Surface Fe2 Research Articles

Accelerated oxygen evolution kinetics on nickel–iron diselenide nanotubes by modulating electronic structure

Development of cost-effective, highly active and durable electrocatalysts is highly demanded for oxygen evolution reaction (OER), which is an indispensable process involved in water splitting cells and metal-air batteries. Here, we accelerate the sluggish OER kinetics by controlling the morphology and engineering electronic structure of FexNi1-xSe2 catalysts. FexNi1-xSe2 nanotubes with tunable stoichiometry were fabricated through the removal of sacrificial templates (Cu2O nanowires) and subsequent low-temperature selenization process. By precise tuning of Fe doping amount in FexNi1-xSe2 nanotubes, the optimized Fe0.125Ni0.875Se2 nanotubes show a low overpotential of 253 mV at a current density of 10 mA cm−2, a small Tafel slope of 49 mV dec−1, and superior durability. By combining analysis of the experimental results with density-functional-theory (DFT) simulations, we reveal that the in-situ formed amorphous hydroxyl group layers on the surface of Fe0.125Ni0.875Se2 (Fe0.125Ni0.875Se2–OH) enable highly efficient oxygen evolution catalysis. The Fe dopant can achieve a near-optimal adsorption energy for OER intermediates (OH*, O*, and OOH*) on the oxidized surface of Fe0.125Ni0.875Se2–OH, which is responsible to the enhanced OER performance of Fe0.125Ni0.875Se2. This work paves a new way for exploring low cost and highly active OER electrocatalysts based on ternary metal selenides with hollow structure.

Heterogeneous Fenton catalysts prepared from modified-fly ash for NOx removal with H2O2

Heterogeneous Fenton catalysts were developed from fly ash by alkali, acid and alkali-acid modification for NOx removal using H2O2.The experimental results showed that the catalyst derived from alkali-acid modification achieved 90% NOx removal efficiency at 140 °C, 0.07 mg/min of H2O2 mass flow rate (2 mol/L H2O2)and 250 mL/min of simulated flue gas stream containing 500 ppm NO. Catalyst characterization revealed that the hematite used contained surface hydroxyl groups, Fe2+, oxygen vacancies and FeOAl, which were considered beneficial to the generation of hydroxyl radicals. This work illustrates potential practical use of fly ash.

Efficient catalytic degradation of bisphenol A by novel Fe0- vermiculite composite in photo-Fenton system: Mechanism and effect of iron oxide shell

Novel Fe0-vermiculite (Fe-Ver-C-H2) composite was synthesized by thermal reduction and acted as catalysts to remove bisphenol A (BPA) in photo-Fenton system. In term of activation ability toward H2O2, separation ability and stability, Fe-Ver-C-H2 presented obvious advantages over other kinds of Fe0-vermiculite composite (Fe-Ver-NaBH4), which obtained by traditional liquid reduction. The reason was that iron oxide shells on the surface of Fe0 were α-Fe2O3 and Fe3O4 for Fe-Ver-NaBH4 and Fe-Ver-C-H2, respectively. And for Fe-Ver-C-H2, the synergistic effect between iron core (Fe0) and iron oxide shell (Fe3O4) is beneficial to catalytic performance. The mechanism and plausible pathway of BPA degradation were also proposed according to the results of radical scavenger studies and gas chromatography-mass spectrometry (GC-MS), respectively. In addition, factorial effects for Fe-Ver-C-H2 in photo-Fenton system were also investigated and optimized as: pH of 5, dosage of 0.2 g L−1 and H2O2 concentration of 20 mM. This study presented a facile method to synthesize novel Fe0-vermiculite composite and provided a new sight to investigate the effect of iron oxide shell on the catalytic performance when Fe0-vermiculite composite acted as catalyst to remove contaminants from the environment in photo-Fenton system.

