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

•1O2 oxidation is efficient and unaffected by coexisting ions and water matrices.•Regulating MgO in MMFBC introduces abundant OV and surface − OH groups.•The co-adsorbed PMS and O2 form a localized high-density electron transfer process.•OV mediates the electron transfer process through the iron cycle of Fe(II)/Fe(III).