Sustainable photocatalytic degradation of perfluoroctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) using chitosan-doped g-C₃N₄ for green water treatment

Per and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants with strong resistance to degradation and significant health risks. This study presents a sustainable and practical photocatalytic approach for PFAS remediation using chitosan doped graphitic carbon nitride (CS@g-C₃N₄) synthesized via thermal polymerization. The composite was thoroughly characterized using X-ray diffraction (XRD) to determine crystal structure, BET analysis to measure surface area, SEM/TEM for morphology and nanostructure, FTIR for functional group identification, XPS for surface elemental composition, and photoluminescence (PL) spectroscopy to assess charge recombination dynamics. Chitosan doping significantly increased surface area, suppressed charge recombination, and enhanced visible light-driven photocatalytic activity. Under optimized conditions after 120 min of irradiation, with an initial PFAS concentration of 10 mg·L⁻¹, catalyst loading of 0.5 g/L, at pH 7 and temperature of 25°C, the CS@g-C₃N₄ composite achieved high degradation efficiencies of 93% for perfluorooctanoic acid (PFOA) and 88% for perfluorooctane sulfonate (PFOS). Kinetic studies revealed pseudo second order degradation behavior, while adsorption data fit the Langmuir isotherm model, indicating monolayer adsorption with maximum capacities of 26.7 mg/g for PFOA and 24.2 mg/g for PFOS. Thermodynamic analysis confirmed the process is spontaneous and exothermic. The catalyst demonstrated excellent stability and reusability over five cycles, underscoring its practical potential. These findings position CS@g-C₃N₄ as a cost-effective and environmentally friendly photocatalyst for PFAS removal. Future work should focus on pilot-scale validation, long-term stability under complex water matrices, and integration with complementary treatment technologies to advance real-world applications. Overall, this work represents a promising step toward sustainable and scalable solutions for mitigating persistent PFAS pollution.