Regularities of the formation of iron(III) nanocrystalline particles during the oxidation of iron(II) compounds in a neutral medium

The regularities of the formation of iron(III) oxide hydroxides as nanocrystalline particles via oxidation of iron(II) compounds in a near-neutral pH region were studied by potentiometric titration, electron microscopy, chemical analysis, and X-ray diffraction. The oxidation process comprises two steps. The first step produces Fe(II)-Fe(III) hydroxo salts having a “green rust” structure in the form of nanocrystalline particles shaped as hexagons. The second step produces anisotropic nanocrystalline particles of iron(III) oxide hydroxides via the dissolution-oxidation-precipitation mechanism and via solid-phase oxidation. The oxidation of chlorine-containing suspensions helps the formation of single-phase nanocrystalline lepidocrocite, while oxidation in the presence of sulfate ions yields nanocrystalline goethite.     

Simultaneous determination of Fe(II) and Fe(III) by kinetic spectrophotometric H-point standard addition method

The H-point standard addition method (HPSAM) for simultaneous determination of Fe(II) and Fe(III) is described. The method is based on the difference in the rate of complex formation of iron in two different oxidation states with Gallic acid (GA) at pH 5. Fe(II) and Fe(III) can be determined in the range of 0.02–4.50 μg ml⁻¹ and 0.05–5.00 μg ml⁻¹, respectively, with satisfactory accuracy and precision in the presence of other metal ions, which rapidly form complexes with GA under working conditions. The proposed method was successfully applied for simultaneous determination of Fe(II) and Fe(III) in several environmental and synthetic samples with different concentration ratios of Fe(II) and Fe(III).     

Complexation equilibria and spectrophotometric determination of iron(III) with 1-amino-4-hydroxyanthraquinone

The complex equilibria of iron(III) with 1-amino-4-hydroxyanthraquinone (AMHA) were studied spectrophotometrically in 40% (v/v) ethanol and an ionic strength of 0.1M (NaClO(4)). The complexation reactions were demonstrated and characterized using graphical logarithmic analysis of the absorbance-pH graphs. A simple, rapid, selective and sensitive method for the spectrophotometric determination of trace amounts of Fe(III) is developed based on the formation of Fe(AMHA) complex at pH 2.5 (lambda(max) = 640 nm, epsilon approximately = 2.1 x 10(4) L. mol(-1) . cm(-1)) in the presence of a large number of foreign ions. Interferences caused by palladium(II) was masked by the addition of cyanide ions. The method has been applied to the determination of iron in some synthetic samples and polymetallic iron ores.     

Effect of foreign ions for the determination of metal ion in the presence of surfactants

Aluminum is the third most abundant metal in the Earth’s crust. Despite its ubiquitous nature it is present in small amount in living organisms. Aluminum toxicity has been implicated in the pathogenesis of renal distinct clinical syndromes, including progressive and fatal encephalopathy and bone diseases. In the present study, Al was selected for the analysis by complexometric method. This method was based on the formation of a red colored ternary complex by the reaction of Aluminum with Aluminon (Aurin tricarboxylic acid triammonium salt) in the presence of micellar medium. The ternary complex of Aluminum with the surfactant Triton X-100 shows a maximum absorbance at 530 nm wavelength at pH 4.0 while with the sodium dodecyl sulfate it shows a maximum absorbance at 525 nm and at pH 5.0. The reaction was proceeded by the variation in pH and concentrations of surfactants, aluminon, aluminum. Their effects on the reaction of aluminum with aluminon complex in micellar media were recorded by UV-visible spectrophotometer. The reaction was found to be extremely rapid at room temperature. The system obeys Lambert Beer’s law between 0.24 and 21.74 μg/mL concentrations with Triton X-100. The values of slope, intercept and correlation coefficients were 0.07, 0.348 and 0.989, respectively. The concentration varied between 0.24 and 24.14 μg/mL with sodium dodecyl sulfate and the values of slope, intercept and correlation coefficients were 0.029, 0.148 and 0.962, respectively. The foreign ion effect was also tested by keeping the constant concentration of metal ion and determining its concentration in the presence of different foreign ions. The method was also applied for the determination of Al(III) in pharmaceutical formulations and water samples, which showed an excellent resemblance between reported and obtained results.     

