FeS Species Research Articles

Innovative strategy for the treatment of oily wastewater by in-situ synthesis of nitrogen-doped biochar supported FeS for activation of peroxymonosulfate

ABSTRACT Disposing of oily wastewater poses a significant challenge in treating oilfield-produced wastewater treatment. This study developed a FeSNC-9/PMS system for the effective degradation of total petroleum hydrocarbons (TPHs) in oily wastewater, while increasing the value of excess sludge, thus achieving the dual purpose of waste treatment. This work involved the in-situ preparation of a porous nitrogen-doped biochar-supported iron sulphide catalyst material using surplus sludge from SBR. Compared to undoped FeS (NC-9), FeSNC-9 exhibited excellent pore structure and abundant functional groups. Fe-Nx served as an effective connecting site between FeS species and the graphite network of biochar. The FeSNC-9/PMS system significantly degraded 74.21% of TPHs within 300 min. The FeSNC-9/PMS system demonstrated remarkable TPHs degradation efficiency across a wide temperature range and under both weak acidity and near-neutral conditions The dominant reactive oxygen species were identified as SO4 •− and •OH, with O2 •− and 1O2 also confirmed as active species. Gas chromatography semi-quantitative analysis showed that the long-chain alkanes of C20-C30 in total petroleum hydrocarbons were significantly degraded into short-chain alkanes or completely mineralized. This work provides new insights for the low-cost and high-efficiency treatment of TPHs in oilfield-produced water, and delves into the activation mechanism of PMS and the degradation pathways of TPHs.

Cations facilitate sulfidation of zero-valent iron by elemental sulfur: Mechanism and dechlorination application

The solid-solid reaction of microscale zero-valent iron (mZVI) with elemental sulfur (S0) in water can form sulfidated mZVI (S-mZVI) with high reactivity and selectivity. However, the inherent passivation layer of mZVI hinders the sulfidation. In this study, we demonstrate that ionic solutions of Me-chloride (Me: Mg2+, Ca2+, K+, Na+ and Fe2+) can accelerate the sulfidation of mZVI by S0. The S0 with S/Fe molar ratio of 0.1 was fully reacted with mZVI in all solutions to form unevenly distributed FeS species on S-mZVIs as confirmed by SEM-EDX and XANES characterization. The cations depassivated the mZVI surface by driving the proton release from the surface site (FeOH) and resulting in localized acidification. The probe reaction test (tetrachloride dechlorination) and open circuit potential (EOCP) measurement demonstrated that Mg2+ was most efficient in depassivating the mZVI and therefore promoting sulfidation. The decrease of surface proton for hydrogenolysis on the S-mZVI synthesized in MgCl2 solution also inhibited the formation of cis-1,2-dichloroethylene by 14–79% compared to other S-mZVIs during trichloroethylene dechlorination. In addition, the synthesized S-mZVIs exhibited the highest reduction capacity reported so far. These findings provide a theoretical basis for the facile on-site sulfidation of mZVI by S0 with cation-rich natural waters for sustainable remediation of contaminated sites.

Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity.

Sulfidated zero-valent iron (S-ZVI) enhances the degradation of chlorinated hydrocarbon (CHC) in contaminated groundwater. Despite numerous studies of S-ZVI, a versatile strategy to improve its dechlorination kinetics, electron efficiency (εe), and dechlorination capacity is still needed. Here, we used heteroatom incorporation of N(C) and S by ball-milling of microscale ZVI with melamine and sulfur via nitridation and sulfidation to synthesize S-N(C)-mZVIbm particles that contain reactive Fe-NX(C) and FeS species. Sulfidation and nitridation synergistically increased the trichloroethene (TCE) dechlorination rate, with reaction constants kSA of 2.98 × 10-2 L·h-1·m-2 by S-N(C)-mZVIbm, compared to 1.77 × 10-3 and 8.15 × 10-5 L·h-1·m-2 by S-mZVIbm and N(C)-mZVIbm, respectively. Data show that sulfidation suppressed the reductive dissociation of N(C) from S-N(C)-mZVIbm, which stabilized the reactive Fe-NX(C) and reserved electrons for TCE dechlorination. In addition to lowering H2 production, S-N(C)-mZVIbm dechlorinated TCE to less reduced products (e.g., acetylene), contributing to the material's higher εe and dechlorination capacity. This synergistic effect on TCE degradation can be extended to other recalcitrant CHCs (e.g., chloroform) in both deionized and groundwater. This multiheteroatom incorporation approach to optimize ZVI for groundwater remediation provides a basis for further advances in reactive material synthesis.

