Study On The Degradation Of Coumarin By PMS Activated With Iron Based Organic Framework/Copper Sulfide

As a class of organic pollutants with potential toxicity,Pharmaceutical and personal care products（PPCPs）have strong biological activity,high chemical stability,potential toxicity,biological accumulation and environmental persistence.Therefore,PPCPs can be enriched in animals and plants participating in the ecological cycle,leading to the decay of their own organs and malignant tumors.Among them,Coumarin（COU）is a kind of common PPCPs,and excessive ingestion of this chemical could greatly damage rodent livers and lead to malignant tumors.In addition,although the toxicity of COU to humans is still unclear,coumarin is in the list of class3 carcinogens in the preliminary collation reference list of carcinogens which was published by the Who International Agency for Research on Cancer.Advanced oxidation processes（AOPs）based on Peroxymonosulfate（PMS）have attracted extensive attention due to their strong oxidation capacity and wide pH application range.Iron-based metal-organic frameworks（Fe-MOFs）are considered as ideal heterogeneous PMS activators because of their characteristics of multiple catalytic active sites,open metal sites,easy functionalization,ordered pore structure,and eco-friendly.However,its unstable activation effect and poor cycling performance limit the application and development of Fe-MOFs in AOPs.Therefore,CuS was introduced into iron-based MOFs in this study to synthesize two efficient and stable heterogeneous composite catalysts for activating PMS to degrade COU.A variety of characterization methods have been attained to analyze the physicochemical properties of the catalysts,and the degradation efficiency of the catalytic system on COU was evaluated,with emphasis on the catalytic mechanism and the formation and transformation process of active species.CuS@MIL-101（Fe）composite catalyst was synthesized in situ using CuS as template and used to activate PMS and degrade COU.Through a variety of characterizations,it was identified that CuS@MIL-101（Fe）prepared by this study were spherical particles with a diameter of about 5μm.Catalytic experiments showed that CuS@MIL-101（Fe）activated PMS system could remove 100.0%COU within 10min,and the reaction rate constants were 11.1 times and 17.0 times of CuS/PMS and MIL-101（Fe）/PMS,respectively.From the results of quenching experiments and ESR analysis,it can be concluded that^·OH,SO₄^·-,O₂^·-and¹O₂were all involved in the degradation of COU,and^·OH and ¹O₂were the main reactive species in the degradation of COU.The catalytic mechanism analysis exhibited that the redox cycles of Cu（Ⅱ）/Cu（Ⅰ）,Fe（Ⅲ）/Fe（Ⅱ）and high state S/low state S,copper-iron synergistic effect and sulfur vacancies promoted the electron transfer,thus promoting the degradation of COU in the catalytic system.Secondly,MIL-88A（Fe）@CuS was composed of MIL-88A（Fe）and CuS,and used to activate PMS degrading COU in solution.Through a variety of characterizations,it was identified that the MIL-88A（Fe）@CuS prepared in this study has a rod-like crystal structure with a diameter of about 2μm and a length of about 13μm.In this part,the effect of the initial pH of solution on the degradation efficiency of COU in the system was analyzed,and the formation and transformation of active substances in the system were explained.When the initial pH is 3.0,5.0,7.0 and 9.0,the corresponding reaction rate constants are 0.903,0.729,0.650 and 0.095 min^-1.The results of ESR characterization,quenching test and estimation of steady state concentration of active substances showed that^·OH,SO₄^·-,O₂^·-and ¹O₂were all involved in the reaction process of the system.In the range of pH studied,the difference of COU degradation efficiency mainly lies in the yield of ¹O₂.When the initial pH of the solution is acidic or neutral,S_Vand lattice oxygen on 65%MIL@CuS contributed to the ¹O₂generation greatly increasing the ¹O₂yield(11.6×10^-11M)and promoting the degradation.At pH=9.0,¹O₂were primarily generated from the reaction between Cu（Ⅱ）and PMS,leading to a low ¹O₂production(1.7×10^-11M)and lower degradation.Liquid chromatography-mass spectrometry（LC-MS）was used to identify degradation intermediates of COU in two systems,and the major degradation pathways of COU were analyzed and proposed.The ecotoxicity of COU and intermediates was calculated and predicted using the ecotoxicity assessment software ECOSAR（United States Environmental Protection Agency）.The results showed that the two catalytic systems could effectively reduce the ecological toxicity of COU,but the toxicity changes and accumulation of toxicity of organic intermediates still need to be paid attention in practical application.And measures such as prolonging the degradation reaction time could better inhibit the ecotoxicity of the targeted pollutants.