高铁酸三钾钠的合成及其物理化学性质研究

首次提出了一种在浓的NaOH溶液中电合成0.83 mol•L^－1 Na₂FeO₄溶液进而高纯度合成固态K₃Na(FeO₄)₂的方法. 研究了合成条件, 并利用多种实验技术研究了该固态样品的性质. 实验表明, K₃Na(FeO₄)₂晶体在混合的NaOH-KOH溶液中, 其溶解-沉淀平衡曲线符合经验方程式: [Na^＋][K^＋]³[ ]^2.8＝1.4×10^－4 ([K^＋]≤1.01 mol•L^－1);在浓的KOH溶液中其溶解度与K₂FeO₄几乎一致. 和K₂FeO₄晶体不同, 所得K₃Na(FeO₄)₂晶体显示3个红外特征峰(787, 801～802和858～862 cm^－1)并具有P m1 (164)空间群的六方晶胞, 其粉末在Ar气中直到197 ℃才分解, 热稳定性低于K₂FeO₄.     

An Aqueous Thermodynamic Model for the Solubility of Potassium Ferrate in Alkaline Solutions to High Ionic Strengths from 283.15 to 333.15 K

Potassium ferrate, K₂FeO₄(cr), has numerous promising environmental applications. An aqueous thermodynamic model applicable to high ionic strengths is essential for guiding its applications. In this study, a thermodynamic model is developed for the solubility of K₂FeO₄(cr) in aqueous alkali metal hydroxide solutions, from 283.15 to 333.15 K to high ionic strengths, up to saturation of KOH and NaOH, based on the Pitzer activity coefficient model for aqueous species. The solubility products for K₂FeO₄(cr) at infinite dilution in the temperature range from 283.15 to 333.15 K were obtained. Based on the thermodynamic solubility product of K₂FeO₄(cr) at 298.15 and its temperature dependence, in combination with thermodynamic properties for $ {\text{FeO}}_{4}^{2 - } $ FeO 4 2 ? and K⁺ from the literature, standard thermodynamic properties of K₂FeO₄(cr) at 298.15 K and 0.1 MPa (1 bar) are derived for the first time as follows: Δ_f G ⁰ = ?(896 ± 8) kJ·mol^?1, Δ_f H ⁰ = ?(1026 ± 4) kJ·mol^?1, and S ⁰ = (130 ± 17) J·mol^?1·K^?1. Using the above thermodynamic properties for K₂FeO₄(cr), the potential presence or preservation of K₂FeO₄(cr) in the Martian soils under the conditions relevant to Mars were quantitatively evaluated. Thermodynamic calculations pertaining to the Martian conditions indicate that the presence or preservation of K₂FeO₄(cr) as a strong oxidant in the Martian soils can be supported.     

Effects of KIO<Subscript>3</Subscript> additive on the direct electrosynthesis of K<Subscript>2</Subscript>FeO<Subscript>4</Subscript>

An electrosynthesis in 14.5 M KOH electrolyte using KIO₃ additive is presented for the direct synthesis of solid K₂FeO₄, with a highest efficiency of 77.6%, purities of 95.3–97.8% and a yield of 68 g l⁻¹ K₂FeO₄ at 65°C. The results show that using the additive during synthesis of ferrate(VI) can increase the current efficiency by 26% than the blank in degree. Its function is similar to the results of using ultrasonic. The techniques of CV, EDX, IR, SEM and XRD are used to feature the Fe electrode or K₂FeO₄ samples. It is found that addition of KIO₃ can increase the potential of oxygen evolution on the CV of Fe anode in KOH significantly. The EDX measurement displays that K₂FeO₄ sample obtained using KIO₃ additive contains no iodine. The sample exhibits similar IR feature absorption spectra and XRD patterns but some dissimilar crystal morphologies to the one with blank.     

The kinetics of oxidation of simple aliphatic sulphur compounds by potassium ferrate

Potassium ferrate (K₂FeO₄) is highly soluble in water and a very strong oxidizing agent^{(1, 2)}. Other properties include a strong bacteriacidal action which has been documented by Murmann and Robinson⁽¹⁾. These characteristics, and others, suggest that potassium ferrate would be useful in the advanced treatment of municipal waste water. The efficiency of oxidation of various organic compounds by potassium ferrate must be investigated before conclusions can be drawn.When K₂FeO₄ is placed into aqueous solution a purple colour is produced which disappears as K₂FeO₄ is reduced. At a spectrophotometric wavelength of 505 nm this affords a convenient method for measuring the decomposition kinetics of K₂FeO₄.Rate constants were obtained by algorithmic analysis of spectral absorbance data by the Cornell method⁽³⁾. This work will present a mechanism of reaction for oxidation of simple aliphatic sulphur compounds by potassium ferrate. The oxidation of simple aliphatic sulphur compounds produces the corresponding sulphoxide or sulphone^{(4, 5)} Compounds studied included dimethyl sulphoxide, diethylsulphide, dimethylsulphone, and 2,2-thiodiethanol.     

