Oriented generation of singlet oxygen in H2O2 activation for water decontamination: regulation of oxygen vacancies over α-MnO2 nanocatalysts

The importance of nonradical Fenton-like catalysis in environmental fields has motivated research for effective singlet oxygen (O-1(2)) production, but realizing the accurate design and regulation of active sites for manipulating oriented O-1(2) generation is still highly challenging. In this study, alpha-, beta-, and gamma-MnO2 catalysts with different oxygen vacancy (OV) abundance were fabricated to activate H2O2 to generate O-1(2) for the degradation of oxytetracycline (OTC). The OV-rich a-MnO2 had a high OTC removal efficiency (>93.5%) at the pH range from 4.0 to 11.0. Moreover, alpha-MnO2 exhibited great applicability for a real water matrix, and the total removal of various kinds of emerging contaminants from hospital wastewater reached up to 97.4%. The excellent performances of alpha-MnO2 were attributed to the rich contents of OVs that induced the oriented generation of O-1(2). Theoretical density functional theory (DFT) calculations validated that the OV-rich alpha-MnO2 had the highest H2O2 adsorption ability (-1.39 eV) and the lowest energy barrier (0.41 eV) for the dissociation of *OH to form the *O intermediate, which promoted the oriented formation of O-1(2). This work provides a strategy of manipulating the oriented generation of O-1(2) towards water decontamination via regulating the abundance of oxygen vacancies in alpha-MnO2 nanocatalysts.