Abstract: Microstructure modification of graphitic carbon nitride (g-C₃N₄) has emerged as a promising approach to improve the separation of photo-excited charge carriers and provide abundant reactive sites for effective photocatalytic H₂ production. Exploring efficient, template-free, and solvent-green methods for microstructure modification of g-C₃N₄ photocatalysts remains highly desirable but is full of challenges. Herein, a supercritical carbon dioxide (scCO₂)-induced exfoliation of a supramolecular precursor strategy was developed for the bottom-up synthesis of a unique fluffy three-dimensional (3D) tremella-like g-C₃N₄ photocatalyst towards efficient photocatalytic H₂ production. During scCO₂-induced exfoliation of supramolecular precursor process, scCO₂ with high diffusivity, low viscosity, and high solubility effectively diffused into the interlayer of layered supramolecular precursor during pressurization process, and quickly released and extricated from the interlayer of layered supramolecular precursor in subsequent rapid depressurization process, which effectively broke the interlayer van der Waals forces and in-plane hydrogen bonds of supramolecular precursor, thereby yielding fragmented and scattered sheets of supramolecular precursor in smaller size and facilitating the formation of fluffy 3D tremella-like g-C₃N₄ photocatalyst in the following pyrolysis process. The obtained 3D tremella-like microstructure of g-C₃N₄ efficiently increased visible-light absorption, improved separation and migration of the photo-excited charge carriers, and offered abundant reactive sites towards efficient photocatalytic H₂ production. Consequently, fluffy 3D tremella-like g-C₃N₄ achieved remarkable visible-light-driven photocatalytic H₂ production activity of 7104 µmol h^-1 g^-1, which was 23.8 times that of pristine g-C₃N₄. This work presents an efficient, template-free, and solvent-green scCO₂-assisted treatment strategy for microstructure regulation of g-C₃N₄, and offers invaluable insights into the application of scCO₂ technology in photocatalyst synthesis.

Key words: Supercritical carbon dioxide, Graphitic carbon nitride, Hydrogen, Microstructure, Supercritical fluid