahan 84156–83111 (Iran, Islamic Republic of); Jalali, Seyed Amir Hossein [Institute of Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan 84156–83111 (Iran, Islamic Republic of); Department of Natural Resources, Isfahan University of Technology, Isfahan 84156–83111 (Iran, Islamic Republic of); Bahramian, Hamid; Ahmadvand, Hossein [Department of physics, Isfahan University of Technology, Isfahan 84156–83111 (Iran, Islamic Republic of)

2016-04-15

We have described a facile fabrication of silver deposited on the TiO{sub 2}, Poly Acrylonitrile Co Maleic Anhydride (PAMA) polymer and nickel ferrite composite (NiFe{sub 2}O{sub 4}/PAMA/Ag–TiO{sub 2}) through a three-step procedure. A pre-synthesized NiFe{sub 2}O{sub 4} was first coated with PAMA polymer and then Ag–TiO{sub 2} was deposited on the surface of PAMA polymer shell. After the characterization of this three-component composite by various techniques, such as FTIR, XRD, FESEM, BET, TEM and VSM, it was impregnated in standard antibiotic discs. The antibacterial activity of NiFe{sub 2}O{sub 4}/PAMA/Ag–TiO{sub 2} nanocomposite was investigated against some gram positive and gram negative bacteria by employing disc diffusion assay and then compared with that of naked NiFe{sub 2}O{sub 4}, NiFe{sub 2}O{sub 4}/Ag, AgNPs and NiFe{sub 2}O{sub 4}/PAMA. The results demonstrated that the AgNPs, when embedded in TiO{sub 2} and combined with NiFe{sub 2}O{sub 4}/PAMA, became an excellent antibacterial agent. The NiFe{sub 2}O{sub 4}/PAMA/Ag–TiO{sub 2} nanocomposite could be readily separated from water solution after the disinfection process by applying an external magnetic field. - Highlights: • A novel NiFe{sub 2}O{sub 4}/PAMA/Ag–TiO{sub 2} magnetic nanocomposite has been prepared. • This nanocomposite displays potent antimicrobial activity. • The antibacterial effect was evaluated by the disk diffusion method. • Recyclable antibacterial activity of NiFe{sub 2}O{sub 4}/PAMA/Ag–TiO{sub 2} was studied.

Surface structure, optoelectronic properties and charge transport in ZnO nanocrystal/MDMO-PPV multilayer films.

Science.gov (United States)

Lian, Qing; Chen, Mu; Mokhtar, Muhamad Z; Wu, Shanglin; Zhu, Mingning; Whittaker, Eric; O'Brien, Paul; Saunders, Brian R

2018-05-07

Blends of semiconducting nanocrystals and conjugated polymers continue to attract major research interest because of their potential applications in optoelectronic devices, such as solar cells, photodetectors and light-emitting diodes. In this study we investigate the surface structure, morphological and optoelectronic properties of multilayer films constructed from ZnO nanocrystals (NCs) and poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV). The effects of layer number and ZnO concentration (C ZnO ) used on the multilayer film properties are investigated. An optimised solvent blend enabled well-controlled layers to be sequentially spin coated and the construction of multilayer films containing six ZnO NC (Z) and MDMO-PPV (M) layers (denoted as (ZM) 6 ). Contact angle data showed a strong dependence on C ZnO and indicated distinct differences in the coverage of MDMO-PPV by the ZnO NCs. UV-visible spectroscopy showed that the MDMO-PPV absorption increased linearly with the number of layers in the films and demonstrates highly tuneable light absorption. Photoluminescence spectra showed reversible quenching as well as a surprising red-shift of the MDMO-PPV emission peak. Solar cells were constructed to probe vertical photo-generated charge transport. The measurements showed that (ZM) 6 devices prepared using C ZnO = 14.0 mg mL -1 had a remarkably high open circuit voltage of ∼800 mV. The device power conversion efficiency was similar to that of a control bilayer device prepared using a much thicker MDMO-PPV layer. The results of this study provide insight into the structure-optoelectronic property relationships of new semiconducting multilayer films which should also apply to other semiconducting NC/polymer combinations.

Effects of phosphorus doping on structural and optical properties of silicon nanocrystals in a SiO2 matrix

International Nuclear Information System (INIS)

Hao, X.J.; Cho, E.-C.; Scardera, G.; Bellet-Amalric, E.; Bellet, D.; Shen, Y.S.; Huang, S.; Huang, Y.D.; Conibeer, G.; Green, M.A.

2009-01-01

Promise of Si nanocrystals highly depends on tailoring their behaviour through doping. Phosphorus-doped silicon nanocrystals embedded in a silicon dioxide matrix have been realized by a co-sputtering process. The effects of phosphorus-doping on the properties of Si nanocrystals are investigated. Phosphorus diffuses from P-P and/or P-Si to P-O upon high temperature annealing. The dominant X-ray photoelectron spectroscopy P 2p signal attributable to Si-P and/or P-P (130 eV) at 1100 o C indicates that the phosphorus may exist inside Si nanocrystals. It is found that existence of phosphorus enhances phase separation of silicon rich oxide and thereby Si crystallization. In addition, phosphorus has a considerable effect on the optical absorption and photoluminescence properties as a function of annealing temperature.

Preparation of orthophosphate glasses in the MgO-CaO-SiO2-Nb2O5-P2O5 system.

Science.gov (United States)

Lee, Sungho; Ueda, Kyosuke; Narushima, Takayuki; Nakano, Takayoshi; Kasuga, Toshihiro

2017-01-01

Niobia/magnesia-containing orthophosphate invert glasses were successfully prepared in our earlier work. Orthophosphate groups in the glasses were cross-linked by tetrahedral niobia (NbO4) and magnesia. The aim of this work is to prepare calcium orthophosphate invert glasses containing magnesia and niobia, incorporating silica, and to evaluate their structures and releasing behaviors. The glasses were prepared by melt-quenching, and their structures and ion-releasing behaviors were evaluated. 31P solid-state nuclear magnetic resonance (NMR) and Raman spectroscopies showed the glasses consist of orthophosphate (PO4), orthosilicate (SiO4), and NbO4 tetrahedra. NbO4 and MgO in the glasses act as network formers. By incorporating SiO2 into the glasses, the chemical durability of the glasses was slightly improved. The glasses reheated at 800°C formed the orthophosphate crystalline phases, such as β-Ca3(PO4)2, Mg3(PO4)2 and Mg3Ca3(PO4)4 in the glasses. The chemical durability of the crystallized glasses was slightly improved. Orthosilicate groups and NbO4 in the glasses coordinated with each other to form Si-O-Nb bonds. The chemical durability of the glasses was slightly improved by addition of SiO2, since the field strength of Si is larger than that of Ca or Mg.

