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Microwave Hydrothermal Synthesis and Photocatalytic Performance of ZnO and M:ZnO Nanostructures (M = V, Fe, Co)

Milao, Thais M.; Mendonca, Vagner R. de; Araujo, Vinicius D.; Avansi, Waldir; Ribeiro, Caue; Longo, Elson; Bernardi, Maria Inês Basso
Fonte: AMER SCIENTIFIC PUBLISHERS; VALENCIA Publicador: AMER SCIENTIFIC PUBLISHERS; VALENCIA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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ZnO and doped M:ZnO (M = V, Fe and Co) nanostructures were synthesized by microwave hydrothermal synthesis using a low temperature route without addition of any surfactant. The transition metal ions were successfully doped in small amount (3% mol) into ZnO structure. Analysis by X-ray diffraction reveals the formation of ZnO with the hexagonal (wurtzite-type) crystal structure for all the samples. The as-obtained samples showed a similar flower-like morphology except for Fe:ZnO samples, which presented a plate-like morphology. The photocatalytic performance for Rhodamine B (RhB) degradation confirmed that the photoactivity of M:ZnO nanostructures decreased for all dopants in structure, according to their eletronegativity. Photoluminescence spectroscopy was employed to correlate M:ZnO structure with its photocatalytical properties. It was suggested that transition metal ions in ZnO lattice introduce defects that act as trapping or recombination centers for photogenerated electrons and holes, making it impossible for them reach the surface and promote the photocatalytical process.; FAPESP; FAPESP; FINEP; FINEP; CNPq; CNPq

Síntese de nanopartículas de óxido de vanádio obtidas pela decomposição de peróxido; Synthesis of Vanadium Oxide Nanoparticles obtained by the decomposition of peroxide

Avansi Junior, Waldir
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/09/2010 PT
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A utilização de novas rotas de síntese de materiais nanoestruturados tem levado à obtenção de materiais apresentando novas propriedades e aplicações. O presente trabalho teve como principal objetivo realizar a síntese e a caracterização de nanopartículas de óxido de vanádio obtidas pelo método da decomposição de peróxido utilizando o tratamento hidrotermal. Por meio do controle do tempo e da temperatura de síntese, foi possível obter nanoestruturas de pentóxido de vanádio com diferentes fases cristalinas e morfologias. Os resultados de espectroscopia Raman e difração de raios X (DRX) mostraram que o tratamento hidrotermal da solução em temperaturas de até 180oC, durante 2 horas, leva à formação da fase V2O5nH2O monoclínica, apresentando uma orientação preferencial na direção 00l. A partir desta temperatura, o material obtido passou a ter a fase ortorrômbica perdendo sua orientação preferencial. Através das medidas de termogravimetria (TG) foi observado que, dependendo da condição de síntese, as amostras apresentam diferentes quantidades de moléculas de água (H2O) intercaladas em sua estrutura. Imagens de microscopia eletrônica mostraram que as nanoestruturas obtidas podem possuir a forma de fitas...

Síntese e caracterização de hidróxidos de alumínio com duas dimensões nanométricas (morfologia fibrilar) ou com uma dimensão nanométrica (morfologia de placas/lâminas).; Synthesis and characterization of aluminum hydroxides with two nanometric dimensions (fibrillar morphology) or one nanometric dimension (morphology boards / blades).

Rocha, Gisele de Araujo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 27/05/2013 PT
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A síntese de nanopartículas com morfologia controlada vem sendo objeto de interesse crescente no campo da Ciência dos Materiais. Devido a essa motivação, o principal objetivo desse trabalho foi a síntese e caracterização de pseudoboemita e boemita apresentando uma ou duas dimensões nanométricas. O método de síntese utilizado para a obtenção de pseudoboemita fibrilar é baseado na reação de um alcóxido de alumínio, em solução aquosa de ácido acético. Para a preparação de boemita, um único método de síntese, a síntese hidrotérmica, foi utilizado, com o emprego de três precursores: uma pseudoboemita, um sal orgânico (o monohidróxido diacetato de alumínio) e o trihidróxido de alumínio gibsita, este último em duas formas: uma gibsita comercial e uma gibsita sintetizada que utiliza iodo como ativador. As pseudoboemitas e as boemitas obtidas foram caracterizadas por difração de raios-X e microscopia eletrônica de varredura. Algumas amostras de pseudoboemita e de boemita foram caracterizadas por análise térmica diferencial e por espectroscopia vibracional na região do infravermelho. Foram obtidas pseudoboemitas com morfologia fibrilar (partículas anisométricas alongadas); no caso das boemitas foram produzidas distintas morfologias (de acordo com o precursor e com as condições de síntese empregadas em sua obtenção): fibrilar (duas dimensões em escala nanométrica)...

