Facile preparation and high photocatalytic activity of crystalline graphitic carbon nitride in hydrogen evolution from electron donor solutions under visible light

[Display omitted] •Crystalline graphitic carbon nitride (CGCN) was obtained by thermal treatment of g-C3N4 in salt melt.•Comparison of CGCN synthesized in both argon and air shows only slight difference between them.•Obtained samples of CGCN show superior photocatalytic activity in visible light hydrogen evolution.•The optimal conditions for obtain CGCN with high photocatalytic activity were determined. The synthesis of nanostructured crystalline graphitic carbon nitride (CGCN) by a treatment of bulk g-C3N4 in a KCl + LiCl melt, both in an argon stream and air, is described. The materials obtained were investigated using X-ray diffraction, infrared, UV-vis, and photoluminescence spectroscopy, scanning electron microscopy, and X-ray photoemission spectroscopy. The activity of the treated samples of CGCN in the photocatalysis of H2 evolution from aqueous solutions of lactic acid and ethanol under visible light exceeds the activity of the initial g-C3N4 by more than an order of magnitude. The CGCN photocatalyst synthesized by the thermal treatment of bulk g-C3N4 in the air is practically not inferior to the materials produced in an inert atmosphere, which opens up the possibility of scaling up their synthesis. The optimum conditions for obtaining initial g-C3N4 for synthesizing CGCN samples with high photocatalytic activity were determined.