Effects of Lewis acid-base site and oxygen vacancy in MgAl minerals on peroxymonosulfate activation towards sulfamethoxazole degradation via radical and non-radical mechanism

Abstract

Radicals of SO4•-, OH•, non-radical of 1O2 and even direct oxidation all occurred in peroxymonosulfate (PMS) activation process. Hence, to regulate the above radical or non-radical mechanism is of great significance for the treatment of organic pollutants in practical water. In this work, MgAl-minerals exhibited a satisfied performance in controlling the contribution of radicals (SO4•-, OH•) and non-radical (1O2) towards PMS activation based on results of reactive oxygen species scavenger experiments and electron spin resonance spectra. Compared with MgAl-1(61.8%) and MgAl-2 (61.4%) (Al/Mg = 1, 2), MgAl-3 (Al/Mg = 3) exhibited the highest sulfamethoxazole (SMX) removal efficiency (92.5%). Moreover, the contribution of radical and non-radical to SMX degradation were 56.7% and 30.1%, which was different from that of MgAl-1(7.8% and 39.5%) and MgAl-2 (5.2% and 41.6%). The roles of Lewis acid-base site and oxygen vacancies (OVs) in MgAl-minerals on radical and non-radical processes were detailed investigated. Lewis acid sites and OVs can enrich SMX and PMS at the solid-water interface. Simultaneously, OVs promote electron transfer from SMX to PMS acts as electron media, resulting in more SO4•- and OH• generation. While the basic sites favored the generation of 1O2 via PMS self-decomposition mechanism. Therefore, in PMS activation process over MgAl-minerals, the involved reactive oxygen species can be regulated via controlling the amounts of Lewis acid-base sites and oxygen vacancies. This finding provided new insights into PMS oxidation over non-transition metal-based catalysts and water remediation with complex water characteristics.