Manifestation of an Enhanced Photoreduction of CO₂ to CO over the <i>In Situ</i> Synthesized rGO–Covalent Organic Framework under Visible Light Irradiation

Abstract

Photocatalytic reduction of CO2 into useful feedstocks has attracted more attention in recent decades. However, the effective and selective conversion of CO2 to the desired product always remains a major challenge in photocatalysis, which relies on the appropriate band edge potential and efficient separation of photogenerated charge carriers in the photocatalysts. In this direction, herein we report the construction of a keto-enamine covalent organic framework (COF) incorporated with reduced graphene oxide with increasing concentrations, rGOx@TpPa-1 (x = 5%, 10%, 15%, and 20%), by the in situ assembling technique to significantly boost up the charge separation thereby to improve the efficiency CO2 photoreduction. The developed rGO15@TpPa-1 nanocomposite showed remarkable efficiencies toward photocatalytic CO2 reduction under visible light irradiation, which yielded the CO at a rate up to ∼200 μmol g–1 h–1 and with a selectivity of 89%, which was 1.57 and 6.97 times higher as compared to the bare COF and rGO counterparts, respectively. The series of control experiments demonstrated that both TpPa-1 and rGO counterparts have a significant synergistic impact on the selectivity and efficiency toward photoreduction of CO2. Under optimized conditions, rGO15@TpPa-1 exhibited an apparent quantum yield of 0.5% at 420 nm, which is one of the few notable values reported in the literature. The covalent interactions between TpPa-1 and rGO facilitated the formation of band edges with required potential and thereby an improved charge separation along with rapid migration of charge carriers to the surface toward the selective reduction of CO2 to CO, which is validated by the 13C labeling. This work could be a promising approach toward energy applications for the potential development of COFs and their analogous structures.