Hexacyanoferrate Ions Research Articles

Synthesis of Cd/(Al+Fe) layered double hydroxides and characterization of the calcination products

Layered double hydroxides (LDHs) containing Cd(II), Al(III), and Fe(III) in the brucite-like layers with different starting Fe/Al atomic ratios and with nitrate as counteranion have been prepared following the coprecipitation method at a constant pH value of 8. An additional Cd(II),Al(III)-LDH sample interlayered with hexacyanoferrate(III) ions has been prepared by ionic exchange at pH 9. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), and FT-IR spectroscopy. Their thermal stability has been assessed by thermogravimetric and differential thermal analyses (TG-DTA) and mass spectrometric analysis of the evolved gases. The PXRD patterns of the solids calcined at 800 °C show diffraction lines corresponding to Cd(Al)O and spinel-type materials, which precise nature (CdAl 2O 4, Cd 1− x Fe 2+ x O 4, or Cd x Fe 2.66O 4) depends on location and concentration of iron in the parent material or precursor.

Iridium(III) catalyzed oxidation of iodide ions in aqueous acidic medium

Oxidation of iodide ions by K3Fe(CN)6, catalyzed by hydrogen ions obtained from hydrochloric acid was found to be further catalyzed by iridium(III) chloride. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated from the rate when iridium(III) and H+ions both, catalyze the reaction. Reactions studied separately in the presence as well as in the absence of IrCl3 under similar conditions were found to follow second order kinetics with respect to [I−]. While the rate showed direct proportionality with respect to [K3Fe(CN)6] and [IrCl3]. At low concentrations the reaction shows direct proportionality with respect to [H+] which tends to become proportional to the square of hydrogen ions at higher concentrations. Strong retarding affect of externally added hexacyanoferrate(II) ions was observed in the beginning but further addition affects the rate to a little extent. Changes in [Cl−] and also ionic strength of the medium have no effect on the rate. With the help of the intercept of catalyst graph, the extent of the reaction, which takes place without adding iridium(III), was calculated and was found to be in accordance with the values obtained from the separately studied reactions in which only H+ ions catalyze the reaction. It is proposed that iridium forms a complex, which slowly disproportionates into the rate-determining step. Thermodynamic parameters at four different temperatures were calculated.

“Green synthesis” of monodisperse Pt nanoparticles and their catalytic properties

A green synthetic strategy to prepare monodisperse Pt nanoparticles was reported. Aminodextran acted as the reductive and protective agents, and Pt nanoparticles were conveniently obtained at one step. The as-prepared Pt nanoparticles were characterized by UV/vis spectroscopy (UV–vis), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). By changing the initial molar ratio of aminodextran to platinum precursor, Pt nanoparticles with different size were obtained. Amino groups of aminodextran could absorb on Pt nanoparticles surfaces and serve as a very good stabilizer. However, dextran without amino groups could not effectively stabilize Pt nanoparticles and aggregation of Pt nanoparticles were obtained. Catalytic activity of these Pt nanoparticles for the electron-transfer reaction between hexacyanoferrate (III) ions and thiosulfate ions was also studied, and they showed good catalytic efficiency.

Kinetic study of ruthenium(VI) -- catalyzed oxidation of 2-methoxy- ethanol by aqueous alkaline hexacyanoferrate(III)

The kinetics of ruthenium(VI) catalyzed oxidation of 2-methoxyethanol by hexacyanoferrate(III) ion in an aqueous alkaline medium at constant ionic strength shows zero order dependence on hexacyanoferrate(III) and first order dependence on Ru(VI). Dependence of substrate concentration shows a Michaelis – Menten type behaviour. The rate increases with the decrease in alkali concentration. A reaction mechanism involves the formation of an intermediate complex between the substrate and ruthenium(VI). This complex decomposes slowly, producing ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in subsequent steps. The theoretical rate law obtained is in complete agreement with the experimental observations.

