Insights from DFT and mechanistic analysis of surface-precision carbon self-doped porous g-C3N4 for enhanced visible light-driven hydrogen evolution

Abstract

Substituting carbon for nitrogen in g-C3N4 enhances π-electrons activity and photocatalytic performance, despite the challenges posed by the higher electronegativity of nitrogen. We successfully achieved the substitution of C atoms for N atoms via the copolymerization of melamine and cytosine utilizing the Schiff base reaction, altering the g-C3N4 band structure from 2.74 to 2.49 eV and enhancing photoinduced electron reduction due to the introduction of −N-C = C- unit into the g-C3N4 network. The C-incorporated g-C3N4 extended the light-response range to 673 nm and improved the electron cloud density around the self-doping sites, significantly reducing the ΔGH* as indicated the DFT results, implying the efficient separation and migration of photoinduced carriers in g-C3N4. As anticipated, the photocatalytic hydrogen evolution (PHE) rate of the optimized C self-doped g-C3N4 was five and seven times higher than that of the pristine g-C3N4 under the full spectrum and the visible light (λ ≥ 400 nm), respectively. Moreover, g-C3N4-n also display superior activity (6.73, 4.48, 3.42, and 0.76 %) under the different wavelengths (λ = 420, 450, 480 nm, and 540 nm respectively). This report reveals a subtle atom-tailoring scheme to control carbon self-doping sites within the g-C3N4 framework, modulating its inherent electronic properties and photoactivity.