Efficient activation of peracetic acid by defect-engineered MoO2-x: Oxygen vacancies and surface Mo(Ⅴ)-mediated electron transfer processes

Abstract

The role of defect regulation of transition metal catalysts in peracetic acid (PAA) activation is equivocal. To reveal the corresponding mechanism, this work provides a high-efficiency and eco-friendly catalyst (MoO_2-x) for PAA activation by introducing various degrees of oxygen vacancies on the MoO₂ surface. Interestingly, 95.83% of tetracycline (TC) is rapidly degraded by MoO_2-x with rich oxygen vacancies within 20 min via PAA activation, which is superior over that of MoO_2-x with poor oxygen vacancies and other typical oxidants (H₂O₂, SO₃²⁻, S₂O₈²⁻, HSO₅⁻, IO₄⁻). In addition, the defect-regulated MoO_2-x exhibits good de-biotoxicity towards TC. Moreover, MoO_2-x shows satisfactory purification of various contaminants and actual pharma wastewater. Active species identification suggests that the electron transfer process triggered by the active complex (MoO_2-x−PAA*) of PAA bonded on the MoO_2-x surface plays the dominant role in TC degradation, while ^•OH plays a minor role. Mechanism analysis reveals that oxygen vacancies play an indispensable role in accelerating the adsorption and complexation of PAA as well as improving electrical conductivity. Active site analysis demonstrates that Mo(Ⅴ) on the MoO_2-x surface acts as an electron shuttle and is the main PAA activation site. This work provides a new approach into the application of MoO₂ in hospital wastewater purification via defect engineering.