The photocatalytic activity of graphitic carbon nitride (CN) is mainly restricted by its high recombination rate of charge carriers and narrow visible light absorption. In the present work, nitrogen-deficient CN (NDCCN) nanosheets with high crystallinity were synthesized using molten salt (NaLiCO3) as an etching agent and high-temperature solvent. The electronic structure and energy band levels of the obtained NDCCN are optimized to extend its optical absorption and enhance separation efficiency of photo-generated charge carriers. With these changes, NDCCN displays high photocatalytic activity for hydrogen evolution under visible light illumination (111 mu mol h(-1)), which is 4.6 times of that over pristine CN. This finding opens up a new window to simultaneously decrease nitrogen composition and increase crystallinity of carbon nitride for higher solar-light-driven hydrogen production efficiency. (C) 2019 Elsevier Inc. All rights reserved.