Fe3S4/Fe7S8-promoted degradation of phenol via heterogeneous, catalytic H2O2 scission mediated by S-modified surface Fe2+ species

Enhancing OH productivity via heterogeneous, catalytic H2O2 activation is a long-standing conundrum in H2O purification and thus requires the renovation of conventional reaction systems. The initial step in realizing advanced H2O2 decomposition via heterogeneous catalytic manner is the exploration of the solid capable of efficiently cleaving OO bond inherent to H2O2 and minimizing the loss of catalytic species during vigorous reaction dynamics. While using phenol as a model compound for recalcitrants, this paper highlights the use of Fe3S4/Fe7S8 as a catalyst to enhance OH productivity and thus promote phenol degradation via electro-Fenton reaction over conventional Fe2O3, Fe3O4, and other sulfide analogue (FeS2). Materials’ characterizations and kinetic interpretation of reaction runs under controlled environments served to substantiate the benefits which were provided by Fe3S4/Fe7S8 during the reaction. Fe3S4/Fe7S8 incorporated greater amount of S-modified, surface-exposed Fe2+ sites to cleave H2O2 than FeS2. This improved catalytic consequence of Fe3S4/Fe7S8 (i.e., phenol conversion and initial reaction rate), as also evidenced by control runs detailing H2O2 decomposition in conjunction with tert-butyl alcohol-driven OH scavenging. Filtration control runs as well as recycle runs were also used to verify that Fe3S4/Fe7S8 could heterogeneously catalyze H2O2 scission under the mild, adequate reaction environments, which were realized by the use of low electrical powers and the catalyst immobilized on a cathode.

Self-organized carbon-rich stripe formation from competitive carbon and aluminium segregation at Fe0.85Al0.15(1 1 0) surfaces

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A2 random alloy Fe0.85Al0.15(110) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼900 K, carbon segregates in the form of self-organized protruding stripes separated by ∼5 nm that run along the [001]B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements.

Fe–Mn Mixed Oxide Catalysts Synthesized by One-Step Urea-Precipitation Method for the Selective Catalytic Reduction of NO x with NH3 at Low Temperatures

A range of Fe–Mn mixed oxide catalysts, FeαMn1−αO x (α = 1, 0.25, 0.33, 0.50, 0 mol%) were prepared via one-step urea-precipitation method and applied to the selective catalytic reduction (SCR) of nitric oxide (NO x ) with NH3. The Fe0.33Mn0.66O x catalyst showed the highest activity in the NH3-SCR process within a broad operation temperature range (75–225 °C) with 90% NO x conversion. Series of characterization have been taken to investigate the physical and chemical properties of the catalysts. The BET results evidenced that the doping of iron species increased the surface area of the catalyst effectively, and this structure could provide more acid sites and active sites on the surface of catalysts for SCR reaction. X-ray powder diffraction results and Raman spectroscopy indicate that the active Mn and Fe species were in poorly crystalline or amorphous states which could increase lattice defects and oxygen vacancies on the surface of Fe0.33Mn0.66O x catalyst. The X-ray photoelectron spectra results suggested that more surface-adsorbed oxygen (OA), Fe3+, Mn4+ species existed on the surface of the Fe0.33Mn0.66O x catalyst compared with that of MnO x and FeO x catalysts, which is favorable to the NH3-SCR performance. Analysis by in situ Fourier transform infrared spectroscopy (FTIR) suggested that Fe-doping can enhance the absorption and the activation ability of NO which could promote the catalytic performance in the SCR process. Catalyst characterization Powder X-ray diffraction (XRD) was carried out on a PAN alytical powder X-ray diffractometer (Model EMPYREAN) with a monochromatic Cu Kα1 radiation (λ = 0.154056 nm) within a 2θ range of 10°–90° in the step of 0.02° at room temperature. The Brunauer–Emmett–Teller (BET) surface areas of the samples were computed by physical adsorption of N2 at − 196 °C using a NOVA 1200 (Quanta Chrome). The samples were pretreated at 300 °C for 5 h in a vacuum state previous to BET measurement. The high-resolution transmission electron microscopy (HR-TEM) determinations were conducted on a JEOL-2100 microscope. The Raman spectrums of samples were computed by a confocal Raman microscope (Labram DILOR) equipped with an Olympus BX-41 microscope (objective ×100) and TEcooled CCD detector (Andor), in a back-scattering configuration using an He–He laser (532 nm excitation line) with power of 510 mW at a sample and spectral resolution of 0.8 cm−1. X-ray photoelectron spectra (XPS) over the samples were by captured Al-Kα radiation (1486.7 eV). Binding energies of Mn 2p and O 1s were calibrated using C 1s (BE = 285.0 eV) as a standard. The in situ FTIR experiments of NO adsorption over MnO x and Fe0.33Mn0.66O x catalysts were performed on a VERTEX70-FTIR. Prior to NO adsorption, the samples (approximately 20 mg each) was pretreated at 250 °C in the He atmosphere for 1 h. The spectrum of NO adsorption at different temperatures were selected over each catalyst. The reaction condition was controlled as follows: 500 ppm NO and He as balance, and the flow rate was 100 mL/min.

Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys exposed to air at 870 K studied by TMS, CEMS and XPS

The room temperature 57Fe Mössbauer and XPS spectra were measured for polycrystalline Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys which were exposed to air at 870 K. The spectra were collected using three techniques: the transmission Mössbauer spectroscopy (TMS), the conversion electron Mössbauer spectroscopy (CEMS) and the X-ray photoelectron spectroscopy (XPS). The combination of these experimental methods allows to determine changes in atomic composition in the bulk, in the subsurface layer and on the surface of the studied alloys. The results obtained by XPS confirm the strong chromium segregation process on the surface of Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys. At the same time, the CEMS and TMS measurements reveal that in both samples, during the exposure to air at 870 K, iron oxides were formed. These findings lead to conclusion that the formation of a stable Cr oxide film on the surface of Fe0.88Cr0.12 and Fe0.85Cr0.15 alloys, does not prevent atmospheric corrosion at 870 K. Moreover, the observed by CEMS and TMS, oxidation process of iron atoms is slower for Fe0.88Cr0.12 than for Fe0.85Cr0.15. This fact is in agreement with XPS results which show that Cr surface segregation process is more effective in case of Fe0.88Cr0.12.

Reduction of Cr(VI) in simulated groundwater by FeS-coated iron magnetic nanoparticles

FeS-coated iron (Fe/FeS) magnetic nanoparticles were easily prepared, characterized, and applied for Cr(VI) removal in simulated groundwater. TEM, XRD, and BET characterization tests showed that FeS coating on the surface of Fe0 inhibited the aggregation of Fe0 and that Fe/FeS at a S/Fe molar ratio of 0.207 possessed a large surface area of 62.1m2/g. Increasing the S/Fe molar ratio from 0 to 0.138 decreased Cr(VI) removal by 42.8%, and a further increase to 0.207 enhanced Cr(VI) removal by 63% within 72h. Moreover, Fe/FeS inhibited the leaching of Fe, reducing the toxicity of the particles. 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. The process of Cr(VI) sorption by Fe/FeS (S/Fe=0.207) was fitted well with a pseudo-second-order kinetic model, and the isotherm data were simulated by Langmuir isotherm model with a maximum sorption capacity of 69.7mg/g compared to 48.9mg/g for Fe0. Low pH and initial Cr(VI) concentration favored Cr(VI) removal. Continuous fixed bed column studies showed that simulated permeable reactive barriers (PRB) with Fe/FeS was considerably effective for in situ removal of Cr(VI) from groundwater. This study demonstrated the high potential of Fe/FeS for Cr(VI) immobilization in water, groundwater, and soil.