Unveiling microbiologically influenced corrosion engineering to transfigure damages into benefits: A textile sensor for H2O2 detection in clinical cancer tissues

With the ongoing increasing research interests in economical electrocatalysts, transforming damages into benefits to prepare useful electrode materials is an ideal strategy to achieve the goals. Corrosion engineering converts harmful corrosion processes into high performance catalyst nanostructures. In this work, we develop an inexpensive, scaled-up corrosion engineering strategy for value-added transformation of low-cost iron substrates into highly efficient Cu-Fe(OH)2-FeS deposited on polyester cloth fabric (PCF) flexible electrode by a process of electroless plating combined with microbes assisted corrosion product. The anaerobic sulfate reducing bacteria (SRB) converting sulfate to sulfide play vital role to carry out the construction of Cu-Fe(OH)2-FeS/PCF electrode which reveals high electrochemical sensing performance for H2O2 with broad linear range and low detection limit of 0.2 nM (S/N = 3). The enhanced activity arises from densely deposited nanosheets of transition metals oxides/hydroxides, plethora of surface active sites and synergistic effect between Cu-Fe(OH)2 and FeS species. More importantly, the S2− ions serving as co-catalyst have been found to continuously fuel electrons during the reduction of Fe(III) and Cu(II) which accelerate the redox cycles of Fe(III)/Fe(II) and Cu(II)/Cu(I) further enhancing electrocatalytic H2O2 reduction. With high sensitivity achieved, the Cu-Fe(OH)2-FeS/PCF electrode has also been practically applied in real-time in vitro tracking of H2O2 excreted from different normal and human brain cancer cell lines as well as in situ sensitive detection of H2O2 released from human brain tumor tissues. This work presents a good way to bridge up the gap between annoying traditional corrosion engineering and emerging electrochemical technologies.

Influence of trace level As or Ni on pyrite formation kinetics at low temperature

Pyrite formation at low temperature during early diagenesis in (sub-)surface sediments is an essential step of Fe and S biogeochemical cycles and the presence of this ubiquitous mineral of surface environments is often used as an indicator of paleo-redox conditions. Pathways of pyrite formation are usually discussed in environmental settings by involving a variety of nanosized Fe-S mineralogical precursors as a function of the local geochemical conditions. However, the influence of trace element impurities such as Ni and As in the solution at the time of pyrite formation has been poorly studied, whereas specific chemical signatures of trace elements are commonly observed in sedimentary pyrites. A better understanding of the impact of Ni and As incorporation at trace levels on pyrite formation is essential to help refining the use of these elements as paleo-redox indicators and to evaluate the role of pyrite as a sink regulating the biogeochemical cycle of potentially toxic trace elements. In this study, we have performed syntheses of pyrite at low temperature via the polysulfide pathway using aqueous Fe(III) and H2S in the presence of trace amounts of Ni(II) (0.001 mol%Fe) and As(III) (0.001 mol%Fe). Analysis of the solids collected at different time steps over the course of the experiments using X-Ray absorption spectroscopy at both the Fe and S K-edges shows that pyrite starts to precipitate within 5 days in presence of Ni(II) and within 32 days in presence of As(III), while the control experiment showed an intermediate precipitation rate of 14 days. Shell-by-shell analysis of Fe K-edge EXAFS data shows that the initial mineralogical precursors are the same in all the experiments and correspond to poorly-crystalline FeS (3.0 ± 0.1 Fe-S@2.25 Å; 1.7 ± 0.2 Fe-Fe@2.67 Å). In addition, XANES qualitative analysis suggests the incorporation of small amounts of Fe(III) within these FeS precursors. Synchrotron-based XRD and WAXS-PDF analysis of the starting solids show that in addition to S(0), the FeS precursors correspond to a continuum of FeS particles that ranges from tetragonal nanocrystalline FeS (a = 3.70(2) Å, c = 5.24(7) Å, MCDab = 41 ± 4 Å MCDc = 21 ± 2 Å) to cluster-type FeS (MCDabc < 8.4 ± 4.3 Å). We propose that Ni(II) and As(III) have a different type of interaction with these FeS precursors, resulting respectively in an increase and a decrease in the rate of pyrite nucleation. While Ni(II) would incorporate within the structure of the FeS precursors, As would interact with (poly)sulfides in solution to form thio-As, possibly binding or precipitating onto FeS surfaces and thus slowing FeS transformation to FeS2. Given that both Ni and As were introduced at trace levels in our experiments, these results suggest that the occurrence of trace amounts of impurities could have a strong influence on pyrite precipitation kinetics in natural settings such as pore-scale microenvironments. In addition to emphasizing the importance of trace elements such as Ni or As on the persistence of mobile colloidal FeS species in anoxic conditions, the results of the present study also point to the importance of considering the actual nature of the impurities when using pyrite composition for ancient environments and past climates reconstruction.

