Study On Activation Of PMS By Scaly Co-Mg-Mn Oxides For The Degradation Of Orange Ⅱ: Performance And Mechanism

In recent years,dye wastewater has gradually become an environmental pollution problem that cannot be ignored.It would cause harm to the ecological environment and human health inevitably.Usually,it is difficult to degrade organic dyes,but the persulfate-based advanced oxidation process（AOP）can generate sulfate radicals with high oxidation activity,so it has great application potential in the eliminating organic dyes.Transition metals can effectively activate persulfate to generate active radicals.Therefore,developing catalytic materials based on transition metal with high catalytic performance and environmental friendliness is of great significance for the treatment of organic wastewater.In this study,layered metal oxides(Co_xMg_3-xMn-LDO)containing Co,Mg,and Mn were prepared by coprecipitation-calcination method and used to activate peroxymonosulfate（PMS）for the degradation of the azo dye Orange II.The following conclusions are obtained:（1）The results of material characterization showed that a hydrotalcite-like intermediate material CoMg₂Mn-LDH with a thin lamellar structure had been successfully prepared.After calcination,a thickly scaly structure of CoMg₂Mn-LDO had been formed,the main component of which was the mixed oxides of Mn Co₂O₄ and Mg O.Through the comparison of material stability and catalytic ability,the suitable material synthesis ratio was determined to be Co:Mg:Mn=1:2:1,and the pseudo-first-order kinetic degradation rate constant(k_obs)of orange II in the CoMg₂Mn-LDO/PMS system could reach 0.539 min^-1.（2）By conducting single-factor influence experiments of orange II catalytic degradation,it was found that the cost-effective degradation efficiency can be obtained by controlling the dosages of CoMg₂Mn-LDO and PMS in an appropriate range.The reaction system showed wide p H adaptability.When the initial p H value ranged from 3.0to 11.0,more than 97%of Orange II（20 mg/L）could be degraded within 15 minutes,and the degradation rate increased with the increase of p H.This system can also be applied to the degradation of high-concentration pollutants,such as the degradation efficiency of 60mg/L orange II can reach 91.6%within 15 minutes.5 mmol/L of coexisting anions Cl^-,NO₃^-,and SO₄^2-can reduce the degradation rate of Orange II in the system.CoMg₂Mn-LDO has good reusability and wide applicability.It can be efficiently circulated four times,and all the degradation efficiencies of Orange II exceeded 97%within 15 minutes.In addition,the CoMg₂Mn-LDO/PMS system can not only efficiently degrade a variety of organic dyes but also degrade other refractory organic pollutants.For example,the degradation efficiencies of dyes such as Orange II,Rhodamine B,and Methyl Orange in this system all exceeded 95%within 15 min.The degradation efficiency of tetracycline hydrochloride was close to 70%,and higher degradation efficiency can be obtained by prolonging the reaction time.（4）In terms of mechanism,multiple free radicals generated by the synergistic catalysis among Co,Mg,and Mn were responsible for the high catalytic performance of CoMg₂Mn-LDO.Through free radical quenching experiments and EPR characterization,it was found that the main active oxygen species for the oxidative degradation of Orange II were sulfate radical,hydroxyl radical,and superoxide radical,and sulfate radical was the dominant one.Based on the results of XPS analysis,UV-vis full spectrum scanning,and LC-MS intermediate product analysis,the activation mechanism of PMS by CoMg₂Mn-LDO and possible degradation pathways of Orange II in this system were proposed.In summary,CoMg₂Mn-LDO,which has good reusability and wide applicability,can efficiently activate PMS to degraded organic dyes in the aqueous environment and has high application potential in the treatment of refractory wastewater.