P.1.017 - A novel tool for transient activation of mesolimbic dopamine neurons using chemogenetics

In this study, a cyclic process of adsorption and persulfate (PS) oxidation-driven regeneration using FeCl3-activated biochar (FA-BC) was suggested as a novel remediation process to remove microcystin-LR (MC-LR) from water. For enhancing overall treatment efficiency and cost effectiveness, the impacts of temperature on adsorption and PS oxidation-driven regeneration were investigated. The increase of temperature resulted in the increase of MC-LR adsorption rate on FA-BC due to the enhanced MC-LR diffusivity in water. Moreover, the MC-LR oxidation and PS reaction rates during the PS regeneration on FA-BC were remarkably improved by factors of 3.4 and 3.5 with increasing temperature from 20 °C to 50 °C. Both diffusion and desorption of MC-LR from FA-BC were thought to be the key factors for controlling the MC-LR oxidation rate during the PS regeneration of MC-LR. In addition, the decrease of pH (from 10 to 4) and increase of PS concentration (from 100 to 400 mg/L) enhanced the regeneration efficiency for MC-LR-spent FA-BC. The four cycles of adsorption-PS regeneration (200 mg/L PS, pH 6, and 50 °C) resulted in 92.81% regeneration efficiency in DI water and 82.89% in lake water. However, the four cycles of adsorption-PS regeneration led to the reduction of surface area (from 835 to 413 m2/g), oxidation of carbon surface and slight reduction of Fe0 on FA-BC. In overall, the cyclic adsorption-PS regeneration at higher temperature could provide practical reuse of FA-BC for cost-effective treatment of aqueous MC-LR.

Characterisation of sphalerite and pyrite surfaces activated by copper sulphate

Adsorption of copper sulphate onto the sphalerite and pyrite surfaces during the selective flotation is not fully understood. In this paper, this phenomenon is investigated by Cryogenic X-ray Photoelectron Spectroscopy (Cryo-XPS) and zeta potential measurements. The Cryo-XPS results have showed that the copper activation occurs in two steps. For sphalerite, surface Zn2+ is substituted by Cu2+ by ion exchange reaction, and then CuS-type layer is formed by reduction of the exchanged Cu2+ to Cu+ and oxidation of surface S2− to S−. Cu2+ can also activate pyrite, first, through reduction of Cu2+ to Cu+ and oxidation of surface S2− species to S−, then surface Fe2+ is oxidised to Fe3+ by reduction of S− to S2−, leading to the formation of CuFeS2-type layer. In the reducing potential of the activation, enhancement of copper adsorption on the pyrite surface is confirmed by XPS. Depth profiling after 10min activation revealed copper diffusion into the sphalerite lattice up to 10nm, while the thickness of the activation product on pyrite surface was less than 3nm. The zeta potential studies confirmed CuS-type layer formation on copper activated sphalerite, whereas the surface product of the activated pyrite was CuFeS2-type. This study leads to a better understanding of sphalerite-pyrite Cu2+ activation during flotation for an effective separation.

Enhanced removal of trace Cr(VI) from neutral and alkaline aqueous solution by FeCo bimetallic nanoparticles

The reactivity of zero valent iron (Fe0) for removing Cr(VI) is self-inhibiting under neutral and alkaline conditions, due to the precipitation of ferrous hydroxide on the surface of Fe0. To overcome this difficulty, we incorporated a second metal (Co) into Fe0 to form FeCo bimetallic nanoparticles (FeCo BNPs), which can achieve higher activity and significant improvement in the reaction kinetics for the removal of Cr(VI) compared with Fe0. The FeCo BNPs were synthesized by a hydrothermal reduction method without using any templates. The characterization analysis indicated that the products were highly uniform in large scale with 120–140nm size in diameter. The obtained FeCo BNPs exhibited a remarkable removal ability for Cr(VI) in the pH range of 5.3–10.0. Especially, FeCo BNPs were able to reduce trace Cr(VI) (1.0mgL−1, pH=7.5) down to about 0.025mgL−1 within 1h. XPS analysis confirmed that Cr(VI) was reduced to Cr(III) by FeCo BNPs, while Fe and Co was oxidized, implying a chemical reduction process. The enhanced removal of trace Cr(VI) could be originated from the introduction of Co, which not only served as a protecting agent against surface corrosion by galvanic cell effect, but also enhanced the efficient flow of electron transfer between iron and Cr(VI). All the results primarily imply that FeCo BNPs can be employed as high efficient material for wastewater treatment.

