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 (V-Ns) 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 V-Ns concentration achieves a CO generation rate of 35.2 mu mol 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 pi 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 CO2 reduction. This work provides a good design concept to regulate catalytic activity by engineering point defects.