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

Abstract

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-C=O 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.