Co3O4 electronic-structure tuning via Se doping for peroxymonosulfate activation: Synergy of reactive-oxygen species generation and adsorption–desorption strength

Abstract

Increasing peroxymonosulfate (PMS) activation efficiency by Co3O4 to produce more reactive sites remains a challenge. Here, we report Se doping to simultaneously tune oxygen vacancy densities, Co2+ active site levels, and the Co3O4 3d-band center for activating PMS to degrade levofloxacin (LEV). The Se-doped Co3O4 (Se@Co3O4) was fabricated by pyrolyzing a mixture of Se powder and Co3O4 precursors. It had many more Co2+ active sites and oxygen vacancies relative to Co3O4. This favored generation of reactive oxygen species that degraded LEV in bulk solution. Density functional theory calculations revealed a downshift of the Co 3d-band in Se@Co3O4 with an enhanced electron-donating ability and an optimized adsorption–desorption strength, which increased reactive oxygen production and subsequent leave from hetero-surface to extinct LEV in bulk solution. Se@Co3O4 exhibited over 95% degradation of 10 mg/L LEV with 0.2 g/L PMS activated within 25 min at 25 °C, while Co3O4 exhibited 20% degradation under the same conditions. The first-order rate constant for LEV degradation by Se@Co3O4 was approximately 42 times that of Co3O4, and it exhibited good PMS activation over the pH range 5.0–9.0. LEV degradation conditions and effects of water matrices were optimized and explored, respectively. The Se@Co3O4/PMS system could still degrade over 85% of LEV after five cycles, as well as pefloxacin, p-nitrophenol, tetracycline and rhodamine B. This suggests its excellent universality. The potential mechanism of PMS activation by the Se@Co3O4 and probable LEV degradation routes were discussed based on the outcomes of active reactive species tests and LEV degradation intermediates confirmed by liquid chromatography-mass spectrometry. This work revealed that Se doping promoted electronic modulation in Se@Co3O4 for PMS activation, and indicated potential high-performance Fenton-like catalysts.