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 crys-tallinity, 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 K2HPO4. 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.