Ruthenium(III) catalysis in the reaction of hexacyanoferrate(III) and iodide ions in perchloric acid medium

RuCl3 can further catalyze the reaction between hexacyanoferrate(III) and iodide ions, which is already catalyzed by the hydrogen ions obtained from perchloric acid. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated graphically from the rate when ruthenium(III) and H+ ions both catalyze the reaction. Reactions studied separately in the presence as well as in the absence of RuCl3 under similar conditions were found to follow second order kinetics w.r.t. [I−]. While the rate showed direct proportionality w.r.t. [Fe(CN)6]3− and [RuCl3]. At low concentrations the reaction shows direct proportionality with respect to [H+] which tends to become proportional to the square of hydrogen ion concentrations. External addition of [Fe(CN)6]4− ions retards the reaction velocity while change in ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, extent of the reaction, which takes place without adding ruthenium(III) was calculated and it was in accordance with the values obtained from the separately studied reaction in which only H+ ions catalyze the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate-determining step. Arrhenius parameters at four different temperatures were also calculated. Open image in new window

Preparation and characterization of carbon paste electrode modified with tin and hexacyanoferrate ions

A carbon paste electrode was modified chemically using Sn(II) or Sn(IV) chlorides and hexacyanoferrate(II) or hexacyanoferrate(III). The electrochemical behavior of such SnHCF carbon paste electrodes was studied by cyclic voltammetry. The study revealed that Sn(IV) and hexacyanoferrate(II) yield the best results. This electrode showed one pair of peaks: the anodic and cathodic peak at the potentials of 0.195 and 0.154 V vs. SCE, respectively, at a scan rate of 20 mV s-1 in a 0.5 M phosphate buffer as the supporting electrolyte. The SnHCF modified electrodes were very stable under potential scanning. The effects of pH and alkali metal cations of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied. The results showed that cations have a considerable effect on the electrochemical behavior of the modified electrode. The diffusion coefficients of hydrated K+ and Na+ in the film, the transfer coefficient and the electron transfer rate constant were determined.

Oxidation of hydrates of cyclic ketones by alkaline hexacyanoferrate(III)

The kinetics of the reaction between cyclopentanone and cyclohexanone with hexacyanoferrate(III) ion in alkaline medium has been investigated at five temperatures. The data show that the reactions are quite fast and follow second order kinetics with respect to hydroxide ion concentrations while the rate follows direct proportionality with respect to the concentrations of hexacyanoferrate(III) ion and cyclic ketones. Rate of the reaction is not affected by the external addition of hexacyanoferrate(II) concentrations. Overall rate of the reaction may be given by − d [ Fe ( CN ) 6 3 − ] d t = k K 1 K 2 [ S ] [ O H − ] 2 [ Fe ( CN ) 6 3 − ] [ H 2 O ] 2 .

NiII(tn)2]5[FeIII(CN)6]2[FeII(CN)6] · 10H2O: A 3-dimensional dimetallic polymer exhibiting ferromagnetic interaction

A three-dimensional cyanide-bridged bimetallic assembly [NiII(tn)2]5[FeIII(CN)6]2[FeII(CN)6] (tn=1,3-propanediamine) has been synthesized. The structure consists of cyanide bridged neutral NiII5FeIII2FeII units. Each hexacyanoferrate(II) ion connects six NiII ions using all six CN– groups and each hexacyanoferrate(III) ion coordinates with two NiII ions. Magnetic studies show that the complex displays a ferromagnetic coupling between Ni(II) and Fe(III).

First coupling between a LINAC and FT-IR spectroscopy: The aqueous ferrocyanide system

New results on the aqueous ferrocyanide system at neutral pH are presented here using the coupling of a 10 MeV LINAC with infrared spectroscopy. Seconds after irradiation, we observe a decrease of the Fe ( CN ) 6 4 - ferrocyanide ion concentration. Hydroxopentacyanoferrate(III) as well as hexacyanoferrate(III) ions are formed. After a 1500 Gy irradiation, we observe de-aquation of the former species, leading to the latter with a characteristic time of about 410 s and reduction of ferricyanide into ferrocyanide ions with a rate constant of 3 mol −1 dm 3 s −1. Berlin green is also detected when the irradiation dose is greater than 2500 Gy.

