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

Herein we reported the first example of preparing α-MnO 2 by selective acid etching from Mn-containing spinel. The defects, facet, and surface area of α-MnO 2 were cooperatively engineered by an all-in-one acid etching method to enhance the defect accessibility to the reactants. The obtained highly porous α-MnO 2 nanorods have rich defects of Mn 3+ (24.9%) and oxygen vacancies (31.4%), mainly active crystal facets of (110), and an ultrahigh surface area of 271.1 m 2 /g. With α-MnO 2 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-MnO 2 with (110) facet promotes the adsorption and activation of ozone directly over the defects or indirectly over H 2 O adsorbed on the defects. Thus, more reactive oxygen species (e.g., •OH, •O 2 - , 1 O 2 , 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.