Carboxymethyl cellulose reinforced graphene oxide-MoS2 for photocatalytic degradation of perfluorooctanoic acid (PFOA): process optimization and mechanism.

Perfluorooctanoic acid (PFOA), remains a major environmental challenge due to its exceptional chemical stability, resistance to conventional treatment technologies. In this study, a sustainable carboxymethyl cellulose-reinforced graphene oxide/molybdenum disulfide hydrogel (MoS₂/GO/CMC) was developed as a visible-light-responsive photocatalyst for PFOA degradation under low-power LED irradiation. The photocatalytic process was optimized using Response Surface Methodology based on a Box-Behnken Design, evaluating the effects of irradiation power (7-12 W), catalyst dosage (0-0.04 g), and initial PFOA concentration (10-50 mg L-¹). The optimized conditions (12 W, 0.04 g catalyst, and 30 mg L-¹ PFOA) achieved 99.8% degradation efficiency, with the developed quadratic model exhibiting excellent predictive capability (R² = 0.9974). Characterization results confirmed integration of MoS₂ and GO within the CMC matrix, producing a heterostructure with a narrow band gap of 1.12 eV, enhanced charge separation, and suppressed electron-hole recombination. Kinetic analysis revealed pseudo-first-order degradation behaviour with a rate constant of 0.013 min-¹ and a half-life of 0.89 h. Radical scavenging experiments identified superoxide radicals (O₂•-) as the dominant reactive species governing PFOA degradation. LC-MS analysis confirmed a stepwise chain-shortening degradation pathway involving intermediates such as PFHpA, PFPeA, and PFBA, indicating progressive defluorination and carbon-carbon bond cleavage. The hydrogel demonstrated excellent stability, retaining over 96% of its initial activity after seven cycles. An Electrical Energy per Order (EEO) value of 444.6 kWh m-³ order-¹ highlights the feasibility of low-energy operation. These findings demonstrate that MoS₂/GO/CMC hydrogels offer an environmentally benign, recoverable, and energy-efficient for PFAS remediation.