Enhanced photodegradation of perfluorocarboxylic acids (PFCAs) using carbon quantum dots (CQDs) doped TiO₂ photocatalysts: A comparative study between exfoliated graphite and mussel shell-derived CQDs

Remediation of perfluorocarboxylic acids (PFCAs) is crucial due to their widespread distribution, persistence, and harmful effects on aquatic life, especially as short-chain fluorinated compounds are increasingly used as substitutes after the global ban on long-chain PFCAs. This pioneering study explores the photodegradation of perfluorooctanoic acid (PFOA-C₈) and several short-chain PFCAs using carbon quantum dot (CQD)-doped TiO₂. We synthesized CQDs via two innovative methods: electrochemical exfoliation of graphite rods (Exfol.CQD) and a hydrothermal process using mussel shell biomass (MCQD). The structural and morphological properties of CQDs, TiO₂, and CQD/TiO₂ composites were characterized. Photodegradation tests showed that Exfol.CQD/TiO₂ significantly improved PFOA degradation under visible light, achieving a twofold increase compared to pure TiO₂. Degradation rates for C₃-C₆ short-chain PFCAs with Exfol.CQD/TiO₂ ranged from 22 % to 40 %. PFOA decomposed stepwise into shorter-chain PFCAs and F⁻ ions, maintaining excellent reusability after three cycles. In contrast, the MCQD/TiO₂ photocatalyst needed further optimization due to decreased performance. Our research has shown that using pure water and ethanol as electrolytes facilitates the synthesis of high-purity CQDs without the need for chemical additives. This study sheds light on the previously underexplored area of photodegradation of PFCAs via CQD/TiO₂ composites, highlighting their potential applications in wastewater treatment.