Uncovering the high-activity origin of sulfur doping in Co3O4 for organic pollutant degradation via peroxymonosulfate activation

Herein, a simple method for effective treatment of organic wastewater containing ofloxacin is proposed. Specifically, sulfur-doped Co 3 O 4 (abbreviated as S-Co 3 O 4 ) is first prepared and used then as a mediator to activate peroxymonosulfate (PMS). The sulfur doping can facilitate the conversion of low spin state Co to high spin state Co, thereby reducing the work function of Co 3 O 4 to improve internal electron escape probability. Meanwhile, the sulfur doping also induces to form more oxygen vacancies, decreasing interface resistance and accelerating charge transfer. As a result, the activation efficiency of PMS over S-Co 3 O 4 is enhanced. More importantly, the adsorption energy of PMS over S-Co 3 O 4 is reduced after the sulfur doping, leading to generate more S-Co 3 O 4 -PMS* complexes. Due to small activation energy, the S-Co 3 O 4 -PMS* complexes can be easily decomposed into SO 4 − and 1 O 2 . As predicted, the S-Co 3 O 4 -mediated PMS system shows excellent performance in ofloxacin degradation, and the removal efficiency is as high as 96.4 % within 20 min. In the S-Co 3 O 4 -2-mediated PMS system, the contribution rate of active species for ofloxacin degradation follows an order of SO 4 −  >  1 O 2  >  Co 4+ O > OH . Furthermore, the S-Co 3 O 4 -2-mediated PMS system with good stability exhibits strong removal ability towards other organic pollutants.