EVALUATING THE RISKS OF THE TECHNOLOGIES FOR TREATING THE GREEN MUD

The green mud results as a waste from the process of wines deferrization using the blue fining method. This is a dangerous waste due to its content in ferrocyanides, but in Romania, there are important stocks, stored under inappropriate conditions for environment and health. Worldwide there are experimental and patented methods for treating the green mud, some of them involving cyanides recuperation, others based on the decomposition of the hexacyanoferrate ions, by means of thermal procedures or by using oxidizing agents. This work analyses the most known and applied procedures and methods to remove the dangerous waste resulted during wine deferrization, rich in ferrocyanides.

Structure and property studies of hybrid xerogels containing bridged positively charged 1,4-diazoniabicycle[2.2.2]octane dichloride

The compound di-3- n-propyltrimethoxysilane (1,4-diazoniabicycle[2.2.2]octane) dichloride, [(MeO) 3Si(CH 2) 3N +(CH 2CH 2) 3N +(CH 2) 3Si(OME) 3]Cl 2 was obtained and was used as a precursor reagent to obtain hybrid xerogels where the organic molecule was bonded to a silica framework by reacting the ends of both sides of the precursor reagent. That is, both Si(OME) 3 groups react with tetraethylorthosilicate (TEOS) by hydrolysis–condensation reactions. The resulting hybrid xerogels with variable C/Si mole ratios were prepared and analyzed and their textural characteristics determined. The samples prepared presented micropores with diameter 1.5 nm, the chain length of which matched with the estimated length of the organic bridging group. The charged organic bridging groups allow the immobilization of hexacyanoferrate ions by an ion exchange process. The electron transfer process of the hexacyanoferrate anionic complex confined in the pores of the matrices was studied by cyclovoltammetry.

Raman Studies on the Interaction of the Reactants with the Platinum Nanoparticle Surface during the Nanocatalyzed Electron Transfer Reaction

Raman studies are conducted to understand the specific interactions between the individual reactants and the platinum nanoparticle surface during the nanocatalyzed electron transfer reaction between hexacyanoferrate (III) ions and thiosulfate ions. When Pt nanoparticles are added to the thiosulfate ion solution, a shift in the symmetric SS stretching mode is observed compared to the frequency observed for the free thiosulfate ions in solution, suggesting that binding to the Pt nanoparticle surface occurs via the S- ion. It is also observed that there are no shifts in the symmetric and asymmetric OSO bending or SO stretching frequencies. This suggests that the thiosulfate ions do not bind to the nanoparticle surface via the O- ion. When platinum nanoparticles are added to the hexacyanoferrate(III) ion solution, evidence is found for both adsorbed hexacyanoferrate(III) ions and a platinum cyanide complex. For adsorbed hexacyanoferrate(III) ions, the CN stretching frequency is observed at 2101 cm(-1) and the Fe-C stretching frequency is found at 368 cm(-1). The observed CN stretching frequencies located at 2147 and 2167 cm(-1) provide strong evidence that there is a Pt(CN)4(2-) platinum cyanide complex formed. In addition, the Pt-CN band is also observed at 2054 cm(-1). These observed bands provide spectroscopic evidence that the hexacyanoferrate(III) ions dissolve by forming a complex with the surface platinum atoms of the nanoparticles. Raman spectra of the product mixtures are obtained after the completion of the reaction when carried out with higher reactant concentrations to observe the Raman spectra, but with a similar 10:1 ratio of thiosulfate to hexacyanoferrate(III) ions as used previously, with and without PVP-Pt nanoparticles at a correspondingly higher concentration. It is observed that there are no shifts in the characteristic Raman bands associated with hexacyanoferrate(II) ions and no evidence for the formation of adsorbed hexacyanoferrate(II) species or platinum cyanide complexes in the presence of the platinum nanoparticles. In addition, there is evidence for the shifted symmetric SS stretching mode, suggesting that some of the unreacted thiosulfate (present in large excess) is bound to the Pt nanoparticle surface. Thus, under the actual reaction conditions, the hexacyanoferrate(III) ions preferentially react with adsorbed thiosulfate ions to form the reaction products, and this supports the surface catalytic mechanism we proposed previously.

