Reduction of Cr(VI) in simulated groundwater by FeS-coated iron magnetic nanoparticles.
TL;DR: Mechanistic analysis indicated that Fe0, Fe2+, and S2- were synergistically involved in the reduction of Cr(VI) to nontoxic Cr(III), which further precipitated as (CrxFe1-x)(OH)3 and Cr( III)-Fe-S.
About: This article is published in Science of The Total Environment.The article was published on 2017-10-01. It has received 200 citations till now.
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TL;DR: Sulfidation may also favor desirable pathways of contaminant removal, such as dechlorination by reductive elimination rather than hydrogenolysis and sequestration of metals as sulfides that could be resistant to reoxidation.
Abstract: Iron-based materials used in water treatment and groundwater remediation—especially micro- and nanosized zerovalent iron (nZVI)—can be more effective when modified with lower-valent forms of sulfur (i.e., “sulfidated”). Controlled sulfidation for this purpose (using sulfide, dithionite, etc.) is the main topic of this review, but insights are derived by comparison with related and comparatively well-characterized processes such as corrosion of iron in sulfidic waters and abiotic natural attenuation by iron sulfide minerals. Material characterization shows that varying sulfidation protocols (e.g., concerted or sequential) and key operational variables (e.g., S/Fe ratio and sulfidation duration) result in materials with structures and morphologies ranging from core–shell to multiphase. A meta-analysis of available kinetic data for dechlorination under anoxic conditions, shows that sulfidation usually increases dechlorination rates, and simultaneously hydrogen production is suppressed. Therefore, sulfidation...
288 citations
TL;DR: This review comprehensively summarized the latest developments in sulfidation of ZVI, particularly that of nanoscale ZVI (S-nZVI), and identifies the current knowledge gaps and future research needs of S-ZVI for environmental application.
Abstract: 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.
211 citations
TL;DR: An understanding of passivation chemistry, and its related mechanisms, is essential not only for effective NZVI application but also for accurately assessing the positive and negative effects of NZVI surface passivation.
Abstract: Nanoscale zerovalent iron (NZVI) is one of the most extensively studied nanomaterials in the fields of wastewater treatment and remediation of soil and groundwater. However, rapid oxidative transfo...
193 citations
TL;DR: The improving effects of sulfidation on the performance of ZVI were mainly due to the following mechanisms: sulfidation increased the specific surface area of Z VI, the FeS x layer facilitated the enrichment of Cr( VI) anions on S-ZVI surface because of its anions selective property and favored the electron transfer from Fe0 core to Cr(VI) at the surfaceBecause of its role as efficient electron conductor.
Abstract: When zerovalent iron (ZVI) is used in reductive removal of contaminants from industrial wastewater, where dissolved oxygen (DO) competes with target contaminant for the electrons donated by ZVI, both the reactivity and the electron selectivity (ES) of ZVI toward target contaminant are critical. Thus, the reactivity and ES of two sulfidated ZVI (S-ZVI) samples, synthesized by ball-milling with elemental sulfur (S-ZVIbm) and reacting with Na2S (S-ZVINa2S), toward Cr(VI) under aerobic conditions were investigated. Sulfidation appreciably increased the reactivity of ZVI and the ratio of the rate constants for Cr(VI) removal by S-ZVIbm or S-ZVINa2S to their counterparts without sulfur fell in the range of 1.4–29.9. ES of S-ZVIbm and S-ZVINa2S toward Cr(VI) were determined to be 14.6% and 13.3%, which were 10.7- and 7.5-fold greater than that without sulfidation, respectively. This was mainly ascribed to the greater improving effect of sulfidation on the reduction rate of Cr(VI) than that of DO by ZVI. The impr...
185 citations
TL;DR: In this paper, an magnetically separable iron sulfide (greigite, Fe3S4) was synthesized by solvothermal method and employed for effective removal of Cr(VI).
132 citations
References
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TL;DR: Biesinger et al. as mentioned in this paper proposed a more consistent and effective approach to curve fitting based on a combination of standard spectra from quality reference samples, a survey of appropriate literature databases and/or a compilation of literature references and specific literature references where fitting procedures are available.
7,498 citations
TL;DR: In this paper, the peak positions and peak shape parameters of Fe 3p for Fe2+ and Fe3+ were derived from the XPS spectra of the standard samples of 2FeO·SiO2 and Fe2O3, respectively.
4,434 citations
TL;DR: In this article, the absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals, and the relationship between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions were reviewed.
Abstract: The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge energies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H2O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H2O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sulfides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H2O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.
3,145 citations
"Reduction of Cr(VI) in simulated gr..." refers background in this paper
...…of Fe0 could facilitate the reduction of Cr(VI) via electron acceptance: (1) electrons generated by Fe0 could be spontaneously transferred to the surface FeS semiconductor due to its higher electronegativity (5.02 eV) (Xu and Schoonen, 2000) than that of Fe0 (4.04 eV) (Pearson, 1988) and Fig....
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TL;DR: In this article, the recent concepts of absolute electronegativity, {chi}, and absolute hardness, {eta}, are briefly reviewed and experimental results for a large number of molecules and radicals are presented.
Abstract: The recent concepts of absolute electronegativity, {chi}, and absolute hardness, {eta}, are briefly reviewed. Experimental values for a large number of molecules and radicals are presented. The values are shown to be in good agreement with the known chemical behavior, both as to nucleophilic-electrophilic properties and as to rates of reaction. Applications are also given for the use of empirical rank orders of the local hardness, {bar {eta}}. The uses of {chi} and {eta} are consistent with frontier orbital theory. To make meaningful comparisons in a series of molecules, it is necessary that these orbitals remain the same. Also it is necessary that the observed I and A values of the molecules relate to the appropriate frontier orbitals. 39 refs., 10 tabs.
2,733 citations
TL;DR: An overview of the recent advances of ZVI and progress obtained during the groundwater remediation and wastewater treatment utilizing ZVI (including nanoscale zero-valent iron (nZVI)) for the removal of contaminants.
1,273 citations
"Reduction of Cr(VI) in simulated gr..." refers background in this paper
...ZVI is regarded as one of the most effective reductants due to its strong reactivity, low cost, and easy separation and disposal (Crane and Scott, 2012; Fu et al., 2014)....
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