Controlled synthesis of Fe3O4/ZIF-8 nanoparticles for magnetically separable nanocatalysts.

Science.gov (United States)

Pang, Fei; He, Mingyuan; Ge, Jianping

2015-04-27

Fe3O4/ZIF-8 nanoparticles were synthesized through a room-temperature reaction between 2-methylimidazolate and zinc nitrate in the presence of Fe3O4 nanocrystals. The particle size, surface charge, and magnetic loading can be conveniently controlled by the dosage of Zn(NO3)2 and Fe3O4 nanocrystals. The as-prepared particles show both good thermal stability (stable to 550 °C) and large surface area (1174 m(2) g(-1)). The nanoparticles also have a superparamagnetic response, so that they can strongly respond to an external field during magnetic separation and disperse back into the solution after withdrawal of the magnetic field. For the Knoevenagel reaction, which is catalyzed by alkaline active sites on external surface of catalyst, small Fe3O4/ZIF-8 nanoparticles show a higher catalytic activity. At the same time, the nanocatalysts can be continuously used in multiple catalytic reactions through magnetic separation, activation, and redispersion with little loss of activity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Free-standing Hierarchical Porous Assemblies of Commercial TiO_2 Nanocrystals and Multi-walled Carbon Nanotubes as High-performance Anode Materials for Sodium Ion Batteries

International Nuclear Information System (INIS)

Liu, Xiong; Xu, Guobao; Xiao, Huaping; Wei, Xiaolin; Yang, Liwen

2017-01-01

Highlights: • Utilization of commercial nanomaterials to freestanding sodium electrode is demonstrated. • Free-standing electrodes composed of TiO_2 and MWCNTs are hierarchically porous. • Hierarchical porous architecture benefits charge transport and interfacial Na"+ adsorption. • Free-standing hierarchical porous electrodes exhibit superior Na storage performance. - Abstract: Freestanding hierarchical porous assemblies of commercial TiO_2 nanocrystals and multi-wall carbon nanotubes (MWCNTs) as electrode materials for sodium ion batteries (SIBs) are prepared via modified vacuum filtration, free-drying and annealing. Microstructure characterizations reveal that TiO_2 nanocrystals are confined in hierarchically porous, highly electrically conductive and mechanically robust MWCNTs networks with cross-linking of thermally-treated bovine serum albumin. The hierarchical porous architecture not only enables rapid charge transportation and sufficient interaction between electrode and electrolyte, but also guarantees abundant interfacial sites for Na"+ adsorption, which benefits substantial contribution from pseudocapacitive Na storage. When it is used directly as an anode for sodium-ion batteries, the prepared electrode delivers high specific capacity of 100 mA h g"−"1 at a current density of 3000 mA g"−"1, and 150 mA h g"−"1 after 500 cycles at a current density of 500 mA g"−"1. The low-cost TiO_2-based freestanding anode has large potential application in high-performance SIBs for portable, flexible and wearable electronics.

Solvothermal Synthesis of Zn2SnO4 Nanocrystals and Their Photocatalytic Properties

Directory of Open Access Journals (Sweden)

Guang Sun

2014-01-01

Full Text Available Crystalline Zn2SnO4 nanoparticles were successfully synthesized via a simple solvothermal route by using Zn(CH3COO2·2H2O and SnCl4·5H2O as source materials, NaOH as mineralizing agent, and water and ethanol as mixed solvents. The used amount of NaOH was found to have an important influence on the formation of Zn2SnO4. When the molar ratio of OH− : Zn2+ : Sn4+ was set in the range from 4 : 2 : 1 to 8 : 2 : 1, Zn2SnO4 nanoparticles with different shape and size were obtained. However, when the molar ratio of OH− : Zn2+ : Sn4+ was set as 10 : 2 : 1, a mixture phase of ZnO and ZnSn(OH6 instead of Zn2SnO4 was obtained. Photodegradation measurements indicated that the Zn2SnO4 nanoparticles own better photocatalytic property to depredate methyl orange than the Zn2SnO4 nanopolyhedrons. The superior photocatalytic properties of Zn2SnO4 nanoparticles may be contributed to their small crystal size and high surface area.

Hydroxyapatite nanocrystals: simple preparation, characterization and formation mechanism.

Science.gov (United States)

Mohandes, Fatemeh; Salavati-Niasari, Masoud; Fathi, Mohammadhossein; Fereshteh, Zeinab

2014-12-01

Crystalline hydroxyapatite (HAP) nanoparticles and nanorods have been successfully synthesized via a simple precipitation method. To control the shape and particle size of HAP nanocrystals, coordination ligands derived from 2-hydroxy-1-naphthaldehyde were first prepared, characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ((1)H-NMR) spectroscopies, and finally applied in the synthesis process of HAP. On the other hand, the HAP nanocrystals were also characterized by several techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to the FE-SEM and TEM micrographs, it was found that the morphology and crystallinity of the HAP powders depended on the coordination mode of the ligands. Copyright © 2014 Elsevier B.V. All rights reserved.

