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Mechanism Study of Photocatalytic Degradation of Several Hazardous Materials Using TiO2 Based Nano-sized Multi-Functionals Photocatalyst

Elahifard, Mohammad Reza | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42807 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Gholami, Mohammad Reza; Haghighi, Saeid
  7. Abstract:
  8. Apatite-coated Ag/AgBr/TiO2 was prepared by deposition of Ag as noble metal to generate electron-hole pairs by extending the excitation wavelength to visible light region, AgBr as photo-sensitizer to increasing yield of photo catalyst, and apatite as adsorption bio ceramic for adsorbing pollutants and micro organisms respectively. The bactericidal experiments in dark media indicated that only novel catalyst show inhibiting growth of bacteria. In this case Transmission electron microscopy image illustrated that catalyst nano particles adhere to the outer membrane of the cell and acts as inhibitor to nourish of bacteria from around media. The mechanism for deactivation E-Coli and B.Sub in the dark can be related to the linkage between phosphate group and the polysaccharide and peptidoglycane layers of the outer membrane of the cells respectively. The novel catalyst also showed approximately two times photo catalytic activity compare with Ag/AgBr/TiO2 photo catalyst under visible light irradiation. The inactivation of E.coli is due to the ability of catalyst to adhere the outer cell in addition of destruction of the cell wall by various reactive species (O˙2, HO˙,H2O˙,…). Also phenol oxidation was achieved under visible light and UVA irradiation using apatite coated Ag/AgBr/TiO2 powders. Under UVA illumination the produced •OH from hole of TiO2 valance band is responsible for photodegredation of phenol, and under visible light AgBr acts as photoactive component of catalyst, that can not produce •OH and oxidize the phenol. In the final section, two types of nano-sized photo-catalyst, TiO2 P-25 and ap/Ag/AgBr/TiO2 were used for decolorization of acid blue 92 in dark, visible light and UV media. Under UV and visible-light, the effect of three possible photo-degradation processes of acid blue 92 including photo-catalytic degradation, self-photo-sensitization and direct photolysis were studied. Results show that in UV/photo-catalysts, photo-catalytic degradation is the major process for photo-decolorization. However in presence of TiO2 P-25, self-photo-sensitization has the major role under visible light. Due to the presence of AgBr as photo-active center in ap/Ag/AgBr/TiO2, the main process is photo-catalytic degradation in visible light. By using iso-propanol and catalase as •OH and H2O2 scavenger, the results showed that in ap/Ag/AgBr/TiO2, •OH and hole act as acid blue 92 oxidizer, while in TiO2 P-25, •OH, hole and also H2O2 play that role. Meanwhile acid blue 92 showed a different regular behavior with KI in photo-degradation processes. This phenomena assisted by formation of I2 in photo-catalytic process. I2 increases the reaction rate (by direct oxidation) and shifts the maximum wavelength absorption of acid blue 92.

  9. Keywords:
  10. Photo Oxidation ; Titanium Oxide ; Pollutant ; Apatite ; Microorganisms ; Adsorption Material ; Photosensitive Material ; Photocatalyst ; Acid-Blue 92 ; Poly-Functional Photocatalyst ; Radical Reactive Species

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