Oxygen Vacancy-Augmented Extracellular ROS Generation and Surface Affinity for Arsenic Sequestration in Rice Iron Plaques

Iron plaques serve as the final barrier for the catalytic transformation and sequestration of pollutants, such as arsenic, on rice roots, yet the role of surface structural properties in their performance remains largely unknown. Here, we demonstrate that the presence of oxygen vacancies (OVs) on iron plaques plays a dual role in augmenting the molecular O₂ activation and sequestration of arsenic. The incorporation of copper (Cu) atoms into lattices increases the OV density, boosting extracellular reactive oxygen species (ROS) generation by enhancing the radial oxygen loss and facilitating electron transfer from Fe(II) that activates O₂ on the plaque surface. This process leads to an elevated H₂O₂ flux and higher yields of ^•O₂^- and ^•OH on rice roots. Notably, the stimulation of extracellular ROS imposes no detectable adverse effects on rice growth. The increase in OVs also significantly enhances the adsorption capacity of rice iron plaques for arsenic sequestration, attributed to the improved surface binding free energy between arsenic and iron plaques. The findings of this study underscore the crucial but previously overlooked role of OVs in regulating arsenic uptake by iron plaques, offering new insights into biogeochemical chemistry of iron coupled to arsenic in the rice rhizospheres.