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Humidity sensing properties of a thick-film titania prepared by a slow spinning process

Faia, P. M.; Furtado, C. S.; Ferreira, A. J.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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A ceramic thick film humidity sensor was produced from an emulsion of titania powders by a spin coating technique using a low speed. Electrical measurements were taken between interdigital electrodes obtained by depositing silver paste on the oxide, then cured at 500 °C for 15 min. Different relative humidities of a dynamic atmosphere were obtained by mixing dry and 23 °C saturated synthetic air in convenient proportions. Complex impedance spectra of the titania sensor at various relative humidities (RH) and different temperatures were measured and compared. The humidity sensing behaviour is due to surface water molecules adsorption and capillary condensation. The proposed sensing mechanisms, explaining the registered impedance spectra, are a combination of proton hopping, hydronium electrical drift and diffusion, and electrolytic conduction. In the frequency range 1-400 Hz, resistance and capacitive reactance show variations of three to four-order magnitude over the RH range 10-100%. The curves representing the variations of resistance and capacitive reactance versus RH show clearly the existence of two dominant electrical charge transport mechanisms. A parameter called characteristic humidity is defined to represent the sensitive response of the sensor. It was found that the sensitivity was highly dependent on the frequency. This work also shows that...

Raman and XRD study on brookite-anatase coexistence in cathodic electrosynthesized titania

Campos, C. S.; Spada, E. R.; Paula, F. R. de; Reis, F. T.; Faria, Roberto Mendonça; Sartorelli, M. L.
Fonte: WILEY-BLACKWELL; MALDEN Publicador: WILEY-BLACKWELL; MALDEN
Tipo: Artigo de Revista Científica
ENG
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Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy-hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solidliquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium-tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X-ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile-free mixture of brookite and anatase at temperatures as low as 200 degrees C that persists up to 800 degrees C, when pure anatase dominates. The amount of brookite in the brookiteanatase mixture reaches a maximum at 400 degrees C. This very simple method for obtaining a brookiteanatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright (C) 2011 John Wiley & Sons...

Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

Barros Filho, D. A.; Benedetti, J. E.; Silva, Marcelo de Assumpção Pereira da; Seriacopi, V.; Gomes Silva, W. R.; Alonso, R. C. B.; Lewgoy, H. R.; Anido-Anido, A.; Amore, R.; Anauate-Netto, C.; Avellaneda, C. O.; Santilli, Celso V.; Nogueira, Ana F.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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In this work, mesoporous titania is prepared by templating latex sphere arrays with four different sphere diameters at the micrometric scale (phi > 1 mu m). The mesoporous titania homogeneously covers the latex spheres and substrate, forming a thin coating characterized by N-2 adsorption isotherm, small angle X-rays scattering, atomic force, field emission and transmission electronic microscopies. Mesoporous titania has been templated into different shapes such as hollow particles and monoliths according to the amount of sol used to fill the voids of the close packed latex spheres. Titania topography strongly depends on the adsorption of polymeric segments over latex spheres surface, which could be decreased by changing the dimensions of latex spheres (phi = 9.5 mu m) generating a lamellar architecture. Thus, micrometric latex sphere arrays can be used to achieve new surface patterns for mesoporous materials via a fast and inexpensive chemical route for construction of functional devices in different technological fields such as energy conversion, inclusion chemistry and biomaterials. (C) 2011 Elsevier Inc. All rights reserved.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2008/00463-2]; Chemistry Institute of the University of Sao Paulo...

