Vegetal route for synthesis of CQDs/CdS nanocomposites for photocatalytic reduction of CO2 to methanol under visible light

Abstract

The green pathway for the synthesis of nanoparticles targeting the photoreduction of CO2 to value-added chemicals is a potential approach to control industrial CO2 emission. In this study, we synthesized bio-based CdS(bio) nanorods using plant-based phytochemicals found in Aegle marmelos and carbon quantum dots (CQDs) using orange peels. CQDs (7 nm) were homogeneously incorporated into CdS(bio) nanorods via simple deposition, forming CQDs/CdS(bio) nanocomposites. The catalysts were thoroughly characterized using diffraction, microscopic, spectroscopic, and electrochemical techniques. CQDs/CdS(bio) composites had a diameter and length of 73 nm and 822 nm with 82.25 m2/g specific surface area. CQDs/CdS(bio) composites showed a fourfold increase in both photocurrent density (0.38 μA/cm2) and CO2 adsorption capacity (0.292 mmol/g) compared to CdS(bio) nanorods alone. The conduction band of the composite (−0.92 eV) becomes more negative compared to CdS(bio) (−0.85 eV). Moreover, the composite formation notably improved decay time by 2.35 folds and reduced photoluminescence intensity by 59.23% compared to CdS(bio), indicating enhanced charge separation and reduced charge carrier recombination. Furthermore, the photocatalytic activity of CQDs/CdS(bio) nanocomposites was investigated for CO2 reduction to methanol under visible light (250 W, λ > 420 nm, 2.2 W/m2, 4.2719 ×1018 photons/m2.s) without any sacrificial reagent. The effect of the mass fraction of CQDs on CdS and catalyst loading on photocatalytic CO2 reduction has been investigated. The optimal CQDs/CdS(bio) loading (0.50% w/w) exhibited the maximum methanol yield of 1060.52 μmol/g·h (apparent quantum efficiency 7%) over 5 h. CQDs/CdS(bio) nanocomposites exhibited strong stability (test up to 25 h in five consecutive cycles), retaining the morphological (0.11% variation in size) and structural (4.2% variation in crystallinity index) attributes. This work would provide valuable insights into the development of bio-based CdS-based composites for efficient PCO2RR into valuable chemicals.