Sulfur-induced nitrogen vacancy modulation in K/S-Codoped g-C3N4 for efficient CO2 photoreduction

Molten salt-assisted pyrolysis has emerged as an effective strategy for engineering defective/doped g-C 3 N 4 photocatalysts for CO 2 reduction. While K + incorporation enhances interlayer charge transport, excessive K + generates detrimental nitrogen vacancies that destabilize the heptazine framework and compromise carrier mobility. Herein, we developed S/K co-doped graphitic carbon nitride (g-C 3 N 4 ) with tunable nitrogen vacancies (denoted SWCN-M) via molten salt (KCl-LiCl) pyrolysis of sulfur-containing supramolecular precursors (melamine with thiourea or thioacetamide). The nitrogen vacancy concentration is precisely modulated by the choice of sulfur precursor (thiourea vs. thioacetamide) to optimize the synergy effect of K + -N-vacancy, and eventually boosting photocatalytic performance. The thiourea-derived SWCN-M TU achieves a CO evolution rate of 165.7 μmol g −1 h −1 , outperforming its thioacetamide analogue (SWCN-M TAA , 90.4 μmol g −1 h −1 ), pristine WCN (53.8 μmol g −1 h −1 ), and K-doped WCN-M (64.3 μmol g −1 h −1 ) by factors of 1.8, 3.1, and 2.6, respectively. DFT calculation results reveal that S-doping induces charge localization, elevating the N-vacancy formation energy via Coulombic repulsion with K + . This work advances the rational design of vacancy-engineered carbon nitride for photocatalytic CO 2 reduction