The Thioredoxin System Reduces Protein Persulfide Intermediates Formed during the Synthesis of Thio-Cofactors in Bacillus subtilis.

The biosynthesis of Fe-S clusters and other thio-cofactors requires the participation of redox agents. A shared feature in these pathways is the formation of transient protein persulfides, which are susceptible to reduction by artificial reducing agents commonly used in reactions in vitro. These agents modulate the reactivity and catalytic efficiency of biosynthetic reactions and, in some cases, skew the enzymes' kinetic behavior, bypassing sulfur acceptors known to be critical for the functionality of these pathways in vivo. Here, we provide kinetic evidence for the selective reactivity of the Bacillus subtilis Trx (thioredoxin) system toward protein-bound persulfide intermediates. Our results demonstrate that the redox flux of the Trx system modulates the rate of sulfide production in cysteine desulfurase assays. Likewise, the activity of the Trx system is dependent on the rate of persulfide formation, suggesting the occurrence of coupled reaction schemes between both enzymatic systems in vitro. Inactivation of TrxA (thioredoxin) or TrxR (thioredoxin reductase) impairs the activity of Fe-S enzymes in B. subtilis, indicating the involvement of the Trx system in Fe-S cluster metabolism. Surprisingly, biochemical characterization of TrxA reveals that this enzyme is able to coordinate Fe-S species, resulting in the loss of its reductase activity. The inactivation of TrxA through the coordination of a labile cluster, combined with its proposed role as a physiological reducing agent in sulfur transfer pathways, suggests a model for redox regulation. These findings provide a potential link between redox regulation and Fe-S metabolism.

Natural weathering of slags from primary Pb–Zn smelting as evidenced by Raman microspectroscopy

Lead (Pb) and zinc (Zn) smelters produce high amount of granulated slags which are currently stored on unconfined slag heaps and exposed to weathering. The environmental risk related to slags disposals can be estimated through the results of a variety of characterization methods coupled with laboratory leaching experiments and in situ monitoring. The present study is focused on the Raman characterization and distribution at a microscopic scale of secondary products resulting to the alteration of glassy slags exposed to natural weathering for at least ten years. The slag alteration is characterized by the formation of a crack network around iron sulfide inclusions and Pb droplets embedded in the glassy matrix. The Raman images clearly point out the gradually weathering processes. The dissolution of the FeS species lead to the formation of Fe (oxy-hydr)oxide phases. The successive layer formation highlights a probable local pH/Eh changes. The fluids-containing sulfates issued from the alteration of sulfide species are conveyed in the crack network inducing a local alteration of the crack edges together with the formation of (Al,Fe)-hydroxide phases. The fluids-containing sulfates when in contact with Pb droplets induce a progressive dissolution of the droplets from the edge to the core to form Pb sulfate species (mainly basic lead sulfates) and Pb oxides in complex mixture. In a last step, carbonation occurs with local increasing pH due to the presence of CO2 from air or HCO3−/CO32− in fluids originating from glassy matrix alteration.