Filmes de ormosils contendo polioxometalatos dopados com nanopartículas de titânia: adsorção de lipídeos e formação de biofilmes de Escherichia coli; Ormosils films containing polixomethalates doped with titania nanoparticles: lipids adsorption and biofilm formation of Escherichia coli

Souza, Luciana Valgas de
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 16/06/2014 PT
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Neste trabalho foram preparados materiais híbridos do tipo silicatos organicamente modificados (ormosils) contendo fosfotungstato, [PW12O40]-3 e dopados com nanopartículas de TiO2. O objetivo é obter uma ação sinérgica destes dois fotocatalisadores na prevenção de formação de biofilmes e/ou sua fotodegradação. O fotocatalisador principal no sistema é o fosfotungstato, sendo o co-adjuvante o TiO2. Sendo assim, procurou-se manter a concentração deste no menor nível possível. Os materiais foram caracterizados por espectroscopias vibracionais, espectroscopia de fotoelétrons de raios X (XPS), Fluorescência de Raios X, Microscopia de força atômica e Microscopia eletrônica de varredura (MEV). Os filmes não mostraram eficácia na fotodegradação de biomoléculas como fosfolipídios encontrados na membrana celular. Os ensaios de inibição de crescimento de biofilmes de Escherichia coli sobre os ormosils mostraram que a maior inibição de bactérias é do filme contendo maior teor de nanopartículas de titânia portanto, são bons candidatos para filmes e revestimentos bactericidas/bacteriostáticos a serem usados em máscaras respiratórias, revestimentos de superfícies em salas de cirurgia e em filtros de ar em sistemas fechados (sistemas de ar condicionado e ventilação em geral).; This thesis deals with hybrid materials named organically modified silicates (Ormosils) with phosphotungstate...

Efeito do conteúdo de titânia e da alteração da superfície por meio da aplicação do recobrimento biomimético nas propriedades mecânicas do compósito Y-TZP/TiO2; Effect of titania content and the change of the surface by applying the biomimetic coating on the mechanical properties of the composite Y-TZP/TiO2

Miranda, Ranulfo Benedito de Paula
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/07/2014 PT
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Os objetivos desse trabalho foram: 1) determinar o efeito do conteúdo de titânia em mol % (zero, 10 e 30) na área de superfície específica (SBET), no tamanho dos aglomerados e na intensidade dos picos correspondentes às fases cristalinas presentes no pó cerâmico de Y-TZP/TiO2; 2) determinar o efeito do conteúdo de titânia em mol % (zero, 10 e 30) na microestrutura, densidade, densidade relativa, módulo de elasticidade, coeficiente de Poisson, módulo de Weibull (m) e resistência à flexão (f) de pastilhas cerâmicas sinterizadas de Y-TZP/TiO2 e, 3) determinar o efeito do recobrimento biomimético no módulo de Weibull (m) e na resistência á flexão de pastilhas cerâmicas sinterizadas de Y-TZP/TiO2. Os pós foram produzidos por meio de uma rota de co-precipitação, obtendo-se três composições do compósito Y-TZP/TiO2, que foram de zero (T0), 10 (T10) e 30 (T30) % mol de titânia. O pó produzido foi prensado (50 MPa) para produzir pastilhas de 15 mm de diâmetro e sinterizado a 1400 °C por 2 horas. Após o polimento com solução diamantada de 45 m, as pastilhas (n=60 para cada grupo) ficaram com aproximadamente 12 mm de diâmetro e 1,0 mm de espessura. Metade das pastilhas foram submetidas ao recobrimento biomimético (sete dias em solução de silicato de sódio e sete dias em solução de 1...

Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

Barros Filho, D. A.; Benedetti, J. E.; Pereira-da-Silva, M. A.; Seriacopi, V.; Gomes Silva, W. R.; Alonso, R. C. B.; Lewgoy, H. R.; Anido-Anido, A.; Amore, R.; Anauate-Netto, C.; Avellaneda, C. O.; Santilli, Celso V.; Nogueira, Ana F.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 84-95
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 08/00463-2; In this work, mesoporous titania is prepared by templating latex sphere arrays with four different sphere diameters at the micrometric scale (phi > 1 mu m). The mesoporous titania homogeneously covers the latex spheres and substrate, forming a thin coating characterized by N-2 adsorption isotherm, small angle X-rays scattering, atomic force, field emission and transmission electronic microscopies. Mesoporous titania has been templated into different shapes such as hollow particles and monoliths according to the amount of sol used to fill the voids of the close packed latex spheres. Titania topography strongly depends on the adsorption of polymeric segments over latex spheres surface, which could be decreased by changing the dimensions of latex spheres (phi = 9.5 mu m) generating a lamellar architecture. Thus, micrometric latex sphere arrays can be used to achieve new surface patterns for mesoporous materials via a fast and inexpensive chemical route for construction of functional devices in different technological fields such as energy conversion, inclusion chemistry and biomaterials. (C) 2011 Elsevier B.V. All rights reserved.

