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Investigation and Optimization of Degradation Process of Contaminants of Chemical Industrial Wastewater Using Enhanced Nanophotocatalysts under Visible and Solar Light

Feilizadeh, Mehrzad | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47371 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Vossoughi, Manoochehr; Aalemzadeh, Iran
  7. Abstract:
  8. Photocatalytic degradation is one of the developing modern and effective methods for decontamination of hazardous pollutants of chemical industrial wastewater. This method has several advantages including the possibility of using free and sustainable energy of sun. However, it is still needed to active photocatalysts under solar light and also the enhancement and optimization of operating parameters, and consequently, these topics are selected as goals of the present thesis. Accordingly in this research, first, to obtain a photocatalyst that is highly efficient (especially under visible and solar light), multi-doping and polyethylene glycol (PEG) were used and for the first time, Ag-S/PEG/TiO2 nanophotocatalyst was synthesized. Morphologies and microstructures of this powder were characterized by means of XRD, BET, SEM, TEM, EDX, PL, FTIR, XPS and the photocatalytic test, and this photocatalyst was compared with Ag-S/TiO2 and TiO2. The results show that simultaneous doping of sulfur and silver and also adding PEG decrease the crystal and particle sizes. In addition, the multi-doping significantly increased the visible light absorption. EDX, FTIR and XPS analysis confirms the doping of sulfur and silver as well as success of the synthesis. On the other hand, decontamination efficiency of methylene blue (which is one of the model and common pollutants for photocatalytic test) under visible light using active Ag-S/TiO2 photocatalyst was about 4.8 times of that by undoped TiO2 and the efficiency using Ag-S/PEG/TiO2 was 45% more than that by Ag-S/ TiO2. Furthermore in this thesis, the design of experiment based on the response surface methodology (RSM) was utilized to investigate effects of main operating parameters on the photocatalytic degradation of 2-nitrophenol (2-NP, one of the toxic and hazardous pollutants) as well as to calculate the optimum values of the parameters. For enhancement of the degradation of 2-NP under solar light, the influence of adding H2O2 to Ag-S/PEG/TiO2 was analyzed and it was indicated that adding appropriate amount of H2O2 to the solution can significantly increase the photocatalytic efficiency (up to 1.5 times in the case of 2-NP degradation). Then, for the first time, the interaction effect between potassium perdisulfate (PDS), H2O2 and the nanophotocatalyst was investigated. Analysis of variance of the results show that interaction effect between PDS and H2O2 is considerable and the simultaneous use of them can increase or decrease the efficiency compared to using just one of them. Although adding photocatalyst to solution containing PDS and H2O2 does not have considerable effect on the interaction effect, it can increase the degradation efficiency 2-fold. Study of photocatalytic disinfection under visible light show that this technique is a proper and effective method for the disinfection. Effects of important operating parameters of this process were investigated and optimized using RSM and ANOVA. Moreover in this research, it was tried to enhance the conversion rate of the hazardous material of aniline to non-hazardous and valuable products (especially azoxybenzene). For this purpose in a new work, M-600 and H2O2 were used. It was found that the combination of M-600 and H2O2 has surprising synergistic effects on the significant enhancement of the conversion rate of aniline and selectivity of azoxybenzene. For more study of these valuable results, aniline oxidation was investigated during the reaction and in different concentrations of M-600 and H2O2. In addition, new and in detail mechanisms are proposed for aniline oxidation, in a way that all the obtained results of this research in the field of aniline oxidation are in accordance with the mechanisms and can be explained using them
  9. Keywords:
  10. Hydrogen Peroxide ; Experiments Design ; Nanophotocatalyst ; Multi-Doping ; Solar Degradation ; Perdisulfate

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