Oxygen-Doped Porous Ultrathin Graphitic Carbon Nitride Nanosheets for Photocatalytic Hydrogen Evolution and Rhodamine B Degradation

Graphite phase carbon nitride (g−C₃N₄) is a highly promising metal-free photocatalyst, but its low activity, due to limited quantum efficiency and small specific surface area, restricts its practical application. While exfoliating bulk crystals into porous thin-layer nanosheets and incorporating dopants have been shown to improve photocatalytic efficiency, these methods are typically complex, time-consuming, and costly processes. In this study, we developed a simple approach to synthesize oxygen-doped porous g−C₃N₄ (OCN) nanosheets. The resulting OCN exhibited significantly enhanced light absorption and visible-light photocatalytic activity compared to bulk g−C₃N₄ (BCN) and g−C₃N₄ (CN). The OCN achieved an impressive hydrogen evolution reaction (HER) rate of 8.02 mmol g⁻¹ h⁻¹, eight times greater than BCN, and demonstrated a high Rhodamine B (RhB) degradation rate of 97.3 % owing to the generation of abundant singlet oxygen. These improvements in photocatalytic performance are attributed to the narrow band gap and enhanced electron transfer properties, suggesting a promising route for the efficient design of g−C₃N₄-based photocatalysts.