Quinones stimulate reactive oxygen species production from zero-valent iron over centimeter distances

Zero-valent iron (ZVI) has demonstrated high potential for in-situ remediation of contaminated groundwater and soils. Upon exposure to oxygen, ZVI generates reactive oxygen species (ROS). In parallel with the electron transfer mediated-reductive path, ROS plays a critical role in the oxidative degradation of organic pollutants during ZVI remediation of groundwater and soil. Yet, the efficiency is often constrained by the confined ROS production localized to the surface or immediate vicinity of ZVI particles. Here, we demonstrate that quinones significantly enhance ROS production from ZVI over centimeter-scale distances. H₂O₂ and ^•OH were detected over 1 cm from ZVI particles after 24 h of incubation, with production increasing alongside quinone concentration and incubation time, reaching 318.3 ± 50.0 µM and 1263.2 ± 143.5 nM at 2 mm, respectively. The broad applicability of quinone in promoting remote ROS generation was demonstrated for various ZVI materials. This remote ROS production is driven by sequential electron transfer from ZVI to quinone, long-distance electron transfer via quinone, and subsequent electron transfer from reduced quinone to oxygen. The resulting increase in ROS production amount and extended range improved ZVI remediation efficiency by 5- to 15-fold for organic pollutant degradation. These findings provide a promising strategy for enhancing ROS-mediated ZVI remediation in heterogeneous environments.