Photochemical Tuning of Tricoordinated Nitrogen Deficiency in Carbon Nitride to Create Delocalized π Electron Clouds for Efficient CO2 Photoreduction

Precisely engineering point defects holds promise for the development of state-of-the-art photocatalysts for CO2 conversion. This study demonstrates the controllable creation of nitrogen vacancies (VNs) in the centers of heptazine rings of graphitic carbon nitrides (g-C3N4) 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-C3N4 heptazine ring and then release an ammonia molecule, accompanied by the photooxidation of the sacrificial agents. The catalyst with an optimal VNs 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-C3N4 materials. The remarkably improved photoactivity is due to the adjustments of the electronic structures and the midgap states of g-C3N4 by the delocalized π electron cloud created in the 12-membered ring surrounding the VN, which maximizes the light-harvesting efficiencies and suppresses the recombination of photogenerated electrons and holes. The VNs also activates the neighboring catalytic carbon centers to reduce the energy barrier for CO2 reduction. This work provides a good design concept to regulate catalytic activity by engineering point defects.