MgFe2O4/MgO modified biochar with oxygen vacancy and surface hydroxyl groups for enhanced peroxymonosulfate activation to remove sulfamethoxazole through singlet oxygen-dominated nonradical oxidation process

Nonradical oxidation plays a crucial role in the contaminant degradation due to their high selectivity and anti-interference ability. In this study, we report that peroxymonosulfate (PMS) activated by MgFe2O4/MgO modified biochar (MMFBC) achieves almost complete nonradical oxidation process dominated by 1O2 for degradation of sulfamethoxazole (SMX). The experimental results show that MMFBC exhibits excellent performance for SMX degradation, and is not susceptible to interference from coexisting ions and different water matrices. Oxygen vacancy (OV) and surface − OH groups on MMFBC surface are detected and considered to be crucial for nonradical processes. Characterizations and theoretical calculations reveal that the co-adsorbed PMS and dissolved oxygen (O2) near OV form a localized high-density electron transfer process. With the premise of hydrogen bonding between PMS and surface − OH groups, PMS acts as an electron donor to OV, which in turn transfers electron to O2 through the iron cycle involving Fe(II)/Fe(III). Finally, the electron acceptor O2 undergoes conversion into O2−, which subsequently transforms into 1O2 to achieve nonradical oxidation processes. This work provides an in-depth investigation into the OV and surface − OH groups mediated nonradical oxidation mechanism, and proposes a novel insight into electron-transfer processes among PMS, O2 and catalyst.