Iron In Aqueous Solutions Research Articles

Hydrothermal synthesis and characterization of monodisperse α‐Fe 2 O 3 nanocubes

Monodisperse α-Fe2O3 nanocubes with a mean size of 85 nm have been prepared by heating an aqueous solution of iron (III) nitrate in the presence of a certain amount of alkali without any additional organic reagents or templates in a hydrothermal route. The structure and morphology of the products were characterised by X-ray diffraction, transmission electron microscopy and field-emission scanning electron microscopy. The results have shown that the crystal morphology continually changes at higher temperatures and α-FeOOH was generated as the intermediate during the hydrothermal dehydration reaction. In addition, the optimum temperature and reaction time of the hydrothermal synthesis of these α-Fe2O3 nanocubes were 200°C and 5 h, respectively.

Potential Scanning Impedance Spectroscopy to Investigate Dissolution Mechanisms of Iron

Electrochemical impedance spectroscopy (EIS) is powerful method to analyze dissolution mechanisms of metals because time constants for elementary reaction steps and formation of reaction intermediate can be discriminated. Impedance spectrum is generally measured by using frequency response analyzer whose principle is on the basis of Fourier transformations of sinusoidal input and output signals. In the present paper, we employ a wavelet transformation to determine impedance spectra of dissolving iron electrode because the wavelet transformation gives the power spectrum densities with recording the time and the time variation of the spectra can be discussed. We used complex Morlet mother wavelet in order to obtain the complex number data in the frequency domain. The time-dependent impedance of the dissolving iron electrode can be determined by calculating cross spectra of the wavelet coefficients of current and potential signals. We developed potential scanning impedance spectroscopy (PSIS) using the impedance determination by wavelet transformation. By PSIS, we can obtain the successive impedance spectra with measuring the potentiodynamic polarization curve of metal electrode simultaneously, and discuss the dissolution mechanisms of iron in aqueous solutions.

BaFe12O19 powder with high magnetization prepared by acetone-aided coprecipitation

BaFe12O19 particles with high magnetization were produced using an acetone-aided coprecipitation process. An aqueous solution of iron and barium nitrates, in an Fe3+/Ba2+ molar ratio of 12, was added in a stirred precipitation liquid medium composed of H2O, CH3(CO)CH3 and NH4OH. After reacting metallic ions with ammonia, the precipitates were formed, centrifugally filtered, freeze dried and calcined. Effects of amount of the acetone in the precipitation liquid medium on the formation of crystalline BaFe12O19 were investigated. The presence of acetone in the precipitation liquid medium can greatly promote formation of the crystalline BaFe12O19 at temperature as low as 650°C and can enhance magnetization of the derived particles. On the other hand, raising the calcination temperature can effectively accelerate development of crystallite morphology and magnetic characters of the barium hexaferrites. While the barium hexaferrite powder obtained without acetone additions and calcined at 1000°C had magnetization (measured at 50kOe; M(50kOe)) of 63.5emu/g, remanence magnetization (Mr) of 31.3emu/g and coercivity (Hc) of 4.7kOe, the single magnetic domain size BaFe12O19 powder with M(50kOe) of 70.6emu/g, Mr of 34.4emu/g and Hc of 3.7kOe was produced at 1000°C, using a precipitation liquid medium of 64vol% acetone.

Super-faradaic charge yields for aluminium dissolution in neutral aqueous solutions

Dissolution of elemental aluminium or iron in aqueous solutions is the essential reaction in electrocoagulation and other processes. These and several other such metals have been reported as exhibiting dissolution rates that are higher than expected from the current/charge passed, assuming electron stoichiometries of three (Al) or two (Fe). In batch dissolution experiments with aluminium electrodes, the addition of 30gm−3 humic acid to a neutral solution of 0.5molm−3 Na2SO4 and 8.8gm−3 NaCl led to an unexpected increase in the charge yield from 1.0 to ca. 1.5, i.e., the measured concentration of aluminium species in solution was 50% higher than expected from Faraday's law. This phenomenon may be explained when net currents are used for the determination of charge yields, whereas partial dissolution currents should be used. The latter may be significantly greater than the former when a concurrent reduction reaction, such as hydrogen evolution, occurs at the dissolving electrode.

