In-situ Produced Manganese Dioxide Activated Persulfate Degradation Of Trimethoprim

Trimethoprim（TMP）is widely used in the medical field as an antibiotic synergist with low price and high yield.In recent years,with the frequent occurrence of epidemics,influenza and other diseases,make the production use and export of methotrexate are on the rise,antibiotics are not fully absorbed in the organism and are more often metabolized out of the body and into the natural environment.In the key control list issued by the state in 2023,such antibiotics have been listed as key pollutants and emission standards have been formulated.Therefore,it is important to study economical,efficient and reusable technologies for the degradation of Trimethoprim.In this paper,we choose to make a new ecological manganese dioxide（Mn O₂）activated sodium persulfate（PS）to degrade Trimethoprim in water,the advantages of this method are the stable nature of the catalyst,good biochemical properties,capable of activating PS at a wide range of p H;the oxidant PS is capable of generating oxidizing radicals and is easy to store and dose.In this paper,we first investigated the apparent performance of the catalyst and deter mined that the specific surface area of the new ecological Mn O₂of 178.3295m²/g was better than that of commercial Mn O₂.Then the effect of different reaction conditions on the efficiency of Mn O₂/PS in degrading TMP was investigated,and the reaction conditions were optimized and compared based on new ecological Mn O₂and commercial Mn O₂respectively,the optimal reaction conditions for the degradation efficiency of TMP by the new ecological Mn O₂/PS were obtained as follows:p H=6,new ecological Mn O₂concentration of 2 mmol/L,PS concentration of 1 mmol/L,TMP concentration of 5 mg/L,temperature 40℃;The optimal reaction conditions for the efficiency of commercial Mn O₂/PS degradation of TMP were:p H=7,commercial Mn O₂concentration of 2 mmol/L,PS concentration of 1 mmol/L,TMP concentration of 2.5 mg/L,and temperature of 40℃.In addition,the degradation profile of the new ecological Mn O₂/PS degradation TMP system based on optimal conditions was deter mined to be consistent with a pseudo first-order kinetic model,then the effects of Cl^-,NO₃^-and Humic acids（HA）on the reaction system were investigated and the degradation rate constants were calculated,and it was concluded that the magnitude of the effects of the three was Cl^-<NO₃^-<HA.The chemical burst method was used to deter mine that the main oxidizing substances in the new ecological Mn O₂/PS system were hydroxyl radicals and sulfate radicals,and the hydroxyl radicals do minated,In order to clarify the degradation path of TMP in this reaction system,the molecular configuration was first optimized using density functional theory（DFT）,and then the active sites of nucleophilic reactions and free radical reactions were calculated by Fukui functions,which showed 4C,5C,3N,15N,1N,6C,14N,and 1N atoms,most of which were located in the pyrimidine ring of TMP.The nucleus ratio m/z of the middle product was obtained by ultra performance liquid chromatography-mass spectrometry（UPLC-MS/MS）analysis,and the structural formula of the middle product was obtained from the mass to nucleus ratio and the molecular formula of the database as well as the active site analysis,finally,the three main degradation pathways of TMP were obtained after the similarity analysis of the middle product structural formula and the peak area of the middle product residence time,which mainly showed hydroxylation,demethylation,breakage of single and double bonds,and the final decomposition of TMP into small organic molecules such as m/z112 and m/z97.