New Barrier Role of Iron Plaque: Producing Interfacial Hydroxyl Radicals to Degrade Rhizosphere Pollutants

Abstract

Iron plaque, as a natural barrier between rice and soil, can reduce the accumulation of pollutants in rice by adsorption, contributing to the safe production of rice in contaminated soil. In this study, we unveiled a new role of iron plaque, i.e., producing hydroxyl radicals (•OH) by activating rootsecreted oxygen to degrade pollutants. The •OH was produced on the iron plaque surface and then diffused to the interfacial layer between the surface and the rhizosphere environment. The iron plaque activated oxygen via a successive three-electron transfer to produce •OH, involving superoxide and hydrogen peroxide as the intermediates. The structural Fe(II) in iron plaque played a dominant role in activating oxygen rather than the adsorbed Fe(II), since the structural Fe(II) was thermodynamically more favorable for oxygen activation. The oxygen vacancies accompanied by the structural Fe(II) played an important role in oxygen activation to produce •OH. The interfacial •OH selectively degraded rhizosphere pollutants that could be adsorbed onto the iron plaque and was less affected by the rhizosphere environments than the free •OH. This study uncovered the oxidative role of iron plaque mediated by its produced •OH, reshaping our understanding of the role of iron plaque as a barrier for rice.

Ferric Oxide Nanomaterials and Plant-Rhizobacteria Symbionts Cogenerate Iron Plaque for Removing Highly Chlorinated Contaminants in Dryland Soils

“…As shown in Figure b, the treatment with Fe 3+ and H 2 O 2 achieved a removal rate of 28.1% within 24 h, and the addition of cysteine further increased the value to 1.23 times. It is known that the Fenton reaction can be triggered by either Fe 3+ or Fe 2+ , which was the major iron species in previously reported iron plaque. , In our study, the Fe 2+ -mediated Fenton reaction had a significantly higher efficiency compared to the Fenton reaction triggered by Fe 3+ ( p = 0.002–0.044), indicating the superior performance of the cysteine-mediated ferrous iron plaque . Meanwhile, the kinetics of •OH were also monitored in the simulation experiment (Figure c).…”

“…Iron plaque can act as both a barrier and a mediator for the degradation of rhizosphere pollutants. For example, the degradation of propane and atrazine was achieved at the interface of iron plaque . In this study, we found that the α-Fe 2 O 3 NM treatment and the cotreatment resulted in the highest PCB101 content in iron plaque; meanwhile, the removal rates of PCB101 in soil were similarly the highest in these two treatments.…”

“…It not only acts as a barrier resistant to the upward transport of pollutants but also acts as a producer of interfacial reactive oxygen species (ROS) for pollutant degradation. For example, iron plaque on rice root surface prevented the migration of Cd and As, and ROS on the iron plaque surface were responsible for the degradation of propane and atrazine . However, iron plaque is known to exist only on the root surfaces of wetland plants such as Oryza sativa, Phragmites austra, Salix jiangsuensis, Spartina alterniflora, and Kandelia obovate due to the demanding submerged anaerobic conditions.…”

Structure Change of Iron Plaque Induced by Iron-Reducing Bacteria Inhibits Ciprofloxacin Uptake by Plants

“…The intermediate byproducts comprised superoxide and hydrogen peroxide . The • OH was generated on the surface of iron plaque and subsequently diffused toward the interface layer between the iron plaque and the rhizosphere environment, facilitating the degradation of pollutants . Consequently, we employed a fluorescence probe to investigate the generation of • OH by iron plaque formed under various treatments.…”

Hydrogen Production via Electrolysis of Wastewater

“…Hydroxyl radical (•OH) with the oxidation potential of 2.8 V is an important reactive oxygen species (ROS) that can efficiently degrade pollutants [48][49][50][51][52]. Efficient production of •OH is the key to achieving synchronous hydrogen production and water purification.…”