Accumulation of Cu(II) cations in poly(3,4-ethylenedioxythiophene) films doped by hexacyanoferrate anions and its application in Cu 2+-selective electrodes with PVC based membranes

Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu 2+ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface. Accumulation of Cu 2+ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu 2+-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu 2+-selective ionophore. Binding of Cu 2+ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu 2+-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10 −7 M CuSO 4.

Alkaline hexacyanoferrate(III) oxidation of substituted 4‐oxo acids: a mechanistic study

AbstractThe kinetics of the oxidation of substituted 4‐oxo‐4‐arylbutanoic acids by hexacyanoferrate(III) in aqueous alkaline medium were studied. The reactions are found to be first order in each of the reagents, the oxo acid, hydroxide ion and the hexacyanoferrate(III) ion. A mechanism involving the formation of enolate anion from the oxo compound and subsequent rate‐determining electron transfer is proposed. Application of the Olson–Simonson rule substantiated the participation of negatively charged ions in the rate‐determining step. The experimental rate constant is found to be composite, being the product of the equilibrium constant for the enolate anion formation and the rate constant of the oxidation step (Kk2). The effect of addition of solvents such as methanol and DMSO is discussed and a quantitative relationship is derived between the ionic strength and the composite rate constant. The low activation energies and even the negative activation energy in the oxidation of 4‐(3‐nitrophey1)‐4‐oxobutanoic acid are explained. The ρ values are positive and decrease with temperature. Contrary to the expected electronic effect, the methyl group in the ortho position accelerates the reaction owing to steric factors. From the intersection of the lines in the Hammett and Arrhenius plots, the isokinetic relationship is discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Zinc hexacyanoferrate film as an effective protecting layer in two-step and one-step electropolymerization of pyrrole on zinc substrate

The two-step and one-step electrosynthesis processes of polypyrrole (PPy) films on the zinc substrate are described. The two-step process includes (i) the zinc surface pretreatment with hexacyanoferrate ion in the aqueous medium in order to form a zinc hexacyanoferrate (ZnHCF) film non-blocking passive layer on the surface and with the view to prevent its reactivity and (ii) electropolymerization of pyrrole on the ZnHCF|Zn-modified electrode in aqueous pyrrole solution. In this context, both the non-electrolytic and electrolytic procedures were adapted, and the effect of some experimental conditions such as supporting electrolyte, pH and temperature of the solution at the zinc surface pretreatment step as well as pyrrole concentration and electrochemical techniques at the polymerization step was investigated. By optimizing the experimental conditions in both steps, we have obtained a homogeneous and strongly adherent PPy films on the zinc substrate. The one-step process is based on the use of an aqueous medium containing Fe(CN) 6 4− and pyrrole. The ferrocyanide ion passivates the substrate by formation of ZnHCF film during the electropolymerization process of pyrrole and therefore makes it possible to obtain strongly adherent PPy films, with controlled thickness, either by cyclic voltammetry or by electrolysis at constant current or constant potential without any previously treatment of the zinc electrode surface. The polypyrrole films deposited on the zinc electrode were characterized by cyclic voltammetry and scanning electron microscopic (SEM) measurement.

Electron transfer across the single micro-water-droplet|oil interface using microcapillary injection and microelectrode methods

Electron transfer (ET) between a hexacyanoferrate(III) ion in a single micro-water-droplet and a ferrocene derivative (Fc), such as decamethylferrocene, in 2-nitrophenyl octyl ether was studied using microcapillary injection and microelectrochemical techniques. The overall ET rate constant increased with the decreasing Gibbs energy (Δ G), consisting of the Galvani potential between the water and oil phases and the redox potential difference of the solutes, and was saturated at a Δ G value less than −15 kJ mol −1. The Δ G dependence of the overall ET rate was discussed in terms of the interfacial ET coupled with the microscopic diffusion of Fc in the vicinity of the water|oil interface.

