Optimization of g‑C<sub>3</sub>N<sub>4</sub> Nanostructures by CH<sub>2</sub> Introduction and Relay Modification\nfor Photocatalytic Hydrogen Evolution

While\nextensive efforts have focused on increasing the level of\nphotocatalytic hydrogen evolution of the g-C<sub>3</sub>N<sub>4</sub> nanostructure, these approaches are often constrained by the excessive\nreliance on single-step modification methodologies, which significantly\nrestricts the potential for performance enhancement. Herein, we propose\na relay-modification strategy that begins with the occupation of the\nCH<sub>3</sub>-induced N defect sites in the g-C<sub>3</sub>N<sub>4</sub> nanostructure with CH<sub>2</sub> groups and is followed\nby the subsequent annealing process in ambient air. Computational\nmodeling and material characterization suggested that the introduced\nCH<sub>2</sub> groups could significantly accelerate change in charge\ncarrier transportation within the g-C<sub>3</sub>N<sub>4</sub>, improve\nvisible light absorption, and decrease the adsorption-free energy\nof hydrogen intermediates. Consequently, the g-C<sub>3</sub>N<sub>4</sub> nanostructure enriched with CH<sub>2</sub> groups yielded\na hydrogen evolution rate of 9.0 mmol g<sup>–1</sup> h<sup>–1</sup>, which is much higher than that of pristine g-C<sub>3</sub>N<sub>4</sub> (2.3 mmol g<sup>–1</sup> h<sup>–1</sup>). The subsequent relay modification, i.e., calcination treatment,\nyields an impressive H<sub>2</sub> evolution rate of 14.3 mmol g<sup>–1</sup> h<sup>–1</sup>, more than 16 times higher\nthan that of the nonfunctionalized g-C<sub>3</sub>N<sub>4</sub>-derived\nsample and superior to most reported g-C<sub>3</sub>N<sub>4</sub>.\nExperimental characterizations showed that the remarkable hydrogen\nproduction activity could be attributed to relay-modification-induced\nenhanced visible light absorption and improved electron–hole\npair separation.