Photochemical Tuning of Tricoordinated Nitrogen Deficiency in Carbon Nitride to Create Delocalized π Electron Clouds for Efficient CO<sub>2</sub> Photoreduction
Lei Li, Huanhuan Liu, Chao Cheng, Xinyan Dai, Fang Chen, Jiqiang Ning, Wentao Wang, Yong Hu
Abstract
Precisely engineering point defects holds promise for the development of state-of-the-art photocatalysts for CO 2 conversion. This study demonstrates the controllable creation of nitrogen vacancies ( V Ns ) in the centers of heptazine rings of graphitic carbon nitrides (g-C 3 N 4 ) via a photochemical-assisted nitrogen etching strategy. Spectroscopic analyses and theoretical simulations elucidate the photochemical process to hydrogenate the nitrogen situated at the center of the g-C 3 N 4 heptazine ring and then release an ammonia molecule, accompanied by the photooxidation of the sacrificial agents. The catalyst with an optimal V Ns concentration achieves a CO generation rate of 35.2 μmol g –1 h –1 with nearly 100% selectivity, comparable to the performance of the reported g-C 3 N 4 materials. The remarkably improved photoactivity is due to the adjustments of the electronic structures and the midgap states of g-C 3 N 4 by the delocalized π electron cloud created in the 12-membered ring surrounding the V N, which maximizes the light-harvesting efficiencies and suppresses the recombination of photogenerated electrons and holes. The V Ns also activates the neighboring catalytic carbon centers to reduce the energy barrier for CO 2 reduction. This work provides a good design concept to regulate catalytic activity by engineering point defects.