Structural study of copper oxide supported on a ceria-modified titania catalyst system

Francisco, M. S P; Mastelaro, V. R.; Florentino, A. O.; Bazin, D.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 105-111
ENG
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A structural study of CuO supported on a CeO2-TiO2 system was undertaken using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. The results of XRD revealed the presence of only two phases, TiO2 anatase and CeO2 cerianite. A trend towards smaller TiO2 crystallites was observed when cerium content increased. When the amount of cerium increased, Ti K-edge XANES analysis showed an increasing distortion of Ti sites. The results of Ce LIII-edge EXAFS showed that Ce atoms are coordinated by eight oxygen atoms at 2.32 Å. For the sample containing a small amount of cerium, the EXAFS analysis indicated that the local structure around Ce atoms was highly distorted. The catalysts presented quite different Cu K-edge XANES spectra compared to the spectra of the CuO and Cu2O reference compounds. The Cu-O mean bond length was close to that of the CuO and the Cu atoms in the catalysts are surrounded by approximately four oxygen atoms in their first shell. Copper supported on the ceria-modified titania support catalysts displayed a better performance in the methanol dehydrogenation when compared to copper supported only on titania or on ceria. © 2002 Plenum Publishing Corporation.

Reduced in vitro immune response on titania nanotube arrays compared to titanium surface

Smith, Barbara S.; Capellato, Patricia; Kelley, Sean; Gonzalez-Juarrero, Mercedes; Popat, Ketul C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 322-332
ENG
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Material surfaces that provide biomimetic cues, such as nanoscale architectures, have been shown to alter cell/biomaterial interactions. Recent studies have identified titania nanotube arrays as strong candidates for use in interfaces on implantable devices due to their ability to elicit improved cellular functionality. However, limited information exists regarding the immune response of nanotube arrays. Thus, in this study, we have investigated the short- and long-term immune cell reaction of titania nanotube arrays. Whole blood lysate (containing leukocytes, thrombocytes and trace amounts of erythrocytes), isolated from human blood, were cultured on titania nanotube arrays and biomedical grade titanium (as a control) for 2 hours and 2 and 7 days. In order to determine the in vitro immune response on titania nanotube arrays, immune cell functionality was evaluated by cellular viability, adhesion, proliferation, morphology, cytokine/chemokine expression, with and without lipopolysaccharide (LPS), and nitric oxide release. The results presented in this study indicate a decrease in short- and long-term monocyte, macrophage and neutrophil functionality on titania nanotube arrays as compared to the control substrate. This work shows a reduced stimulation of the immune response on titania nanotube arrays...

Propriedades estruturais do material vitreo silica-titania produzido pelo metodo do aerosol em chama; Structural properties of silica-titania vitreous material produced by flame aerosol method

