The structure tuning of bulk graphitic carbon nitride
(g-C3N4) is a critical way to promote the charge
carriers
dynamics for enhancing photocatalytic H2-evolution activity.
Exploring feasible post-treatment strategies can lead to effective
structure tuning, but it still remains a great challenge. Herein,
a supercritical CH3OH (ScMeOH) post-treatment strategy
(250–300 °C, 8.1–11.8 MPa) is developed for the
structure tuning of bulk g-C3N4. 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,
CH3OH molecules diffused into the interlayers of g-C3N4 and subsequently participated in N-methylation and hydroxylation reactions with the intralayers, resulting
in a partial phase transformation from g-C3N4 into carbon nitride with a poly(heptazine imide)-like structure
(Q-PHI) as well as abundant methyl and hydroxyl groups. The modified
g-C3N4 showed enhanced photocatalytic activity
with an H2-evolution rate 7.2 times that of pristine g-C3N4, which was attributed to the synergistic effects
of the g-C3N4/Q-PHI isotype heterojunction construction,
group modulation, and surface area increase. This work presents a
post-treatment strategy for structure tuning of bulk g-C3N4 and serves as a case for the application of supercritical
fluid technology in photocatalyst synthesis.