Regulating Crystal Facets of MnO2 for Enhancing Peroxymonosulfate Activation to Degrade Pollutants: Performance and Mechanism

Abstract

On the catalyst surface, crystal facets with different surface atom arrangements and diverse physicochemical properties lead to distinct catalytic activity. Acquiring a highly reactive facet through surface regulation is an efficient strategy to promote the oxidative decomposition of wastewater organic pollutants via peroxymonosulfate (PMS) activation. However, the mechanism through which crystal facets affect PMS activation is still unclear. In this study, three facet-engineered α-MnO2 with different exposed facets were prepared via a facile hydrothermal route. The prepared 310-MnO2 exhibited superior PMS activation performance to 100-MnO2 and 110-MnO2. Moreover, the 310-MnO2/PMS oxidative system was active over a wide pH range and highly resistant to interfering substances from wastewater. These advantages of the 310-MnO2/PMS system make it highly promising for practical wastewater treatment. Based on quenching experiments, electron paramagnetic resonance (EPR) analysis, solvent exchange, and electrochemical measurements, mediated electron transfer was found to be the dominant nonradical pathway for p-chloroaniline (PCA) degradation. A sulfhydryl group (-SH) masking experiment showed that the highly exposed Mn atoms on the 310-MnO2 surface were sites of PMS activation. In addition, density functional theory (DFT) calculations confirmed that the dominant {310} facet promoted adsorption/activation of PMS, which favored the formation of more metastable complexes on the α-MnO2 surface. The reaction mechanism obtained here clarifies the relationship between PMS activation and crystal facets. This study provides significant insights into the rational design of high-performance catalysts for efficient water remediation.

α-MnO2 Nanowire Structure Obtained at Low Temperature with Aspects in Environmental Remediation and Sustainable Energy Applications

“…MnO 2 is one of the most appealing materials because of its technological significance and potential applications in various catalytic and electrochemical processes where their properties are significantly influenced by its structure and morphology, allowing researchers to investigate the effect of the support structure on catalytic activity [13]. Different catalytic activity can be caused by the phase structure, catalyst surface, crystal facets with various surface atom configurations, metal loading and doping, and different physicochemical parameters [14,15]. Furthermore, MnO 2 is an n-type semiconductor with oxidative catalytic [16] properties that depend upon its crystallographic forms.…”

Facet-Dependent Catalytic Activity of MnFe Prussian Blue Analogues in Peroxymonosulfate-Activated System for Efficient Degradation of Acetamiprid

“…The principle of high-performance catalyst design is to precisely customize the active site for the desired catalytic reaction with optimal geometric and electronic properties. , Notably, the crystal facets that make up the semiconductor surface have different atomic configurations, which largely determine the exposed active sites and electronic structure, thereby endowing them with distinctive surface properties and catalytic activity. − As published, compared to other MnO 2 crystal forms, α-MnO 2 stands out as the most efficient PMS activator to degrade organic pollutants such as phenol, p -chloroaniline, and carbamazepine . Subsequently, more α-MnO 2 -based catalysts such as α-MnO 2 /palygorskite, MnFe 2 O 4 /α-MnO 2 , and α-MnO 2 /graphite were manufactured, and they displayed excellent catalytic performance for PMS activation.…”

Treatment of Coking Wastewater by α-MnO2/Peroxymonosulfate Process via Direct Electron Transfer Mechanism

“…MnO 2 was widely employed as highly efficient PMS activator [40,41]. The mechanism of organic degradation was highly dependent on its crystal facets [42]. Very recently, we disclosed the underlying mechanism of PMS activation by a series of crystallographic MnO 2 as oxidation by surface bound metastable PMS and direct electron transfer from organic contaminants to surface Mn(IV, III) [34].…”