Caracterização e aplicação fotocatalítica de compósitos óxidos TiO2/CuO, TiO2/ZnO E TiO2/ZrO2 sintetizados pelos processos Sol-gel e Poliol.
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Data
2018-09-17
Autores
Modesto Junior, Olayr
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Universidade Estadual Paulista (Unesp)
Resumo
O desenvolvimento de materiais cerâmicos é um campo de pesquisa cujos resultados são extremamente promissores para aplicações tecnológicas. Particularmente, no caso dos materiais nanoestruturados baseados no óxido titânio, observa-se grande potencial de aplicação em dispositivos optoeletrônicos, bem como, para processos de fotocatálise, visto que apresenta um bandgap direto de 3,2 eV. Além disso, o aperfeiçoamento das propriedades ópticas, por meio da interação entre óxidos de diferentes bandas eletrônicas, têm sido estudado por muitos autores. Por esta razão, compósitos nanoestruturados formados de dois ou mais óxidos, cujas propriedades são distintas quando isolados, têm sido sintetizados juntos e caracterizados a fim de avaliar possíveis interações sinérgicas. Neste trabalho, foram preparados e caracterizados os compósitos TiO2/CuO, TiO2/ZnO e TiO2/ZrO2. As sínteses foram realizadas pelo método Sol-gel original e pelo método Poliol modificado, e ambos os processos se mostraram propícios para a obtenção de nanocompósitos e óxidos nanoparticulados. O método Poliol produziu compósitos formados de partículas micrométricas de dióxido de titânio revestidas do segundo óxido, enquanto o processo Sol-gel resultou em material constituído de agregados de nanocristais com alta mesoporosidade. Por meio da difração de raios X dos pós tratados gradualmente até 1000 °C observou-se que a formação e cristalização dos óxidos ocorrem em temperatura mais alta quando o material é resultante do processo Sol-gel. Com a observação das fases desejadas no tratamento a 500 °C selecionou-se os materiais assim tratados para serem avaliados quanto a sua funcionalidade, especialmente na fotocatálise. Quanto ao material contendo zirconio obtido por Sol-gel, destacou-se a estabilidade da fase anatase do TiO2 até 700 °C, cerca de 200 °C acima do observado para este óxido preparado individualmente pelo mesmo processo. Em ambos os processos de síntese notou-se que a adição do segundo óxido reduz a taxa de cristalização dos óxidos comparativamente ao processo de obtenção de cada um deles isoladamente. Os bandgaps dos compósitos desviaram levemente daquele obtido para o dióxido de titânio, com exceção dos materiais contendo óxido de cobre nos quais a extrapolação de Kubelka-Munk levou a bandgaps próximos dos valores conhecidos para este óxido. Em ensaios de descoloração da solução de azul de metileno as atividades fotocatalíticas dos compósitos preparados pelo processo Sol-gel STi500, STiZn500 e STiZr500 se mostraram comparáveis, com cerca de 99% de descoloração após 120 min de exposição. Porém, a maior taxa foi encontrada para este último compósito, cuja descoloração alcançou cerca de 71 % em 30 min de exposição sob lâmpada UVC - 254nm (9W). Os compósitos sintetizados pelo método Poliol apresentaram menor atividade fotocatalítica comparativamente àqueles sintetizados pelo método Sol-gel com menor teor do segundo óxido. Dentre estes o compósito PTiZr500 foi o que apresentou maior eficiência fotocatalítica alcançando cerca de 41 % de descoloração após 120 min sob a mesma exposição.
