Iron directional regulated MXene to construct Ti/O double vacancies for synergistic catalytic ozone to degrade benzotriazole: Enhanced surface hydroxyl groups and electron transfer

Fe-MXene catalyst featuring Ti/O dual vacancies and multiple active sites was directional designed and synthesized via Molten Salt Self-Assemble, which could realize 96.73% degradation and 77.45% mineralization to 20 mg/L benzotriazole (BTA) within 20 min with amendment of 0.5 g/L Fe-MXene and 15 mg/L O 3 at pH 7.0. The degradation rate attained 0.1836 min −1 with 2.6 times enhancement compared to single O 3 . This highly efficient degradation was ascribed to synergetic effects from 55.92% hydroxyl radicals (•OH), 28.3% superoxide radicals (•O 2 − ), and 9.24% singlet oxygen ( 1 O 2 ). These approximately fivefold •OH and threefold •O 2 − active species generation were attributed to superior catalytic activity from Fe-MXene with multivalent redox couples (Fe (II)/Fe (III), Ti (III)/Ti (IV)) and Ti O double vacancies, which enhanced O 3 and electron transport. Fe-Mxene catalyst efficiency maintained over 96% after 5 recycle. This efficient and stable degradation mechanism is mainly driven by Ti O double vacancies, which accelerated direct adsorption O 3 conversion to •O 2 − and indirect chemical generation •OH driven by Fe/Ti electron transfer acceleration. This generation of multiple oxidizing active species accelerated three types of ring-opening behaviors for BTA from hydroxy substitution on benzene ring, oxidation ring-opening of triazole ring, and assistive double bond rupture driven by non-radical pathway. This rapid benzene ring-open induced ecotoxicity reduction, while triazole ring degradation triggered ecotoxicity increase. The extensive application of Fe-MXene catalyst demonstrated that the highly efficient and selective characteristics to refractory coal chemical wastewater containing toxic benzene rings and azole rings.