Regulating Intermediate Concentration to Synthesize Highly Crystalline g‐C₃N₄ under Spontaneous Ultrahigh Pressure

Abstract Improving polymerization and crystallization properties has become a key point to maximize the intrinsic photocatalytic performance of graphitic carbon nitride (g‐C₃N₄), however, the critical roles of intermediates in the polymerization and crystallization process are not clear. Herein, highly crystalline g‐C₃N₄ is obtained by calcinating different amount of dicyandiamide in a closed environment. Ultrahigh atmospheric pressure up to 6.2 MPa can be spontaneously formed due to the produced gaseous intermediates. The best crystallization properties were achieved when 1.8 g of dicyandiamide was used. The photocatalytic hydrogen production rate reaches 9241.3 μmol ⋅ g⁻¹ ⋅ h⁻¹, which is improved by about 12.5 times by comparison. The crystallization and hydrogen production activities cannot be enhanced only by adding an initial gas pressure meanwhile keeping the quality of dicyandiamide constant, confirming that the intermediate concentration determines the polymerization and hydrogen production performance of g‐C₃N₄. This study is important to improve the intrinsic photocatalytic performance of g‐C₃N₄ and the composites.