Weak Magnetic Field Accelerates Chromate Removal by Zero-Valent Iron

Weak magnetic field (WMF) was employed to improve the removal of Cr(VI) by zero-valent iron (ZVI) for the first time. The removal rate of Cr(VI) was elevated by a factor of 1.12-5.89 due to the application of a WMF, and the WMF-induced improvement was more remarkable at higher Cr(VI) concentration and higher pH. Fe2+ was not detected until Cr(VI) was exhausted, and there was a positive correlation between the WMF-induced promotion factor of Cr(VI) removal rate and that of Fe2+ release rate in the absence of Cr(VI) at pH 4.0-5.5. These phenomena imply that ZVI corrosion with Fe2+ release was the limiting step in the process of Cr(VI) removal. The superimposed WMF had negligible influence on the apparent activation energy of Cr(VI) removal by ZVI, indicating that WMF accelerated Cr(VI) removal by ZVI but did not change the mechanism. The passive layer formed with WMF was much more porous than without WMF, thereby facilitating mass transport. Therefore, WMF could accelerate ZVI corrosion and alleviate the detrimental effects of the passive layer, resulting in more rapid removal of Cr(VI) by ZVI. Exploiting the magnetic memory of ZVI, a two-stage process consisting of a small reactor with WMF for ZVI magnetization and a large reactor for removing contaminants by magnetized ZVI can be employed as a new method of ZVI-mediated remediation

Inhibitory Effect of Sulfite on the SO₄·^–‑Induced Transformation of Selected Organic Contaminants in Sulfite-Based Advanced Oxidation Processes

Sulfite (S(IV))-based advanced oxidation processes (AOPs), with SO4·– being the primary oxidant, have attracted increasing attention for degrading organic contaminants in water. However, the side effect of S(IV) as a reductant on the SO4·–-induced transformation of organic contaminants has never been revealed. For the first time, we demonstrated such an effect of S(IV) by taking the MnO2/S(IV) system as the surrogate S(IV)-based AOP. Multiple evidence confirmed that SO4·– is the sole active oxidant in the MnO2/S(IV) system. The relative-rate experiments in the UV/S2O82– system, a SO4·–-dominated process with the presence of excess tert-butanol, and the MnO2/S(IV) system showed that S(IV) can inhibit the SO4·–-induced transformation of some organic contaminants, with the inhibiting effect being strongly dependent on the solution pH. Flash photolysis experiments and reduction potential calculations clarified the necessary reaction conditions for the inhibiting effect of S(IV) to occur, i.e., the reduction of oxidation intermediate of organic contaminants (TC·+) by S(IV) to parent compound (TC) is exergonic (ΔE > 0), and its rate is faster or comparable to that of the transformation of TC·+ to stable products. This work updates the fundamental understanding of the degradation of organic contaminants in S(IV)-based AOPs

Aging of Zerovalent Iron in Synthetic Groundwater: X‑ray Photoelectron Spectroscopy Depth Profiling Characterization and Depassivation with Uniform Magnetic Field

Scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) depth profiling were employed to characterize the aged zerovalent iron (AZVI) samples incubated in synthetic groundwater. The AZVI samples prepared under different conditions exhibited the passive layers of different morphologies, amounts, and constituents. Owing to the accumulation of iron oxides on their surface, all the prepared AZVI samples were much less reactive than the pristine ZVI for Se­(IV) removal. However, the reactivity of all AZVI samples toward Se­(IV) sequestration could be significantly enhanced by applying a uniform magnetic field (UMF). Moreover, the flux intensity of UMF necessary to depassivate an AZVI sample was strongly dependent on the properties of its passive layer. The UMF of 1 mT was strong enough to restore the reactivity of the AZVI samples with Fe₃O₄ as the major constituent of the passive film or with a thin layer of α-Fe₂O₃ and γ-FeOOH in the external passive film. The flux intensity of UMF necessary to depassivate the AZVI samples would increase to 2 mT or even 5 mT if the AZVI samples were covered with passive films being thicker, denser, and contained more γ-FeOOH and α-Fe₂O₃. Furthermore, increasing the flux intensity of UMF facilitated the reduction of Se­(IV) to Se(0) by AZVI samples

Effect of Weak Magnetic Field on Arsenate and Arsenite Removal from Water by Zerovalent Iron: An XAFS Investigation