Studies on the electrochemical characteristics of K2Sr(FeO4)2 electrode

K₂Sr(FeO₄)₂ was prepared from K₂FeO₄ and characterized by SEM, XRD, IR and AAS. The measured solubility of K₂Sr(FeO₄)₂ is lower than that of K₂FeO₄ either in various concentrations of aqueous potassium hydroxide at room temperature (25 °C) or in saturated KOH solution at different temperatures. Discharge performance of K₂Sr(FeO₄)₂ electrode under different conditions was studied by the constant current discharge method. The discharge efficiency of K₂Sr(FeO₄)₂ electrode is higher than that of K₂FeO₄ electrode at the same discharge condition. The electrochemical characteristics of K₂Sr(FeO₄)₂ electrode were also investigated by means of electrochemical impedance spectroscopy (EIS).     

A critical study of the application of ultraviolet spectroscopy to the self-association of adenine,adenosine and 5′-AMP in aqueous solution

UV spectra of adenine, adenosine and 5′-AMP in aqueous solution have been measured over the concentration range 1 × 10⁻⁶−5 × 10⁻² M. The apparent molar absorptivity of these compounds changes upon concentration, showing two hypochromic effects at c < 5 × 10⁻³ M and c &>; 5 × 10⁻³ M, respectively, which may be explained in terms of self-association.A method for calculating self-association constants from these experimental data is developed, based on an association model in which the first hypochromic effect is interpreted in terms of formation of dimers, with an equilibrium constant K₂, and the second effect is interpreted in terms of formation of polymers, with an equilibrium constant K_n. The value of K₂ is of the order of magnitude of 10⁴ for the three compounds. The value of K_n is dependent on the model chosen for the analysis of the second effect, having an order of magnitude of 10².The features of the self-association model are discussed, as well as the method for calculating self-association parameters from experimental data.     

Evaluation of potassium ferrate(VI) cathode material coated with 2,3-Naphthalocyanine for alkaline super iron battery

The stability of potassium ferrate(VI) (K₂FeO₄) electrodes was dramatically improved by using 2,3-Naphthalocyanine (C₄₈H₂₆N₈) as coating. The electrode material with the coating was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). K₂FeO₄ electrodes coated with 2,3-Naphthalocyanine provided a superior capacity and stability to uncoated K₂FeO₄ electrodes. Cathodic charge capacity of K₂FeO₄ coated with 2,3-Naphthalocyanine is 42% higher than that of K₂FeO₄ uncoated when discharged at rate of 0.25 C to a cutoff of 0.8 V after storing in the 10 mol/L KOH solution for 3 h.     

Das erste Oxoferrat(I): Zur Konstitution von K3[FeO2] und K3[NiO2]

The First Oxoferrate(I): On the Constitution of K₃[FeO₂] and K₃[NiO₂] Garnet-red single crystals of K₃[FeO₂] were obtained for the first time by heating intimate mixtures of K₆[CdO₄] and CdO (molar ratio 1:1.16) in closed Fe-cylinders at 450°C during 40 d. The same way of preparation via “reaction with the cylinder surface” was applied to prepare similarly coloured single crystals of K₃[NiO₂] (K₆CdO₄ in closed Ni-cylinders at 500°C during 49 d). The structure determination by four circle diffractometer data (MoKα , K₃[FeO₂]: 731 out of 731 I_o(hkl), R = 5.76%, R_w = 5.33%, K₃[NiO₂]: 755 out of 755 I_o(hkl), R = 8.70%, R_w = 4.25%) confirms the space groups P 4₁2₁2 and P 4₃2₁2, respectively. K₃[FeO₂]: a = 604.2(2) pm, c = 1 402.7(3) pm, Z = 4 K₃[NiO₂]: a = 603.6(1) pm, c = 1 405.2(2) pm, Z = 4. (powder data, standard deviations in parentheses) Essential feature of the structure are the dumb-bell-like anions [O? M? O]^3? (M = Fe, Ni). Their arrangement corresponds to a stuffed derivative of the KrF₂-type. Magnetic properties of K₃[FeO₂] were determined and cover the monovalence of Fe. MAPLE-calculations reveal the strong coincidence of monovalent VIIIb-cations.     