[Na4(H2O)7][Fe(OH)6Mo6O18]: A new [12] metallacrown-6 structure with an octahedrally coordinated iron at the center

The reaction of an aqueous solution of sodium molybdate with iron powder at low pH (∼0.184) gives rise to the formation of a six-member Mo ring-shape cluster with an Fe (II) encapsulated at the center, [Na₄(H₂O)₇][Fe(OH)₆Mo₆O₁₈](1), which is further linked to a remarkable three-dimensional network via sodium ions.     

Determination of iron(II) with bipyridylglyoxal dithiosemicarbazone

Bipyridylglyoxal dithiosemicarbazone reacts with iron(II) or (III). The Fe(III) complex is yellow (lambda(max) 400 nm). Fe(II) forms a red-violet 1:2 complex at pH 2.5 (lambda(max) 550 nm) and a green-blue 1:1 complex at pH 5-10 (lambda(max) 590-610 nm). Both ferrous complexes can be oxidized to the ferric complex; this reaction is reversible. The quantitative application of the ferrous complex has been studied.     

Indirect Complexometric Determination of Mercury(II) Using Potassium Bromide as Selective Masking Agent

 A complexometric method for the determination of mercury in presence of other metal ions based on the selective masking ability of potassium bromide towards mercury is described. Mercury(II) present in a given sample solution is first complexed with a known excess of EDTA and the surplus EDTA is titrated against zinc sulfate solution at pH 5–6 using xylenol orange as the indicator. A known excess of 10% solution of potassium bromide is then added and the EDTA released from Hg-EDTA complex is titrated against standard zinc sulfate solution. Reproducible and accurate results are obtained for 8 mg to 250 mg of mercury(II) with a relative error ± 0.28% and standard deviations ≤0.5 mg. The interference of various ions is studied. This method was applied to the determination of mercury(II) in its alloys. Received April 18, 2001 Revision October 10, 2001     

H+-Cu2+ ion exchange on a Cu0-KU-23 sulfocation exchanger nanocomposite in solutions with various pH values

The influence of solution pH on H⁺-Cu²⁺ exchange equilibrium was studied for the disperse copper- KU-23 (15/100 S) macroporous strongly acid sulfocation exchanger nanocomposite. In dilute solutions of copper(II) sulfate in weakly acid media (pH 3–6), ion exchange limitation is related to the consumption of hydrogen counterions and the formation of copper counterions in a side reaction between copper particles and impurity oxygen. The concentration of hydrogen counterions in the nanocomposite is replenished as pH decreases because of their sorption from solution together with copper ions. Original Russian Text ? E.V. Zolotukhina, T.A. Kravchenko, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 934–938.     

Reverse flow injection spectrophotometric determination of iron(III) using norfloxacin

A reversed flow injection colorimetric procedure for determining iron(III) at the μg level was proposed. It is based on the reaction between iron(III) with norfloxacin (NRF) in 0.07 mol l⁻¹ ammonium sulfate solution, resulting in an intense yellow complex with a suitable absorption at 435 nm. Optimum conditions for determining iron(III) were investigated by univariate method. The method involved injection of a 150 μl of 0.04% w/v colorimetric reagent solution into a merged streams of sample and/or standard solution containing iron(III) and 0.07 mol l⁻¹ ammonium sulfate in sulfuric acid (pH 3.5) solution which was then passed through a single bead string reactor. Subsequently the absorbance as peak height was monitored at 435 nm. Beer's law obeyed over the range of 0.2–1.4 μg ml⁻¹ iron(III). The method has been applied to the determination of total iron in water samples digested with HNO₃–H₂O₂ (1:9 v/v). Detection limit (3σ) was 0.01 μg ml⁻¹ the sample through of 86 h⁻¹ and the coefficient of variation of 1.77% (n=12) for 1 μg ml⁻¹ Fe(III) were achieved with the recovery of the spiked Fe(III) of 92.6–99.8%.     

