Synthesis of an S-scheme heterojunction g-C3N4/MIL-100(Fe) photocatalyst for efficient inactivation of a freshwater dinoflagellate and elucidation of its ROS-mediated damage mechanisms

Freshwater dinoflagellate blooms present a growing global challenge requiring effective and green remediation solutions. Here, we report the synthesis of a novel g-C 3 N 4 /MIL-100(Fe) S-scheme heterojunction photocatalyst and systematically evaluate its efficacy against the harmful dinoflagellate Peridinium umbonatum . The optimized composite exhibited superior performance under simulated solar light, achieving over 90 % inactivation of algal cells within 3 h. Mechanistic investigations, including electron paramagnetic resonance (EPR), confirmed that the S-scheme heterojunction enabled the efficient generation of multiple reactive oxygen species (ROS), namely •OH, •O 2 − , and 1 O 2 . Furthermore, radical quenching experiments identified the hydroxyl radical (•OH) as the primary species responsible for the rapid algal inactivation. These ROS launched a multi-targeted attack, initiating rapid loss of cell membrane integrity, which led to massive leakage of intracellular components and the collapse of the algal antioxidant system. This study elucidates a detailed ROS-mediated damage pathway and provides a robust framework for designing advanced Metal-Organic Framework (MOF)-based photocatalysts to control harmful freshwater dinoflagellate blooms. • S-scheme g-C 3 N 4 /MIL-100(Fe) was synthesized via the facile grinding method. • Optimized 25CN/MIL had 91 % algal inhibition and 87.5 % carotenoid loss in 3 h solar light. • EPR confirmed .•OH, •O 2 − , and 1 O 2 as primary ROS in photocatalysis. • ROS caused membrane damage, component leakage, and antioxidant imbalance.