Facet selectively exposed α-MnO2 for complete photocatalytic oxidation of carcinogenic HCHO at ambient temperature

Abstract

• The {1 0 0}, {1 1 0} and {3 1 0} facets in α-MnO 2 were selectively exposed. • α-MnO 2 with exposed {3 1 0} facets can complete photocatalytic oxidation of HCHO. • Photothermal activity of {3 1 0} facet is consistent with photocatalysis mechanism. • This is the first report on facets control of α-MnO 2 as efficient photocatalysts. Formaldehyde (HCHO) causes increasing concerns due to its ubiquitously found in the indoor environment and being irritative and carcinogenic to humans. Therefore, the complete removal of HCHO at room temperature is meaningful. Crystal facet engineering has appeared as a significant strategy for designing efficient catalysts. It is an effective way to improve the catalytic activity by selectively exposing the highly reactive crystal facets. Herein, the {1 0 0}, {1 1 0}, and {3 1 0} facets in α-MnO 2 were selectively exposed, and the differences in the properties and photocatalytic activity of crystal facets have been carefully compared. Specifically, α-MnO 2 with exposed {3 1 0} facets exhibited superior photocatalytic activity, achieving 100% conversion of carcinogenic airborne HCHO under the solar-light irradiation and even 78% removal efficiency under visible light. Interestingly, it is found that the high activity of {3 1 0} facet with solar-light irradiation is consistent with the photocatalysis mechanism, rather than solar-light-driven thermocatalysis mechanism. Furthermore, it is confirmed that the {3 1 0} facet can not only promote the effective separation of electron and hole, but also benefit the activation of O 2 , which leads to substantially improved photocatalytic activity. This is the first report on engineering surface structures and facets control in the preparation of α-MnO 2 as highly efficient photocatalysts.