Plasma-based surface modification of g-C3N4 nanosheets for highly efficient photocatalytic hydrogen evolution

The surface properties of photocatalysts strongly affect interfacial catalytic reaction and determine photocatalytic activity. In this work, surface-modified graphitic carbon nitride (g-C3N4) nanosheets were prepared via plasma treatment in H2, H2-CH4, and Ar atmosphere. Hydrogenated g-C3N4 nanosheets with hydrophilic group C-N-H, defect state, and exfoliated morphology were obtained via treating g-C3N4 nanosheets with H2 plasma at room temperature. The hydrogenated g-C3N4 nanosheets possessed the improved photocatalytic activity for hydrogen evolution, and the rate of hydrogen evolution exceeded that of pristine g-C3N4 by a factor of 4.8. Photocatalytic activity improvement is due to the introduction of hydrophilic group C-N-H, defect states, and exfoliated nanosheet morphology. Hydrophilic functional group of C-N-H can effectively capture water molecules. Defect states generated via plasma treatment acted as a capture center to suppress carrier recombination and transfer the trapped electrons to the adsorbed water molecules. Exfoliated nanosheet morphology provided a large number of active sites for catalytic reaction. Optical emission spectroscopy supported the introduction of hydrogen species during H2 plasma treatment of g-C3N4. First-principle density functional theory calculations confirmed the enhanced adsorption capacity of hydrogenated g-C3N4 for water molecules. The mechanism of enhanced photocatalytic H2-production activity was further proposed.