Direct electron transfer process-based peroxymonosulfate activation via surface labile oxygen over mullite oxide YMn2O5 for effective removal of bisphenol A

Abstract

The development of efficient and eco-friendly Mn-based catalysts for peroxymonosulfate (PMS) activation and revealing the mechanism are highly desired for pollutants removal in wastewater. In this study, a ternary mullite oxide YMn2O5 (YMO) was synthesized for bisphenol A (BPA) degradation in the presence of PMS for the first time. Combined with XPS, EPR and TG, abundant surface labile oxygen species (Olab) with a ratio of 39.7% were identified in the mullite materials, which was higher than that for α-, β-, γ- and δ-MnO2. YMO also exhibited higher interfacial conductivity and stronger interactions among the catalyst, PMS and BPA than other MnO2. Superior performance in BPA degradation was observed with YMO, and Olab was suggested as the main active sites, for the normalized first-order rate constant was linearly dependent on the ratio of the oxygen species. 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. The influence of YMO concentration, PMS concentration, solution pH, different anions and reaction temperature was thoroughly studied. Moreover, the intermediates were identified and the possible degradation pathways were proposed. This work demonstrated that mullite oxide YMO with enriched Olab species can be used as eco-friendly catalysts for efficient PMS activation to remove recalcitrant organic compounds in wastewater.