The development of ceramic materials is a field of research whose results are extremely promising for technological applications. Particularly, in the case of nanostructured materials based on titanium oxide, there is a great potential for application in optoelectronic devices, as well as for photocatalysis processes, since it has a direct bandgap of 3.2 eV. In addition, the improvement of the optical properties through the interaction between oxides of different electronic bands has been studied by many authors. For this reason, nanostructured composites formed of two or more oxides, whose properties are distinct when isolated, have been synthesized together and characterized in order to evaluate possible synergistic interactions. In this work the TiO2 / CuO, TiO2 / ZnO and TiO2 / ZrO2 composites were prepared and characterized. The syntheses were carried out using the original Sol-gel method and the modified Polyol method, and both processes proved to be suitable for nanocomposites and nanoparticulate oxides. The polyol method produced composites formed of micrometric titanium dioxide particles coated with the second oxide, while the sol-gel process resulted in material composed of nanocrystalline aggregates with high mesoporosity. By X-ray diffraction of the powders gradually treated to 1000 °C it was observed that the formation and crystallization of the oxides occur at a higher temperature when the material is produced by the Sol-gel process. With the observation of the desired phases in the treatment at 500 °C the materials thus treated were selected to be evaluated for their functionality, especially in photocatalysis. As for the zirconium containing material obtained by Sol-gel, the stability of the anatase phase of TiO2 to 700 ° C was observed, about 200 °C above that observed for this oxide prepared individually by the same process. In both the synthesis processes it was noted that the addition of the second oxide reduces the rate of crystallization of the oxides compared to the process of obtaining each of them alone. The composite bandgap deviated slightly from that obtained for titanium dioxide, except for materials containing copper oxide in which the Kubelka-Munk extrapolation led to bandgaps close to known values for this oxide. In discoloration tests of the methylene blue solution the photocatalytic activities of the composites STi500, STiZn500 and STiZr500, prepared by the Sol-gel process, were shown to be comparable, with about 99% discoloration after 120 min exposure. However, the highest rate was found for the latter composite, whose discoloration reached about 71% in 30 min exposure under UVC - 254nm (9W) lamp. The composites synthesized by the Polyol method had lower photocatalytic activity compared to those synthesized by the Sol-gel method with lower content of the second oxide. Among these, the PTiZr500 composite showed the highest photocatalytic efficiency reaching about 41% discoloration after 120 min under the same exposure
The development of ceramic materials is a field of research whose results are extremely promising for technological applications. Particularly, in the case of nanostructured materials based on titanium oxide, there is a great potential for application in optoelectronic devices, as well as for photocatalysis processes, since it has a direct bandgap of 3.2 eV. In addition, the improvement of the optical properties through the interaction between oxides of different electronic bands has been studied by many authors. For this reason, nanostructured composites formed of two or more oxides, whose properties are distinct when isolated, have been synthesized together and characterized in order to evaluate possible synergistic interactions. In this work the TiO2 / CuO, TiO2 / ZnO and TiO2 / ZrO2 composites were prepared and characterized. The syntheses were carried out using the original Sol-gel method and the modified Polyol method, and both processes proved to be suitable for nanocomposites and nanoparticulate oxides. The polyol method produced composites formed of micrometric titanium dioxide particles coated with the second oxide, while the sol-gel process resulted in material composed of nanocrystalline aggregates with high mesoporosity. By X-ray diffraction of the powders gradually treated to 1000 °C it was observed that the formation and crystallization of the oxides occur at a higher temperature when the material is produced by the Sol-gel process. With the observation of the desired phases in the treatment at 500 °C the materials thus treated were selected to be evaluated for their functionality, especially in photocatalysis. As for the zirconium containing material obtained by Sol-gel, the stability of the anatase phase of TiO2 to 700 ° C was observed, about 200 °C above that observed for this oxide prepared individually by the same process. In both the synthesis processes it was noted that the addition of the second oxide reduces the rate of crystallization of the oxides compared to the process of obtaining each of them alone. The composite bandgap deviated slightly from that obtained for titanium dioxide, except for materials containing copper oxide in which the Kubelka-Munk extrapolation led to bandgaps close to known values for this oxide. In discoloration tests of the methylene blue solution the photocatalytic activities of the composites STi500, STiZn500 and STiZr500, prepared by the Sol-gel process, were shown to be comparable, with about 99% discoloration after 120 min exposure. However, the highest rate was found for the latter composite, whose discoloration reached about 71% in 30 min exposure under UVC - 254nm (9W) lamp. The composites synthesized by the Polyol method had lower photocatalytic activity compared to those synthesized by the Sol-gel method with lower content of the second oxide. Among these, the PTiZr500 composite showed the highest photocatalytic efficiency reaching about 41% discoloration after 120 min under the same exposure
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Palavras-chave
Síntese de nanocompósitos, Nanocompósitos com matriz de TiO2, Método Sol-gel, Método poliol, Fotocatálise heterogênea, Synthesis of nanocomposites, Nanocomposites with TiO2 matrix, Sol-gel method, Polyol method, Heterogeneous photocatalysis