Claudia Carvalho Nunes
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/02/2008 PT
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O sistema binário sílica titânia, SiO2-TiO2,apresenta grande interesse tecnológico devido as suas propriedades: ultra-baixo coeficiente de expansão térmico e alto índice de refração. As propriedades são dependentes da quantidade de dopante presente no material. A SiO2-TiO2 é usada na indústria de componentes fotônicos, tais como, lentes, micro-lentes, espelhos e fibras ópticas especiais. Um importante material óptico para litografia no extremo ultravioleta (EUVL) é caracterizado por concentrações próximas a 8 % em peso de TiO2, com estrutura amorfa e transparente num amplo espectro da região UV, visível e IV. A indústria óptico-eletrônica necessita de fibras ópticas sensoras com alto índice de refração. Este tipo de fibra pode ser obtido através da fabricação de uma fibra de SiO2-TiO2. Amostras com concentrações que variam de 1 a 14 % em peso TiO2 fabricadas pelo método do aerosol em chama foram caracterizadas quanto a suas propriedades estruturais e ópticas. As amostras com concentrações superiores a 7,5 % em peso apresentaram-se translúcidas ou opacas, e com estrutura octaédrica segundo dados de XANES (Absorção de Raios-X próximo à estrutura da borda). A difração de raios-X identificou a fase anatásio da titânia como estrutura octaédrica. Através de tratamentos térmicos a altas temperaturas em chama (> 1500 ºC) obtivemos amostras transparentes no visível...

Sintese e caracterização de hidroxiapatita e titania nanoestruturadas para a fabricação de compositos; Synthesis and characterization of nanostructured hydroxyapatite and titania for fabrication of composites

Leonardo Ribeiro Rodrigues
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/07/2008 PT
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A hidroxiapatita e a titânia são cerâmicas muito pesquisadas no mundo inteiro, graças às suas excelentes qualidades em diversas áreas, porém neste trabalho o foco foi a sua utilização como biomateriais. Neste trabalho é apresentada a síntese e a caracterização de hidroxiapatita e titânia nanoestruturadas e a fabricação e caracterização de compósitos a partir destes materiais. Os métodos de obtenção de hidroxiapatita foram as rotas sol-gel convencional, sol-gel com sacarose e sol-gel com glicose. Para a síntese da titânia foi utilizado um método desenvolvido no laboratório. Foram utilizados na caracterização da hidroxiapatita: difração de raios X associado com a equação de Scherrer, fluorescência de raios X, microscopia eletrônica de varredura e ensaio mecânico de compressão. Para a titânia foram utilizados os mesmos tipos de caracterização, porém com a adição da espectroscopia Raman. Os resultados foram excelentes podendo ser destacados: baixo custo dos reagentes, facilidade de realização dos processos de síntese, pequenos nanocristalitos com 52 a 100nm para hidroxiapatita e 27 a 62nm para a titânia. O compósito apresentou boa distribuição entre as partículas de hidroxiapatita e titânia e uma evidente melhora na resistência à compressão quando comparado com o pó compactado de hidroxiapatita sem reforço.; Hydroxyapatite and titania are ceramics which have been given a lot of attention around world because of their outstanding properties in multiple fields such as the one of biomaterials which is the aim of this work. The synthesis and caracterization of nanostructured hydroxyapatite and titania...

Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

Barros Filho, D. A.; Benedetti, J. E.; Pereira-da-Silva, M. A.; Seriacopi, V.; Gomes Silva, W. R.; Alonso, R. C. B.; Lewgoy, H. R.; Anido-Anido, A.; Amore, R.; Anauate-Netto, C.; Avellaneda, C. O.; Santilli, Celso V.; Nogueira, Ana F.
Fonte: Elsevier; Amsterdam Publicador: Elsevier; Amsterdam
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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In this work, mesoporous titania is prepared by templating latex sphere arrays with four different sphere diameters at the micrometric scale (phi > 1 mu m). The mesoporous titania homogeneously covers the latex spheres and substrate, forming a thin coating characterized by N-2 adsorption isotherm, small angle X-rays scattering, atomic force, field emission and transmission electronic microscopies. Mesoporous titania has been templated into different shapes such as hollow particles and monoliths according to the amount of sol used to fill the voids of the close packed latex spheres. Titania topography strongly depends on the adsorption of polymeric segments over latex spheres surface, which could be decreased by changing the dimensions of latex spheres (phi = 9.5 mu m) generating a lamellar architecture. Thus, micrometric latex sphere arrays can be used to achieve new surface patterns for mesoporous materials via a fast and inexpensive chemical route for construction of functional devices in different technological fields such as energy conversion, inclusion chemistry and biomaterials. (C) 2011 Elsevier Inc. All rights reserved.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparação e estudo da atividade fotocatalítica de titânia pura e dopada