Inhibition of Cast Iron Corrosion in Acid, Base, and Neutral Media Using Schiff Base Derivatives

AbstractThree Schiff bases, 2‐acetylpyridine thiosemicarbazone (I1), 2‐acetylpyridine‐(4‐methylthiosemicarbazone) (I2), and 2‐acetylpyridine‐(4‐phenylthiosemicarbazone) (I3) were tested against corrosion of cast iron in aqueous solutions of HCl, NaOH, NH4Cl, and NaCl by means of a mass loss method and electrochemical measurements. The inhibition efficiency is directly proportional to inhibitor concentration, while it decreases with prolonged immersion time and at low temperatures. In order to study the effect of an additive, synergism of KI was also studied. The adsorption of Schiff bases in corrosive media obeys Langmuir's isotherm, both in the presence and absence of KI. The UV–Vis, FT‐IR, WAXD and SEM analyses were carried out to support the mechanism of corrosion inhibition. The ΔGads values reveal that the inhibition was mainly due to physisorption of the inhibitor molecules on the surface of cast iron. The electrochemical polarization results showed the predominantly cathodic nature of the inhibitors.

Iron Dialyzability in a Multiple Nutrient Formulation and Effect of the Addition of Separate Nutrients

Introduction: Different nutrients added to nutritional formulations can facilitate, reduce or block the iron absorption. Objective: The aims of this study was to assess the modulation of iron bioavailabily by other minerals and vitamins in an multiple nutrient formulation and in an aqueous iron solution. Material and Methods: We analyzed the iron dialyzability in the multiple nutrients formulation developed to simulate an enteral diet. Furthermore, the iron dialyzability was determined in aqueous solutions containing 25 mg of iron, which were added separately usual amounts of soluble fiber, salt mixture, vitamin mixture, calcium and vitamin C. The dialysed iron was measured by atomic absorption spectrometry. Results: In the multiple nutrients formulation, we documented low bioavailability of iron (0.80 ± 0.01%). Compared with the aqueous iron solution (70.0 ± 6.0%), the addition of 135 mg of vitamin C increased the iron dialyzability (90.0 ± 3.0%). There was reduction of iron dialysis after addition of soluble fiber (1.00 ± 0.01%), the vitamin mixture (25.00 ± 0.12%), salt mixture (2.00 ± 0.06%) and calcium (0.80 ± 0.02%). Conclusion: The low iron bioavailability in the multiple nutrients formulation can be attributed to the protein source and supply of fiber and calcium, thereby affecting the absorption of iron.

Effect of Increasing Concentrations of Zinc on the Absorption of Iron from Iron-Fortified Milk

The cofortification of milk with iron (Fe) and zinc (Zn) is a strategy used to prevent these deficiencies during childhood. Given that Zn can negatively interact with iron in aqueous solutions, the objective of the present study was to determine the effect of Zn on Fe absorption of milk fortified with Fe and Zn. Twenty-eight women between 33 and 47 years of age, with contraception and a negative pregnancy test, participated in one of two absorption studies. They received on four different days, after an overnight fast, 200 mL of milk (26 % fat) fortified with 10 mg Fe/L, as (A) ferrous sulfate, or the same milk but with graded doses of added Zn, as Zn sulfate of (B) 5, (C) 10, and (D) 20 mg/L (study 1, n = 15). In study 2 (n = 13), subjects received the same milk formulations, but these were also fortified with ascorbic acid (70 mg/L). Milk was labeled with radioisotopes ⁵⁹Fe or ⁵⁵Fe, and the absorption of iron was measured by erythrocyte incorporation of radioactive Fe. The geometric mean and range of ±1 SD of Fe absorption in study 1 were as follows: formula A = 6.0 % (2.8-13.0 %); B = 6.7 % (3.3-13.6 %); C = 5.4 % (2.2-13.2 %); and D = 5.2 % (2.8-10.0 %) (ANOVA for repeated measures, not significant). For study 2, data are as follows: 8.2 % (3.6-18.7 %); B = 6.4 % (2.5-16.4 %); C = 7.7 % (3.2-18.9 %); and D = 5.2 (1.8-14.8 %) (ANOVA for repeated measures, not significant). In conclusion, according to the results from this study, it appears that the addition of zinc up to 20 mg/L does not significantly inhibit iron absorption from milk fortified with 10 mg/L of iron.

