Enhanced photoreduction of perfluorooctane sulfonate via a confined nitrilotriacetic acid system augmented by CTAB.

Perfluorooctane sulfonate (PFOS) is a persistent "forever chemical". The degradation of PFOS was previously achieved using hydrated electron (eaq-) generated from nitrilotriacetic acid (NTA). However, eaq- generation requires highly alkaline and anaerobic conditions, and is easily quenched by the matrices in aquatic environments, limiting its practical application. To address the issues of low quantum yield of eaq- in UV/NTA system and the stringent reaction conditions required, we report a novel UV/NTA/Cetyltrimethylammonium bromide (CTAB) system. Compared to the UV/NTA and UV/NTA/FeII systems, the new system demonstrates higher efficiency, a broader applicable pH range, and strong tolerance to both aerial and complex aqueous matrix interference. Under an air atmosphere at pH 7.0, the system achieved 98.56% PFOS degradation with 42.88% defluorination within 10 h (using a 16 W low-pressure mercury UV lamp). Zebrafish toxicological assays confirmed a significant reduction in the biological toxicity of the treated water. Interaction experiment, dynamic light scattering (DLS), zeta potential, small angle X-ray scattering (SAXS), and UV-vis spectra revealed that the positively charged CTAB reverses the electrostatic repulsion between negatively charged NTA and PFOS, confining them in a restricted space. Quenching studies, electron paramagnetic resonance (EPR) spectra, and laser flash photolysis (LFP) experiment identified eaq- as the primary reactive species. Notably, CTAB enhances the quenching of •OH by NTA, thereby promoting eaq- generation. This work highlights a strategy based on electrostatic confinement and spatial restriction for efficient PFOS degradation, effectively mitigating the influence of environmental factors and matrix interference during photoreduction.