Nitrogen vacancies induce sustainable redox of iron-cobalt bimetals for efficient peroxymonosulfate activation: Dual-path electron transfer

Abstract The construction of surface defect was a promising modification strategy to accelerate peroxymonosulfate (PMS) activation mediated by metal for water purification, but intrinsic impact on electron transfer path has been unclear. In this study, nitrogen vacancies (Vn) were introduced into graphite carbon nitride and coupled with iron-cobalt bimetals (FeCoOx/CN-Vn). Experimental and theoretical results confirmed that Vn not only provided abundant electrons to reduce Fe(III)/Co(III) into Fe(II)/Co(II), but also induced the extraction of electrons from pollutant to electron-poor Co(III) for a faster Co(III)/Co(II) cycle. The sustainable dual-path electron transfer effectively overcame the obstacle of low-valence metal regeneration in conventional PMS-based oxidation, increasing the degradation rate constant of tetracycline hydrochloride, a typical refractory pollutant, from 0.2479 to 0.6674 min−1 in the first 2 min. The impacts of environmental factors (pH, PMS dosage, types of oxidants, water matrix) were investigated. Also, the effect of co-existing inorganics and organics was explored using a response surface quadratic model. The evaluation of electrical energy consumption and stability confirmed the outstanding practical application prospect of FeCoOx/CN-Vn. Finally, degradation pathways of TCH were elucidated and toxicity of the products was evaluated using quantitative structure activity relationship (QSAR). This study not only furnished a novel insight into the defect-assisted PMS activation, but also achieved in-situ utilization of contaminant for efficient wastewater treatment.