Crystal structures of M2FeO4 (M = K,Rb, Cs)

The crystal structure of K₂FeO₄, which is isomorphous with β-K₂SO₄, K₂MnO₄ and K₂CrO₄, has been determined in detail. In addition, Rb₂FeO₄ and Cs₂FeO₄ are shown to be of the same structural type. Crystals of K₂FeO₄ are orthorhombic, space group Pnma, a = 7.694(5), b = 5.858(7), c = 10.335(7) with Z = 4. The integrated intensities of 1174 independent reflections were measured with an automated diffractometer and refined to a weighted least-squares residue of 0.046. The average tetrahedral [FeO] bond length, corrected for libration effects, is 1.656(6) Å which is equal within experimental error to values observed for [CrO] and [MnO] tetrahedral bonds.     

Bridge‐Splitting Reactions of Platinum(II) Complexes with Parametalated Pyridine Spacer Groups: A Kinetic and Mechanistic Study

Substitution reactions of three dinuclear Pt(II) complexes connected by a pyridine‐bridging ligand of variable length, namely [ cis‐{PtOH₂(NH₃)₂}₂–μ–L]⁴⁺, where L = 4,4′‐bis(pyridine)sulfide ( Pt1 ), 4,4′‐bis(pyridine)disulfide ( Pt2 ), and 1,2‐bis(4‐pyridyl)ethane ( Pt3 ) with S‐donor nucleophiles (thiourea, 1,3‐dimethyl‐2‐thiourea, and 1,1,3,3‐tetramethyl‐2‐thiourea) and anionic nucleophiles (SCN^?, I^?, and Br^?) were investigated. The substitutions were followed under pseudo–first‐order conditions as a function of the nucleophile concentration and temperature, using stopped‐flow and UV–visible spectrophotometric methods. The observed pK_a values were, respectively, Pt1 (pK_a1: 4.86; pK_a2: 5.53), Pt2 (pK_a1: 5.19; pK_a2: 6.42), and Pt3 (pK_a1: 5.04; pK_a2: 5.45). The second‐order rate constants for the lability of aqua ligands in the first step decreased in the order Pt2 > Pt3 > Pt1 , whereas for the second step it is Pt1 > Pt2 > Pt3 . The obtained results indicate that introduction of a spacer atom(s) on the structure of the bridging ligand influences the substitution reactivity as well as acidity of the investigated dinuclear Pt(II) complexes. Also nonplanarity of the bridging ligand of Pt1 complex significantly slows down the rate of substitution due to steric hindrance, whereas release of the strain enhances the dissociation of the bridging ligand. The release of the bridging ligand in the second step was confirmed by the ¹H NMR of Pt1‐Cl with thiourea in DMF‐d₇. The temperature dependence of the second–order rate constants and the negative values of entropies of activation (ΔS^#) support an associative mode of the substitution mechanism.     

Charge-discharge behavior of K2FeO4 electrodes in concentrated KOH solutions

The charge-discharge behavior of the K₂FeO₄ electrodes with different current collectors is investigated by various electrochemical techniques. Due to higher electrochemical stability of platinum, the K₂FeO₄ electrode using platinum lattice as current collector displays better primary discharge performance than those with silver lattice and nickel foam as current collectors. The galvanostatic charge-discharge experiments indicate that the K₂FeO₄ electrodes have low electrochemical reversibility, which may result from their relatively lower oxygen evolution potentials or the effects of the oxidation/reduction of current collectors. The experimental results of intermittent discharge, cycle voltammetry, and XRD show that the discharge reaction of the K₂FeO₄ electrode may consist of two steps. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 4, pp. 355–360. The text was submitted by the authors in English.     

Oxidation of dimethylsulphoxide by sodium m-bromobenzene- sulphonamide: A kinetic and mechanistic study

The kinetics of oxidation of dimethylsulphoxide (DMSO) by sodium N-bromobenzenesulphonamide or bromamine-B (BAB) has been studied in HClO₄, HCl and NaOH media, at 35°C, with OsO₄ as a catalyst in the latter medium. In acid medium, the rate shows a first order dependence on [BAB] and second order in [H⁺], but Is Independent of substrate concentration. Alkali retards the reaction (Inverse first order) and the rate is independent of oxidant concentration, but shows fractional order in [DMSO] and depends on (0sO4]². The solvent isotope effect was studied by using D₂O. Activation parameters have also been determined. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics.     