Pereira, Andreia Raquel da Silva
Fonte: Universidade de Trás-os-Montes e Alto Douro Publicador: Universidade de Trás-os-Montes e Alto Douro
Tipo: Dissertação de Mestrado
POR
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Dissertação de Mestrado em Engenharia do Ambiente; A poluição ambiental, em particular a contaminação da água, tem apresentado profundas consequências negativas na vida dos seres humanos, havendo assim necessidade de encontrar novas formas de descontaminação. Os Processos de Oxidação Avançados (POA) estão entre os novos processos de descontaminação ambiental e têm atraído grande interesse da comunidade científica. A fotocatálise heterogénea é um POA que tem sido objeto de muitos estudos, apresentando, no entanto, baixa eficiência sob a ação de radiação visível. O dióxido de titânio apresenta boas propriedades como material fotocatalisador para aplicação em processos de degradação fotocatalítica devendo, no entanto, ser fixado num suporte adequado de modo a evitar os dispendiosos e demorados processos de separação. A presente dissertação caracteriza detalhadamente três pós de titânia comercial: Aldrich, Kronos e Degussa P-25. Na tentativa de estender a absorção da radiação das titânias para a região do visível, estas foram dopadas com WO3, pelo método de reação no estado sólido (calcinação a elevadas temperaturas) e pelo método sol-gel. O estudo da atividade fotocatalítica dos pós de titânia em suspensão foi efetuado na degradação de soluções aquosas de azul de metileno. Entre todos os pós dopados preparados no presente trabalho a Degussa P-25 foi a que apresentou melhor desempenho fotocatalítico. Os pós de titânia foram depositados em substratos cerâmicos...

Synthesis of mesoporous titania in rutile phase with pore-stable structure

Santos,J. G. dos; Ogasawara,T.; Corrêa,R. A.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2009 EN
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Metastable-to-stable transformation in oxides is always associated with drastic reduction in surface area and/or porosity. Therefore, all earlier efforts to stabilize the pore structure of oxides undergoing a metastable-to-stable phase transformation are interesting for both scientific and technological concerns. This work presents a new experimental technique for catalytic oxide production through sonication in acid solution for attainment of the anatase-rutile transformation. Mesoporous structure of titania and surface area were stabilized in the rutile phase after calcinations at 430 and 730ºC. Analysis by scanning electron microscopy (SEM) and nitrogen isotherms showed that the mesoporous structure was preserved after calcinations. After the sonication of titania for 32 hours, rutile phase was obtained at 730ºC and still kept a surface area of 28m²/g. When sonicated for 64 h, rutile was obtained at 430ºC, still preserving an area of 52m²/g.

Phosphine-stabilised Au9 clusters interacting with titania and silica surfaces: The first evidence for the density of states signature of the support-immobilised cluster; The Journal of Chemical Physics

Andersson, Gunther G.; Golovko, Vladimir B.; Alvino, Jason F.; Bennett, Trystan; Wrede, Oliver; Mejia, Sol M.; Al Qahtani, Hassan S.; Adnan, Rohul; Gunby, Nathaniel; Anderson, David P.; Metha, Gregory F.
Fonte: Pontifícia Universidade Javeriana Publicador: Pontifícia Universidade Javeriana
Formato: 1 -12
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Vol. 141, no. 1; Chemically made, atomically precise phosphine-stabilized clusters Au9(PPh3)8(NO3)3 were deposited on titania and silica from solutions at various concentrations and the samples heated under vacuum to remove the ligands. Metastable induced electron spectroscopy was used to determine the density of states at the surface, and X-ray photoelectron spectroscopy for analysing the composition of the surface. It was found for the Au9 cluster deposited on titania that the ligands react with the titania substrate. Based on analysis using the singular value decomposition algorithm, the series of MIE spectra can be described as a linear combination of 3 base spectra that are assigned to the spectra of the substrate, the phosphine ligands on the substrate, and the Au clusters anchored to titania after removal of the ligands. On silica, the Au clusters show significant agglomeration after heat treatment and no interaction of the ligands with the substrate can be identified.