Poly(methyl methacrylate) Coating of Soft Magnetic Amorphous and Crystalline Fe,Co-B Nanoparticles by Chemical Reduction

The structural and magnetic properties of a collection of nanoparticles coated by Poly(methyl methacrylate) through a wet chemical synthesis have been investigated. The particles display either an amorphous (M = Fe, Co) M-B arrangement or a mixed structure bcc-Fe and fcc-Co + amorphous M-B. Both show the presence of a metal oxi-hydroxide formed in aqueous reduction. The organic coating facilitates technological handling. The cost-effective synthesis involves a reduction in a Poly(methyl methacrylate) aqueous solution of iron(II) or cobalt(II) sulphates (< 0.5 M) by sodium borohydride (< 0.5 M). The particles present an oxidized component, as deduced from X-ray diffraction, Mössbauer and Fe- and Co K-edge X-ray absorption spectroscopy and electron microscopy. For the ferrous alloys, this Fe-oxide is alpha-goethite, favoured by the aqueous solution. The Poly(methyl methacrylate) coating is confirmed by Fourier transform infrared spectroscopy. In pure amorphous core alloys there is a drastic change of the coercivity from bulk to around 30 Oe in the nanoparticles. The mixed structured alloys also lie in the soft magnetic regime. Magnetisation values at room temperature range around 100 emu/g. The coercivity stems from multidomain particles and their agglomeration, triggering the dipolar interactions.

Hydrothermal precipitation of artificial violarite

The nonstoichiometric nickel-ore mineral, violarite, (Ni,Fe)3S4 was prepared as a phase-pure fine powder by a comparatively quick hydrothermal method from an aqueous solution of iron(II) acetate, nickel(II) acetate and DL-penicillamine in an autoclave at 130°C for 45h. Powder-XRD showed that the violarite crystallised with the thiospinel structure, a=9.478(3) Å, Z=8; SEM revealed platy crystals 10×10×1μm; EMPA gave a mean composition, Fe0.31Ni2.36S4. Violarite compositions with a higher Fe/Ni ratio than this were concluded to be metastable in this aqueous system. When DL-penicillamine was used in excess, nickeliferous pyrite formed in addition to violarite. This is the first successful method for preparing violarite directly from aqueous solution, and demonstrates that it is feasible for nickel-rich violarite to precipitate from aqueous media in a geochemical environment. The mechanism for the pseudomorphic replacement of pentlandite, (Fe,Ni)9S8 by violarite is discussed in the light of these new results. The Fe-free end-member, polydymite, Ni3S4 was also prepared by this method.

Evaluation of chitosan tripolyphosphate gel beads as bioadsorbents for iron in aqueous solution and in human blood in vitro

