Specific activation pathways of peroxymonosulfate to facilitate singlet oxygen evolution via hole-induced oxidation and hydroxyl radical disproportionation

This work investigated a novel pathway for selective singlet oxygen (¹O₂) evolution through peroxymonosulfate (PMS) activation without O₂/·O₂^- participation. The titanium dioxide/graphene/tri-iron tetroxide (TiO_2-x/rGO/Fe₃O₄, TRF_-5–500) nanomaterial with specific oxygen vacancies concentration was prepared to evaluate the crucial role of directed separation of photogenerated electron-hole (e^--h⁺) pairs in the PMS activation for imidacloprid degradation by quenching and probe experiments, in situ spectroscopy, and site-specific adsorption energy calculations. The TRF_-5–500/PMS system achieved 99.9 % removal of imidacloprid under high ¹O₂ generation (2.44 μmol/L) within 30 min and demonstrated stable removal of > 80 % of pollutants within 2 h under natural sunlight in an extended plate reactor. The electron transfer mechanism suggests that h⁺ could oxidize the adsorbed PMS on Ti sites to promote substantial ¹O₂ evolution, while the self-disproportionation of hydroxyl radicals generates additional ¹O₂. This work provides a potential strategy for selectively regulating reactive oxygen species and for practical wastewater treatment.