Supercritical CHOH-Triggered Isotype Heterojunction and Groups in g-CN for Enhanced Photocatalytic H Evolution.

The structure tuning of bulk graphitic carbon nitride (g-CN) is a critical way to promote the charge carriers dynamics for enhancing photocatalytic H-evolution activity. Exploring feasible post-treatment strategies can lead to effective structure tuning, but it still remains a great challenge. Herein, a supercritical CHOH (ScMeOH) post-treatment strategy (250-300 °C, 8.1-11.8 MPa) is developed for the structure tuning of bulk g-CN. This strategy presented advantages of time-saving (less than 10 min), high yield (over 80%), and scalability due to the enhanced mass transfer and high reactivity of ScMeOH. During the ScMeOH post-treatment process, CHOH molecules diffused into the interlayers of g-CN and subsequently participated in -methylation and hydroxylation reactions with the intralayers, resulting in a partial phase transformation from g-CN into carbon nitride with a poly(heptazine imide)-like structure (Q-PHI) as well as abundant methyl and hydroxyl groups. The modified g-CN showed enhanced photocatalytic activity with an H-evolution rate 7.2 times that of pristine g-CN, which was attributed to the synergistic effects of the g-CN/Q-PHI isotype heterojunction construction, group modulation, and surface area increase. This work presents a post-treatment strategy for structure tuning of bulk g-CN and serves as a case for the application of supercritical fluid technology in photocatalyst synthesis.