Dual-Ligand-Driven\nDark Reactive Oxygen Species Generation\non Iron Oxyhydroxides: Implications for Environmental Remediation

The dark generation of reactive oxygen species (ROS),\nparticularly\nhydroxyl radicals (·OH), is crucial in the oxidative transformation\nof various pollutants. However, the mechanisms behind this process\nare predominantly linked to direct O<sub>2</sub> activation by reduced\nsubstances such as Fe(II) and natural organic matter. In this study,\nwe introduce a previously overlooked dual-ligand mechanism that significantly\namplifies ·OH generation on iron oxyhydroxides, facilitated by\ncysteine and pyrophosphate. Our findings reveal that these ligands\ncollaboratively boost ·OH generation by 99.5–125.7% compared\nto Fe(II) alone. This enhancement occurs through a two-step electron\ntransfer (ET) process, where cysteine transfers electrons to O<sub>2</sub> through iron oxyhydroxides. The complexation of pyrophosphate\nwith iron oxyhydroxides further reduces the thermodynamic barriers,\nnotably promoting this ET process and significantly improving the\nelectron utilization efficiency for O<sub>2</sub> activation by the\nelectron donor cysteine. Such a process has shown its great potential\nfor effectively driving the oxidative transformation of various pollutants,\nincluding As(III), dichlorophenol, and carbamazepine. These findings\noffer valuable insights for nature-based pollutant mitigation in soil\nand subsurface environments.