AbstractNonimprinted and Fe3+ imprinted chitosan tripolyphosphate gel beads were prepared via physical gel formation. A method based on in situ crosslinking using ethylene glycol diglycidyl ether was developed to imprint the chitosan tripolyphosphate gels with Fe3+ ion without deteriorating the gel beads. The beads were characterized by FTIR, SEM, XRD, and DSC with respect to the chemical structure, surface morphology, crystallinity, and thermal behavior. Swelling kinetics and Fe3+ ion adsorption behavior from aqueous solution were studied. The Fe3+ imprinted and in situ crosslinked beads proved to be durable and effective adsorbents for Fe3+ in solution. The bead prepared by in situ crosslinking and in the presence of 10 mM template ion had an equilibrium iron adsorption capacity of 53.9 mg/g after 3‐hour contact with 5 mM Fe3+ solution. The pros and cons of the beads as biomedical iron adsorbents were tested by evaluating their serum iron removal capacities from human blood. The preliminary tests carried out showed that Fe3+ imprinted beads were more effective in decreasing serum iron in human blood when compared to the nonimprinted beads. The decrease in serum iron level accompanied a parallel decrease in the hemoglobin level. The calcium level was also affected upon contact with the beads. The Fe3+ imprinted beads were less effective than the nonimprinted ones in decreasing the calcium level indicating selectivity towards iron containing species. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesize and Characterization of Multifunctional Silica Coated Magnetic Nanoparticles Using Polyvinylpyrrolidone (PVP) as a Mediator

Magnetic iron oxide nanoparticles with proper surface coatings are increasingly being evaluated for clinical applications such as hyperthermia, drug delivery, magnetic resonance imaging, transfection and cell/protein separations. In this work, silica coated iron oxide magnetic nanoparticles, which are very useful for delivering chemotherapeutic drugs, has been prepared by precipitation in an aqueous solution of iron (II) and iron (III) chlorides under basic condition. In this process, polyvinylpyrrolidone (PVP) has been used as a stablizer. Surface modifications of the as-prepared Fe3O4 Nps have been carried out by using tetraethoxysilane (TEOS). Silica coated nanoparticles have been characterized by Fourier transform infrared (FTIR) spectroscopy, Powder X- ray diffraction (XRD), Transmission electron microscopy (TEM) and Infrared (IR) spectroscopy

Application of Mössbauer spectroscopy to the study of tannins inhibition of iron and steel corrosion

The inhibitory effect of tannins was investigated using, among others, potentiodynamic polarizations and Mossbauer spectroscopy. These techniques confirmed that the nature, pH and concentration of tannic solution are of upmost importance in the inhibitory properties of the solutions. It is observed that at low tannin concentration or pH, both, hydrolizable and condensed tannins, effectively inhibit iron corrosion, due to the redox properties of tannins. At pH ≈ 0, Mossbauer spectra of the frozen aqueous solutions of iron(III) with the tannin solutions showed that iron is in the form of a monomeric species [Fe(H2O)6]3 + , without coordination with the functional hydroxyl groups of the tannins. The suspended material consisted of amorphous ferric oxide and oxyhydroxides, though with quebracho tannin partly resulted in complex formation and in an iron (II) species from a redox process. Other tannins, such as chestnut hydrolysable tannins, do not complex iron at this low pH. Tannins react at high concentrations or pH (3 and 5) to form insoluble blue–black amorphous complexes of mono-and bis-type tannate complexes, with a relative amount of the bis-ferric tannate generally increasing with pH. Some Fe2 + in the form of hydrated polymeric ferrous tannate could be obtained. At pH 7, a partially hydrolyzed ferric tannate complex was also formed. The latter two phases do not provide corrosion protection. Tannin solutions at natural pH react with electrodeposited iron films (approx. 6 μm) to obtain products consisting only on the catecholate mono-complex of ferric tannate. Some aspects of the mechanism of tannins protection against corrosion are discussed.

Kinetics and mechanical study of plasma electrolytic carburizing for pure iron

In this work, plasma electrolytic surface carburizing of pure iron in aqueous solution consisting of water, glycerin and NH4Cl was investigated. Surface carburizing was carried out in 20% glycerin solution treated at 750°C, 800°C, 900°C and 950°C temperatures for 5, 10 and 30min. The formation of hard carbon-rich layer on the surface of pure iron was confirmed by XRD analysis. Metallographic and SEM studies revealed a rough and dense carburized layer on the surface of the pure iron. Experimental results showed that the thickness of the carburized layers changes with the time and temperature. The average thickness of the carburized layer ranged from 20 to 160μm. The hardness of the carburized samples decreased with the distance from the surface to the interior of the test material. The average hardness values of the carburized layers on the substrate ranged 550–850HV, while the hardness of the substrate ranged from 110HV to 170HV. The dominant phases formed on the pure iron were found to be a mixture of cementite (Fe3C), martensite (Fe+C) and austenite (FCC iron) confirmed by XRD. Wear resistance in all plasma electrolytic carburized samples is considerably improved in relation to the untreated specimen. After carburizing, surface roughness of the samples was increased. Friction coefficients were also increased because of high surface roughness.