Influence of Hydrothermal Synthesis Conditions and Device Configuration on the Photoresponse of UV Sensors Based on ZnO Nanorods

Savu, Raluca; Parra, Rodrigo; Jancar, Bostjan; Zaghete, Maria Aparecida; Joanni, Ednan
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Artigo de Revista Científica Formato: 1820-1825
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 05/59270-0; Zinc oxide nanorods in the form of powder or nanostructured films were synthesized by the hydrothermal method using aqueous solutions. Once the synthesis time was completed, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy techniques were employed to characterize the crystallinity, morphology, and dimensions of the nanorods, as well as their growth direction. Suspensions of powder material were spin-coated over oxidized silicon substrates in order to obtain nanostructured layers. Photodetectors based on in-situ grown and spin-coated films were prepared in order to evaluate the influences of cooling rate and device configuration on the UV sensing characteristics. Spin-coated layers showed an excellent performance (current change by more than four orders of magnitude), better than nanorods grown directly on the substrate during the hydrothermal process. For both configurations, the sensitive layers built from quenched samples exhibited enhanced UV photoresponses when compared to the naturally cooled ones.

Microwave-assisted hydrothermal synthesis of structurally and morphologically controlled sodium niobates by using niobic acid as a precursor

Paula, Amauri J.; Zaghete, Maria A.; Longo, Elson; Varela, José Arana
Fonte: Wiley-v C H Verlag Gmbh Publicador: Wiley-v C H Verlag Gmbh
Tipo: Artigo de Revista Científica Formato: 1300-1308
ENG
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There are many advantages to using a microwave as a source of heat in hydrothermal reactions. Because it is a quick and homogeneous way to crystallize ceramic powders, it was used in this work for the production of antiferroelectric sodium mobate (NaNbO3) in a cubic-like form and its intermediary phase, disodium diniobate hydrate (Na2Nb2O6 center dot H2O), with a fiber morphology. The syntheses were carried out by treating niobic acid (Nb2O5 center dot nH(2)O) with NaOH. By changing the reaction time and the concentration of the reactants, particles with different structures and different morphologies could be obtained. The structural evolution of the products of this reaction was elucidated on the basis of the arrangement of the NbO6 octahedral units. Conclusive results were obtained with morphological and structural characterizations through XRD, TEM, MEV, and NMR and Raman spectroscopy. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Synthesis and characterization of mesoporous TiO2 nanostructured films prepared by a modified sol-gel method for application in dye solar cells

Muniz, E. C.; Goes, M. S.; Silva, J. J.; Varela, José Arana; Joanni, E.; Parra, R.; Bueno, P. R.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 1017-1024
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Anatase TiO2 colloidal dispersions were obtained by hydrothermal synthesis at 200 degrees C from titanium isopropoxide gels modified with acetic acid in the presence of a non-ionic surfactant. Absolute ethanol, anhydrous terpineol and ethyl cellulose were added to this anatase dispersion resulting in a 23 wt% TiO2 paste. Mesoporous films for application as working electrodes in dye-sensitized solar cells were prepared by the screen-printing method, yielding reproducible films with thicknesses about 10 mu m and desired porosity levels in a single printing operation. An average energy conversion efficiency of 5.2%, and a fill factor of 0.66 were achieved with anatase particle sizes ranging between 15 and 20 nm. The reproducibility of the results was confirmed by electrochemical impedance spectroscopy analysis. (c) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Microwave Hydrothermal Synthesis and Photocatalytic Performance of ZnO and M:ZnO Nanostructures (M = V, Fe, Co)