Preparation of flexible TiO2 photoelectrodes for dye-sensitized solar cells

Science.gov (United States)

Li, Wen-Ren; Wang, Hsiu-Hsuan; Lin, Chia-Feng; Su, Chaochin

2014-09-01

Dye-sensitized solar cells (DSSCs) based on nanocrystalline TiO2 photoelectrodes on indium tin oxide (ITO) coated polymer substrates have drawn great attention due to its lightweight, flexibility and advantages in commercial applications. However, the thermal instability of polymer substrates limits the process temperature to below 150 °C. In order to assure high and firm interparticle connection between TiO2 nanocrystals (TiO2-NC) and polymer substrates, the post-treatment of flexible TiO2 photoelectrodes (F-TiO2-PE) by mechanical compression was employed. In this work, Degussa P25 TiO2-NC was mixed with tert-butyl alcohol and DI-water to form TiO2 paste. F-TiO2-PE was then prepared by coating the TiO2 paste onto ITO coated polyethylene terephthalate (PET) substrate using doctor blade followed by low temperature sintering at 120 °C for 2 hours. To study the effect of mechanical compression, we applied 50 and 100 kg/cm2 pressure on TiO2/PET to complete the fabrication of F-TiO2-PE. The surface morphology of F-TiO2-PE was characterized using scanning electron microscopy. The resultant F-TiO2-PE sample exhibited a smooth, crack-free structure indicating the great improvement in the interparticle connection of TiO2-NC. Increase of compression pressure could lead to the increase of DSSC photoconversion efficiency. The best photoconversion efficiency of 4.19 % (open circuit voltage (Voc) = 0.79 V, short-circuit photocurrent density (Jsc) = 7.75 mA/cm2, fill factor (FF) = 0.68) was obtained for the F-TiO2-PE device, which showed great enhancement compared with the F-TiO2-PE cell without compression treatment. The effect of compression in DSSC performance was vindicated by the electrochemical impedance spectroscopy measurement.

Incorporation of Cu{sub 2}O nanocrystals into TiO{sub 2} photonic crystal for enhanced UV–visible light driven photocatalysis

Energy Technology Data Exchange (ETDEWEB)

Geng, Zhi; Zhang, Yu; Yuan, Xing; Huo, Mingxin; Zhao, Yahui; Lu, Ying, E-mail: luy332@nenu.edu.cn; Qiu, Yue

2015-09-25

Highlights: • The Cu{sub 2}O NCs/TiO{sub 2} PC composite was synthesized and exhibited high photocatalysis. • The improved light harvesting and increased quantum yield was achieved. • The hydroxyl radical was the primary oxidant in Cu{sub 2}O NCs/TiO{sub 2} PC photocatalysis. - Abstract: A 3D UV–visible light responsive photocatalyst was fabricated by infiltrating Cu{sub 2}O nanocrystals (NCs) into TiO{sub 2} photonic crystal (PC). Morphology characterization presented that Cu{sub 2}O NCs with average diameter around 10 nm were dispersed uniformly into TiO{sub 2} PC. The transmittance spectra showed that Cu{sub 2}O NCs/TiO{sub 2} 260, prepared by integrating Cu{sub 2}O NCs with TiO{sub 2} 260 which was fabricated from 260 nm polystyrene spheres, exhibited the highest light harvesting. The photoluminescence spectra confirmed the electron/hole pairs recombination of Cu{sub 2}O NCs/TiO{sub 2} 260 was efficiently inhibited due to the unique heterojunction structure between TiO{sub 2} and Cu{sub 2}O. In the photocatalytic degradation of Rhodamine B and Bisphenol A under UV–visible light (320 nm < λ < 780 nm) irradiation, the kinetic constant using Cu{sub 2}O NCs/TiO{sub 2} 260 was 3.99 and 8.37-fold larger than that using TiO{sub 2} nanoparticle (NP), respectively. The enhanced photocatalysis benefited from the increased light harvesting owing to the excitation of both TiO{sub 2} and Cu{sub 2}O NCs whose optical absorption was intensified by the photonic effect of TiO{sub 2} 260 and the high quantum efficiency due to the Cu{sub 2}O/TiO{sub 2} heterojunction. The hydroxyl radical, generated from the protonation of superoxide radical which was derived from the reduction of oxygen by photogenerated electrons, was the main oxidant responsible for pollutant degradation.

Third symposium on coal preparation. NCA/BCR coal conference and Expo IV

Energy Technology Data Exchange (ETDEWEB)

None

1977-01-01

The third Symposium on Coal preparation, sponsored by the National Coal Association and Bituminous Coal Research, Inc., was held at the Kentucky Fair and Exposition Center, Louisville, Kentucky, October 18-20, 1977. Fourteen papers from the proceedings have been entered individually into EDB and ERA; five additional papers had been entered previously from other sources. Topics covered involved chemical comminution and chemical desulfurization of coal (aimed at reducing sulfur sufficiently with some coals to meet air quality standards without flue gas desulfurization), coal cleaning concepts, removing coal fines and recycling wash water, comparative evaluation of coal preparation methods, coal refuse disposal without polluting the environment, spoil bank reprocessing, noise control in coal preparation plants, etc. (LTN)

Detailed investigations of ZnO photoelectrodes preparation for dye sensitized solar cells.

Science.gov (United States)

Marczak, Renata; Werner, Fabian; Ahmad, Rameez; Lobaz, Volodymyr; Guldi, Dirk M; Peukert, Wolfgang

2011-04-05

Wurtzite ZnO hexagonal nanopyramids were successfully synthesized in the liquid phase from homogeneous methanolic solutions of zinc acetate and tetramethylammonium hydroxide at an excess of zinc ions. The formation and properties of the nanocrystals were examined as a function of synthesis conditions. No significant influence of the [Zn(2+)]/[OH(-)] ratio was noticed on the final particle size, in spite of increased amounts of OH(-) ions, which tend to accelerate the particle nucleation and growth. Nevertheless, the reactant concentration ratio influences the surface properties of the ZnO nanocrystals. Mesoporous ZnO films were prepared by doctor blading ethanolic pastes containing ZnO nanoparticles and ethyl cellulose onto FTO conductive glass substrate followed by calcination. Additionally, the influence of a plasticizer (triacetin)-used during the paste preparation-on the film quality was investigated. A higher content of ZnO nanoparticles and plasticizer in the pastes improved the film quality. Four different temperatures (i.e., 400, 425, 450, and 475 °C) were used for the film calcination and their influence on the structural properties of the films was characterized. In principle, increasing the calcination temperature goes hand in hand with an increase of particle size, as well as the pore diameter and reduction of the surface area. Suitable mesoporous films were employed as photoanodes in dye sensitized solar cells (DSSCs). In order to assess the effect of the varied parameters on complete DSSC devices-using cis-diisothiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II)bis(tetrabutylammonium (N719) as a sensitizer-incident photon to current efficiency (IPCE) and current voltage measurements were carried out. The IPCE measurements confirmed photoinduced electron injection from the dye, reaching IPCE values up to 76%. Furthermore, current-voltage characteristics of complete cells emphasized the importance of the proper preparation methods and

