Precursor‐Engineering Coupled Microwave Molten‐Salt Strategy Enhances Photocatalytic Hydrogen Evolution Performance of g‐C 3 N 4 Nanostructures

A precursor‐engineering strategy coupled with a microwave molten‐salt process (PE‐MWMS) is developed to synthesize graphitic carbon nitride (g‐C 3 N 4 ) with an isotype triazine/heptazine‐based g‐C 3 N 4 heterojunction as a photocatalyst for the hydrogen evolution reaction (HER) under visible light illumination. Four hybrid precursor combinations—thiourea/melamine, thiourea/dicyandiamide, urea/melamine, and urea/dicyandiamide—are used to synthesize g‐C 3 N 4 heterojunctions by the PE‐MWMS process. Control experiments indicate that the precursor components and microwave treatment have a great effect on the HER performance of the g‐C 3 N 4 samples. Samples synthesized with the optimal molar ratios of thiourea/melamine (2:1), thiourea/dicyandiamide (2:1), urea/melamine (3:1), and urea/dicyandiamide (3:1), exhibit the highest HER rates of 3135, 2519, 2844, and 2565 μmol g −1 h −1 , respectively. The amounts of heptazine and triazine units in the g‐C 3 N 4 samples can be easily adjusted by changing the ratios of the hybrid precursors and play a decisive role in improving the photocatalytic HER activity. Because of the unique composition and microstructure, the efficient separation of electron–hole pairs, the broadened photo‐absorption edges, and the narrowed band gaps, the as‐obtained triazine/heptazine‐based g‐C 3 N 4 nanostructures exhibit promising activity for HER application.