Sustaining reactivity of Fe0 for nitrate reduction via electron transfer between dissolved Fe2+ and surface iron oxides

The mechanism of the effects of Fe2+aq on the reduction of NO3− by Fe0 was investigated. The effects of initial pH on the rate of NO3− reduction and the Fe0 surface characteristics revealed Fe2+aq and the characteristics of minerals on the surface of Fe0 played an important role in NO3− reduction. Both NO3− reduction and the decrease of Fe2+aq exhibited similar kinetics and were promoted by each other. This promotion was associated with the types of the surface iron oxides of Fe0. Additionally, further reduction of NO3− produced more surface iron oxides, supplying more active sites for Fe2+aq, resulting in more electron transfer between Fe2+ and surface iron oxides and a higher reaction rate. Using the isotope specificity of 57Fe Mossbauer spectroscopy, it was verified that the Fe2+aq was continuously converted into Fe3+ oxides on the surface of Fe0 and then converted into Fe3O4 via electron transfer between Fe2+ and the pre-existing surface Fe3+ oxides. Electrochemistry measurements confirmed that the spontaneous electron transfer between the Fe2+ and structural Fe3+ species accelerated the interfacial electron transfer between the Fe species and NO3−. This study provides a new insight into the interaction between Fe species and contaminants and interface electron transfer.

Residue-based iron catalyst for the degradation of textile dye via heterogeneous photo-Fenton

In this work, the use of a residue-based catalyst for heterogeneous photo-Fenton of Reactive black 5 (RB5) textile dye was evaluated. The catalyst was prepared by chemical vapor deposition of ethanol on a red mud residue, an important waste of the aluminum industry rich in iron oxide. The catalyst was characterized by different techniques, i.e., Mössbauer spectroscopy, Raman spectroscopy, CHN elemental analysis, BET surface area, and scanning and transmission electron microscopies. Results showed that the iron phases present in the red mud are reduced and a carbon coating is formed, protecting the catalyst from excessive iron leaching. The photo-Fenton experiments were carried out by varying pH, H2O2 concentration and radiation power and assessing dye conversion as the response variable. Studies on textile dye degradation showed that low pH favors the reaction and 100% photo-degradation efficiency was obtained, reducing the toxicity of the dye. The best operational condition was achieved at pH 3 and H2O2 initial concentration of 11mM, after 60min of reaction. Kinetic data related to RB5 dye degradation were well fitted to the Langmuir–Hinshelwood model in the range of 20–50mgL−1 of RB5 initial concentration with obtained initial rate constant of 9.4×10−8molL−1min−1. A reaction pathway was proposed in which the H2O2 is activated by surface Fe2+ sites on RM based catalyst, especially in the presence of light, producing OH radicals in a heterogeneous photo-Fenton-like mechanism to oxidize the organic pollutant Reactive black 5 dye.

Sodium Dodecyl Sulfate Modified FeCo2O4 with Enhanced Fenton-Like Activity at Neutral pH

In this work, FeCo2O4 was prepared by a simple coprecipitation method and investigated as a heterogeneous Fenton catalyst. The influences of sodium dodecyl sulfate (SDS) on the structure, surface charge, electron transfer ability, and catalytic activity of FeCo2O4 were investigated. FeCo2O4–S prepared with SDS exhibited much higher catalytic activity for the degradation of methylene blue (MB) in aqueous solution than pure FeCo2O4, which can be attributed to its higher electron transfer ability. The adsorbed SDS accelerated the reduction of surface Fe3+ to Fe2+ by H2O2 and •O2–. The high concentration of surface Fe2+ on FeCo2O4–S during the reaction promoted the decomposition of H2O2 into •OH, which was the main active specie for the degradation of MB. Furthermore, SDS increased the adsorption capacity of the catalyst toward MB, thus facilitating the reaction between adsorbed MB and •OH generated on the catalyst surface.

