Shape-engineered carbon quantum dots embedded on CdS-nanorods for enhanced visible light harvesting towards photocatalytic application

Abstract

Shape-engineered yellow-emissive carbon quantum dots (Y-CQDs) with discernible edges were synthesized. Three-fold-symmetric benzene-1,3,5-triol was a suitable precursor for controlling the specific structure and shape of CQDs via dehydration-facilitated covalent polymerization in sulfuric acid within 90 min of a thermal reaction at 190 °C. The formation mechanism involves ring cyclization of benzene-1,3,5-triol via a six-membered fashion through elimination of the neighboring active -H and –OH groups. Binary heterostructure nanocomposites, comprising CdS-nanorods (NRs) and Y-CQDs, were prepared using simple sonication followed by solvent evaporation under stirring. The nanocomposite with 6 wt% YCQDs (CdS@Y-CQDs-6) exhibited the highest enhanced photocatalytic degradation of rhodamine B (RhB) with a degradation efficiency of 98% within 45 min, and the degradation rate constant was ~4.8 times higher than that of pristine CdS-NRs under visible light irradiation. The degradation of RhB is carried out through the formation of a green emissive intermediate N-deethylated RhB. The improved photocatalytic degradation performance of CdS@Y-CQDs nanocomposites is attributed to the formation of near-surface heterojunction of surface-adsorbed specific-shaped Y-CQDs, which can widen the range of light absorption and promote the separation of photogenerated electron-hole pairs in CdS-NRs by trapping and boosting the transfer of photo excited charge carriers over the surface.