Facet-Controlled Synthesis of Mn₃O₄ Nanorods for Photothermal Synergistic Catalytic Oxidation\nof Carcinogenic Airborne Formaldehyde

Abstract

Crystal facet engineering, the selective\nexposure of reactive crystal\nfacets, has emerged as an important technique for the design of efficient\ncatalysts. However, in the facet-controlled synthesis of nanocrystals\nby either traditional top-down or bottom-up routes, the selection\nof capping agents is crucial and challenging. Herein, a phase transition\nstrategy that does not require the assistance of capping/etching agents\nwas developed to achieve the selective exposure of {103}, {101}, and\n{112} facets in Mn₃O₄. Facet-dependent activity\nin the photothermal decomposition of the carcinogen formaldehyde was\ninvestigated. The resulting Mn₃O₄ with exposed\n{103} facets showed the best photothermal catalytic activity, achieving\nthe complete mineralization of formaldehyde at ambient temperature.\nThe synergistic mechanism of the photothermal catalysis of Mn₃O₄ was discovered to be a thermal-assisted photocatalytic\nprocess rather than solar-light-driven thermal catalysis. In addition,\nthe photothermal synergistic decomposition process of HCHO was also\nrevealed. The photothermal decomposition of HCHO undergoes the processes\nof HCHO → DOM (dioxymethylene) → formates → carbonates\n→ CO₂. The findings proposed in this work not only\nbroaden the study of crystal facet engineering but also provide suggestions\nfor the purification of volatile organic compounds (VOCs) in indoor\nair.