Highly efficient and selective photoreduction of CO₂ to CO with nanosheet g-C₃N₄ as compared with its bulk...

Artificial photoreduction of CO₂ to clean energy utilizing the unlimited solar energy has shown promise to suppress the greenhouse effect and alleviate the energy shortage. In this study, a simple one-step calcination method was utilized to synthesize ultrathin nanosheet g-C₃N₄ (NS-g-C₃N₄). The prepared NS-g-C₃N₄ with a thickness of 10 nm was demonstrated to exhibited higher efficiency and selectivity than that of bulk counterpart (B-g-C₃N₄) for the photocatalytic reduction of CO₂ to CO under visible light irradiation. The yield of CO in the system with obtained NS-g-C₃N₄ was 5.8 times higher than that of B-g-C₃N₄. CO was measured to be the sole product detected in the system with NS-g-C₃N₄, while CO₂ can be reduced into CO, CH₄ and CH₃OH in the system with B-g-C₃N₄ under the same photocatalytic reduction conditions. The ultrathin nanostructures and abundant surface defect sites of NS-g-C₃N₄ could enhance the visible light adsorption efficiency, favor the separation and transfer of photogenerated carriers, and provide strong chemisorption sites for CO₂, and thus resulting in its remarkable photocatalytic activity to CO₂ reduction. More importantly, the surface defects of nanosheet could shift the adsorption mode of CO₂ from N-CO₂^- for the B-g-C₃N₄ to N-O-CO for NS-g-C₃N₄, and eventually contributing the selective photoreduction of CO₂ to CO. The obtained also NS-g-C₃N₄ exhibited excellent stability for CO₂ photoreduction. No significant change in the photoreduction efficiency of CO₂ in the system with NS-g-C₃N₄ was observed after four cycles. This study could not only provide a novel strategy to realize the high selectivity and efficiency photocatalytic conversion CO₂ to CO, but also aims to clarify the interactions between the adsorption model of CO₂ on g-C₃N₄ surface and the selectivity and efficiency of CO₂ photoreduction.