Unique Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C₃N₄

TLDR

Electronic structure governs light absorption, redox potential, and charge‑carrier mobility, determining photocatalyst photoreactivity, yet anion doping to broaden absorption often reduces redox potentials or mobility, limiting photoreactivity and preventing some reactions. The study reports sulfur‑doped graphitic C3N4 (C3N4−xSx) designed to exhibit a unique electronic structure with increased valence bandwidth and elevated conduction band minimum. The authors achieved this by homogeneously substituting sulfur for lattice nitrogen, inducing quantum confinement that expands valence bandwidth and raises the conduction band minimum. Sulfur‑doped C3N4 achieves 7.2–8.0× higher H₂ evolution under λ>300 and 420 nm and enables complete phenol oxidation under λ>400 nm, demonstrating superior photoreactivity and informing general doping strategies.

Abstract

Electronic structure intrinsically controls the light absorbance, redox potential, charge-carrier mobility, and consequently, photoreactivity of semiconductor photocatalysts. The conventional approach of modifying the electronic structure of a semiconductor photocatalyst for a wider absorption range by anion doping operates at the cost of reduced redox potentials and/or charge-carrier mobility, so that its photoreactivity is usually limited and some important reactions may not occur at all. Here, we report sulfur-doped graphitic C3N4 (C3N4−xSx) with a unique electronic structure that displays an increased valence bandwidth in combination with an elevated conduction band minimum and a slightly reduced absorbance. The C3N4−xSx shows a photoreactivity of H2 evolution 7.2 and 8.0 times higher than C3N4 under λ > 300 and 420 nm, respectively. More strikingly, the complete oxidation process of phenol under λ > 400 nm can occur for sulfur-doped C3N4, which is impossible for C3N4 even under λ > 300 nm. The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and, consequently, the excellent photoreactivity of C3N4−xSx. The results acquired may shed light on general doping strategies for designing potentially efficient photocatalysts.