Abstract:The dark production of reactive oxygen species (ROS)
coupled to
biogeochemical cycling of iron (Fe) plays a pivotal role in controlling
arsenic transformation and detoxification. However, the effect of
secondary atom incorporation into Fe(III) oxyhydroxides on this process
is poorly understood. Here, we show that the presence of oxygen vacancy
(OV) as a result of Cu incorporation in goethite substantially enhances
the As(III) oxidation by Fe(II) under oxic conditions. Electrochemical
and density functional the… Show more
“…During the process of oxygen activation, OVs frequently served as sites for oxygen adsorption and activation (Figure 3a). 35 The EPR analysis of the iron plaque showed a characteristic signal of OVs with a g value of 2.004, demonstrating the presence of OVs in the iron plaque (Figure 3f). 36 This OV signal decreased markedly after oxygen activation (Figure 3f), implying the involvement of OVs in the process of •OH production from oxygen activation by iron plaque.…”
Section: ■ Resultsmentioning
confidence: 93%
“…The results of XPS revealed the presence of approximately 3% Fe(II) in the iron plaque, and the Fe(II) signal in the iron plaque disappeared after oxygen activation (Figures d and e), suggesting the involvement of Fe(II) in oxygen activation. During the process of oxygen activation, OVs frequently served as sites for oxygen adsorption and activation (Figure a) . The EPR analysis of the iron plaque showed a characteristic signal of OVs with a g value of 2.004, demonstrating the presence of OVs in the iron plaque (Figure f) .…”
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.
“…During the process of oxygen activation, OVs frequently served as sites for oxygen adsorption and activation (Figure 3a). 35 The EPR analysis of the iron plaque showed a characteristic signal of OVs with a g value of 2.004, demonstrating the presence of OVs in the iron plaque (Figure 3f). 36 This OV signal decreased markedly after oxygen activation (Figure 3f), implying the involvement of OVs in the process of •OH production from oxygen activation by iron plaque.…”
Section: ■ Resultsmentioning
confidence: 93%
“…The results of XPS revealed the presence of approximately 3% Fe(II) in the iron plaque, and the Fe(II) signal in the iron plaque disappeared after oxygen activation (Figures d and e), suggesting the involvement of Fe(II) in oxygen activation. During the process of oxygen activation, OVs frequently served as sites for oxygen adsorption and activation (Figure a) . The EPR analysis of the iron plaque showed a characteristic signal of OVs with a g value of 2.004, demonstrating the presence of OVs in the iron plaque (Figure f) .…”
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.
“…Direct evidence of the presence of OVs was provided by the deconvoluted high-resolution O 1s XPS spectrum, with OVs indicated by the convolution peak at approximately 532.6 eV (Figure S3a). OVs on goethite favor electron transfer toward Fe(III) sites to maintain charge balance, leading to the formation of Fe(II). ,, This mechanism aligned with the Fe 2p spectra (Figure S3b) recorded for goethite, with two peaks at 725.0 and 712.0 eV corresponding to Fe 2p 1/2 and Fe 2p 3/2 , respectively. The Fe 2p peak could be split into six peaks at 709.9 eV [Fe(II)], 710.9 eV [Fe(III)], 712.3 eV [Fe(III)], 723.6 eV [Fe(II)], 725.0 eV [Fe(III)], and 726.7 eV [Fe(III)] .…”
Investigating the fate of persistent organic pollutants in water distribution systems (WDSs) is of great significance for preventing human health risks. The role of iron corrosion scales in the migration and transformation of organics in such systems remains unclear. Herein, we determined that hydroxyl ( • OH), chlorine, and chlorine oxide radicals are generated by Fenton-like reactions due to the coexistence of oxygen vacancy-related Fe(II) on goethite (a major constituent of iron corrosion scales) and hypochlorous acid (HClO, the main reactive chlorine species of residual chlorine at pH ∼ 7.0). • OH contributed mostly to the decomposition of atrazine (ATZ, model compound) more than other radicals, producing a series of relatively low-toxicity small molecular intermediates. A simplified kinetic model consisting of mass transfer of ATZ and HClO, • OH generation, and ATZ oxidation by • OH on the goethite surface was developed to simulate iron corrosion scale-triggered residual chlorine oxidation of organic compounds in a WDS. The model was validated by comparing the fitting results to the experimental data. Moreover, the model was comprehensively applicable to cases in which various inorganic ions (Ca 2+ , Na + , HCO 3 − , and SO 4 2−) and natural organic matter were present. With further optimization, the model may be employed to predict the migration and accumulation of persistent organic pollutants under real environmental conditions in the WDSs.
