Unravelling the synergy of Eu dopant and surface oxygen vacancies confined in bimetallic oxide for peroxymonosulfate activation

The rational regulation of electron transfer between Co-based catalysts and peroxymonosulfate (PMS) plays a key role in the photo-Fenton catalytic oxidation process. In this study, a novel Eu-doped ZnCo₂O₄ composite was successfully prepared via a simple hydrothermal calcination method, and firstly used for PMS activation to degrade 1,1-diamino-2,2-dinitroethene (FOX-7). Among all samples, Eu_0.4-ZnCo₂O₄ exhibited remarkable PMS activation performance, which was about 5.67 times higher than that of undoped ZnCo₂O₄. The enhanced catalytic performance could be attributed to the generation of abundant oxygen vacancies (OVs), which greatly promoted the separation of carriers and accelerated the cycling of the Co³⁺/Co²⁺ redox pairs. The corresponding Co³⁺/Co²⁺ and oxygen defects/lattice oxygen (O_Def/O_Lat) ratios regulated catalytic-activity relationship were successfully established by regression analysis. Radical quenching tests and electron paramagnetic resonance (EPR) revealed that non-radical pathway dominated the degradation process, and singlet oxygen (¹O₂) was the main active species. Importantly, theoretical calculations demonstrated that the synergy of doping and OVs could effectively improve adsorption energy and enhance electron transfer for promoting the activation of PMS. This study offers a deep insight into the catalytic reaction mechanism and provides a new strategy for developing heterogeneous photocatalysts in activating PMS for environmental remediation.