Synthesis, characterisation and in situ colorimetry of electrochromic Ruthenium purple thin films

Ruthenium purple (RP) films on transmissive tin-doped indium oxide (ITO)/glass substrates have been synthesised by an electrochemical coagulation technique using an aqueous RP colloidal suspension prepared from separate very dilute aqueous solutions of iron(III) chloride and potassium hexacyanoruthenate(II), with dilute potassium chloride as supporting electrolyte solution. To aid stability of the RP films, ruthenium(III) chloride was added to the RP colloidal suspension. Using the CIE (Commission Internationale de l’Eclairage) system of colorimetry, the colour stimulus of the electrochromic RP films and the changes that take place on reversibly switching to the colourless form have been calculated from in situ visible spectra recorded under electrochemical control. On electrochemical reduction, the intensely absorbing bright purple mixed-valence iron(III) hexacyanoruthenate(II) chromophore is reduced to the colourless iron(II) hexacyanoruthenate(II) form. Sharp and reversible changes in the hue and saturation occur, as shown by the track of the CIE 1931 xy chromaticity coordinates. Concurrently, as the purple chromophore is bleached, a large increase in the relative luminance of the electrochromic film is observed. For the purple state, the CIELAB 1976 colour space coordinates were L* = 64, a* = 27 and b* = −36, with a complementary wavelength ( λ c) calculated as 555 nm, in excellent agreement with the absorption maximum ( λ max) of 550 nm for the intervalence charge-transfer (IVCT) band.

Copper coprecipitation with hydrous iron oxide in aqueous solutions: spectroscopic, thermal and macroscopic analyses

Copper co-precipitation with hydrous iron oxide was investigated through spectroscopic, thermal and macroscopic analyses at different pH. Solid samples were prepared from aqueous solutions of iron (III) and copper(II) and characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction analysis (DRX) and thermal analyses. The co-precipitation of copper with Fe (III) retards the hydrous iron oxide transformation at pH <8. The X-ray diffraction patterns of the heated samples suggest the formation of hematite and copper ferrite. The results of desorption experiments indicate that copper is bound to the surface and incorporated within the oxide.

Preparation and characterization of silica coated iron oxide magnetic nano-particles

Iron oxide magnetic nano-particles have been prepared by precipitation in an aqueous solution of iron(II) and iron(III) chlorides under basic condition. Surface modifications have been carried out by using tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MPTMS). The uncoated and coated particles have been characterized with transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, thermal gravimetric analysis (TGA), and infrared (IR) and Raman spectroscopy. The particle sizes as measured from TEM images were found to have mean diameters of 13 nm for the uncoated and about 19 nm for the coated particles. The measured IR spectra of the uncoated and MPTMS coated particles showed the conversion of magnetite to hematite at high temperature. The results obtained from both IR spectroscopy and TGA revealed that the mercaptopropylsilyl group in the MPTMS coated magnetite decomposed at 600 °C and the silica layer of the TEOS coated magnetite was rather stable. Raman spectroscopy has shown the laser heating effect through the conversion of magnetite to maghemite and hematite.