Key insights on the structural characterization of textured Er2O3–ZrO2 nano-oxides prepared by a surfactant-free solvothermal route

International Nuclear Information System (INIS)

Julián-López, Beatriz; Luz, Verónica de la; Gonell, Francisco; Cordoncillo, Eloisa; López-Haro, Miguel; Calvino, Jose J.; Escribano, Purificación

2012-01-01

Highlights: ► Structural resolution of fluorite vs. pyrochlore in small nanocrystals. ► Simple template-free solvothermal synthesis of Er 2 O 3 –ZrO 2 nanooxides. ► Good control over size, morphology and surface properties (280 m 2 g −1 ). - Abstract: Zirconia-mixed oxides can exhibit cubic fluorite and pyrochlore structure. Their discrimination is not easy in nanooxides with a crystal size close to that of a few unit cells. In this work, high resolution transmission electron microscopy (HRTEM) has been employed to provide key insights on the structural characterization of a nanometric and porous mixed Er 2 O 3 –ZrO 2 oxide. The material was prepared by a simple template-free solvothermal route that provided nanocrystalline powders at low temperature (170 °C) with spherical morphology, and high surface area (∼280 m 2 g −1 ). The porosity was mainly originated from the assembling of organic complexing agents used in the synthesis to limit the crystal growth and to control hydrolysis and condensation reaction rates. The samples were characterized by thermal analysis, X-ray diffraction, scanning electron microscopy and N 2 adsorption measurements. A detailed study by HRTEM was conducted on microtomed samples. It was observed that the material was made of nanocrystals packed into spherical agglomerates. HRTEM simulations indicated that it is not possible to identify the pyrochlore phase in nanoparticles with diameter below 2 nm. In our samples, the analysis of the HRTEM lattice images by means of fast Fourier transform (FFT) techniques revealed well defined spots that can be assigned to different planes of a cubic fluorite-type phase, even in the raw material. Raman spectroscopy was also a powerful technique to elucidate the crystalline phase of the materials with the smallest nanoparticles. HREM and Raman results evidenced that the material is constituted, irrespective of the temperature of the final calcination step, by an ensemble of randomly

Far-infrared spectroscopic study of CeO{sub 2} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Popović, Z. V., E-mail: zoran.popovic@ipb.ac.rs; Grujić-Brojčin, M.; Paunović, N. [University of Belgrade, Center for Solid State Physics and New Materials, Institute of Physics (Serbia); Radonjić, M. M. [University of Belgrade, Scientific Computing Laboratory, Institute of Physics Belgrade (Serbia); Araújo, V. D.; Bernardi, M. I. B. [Universidade de São Paulo-USP, Instituto de Fisica (Brazil); Lima, M. M. de; Cantarero, A. [Universidad de Valencia, Instituto de Ciencia de Los Materiales (Spain)

2015-01-15

We present the far-infrared reflectivity spectra of 5 nm-sized pure and copper-doped Ce{sub 1−x}Cu{sub x}O{sub 2−y} (x = 0; 0.01 and 0.10) nanocrystals measured at room temperature in the 50–650 cm{sup −1} spectral range. Reflectivity spectra were analyzed using the factorized form of the dielectric function, which includes the phonon and the free carriers contribution. Four oscillators with TO energies of approximately 135, 280, 370, and 490 cm{sup −1} were included in the fitting procedure. These oscillators represent local maxima of the CeO{sub 2} phonon density of states, which is also calculated using the density functional theory. The lowest energy oscillator represents TA(L)/TA(X) phonon states, which become infrared-active E{sub u} modes at the L and X points of the Brillouin zone (BZ). The second oscillator originates from TO(Γ) phonon states. The oscillator at ∼400 cm{sup −1} originates from Raman mode phonon states, which at the L point of BZ also becomes infrared-active E{sub u} mode. The last oscillator describes phonons with dominantly LO(Γ) infrared mode character. The appearance of phonon density of states related oscillators, instead of single F{sub 2u}infrared-active mode in the far-infrared reflectivity spectra, is a consequence of the nanosized dimension of the CeO{sub 2} particles. The best fit spectra are obtained using the generalized Bruggeman model for inhomogeneous media, which takes into account the nanocrystal volume fraction and the pore shape.

An experimental and mathematical modeling study comparing the reactivity and burnout of pulverized coal in air (O{sub 2}/N{sub 2}) and oxyfuel (O{sub 2}/CO{sub 2}) environments

Energy Technology Data Exchange (ETDEWEB)

Liza Elliott; Yinghui Liu; Bart Buhre; Jennifer Martin; Raj Gupta; Terry Wall [University of Newcastle, Callaghan, NSW (Australia). Cooperative Research Centre for Coal in Sustainable Development, Chemical Engineering

2005-07-01

Carbon dioxide in flue gas from conventional combustion processes is present as a dilute gas. CO{sub 2} capture is more easily achieved from a concentrated CO{sub 2} stream, which can be achieved by firing fuels with oxygen to obtain a sequestration ready gas stream, called oxy-fuel combustion. In this technology, the oxygen stream is usually diluted by recycled flue gas (RFG), so that the coal burns in an environment which is primarily O{sub 2}/CO{sub 2}. A size cut of a number of pulverised coals were devolatalised in N{sub 2} and CO{sub 2}. These sized coals were also combusted in a drop-tube furnace in an O{sub 2}/N{sub 2} environment simulating air combustion, and O{sub 2}/CO{sub 2} simulating oxyfuel combustion, with varying O{sub 2} levels from 3 to 30% v/v. Measurements of the extent of devolatilisation and coal burnout were completed. The detailed data provided for one coal indicated that the devolatilisation process in the O{sub 2}/CO{sub 2} environments is influenced by char gasification, and the char reaction rates are fitted better by a fractional order rate than first order in oxygen. Combustion rates in the oxyfuel environment were slightly higher. Estimates of the burnout for furnaces retrofitted from air to oxyfuel indicate that a better burnout can be expected. These trends were common for all coals. 14 refs., 4 figs., 5 tabs.