Milao, Thais M.; de Mendonca, Vagner R.; Araujo, Vinicius D.; Avansi, Waldir; Ribeiro, Caue; Longo, Elson; Bernardi, Maria I.
Fonte: Amer Scientific Publishers Publicador: Amer Scientific Publishers
Tipo: Artigo de Revista Científica Formato: 54-60
ENG
Relevância na Pesquisa
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); ZnO and doped M:ZnO (M = V, Fe and Co) nanostructures were synthesized by microwave hydrothermal synthesis using a low temperature route without addition of any surfactant. The transition metal ions were successfully doped in small amount (3% mol) into ZnO structure. Analysis by X-ray diffraction reveals the formation of ZnO with the hexagonal (wurtzite-type) crystal structure for all the samples. The as-obtained samples showed a similar flower-like morphology except for Fe:ZnO samples, which presented a plate-like morphology. The photocatalytic performance for Rhodamine B (RhB) degradation confirmed that the photoactivity of M:ZnO nanostructures decreased for all dopants in structure, according to their eletronegativity. Photoluminescence spectroscopy was employed to correlate M:ZnO structure with its photocatalytical properties. It was suggested that transition metal ions in ZnO lattice introduce defects that act as trapping or recombination centers for photogenerated electrons and holes, making it impossible for them reach the surface and promote the photocatalytical process.

Microwave-assisted hydrothermal synthesis of nanocrystalline SnO powders

Pires, F. I.; Joanni, E.; Savu, R.; Zaghete, M. A.; Longo, Elson; Varela, José Arana
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 239-242
ENG
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Tin oxide (SnO) powders were obtained by the microwave-assisted hydrothermal synthesis technique using SnCl2 center dot 2H(2)O as a precursor. By changing the hydrothermal processing time, temperature, the type of mineralizing agent (NaOH, KOH or NH4 OH) and its concentration, SnO crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (X-ray), Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM) and Selected Area Electron Diffraction (SAED). The results showed that plate-like form is the characteristic morphology of growth and the TEM analyses indicate the growth direction as (200). (c) 2007 Elsevier B.V. All rights reserved.

Microwave-assisted hydrothermal synthesis of ZnO powders with different reagents

Xavier, C. S.; De Moura, A. P.; Li, M. S.; Varela, José Arana; Longo, Elson; Cava, S.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 405-408
ENG
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In this work, zinc oxide powders were synthesized by microwave-assisted hydrothermal method in basic medium. These powders were analyzed by X-ray diffraction (XRD), Field-emisson gum scanning electron microscopy (FEG-SEM), Ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD pattern confirmed that the pure ZnO phases were obtained after MH processing performed at 130°C/ 1h. FEG-SEM micrographs reveals that these nanostructures are made up of ZnO plates. UV-vis results were employed to determine the optical band gap these materials. Also, it showed existence of photoluminescence (PL) in the different zinc powders. An orange PL emission when excited by 350 nm wavelength at room temperature was observad in the different powders.

Microwave hydrothermal synthesis, characterisation, and catalytic performance of Zn1-xMnxO in cellulose conversion

Bernardi, Maria I.B.; Araújo, Vinícius D.; Ribeiro, Caue; Avansi, Waldir; Longo, Elson; de Albuquerque, Nilson J.A.; Meneghetti, Simoni M.P.; Almeida, Rusiene M.; Fajardo, Humberto V.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1-6
ENG
Relevância na Pesquisa
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Wurtzite-type Zn1-xMnxO (x = 0, 0.03, 0.05, 0.07) nanostructures were successfully synthesised using a simple microwave-assisted hydrothermal route and their catalytic properties were investigated in the cellulose conversion. The morphology of the nanocatalysts is dopant-dependent. Pure ZnO presented multi-plate morphology with a flower-like shape of nanometric sizes, while the Zn0.97Mn0.03O sample is formed by nanoplates with the presence of spherical nanoparticles; the Zn0.95Mn0.05O and Zn0.93Mn0.07O samples are mainly formed by nanorods with the presence of a small quantity of spherical nanoparticles. The catalyst without Mn did not show any catalytic activity in the cellulose conversion. The Mn doping promoted an increase in the density of weak acid sites which, according to the catalytic results, favoured promotion of the reaction. © 2013 Institute of Chemistry, Slovak Academy of Sciences.

