The function of carbon quantum dots (CQDs) derived from peapod biomass in composite photocatalysts for the enhanced photodegradation of perfluoroalkyl carboxylic acids (PFCAs) under UVC and visible light irradiation

The remediation of perfluoroalkyl carboxylic acids (PFCAs) presents a significant challenge due to their environmental persistence and detrimental impact. In this study, carbon quantum dots (CQDs) were sustainably prepared using peapod biomass via the hydrothermal method and incorporated into a titanium dioxide (TiO2) composite photocatalyst. Chemical, morphological, and optical analysis confirmed the efficient synthesis of the CQD/TiO2 composite, which exhibited enhanced optical properties. Photocatalytic oxidation experiments demonstrated that the CQD/TiO2 composite achieved significantly higher degradation efficiencies for perfluorooctanoic acid (PFOA-C8) compared to pristine TiO2, with 26.3 % and 24.5 % improvements when irradiated under Ultraviolet-C (UVC) and visible light, respectively. Furthermore, the photocatalytic oxidation of short-chain PFCAs, specifically perfluorohexanoic acid (PFHxA-C6), perfluoropentanoic acid (PFPeA-C5), perfluorobutanoic acid (PFBA-C4), and perfluoropropanoic acid (PFPrA-C3), were evaluated under visible light irradiation. Degradation rates for PFHxA-C6 and PFPeA-C5 significantly enhanced from 14.6 % and 19.6 % to 41.3 % and 52.1 %, respectively, when using CQD-coupled TiO2 (CQD/TiO2) compared to pure TiO2. The first-order rate constants revealed accelerated PFCA degradation using PPCQD/TiO2 photocatalysts. Intermediate formation (C3-C6) and defluorination analyses revealed stepwise decomposition of PFCAs, with enhanced CFA detachment in the presence of the CQD/TiO2 composite. The role of scavengers in PFOA degradation under visible light was also examined. This research underscores the potential of CQD-enhanced TiO2 photocatalysts for effective PFCA remediation under sustainable conditions.