Spectrophotometric determination of traces of iron after extraction of Fe(II)-phenanthroline complex on polyurethane foam

A spectrophotometric method for the determination of traces of iron in glass and ceramic materials has been developed. The method involves formation of the Fe(II)-phenanthroline complex at pH 3-4 in aqueous medium, followed by its selective extraction and preconcentration on polyurethane foam from 2.5M perchloric acid and finally elution of the complex with acetone for spectrophotometric measurement at 510 nm. A wide linearity range from 0.05 to 3 mu g/ml Fe is obtained with the method. Co, Cu and Ni have no significant effect when they are present in the weight ratios Fe:Co < 1:2, Fe: Cu < 1:10 and Fe: Ni < 1:50. The method yielded satisfactory results when applied to various glass and ceramic samples.     

A ratiometric fluorescent chemosensor for iron: discrimination of Fe2+ and Fe3+ and living cell application

A newly designed probe, 6-thiophen-2-yl-5,6-dihydrobenzo[4,5]imidazo-[1,2-c] quinazoline (HL(1)) behaves as a highly selective ratiometric fluorescent sensor for Fe(2+) at pH 4.0-5.0 and Fe(3+) at pH 6.5-8.0 in acetonitrile-HEPES buffer (1/4) (v/v) medium. A decrease in fluorescence at 412 nm and increase in fluorescence at 472 nm with an isoemissive point at 436 nm with the addition of Fe(2+) salt solution is due to the formation of mononuclear Fe(2+) complex [Fe(II)(HL)(ClO(4))(2)(CH(3)CN)(2)] (1) in acetonitrile-HEPES buffer (100 mM, 1/4, v/v) at pH 4.5 and a decrease in fluorescence at 412 nm and increase in fluorescence at 482 nm with an isoemissive point at 445 nm during titration by Fe(3+) salt due to the formation of binary Fe(3+) complex, [Fe(III)(L)(2)(ClO(4))(H(2)O)] (2) with co-solvent at biological pH 7.4 have been established. Binding constants (K(a)) in the solution state were calculated to be 3.88 × 10(5) M(-1) for Fe(2+) and 0.21 × 10(3) M(-1/2) for Fe(3+) and ratiometric detection limits for Fe(2+) and Fe(3+) were found to be 2.0 μM and 3.5 μM, respectively. The probe is a "naked eye" chemosensor for two states of iron. Theoretical calculations were studied to establish the configurations of probe-iron complexes. The sensor is efficient for detecting Fe(3+)in vitro by developing a good image of the biological organelles.     

Solution properties of iron(III) complexes with 5-fluorosalicylic acid — spectra,speciation, and redox stability

Iron(III)-5-fluorosalicylic acid systems were investigated in water by pH potentiometry combined with UV-VIS spectrophotometry. The data revealed that stable aquated mono-, bis-, and tris(5-fluorosalicylato) iron(III) complexes are formed together with their monohydroxo and dihydroxo analogues. The stability constants of all present iron(III) species were calculated. Based on pH and the metal: ligand ratio dependent distribution of the species, electronic absorption spectra of the complexes in the visible region were obtained. Redox stability was monitored as an ability to undergo both spontaneous and photoinduced reduction of iron(III) to iron(II). Complexes do not undergo any redox changes when in dark neither in methanol nor in water. While aqueous solutions of complexes are stable under the influence of incident visible radiation, steady-state irradiation of the methanolic systems by visible light led to photoreduction of iron(III) to iron(II), the quantum yield of iron(II) photoformation was determined. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

Rapid speciation of trace iron in rainwater by reverse flow injection analysis coupled to a long path length liquid waveguide capillary cell and spectrophotometric detection

