Síntese e caracterização de TiO2 puro e modificado para aplicações ambientais

• Ano de defesa: 2012
• Autor(a) principal: Moreira, Elizabeth Lima
• Orientador(a): Santos, Joana Mara Teixeira
• Banca de defesa: Araujo, Lucia Regina Raddi de , Maria, Luiz Cláudio de Santa , Carvalho, Marcos de Castro
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade do Estado do Rio de Janeiro
• Programa de Pós-Graduação: Programa de Pós-Graduação em Química
• Departamento: Centro de Tecnologia e Ciências::Instituto de Química
• País: BR
• Palavras-chave em Português: Titânia; TiO2; óxidos mistos; titânias modificadas com SiO2 e dopadas com N; método sol-gel; fotocatálise heterogênea
• Palavras-chave em Inglês: Titania; TiO2; mixed oxides; silicon-modified titania and doped with N; sol-gel method; heterogeneous photocatalysis
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA
• Link de acesso: http://www.bdtd.uerj.br/handle/1/15773

Photocatalysts based on modified titanium dioxide nanoparticles yield potential solutions for the mineralization of organic pollutants in aqueous media. Modifiers agents have been exten-sively investigated with the aim of promoting photoactivation by visible light. In a fundamen-tal level so far, structural, textural, and optic modifications caused by inserting silicon and nitrogen in the titania lattice, were studied. Nanostructured pure and modified titania (TiO2), mainly modified titania with silicon (TiO2-SiO2), with atomic ratios, Si/Ti, of 0.1, 0.2, and 0.3, were synthesized by the sol-gel method acid hydrolysis of titanium(IV) isopropoxide and tetraoxisilane. The developed synthetic methodologies tried to adhere to the Green Chemistry principles, not being necessary the use of inert atmosphere and elevated temperature and pressure; that was achieved, mainly, by the use of sonication. Silicon-modified titania doped with nitrogen (TiO2-SiO2-N) were obtained by pre-treating TiO2-SiO2 at 500 °C in a air stream, then at 600 °C in an ammonia (NH3) stream for 1-3 h and, after cooling, annealing at 400 °C in a air stream. Distinct samples were characterized as a dry powder, after calcination at 400 600 °C, by X-ray diffraction, nitrogen adsorption, scanning electronic microscopy, and UV-Visible diffuse reflectance spectroscopy. Pure titania, primarily obtained by varying the hydrolysis ratio, were predominantly crystallized as anatase up to 600 °C with traces of broo-kite present up to 500 °C. Rutile was identified over 600 °C as a minor phase, but presenting crystal sizes significatively larger than the estimated ones for anatase crystals. Silicon-modified titania up to 20% silicon showed a remarkable thermal stability, highlighted by the sole presence of anatase up to 900 °C. It was also observed the formation of macropores with an average diameter of 55 nm after calcination at 400 °C, unlike the other samples. Small contents of silicon promoted high surface areas in the calcinated titania, probably due to the a pronounced containment of the crystals growth rate. Pure and silicon-modified titania ob-tained with a hydrolysis ratio (H2O:Ti) of 25:1 presented medium mesopores with the same size of the crystals. Silicon-modified titania doped with nitrogen showed visible absorption in the 400-480 nm range, and a slight decrease of the band gap energy for the electronic transi-tions considered. Titania calcinated at 300-400 °C presented a photocatalytic performance similar to Degussa s P25 under UV irradiation, in the degradation of the azo dye Reactive Yellow 145 in aqueous solutions at pH 5 and 20±1°C