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

Abstract

While extensive efforts have focused on increasing the level of photocatalytic hydrogen evolution of the g-C₃N₄ 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 CH₃-induced N defect sites in the g-C₃N₄ nanostructure with CH₂ groups and is followed by the subsequent annealing process in ambient air. Computational modeling and material characterization suggested that the introduced CH₂ groups could significantly accelerate change in charge carrier transportation within the g-C₃N₄, improve visible light absorption, and decrease the adsorption-free energy of hydrogen intermediates. Consequently, the g-C₃N₄ nanostructure enriched with CH₂ groups yielded a hydrogen evolution rate of 9.0 mmol g^–1 h^–1, which is much higher than that of pristine g-C₃N₄ (2.3 mmol g^–1 h^–1). The subsequent relay modification, i.e., calcination treatment, yields an impressive H₂ evolution rate of 14.3 mmol g^–1 h^–1, more than 16 times higher than that of the nonfunctionalized g-C₃N₄-derived sample and superior to most reported g-C₃N₄. 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.