FerriCast: A Macrocyclic Photocage for Fe3+

The non-siderophoric Fe(3+) photocage FerriCast (4,5-dimethoxy-2-nitrophenyl)-[4-(1-oxa-4,10-dithia-7-aza-cyclododec-7-yl)phenyl] methanol (2) has been prepared in high yield using an optimized two-step reaction sequence that utilizes a trimethylsilyl trifluoromethanesulfonate (TMSOTf) assisted electrophilic aromatic substitution as the key synthetic step. Spectrophotometric assessment of Fe(3+) binding to FerriCast revealed a binding stoichiometry and metal ion affinity dependent on the nature of the counterion. Exposure of FerriCast to 350 nm light initiates a photoreaction that converts FerriCast into FerriUnc (4,5-dimethoxy-2-nitrosophenyl)-[4-(1-oxa-4,10-dithia-7-aza-cyclododec-7-yl)phenyl]-methanone), which binds Fe(3+) less strongly owing to resonance delocalization of the anilino lone pair into the benzophenone pi-system. The release of Fe(3+) upon photolysis of FerriCast also was evaluated using a previously reported turn-on fluorescent sensor that utilizes the same macrocyclic ligand (4-(1-oxa-4,10-dithia-7-aza-cyclododec-7-yl)phenyl, AT(2)12C4). In contrast to the original reports on AT(2)12C4-based Fe(3+) sensors, FerriCast does not interact with ferric iron in aqueous solution. Introduction of oxygen containing solvents (MeOH, H(2)O, DMSO, MES, and phosphate buffers) to CH(3)CN solutions of metalated FerriCast lead to rapid decomplexation as measured by UV-visible spectroscopy. Further investigations contradicted the published conclusions on the aqueous coordination chemistry of AT(2)12C4, but also confirmed the unique and unexpected selectivity of the macrocycle for Fe(3+) in nonaqueous solvents. The crystallographic analysis of [Cu(AT(2)12C4)Cl](+) provides a rare example of a bifurcated hydrogen bond, and evidence for redox chemistry with the ligand. Spectrophotometric analysis of the model ligand with redox active metal ions provide evidence for AT(2)12C4(*+), a quasi-stable species the presence of which suggests caution should be taken when evaluating the interaction of aniline-containing systems with redox active metal ions.

Investigation of sorption capability of reverse osmosis membranes in aqueous solutions of iron, zinc, and sodium sulfates

Experimental data and equations to calculate a sorption capacity of reverse osmosis membranes MGA-95, ESPA and OPM-K in aqueous solutions of iron, zinc and sodium sulfates were obtained and analyzed depending on temperature and concentration of the solution.

Synthesis and crystal structure of [Fe4O2(H2O)10(C5H5NCOO)4](NO3)8 · 2H2O

Crystals of the tetranuclear complex [Fe4O2(H2O)10(C5H5NCOO)4](NO3)8 · 2H2O are obtained by the slow evaporation of an aqueous solution of iron(III) nitrate and isonicotinic acid. According to the X-ray diffraction data, four metal atoms lie in the same plane and together with two μ3-O oxygen atoms form the fragment [Fe4(μ3-O)2]10+. The [Fe4O2(H2O)10(C5H5NCOO)4]8+ cation has been obtained and structurally characterized for the first time.

Oxygen Reduction in PEM Fuel Cells: Fe-Based Electrocatalysts Made with High Surface Area Activated Carbon Supports

Catalysts for the oxygen reduction reaction in polymer electrolyte membrane (PEM) fuel cells were prepared by impregnating four high surface area activated carbons (ACs), namely, Ax-21, CNS-201, IRH-33, and IRH-40, with 0.2 wt % nominal Fe as ferrous acetate, and then by pyrolyzing them for various times in at . Among the catalysts made with as-received ACs, high activity was only obtained for those made with Ax-21, which is the only AC having mainly carboxylate surface groups. In the aerated aqueous solution of iron(II) acetate used for Fe impregnation, these surface functionalities ligated with free ions and subsequently yielded active sites upon pyrolysis in . It is, nonetheless, possible to obtain high activities using other ACs provided that they are first treated in concentrated to generate carboxylic functionalities at their surface. It is believed that Fe/N/C-type catalytic sites are hosted in AC micropores. Fuel cell tests performed with the best catalyst from each AC series show very similar polarization curves with an initial mass activity at 0.8 V ranging from 11 to .