Singlet Oxygen‐Mediated Photocatalytic Removal of Perfluoroalkyl Substances by Sulfur Vacancy‐Engineered ZnIn ₂ S ₄

Abstract Per and polyfluoroalkyl substances (PFAS) present profound environmental and health hazards owing to their chemical persistence. Photocatalytic technology harnesses solar energy to generate reactive oxygen species for pollutant degradation. However, prevailing studies have emphasized hydroxyl radical mediated pathways. The short lifetime of hydroxyl radical and the stringent conditions required for its formation constrain the efficiency of this approach against recalcitrant PFAS such as perfluorooctanoic acid (PFOA). In this study, a ZnIn 2 S 4 photocatalyst enriched with sulfur vacancies is synthesized via a facile hydrothermal‐calcination approach. The introduction of sulfur vacancies enhances visible light absorption and promotes efficient separation of photogenerated electron‐hole pairs. Theoretical calculations further reveal that sulfur vacancies enhance the kinetics of oxygen evolution, oxygen adsorption capacity, and the efficiency of singlet oxygen ( 1 O 2 ) generation, reducing the activation barriers throughout the oxygen activation cascade. Combined electron paramagnetic resonance spectroscopy and radical quenching experiments confirm 1 O 2 as the dominant reactive oxygen species responsible for PFOA degradation, operating via a non‐hydroxyl radical mechanism. The catalyst achieves over 93% degradation efficiency for 50 µg L −1 PFOA in surface water and aquaculture wastewater, demonstrating the application potential of sulfur vacancy‐engineered photocatalytic systems for the effective remediation of trace emerging contaminants in actual environments.