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| Author(s): |
Cibele Aparecida de Oliveira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Araraquara. 2016-07-11. |
| Institution: | Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara |
| Defense date: | 2016-06-23 |
| Advisor: | Elson Longo; Diogo Paschoalini Volanti; Carlos Eduardo Vergani |
| Abstract | |
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. (AU) | |
| FAPESP's process: | 12/09980-5 - Multifunctional TiO2@Ag2MoO4: antimicrobial and photocatalytic properties |
| Grantee: | Cibele Aparecida de Oliveira |
| Support Opportunities: | Scholarships in Brazil - Doctorate |