Degradation Efficiency And Mechanism Of Halogenated Phenolic Organic Pollutants Under UV/PDS And UV/H₂O₂ Advanced Oxidation Processes

In recent years,Halophenols?HPs?have been frequently detected in the water environment,which makes more and more attention and research.Advanced oxidation processes?AOPs?have been proved to have a good removal effect on all kinds of organic pollutants,among which the AOPs based on hydroxyl radical?HO^·?and sulfate radical(SO₄^·-)were the research hotspot at home and abroad.The production of SO₄^·-and HO^·from PDS and H₂O₂ by UV catalysis has the advantages of energy saving,environmental protection,simple operation and significant effect,which has a good prospect in the removal of HPs.UV/peroxydisulfate?PDS?and UV/hydrogen peroxide?H₂O₂?could effectively degrade halophenols,while information about the discrepancies of the concerned degradation kinetics and mechanism in these two processes was limit.In order to better understand this problem,this paper selected two typical HPs?bromophenol and chlorophenol?as the research object,and the degradation of HPs in UV/PDS and UV/H₂O₂ were investigated and compared.The results showed that in the UV/PDS system,the reaction rate constants(k_obs)of 2-BP,3-BP,4-BP,2-CP,3-CP and 4-CP were 0.0471,0.0282,0.0542,0.0345,0.0255 and 0.0386 min^-1.In the UV/H₂O₂ system,the k_obs of 2-BP,3-BP,4-BP,2-CP,3-CP and 4-CP were0.0301,0.0348,0.0379,0.0238,0.0330 and 0.0360 min^-1.The results showed that the degradation rates of HPs with different substitution positions in UV/PDS process were in order of para-substituted>ortho-substituted>meta-substituted,while in UV/H₂O₂process these rates were in order of para->meta->ortho-.These discrepancies were ascribed to the different reaction activity of SO₄^·-and HO^·with HPs,which were calculated based the competition method.Further density functional theory?DFT?calculation suggested that SO₄^·-was more readily to react with HPs via electron transfer compared with HO^·.The effects of background materials?such as Cl^-,HCO₃^-and natural organics?NOM??on the degradation of HPs in UV/PDS and UVH₂O₂ systems were investigated.The results showed that the presence of several background substances inhibited the degradation of halogenated phenolic organic pollutants in two kinds of advanced oxidation systems,mainly because these substances had certain scavenging effects on free radicals.The degradation products of pollutants were analyzed by mass spectrometry,and the intermediate products and final products were identified.Then according to the product speculated reaction path.Finally,the oxidation products and reaction paths produced by the degradation of HPs by UV/PDS and UV/H₂O₂ oxidation systems were compared and analyzed.