Optimization of g-C₃N₄ Nanostructures by CH₂ Introduction and Relay Modification for Photocatalytic Hydrogen Evolution

While extensive efforts have focused on increasing the level of photocatalytic hydrogen evolution of the g-C 3 N 4 nanostructure, these approaches are often constrained by the excessive reliance on single-step modification methodologies, which significantly restricts the potential for performance enhancement. Herein, we propose a relay-modification strategy that begins with the occupation of the CH 3 -induced N defect sites in the g-C 3 N 4 nanostructure with CH 2 groups and is followed by the subsequent annealing process in ambient air. Computational modeling and material characterization suggested that the introduced CH 2 groups could significantly accelerate change in charge carrier transportation within the g-C 3 N 4, improve visible light absorption, and decrease the adsorption-free energy of hydrogen intermediates. Consequently, the g-C 3 N 4 nanostructure enriched with CH 2 groups yielded a hydrogen evolution rate of 9.0 mmol g –1 h –1, which is much higher than that of pristine g-C 3 N 4 (2.3 mmol g –1 h –1 ). The subsequent relay modification, i.e., calcination treatment, yields an impressive H 2 evolution rate of 14.3 mmol g –1 h –1, more than 16 times higher than that of the nonfunctionalized g-C 3 N 4 -derived sample and superior to most reported g-C 3 N 4 . Experimental characterizations showed that the remarkable hydrogen production activity could be attributed to relay-modification-induced enhanced visible light absorption and improved electron–hole pair separation.