Propriedades fotocatalíticas do TiO2, β-Ag2MoO4 e da heteroestrutura TiO2/Ag2MoO4: síntese e caracterização
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Data
2016-06-23
Autores
Oliveira, Cibele Aparecida de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho propôs-se sintetizar partículas fotocatalisadoras de óxido de titânio (TiO2), beta molibdato de prata (β-Ag2MoO4) e a heteroestrutura TiO2/Ag2MoO4 para principal aplicação em fotocatálise. As partículas de TiO2 e a heteroestrutura foram sintetizadas utilizando o método solvotérmico assistido por micro-ondas (SAMO), enquanto que as partículas de β-Ag2MoO4 foram sintetizadas pelo método de co- precipitação. As sínteses foram realizadas a partir das soluções diluídas dos sais de partida, em diferentes solventes, tempos de reação e temperaturas para o controle do tamanho e forma dos cristais. A atividade fotocatalítica destes materiais foi analisada para a degradação dos corantes orgânicos alaranjado de metila e rodamina 6G sob irradiação com lâmpada ultravioleta (UV) de 254 nm. Foram realizadas caracterizações por difração de raios X (DRX), espectroscopia vibracional na região do infravermelho, fotoluminescência (FL) e medida de área de superfície específica (método BET). As morfologias dos cristais foram analisadas por intermédio de microscopia eletrônica de varredura de alta resolução e feixe de íon focalizado (FIB). As propriedades ópticas foram investigadas por espectroscopia na região do ultravioleta-visível (UV-vis). Os resultados de DRX mostram uma estrutura tetragonal para os pós de TiO2 e uma estrutura cúbica do tipo espinélio para as partículas de β-Ag2MoO4. Os espectros de infravermelho apresentaram bandas de absorção caraterísticas para cada material. A bandas de FL indicaram ampla emissão com o máximo no comprimento de onda de 605 nm, correspondente à emissão na região do amarelo para os pós de TiO2. Para os pós de β-Ag2MoO4 foram observadas bandas de emissão em torno de 467 nm que corresponde à emissão na faixa do azul e também sub-bandas em 600 e 739 nm, que correspondem à emissão na faixa do amarelo e vermelho, respectivamente. Para a FL da heteroestrutura houve uma diminuição na intensidade fotoluminescente com banda de emissão mais intensa na faixa do azul, caracterizando a adsorção do β- Ag2MoO4 nas partículas de TiO2 e, na decomposição desta mesma banda foi possível observar tanto emissão no verde como no vermelho. Nos espectros de absorção óptica na região do UV-Vis foram observados band gap de 3,26 eV para os pós de TiO2 que corresponde a fase anatase sintetizada. Para os pós de β-Ag2MoO4 foi encontrado o valor de band gap de 3,33 eV, correspondente a existência de níveis intermediários de energia. Para os pós da heteroestrutura não se obteve um resultado válido para o valor de band gap devido a amostra ter coloração preta. Por fim, foi realizado o teste da concentração inibitória mínima (MIC) para as estruturas sintetizadas sendo que as partículas de β-Ag2MoO4 apresentaram melhor resultado bactericida contra a bactéria Echerichia coli (E. coli). Verificou-se, através deste estudo, que a otimização do tamanho das partículas foi importante na formação da heteroestrutura e também na degradação dos corantes orgânicos, alcançando boa atividade fotocatalítica.
