Single LiCl-driven synthesis of heptazine-/triazine-based crystalline carbon nitride homojunction for enhanced solar hydrogen evolution

LiCl-based molten salts have been widely used to induce the polymerization of melamine-derived monomer or intermediate into triazine-based or heptazine-based crystalline carbon nitride. Nevertheless, the role of LiCl beyond lowering melting point has not been fully revealed, and pure LiCl was exclusively reported to induce the formation of triazine-based crystalline counterpart. Herein, we firstly found that single LiCl can promote the deep deamination of melon-based pristine carbon nitride (PCN) to heptazine-based crystalline counterpart. As a result, a heptazine-/triazine-based crystalline carbon nitride homojunction was in situ formed by single LiCl-induced deamination and phase transition of PCN. It exhibits a favorable photocatalytic H2 evolution reaction rate 18.3 times higher than PCN, which benefits from the promoted charges separation between heptazine and triazine units in phase homojunction. This work emphasizes that single LiCl can realize diverse modulation of carbon nitride framework with advanced photocatalytic activity.