Switching of radical and nonradical pathways through the surface defects of Fe3O4/MoOxSy in a Fenton-like reaction

Abstract

Coexistence of radical and nonradical reaction pathways during advanced oxidation processes (AOPs) makes it challenging to obtain flexible regulation of high efficiency and selectivity for the requirement of diverse degradation. Herein, a series of Fe3O4/MoOxSy samples coupling peroxymonosulfate (PMS) systems enabled the switching of radical and nonradical pathways through the inclusion of defects and adjustment of Mo4+/Mo6+ ratios. The silicon cladding operation introduced defects by disrupting the original lattice of Fe3O4 and MoOxS. Meanwhile, the abundance of defective electrons increased the amount of Mo4+ on the catalyst surface, promoting PMS decomposition with a maximum k value up to 1.530 min−1 and a maximum free radical contribution of 81.33%. The Mo4+/Mo6+ ratio in the catalyst was similarly altered by different Fe contents, and Mo6+ contributed to the production of 1O2, allowing the whole system to attain a nonradical species–dominated (68.26%) pathway. The radical species-dominated system has a high chemical oxygen demand (COD) removal rate for actual wastewater treatment. Conversely, the nonradical species-dominated system can considerably improve the biodegradability of wastewater (biochemical oxygen demand (BOD)/COD = 0.997). The tunable hybrid reaction pathways will expand the targeted applications of AOPs.