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

Crystal facet engineering, the selectiveexposure of reactive crystalfacets, has emerged as an important technique for the design of efficientcatalysts. However, in the facet-controlled synthesis of nanocrystalsby either traditional top-down or bottom-up routes, the selectionof capping agents is crucial and challenging. Herein, a phase transitionstrategy that does not require the assistance of capping/etching agentswas developed to achieve the selective exposure of {103}, {101}, and{112} facets in Mn3O4. Facet-dependent activityin the photothermal decomposition of the carcinogen formaldehyde wasinvestigated. The resulting Mn3O4 with exposed{103} facets showed the best photothermal catalytic activity, achievingthe complete mineralization of formaldehyde at ambient temperature.The synergistic mechanism of the photothermal catalysis of Mn3O4 was discovered to be a thermal-assisted photocatalyticprocess rather than solar-light-driven thermal catalysis. In addition,the photothermal synergistic decomposition process of HCHO was alsorevealed. The photothermal decomposition of HCHO undergoes the processesof HCHO -> DOM (dioxymethylene) -> formates -> carbonates -> CO2. The findings proposed in this work not onlybroaden the study of crystal facet engineering but also provide suggestionsfor the purification of volatile organic compounds (VOCs) in indoorair.

Automated summary

Crystal facet engineering is an important technique for designing efficient catalysts. A phase transition strategy was developed to selectively expose {103}, {101}, and {112} facets in Mn3O4. Among these facets, {103}-exposed Mn3O4 showed the best photothermal catalytic activity in decomposing formaldehyde, achieving complete mineralization at ambient temperature. The study also revealed the photothermal synergistic decomposition process of formaldehyde. These findings not only broaden the understanding of crystal facet engineering but also provide suggestions for the purification of volatile organic compounds in indoor air.