Quinone structure regulates sulfide-driven reactive oxygen species generation for aquatic pollutant degradation

Organic pollutant remediation in sulfidic aquatic systems (e.g., pore water) is hampered by inefficient reactive oxygen species (ROS) production during sulfide oxidation. Although ubiquitous quinones can accelerate ROS generation for pollutant degradation during this process, the impact of their chemical structure has not been thoroughly studied. This study demonstrates that structurally diverse quinones (10-50 μM) with varying aromaticity and substituents increase ROS (specifically ·OH and ¹O₂) yields by 47-403 % and accelerate the degradation kinetics of 17-β-estradiol (E2) in aerobic sulfide oxidation systems. Mechanistic results show that in addition to the electron-transfer mediator quinones/semiquinone radicals/hydroquinone, the nucleophilic addition products of quinones and sulfide may also contribute to the ROS generation. The newly established structure-activity relationship for quinones structure and redox property highlights that: quinones with higher aromaticity and electron-donating groups (EDG) promote ROS generation by accelerating semiquinone radical oxidation; electron-accepting groups (EAG) facilitate ROS production by enhancing quinones reduction; and ortho-positioned EDG activate the quinones ring through strong electronic conjugation. Notably, semiquinone radical properties exhibit a more pronounced impact on ROS generation than those of parent quinones. Overall, this work advances the mechanistic understanding of how quinones structure regulates sulfide-driven ROS generation in aquatic systems.