Insight into the extremely different catalytic behaviors of asymmetric and symmetric oxygen vacancies for peroxymonosulfate activation

Oxygen vacancies (OVs) play crucial role in peroxymonosulfate (PMS) activation, however, the corresponding catalytic mechanism is ambiguous. Herein, we constructed abundant interfacial asymmetric oxygen vacancies (As-OVs) in OVs-ZnO/Co3O4 that displayed remarkable different catalytic behavior from the symmetric oxygen vacancies (S-OVs) in OVs-CoOx. Specifically, the As-OVs achieved ultra-fast contaminants degradation (~ 1 min) through both radical attack and electron-transfer process (ETP), while S-OVs exhibited sluggish kinetics for both pathways. Experimental and theoretical analyses revealed that PMS was easily adsorbed on the As-OVs to form PMS*, then ETP immediately occurred once OVs-ZnO/Co3O4 encountered with electron-rich bisphenol A. When electron-poor benzoic acid replaced bisphenol A, the peroxide bond was quickly broken to produce radicals due to the largely polarized PMS* on the asymmetric sites. Conversely, the S-OVs cannot realize rapid removal of both targets because the symmetric sites weakened ETP. This work provides atomic-level insights to understand the catalytic behaviors of OVs.