Activation Of Peroxymonosulfate Via Co/Mn-Based Metal Oxides For Degradation Of Organic Contaminants: Performance And Mechanism

Organic pollutants have many kinds and complex structures,which is one of the key object of water pollution control.Advanced oxidation method is an important means of organic pollutants treatment,and the advanced oxidation method based on persulfate activation has the characteristics of lower cost,high efficiency of treatment,and can be effectively applied to the treatment of refractory organic pollutants.Heterogeneous transition metal activated persulfate has the advantages of high activation efficiency,easy recycling,no secondary pollution and so on,and has been widely studied and applied in many areas.However,there are still many controversies about the related reaction mechanism,mainly reflected in the active species of pollutant degradation（problems faced by transition metal activation of PMS）.In this paper,two transition metals,cobalt and manganese,were selected to study the main mechanism of the degradation of organic pollutants by the activation of peroxymonosulfate（PMS）over heterogeneous catalysts related to these two metals.The main research results and contents are as follows:（1）The activation mechanism of cobalt ferrite activated persulfate was studied.Cobalt ferrite（Co Fe₂O₄）has been widely employed as a catalyst for the activation of peroxymonosulfate（PMS）,in which hydroxyl radicals（^·OH）and sulfate radicals(SO₄^·-)are generally recognized as the main reactive species responsible for the degradation of pollutants.In this study,electron transfer,radical quenching and electron paramagnetic resonance（EPR）experiments were performed to demonstrate that free radicals(^·OH and SO₄^·-)have little effect on sulfamethoxazole（SMX）degradation in Co Fe₂O₄/PMS system.Based on the above experimental results,a mechanism involving Co（II）-PMS complex both on the surface of Co Fe₂O₄ and in solution as the dominant reactive species is proposed.Furthermore,the degradation performance of SMX under different conditions were investigated to further cognize the Co（II）-PMS complex-mediated oxidation process.（2）The activation mechanism of MnO₂,Mn₂O₃ and MnO oxides by peroxymonosulfate was studied.Firstly,the performance of three kinds of commercial manganese oxides activated by peroxymonosulfate to degrade pollutants was studied.It was found that the activation efficiency order was MnO₂>Mn₂O₃>MnO,which is somewhat different from previous studies.Then,radical quenching,electron paramagnetic resonance（EPR）and PMS decomposition experiments proved that free radicals(^·OH and SO₄^·-)were not the primary active species in MnO₂,Mn₂O₃ and MnO activated PMS system,and further proposed the action mechanism of Mn-PMS complex as the main active species in the system.