Highly crystalline carbon nitride with small-sized sea urchin-like structure for efficient photocatalytic hydrogen production under visible-light irradiation

Molten-salt method has been deemed as a feasible strategy to increase the crystallinity of graphitic carbon nitride (abbreviated as CN), thereby improving its photocatalytic activity. However, highly crystalline CN prepared by molten-salt method using bulk carbon nitride (BCN) as the precursor still suffers from a small specific surface area, which is unfavorable to the separation of photogenerated carriers. Here, we report a facile approach to obtain highly crystalline CN with a large specific surface area using tubular carbon nitride (TCN) as raw material, and the final sample is named as tubular carbon nitride-molten salt (TCN-M). Compared with bulk carbon nitride-molten salt (BCN-M) sample, the obtained TCN-M sample not only retains the advantage of high crystallinity, but also exhibits a smaller-sized sea urchin-like structure owing to the CN precursor pretreatment process. The experiment results demonstrate that TCN-M displays an excellent hydrogen production activity of 4.9 mmol g -1 h -1 under visible-light, and its hydrogen production performance can be further enhanced to 14.7 mmol g -1 h -1 after adding 0.5 M K 2 HPO 4 . Thus, this work may supply valuable ideas to further optimize the photocatalytic activity of highly crystalline CN prepared by molten-salt method from the perspective of CN precursor pretreatment. • A highly crystalline carbon nitride with small-sized sea urchin-like structure was successfully prepared. • Large specific surface area and the presence of cyano groups greatly improve the photocatalytic H 2 production activity. • Optimizing the photocatalytic activity of highly crystalline CN from the perspective of CN precursor pretreatment. • A typical H + -reduction cycle can be constructed by introducing K 2 HPO 4 into the reaction system.