Solubility and partitioning behavior of Au, Cu, Ag and reduced S in magmas

Experiments have been conducted at 200MPa, 800–1030°C, and fO2 0.8 log units below the Ni–NiO buffer to determine the solubility of Au, Cu and Ag in silicate melts and pyrrhotite. The metal activities were imposed by using Au965Ag020Cu015 alloy capsules. Sulfur-free and sulfur-bearing systems were studied with otherwise identical melt compositions to assess the relative effect of S on the solubility of these metals. The data show that the major element composition of the silicate melt only moderately affects the solubility of Au, Ag and Cu between basalt and dacite, yielding solubilities identical within 50% relative. In comparison, solubilities in the rhyolite melts are lower by a factor of 1.5–2.5 for Cu and higher by up to a factor of 5 for Ag, depending on the aluminum saturation index of the melt. The solubilitiy of Ag significantly increases with increasing peraluminousity above an aluminum saturation index of 1. The effect of melt composition is significant on the solubility of Au in S-bearing melts, in part due to its effect on the sulfur concentration at sulfide saturation. The effect of S is the most pronounced in peralkaline rhyolites and mafic melts, and minimal in peraluminous rhyolites. The solubilities of all three metals significantly decrease with decreasing temperature. The concentration of sulfur in the melt at sulfide saturation and its volatile/melt partition coefficient are primarily determined by the FeO activity in the melt and the activity coefficients of dissolved FeS species, which appear to correlate with the degree of melt polymerization. The volatile/melt partition coefficient of reduced S increases from 79±4 (1σ) to 635±80 as the melt composition changes from basalt to slightly peraluminous rhyolite, and from 225±13 to 776±148 as the aluminium saturation index increases from 0.7 to 1.1 in rhyolites.At 1000°C, pyrrhotite/silicate melt partition coefficients for Cu increase from 540±30 (1σ) to 1140±110 from basalt to dacite, whereas the partition coefficients for Ag are nearly constant at 50±10. The partition coefficients of Au increase from 180±20 to 900±210 from basalt to dacite. Pyrrhotite/rhyolite melt partition coefficients for Cu, Ag and Au increase by about an order of magnitude as temperature drops from 1000°C to 800°C.At typical S concentrations for arc magmas (500–2000μg/g), the budget of Ag in the magma will not be controlled by pyrrhotite, whereas primary control on the Au and Cu budget by pyrrhotite may only be relevant in intermediate to felsic magmas.

The effect of sulphide and moisture content on steel corrosion during transport of fine wet coal

In the present investigation the influence of compaction pressure (stress) on the corrosivity of wet coal was investigated. Two coal samples, one high in sulphur content (3 %) and the other low in sulphur content (0.6 %) were used to determine the influence of compaction stress on the corrosion rates of steel samples in contact with compacted coal. It was found that the pressure exerted on finely divided wet coal is an important factor in determining its water content and corrosivity towards mild steel. Corrosion of the steel was typically in the form of pitting and the sulphur content of the coal was an important factor in determining the corrosivity of the coal. The corrosion rate of the high sulphur content coal was higher than that of the low sulphur coal. Mossbauer spectroscopy showed that a FeS species developed on the steel surface.

Kinetics and interactions of molybdenum and iron-sulfur centers in bacterial enzymes of the xanthine oxidase family: mechanistic implications.

For isoquinoline 1-oxidoreductase (IsoOr), the reaction mechanism under turnover conditions was studied by EPR spectroscopy using rapid-freeze methods. IsoOr displays several EPR-active Mo(V) species including the "very rapid" component found also in xanthine oxidase (XanOx). For IsoOr, unlike XanOx or quinoline 2-oxidoreductase (QuinOr), this species is stable for about 1 h in the absence of an oxidizing substrate [Canne, C., Stephan, I., Finsterbusch, J., Lingens, F., Kappl, R., Fetzner, S., and Hüttermann, J. (1997) Biochemistry 36, 9780-9790]. Under rapid-freeze conditions in the presence of ferricyanide the very rapid species behaves as a kinetically competent intermediate present only during steady-state turnover. To explain the persistence of the very rapid species in IsoOr in the absence of an added oxidant, extremely slow product dissociation is required. This new finding that oxidative conditions facilitate decay of the very rapid signal for IsoOr supports the mechanism of substrate turnover proposed by Lowe, Richards, and Bray [Lowe, D. J., Richards, R. L., and Bray, R. C. (1997) Biochem. Soc. Trans. 25, 774-778]. Additional stopped-flow data reveal that alternative catalytic cycles occur in IsoOr and show that the product dissociates after transfer of a single oxidizing equivalent from ferricyanide. In rapid-freeze measurements magnetic interactions of the very rapid Mo(V) species and the iron-sulfur center FeSI of IsoOr and QuinOr were observed, proving that FeSI is located close to the molybdopterin cofactor in the two proteins. This finding is used to relate the two different iron-sulfur centers of the aldehyde oxidoreductase structure with the EPR-detectable FeS species of the enzymes.