Síntese de nanofios de óxidos semicondutores para aplicações em dispositivos ópticos e eletrônicos

Savu, Raluca
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 228 f. : il.
POR
Relevância na Pesquisa
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Pós-graduação em Ciência e Tecnologia de Materiais - FC; A presente pesquisa teve como principal objetivo a obtenção de estruturas nanométricas de óxido de índio, óxido de estanho e óxido de zinco por evaporação térmica e síntese hidrotérmica e a construção e teste de sensores de gases e de fotodetectores de ultravioleta baseados nessas nanoestruturas. Foram realizados estudos da influência dos parâmetros experimentais das duas rotas de síntese usadas sobre as morfologias e as propriedades das estruturas. Para a obtenção das camadas nanoestruturadas por evaporação térmica foi especialmente construído um forno tubular que permitiu o controle da temperatura de deposição independente da temperatura de evaporação e da distância entre a fonte de evaporação e o substrato. Esses parâmetros, pouco explorados nas pesquisas reportadas na literatura, exerceram uma grande influência sobre a morfologia e as propriedades dos nanofios obtidos. O equipamento permitiu ainda um controle preciso da composição da atmosfera e da pressão de síntese. Na síntese química em solução, a construção de um reator hidrotérmico permitiu o estudo da influência da taxa de resfriamento sobre as dimensões...

Optimised hydrothermal synthesis of multi-dimensional hybrid coordination polymers containing flexible organic ligands

Paz, Filipe A. Almeida; Rocha, João; Klinowski, Jacek; Trindade, Tito; Shi, Fa-Nian; Mafra, Luis
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H4pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V2O2(pmida)2]4 anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V2O2(pmida)2]4 in solution, we have isolated [M2V2O2(pmida)2 (H2O)10] species (where M2þ ¼ Mn2þ, Co2þ or Cd2þ) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4#-bpy)(H2O)2]$(4,4#-bpy)0.5$(H2O), [CoVO(pmida)(4,4#-bpy)(H2O)2]$(4,4#-bpy)0.5, [Co(H2O)6][CoV2O2(pmida)2(pyr)(H2O)2]$2(H2O) and [Cd2V2O2(pmida)2(pyr)2(H2O)4]$4(H2O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4#-bipyridine (4,4#-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V4þ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V2O2(pmida)2]4 anionic units. A closely related anionic moiety...

Design of experiments (DOE) for the optimization of hydrothermal synthesis of hydroxyapatite nanoparticles

Sadat-Shojai,Mehdi; Atai,Mohammad; Nodehi,Azizollah
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2011 EN
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The aim of this work was to investigate the influence of different reaction parameters on the properties of hydroxyapatite (HAp) nanoparticles prepared by the hydrothermal method. The literature data describe widely different experimental conditions for the hydrothermal synthesis of HAp. A specific approach was therefore used to evaluate the statistically influential factors among those described in the literature. The role of each experimental parameter was also discussed within the framework of particle nucleation and crystal growth mechanism. Among the selected variables, temperature and pH were found to be the most significant factors affecting the composition and morphology of the HAp. Moreover, in the present study, different morphologies ranging from rod-like to spherical nanoparticles with various characteristics were successfully obtained, which can be applicable for the preparation of various HAp bioceramics.

ZnO Nanorods Grown on p-GaN Using Hydrothermal Synthesis and Its Optoelectronic Devices Application

