Supercritical CH<sub>3</sub>OH-Triggered Isotype Heterojunction and Groups in g-C<sub>3</sub>N<sub>4</sub> for Enhanced Photocatalytic H<sub>2</sub> Evolution
Liuhao Mao, Binjiang Zhai, Jinwen Shi, Xin Kang, Bingru Lu, Yanbing Liu, Cheng Cheng, Hui Jin, Éric Lichtfouse, Liejin Guo
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.