Determination of the Electrochemical Properties of a Soluble Aqueous FeS Species Present in Sulfidic Solutions

Field and laboratory data are presented that show a soluble FeS species(FeSaq) exists in sulfidic seawater solutions, and is observedwhen the IAP exceeds the Ksp of amorphous FeS. TheFeSaq yields a discrete signal (double peak) using square-wavevoltammetry and two one-electron waves in sampled DC polarographyexperiments at the Hg electrode. The aqueous FeS species reacts irreversiblyat the electrode as a single FeS subunit and not as a polymeric entity. Thepeak potential of FeSaq occurs at -1.1 V whereas the peakpotential of Fe $$(H_2 O)_6^{2 + } $$ occurs at-1.45 V; the positive shift for Fe2+ reduction inFeSaq indicates a change in geometry for Fe2+from octahedral to tetrahedral. The kinetics of electron transfer at theelectrode are determined to be similar for both Fe2+ andFeSaq. Molecular orbital energy diagrams, further indicatethat Fe(II) does change from octahedral to tetrahedral geometry in solution.First, Fe(II) exists as octahedralFe $$(H_2 O)_6^{2 + } $$ in solution whichundergoes a substitution reaction of bisulfide for water. The resultingcomplex, Fe(H2O)5(HS)+, thentransforms to a tetrahedral complex on further addition of sulfide. Thisgeometry change is consistent with the formation of amorphous FeS thatconverts to mackinawite which has tetrahedral Fe(II). The process is entropydriven because of the water loss that occurs. The overall sequence can berepresented as: $$\begin{gathered} 3Fe(H_2 O)_6^{2 + } + 3HS^ - \to 3Fe(H_2 O)_5 (HS)^ + + 3H_2 O \hfill \\ 3Fe(H_2 O)_5 (HS)^ + + 3HS^ - \to Fe_3 S_3 (H_2 O)_6 + 3H_2 S + 9H_2 O \hfill \\ \end{gathered} $$ Soluble FeS species are important asreactants in the formation of iron-sulfide minerals including pyrite.

Sulphur speciation and pyrite formation in meromictic ex-fjords

Powell and Sakinaw Lakes are stably stratified ex-fjords, which became isolated from the Strait of Georgia approximately 11000 years ago by emerged sills due to post-glacial isostatic rebound. Both lakes contain highly sulphidic relict seawater (Powell 3.0 mM; Sakinaw 5.5 mM) at depth chemically analogous to porewaters of reducing marine sediments. Sakinaw has a very sharp chemocline located just below the oxic/anoxic interface, whereas in Powell, the interface is spread out over 200 m of the water column. Sulphate is present in the oxic part of the water column at much higher concentrations in Sakinaw Lake (up to 65 μM) than in Powell Lake (10 μM), and increases in concentration with depth until reaching the interface, below which it is rapidly depleted. Sulphur oxyanions of intermediate oxidation state (thiosulphate, sulphite, and tetrathionate) are not detectable in either lake. Particulate elemental sulphur was also not found in either lake. High concentrations of reduced iron and hydrogen sulphide result in formation of iron monosulphides and pyrite in the anoxic water columns of both lakes. The presence of these two minerals correlates well with their calculated saturation states. Pyrite precipitates with no apparent monosulphide precursor at depths where dissolved sulphide concentrations are low and monosulphide phases are undersaturated. As sulphide levels increase at greater depths, the waters become saturated with respect to iron monosulphides and particulate FeS species are detected in the water column. The large separation of the oxic/anoxic interface and the chemocline in Sakinaw (~10 m) and especially in Powell Lake (~100 m) relative to that of sediment porewaters allows excellent resolution of these processes.

