Incorporation of Cu into Goethite Stimulates Oxygen Activation by Surface-Bound Fe(II) for Enhanced As(III) Oxidative Transformation

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 theory (DFT) evidence reveals that the electron transfer (ET) rate constant is enhanced from 0.023 to 0.197 s–1, improving the electron efficiency of the surface-bound Fe(II) on OV defective surfaces. The cascade charge transfer from the surface-bound Fe(II) to O2 mediated by Fe(III) oxyhydroxides leads to the O–O bond of O2 stretching to 1.46–1.48 Å equivalent to that of superoxide (•O2 –), and •O2 – is the predominant ROS responsible for As(III) oxidation. Our findings highlight the significant role of atom incorporation in changing the ET process on Fe(III) oxyhydroxides for ROS production. Thus, such an effect must be considered when evaluating Fe mineral reactivity toward changing their surface chemistry, such as those noted here for Cu incorporation, which likely determines the fates of arsenic and other redox sensitive pollutants in the environments with oscillating redox conditions.

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

“…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.…”

“…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) .…”

Unveiling the Mechanism and Kinetics of Pollutant Attenuation by Free Radicals Triggered from Goethite in Water Distribution Systems

“…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)] .…”

Direct Nanoscale Imaging Reveals the Mechanism by Which Organic Acids Dissolve Vivianite through Proton and Ligand Effects

“…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+ ).…”

“…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+ ).…”