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.