Radiofrequency-triggered release for on-demand delivery of therapeutics from titania nanotube drug-eluting implants

Bariana, M.; Aw, M.S.; Moore, E.; Voelcker, N.H.; Losic, D.
Fonte: Future Medicine Publicador: Future Medicine
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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AIM: This study aimed to demonstrate radiofrequency (RF)-triggered release of drugs and drug carriers from drug-eluting implants using gold nanoparticles as energy transducers. MATERIALS & METHODS: Titanium wire with a titania nanotube layer was used as an implant loaded with indomethacin and micelles (tocopheryl PEG succinate) as a drug and drug carrier model. RF signals were generated from a customized RF generator to trigger in vitro release. RESULTS & DISCUSSION: Within 2.5 h, 18 mg (92%) of loaded drug and 14 mg (68%) of loaded drug carriers were released using short RF exposure (5 min), compared with 5 mg (31%) of drug and 2 mg (11%) of drug carriers without a RF trigger. Gold nanoparticles can effectively function as RF energy transducers inside titania nanotubes for rapid release of therapeutics at arbitrary times. CONCLUSION: The results of this study show that RF is a promising strategy for triggered release from implantable drug delivery systems where on-demand delivery of therapeutics is required.; Manpreet Bariana, Moom Sinn Aw, Eli Moore, Nicolas H Voelcker, Dusan Losic

Mesoporous titania powders: the role of precursors, ligand addition and calcination rate on their morphology, crystalline structure and photocatalytic activity

Masolo, Elisabetta; Meloni, Manuela; Garroni, Sebastiano; Mulas, Gabriele; Enzo, Stefano; Baró, M. D.; Rossinyol Casals, Emma; Rzeszutek, Agnieszka; Herrmann-Geppert, Iris; Maria Pilo, Maria
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2014 ENG
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We evaluate the influence of the use of different titania precursors, calcination rate, and ligand addition on the morphology, texture and phase content of synthesized mesoporous titania samples, parameters which, in turn, can play a key role in titania photocatalytic performances. The powders, obtained through the evaporation-induced self-assembly method, are characterized by means of ex situ X-Ray Powder Diffraction (XRPD) measurements, N2 physisorption isotherms and transmission electron microscopy. The precursors are selected basing on two different approaches: the acid-base pair, using TiCl4 and Ti(OBu)4, and a more classic route with Ti(OiPr)4 and HCl. For both precursors, different specimens were prepared by resorting to different calcination rates and with and without the addition of acetylacetone, that creates coordinated species with lower hydrolysis rates, and with different calcination rates. Each sample was employed as photoanode and tested in the water splitting reaction by recording I-V curves and comparing the results with commercial P25 powders. The complex data framework suggests that a narrow pore size distribution, due to the use of acetylacetone, plays a major role in the photoactivity, leading to a current density value higher than that of P25.

Controlled nanophase development in photocatalytic titania

Ying, Li; Hon, Lim; White, Tim; Withers, Raymond; Hai, Liu
Fonte: Japan Institute of Metals Publicador: Japan Institute of Metals
Tipo: Artigo de Revista Científica
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Acid catalyzed hydrolysis of titanium butoxide was used to synthesize homogeneous titania gels, which were converted to the anatase and rutile polytypes through controlled firing. The mechanism of this phase transformation was investigated by quantitative powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Condensation to titania is a function of annealing time, temperature and atmosphere. In air, calcinations below 600°C favored the formation of anatase, with rutile only appearing at >600°C. However, in situ transformation where titania nanoparticles were treated under vacuum in the TEM required heating at higher temperatures up to 900°C. This is may be due to the formation of surface layers of reduced titanium oxide that passivate and retard the anatase to rutile transformation. Grain growth and specific surface area varied inversely, with especially rapid crystallization observed at and beyond the transformation temperature. Potential photocatalytic activity was identified with ultraviolet-visible (UV-Vis) spectroscopy. A red shift of the absorption edge for nano-titania was observed due to quantum size effects.

