Efficient peroxymonosulfate (PMS) activation by visible-light-driven formation of polymorphic amorphous manganese oxides.

Heterogeneous sulfate radical-based advanced oxidation processes (SR-AOPs) have been widely reported over the last decade as a promising technology for pollutant removal from wastewater. In this study, a novel peroxymonosulfate (PMS) activator was obtained by visible-light-driven Mn(II) oxidation in the presence of nitrate. The photochemically synthesized manganese oxides (PC-MnO) were polymorphic amorphous nanoparticles and nanorods, with an average oxidation state of approximately 3.0. It possesses effective PMS activation capacity and can remove 20 mg L acid organic II (AO7) within 30 min. The AO7 removal performance of PC-MnO was slightly decreased in natural waterbodies and in the presence of CO, while it showed an anti-interference capacity for Cl, NO and humic acid. Chemical quenching, reactive oxygen species (ROS) trapping, X-ray photoelectric spectroscopy (XPS), in-situ Raman spectroscopy, and electrochemical experiments supported a nonradical mechanism, i.e., electron transfer from AO7 to the metastable PC-MnO-PMS complex, which was responsible for AO7 oxidation. The PC-MnO-PMS system also showed substrate preferences based on their redox potentials. Moreover, PC-MnO could activate periodate (PI) but not peroxydisulfate (PDS) or HO. Overall, this study provides a new catalyst for PMS activation through a mild and green synthesis approach.