An electrochemical study of the oxidative dissolution of iron monosulfide (FeS) in air-equilibrated solutions

The oxidative dissolution of FeS in air-equilibrated solutions at 25°C and pH between 2.5 and 5 was investigated by electrochemical methods. In order to understand the role played by S-Fe bonds polarized by H+ attack in the overall reaction, we added 1,10-phenanthroline (a Fe2+ ligand) to the reaction system at initial concentrations from 0 to 1mmoldm−3. It was found that, at all concentrations of 1,10-phenanthroline, the oxidation current density (jox) decreases when pH increases from 2.5 to 4. A further increase of pH to 5 causes a slight increase of jox. Most probably, the rapid precipitation of Fe(III) oxyhydroxides at pH>4 induces a local decrease of pH and promotes the oxidative dissolution of FeS. The current density decreases when 1,10-phenanthroline is added in the system, but after a moderate decrease, in the range of 0.1–0.5mmoldm−3 1,10-phenanthroline, it slightly increases. The oxidation potential of FeS electrode increases when 1,10-phenanthroline is added to the solutions. This behavior can be explained by the mixed potential theory. The largest shift of Eox is registered at pH 2.5 (303.2mV) and it decreases when pH increases up to 5 (48.8mV).The analysis of experimental data highlights the importance of the surface concentration of S-Fe bonds polarized by H+ attack ({>Fe2+}) in the oxidative dissolution of FeS and confirms that the reaction rate is controlled by a mix regime of electron transfer from surface Fe2+ to the cathodic centers and diffusion. We expect that the organic ligands which increase the lability of S-Fe bonds and stabilize the dissolved ferrous iron will control {>Fe2+} and implicitly the oxidative dissolution of FeS.

Sr2Fe2−xMoxO6−δ perovskite as an anode in a solid oxide fuel cell: Effect of the substitution ratio

Double perovskite, Sr2Fe2−xMoxO6−δ (SFMO), as an anode material of the solid oxide fuel cell (SOFC) exhibits excellent performance. The effects of the substitution ratio of Mo on its properties and electro-catalytic activity are examined. The SFMO anode shows a porous structure with a pore size of several micrometers. Using hydrogen and dry methanol as the fuels, the single cell with the SFMO anode with x between 0.4 and 0.6 gives the maximum power outputs of 541 and 387mWcm−2 at 1073K, respectively. The electro-catalytic activity of SFMO anodes exhibits an order of Sr2Fe1.4Mo0.6O6−δ>Sr2Fe1.5Mo0.5O6−δ>Sr2Fe1.6Mo0.4O6−δ. However, the overall conductivity of SFMO displays a reverse order. With the increase of the Mo content, the surface Fe2+/Fe3+ ratio increases regularly, but the Mo5+/Mo6+ radio shows a peak in Sr2Fe1.5Mo0.5O6−δ. It is concluded that the electro-activity of the SFMO anodes for the electro-oxidation of hydrogen and methanol is not limited by their conductivity, but their surface Fe2+/Fe3+ redox couple.

Study on Removal of NH<sub>4</sub><sup>+</sup>-N by Zero-Valent Iron (ZVI or Fe<sup>0</sup>) in Advanced Coking Wastewater Treatment

In this study, the feasibility of a new chemical agent named zero-valent iron (ZVI or Fe0) was used to investigate for removal of NH4+-N from coking wastewater. Reaction pH, dose of Fe0, initial NH4+-N concentration and temperature were considered variable parameters. The pH was observed as the major critical parameter. The removal rate of NH4+-N decreased as the pH increased from 3 to 6 and then increased from pH 6 to pH 9. At pH of 8.0 about in coking wastewater, the NH4+-N removal might be depended on the types and quantity of corrosion products on the surface of Fe0. The removal rate of NH4+-N increased with increase of temperature in the studied range of 10–60°C. At an initial NH4+-N concentration of 134.17 mg/L, Fe0 concentration of 6 g/L, temperature of 60°C and initial pH of 8.0, the removal rate of NH4+-N increased to 54.94%. The dose of Fe0 is determined according to the nitrogen content in coking wastewater.