In this study, a weak magnetic field (WMF), superimposed with a permanent magnet, was utilized to improve ZVI corrosion and thereby enhance As­(V)/As­(III) removal by ZVI at pH_ini 3.0–9.0. The experiment with real arsenic-bearing groundwater revealed that WMF could greatly improve arsenic removal by ZVI even in the presence of various cations and anions. The WMF-induced improvement in As­(V)/As­(III) removal by ZVI should be primarily associated with accelerated ZVI corrosion, as evidenced by the pH variation, Fe²⁺ release, and the formation of corrosion products as characterized with X-ray absorption fine structure spectroscopy. The arsenic species analysis in solution/solid phases at pH_ini 3.0 revealed that As­(III) oxidation to As­(V) in aqueous phase preceded its subsequent sequestration by the newly formed iron (hydr)­oxides. However, both As­(V) adsorption following As­(III) oxidation to As­(V) in solution and As­(III) adsorption preceding its conversion to As­(V) in solid phase were observed at pH_ini 5.0–9.0. The application of WMF accelerated the transformation of As­(III) to As­(V) in both aqueous and solid phases at pH_ini 5.0–9.0 and enhanced the oxidation of As­(III) to As­(V) in solution at pH_ini 3.0

Combined Effect of Weak Magnetic Fields and Anions on Arsenite Sequestration by Zerovalent Iron: Kinetics and Mechanisms

In this study, the effects of major anions (e.g., ClO₄^–, NO₃^–, Cl^–, and SO₄^2–) in water on the reactivity of zerovalent iron (ZVI) toward As­(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO₄^– and NO₃^– had negligible influence on As­(III) removal by ZVI, but Cl^– and SO₄^2– could improve As­(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As­(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As­(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO₄^2– > Cl^– > NO₃^– ≈ ClO₄^– (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO₃^–, HCO₃^–, and H₂PO₄^– on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO₄^2–. The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe²⁺ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect

Advances in Sulfidation of Zerovalent Iron for Water Decontamination

Sulfidation has gained increasing interest in recent years for improving the sequestration of contaminants by zerovalent iron (ZVI). In view of the bright prospects of the sulfidated ZVI (S-ZVI), this review comprehensively summarized the latest developments in sulfidation of ZVI, particularly that of nanoscale ZVI (S-nZVI). The milestones in development of S-ZVI technology including its background, enlightenment, synthesis, characterization, water remediation and treatment, etc., are summarized. Under most circumstances, sulfidation can enhance the sequestration of various organic compounds and metal­(loid)­s by ZVI to various extents. In particular, the reactivity of S-ZVI toward contaminants is strongly dependent on S/Fe molar ratio, sulfidation method, and solution chemistry. Additionally, sulfidation can improve the selectivity of ZVI toward targeted contaminant over water under anaerobic conditions. The mechanisms of sulfidation-induced improvement in contaminants sequestration by ZVI are also summarized. Finally, this review identifies the current knowledge gaps and future research needs of S-ZVI for environmental application

Highly Efficient Preparation of Multiscaled Quantum Dot Barcodes for Multiplexed Hepatitis B Detection

Both disease diagnosis and therapeutic treatments require real-time information from assays capable of identifying multiple targets. Among various multiplexed biochips, multiplexed suspension assays of quantum dot (QD)-encoded microspheres are highly advantageous. This arises from the excellent fluorescent properties of the QDs incorporated into these microspheres, thus allowing them to serve as “QD barcodes”. QD barcodes can be prepared through various approaches. However, the formulation of improved synthetic techniques that may allow more efficient preparation of QD barcodes with better encoding accuracy still remains a challenge. In this report, we describe a combined membrane emulsification–solvent evaporation (MESE) approach for the efficient preparation of QD barcodes. By combining the advantages of the MESE approach in controlling the barcode sizes with accurate encoding, a three-dimensional barcode library that integrates the signals of the forward scattering, fluorescence 1, and fluorescence 4 channels was established <i>via</i> flow cytometry. The five indexes of hepatitis B viruses were chosen as diagnostic targets to examine the feasibility of the QD barcodes in high-throughput diagnosis. On the basis of showing that singleplex detection is feasible, we demonstrate the ability of these QD barcodes to simultaneously and selectively detect a multitude of diverse biomolecular targets