“…2−7 Moreover, the structural defects of Fe (oxyhydr)oxides such as oxygen vacancies or Fe vacancies will increase their activity, thus resulting in P sequestration. 8,9 When the K sp value reaches 1.3 × 10 −22 , highly insoluble Fe(III)-P minerals such as strengite (FePO 4 •2H 2 O) can be formed. In a relatively anoxic aquatic environment, Fe is often in a reduced state (Fe 2+ ).…”
Section: Introductionmentioning
confidence: 99%
“…However, their bioavailability is often limited due to their coexistence in the environment . For example, in an aerobic dry land environment, P tends to be adsorbed onto Fe (oxyhydr)oxides, even resulting in the burial of P during the transformation process of Fe (oxyhydr)oxides. − Moreover, the structural defects of Fe (oxyhydr)oxides such as oxygen vacancies or Fe vacancies will increase their activity, thus resulting in P sequestration. , When the K sp value reaches 1.3 × 10 –22 , highly insoluble Fe(III)-P minerals such as strengite (FePO 4 ·2H 2 O) can be formed. In a relatively anoxic aquatic environment, Fe is often in a reduced state (Fe 2+ ).…”
The coprecipitation of iron (Fe) and phosphorus (P) in natural environments limits their bioavailability. Plant rootsecreted organic acids can dissolve Fe−P precipitates, but the molecular mechanism underlying mobilizing biogenic elements from highly insoluble inorganic minerals remains poorly understood. Here, we investigated vivianite (Fe 3 (PO 4 ) 2 •8H 2 O) dissolution by organic acids (oxalic acid (OA), citric acid (CA), and 2′-dehydroxymugineic acid (DMA)) at three different pH values (4.0, 6.0, and 8.0). With increasing pH, the vivianite dissolution efficiency by OA and CA was decreased while that by DMA was increased, indicating various dissolution mechanisms of different organic acids. Under acidic conditions, weak ligand OA (HC 2 O 4 − > C 2 O 4 2− at pH 4.0 and C 2 O 4 2− at pH 6.0) dissolved vivianite through the H + effect to form irregular pits, but under alkaline condition (pH 8.0), the completely deprotonated OA was insufficient to dissolve vivianite. At pH 4.0, CA (H 2 Cit − > HCit 2 − > H 3 Cit) dissolved vivianite to form irregular pits through a proton-promoted mechanism, while at pH 6.0 (HCit 2− > Cit 3− ) and pH 8.0 (Cit 3− ), CA dissolved vivianite to form near-rhombohedral pits through a ligand-promoted mechanism. At three pH values ((H 0 )DMA 3− > (H 1 )DMA 2− at pH 4.0, (H 0 )DMA 3− at pH 6.0, and (H 0 )DMA 3− and one deprotonated imino at pH 8.0), strong ligand DMA dissolved vivianite to form near-rhombohedral pits via ligand-promoted mechanisms. Raman spectroscopy showed that the deprotonated carboxyl groups (COO − ) and imino groups were bound to Fe on the vivianite (010) face. The surface free energy of vivianite coated with OA decreased from 29.32 mJ m −2 to 24.23 mJ m −2 and then to 13.47 mJ m −2 with increasing pH, and that coated with CA resulted in a similar pH-dependent vivianite surface free-energy decrease while that coated with DMA increased the vivianite surface free energy from 31.92 mJ m −2 to 39.26 mJ m −2 and then to 49.93 mJ m −2 . Density functional theory (DFT)-based calculations confirmed these findings. Our findings provide insight into the mechanism by which organic acids dissolved vivianite through proton and ligand effects.
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