Characterizations on the microstructures of LiMn2O4 prepared by a simple soft-chemical technique

International Nuclear Information System (INIS)

Wei Yingjin; Kim, Kwang Bum; Chen Gang; Park, Chul W.

2008-01-01

LiMn 2 O 4 powders were prepared by a simple soft-chemical technique at different temperatures. X-ray diffraction and thermogravimetric analysis suggested that the material prepared at 800 deg. C was stoichiometric LiMn 2 O 4 , whereas those prepared at 600 and 700 deg. C were Li[Mn 0.77 3+ Mn 1.23 4+ ]O 4.115 and Li[Mn 0.85 3+ Mn 1.15 4+ ]O 4.075 . Several typical XRD peaks of the compounds were investigated with an aim to elucidate (i) the Li immigration to the 16d octahedral sites, (ii) the partial tetragonal phase transition of the material and (iii) the mean coherent domain size and microstrain. SEM study showed that the particle size of the materials increased with heating temperature. The activation energy for the material particle growth was determined as 30.4 kJ mol -1

Thermal expansion studies on Th(MoO4)2, Na2Th(MoO4)3 and Na4Th(MoO4)4

International Nuclear Information System (INIS)

Keskar, Meera; Krishnan, K.; Dahale, N.D.

2008-01-01

Thermal expansion behavior of Th(MoO 4 ) 2 , Na 2 Th(MoO 4 ) 3 and Na 4 Th(MoO 4 ) 4 was studied under vacuum in the temperature range of 298-1123 K by high temperature X-ray diffractometer. Th(MoO 4 ) 2 was synthesized by reacting ThO 2 with 2 mol of MoO 3 , at 1073 K in air and Na 2 Th(MoO 4 ) 3 and Na 4 Th(MoO 4 ) 4 were prepared by reacting Th(MoO 4 ) 2 with 1 and 2 mol of Na 2 MoO 4 , respectively at 873 K in air. The XRD data of Th(MoO 4 ) 2 was indexed on orthorhombic system where as XRD data of Na 2 Th(MoO 4 ) 3 and Na 4 Th(MoO 4 ) 4 were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO 4 ) 2 , Na 2 Th(MoO 4 ) 3 and Na 4 Th(MoO 4 ) 4 were determined from the high temperature data

X-Ray Absorption Studies of Vanadium-Containing Metal Oxide Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Hohn, Keith, L.

2006-01-09

Metal oxide nanocrystals offer significant potential for use as catalysts or catalyst supports due to their high surface areas and unique chemical properties that result from the high number of exposed corners and edges. However, little is known about the catalytic activity of these materials, especially as oxidation catalysts. This research focused on the preparation, characterization and use of vanadium-containing nanocrystals as selective oxidation catalysts. Three vanadium-containing nanocrystals were prepared using a modified sol-gel procedure: V/MgO, V/SiO2, and vanadium phosphate (VPO). These represent active oxidation catalysts for a number of industrially relevant reactions. The catalysts were characterized by x-ray diffraction and Raman, UV-VIS, infrared and x-ray absorption spectroscopies with the goal of determining the primary structural and chemical differences between nanocrystals and microcrystals. The catalytic activity of these catalysts was also studied in oxidative dehydrogenation of butane and methanol oxidation to formaldehyde. V/MgO nanocrystals were investigated for activity in oxidative dehydrogenation of butane and compared to conventional V/MgO catalysts. Characterization of V/MgO catalysts using Raman spectroscopy and x-ray absorption spectroscopy showed that both types of catalysts contained magnesium orthovanadate at vanadium loadings below 15 weight%, but above that loading, magnesium pyrovanadate may have been present. In general, MgO nanocrystals had roughly half the crystal size and double the surface area of the conventional MgO. In oxidative dehydrogenation of butane, nanocrystalline V/MgO gave higher selectivity to butene than conventional V/MgO at the same conversion. This difference was attributed to differences in vanadium domain size resulting from the higher surface areas of the nanocrystalline support, since characterization suggested that similar vanadium phases were present on both types of catalysts. Experiments in

The MgSeO4-UO2SeO4-H2O system at 25 deg C

International Nuclear Information System (INIS)

Serezhkina, L.B.; Serezhkin, V.N.

1984-01-01

The method of isothermal solubility at 25 deg C has been used to study MgSeO 4 -UO 2 SeO 4 -H 2 O system. Formation of the new compound Mg 2 (UO 2 ) 3 (SeO 4 ) 5 X32H 2 O, congruently soluble in water is stated. Thermographic and X-ray diffraction investigations of the prepared magnesium selenato-uranylate and products of its dehydration are conducted

TiO2 nanocrystals decorated Z-schemed core-shell CdS-CdO nanorod arrays as high efficiency anodes for photoelectrochemical hydrogen generation.

Science.gov (United States)

Li, Chia-Hsun; Hsu, Chan-Wei; Lu, Shih-Yuan

2018-07-01

TiO 2 nanocrystals decorated core-shell CdS-CdO nanorod arrays, TiO 2 @CdO/CdS NR, were fabricated as high efficiency anodes for photoelctrochemical hydrogen generation. The novel sandwich heterostructure was constructed from first growth of CdS nanorod arrays on a fluorine doped tin oxide (FTO) substrate with a hydrothermal process, followed by in situ generation of CdO thin films of single digit nanometers from the CdS nanorod surfaces through thermal oxidation, and final decoration of TiO 2 nanocrystals of 10-20 nm via a successive ionic layer absorption and reaction process. The core-shell CdS-CdO heterostructure possesses a Z-scheme band structure to enhance interfacial charge transfer, facilitating effective charge separation to suppress electron-hole recombination within CdS for much improved current density generation. The final decoration of TiO 2 nanocrystals passivates surface defects and trap states of CdO, further suppressing surface charge recombination for even higher photovoltaic conversion efficiencies. The photoelectrochemical performances of the plain CdS nanorod array were significantly improved with the formation of the sandwich heterostructure, achieving a photo current density of 3.2 mA/cm 2 at 1.23 V (vs. RHE), a 141% improvement over the plain CdS nanorod array and a 32% improvement over the CdO/CdS nanorod array. Copyright © 2018 Elsevier Inc. All rights reserved.