A method for speciation and determination of low levels of dissolved iron in rainwater was established by coupling reverse flow injection analysis with a 2-m liquid waveguide capillary cell and spectrophotometric detection. Ferrozine solution was injected into a sample stream to form an Fe(II)-ferrozine complex with Fe(II), and the absorbance of this complex was detected at both 562 nm and 625 nm with a reference wavelength at 700 nm. Fe(III) was analyzed in the same manner after being reduced to Fe(II) by ascorbic acid. The optimum conditions and the interference of Cu(I), Ni(II) and Co(II) were investigated. The limits of detection were 0.1 nM for Fe(II) and 0.2 nM for Fe(III), while the linear ranges were 0.4 – 200 nM for Fe(II) and 0.8 – 287 nM for Fe(III) at 562 nm, and can be extended to higher concentrations with the detection at a less sensitive wavelength of 625 nm. The sample throughput was 6 h^?1, and the total sample volume consumed was 10 mL. This method has been successfully applied to analyze dissolved iron in rainwater of Xiamen from August to November, 2008. The lowest level of iron in rainwater was observed during typhoon events. By adopting reverse flow injection analysis coupled with liquid waveguide long path length capillary cell, the reagent consumption was low and the sensitivity was enhanced. The other advantages of this method are high sample throughput, wide linear dynamic range and high selectivity for Fe(II).     

Polarography of metal-gallic complexes

The polarographic behavior of metal ions in perchlorate media containing gallic acid is described. Tungsten(VI) forms a complex with gallic acid which yields a single wave in these media, useful in the polarographic determination of tungsten. Evidence for complexation of chromium(III), copper(II), iron(III), molybdenum(VI), uranium(VI), vanadium(V), tungsten(VI), praseodymium(III), samarium(III), neodymium(III) and gadolinium(III) is obtained and the behavior of these metal ions is summarized.     

基于三联吡啶衍生物的Fe~(2+)/Fe~(3+)化学比色敏感器

合成和表征了一种新的化合物(E)-4-′(4-(2-(2-萘)乙烯基)苯基)-2,2′:6′,2″-三联吡啶L.用Fe2+或Fe3+来滴定时,L的溶液(三氯甲烷和乙醇的体积比为1∶20)颜色分别从无色变成洋红色和橙红色,相应的紫外可见吸收光谱都在374和574 nm出现特征吸收峰.此外,即使存在其它过量金属阳离子时,L对Fe2+或Fe3+离子仍然表现出很强的敏感性和选择性.另外,还研究了L对Fe2+或Fe3+离子及两者共同存在时的线性检测浓度范围和最低检测极限(LOD).     

Defining chemical species in complex environments using K-edge X-ray absorption spectroscopy: vanadium in intact blood cells and Henze solution from the tunicate Ascidia ceratodes

A K-edge X-ray absorption spectrum (XAS) fitting approach has been developed to speciate elements of interest in complex materials and used here to model the storage of biological vanadium within whole blood cells from the tunicate Ascidia ceratodes. The response of the K-edge XAS of solution-phase V(III) to increasing c(sulfate) at constant pH 1.8 produced specific and systematic effects in the preedge transition at 5468.8 eV (preedge transitions: 1s-->4A2 at 5464.9 +/- 0.1 eV, 1s-->4T2 at 5466.9 +/- 0.1 eV, and 1s-->4T1 at 5468.8 +/- 0.1 eV for 11 different V(III)/sulfate solutions). In contrast, variations in acidity (as pH) at constant c(sulfate) systematically modified the V(III) preedge XAS at 5466.9 eV. The energy position of the K-edge absorption maximum also serially shifted -0.32 eV/pH unit, from 5483.7 eV (pH 3.0) to 5484.7 eV (pH 0.3). Fits to the V-K XAS of two samples of A. ceratodes whole blood cells representing dozens of animals implied storage of V(III) ions in four predominant solution regimes: approximately 10% high sulfate/pH 0 acid; approximately 40% high sulfate/pH 1.8 acid; approximately 40% moderate sulfate/pH 1.8 acid; approximately 10% moderate sulfate/pH 3 acid. For lysed blood cells, the best fit represented 63% of the V(III) in a pH 1.6 sulfate-free environment and a further 16% in acidic sulfate solution. Nearly 18% of lysed cells vanadium(III) appeared in a tris(catecholate)-like environment. A detailed speciation of biological vanadium complex ions was calculated from these fits by application of the known equilibrium constants governing V(III) and sulfate in acidic aqueous solution. The utility of blood cell V(III) to ascidians is discussed. Fits to K-edge XAS spectra using the XAS spectra of appropriate models are suggested to be generally applicable to elucidating the state of metal ions in a wide variety of complex environments.     