Le, Hong Quang; Chua, Soo-Jin; Fitzgerald, Eugene A.; Loh, Kian Ping
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 187324 bytes; application/pdf
EN
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The ZnO nanorods with the length of 1-1.5 μm were deposited on p-GaN by hydrothermal synthesis at low temperature 100°C. The structural and optical properties of the as-grown ZnO rods were investigated by X-Ray diffraction (XRD) and photoluminescence (PL) spectra. After annealing treatment the as-grown films in air at 600°C, 30min, and the ZnO rods showed good crystallinity and optical properties with strong UV emission at 378 nm. In addition, a sharp UV emission peak at 369.45 nm with the FWHM 20 meV, which attributed to the bound exciton recombination, was also observed from the ZnO rods at 80K. Next, the e-beam evaporation method was used to deposit metal contact on n-ZnO and p-GaN. Here, we use Au and Ni/Au as metal contacts for n-ZnO and p-GaN, respectively. The current-voltage characteristics of the fabricated n-ZnO/p-GaN heterojunction revealed rectifying behavior with a leakage current of 10⁻⁸ A at -10V, a forward current 4x10⁻⁶ A at 10V bias. The heterojunction also showed a good photoresponse, with the change of the current – voltage characteristics under ultraviolet illumination. Under UV illumination, the forward turn on voltage changed to 7.5V. This result showed the ability to manipulate the electron transport in the ZnO based heterojunction devices.; Singapore-MIT Alliance (SMA)

Obtenção de ferrita de cobalto através de dois métodos de síntese: método de complexação combinando EDTA/Citrato e método hidrotérmico; Obtaining cobalt ferrite through two synthesis methods: Complexation Method Conbining EDTA/Citrate and Hydrothermal Method

Medeiros, Indira Aritana Fernandes de
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Dissertação Formato: application/pdf
POR
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In this work it was synthesized and characterized the cobalt ferrite (CoFe2O4) by two methods: complexation combining EDTA/Citrate and hydrothermal investigating the influence of the synthesis conditions on phase formation and on the crystallite size. The powders were mainly characterized by x-ray diffraction. In specific cases, it was also used scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray fluorescence (XRF) and isotherms of adsorption and desorption of nitrogen (BET method). The study of the crystallite size was based on the interpretation of x-ray diffractograms obtained and estimated by the method of Halder-Wagner-Scherrer and Langford. An experimental design was made in order to assist in quantifying the influence of synthesis conditions on the response variables. The synthesis parameters evaluated in this study were: pH of the reaction medium (8, 9 and 10), the calcination temperature (combined complexation method EDTA/Citrate 600°C, 800°C and 1000°C), synthesis temperature (hydrothermal method 120°C, 140°C and 160°C), calcination time (combined complexation method EDTA/Citrate - 2, 4 and 6 hours) and time of synthesis (hydrothermal method 6, 15 and 24 hours). By the hydrothermal method was possible to produce mesoporous powders with high purity...

Avaliação da síntese e caracterização de zeólita ZSM-5 ausente de direcionador orgânico estrutural

Caldeira, Vinícius Patrício da Silva
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Química; Físico-Química; Química Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Química; Físico-Química; Química
Tipo: Dissertação Formato: application/pdf
POR
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The catalytic processes play a vital role in the worldwide economy, a business that handles about US$ 13 billion per year because the value of products depends on the catalytic processes, including petroleum products, chemicals, pharmaceuticals, synthetic rubbers and plastics, among others. The zeolite ZSM-5 is used as catalyst for various reactions in the area petrochemical, petroleum refining and fine chemicals, especially the reactions of cracking, isomerization, alkylation, aromatization of olefins, among others. Many researchers have studied the hydrothermal synthesis of zeolite ZSM-5 free template and they obtained satisfactory results, so this study aims to evaluate the hydrothermal synthesis and the physicochemical properties of ZSM-5 with the presence and absence of template compared with commercial ZSM-5. The methods for hydrothermal synthesis of zeolite ZSM-5 are of scientific knowledge, providing the chemical composition required for the formation of zeolitic structure in the presence and absence of template. Samples of both zeolites ZSM-5 in protonic form were obtained by heat treatment and ion exchange, according to procedures reported in the literature. The sample of commercial ZSM-5 was acquired by the company Sentex Industrial Ltda. All samples were characterized by XRD...

Facile hydrothermal synthesis and optical limiting properties of TiO2-reduced graphene oxide nanocomposites

Wang, Aijian; Yu, Wang; Fang, Yu; Song, Yinglin; Jia, Ding; Long, Lingliang; Cifuentes, Marie P.; Humphrey, Mark G.; Zhang, Chi
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: 12 pages
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TiO2/reduced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03 g RGO, x = 0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO2 on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite; Financial support from the National Natural Science Foundation of China (51432006, 50925207, 51172100), the Ministry of Science and Technology of China for the International Science Linkages Program (2009DFA50620...

