| TiO2 heterogeneous photocatalytic oxidation(PCO) has been successfully used in wastewater treatment and continues to be an active field of application and research since 1980's. However, there are some drawbacks, such as the low photocatalytic quantum efficiency, only more or less 4% sunlight can be used, and so on, which hamper successful application of PCO on industrial scale operation for wastewater treatment. Thus, research on improving the photocatalytic efficiency by coupling microwave technology(MW) ,ultraviolet technology(UV),ultrasound technology(US) or preparation modified nano-TiO2 catalysts is becoming one of the key research contents in PCO field nowadays.In this dissertation the recent research on the degradation of organic pollutants by PCO, MW and US technology and hybrid technologies for the treatment of chlorophenols(CPs) were reviewed at first. Then the research on the microwave assisted UV degradation (MW/UV), microwave assisted UV TiO2 photocatalytic degradation (MW/UV/P25), ultrasound assisted UV TiO2 photocatalytic degradation (US/UV/P25) were used to degrade CPs respectively. The factors which influenced on the efficiency and mechanism of degradation were investigated. Meanwhile, carbon materials (graphite, actived carbon powder, carbon nanometer tube) modified nano-TiO2 catalysts were prepared by sol-gel method and their activity were also studied. The experimentation showed that not only both MW/PCO and US/PCO technolygies might provide a potential method for industrial wastewater treatment, but also CNTs-TiO2 ,AC-TiO2 catalysts might make it possible to improve the PCO quantum efficiency.1. Results of microwave assisted oxidation degradation of 4CP are summarized as follows:â‘ The pseudo-first-order degradation kinetics of 4CP were observed for both MW/UV and MW/UV/P25. In MW/UV/P25 system, degradation rate increases with dosage of TiO2, but overdoses may cause rate retardation, degradation was slightly enhanced in acid or alkaline solutions, reaction can be enhanced while increasing the irradiation intensity, purging oxygen or adding H2O2 to the dispersions. In MW/UV system, the degradation was enhanced in alkaline solution, the reaction can be enhanced while increasing the irradiation intensity, purging oxygen or adding H2O2 to the solution.â‘¡The sequence of the degradation rate of 4CP in different system is MW/UV/P25/H2O2> MW/UV/P25> MW/UV/H2O2> MW/UV> UV/P25/H2O2> UV/H2O2 >UV/P25 > UV > MW/H2O2> H2O2. The degradation was enhanced with the MW because of signicicant synergistic effects between MW and UV,TiO2,H2O2.2. Results of microwave assisted photo-degradation of CPs are summerized as follows: â‘ Six kinds of selected CPs as 2CP, 4CP, 4C3MP, 2,4-DCP, 2,4,6-TCP, PCP were degradation in MW/UV or MW/UV/P25 system respectively. The degradation of CPs in MW/UV/P25 is more efficient than that in the MW/UV one as more free radicals(?OH) generated with the present of TiO2 conditions. The degradation is faster for monohalogenated phenols than poly-substituted phenols with an exception of 4CP and the reaction rate of degradation in is 2CP > 4C3MP > 2,4-DCP =4CP > 2,4,6-TCP > PCP the presence of MW/UV and is 4C3MP > 2,4-DCP > 2CP > 4CP > 2,4,6-TCP > PCP in MW/UV/P25. â‘¡ The degradation of 4CP in MW/UV/P25 system appears to go through the mechanism which generating intermediates as phenol,chlorobenzene,hydroquinone and benzoquinone. The main intermediates are TTCP, tetrachloro-hydroquinone and tetrachloro-benzoquinone when PCP was degraded in MW/UV/P25 method. The mechanism for the degradation of CPs involves both radical reactions and direct photolysis.â‘¢ By the use of partial least squares(PLS) method, two models for the degradation rate constants of 6 kinds of CPs were successfully developed while reacting in the the MW/UV/P25 system and MW/UV system, Q2cum of the two models are 0.8776 and 0.9545 respectively(>0.5). The PM3 results show that it is mainly the Ehomo,Elumo+Ehomo,Elumo,N ,Mw,Elumo-Ehomo, (Elumo-Ehomo)2 that determine the degradation rate constan...
|
PDF Full Text Request