Bandgap Modulation via Al Photodeposition on C-Doped g-C₃N₄ for Enhanced Photocatalytic Hydrogen Production

g-C3N4 has drawn more and more attention because of its visible-light activity, facile synthesis from easily available and low-cost precursor materials, chemical stability, and layered structure. However, the photocatalytic activity of a pure g-C3N4 photocatalyst is hindered by its narrow absorption range, small surface area, and fast electron–hole recombination rate. To cope with this issue, aluminum-deposited C-doped g-C3N4 (Aln/C7.5-MA) was synthesized by the polycondensation of melamine and sucrose, followed by in situ photodeposition of Al. The XPS and EDX analyses confirmed the successful deposition of Al nanoparticles over the C7.5-MA surface. The synthesized photocatalyst was employed to generate hydrogen (H2) via photocatalytic water splitting. Al10/C7.5-MA showed the most significant photocatalytic efficiency, achieving an H2 evolution rate of 14167 μmol g–1 h–1, which is 1.6 and 11.5 times greater than that of C-doped g-C3N4 and pristine g-C3N4, respectively. The comprehensive analysis demonstrated that C-doping followed by deposition of Al considerably narrowed its bandgap, expanded the light absorption range, boosted photoresponse, and improved photogenerated charge carrier separation due to the surface plasmon resonance (SPR) effect of Al. The findings emphasize the synergistic effect of C-doping and Al deposition in improving the photocatalytic ability of g-C3N4, presenting a viable approach for sustainable H2 production under visible-light irradiation.