Molten salt-assisted precursor regulation of crystalline g-C3N4 for high-efficient photocatalytic H2O2 production

Graphitic phase carbon nitride (g-C3N4) is considered one of the most promising catalysts for photocatalytic production of hydrogen peroxide (H2O2) due to its green and non-polluting nature and stability. However, the conventional g-C3N4 prepared by direct thermal polymerization has insufficient reaction sites due to its excessive bulk defects derived from incomplete polymerization and low specific surface area, leading to rapid carrier recombination and limited photocatalytic activity. In this work, a series of crystalline g-C3N4 (CN-UxM) with large specific surface areas have been prepared by a molten salt post-treatment strategy with regulating the precursor ratio of urea to melamine. In-situ KPFM, photoelectrochemical experiment and DFT calculation results show that the sample with an optimized urea/melamine ratio of 20 (CN-U20M) has the highest charge separation and transfer efficiency derived from the internal electric field. And its H2O2 production rate under simulated visible light reaches as high as 10.94 mmol center dot g(-1) center dot h(-1), far exceeding that of most g-C3N4-based photocatalysts in reported literatures. The present work provides an effective strategy to enhance the photocatalytic activity of g-C3N4, which is expected to be applied to other organic semiconductor catalytic systems.