Photoelectron spectroscopic study of the interaction of thin Fe films with the MoS 2(0001) surface

The Fe/MoS 2(0001) interface has been studied by high-resolution photoelectron spectroscopy using synchrotron radiation. The evolution of the Mo3d, Fe3p, and S2p core levels and of the valence band spectra ( hν = 152 eV) during growth of vapor-deposited Fe films (1–10 Å) indicates the production of sulfur vacancy defects in the MoS 2(0001) surface. Several submonolayer sulfur surface species were formed, including sulfur adsorbed on the Fe surface and a reacted Fe-S species. The MoS 2 surface was found to be covered for Fe film thicknesses of ~10 Å. Annealing a 10 Å film to 600 K resulted in the Fe film beginning to agglomerate, while annealing to 700–900 K resulted in further agglomeration of the Fe film. Annealing to 700–900 K also resulted in reformation of a partially disordered MoS 2(0001)-1 × 1 surface with ~5% defects, as determined from photoelectron spectroscopy and low-energy electron diffraction. The overlayer film remained primarily in the form of metallic Fe, before and after annealing to temperatures ≲ 900 K, which was shown by the behavior of the Fe3p core level spectra and valence band spectra. Annealing the sample to 1200 K resulted in decomposition of the MoS 2(0001) surface. The results indicate that the Fe/MoS 2(0001) system exhibits some interfacial reactivity but does not form bulk Fe-S compounds. The results have been compared to those of previous studies of the Fe/MoS 2(0001) system.

Photoelectron spectroscopic study of the interaction of thin Fe films with the MoS 2(0001) surface

Abstract The Fe/MoS2(0001) interface has been studied by high-resolution photoelectron spectroscopy using synchrotron radiation. The evolution of the Mo3d, Fe3p, and S2p core levels and of the valence band spectra (hν = 152 eV) during growth of vapor-deposited Fe films (1–10 A) indicates the production of sulfur vacancy defects in the MoS2(0001) surface. Several submonolayer sulfur surface species were formed, including sulfur adsorbed on the Fe surface and a reacted Fe-S species. The MoS2 surface was found to be covered for Fe film thicknesses of ~10 A. Annealing a 10 A film to 600 K resulted in the Fe film beginning to agglomerate, while annealing to 700–900 K resulted in further agglomeration of the Fe film. Annealing to 700–900 K also resulted in reformation of a partially disordered MoS2(0001)-1 × 1 surface with ~5% defects, as determined from photoelectron spectroscopy and low-energy electron diffraction. The overlayer film remained primarily in the form of metallic Fe, before and after annealing to temperatures ≲ 900 K, which was shown by the behavior of the Fe3p core level spectra and valence band spectra. Annealing the sample to 1200 K resulted in decomposition of the MoS2(0001) surface. The results indicate that the Fe/MoS2(0001) system exhibits some interfacial reactivity but does not form bulk Fe-S compounds. The results have been compared to those of previous studies of the Fe/MoS2(0001) system.

An investigation of hydrogenase I and hydrogenase II from Clostridium pasteurianum by resonance Raman spectroscopy. Evidence for a [2Fe-2S] cluster in hydrogenase I.

Resonance Raman spectra are reported for hydrogenase I and II from Clostridium pasteurianum. These spectra show overlapping bands with contributions from [4Fe-4S] clusters, known to be present in these enzymes, and from novel FeS centers of hitherto undefined structure. For hydrogenase I there are strong bands at 288 and 394 cm-1, which are seen in [2Fe-2S] proteins and in no other FeS species so far examined. In contrast these bands do not appear for hydrogenase II, whose resonance Raman spectrum is dominated by [4Fe-4S] cluster modes. These results provide the first structural information on the hydrogenase I FeS center involved in H2 activation and demonstrate structural differences between hydrogenase I and hydrogenase II.