Crystal phase transition in LixNa1-xGdF4 solid solution nanocrystals - Tuning of optical properties

KAUST Repository

Bański, Mateusz

2014-01-01

The influence of precursor composition on the crystallization of LixNa1-xGdF4 is investigated and discussed. Nanocrystals are prepared from the thermal decomposition of trifluoroacetates in the presence of trioctylphosphine oxide to provide control over particle size. A crystal phase transition from hexagonal to cubic and to tetragonal is observed by increasing lithium trifluoroacetate (Li-TFA) in the solution. Controlling the composition of LixNa1-xGdF4 nanocrystals results in modified crystal field symmetry and emission properties from doped europium (Eu3+) ions. We report that for lithium (Li+) substitution <15%, the hexagonal crystal field is preferred, while the Eu3+ emission is already tuned, whereas at higher Li+ substitution, a phase change takes place and the number of crystalline matrix defects increases which is reflected in the optical properties of Eu3+. From Eu3+ emission properties, the optimum Li+ content is determined to be ∼6.2% in the prepared LixNa1-xGdF4 nanocrystals.

Properties of magnetically diluted nanocrystals prepared by mechanochemical route

International Nuclear Information System (INIS)

Balaz, P.; Skorvanek, I.; Fabian, M.; Kovac, J.; Steinbach, F.; Feldhoff, A.; Sepelak, V.; Jiang, J.; Satka, A.; Kovac, J.

2010-01-01

The bulk and surface properties of magnetically diluted Cd 0.6 Mn 0.4 S nanocrystals synthesized by solid state route in a planetary mill were studied. XRD, SEM, TEM (HRTEM), low-temperature N 2 sorption, nanoparticle size distribution as well as SQUID magnetometry methods have been applied. The measurements identified the aggregates of small nanocrystals, 5-10 nm in size. The homogeneity of produced particles with well developed specific surface area (15-66 m 2 g -1 ) was documented. The transition from the paramagnetic to the spin-glass-like phase has been observed below ∼40 K. The changes in the magnetic behaviour at low temperatures seem to be correlated with the formation of the new surface area as a consequence of milling. The magnetically diluted Cd 0.6 Mn 0.4 S nanocrystals are obtained in the simple synthesis step, making the process attractive for industrial applications.

Photoelectrochemical properties of ZnO nanocrystals/MEH-PPV composite: The effects of nanocrystals synthetic route, film deposition and electrolyte composition

Energy Technology Data Exchange (ETDEWEB)

Petrella, A. [Dipartimento di Ingegneria Civile, Ambientale, del Territorio, Edile e Chimica, Politecnico di Bari, Via Orabona 4, 70125 Bari (Italy); Curri, M.L.; Striccoli, M. [CNR IPCF Sez. Bari c/o Dip. Chimica, Università di Bari, Via Orabona 4, 70126 Bari (Italy); Agostiano, A. [Dipartimento di Chimica, Università di Bari, via Orabona 4, 70126 Bari (Italy); CNR IPCF Sez. Bari c/o Dip. Chimica, Università di Bari, Via Orabona 4, 70126 Bari (Italy); Cosma, P., E-mail: pinalysa.cosma@uniba.it [Dipartimento di Chimica, Università di Bari, via Orabona 4, 70126 Bari (Italy); CNR IPCF Sez. Bari c/o Dip. Chimica, Università di Bari, Via Orabona 4, 70126 Bari (Italy)

2015-11-30

This paper reports a study on the photoelectrochemical processes occurring at the interface of ZnO nanocrystals/MEH-PPV composites. Colloidal chemical routes were used to obtain size controlled non-hydrolytic ZnO nanocrystals (NCs) dispersible in organic solvents, while a low molecular weight poly[2-methoxy-5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEH-PPV), characterized by high degree of structural order, was synthesized via an organometallic method. The optical properties of the nanocomposite material were comprehensively investigated on solution and on films deposited by spin coating. Remarkably, a significant fluorescence quenching of the polymer at the MEH-PPV/ZnO junction was observed. Photoelectrochemical measurements demonstrated that the photoactivity of the composite material was significantly improved in the case of non-hydrolytic NCs with respect to hydrolytic route prepared ZnO. Moreover, the effective role of the organic/inorganic blend to improve the charge transfer with respect to the double layer hetero-junction was confirmed, thanks to the extended interfaces which enable an effective electron transfer between the hetero-junction components. The system was also studied at different film thicknesses and electrolyte compositions. The results indicated that film photoactivity increased with film thickness up to 300 nm due to the presence of a large number of interfaces, while the change of cation size influenced the ionic conductivity through the nanocomposite film. It was shown that efficient photoconductivity requires not only efficient charge separation, but also efficient transport of the carriers to the electrodes without recombination. - Highlights: • The photoelectrochemical processes at ZnO nanocrystals/MEH-PPV hetero-junction were studied. • Fluorescence quenching of the polymer at the MEH-PPV/ZnO interface was observed. • Non-hydrolytic ZnO junction showed higher photocurrents than hydrolytic equivalent. • The blends showed

Photoelectrochemical properties of ZnO nanocrystals/MEH-PPV composite: The effects of nanocrystals synthetic route, film deposition and electrolyte composition

International Nuclear Information System (INIS)

Petrella, A.; Curri, M.L.; Striccoli, M.; Agostiano, A.; Cosma, P.