This research proposed to synthesize photocatalytic particles of titanium dioxide (TiO2), beta silver molybdate (β-Ag2MoO4), and TiO2/Ag2MoO4 heterostructures for application in photocatalytic processes mainly. TiO2 particles and heterostructures were synthesized using microwave-assisted solvothermal (SAMO) method, while β- Ag2MoO4 particles were synthesized via co-precipitation method. All syntheses were made from the starting dilute salt solutions in different solvents, temperatures, and reaction times in order to control the size and the shape of the crystals. Photocatalytic activity of these materials was analyzed for degradation of the organic dyes methyl orange and rhodamine 6G under ultraviolet light (UV) irradiation at 254 nm. Characterizations were performed using X-ray diffraction (XRD), infrared vibrational spectroscopy, photoluminescence (PL) and specific surface area determination (BET method). The morphologies of the crystals were examined by high resolution scanning electron microscopy (HRSEM) and focused ion beam (FIB). The optical properties were investigated by UV-Vis spectroscopy. XRD results showed a tetragonal structure for the powders of TiO2, and a cubic spinel structure for β-Ag2MoO4 particles. Infrared spectra presented characteristic absorption bands for each material. PL bands indicated a broad emission with a maximum at wavelength of 605 nm, which corresponds to the emission in the yellow region for TiO2 powder. Regarding the β-Ag2MoO4 powders emission bands were observed at a wavelength of 467 nm corresponding to the emission in the blue range, and subbands at 600 and 739 nm which correspond to the emissions in the yellow and red range, respectively. For the PL heterostructures there was a decrease in the photoluminescence intensity, with more intense emission band in the blue range, characteristic of adsorption of β-Ag2MoO4 on TiO2 particles. When this band was decomposed it was observed emissions on both green and red ranges. A band gap of 3,26 eV were observed in the optical absorption spectra in the UV-Vis region for TiO2 powders which corresponds to the synthesized anatase phase. For the β- Ag2MoO4 powders the band gap value found was of 3,33 eV, corresponding to the existence of intermediate energy levels. Due to the fact that the powders of the heterostructure have black color, a valid result for its band gap was not obtained. Finally, a minimum inhibitory concentration (MIC) test was conducted for the synthesized structures wherein the particles of β-Ag2MoO4 showed a better antibacterial effect against Escherichia coli (E. coli). The findings of this study demonstrated that the optimization of particle size was important on the formation of the heterostructure and on the degradation of organic dyes as well, achieving a good photocatalytic activity.
This research proposed to synthesize photocatalytic particles of titanium dioxide (TiO2), beta silver molybdate (β-Ag2MoO4), and TiO2/Ag2MoO4 heterostructures for application in photocatalytic processes mainly. TiO2 particles and heterostructures were synthesized using microwave-assisted solvothermal (SAMO) method, while β- Ag2MoO4 particles were synthesized via co-precipitation method. All syntheses were made from the starting dilute salt solutions in different solvents, temperatures, and reaction times in order to control the size and the shape of the crystals. Photocatalytic activity of these materials was analyzed for degradation of the organic dyes methyl orange and rhodamine 6G under ultraviolet light (UV) irradiation at 254 nm. Characterizations were performed using X-ray diffraction (XRD), infrared vibrational spectroscopy, photoluminescence (PL) and specific surface area determination (BET method). The morphologies of the crystals were examined by high resolution scanning electron microscopy (HRSEM) and focused ion beam (FIB). The optical properties were investigated by UV-Vis spectroscopy. XRD results showed a tetragonal structure for the powders of TiO2, and a cubic spinel structure for β-Ag2MoO4 particles. Infrared spectra presented characteristic absorption bands for each material. PL bands indicated a broad emission with a maximum at wavelength of 605 nm, which corresponds to the emission in the yellow region for TiO2 powder. Regarding the β-Ag2MoO4 powders emission bands were observed at a wavelength of 467 nm corresponding to the emission in the blue range, and subbands at 600 and 739 nm which correspond to the emissions in the yellow and red range, respectively. For the PL heterostructures there was a decrease in the photoluminescence intensity, with more intense emission band in the blue range, characteristic of adsorption of β-Ag2MoO4 on TiO2 particles. When this band was decomposed it was observed emissions on both green and red ranges. A band gap of 3,26 eV were observed in the optical absorption spectra in the UV-Vis region for TiO2 powders which corresponds to the synthesized anatase phase. For the β- Ag2MoO4 powders the band gap value found was of 3,33 eV, corresponding to the existence of intermediate energy levels. Due to the fact that the powders of the heterostructure have black color, a valid result for its band gap was not obtained. Finally, a minimum inhibitory concentration (MIC) test was conducted for the synthesized structures wherein the particles of β-Ag2MoO4 showed a better antibacterial effect against Escherichia coli (E. coli). The findings of this study demonstrated that the optimization of particle size was important on the formation of the heterostructure and on the degradation of organic dyes as well, achieving a good photocatalytic activity.
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Palavras-chave
Fotocatálise, Corantes, Heteroestrutura, Dióxido de titânio, Photocatalysis, Dyes, Heterostructure