Precisely Tailoring Nitrogen Defects in Carbon Nitride for Efficient Photocatalytic Overall Water Splitting

Precisely tailoring the nitrogen defects has been verified to be a promising approach for promoting the photocatalytic efficiency of C₃N₄. Herein, two-coordinated-N vacancies are selectively introduced into the C₃N₄ framework by a facile Cl^- modification method, whereas its concentration can be facilely tuned by varying Cl^- usage in the process of thermal polymerization. Impressively, the optimal defective C₃N₄ (20 mg) exhibited superior hydrogen and oxygen evolution rates of 48.2 and 21.8 μmol h^-1, respectively, in photocatalytic overall water splitting and an apparent quantum efficiency of 6.9% at 420 nm, the highest of reported single-component C₃N₄ photocatalysts for overall water splitting. Systematic studies including XPS, DFT simulations, and NEXAFS reveal that Cl^- modification preferentially facilitates the introduction of two-coordinated-N vacancies through tuning the formation energy and promotes charge carrier separation efficiency, thereby greatly enhancing the photocatalytic efficiency. This work allows for a viable approach to rationally designing defective C₃N₄ for efficient photocatalysis.