Study On The Performance And Mechanism Of Sulfamethoxazole Degradation By Activating Periodate With Different Crystalline MnO₂

Sulfamethoxazole（SMX）,one of the typical antibiotics used in humans and livestock,is often detected in effluent from sewage treatment plants and natural water bodies.Compared with traditional wastewater treatment technology,advanced oxidation technology（AOPs）can degrade antibiotic pollutants in water efficiently and green.Among them,the advanced oxidation technology of periodate（PI）based on the activation of manganese dioxide（MnO₂）has the ability to efficiently degrade organic pollutants,but the catalytic mechanism and active site of the MnO₂ activated PI system are still unclear and controversial.Therefore,in this study,SMX was selected as the target pollutant and three different crystalline MnO₂（α-MnO₂,β-MnO₂ andγ-MnO₂）were used as catalysts to further study the performance and catalytic mechanism of SMX degradation by MnO₂ activated PI system.The main research results are as follows:（1）α-MnO₂,β-MnO₂ andγ-MnO₂ were characterized by XRD,XPS and BET.The results of the control experiment showed that different crystal MnO₂ had better catalytic capacity for PI,but there were some differences.The catalytic efficiency was in order ofγ-MnO₂>α-MnO₂>β-MnO₂.（2）The effects of operating parameters（catalyst dosage,PI dosage,initial p H value,initial concentration of SMX）,natural water composition(Cl^-,SO₄^2-,HCO₃^-,PO₄^3-,NO₃^-,Ca²⁺,Mg²⁺and HA)and actual water background on SMX degradation performance of MnO₂/PI system were studied.It was found that the dosage of MnO₂ was proportional to the degradation efficiency of SMX,while the change of PI dosage had no effect on the degradation efficiency of SMX.MnO₂/PI system can effectively degrade SMX in the initial p H range of 3.0～9.0.The MnO₂/PI system is less affected by natural water composition and actual water body,and only PO₄^3-has a certain inhibitory effect.The cycle life experiment and the XPS characterization of MnO₂ before and after the reaction verified that MnO₂ had good life and stability.In addition,it was found that MnO₂/PI system has A strong selective degradation ability for electron-rich pollutants（SMX,SIZ,bisphenol A,etc.）,and no I₂、I₃^-and HOI generation was detected.（3）It was proved that^·OH、¹O₂、O₂^·-and IO₃^·were not produced in the system by radical quenching experiment,chemical probe experiment and EPR test.Combined with the results of pre-mixing experiment,Raman experiment,electrochemical experiment and salt bridge experiment,the mediated electron transfer pathway of SMX degradation by MnO₂/PI system was further explained,in which the highly active intermediate complex（MnO₂/PI*）was the main active oxidizing substance.The surface Mn（IV）was confirmed as the active site by quantitative structure-activity relationship.（4）The possible degradation pathway of SMX in MnO₂/PI system was proposed based on the intermediates and degradation mechanism.Microtox（?）has demonstrated that MnO₂/PI system can effectively reduce the toxicity of SMX.