Photoreduction of chlorohemin in pure pyridine

Chlorohemin (Fe(III)PPCl) undergoes photoreduction when irradiated in pure pyridine solution with 400–450 nm light. A thermal reduction is observed to occur simultaneously with the photochemical one, but after a one hour irradiation about 75% of the reduction product is formed in a photochemical way. Both five and six-coordinated species are observed to be present in solution; however, only the Fe(III)PPpy⁺ five coordinated complex is photoreducible. A mechanism is proposed whereby the primary photochemical act is an axial pyridine → iron electron transfer process yielding Fe(II)PP and py⁺ species. The Fe(II)PP moiety gives rise to the formation of the spectrophotometrically detectable Fe(II)(PP(py)₂ complex. ESR spin trapping results are consistent with the formation of 2-pyridyl radicals from py⁺ cation by fast transfer of a proton to a pyridine molecule.     

Decomposition of di-tert-butyl nitroxide in aqueous solutions

Di-tert-butyl nitroxide (DTBN) decomposes in aqueous solutions producing 2-methyl-2-nitroso propane (MNP) and tert-butanol. The process is acid catalyzed, it is of second order in DTBN, and takes place with a rate constant of (1.0 ± 0.1) M^?2 s^?1. The reaction is also catalyzed by the anionic surfactant sodium dodecyl sulfate and by Fe(II) and Fe(III) ions. The catalysis by Fe(III) involves a very fast reduction of Fe(III) ions with concomitant formation of 2-methyl-2-nitroso propane. The reaction catalyzed by Fe(II) also produces 2-methyl-2-nitroso propane with a formation rate given by: d[MNP]/dt = (0.25 ± 0.10) [Fe(II)] [DTBN]. This reaction rate is nearly pH independent.     

Simple and Selective Spectrophotometric Method for the Determination of Iron (III) and Total Iron Content, Based on the Reaction of Fe(III) with 1,2-Dihydroxy-3,4-Diketocyclo-Butene (Squaric Acid)

 Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95×10³ L·mol⁻¹·cm⁻¹, at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5–20 mgL⁻¹, with a detection limit of 0.3 mgL⁻¹ and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL⁻¹ standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Author for correspondence: University of Ioannina, Department of Chemistry, Laboratory of Analytical Chemistry, Ioannina 451 10, Greece. E-mail: panavelt@cc.uoi.gr Received July 27, 2002; accepted December 20, 2002 Published online April 11, 2003     

A rapid synthesis of iron phosphate nanoparticles via surface-mediated spontaneous reaction for the growth of high-yield, single-walled carbon nanotubes

The direct formation of iron phosphate nanoparticles on hydroxyl-terminated SiO(2)/Si substrates with a narrow size distribution (average diameter = 2.2 nm) is achieved by a simple room temperature spontaneous reaction of ferric chloride and phosphoric acid. Single-walled carbon nanotubes (SWNTs) are grown in high yield from the synthesized iron phosphate nanoparticles by the thermal chemical vapor deposition (CVD) method, as confirmed by atomic force microscopy (AFM) and Raman spectroscopy. Furthermore, three-terminal, p-type, nanotube network field effect transistor (FET) devices are successfully fabricated using the synthesized SWNTs via the photolithography technique. The reduced solubility of Fe(III) ions when they form iron phosphate salts in aqueous media is the main driving force for the nanoparticle formation. Systematic control experiments reveal that the surface property, concentration, and pH of the reaction solution play equally important roles in the formation of nanoparticles.