Plasma-Induced Bandgap Engineering and Defect Modulation in g-C3N4 for Photocatalytic H2O2 Production

Graphitic carbon nitride (g-C3N4) is a promising metal-free photocatalyst for solar-driven H2O2 production, yet its activity is intrinsically limited by a narrow visible-light response, rapid charge recombination and low surface area. This work reports a cold plasma engineering strategy using radio frequency (RF), dielectric-barrier-discharge (DBD) and glow-discharge (GD) treatments to simultaneously modulate the morphology, defect chemistry and electronic structure of g-C3N4. Among the three protocols, RF plasma yields a “sponge-like” architecture with a 53% larger specific surface area (43.7 m2 g–1) and introduces nitrogen/oxygen-containing surface species that narrow the bandgap from 2.32 to 2.12 eV while preserving the crystalline framework. As a result, NCN-RF exhibits the highest H2O2 evolution rate among the investigated samples, reaching 1239 μmol g–1 h–1 under visible light irradiation (λ ≥ 420 nm), which is 4.7 times that of pristine NCN, and retains ∼80% activity after three cycles. Radical trapping and in situ EPR spectroscopy reveal a sequential two-electron oxygen-reduction pathway dominated by ·O2– intermediates. The enhanced activity is mainly attributed to the combined contribution of defect-modulated electronic structure, oxygen-containing surface species that may facilitate interfacial charge regulation, and a mesoporous network that improves mass transport. This work demonstrates a simple dry plasma-assisted surface modification strategy based on combined electronic-structure and morphology modulation for designing carbon nitride based photocatalysts for photocatalytic H2O2 production.