Highly porous α-MnO₂ nanorods with enhanced defect accessibility for efficient catalytic ozonation of refractory...

Herein we reported the first example of preparing α-MnO₂ by selective acid etching from Mn-containing spinel. The defects, facet, and surface area of α-MnO₂ were cooperatively engineered by an all-in-one acid etching method to enhance the defect accessibility to the reactants. The obtained highly porous α-MnO₂ nanorods have rich defects of Mn³⁺ (24.9%) and oxygen vacancies (31.4%), mainly active crystal facets of (110), and an ultrahigh surface area of 271.1 m²/g. With α-MnO₂ nanorods as the catalysts, more than 90.9% of 4-chlorophenol can be degraded within 12 min by catalytic ozonation in a wide work pH of 4.5-10.5. The experiments and DFT theory calculations reveal that α-MnO₂ with (110) facet promotes the adsorption and activation of ozone directly over the defects or indirectly over H₂O adsorbed on the defects. Thus, more reactive oxygen species (e.g., •OH, •O₂^-, ¹O₂, surface *O) are generated and get involved in pollutant degradation. This work provides a facile method to maximize the defect accessibility, and a deeper mechanistic study to understand the roles of the defects.