An X-ray reflectivity study of evaporation-induced self-assembled titania-based films

Henderson, Mark; Gibaud, Alain; Bardeau, Jean-Francois; White, John
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
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X-Ray reflectivity was used to monitor the structural development of a titania-based film at the solid/air interface by evaporation-induced self-assembly (EISA). A nonionic poly(ethylene oxide)-based surfactant, Brij 58, was used as the template and titanium chloride as the inorganic precursor. The reflectivity pattern, film thickness and refractive index were shown to be dependent on film deposition method, whether by casting or by dip-coating onto a silicon wafer, the Brij 58 TiO2 ratio and the relative humidity. At Brij 58 contents of 40 wt%, the reflectivity profile displayed only a single diffraction peak. At 70 wt% Bragg diffraction indicated a lamellar ordering of film components. Modelled reflectivity data suggested a 1060 Å thick film that comprised 17 layers of alternating surfactant and titania with a d spacing of about 60 Å. The effect of relative humidity on film structure was explored.

Structural study of copper oxide supported on a ceria-modified titania catalyst system

Francisco, M. S. P.; Mastelaro, V. R.; Florentino, A. O.; Bazin, D.
Fonte: Kluwer Academic/plenum Publ Publicador: Kluwer Academic/plenum Publ
Tipo: Conferência ou Objeto de Conferência Formato: 105-111
ENG
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A structural study of CuO supported on a CeO2-TiO2 system was undertaken using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. The results of XRD revealed the presence of only two phases, TiO2 anatase and CeO2 cerianite. A trend towards smaller TiO2 crystallites was observed when cerium content increased. When the amount of cerium increased, Ti K-edge XANES analysis showed an increasing distortion of Ti sites. The results of Ce LIII-edge EXAFS showed that Ce atoms are coordinated by eight oxygen atoms at 2.32 Å. For the sample containing a small amount of cerium, the EXAFS analysis indicated that the local structure around Ce atoms was highly distorted. The catalysts presented quite different Cu K-edge XANES spectra compared to the spectra of the CuO and Cu2O reference compounds. The Cu-O mean bond length was close to that of the CuO and the Cu atoms in the catalysts are surrounded by approximately four oxygen atoms in their first shell. Copper supported on the ceria-modified titania support catalysts displayed a better performance in the methanol dehydrogenation when compared to copper supported only on titania or on ceria. © 2002 Plenum Publishing Corporation.

Multiwalled carbon nanotube-titania nanocomposites: Understanding nano-structural parameters and functionality in dye-sensitized solar cells

Mombeshora,Edwin T.; Simoyi,Reuben; Nyamori,Vincent O.; Ndungu,Patrick G.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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Nanocomposites consisting of multiwalled carbon nanotubes and titania were synthesized by two methods, namely, sol-gel and chemical vapour deposition (CVD) methods. The work takes advantage of the bridging ability of nanotechnology between macromolecules and the solid state process in engineering alternative nanomaterials for various applications including solar cell fabrication. Physical and chemical characterization of the mesoporous nanocomposites from the two synthetic methods were investigated using Raman spectroscopy, thermogravimetric analysis, Fourier transformation infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, surface characterization and X-ray diffraction analysis. Physicochemical properties in the nanocomposites such as thermal stability, pore volume, crystallinity and surface area were observed to be a subject of MWCNT: titania ratios and synthetic methods. From the CVD synthetic method, observed attributes include more uniform and smoother coating; better crystallinity and larger pore width than sol-gel method. On the other hand, nanocomposites from sol-gel synthetic method had larger surface areas, were more defective and less thermally stable than those from CVD. Nanocomposites by the CVD method performed 39.2 % more efficient than those from sol-gel in light-harvesting experiments. The study shows that the nanocomposites synthesized were more effective than titania alone when the cheaper natural dye...