Dual-Ligand-Driven Dark Reactive Oxygen Species Generation on Iron Oxyhydroxides: Implications for Environmental Remediation

The dark generation of reactive oxygen species (ROS), particularly hydroxyl radicals (·OH), is crucial in the oxidative transformation of various pollutants. However, the mechanisms behind this process are predominantly linked to direct O2 activation by reduced substances such as Fe(II) and natural organic matter. In this study, we introduce a previously overlooked dual-ligand mechanism that significantly amplifies ·OH generation on iron oxyhydroxides, facilitated by cysteine and pyrophosphate. Our findings reveal that these ligands collaboratively boost ·OH generation by 99.5–125.7% compared to Fe(II) alone. This enhancement occurs through a two-step electron transfer (ET) process, where cysteine transfers electrons to O2 through iron oxyhydroxides. The complexation of pyrophosphate with iron oxyhydroxides further reduces the thermodynamic barriers, notably promoting this ET process and significantly improving the electron utilization efficiency for O2 activation by the electron donor cysteine. Such a process has shown its great potential for effectively driving the oxidative transformation of various pollutants, including As(III), dichlorophenol, and carbamazepine. These findings offer valuable insights for nature-based pollutant mitigation in soil and subsurface environments.