Construction Of Mn-Based Binary-Metal Catalysts To Activate Permonosulfate For The Removal Of Organic Phenolic Contaminants

In recent years,Advanced oxidation processes based on peroxymonosulfate（PMS）activation have been extensively studied in the field of wastewater treatment.Manganese based materials are a promising catalyst for PMS activation due to their low toxicity and high abundance.However,simple manganese oxides（Mn O₂,Mn₂O₃,Mn₃O₄,Mn O）are effective catalysts for activating PMS to degrade organic pollutants,but the conversion efficiency of high-valent Mn species generated during the reaction process to low-valent states is too slow,resulting in low catalytic efficiency.In this paper,Mn-based bimetallic catalysts were constructed and applied to activate PMS,and phenolic organics were used as target pollutants to study the interaction between transition metals and Mn species,as well as the performance and mechanism of activated PMS to degrade pollutants.The specific work carried out is summarized as follows:（1）The crednerite CuMnO₂ nanoflake was prepared and used to degrade PNP with peroxymonosulfate（PMS）as the oxidant.It was found that CuMnO₂ exhibited much higher activity than other Cu-based catalysts such as Cu O,Cu₂O,Cu Fe₂O₄ and Cu Fe O2.Under the reaction conditions of CuMnO₂ dosage of 0.2 g/L,PMS concentration of 0.65 m M,initial PNP concentration of 5 mg/L,and temperature of25°C,about 90%of PNP was removed by the CuMnO₂/PMS system within 10minutes.The catalyst still maintained a removal rate above 90%after four consecutive runs.Sulfate and hydroxyl radicals produced from PMS reduction by Cu（I）species,as well as superoxide ions and single oxygen.It was implied that the high valent Mn（III）species in the catalyst acted as Lewis acids to withdraw electron from PMS,resulting that the Cu（I）species can be easier oxidized to Cu（II）by PMS with the formation of radicals,based on the analysis of X-ray photoelectron spectroscopy（XPS）,fourier transform infrared spectroscopy（FTIR）,EPR and linear sweep voltammetry（LSV）results.（2）A ternary mullite oxide YMn₂O₅ was synthesized for bisphenol A degradation in the presence of PMS for the first time.The degradation experiments showed that YMn₂O₅ showed efficient reaction rate of 1.41 mg·min^-1·m^-2,much higher than single manganese oxides ofα-Mn O₂（0.94）,γ-Mn O₂（0.92）,β-Mn O₂（0.48）andδ-Mn O₂（0.49）,with the catalyst dosage of 0.2 g/L,PMS concentration of 0.65 m M,BPA concentration of 20 mg/L,and reaction p H of 8.2.Combined with the analysis of XPS,EPR and TG results,the higher catalytic performance of YMn₂O₅ was attributed to the large amount of surface labile oxygen species Olab（39.7%）as the main active site.Furthermore,YMn₂O₅ also exhibited higher interfacial conductivity and stronger interactions among the catalyst,PMS and BPA than other Mn O2.The results of chemical quenching experiments,EPR and open circuit potential suggested that the degradation of BPA was mainly caused by the direct electron transfer process through the reactive Olab-PMS complexes.This work demonstrated that YMn₂O₅ with enriched Olab species can be used as eco-friendly catalysts for efficient PMS activation to remove recalcitrant organic compounds in wastewater.