One-step hydrothermal synthesis and photocatalytic performance of ZnWO4/Bi2WO6 composite photocatalysts for efficient degradation of acetaldehyde under UV light irradiation

Hojamberdiev, Mirabbos; Katsumata, Ken-ichi; Morita, Koji; Aldabe, Sara Alfonsina; Matsushita, Nobushiro; Okada, Kiyoshi
Fonte: Elsevier Science Bv Publicador: Elsevier Science Bv
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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Bi2WO6 with different Bi3+ ion concentrations (0?30 mol%) is incorporated with the ZnWO4 photocatalyst to improve the photocatalytic efficiency by forming a ZnWO4/Bi2WO6 composite photocatalyst with hierarchical heterostructure via a one-step hydrothermal method. X-ray diffraction and Raman spectroscopy analyses confirm the presence of ZnWO4 and Bi2WO6 as main phases in the composite photocatalyst. Scanning electron microscopy and transmission electron microscopy observations reveal that the rice- and plate-like Bi2WO6 nanoparticles were either separate or attached to the surface of quasi-spherical ZnWO4 particles. A gradual increase in the Bi2WO6 content of the composite photocatalyst results in a monotonic shift of the absorption edge from ca. 355 nm to longer wavelengths up to ca. 450 nm. The photocatalytic performance of the ZnWO4/Bi2WO6 composite photocatalyst was evaluated by investigating the degradation of gaseous acetaldehyde (AcH) under UV light irradiation. Only the composite photocatalyst synthesized with 30 mol% Bi3+ exhibits higher photocatalytic activity under UV light irradiation compared with both individual ZnWO4 and Bi2WO6, and with a mechanically mixed ZnWO4/Bi2WO6 composite photocatalyst. The enhanced photocatalytic activity is attributed to the n-n isotype junction formed between the two semiconductors and the charge separation of each semiconductor.; Fil: Hojamberdiev...

In-situ hydrothermal synthesis of zinc oxide nanostructures using microheaters

Lin, Wei-Chih; Lin, Yu-Ching; Esashi, Masayoshi; Seshia, Ashwin A.
Fonte: IEEE Publicador: IEEE
Tipo: Article; accepted version
EN
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This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/TNANO.2015.2468076; A technique for in-situ hydrothermal synthesis of transversely suspended zinc oxide nanowires (ZnO NWs) using microfabricated heaters is presented. A number of issues relating to seed layer preparation, directed alignment, local heating control and the concentration of the synthesis solution are investigated for this method. It is shown that ZnO NWs can be synthesized and aligned from the ZnO seed surface to bridge two adjacent microheater elements. Moreover, hybrid ZnO nanotubes and nanorods are also synthesized by controlling the concentration of the synthesis solution employed. The crystalline structure of synthesized ZnO nanostructures are characterized by the transmission electron microscope (TEM) and selective area electron diffraction (SAED). Finally, ZnO NW devices based on proposed microheater synthesis approach are characterised for UV photoresponsivity demonstrating the potential of this approach to address practical device applications.; Funding support by the WPI-AIMR, Tohoku University and by the Royal Society is gratefully acknowledged.

Hydrothermal Synthesis of Mesoporous Silica MCM-41 Using Commercial Sodium Silicate

Meléndez-Ortiz,Héctor Iván; Mercado-Silva,Alfonso; García-Cerda,Luis Alfonso; Castruita,Griselda; Perera-Mercado,Yibran Argenis
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2013 EN
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In this work, ordered mesoporous silica MCM-41 was prepared by hydrothermal synthesis using industrial-grade sodium silicate (Na2SiO3) as silica source, hexadecyltrimethyl-ammonium bromide (CTAB) as template agent and ethyl acetate as pH regulator. The influence of CTAB/SiO2 molar ratio, reaction time, aging temperature, and co-surfactant type on the structural and morphological properties of the obtained silica was studied. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-desorption isotherms. Ordered mesoporous MCM-41 silica was obtained at 80 °C by using a range of CTAB/SiO2 molar ratio from 0.35 to 0.71 and reaction times up to 72 h and isopropanol (i-PrOH) as co-surfactant.