Kombination von Ionenaustausch und Gefriertrocknung als Syntheseweg zu neuen Oxoferraten(VI) M2FeO4 mit M = Li,Na, N(CH3)4, N(CH3)3Bzl,N(CH3)3Ph

Combination of Ion Exchange and Freeze Drying as a Synthetic Route to New Oxoferrates(VI) M₂FeO₄ with M = Li, Na, N(CH₃)₄, N(CH₃)₃Bzl, N(CH₃)₃Ph For the first time Oxoferrates(VI) M₂FeO₄ with M = Li, Na, N(CH₃)₄, N(CH₃)₃Bzl and N(CH₃)₃Ph have been prepared by cation exchange reaction on K₂FeO₄ and freeze drying of the resulting aqueous solutions. Li₂FeO₄ crystallizes as a monohydrate and decomposes at –10 ± 3 °C. Na₂FeO₄ crystallizes orthorhombically (Cmcm, a = 5.675(3) Å, b = 9.349(4) Å, c = 7.160(2) Å) and is isostructural to Na₂CrO₄. [N(CH₃)₄]₂FeO₄ crystallizes tetragonally (P4/nbm, a = 11.010(3) Å, c = 10.902(4) Å) and is isostructural to the room temperature modification of [N(CH₃)₄]₂SO₄. Infrared spectra of the alkylammonium ferrates(VI) show a decreasing influence of lattice forces on the vibrations of the FeO₄^2– ions with increasing cation size. Magnetic measurements show the expected paramagnetism for a d² ion.     

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from mono(aminocarboxylato)iron(III) complexes

Summary The kinetics and mechanism of the system: [FeL(OH)]^2–n + 5 CN^– [Fe(CN)₅(OH)]^3– + L^n–, where L=DTPA or HEDTA, have been investigated at pH= 10.5±0.2, I=0.25 M and t=25±0.1 C.As in the reaction of [FeEDTA(OH)]^2–, the formation of [Fe(CN)₅(OH)]^3– through the formation of mixed ligand complex intermediates of the type [FeL(OH)(CN)_x]^2–n–x, is proposed. The reactions were found to consist of three observable stages. The first involves the formation of [Fe(CN)₅(OH)]^3–, the second is the conversion of [Fe(CN)₅(OH)]^3– into [Fe(CN)₆]^3– and the third is the reduction of [Fe(CN)₆]^3– to [Fe(CN)₆]^4– by oxidation of L^n– The first reaction exhibits a variable order dependence on the concentration of cyanide, ranging from one at high cyanide concentration to three at low concentration. The transition between [FeL(OH)]^2–n and [Fe(CN)₅(OH)]^3– is kinetically controlled by the presence of four cyanide ions around the central iron atom in the rate determining step. The second reaction shows first order dependence on the concentration of [Fe(CN)₅(OH)]^3– as well as on cyanide, while the third reaction follows overall second order kinetics; first order each in [Fe(CN)₆]^3– and L^n–, released in the reaction. The reaction rate is highly dependent on hydroxide ion concentration.The reverse reaction between [Fe(CN)₅(OH)]^3– and L^n– showed an inverse first order dependence on cyanide concentration along with first order dependence each on [Fe(CN)_5– (OH)]^3– and L^n–. A five step mechanism is proposed for the first stage of the above two systems.     

Ca2+‐Induced Oxygen Generation by FeO42− at pH 9–10

Although FeO₄^2? (ferrate(IV)) is a very strong oxidant that readily oxidizes water in acidic medium, at pH 9–10 it is relatively stable (<2 % decomposition after 1 h at 298 K). However, FeO₄^2? is readily activated by Ca²⁺ at pH 9–10 to generate O₂. The reaction has the following rate law: d[O₂]/dt=k_Ca[Ca²⁺][FeO₄^2?]². ¹⁸O‐labeling experiments show that both O atoms in O₂ come from FeO₄^2?. These results together with DFT calculations suggest that the function of Ca²⁺ is to facilitate O–O coupling between two FeO₄^2‐ions by bridging them together. Similar activating effects are also observed with Mg²⁺ and Sr²⁺.     

Reaction of copper(I) chloride pyridine complexes with dioxygen. A kinetic study

Summary Copper(I) complexes [CuClL]₂ (L=Py, 4-PhPy, 4-MePy, 4-Me₂NPy, and 4-PhCOPy) react with dioxygen in dichloromethane according to the rate law: r=K_D ^1/2 k₂ [CuClL]₂ ^1/2[O₂] where KD is the dissociation constant of the equilibrium [CuClL]₂ 2 CuCIL and k₂ the second order rate constant of the reaction of the latter with dioxygen.The K_D values were determined by molecular weight measurements in dichloromethane and a correlation has been developed between the experimental rate constants obtained and the acid dissociation constants (pK_a) for the ligands. The reaction fits a Hammett linear free energy relationship and the rate-determining step is attributed to the first electron transfer to the dioxygen molecule from the mononuclear copper(I) complex, which is influenced by changes in the electron density on the copper.     

