Supercritical CH₃OH-Triggered Isotype Heterojunction and Groups in g-C₃N₄ for Enhanced Photocatalytic H₂ Evolution

Abstract

The structure tuning of bulk graphitic carbon nitride (g-C 3 N 4 ) is a critical way to promote the charge carriers dynamics for enhancing photocatalytic H 2 -evolution activity. Exploring feasible post-treatment strategies can lead to effective structure tuning, but it still remains a great challenge. Herein, a supercritical CH 3 OH (ScMeOH) post-treatment strategy (250− 300 °C, 8.1−11.8 MPa) is developed for the structure tuning of bulk g-C 3 N 4 . 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, CH 3 OH molecules diffused into the interlayers of g-C 3 N 4 and subsequently participated in N-methylation and hydroxylation reactions with the intralayers, resulting in a partial phase transformation from g-C 3 N 4 into carbon nitride with a poly(heptazine imide)-like structure (Q-PHI) as well as abundant methyl and hydroxyl groups. The modified g-C 3 N 4 showed enhanced photocatalytic activity with an H 2 -evolution rate 7.2 times that of pristine g-C 3 N 4 , which was attributed to the synergistic effects of the g-C 3 N 4 /Q-PHI isotype heterojunction construction, group modulation, and surface area increase. This work presents a post-treatment strategy for structure tuning of bulk g-C 3 N 4 and serves as a case for the application of supercritical fluid technology in photocatalyst synthesis.