2015-01-01

This paper reports a study on the photoelectrochemical processes occurring at the interface of ZnO nanocrystals/MEH-PPV composites. Colloidal chemical routes were used to obtain size controlled non-hydrolytic ZnO nanocrystals (NCs) dispersible in organic solvents, while a low molecular weight poly[2-methoxy-5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEH-PPV), characterized by high degree of structural order, was synthesized via an organometallic method. The optical properties of the nanocomposite material were comprehensively investigated on solution and on films deposited by spin coating. Remarkably, a significant fluorescence quenching of the polymer at the MEH-PPV/ZnO junction was observed. Photoelectrochemical measurements demonstrated that the photoactivity of the composite material was significantly improved in the case of non-hydrolytic NCs with respect to hydrolytic route prepared ZnO. Moreover, the effective role of the organic/inorganic blend to improve the charge transfer with respect to the double layer hetero-junction was confirmed, thanks to the extended interfaces which enable an effective electron transfer between the hetero-junction components. The system was also studied at different film thicknesses and electrolyte compositions. The results indicated that film photoactivity increased with film thickness up to 300 nm due to the presence of a large number of interfaces, while the change of cation size influenced the ionic conductivity through the nanocomposite film. It was shown that efficient photoconductivity requires not only efficient charge separation, but also efficient transport of the carriers to the electrodes without recombination. - Highlights: • The photoelectrochemical processes at ZnO nanocrystals/MEH-PPV hetero-junction were studied. • Fluorescence quenching of the polymer at the MEH-PPV/ZnO interface was observed. • Non-hydrolytic ZnO junction showed higher photocurrents than hydrolytic equivalent. • The blends showed

Self-assembled ultra small ZnO nanocrystals for dye-sensitized solar cell application

Energy Technology Data Exchange (ETDEWEB)

Patra, Astam K.; Dutta, Arghya; Bhaumik, Asim, E-mail: msab@iacs.res.in

2014-07-01

We demonstrate a facile chemical approach to produce self-assembled ultra-small mesoporous zinc oxide nanocrystals using sodium salicylate (SS) as a template under hydrothermal conditions. These ZnO nanomaterials have been successfully fabricated as a photoanode for the dye-sensitized solar cell (DSSC) in the presence of N719 dye and iodine–triiodide electrolyte. The structural features, crystallinity, purity, mesophase and morphology of the nanostructure ZnO are investigated by several characterization tools. N{sub 2} sorption analysis revealed high surface areas (203 m{sup 2} g{sup −1}) and narrow pore size distributions (5.1–5.4 nm) for different samples. The mesoporous structure and strong photoluminescence facilitates the high dye loading at the mesoscopic void spaces and light harvesting in DSSC. By utilizing this ultra-small ZnO photoelectrode with film thickness of about 7 μm in the DSSC with an open-circuit voltage (V{sub OC}) of 0.74 V, short-circuit current density (J{sub SC}) of 3.83 mA cm{sup −2} and an overall power conversion efficiency of 1.12% has been achieved. - Graphical abstract: Ultra-small ZnO nanocrystals have been synthesized with sodium salicylate as a template and using it as a photoanode in a dye-sensitized solar cell 1.12% power conversion efficiency has been observed. - Highlights: • Synthesis of self-assembled ultra-small mesoporous ZnO nanocrystals by using sodium salicylate as a template. • Mesoporous ZnO materials have high BET surface areas and void space. • ZnO nanoparticles serve as a photoanode for the dye-sensitized solar cell (DSSC). • Using ZnO nanocrystals as photoelectrode power conversion efficiency of 1.12% has been achieved.

Preparation of MAl 2 O 4 : Eu 2+ , Sm 3+ (M = Ca, Sr, Ba) Phosphors ...

African Journals Online (AJOL)

A series of MAl2O4: Eu2+, Sm3+ (M = Ca, Sr, Ba) phosphors was prepared by the combustion method, and the influence of these alkaline earth metals on the structure and luminescent performances for these phosphors was investigated. A relationship was established between their composition, crystallization capacity and ...

Luminescent and morphological study of Sr2CeO4 blue phosphor prepared from oxalate precursors

International Nuclear Information System (INIS)

Ferrari, Jefferson L.; Pires, Ana M.; Serra, Osvaldo A.; Davolos, Marian R.

2011-01-01

Luminescent and morphological studies of Sr 2 CeO 4 blue phosphor prepared from cerium-doped strontium oxalate precursor are reported. Powder samples were prepared from 5 and 25 mol% Ce 3+ -doped strontium oxalate as well as from a mechanical mixture of strontium oxalate and cerium oxalate at a 4:1 ratio, respectively. All the samples were characterized by XRD, IR, PLS, and SEM. The luminescent and structural properties of the Sr 2 CeO 4 material are little affected by the SrCO 3 remaining from precursors. The Sr 2 CeO 4 material consists in one-dimensional chains of edge-sharing CeO 6 octahedra that are linked together by Sr 2+ ions. The carbonate ion might be associated with oxygen ions of the linear chain, and also with the oxygen atoms located in the equatorial position, which consequently affects the charge transfer bands between O 2- and Ce 4+ . As observed by SEM, the morphological changes are related to each kind of precursor and thermal treatment, along with irregular powder particles within the size range 0.5-2 μm.

Preparation, characterization of Sb-doped ZnO nanocrystals and their excellent solar light driven photocatalytic activity

Energy Technology Data Exchange (ETDEWEB)

Nasser, Ramzi; Othmen, Walid Ben Haj [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Département de Physique, Faculté des Sciences de Tunis, University of Tunis El Manar 2092 (Tunisia); Elhouichet, Habib, E-mail: habib.elhouichet@fst.rnu.tn [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Département de Physique, Faculté des Sciences de Tunis, University of Tunis El Manar 2092 (Tunisia); Férid, Mokhtar [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia)