Preparation of magnetic material containing MgFe2O4 spinel ferrite from a Mg?Fe(III) layered double hydroxide intercalated by hexacyanoferrate(III) ions

In this research communication, a novel method for improving magnetic properties of material containing MgFe2O4 spinel ferrite is presented. The key feature of this method is using a single molecular precursor. Mg–Fe(III) layered double hydroxide intercalated by [Fe(CN)6]3− ions with the low Mg/Fe molar ratio can be prepared by coprecipitation method. Compared with conventional ceramic method, the saturation magnetization for MgFeO4 ferrite produced by calcination of the intercalated LDH precursor is improved obviously. The major advantage of the method is that it affords uniform distribution of all metal cations on an atomic level in the intercalated LDH precursor, and supplies additional Fe3+ ions from the interlayer [Fe(CN)6]3− ions; hence the formation of a great amount of spinel ferrite starting from the LDH rather than a mixture requires a much shorter time and lower temperature.

Preparation and thermal decomposition of magnesium/iron(III) layered double hydroxide intercalated by hexacyanoferrate(III) ions

Preparation and thermal decomposition of magnesium/iron(III) layered double hydroxide intercalated by hexacyanoferrate(III) ions

Preparation of magnetic material containing MgFe 2O 4 spinel ferrite from a Mg–Fe(III) layered double hydroxide intercalated by hexacyanoferrate(III) ions

In this research communication, a novel method for improving magnetic properties of material containing MgFe 2O 4 spinel ferrite is presented. The key feature of this method is using a single molecular precursor. Mg–Fe(III) layered double hydroxide intercalated by [Fe(CN) 6] 3− ions with the low Mg/Fe molar ratio can be prepared by coprecipitation method. Compared with conventional ceramic method, the saturation magnetization for MgFeO 4 ferrite produced by calcination of the intercalated LDH precursor is improved obviously. The major advantage of the method is that it affords uniform distribution of all metal cations on an atomic level in the intercalated LDH precursor, and supplies additional Fe 3+ ions from the interlayer [Fe(CN) 6] 3− ions; hence the formation of a great amount of spinel ferrite starting from the LDH rather than a mixture requires a much shorter time and lower temperature.

Effect of Nanocatalysis in Colloidal Solution on the Tetrahedral and Cubic Nanoparticle SHAPE: Electron-Transfer Reaction Catalyzed by Platinum Nanoparticles

The stability of tetrahedral and cubic platinum nanoparticles during the catalysis of the electron-transfer reaction between hexacyanoferrate (III) and thiosulfate ions in colloidal solution at room temperature was studied by using TEM and HRTEM. Before the reaction, the dominantly tetrahedral nanoparticles have a shape distribution of 55 ± 4% regular tetrahedral, 22 ± 2% distorted tetrahedral, and 23 ± 2% spherical nanoparticles, and the dominantly cubic nanoparticles have an initial shape distribution of 56 ± 4% regular cubes, 13 ± 1% distorted cubes, and 31 ± 3% truncated octahedral nanoparticles. The amount of tetrahedral nanoparticles decreases by 60 ± 5% after the first cycle and by 62 ± 4% after the second cycle of the reaction. In the case of cubic nanoparticles, the amount of cubic nanoparticles decreases by 39 ± 5% after the first cycle and by 66 ± 5% after the second cycle compared to before the reaction. After the first and second cycles of the reaction, there are a greater percentage of distorted tetrahedral and distorted cubic nanoparticles present. The rate of the dissolution of the surface Pt atoms is faster for the tetrahedral nanoparticles than for the cubic nanoparticles. This suggests that tetrahedral nanoparticles, with their sharp corners and edges, are more sensitive and more liable to shape changes during nanocatalysis. The presence of just hexacyanoferrate ions in the solution with the nanoparticles is found to increase the amount of distorted tetrahedral and distorted cubes present much more than during the reaction. The presence of only the thiosulfate ions does not seem to affect the size or shape distribution which might result from the capping ability of this anion and thus protects the nanoparticles.