Degradation of benzophenone-4 by peroxymonosulfate activated with microwave synthesized well-distributed CuBi2O4 microspheres: Theoretical calculation of degradation mechanism

[Display omitted] •Well-distributed CuBi2O4 microsphere was synthesized by microwave-assisted method.•The degradation pathway of BP-4 in the presence and absence of Cl− was proposed.•The first and dominant step of BP-4 oxidation with SO4−/OH is radical addition.•The presence of Cl− did not increase the ecotoxicity of intermediates.•Feasibility of CuBi2O4/PMS was proved by micropollutants degradation in effluent. Well-distributed CuBi2O4 microspheres prepared by microwave-assisted co-precipitation method and subsequent calcination treatment were used to activate peroxymonosulfate (PMS) for benzophenone-4 (BP-4) degradation. Uniformly distributed active sites, hydroxyl groups, and the cycle of Cu(I)/Cu(II) on the surface of CuBi2O4 microspheres effectively facilitated PMS activation to generate SO4−, OH and 1O2, but 1O2 was not the dominant reactive oxygen species. The degradation mechanism of BP-4 was proposed through theoretical calculations and intermediates identification that the first and dominant step of BP-4 oxidation with SO4−/OH is radical addition reaction rather than single electron transfer. It breaks through previous reports that reaction between SO4− and electron-rich aromatic organics is mainly via single electron transfer. Ecotoxicity assessment by ECOSAR program indicated that the presence of Cl− did not increase the toxicity of intermediates because generated chlorinated intermediates are hydrophilic.