Low-temperature synthesis of mesoporous boron carbides as metal-free photocatalysts for enhanced CO2 reduction and generation of hydroxyl radicals

Abstract

Boron-rich semiconductors make significant contributions to the family of explored metal-free photocatalysts, which have attracted much attention in recent years. Boron carbide (B4C) belongs to a typical metal-free boron-rich photocatalyst which is facing difficulties in further optimization mainly due to the extreme conditions required for the synthesis of this material. In the present work, five different transition-metal catalysts (Fe, Co, Ni, Cu, and Zn) were investigated for lowering the crystallization temperature of B4C. Ni is the best catalyst for the reaction, and the crystalline mesoporous B4C powders can be obtained at merely 850 °C with a surface area of 130.55 m2 g−1, which is 27 times larger than commercial B4C. The photocatalytic properties of B4C prepared with Ni catalyst at different calcination temperatures were further evaluated by photocatalytic CO2 reduction and generation of hydroxyl radicals. Both the crystallinity and surface area of the B4C would influence the final photocatalytic properties. For B4C photocatalysts, we firstly found that the crystallinity would influence the photogenerated holes more significantly while the surface area would have more significant influence on the photogenerated electrons. The B4C obtained at 950 °C exhibits the best photocatalytic activities for both CO2 reduction and generation of ·OH radicals, which are 3.1 and 2.1 times higher than the commercial B4C, respectively. This present study may provide crucial references for the low-temperature synthesis of crystalline B4C and new opportunities for the application of the metal-free B4C photocatalysts to solar energy conversion.