2017-01-30

Highlights: • Sb-ZnO was obtained by modified sol-gel method using citric acid as stabilizing agent. • Sb incorporated both in lattice and interstitial sites. • The formation of (Sb{sub Zn}–2 V{sub Zn}) acceptor level was revealed by photoluminescence studies. • Optimum Sb content to show higher photocatalytic activity was found to be 3%. - Abstract: In the present study, undoped and antimony (Sb) doped ZnO nanocrystals (NCs) were prepared by a simple and economical sol-gel method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the purity of the obtained phase and its high crystallinity. Raman analysis confirms the hexagonal Wurtzite ZnO structure. According to the diffuse reflectance results, the band gap was found to decrease up to 3% of Sb doping (ZSb3 sample). The results of X-ray photoelectron spectroscopy (XPS) measurements reveal that Sb ions occupied both Zn and interstitials sites. The successful substitution of antimony in ZnO lattice suggests the formation of the complex (Sb{sub Zn}–2 V{sub Zn}) acceptor level above the valence band. Particularly for ZSb3 sample, the UV photoluminescence (PL) band presents an obvious red-shift attributed to the formation of this complex. Rhodamine B (RhB) was used to evaluate the photocatalytic activity of Sb-doped ZnO NCs under sunlight irradiation. It was found that oxygen vacancies play a major role in the photocatalytic process by trapping the excited electrons and inhibiting the radiative recombination. During the photocatalytic mechanism, the Sb doping, expressed through the apparition of the (Sb{sub Zn}–2 V{sub Zn}) correspondent acceptor level, enhances the sunlight absorption within the ZnO band gap, which stimulates the generation of hydroxyl radicals and promotes the photocatalytics reaction rates. Such important contribution of the hydroxyl radicals was confirmed experimentally when using ethanol as scavenger in the photocatalytic reaction. The photodegradation

Increased electronic coupling in silicon nanocrystal networks doped with F4-TCNQ.

Science.gov (United States)

Carvalho, Alexandra; Oberg, Sven; Rayson, Mark J; Briddon, Patrick R

2013-02-01

The modification of the electronic structure of silicon nanocrystals using an organic dopant, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), is investigated using first-principles calculations. It is shown that physisorbed F4-TCNQ molecules have the effect of oxidizing the nanocrystal, attracting the charge density towards the F4-TCNQ-nanocrystal interface, and decreasing the excitation energy of the system. In periodic F4-TCNQ/nanocrystal superlattices, F4-TCNQ is suggested to enhance exciton separation, and in the presence of free holes, to serve as a bridge for electron/hole transfer between adjacent nanocrystals.

Precipitation-lyophilization-homogenization (PLH) for preparation of clarithromycin nanocrystals: influencing factors on physicochemical properties and stability.

Science.gov (United States)

Morakul, Boontida; Suksiriworapong, Jiraphong; Leanpolchareanchai, Jiraporn; Junyaprasert, Varaporn Buraphacheep

2013-11-30

Nanocrystals is one of effective technologies used to improve solubility and dissolution behavior of poorly soluble drugs. Clarithromycin is classified in BCS class II having low bioavailability due to very low dissolution behavior. The main purpose of this study was to investigate an efficiency of clarithromycin nanocrystals preparation by precipitation-lyophilization-homogenization (PLH) combination method in comparison with high pressure homogenization (HPH) method. The factors influencing particle size reduction and physical stability were assessed. The results showed that the PLH technique provided an effective and rapid reduction of particle size of nanocrystals to 460 ± 10 nm with homogeneity size distribution after only the fifth cycle of homogenization, whereas the same size was attained after 30 cycles by the HPH method. The smallest nanocrystals were achieved by using the combination of poloxamer 407 (2%, w/v) and SLS (0.1%, w/v) as stabilizers. This combination could prevent the particle aggregation over 3-month storage at 4 °C. The results from SEM showed that the clarithromycin nanocrystals were in cubic-shaped similar to its initial particle morphology. The DSC thermogram and X-ray diffraction pattern of nanocrystals were not different from the original drug except for intensity of peaks which indicated the presenting of nanocrystals in the crystalline state and/or partial amorphous form. In addition, the dissolution of the clarithromycin nanocrystals was dramatically increased as compared to the coarse clarithromycin. Copyright © 2013 Elsevier B.V. All rights reserved.

Preparation and dual microwave-absorption properties of carboxylic poly(arylene ether nitrile)/Fe3O4 hybrid microspheres

International Nuclear Information System (INIS)

Ma Zhen; Meng Fanbin; Zhao Rui; Zhan Yingqing; Zhong Jiachun; Liu Xiaobo

2012-01-01

The carboxylic poly(arylene ether nitrile)/Fe 3 O 4 hybrid microspheres were prepared via solvothermal method. The carboxylic poly(arylene ether nitrile) (PEN-COOH) was introduced into the Fe 3 O 4 microspheres by chemisorption with mass content up to 15% as defined by infrared spectra and thermal gravimetric analysis. The hybrid sphere is of hierarchical polymer–inorganic microstructure as observed by transmission electron microscopy. The microwave-absorption of the sample owns a shifting peak and a special immobilized peak with the variation of absorber thickness from 3 to 5 mm. Maximum microwave-absorption of the product is capable of over −30 dB in the range of 10–12 GHz. By proposed equivalent filter circuit model, the immobilized peak was attributed to the ordered nanostructure where the Fe 3 O 4 nanocrystals were isolated by PEN-COOH. The product has the potential to be applied as microwave absorber with high microwave-absorption, good dispersibility and robust polymer–inorganic interfacial adherence. - Highlights: ► We prepared poly(arylene ether nitrile)/Fe 3 O 4 hybrid microspheres with hierarchical polymer–inorganic nanostructure. ► A shifting and an immobilized microwave absorbing peaks were observed on the sample. ► Possible mechanism was proposed on the basis of electromagnetic data.

Computer application in coal preparation industry in China

Energy Technology Data Exchange (ETDEWEB)

Lu, M.; Wu, L.; Ni, Q. (China Univ. of Mining and Technology, Xuzhou (China))

1990-01-01

This paper describes several packages of microcomputer programs developed for designing and managing the coal preparation plants. Three parts are included: Coal Cleaning Package (CCP), Coal Preparation Optimization Program (CPO) and Coal Preparation Computer Aided Design System (CPCAD). The function of CCP is: evaluating and predicting coal cleaning result. Coal presentation process modelling and optimization; coal preparation flowsheet design and optimization. The CPO is a nonlinear optimization program. It can simulate and optimize the profit for different flowsheet to get the best combination of the final products. The CPCAD was developed based upon AutoCAD and makes full use of AutoLISP, digitizer menus and AutoCAD commands, combining the functions provided by AutoCAD and the principle used in conventional coal preparation plant design, forming a designer-oriented CPCAD system. These packages have proved to be reliable, flexible and easy to learn and use. They are a powerful tool for coal preparation plant design and management. (orig.).