Degradation 2,4-dichlorophenol By Aminopolycarboxylic Acids Modified Photo-Fenton System:Efficiency And Mechanism

Advanced oxidation processes（AOPs）have been proven to effectively remove organic pollutants from wastewater.Photo-Fenton oxidation technology is a kind of typical AOPs,which has the characteristics of simple operation,fast oxidation speed and high oxidation efficiency.However,the traditional photo-Fenton technology has some problems,such as narrow p H range,low oxidant utilization,easy to produce iron mud and secondary pollution.Considered the above facts,two different environment-friendly amino polycarboxylic acids（APCAs）,ethylenediamine-N,N’-disuccinic acid（EDDS）and nitrilotriacetic acid（NTA）were used to form complexes with iron ions,so as to develop a novel photo-Fenton system for the treatment of refractory organic pollutant 2,4-dichlorophenol（2,4-DCP）,and the degradation efficiency and mechanism were studied.Main experimental contents and conclusions are as follows:Firstly,the effects of complexation ratio of Fe and APCAs,Fe-L（in this paper,Fe-L complex is referred to as Fe-APCAs complexes）concentration,H₂O₂concentration,p H value and the initial concentration of 2,4-DCP on the APCAs modified photo-Fenton degradation 2,4-DCP were investigated.The results showed that under neutral condition,the both of two systems had a significant degradation effect on 2,4-DCP.After 120 min reaction,the degradation efficiency of 2,4-DCP was over95%.Thus,the existence of APCAs has broadened the applicable p H range of the traditional photo-Fenton system.In addition,APCAs modified photo-Fenton technology can also effectively degrade high concentrations of 2,4-DCP pollutants in water.Secondly,the influence of external factors,including inorganic ions,organic matter and actual water bodies,on 2,4-DCP degradation by APCAs modified photo-Fenton system were studied.The experimental results showed that APCAs modified photo-Fenton system effectively degraded pollutants even in the presence of common inorganic ions and organic substances.In the actual water bodies,the degradation in secondary effluent from pulp and paper mill wastewater（PPMW）was most seriously inhibited.This phenomenon was related to the chroma,TOC concentration and inorganic ion content of actual water.It is an important step to push it to industrial application to study the influence of external factors on 2,4-DCP degradation by APCAs modified photo-Fenton system.Finally,the degradation mechanism and material transformation pathway of the system were analyzed.The results showed that Fe-L complexes promoted the Fe²⁺ions production,accelerate the H₂O₂consumption and significantly enhance the degradation efficiency of photo-Fenton system.At the same time,the generation and function of radicals in the system were studied.The^·OH radicals were shown the main active species in the system,and the superoxide anion radicals(O₂^·-)affect the system degradation by affected the^·OH radicals production.Combined with these two parts,it could be concluded that APCAs not only promoted Fe（III）/Fe（II）transformation,improved iron solubility,and accelerated H₂O₂consumption,but also was a medium that produces O₂^·-radicals,thus increased the yield of^·OH radicals.Foremost,in the EDDS system,75.9%^·OH radicals were used for 2,4-DCP degradation.And in the NTA system,91.8%^·OH radicals reacted with 2,4-DCP.In addition,the degradation products of complexes and pollutant 2,4-DCP in the system were analyzed by LC-MS,and 2,4-DCP degradation pathway was analyzed by density functional theory（DFT）calculation.The results showed that the degradation of ligand EDDS and NTA were mainly caused by the C-N bond breaked,which led to a series of decomposition reactions to produce small carboxylic acids including glycine and oxalic acid and other small molecule carboxylic acids.On the other hand,2,4-DCP degradation was closely related to molecular dechlorination,which was the main initial reaction of 2,4-DCP oxidative degradation.The 2,4-DCP degradation pathway mainly includes dechlorination,dehydrogenation and hydroxylation,resulting in a series of chlorinated and hydroxylated aromatic and maleic acid fatty oxidation products,and finally mineralized into carbon dioxide and water.