Study On The Kinetics And Mechanism Of Photodegradation Of Typical Organic Pollutants

With rapid growth of economy, the categories and amounts of the organic pollutants are dramatically increased. The toxic organic chemicals polluted ecosystem and environment, and threatened the heath of human beings as well.Advanced Oxidation Processes (AOPs) have attracted much attention of many researchers because of its many advantages, such as high mineralization rate, high degradation performance, and no secondary pollutants, compared with other common waste water treatment technologies.UV/H2O2/Ammonium ferric oxalate system, a simple and convenient AOPs method was applied to carry out the following research in this paper:1) Under UV/H2O2/Ammonium ferric oxalate system, the influence factors of photodegradation of Toluidine blue (TB) were studied, which included initial concentration of TB, initial pH, H2O2concentration and ammonium ferric oxalate concentration.2) Under UV/H2O2/Ammonium ferric oxalate system, the influence factors of photodegradation of Malachite green (MG) were studied, which included initial concentration of MG, initial pH, H2O2concentration and ammonium ferric oxalate concentration.3) Under UV/H2O2/Ammonium ferric oxalate system, the influence factors of photodegradation of Phenol were studied, which included initial concentration of phenol, initial pH, H2O2concentration and ammonium ferric oxalate concentration.4) Additionally, the degradation intermediates were enriched by SPE (solid phase extraction) tubes, and then identified by GC-MS. Furthermore, the degradation mechanisms of MG and Phenol were briefly discussed based on the degradation intermediates.The experimental results indicated that:1) The degradation efficiency of TB increased with decrease of initial concentration of TB; TB showed higher degradation efficiency in acidic medium, and the optimum pH was4.0; Furthermore, the degradation efficiency of TB increased at first and then decreased with addition of H2O2concentration; with increasing the ammonium ferric oxalate concentration, the degradation efficiency of TB was also increased. Therefore, the optimum H2O2concentration was100mmol/L and the optimum ammonium ferric oxalate concentration was10.Ommol/L respectively. Additionally, UV/H2O2/Ammonium ferric oxalate system was relatively higher degradation efficiency. The results showed that when H2O2:Ammonium ferric oxalate concentration was10:2and40:4, the degradation efficiency was over than88%.2) The degradation efficiency of MG increased with decrease of initial concentration of MG; MG showed higher degradation efficiency in alkaline medium, and the optimum pH was11.0; Furthermore, the degradation efficiency of MG increased at first and then decreased with addition of H2O2concentration; with increasing the ammonium ferric oxalate concentration, the degradation efficiency of MG was also increased. Therefore, the optimum H2O2concentration was100mmol/L and the optimum ammonium ferric oxalate concentration was10.0mmol/L, respectively. Additionally, UV/H2O2/Ammonium ferric oxalate system was relatively higher degradation efficiency. The results showed that when H2O2:Ammonium ferric oxalate concentration was in the range of1～20:1, the degradation efficiency was over than90%.3) The degradation efficiency of Phenol increased with decrease of initial concentration of Phenol; Phenol showed higher degradation efficiency in acidic medium, and the optimum pH was4.0; Furthermore, the degradation efficiency of Phenol increased at first and then decreased with addition of H2O2concentration; with increasing the ammonium ferric oxalate concentration, the degradation efficiency of Phenol was also increased. Therefore, the optimum H2O2concentration was100mmol/L and the optimum ammonium ferric oxalate concentration was10.Ommol/L, respectively. Additionally, UV/H2O2/Ammonium ferric oxalate system was relatively higher degradation efficiency. The results showed that when H2O2:Ammonium ferric oxalate concentration was in the range of40:5, the degradation efficiency was over than98.89%.4) After SPE enrichment and GC-MS identification, a few degradation intermediates were founded:(dimethyl-amino-phenyl)-benzophenone and N-methyl-3-hydroxyl-aniline for MG, and1,2,3-trihydroxyl-propane for phenol, respectively.5) The degradation mechanisms are mainly involved two pathways, namely, cleavage of C-C and C-N, owing to attacking of hydroxyl radical.