Synthesis of Crystalline Heptazine-Based Carbon Nitride Microtubes for Highly Efficient Hydrogen Evolution Photocatalysis

Increasing the crystallinity of carbon nitride can accelerate the photogenerated carrier migration rate and reduce the structural defects, which is an effective strategy to improve the photocatalytic performance of carbon nitride. In this work, carbon nitride microtubes were post-treated in KCl-LiCl molten salts to create crystalline heptazinyl carbon nitride microtubes. The results show that photocatalytic hydrogen production rate of the as-prepared crystalline heptazine-based carbon nitride microtubes can reach 3440.21 μmol·g–1·h–1, which is approximately 28.8, 2.1, and 22.2 times higher than that of bulk carbon nitride, sulfur doped g-C3N4 microtubes, and microtubes with triazine-based structure prepared by a one-step molten salt method, respectively. The carbon nitride microtubes prepared by this method have a heptazine-based structure, possessing not only high crystallinity but also significantly increased specific surface area. This study offers a reliable guide for designing an innovative approach to prepare semiconductor photocatalysts in the molten salt system.