New insights into MnOOH/peroxymonosulfate system for catalytic oxidation of 2,4-dichlorophenol: Morphology dependence and mechanisms.

Sulfate radical-based advanced oxidation processes (SR-AOPs) have received increasing attention as viable technology for recalcitrant organics removal from polluted waters. As for heterogeneous catalyst, it is crucial to reveal the effect of morphology on its catalytic activity and mechanism, providing guidelines for rational design of morphology-dependent catalysts. Hence, in this study, we selected manganese oxyhydroxide (MnOOH) as the peroxymonosulfate (PMS) activator and synthesized different morphological MnOOH with the same crystal structure. The catalytic activity of MnOOH follows: nanowires > multi-branches > nanorods. Different morphological MnOOH had different physical and chemical characterization such as specific surface area, Lewis sites, ζ-potential and redox potential, which played positive roles in catalytic activity of MnOOH as PMS activator. Unexpectedly, it was found that ζ-potential was more crucial than specific surface area, redox potential and Lewis sites. Notably, nanowires exhibited higher positive zeta potential, which was favor of promoting interfacial reactivity between HSO5- and surface of MnOOH. Furthermore, •OH, SO4•-, O2•- and 1O2, were involved in the MnOOH/PMS system. Moreover, the cycle of Mn (III)/Mn (II) accelerated MnOH+ formation. This study provided a new understanding of manganese-catalyzed peroxymonosulfate activation and elucidated the relationships between morphology of catalyst and its catalytic activity.