Oxygen\nVacancy-Induced Nonradical Degradation of Organics:\nCritical Trigger of Oxygen (O₂) in the Fe–Co LDH/Peroxymonosulfate\nSystem

Abstract

Ubiquitous oxygen vacancies (Vo)\nexisting in metallic compounds\ncan activate peroxymonosulfate (PMS) for water treatment. However,\nunder environmental conditions, especially oxygenated surroundings,\nthe interactions between Vo and PMS as well as the organics degradation\nmechanism are still ambiguous. In this study, we provide a novel insight\ninto the PMS activation mechanism over Vo-containing Fe–Co\nlayered double hydroxide (LDH). Experimental results show that Vo/PMS\nis capable of selective degradation of organics via a single-electron-transfer\nnonradical pathway. Moreover, O₂ is firstly demonstrated\nas the most critical trigger in this system. Mechanistic studies reveal\nthat, with abundant electrons confined in the vacant electron orbitals\nof Vo, O₂ is thermodynamically enabled to capture electrons\nfrom Vo to form O₂^•– under the\nimprinting effect and start the activation process. Simultaneously,\nVo becomes electron-deficient and withdraws the electrons from organics\nto sustain the electrostatic balance and achieve organics degradation\n(32% for Bisphenol A without PMS). Different from conventional PMS\nactivation, under the collaboration of kinetics and thermodynamics,\nPMS is endowed with the ability to donate electrons to Vo as a reductant\nother than an oxidant to form ¹O₂. In this case, ¹O₂ and O₂^•– act as the indispensable intermediate species to accelerate the\ncirculation of O₂ (as high as 14.3 mg/L) in the micro area\naround Vo, and promote this nano-confinement electron-recycling process\nwith 67% improvement of Bisphenol A degradation. This study provides\na brand-new perspective for the nonradical mechanism of PMS activation\nover Vo-containing metallic compounds in natural environments.