Establishment And Research Of Ozone Peroxymonosulfate Coupling Catalytic Oxidation System

Ozone peroxymonosulfate（O₃/PMS）coupling catalytic oxidation system has received extensive attention from researchers because it not only has the advantages of ozone catalytic oxidation system and persulfate oxidation system,but also can make up for the shortcomings of the two.However,there are also problems such as the lack of efficient and stable catalysts,the optimal operating conditions of the system and the catalytic mechanism to be determined.Therefore,this article further explores the O₃/PMS system in view of the issues raised above.The Box-Behnken Design in Design Expert 12.0 software takes the concentration of impregnating solution,calcination time and calcination temperature during the preparation of Mn-Fe/GAC catalyst as independent variables,and takes the TOC removal rate of the system as the response value to design the response surface method to optimize the catalyst preparation conditions.It is finally determined that the optimal preparation conditions of the catalyst are:the concentration of the impregnating solution is 1.25 mol/L,the calcination time is 2 h,and the calcination temperature is 497℃.The Mn-Fe/GAC catalyst was determined that the active material loaded on it was one or a mixture of Mn O,Fe₂O₃,and Mn Fe₂O₄.The operating conditions of the O₃/PMS coupling catalytic oxidation system and the stability of the catalyst are explored.The optimal operating conditions of the system are as follows:initial p H=3,ozone gas volume 0.8 L/min,ozone concentration30 mg/L,PMS concentration 5 mmol/L,Mn-Fe/GAC catalyst dosage 2 g/L.The removal of TOC of the system is 71.3%under these conditions.The influence of different anions and natural organic matter on the system is obtained,Cl^->H₂PO₄^->HA>HCO₃^-.The catalytic effect of the system is reduced to 62.1%of the initial effect with three times usages of the Mn-Fe/GAC catalyst,and further improvements and optimizations will be made to enhance its reusability.The catalytic path and mechanism of the catalyst are explored.It is concluded that the catalytic path of the catalyst may be as follows.It catalyzes O₃ to generate more active free radicals,and the free radicals further activate PMS to generate more active free radicals to attack organic pollutants in the system.The catalytic mechanism of the catalyst may be as follows.The activation and catalytic process of PMS and O₃ takes place on the surface of the catalyst.The Mn-Fe/GAC catalyst first catalyzes the decomposition of O₃ adsorbed on the surface of the catalyst,and then further activates the PMS through the generated active free radicals such as·OH.Mn-Fe/GAC can bind a large number of hydroxyl groups,and provide hydroxyl groups to nearby Mn（II）during the catalytic process to further promote the activation of PMS.Both Mn²⁺and Fe³⁺in the Mn-Fe/GAC catalyst provide electrons to the PMS to promote its decomposition to produce SO₄^·-,and then the high-valence states of Mn and Fe are reduced by HSO₅^-,completing the metal redox cycle.The redox cycle of metals promotes the generation of free radicals in the system.