“Carbon diffusion” engineered carbon nitride nanosheets for high-efficiency photocatalytic solar-to-fuels conversion

The fabrication of graphitic carbon nitride (g-C₃N₄) has received much attention for its superior photoelectronic properties, it remains a remarkable challenge with a feasible methodology. Herein, inspired by carburization, a novel method with carbon diffusion was proposed to prepare g-C₃N₄ nanosheets (CNNS). The carbon diffusion was caused by the gradient difference in carbon concentration between the gaseous environment and the C15 (mild steel with low carbon content) during thermal polymerization. Eventually, the CNNS with approximately 1.5 nm thickness was successfully fabricated and exhibited larger surface area (98.08 m² g⁻¹), which was 15.42 times higher than that of bulk g-C₃N₄ (BCN). In the evaluation of photocatalytic CO₂ reduction activity, the CH₃OH formation rate over CNNS (2.10 μmol g⁻¹ h⁻¹) was 3.28 times greater than BCN. Meanwhile, the designed CNNS exhibited dramatic improvement on H₂ evolved rate (HER) of 2507.02 μmol g⁻¹ h⁻¹, which was 6.99 times higher than BCN. More importantly, the C15 possessed the advantage of 10 times recycled to use for the fabrication of CNNS accompanied by a moderate decrease of HER. Moreover, the density functional theory (DFT) calculations were carried out based on the results. This work highlights an ingenious tactic with carbon diffusion for preparing CNNS towards renewable solar energy conversion.