Tuning Metal-Free Hierarchical Boron Nitride-like Catalyst for Enhanced Photocatalytic CO2 Reduction Activity

Boron nitride (BN)-based materials, which are commonly used as metal-free catalysts for thermal catalysis and pollution degradation, have shown potential for photocatalytic reduction of CO2 into valuable carbon fuels. However, the poor performance and the insufficient explanation of the reaction mechanism of the very few reported BN-based catalysts still seriously restrict the practical development. Herein, we synthesize a hierarchical BN-like flower catalyst composed of nanofibers (∼50 nm) by combining an in situ self-assembly strategy with a self-modification method. The photocatalytic CO2-to-CO reduction rate of BN-like flowers with low B–O species content is over 3-fold than that of BN-like flowers with high B–O species content and even more than 26.7 and 7.3 times than that of bulk BN and bulk carbon nitride (CN), respectively. Notably, the performance of the as-prepared catalysts is much higher than that of the reported BN-based catalysts and nearly all the popular metal-free CN and even comparable to most metal-based catalysts. Importantly, we in-depth investigate the reasons and mechanisms for the enhancement of photocatalytic CO2 reduction activity of BN-like flowers by combining various advanced characterizations and DFT calculations. It is found that in the BN-like flowers, B atoms linked to O atoms act as active sites, and the low B–O species content is beneficial for dynamic charge transfer and *CO desorption. In addition, the catalyst also shows good stability which is verified by cycling experiments together with molecular dynamics computation. The synthesis of the metal-free BN-based catalyst and systematic theoretical investigation will be beneficial to the development of advanced catalysts for solar fuel production.