Crystalline sulfur-doped poly(heptazine imide) for enhanced photocatalytic H₂ evolution under visible-light irradiation

Poly(heptazine imide) (PHI) is a representative crystalline carbon nitride material widely utilized as a photocatalyst for hydrogen production. However, the practical photocatalysis performance of PHI is restricted by its limited crystallinity and low photo-generated charge-carrier utilization efficiency. To solve these problems, herein, we report a highly crystalline sulfur-doped PHI (S-PHI) synthesized using the sulfur-containing compound 1H-1,2,4-triazole-3-thiol as a precursor. The introduction of sulfur during synthesis promotes polymerization and enhances the crystallinity of PHI, with sulfur incorporated into the framework of PHI as a form of sulfur doping. Consequently, S-PHI exhibits improved light utilization, an enlarged surface area, and enhanced charge-carrier separation and migration efficiency compared to PHI synthesized from melamine, with apparent quantum yield (AQY) of photocatalytic H₂ evolution achieving 13.6% at 420 nm and impressive value of 2.8% at 520 nm.