Association of sodium dodecyl sulfate in aqueous solutions according to chemical shifts in 1H NMR spectra

Proton chemical shifts of different atomic groups in sodium dodecyl sulfate (SDS) have been studied by ¹H NMR spectroscopy as functions of surfactant concentration in aqueous solutions. Three surfactant concentration ranges of the chemical shifts have been revealed. The first range corresponds to the premicellar solutions, the second one is in the vicinity of critical micelle concentration (CMC₁), and the third range corresponds to high surfactant concentrations, at which intermicellar interactions play a significant role. The parameters of SDS association (CMC₁ and CMC₂) determined based on the concentration dependences of the chemical shifts are in satisfactory agreement with the data available from the literature. The concept of critical dimerization concentration (CDC) has been introduced for the first concentration range. The values of CDC and dimerization constant K ₂ (210 × 60 dm³/mol) have been estimated within the framework of the two-state model.     

Insoluble Fe(VI) compounds: effects on the super-iron battery

Cathodes composed of Fe(VI) salts are capable of three-electron reduction, and are useful for energetic super-iron batteries. This study investigates the solubility of BaFeO₄ and K₂FeO₄ Fe(VI) salts. Electrolytes are determined in which Fe(VI) has a low aqueous or non-aqueous solubility, or is insoluble. Insoluble Fe(VI) salts have the duel benefits of preventing Fe(VI) solution-phase (i) decomposition and (ii) diffusion to the anode; thereby preventing super-iron battery self-discharge. BaFeO₄ is insoluble in water, and has a solubility of less than 2×10⁻⁴ M in 5 M KOH containing Ba(OH)₂. A BaFeO₄ super-iron battery has a high discharge efficiency when containing an electrolyte of either 12 M KOH, or 6 M KOH saturated in Ba(OH)₂. Fe(VI) cathodes in non-aqueous media may be useful in providing a high-capacity Li or Li-ion super-iron battery. We illustrate that Fe(VI) salts are insoluble and chemically unreactive with a range of organic electrolytes, and can be discharged as cathodes in non-aqueous electrolytes. In acetonitrile containing 1 M LiClO₄, the discharge of an Fe(VI) cathode is demonstrated to a capacity over 394 mAh g⁻¹ K₂FeO₄.     

Step Complex Formation in the Dichloro(5,10,15,20-tetraphenylporphinate)hafnium(IV)—Pyridine—Toluene System

The thermodynamic characteristics and kinetics of step reactions between dichloro(5,10,15,20-tetraphenylporphinate)hafnium(IV) (Cl)₂HfTPP and a “small” organic base, pyridine (Py), in toluene were studied. The coordination of the Py molecule (K ₁ = 1.50 × 10⁴ l/mol) was determined. The slow irreversible displacement of Cl^? in (Cl)₂(Py)HfTPP into the second coordination sphere (k ₁ = 9.74 × 10si?4 s^?1), the substitution of the second Py molecule for Cl^? in (Cl)₂(Py)HfTPP (K ₂ = 14.15 l/mol), subsequent irreversible displacement of the second Cl^? ion into the outer sphere (k ² = 6.05 × 10^?4 s^?1), and the coordination of the third Py molecule as a result of the replacement of Cl^? with the formation of [(Py)₃HfTPP]²⁺ 2Cl^? (K ₃ = 0.23 l/mol) at the first, second, and third stages, respectively, were observed. Prospects for the use of the metalloporphyrin as a receptor of organic N-bases were considered.     

Kinetics and mechanism of the reaction between dimethylformamide and chromium(VI)

The kinetics of oxidation of N,N‐dimethylformamide by chromium(VI) has been studied spectrophotometrically in aqueous perchloric acid media at 20°C. The rate showed a first‐order dependence on both [Cr(VI)] and [DMF], and increased markedly with increasing [H⁺]. The order with respect to [HClO₄] was found to lie between 1 and 2. The rate was found to be independent of ionic strength as well as of any inhibition effect of Mn(II). The formation of superoxochromium(III) ion was detected in an aerated solution of chromium(VI), DMF and HClO₄. The proposed mechanism, involving two reaction pathways, leads to the rate law, rate = K_a1 [HCrO₄⁻] [DMF] (k_I K_a2 [H⁺]²+k_II[H⁺]). The first pathway, with rate constant k_I, involves the formation of chromium(V) and a free radical. The second pathway, with rate constant k_II, involves the formation of Cr(IV), CO₂ and dimethylamine. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 409–415, 1999