Selective oxidation of glycerol to value-added chemicals over green carbon dots modified graphitic carbon nitride charge-transfer photocatalyst

The ultrathin nanosheets of graphitic carbon nitride (CN) were modified by biomass-derived green carbon dots (CDs) by an in-situ method and investigated for photo-oxidation of glycerol. The amount of CDs was varied and CDCN composites were analyzed by physicochemical, optical, and photoelectrochemical characterization techniques. The band gap was reduced for all modified CDCN catalysts in the range of 2.53–2.69 eV compared to 2.78 eV for bare CN. The lower PL intensity of all modified CDCN photocatalysts suggested the prevention of recombination of their electron/hole pairs and thereby greater stabilization. After the addition of CDs, the decrease in TRPL lifetime suggested rapid charge transfer ability of CDCN samples. The photocurrent density was enhanced for modified photocatalysts than that of bare CN, which was further enhanced in the presence of light and glycerol. It was noted that product distribution changed as the loading or amount of CDs changed in photocatalysts. The 2.5CDCN showed highest selectivity (61.3%) and yield (11.7%) for glycolic acid, whereas 5CDCN showed highest selectivity and yield for glyceraldehyde at 52.3% and 18.7%, respectively. The 10CDCN, with highest CDs content, demonstrated highest selectivity (53.5%) and yield (15.6%) towards the glycolic acid. This study demonstrated the synthesis of waste biomass-derived CDs and their utilization in metal-free photocatalytic systems for glycerol photo-oxidation. The findings provided a sustainable route for glycerol conversion, contributing to the fields of waste utilization and valorization.