Treatment Of Typical Organochlorine Pesticides Contaminats By Persulfate With Lanthanum Ferrite Perovskite

In recent years,surface water and groundwater contaminated by the organochlorine pesticides atrazine and 2,4-dichlorophenoxy acetic acid?2,4-D?has been frequently reported.The health of creature and eco-system has been threatened by these organochlorine pesticides due to their high persistence,mobility and endocrine disrupting properties.Thus,it is urgent to develop efficient technologies to eliminate organochlorine pesticides from contaminated waters.In this study,atrazine and 2,4-D were chosen as the target pollutants.Based on LaFeO₃,Cu-doping in B site perovskite-like catalyst LaFe_1-xCu_xO₃?x=0.1,0.2,0.3,0.4,and 0.5?and Sr-doping in A site catalyst La_1-xSr_xFeO₃?x=0.2,0.5,0.8,and 1?were prepared and introduced to the peroxymonosulfate?PMS?heterogeneous activation for the pollutant degradation.The degradation efficiency of atrazine and 2,4-D and the impact factors,involving catalyst dosage,PMS concentration and initial pH were investigated.The active sites for PMS activation and activation mechanism were explored.The possible transformation of atrazine and 2,4-D were proposed.The main results are as follows:For the degradation of atrazine by LaFe_1-xCu_xO₃ catalyzing PMS,the degradation efficiency was significantly enhanced by the substitution of Cu.Atrazine of 5 mg/L was removed completely within 60 min in the presence of 0.5g/L LaFe_0.8Cu_0.2O₃ catalyst and 0.5 mmol/L PMS.The degradation efficiency of90%was remained after three consecutive experiments.The degradation of atrazine was accelerated with the increase of catalyst dosage and PMS concentration.However,it could be inhibited by excess PMS.Atrazine could be removed efficient when initial pH ranged from 2 to 10.The degradation of atrazine fitted well with the pseudo-first order kinetics.The reactive species involving hydroxyl radicals,sulfate radicals were generated during the reaction and sulfate radicals played a dominated role.Fe and Cu on the catalyst surface were acted as the active sites for PMS activation.The introduction of Cu resulted in the mixed valence state of Fe?III?/Fe?II?and Cu?II?/Cu?I?in perovskite structure,which promoted the efficiency of PMS activation.The synergistic effect between Fe and Cu could promote the cycle of the active metal.Furthermore,the surface hydroxyl groups were also participated in the PMS activation.The transformation products of atrazine were detected by LC-MS and the degradation mechanisms were further proposed.For the degradation of 2,4-D by La_1-xSr_xFeO₃ catalyzing PMS,the degradation efficiency could be remarkably facilitated by the introduction of Sr.2,4-D of 10 mg/L was removed completely within 60 min in the presence of 0.6g/L La_0.5Sr_0.5FeO₃ catalyst and 1 mmol/L PMS.The degradation efficiency of 85%was maintained after three consecutive experiments.The effect of catalyst dosage and PMS concentration on 2,4-D degradation in La_0.5Sr_0.5FeO₃/PMS system was similar with that in LaFe_0.8Cu_0.2O₃/PMS system.2,4-D could be degraded efficiently when initial pH ranged from 3 to 11.The degradation of 2,4-D also fitted well with the pseudo-first order kinetics.The reactive species generated in the reaction were hydroxyl radicals,sulfate radicals and singlet oxygen.Among them,sulfate radicals played a dominated role for 2,4-D degradation.The introduction of Sr resulted in the lower average valence state of Fe,more amounts of oxygen vacancies and higher charge transport rate.The complex between active metal and the surface hydroxyl groups was generated and then reacted with PMS resulting in the formation of radicals.The oxygen vacancies could promote the chemical bonding with PMS and was participated in the singlet oxygen generation.The transformation products of 2,4-D were detected by GC-MS and the degradation mechanisms were further proposed.