Trichloroethylene Degradation by Zero Valent Iron Activated Persulfate Oxidation

The present study describes the use of zero valent iron (Fe0 ) as a source for ferrous ion activated persulfate (PS) oxidation of trichloroethylene (TCE). The experimental results indicated that in the absence of TCE there was a lag time for persulfate decomposition when the reaction was activated by Fe0 . An initial pH drop in the Fe0 /PS system to acidic conditions was accompanied by the persulfate decomposition and a decrease in oxidation-reduction potential (ORP) values. Furthermore, in the TCE/Fe0 /PS system, the rapid TCE degradation was accompanied by the rapid persulfate decomposition and chloride ion formation as evidence of TCE mineralization. SEM images of Fe0 before and after persulfate oxidation exhibited significant corrosions of Fe0 . Acicular aggregate formation in the absence of TCE and coarse aggregate formation in the presence of TCE were observed. Moreover, the XRD spectrum revealed the formation of magnetite over the surface of Fe0 after contact with persulfate. Thus, Fe0 activated pe...

Nitrate reduction by zerovalent iron: effects of formate, oxalate, citrate, chloride, sulfate, borate, and phosphate.

Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L(-1) (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 degrees C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h(-1), corresponding to surface area normalized rates ranging from 0.126 to 4.15 h(-1) m(-2) mL. Correlation analysis showed a negative linear relationship between the nitrate reduction rates for the ligands and the conditional stability constants for the soluble complexes of the ligands with Fe2+ (R2 = 0.701) or Fe3+ (R2 = 0.918) ions. This sequence of reactivity corresponds also to surface adsorption and complexation of the three organic ligands to iron oxides, which increase in the order formate < oxalate < citrate. The results are also consistent with the sequence of strength of surface complexation of the inorganic ligands to iron oxides, which increases in the order: chloride < sulfate < borate < phosphate. The blockage of reactive sites on the surface of Fe0 and its corrosion products by specific adsorption of the inner-sphere complex forming ligands (oxalate, citrate, sulfate, borate, and phosphate) may be responsible for the decreased nitrate reduction by Fe0 relative to the chloride system.

Reaction of cysteine and glutathione (GSH) at the freshly fractured quartz surface: a possible role in silica-related diseases?

The reactivity of quartz dusts towards glutathione (GSH) and cysteine (Cys) has been investigated. Cys and GSH react, without being adsorbed (UV-Vis spectroscopy), with commercial quartz dusts in an exposed surface-dependent way, but not with amorphous silica. GSH and Cys have been contacted with freshly ground quartz (agate jar QZg-a and steel jar QZg-s) and quartz heated in air at 500 degrees C (QZs-500) and with a dust generated from a purified quartz (99.9999%) to detect the nature of the reacting surface sites. With both GSH and Cys, the highest reactivity was found on the particles ground in a steel jar, while pure quartz was fully inactive. Detection of the radical GS* (spin trapping) suggests a radical mechanism of oxidation to disulphide onto surface-bound iron traces, more abundant on QZg-s and absent on the pure quartz. Oxidation of thiol groups occurs at surface sites different from those involved in the homolytic rupture of a C-H bond. Both reactions are more pronounced on freshly ground samples, but the C-H rupture takes place at silicon-based surface radicals and Fe2+ centers, while oxidation of GSH and Cys requires Fe3+ centers. As all commercial quartz dusts contain surface iron as an impurity, depletion of extracellular or intracellular GSH may contribute to the oxidative damage caused by particle-derived and cell-derived reactive oxygen species.