Diffusion Coefficient Of Ferrocene Research Articles

Liquid- and Gas-Phase Diffusion of Ferrocene in Thin Films of Metal-Organic Frameworks

The mass transfer of the guest molecules in nanoporous host materials, in particular in metal-organic frameworks (MOFs), is among the crucial features of their applications. By using thin surface-mounted MOF films in combination with a quartz crystal microbalance (QCM), the diffusion of ferrocene vapor and of ethanolic and hexanic ferrocene solution in HKUST-1 was investigated. For the first time, liquid- and gas-phase diffusion in MOFs was compared directly in the identical sample. The diffusion coefficients are in the same order of magnitude (~10−16 m2·s−1), whereas the diffusion coefficient of ferrocene in the empty framework is roughly 3-times smaller than in the MOF which is filled with ethanol or n-hexane.

Fabrication of disposable gold macrodisc and platinum microband electrodes for use in room-temperature ionic liquids

We report a simple and facile methodology for constructing gold macrodisc and platinum microband electrodes for use in room temperature ionic liquids (RTILs). To validate the use of gold macrodisc electrodes, the voltammetry of Ru(NH3)6(3+) was studied in 0.1 M aqueous KCl. The Randles-Ševčík equation was used to calculate the diffusion coefficient, giving excellent agreement with literature values, suggesting that the gold macrodisc electrode is capable of performing quantitative electroanalysis in aqueous media. Gold macrodisc electrodes were used to study oxidation of ferrocene in N-butyl-N-methylpyrrolidinium bis(fluoromethylsulfonyl)imide ([C4mpyrr][NTf2]) using cyclic voltammetry. The diffusion coefficient of ferrocene, (2.43 ± 0.07) × 10(-11) m(2) s(-1), was obtained. This value is very close to the literature value, indicating good performance of gold electrodes in RTILs. Platinum microband electrodes were tested in 1-propyl-3-methylimidazolium bis-trifluoromethylsulfonylimide ([Pmim][NTf2]) containing decamethylferrocene. Diffusion coefficients and electron transfer rates were obtained by fitting relevant simulations to the experimental data. For comparison, analogous experiments and analyses were performed on a commercial platinum microdisc, where the results obtained from both microdisc and microband agree well, further suggesting that the platinum microband electrode is suitable to be used in RTILs. Finally, gold macrodisc and platinum microband electrodes were used for oxygen detection. Gold macrodisc electrodes were used to find the peak currents of oxygen at each volume percentage analysed. Platinum microband electrodes showed steady-state currents of different volumes of oxygen. These two results are compared which resulted in excellent agreement. This is further confirmed by studying Henry's law constants obtained from both electrodes. The excellent behaviour of these two fabricated electrodes suggests that they are suitable for quantitative measurements and practicable for real world applications.

Electrochemical and physicochemical properties of cyclic amine-based Brønsted acidic ionic liquids

Several low-cost ionic liquids (ILs) containing pyrrolidinium, piperidinium, or azepanium units as cations, and formate, trifluoroacetate, or hydrogen sulfate groups as anions, are synthesized. The electrochemical and physicochemical properties, such as viscosity, density, conductivity, electrochemical window of the ILs, and the diffusion coefficient of ferrocene in the ILs are studied. All ILs studied here are liquid at room temperature with a high ionic conductivity (up to 30.7 mS cm −1) at room temperature. Hydrogen sulfate-based ILs exhibits a larger electrochemical window (3.98–3.99 V) than formate- and trifluoroacetate-based ILs (3.22–3.29 V). The results of this study can be used to choose the proper combination of cations and anions for the desired applications.

The electrochemical redox processes in methacrylate-based polymer electrolytes II. – Study on microelectrodes

The electrochemical behaviour of ferrocene was studied in different gel polymer electrolytes based on methyl, ethyl and 2-ethoxyethyl methacrylate and compared to the liquid aprotic solution (propylene carbonate). Voltammetric and chronoamperometric measurements on microelectrodes were conducted in order to describe the qualitative as well as quantitative behaviour of ferrocene in different conditions. Heterogeneous electron-transfer rate constants and diffusion coefficients of ferrocene in polymer electrolytes were estimated to be 1.1–7.8 × 10 −3 cm s −1 and 4–13 × 10 −8 cm 2 s −1 depending on the electrolyte composition. The influence of the polymer polarity, ferrocene concentration and level of polymer cross-linkage on the kinetics of ferrocene oxidation and its transport was discussed. The electrolytes with poly(2-ethoxyethyl methacrylate) exhibit the highest ionic conductivity (2–4 × 10 −4 S cm −1) as well as diffusion coefficient of ferrocene (1.3 × 10 −7 cm 2 s −1) in their structure.

A New Series of Ionic Liquids Based on the Difluorophosphate Anion

A new series of ionic liquids based on the difluorophosphate anion (PO(2)F(2)(-)) has been synthesized by metathesis from the corresponding chloride. Incorporation of the PO(2)F(2)(-) anion with an N-heterocyclic cation (1-ethyl-3-methylimidazolium (EMIm(+)), 1-butyl-3-methylimidazolium, 1-butyl-1-methylpyrrolidinium, or 1-butyl-1-methylpiperidinium (BMPip(+))) produces ionic liquids with low melting points, including some room-temperature ionic liquids. The vibrational frequencies of PO(2)F(2)(-) in the obtained ionic liquids were assigned with the aid of quantum mechanical calculations. The ionic conductivities of the ionic liquids are comparable to those of the corresponding tetrafluoroborate-based ionic liquids (e.g., 12 mS cm(-1) for 1-ethyl-3-methylimidazolium difluorophosphate, [EMIm][PO(2)F(2)]). The stability of ionic liquids against hydrolysis is significantly improved by replacing the hexafluorophosphate anion with the difluorophosphate anion, which suppresses the subsequent liberation of hydrogen fluoride. According to the solvatochromic method, the donor ability of ionic liquids based on PO(2)F(2)(-) is stronger than those of ionic liquids based on BF(4)(-), PF(6)(-), and N(SO(2)CF(3))(2)(-), due to the large negative charge on the oxygen atoms in PO(2)F(2)(-). The electrochemical window of [EMIm][PO(2)F(2)] is around 4.2 V, and the diffusion coefficients of ferrocene in [EMIm][PO(2)F(2)] are 2.83 x 10(-7) cm(2) s(-1) by cyclic voltammetry and 3.03 x 10(-7) cm(2) s(-1) by chronoamperometry, both of which are comparable to those in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF(4)]). The X-ray structure of [BMPip][PO(2)F(2)] contains two cations and two anions in the asymmetric unit, where one of the two cations is disordered into two positions (chair configurations) even at -173 degrees C. The oxygen atoms in PO(2)F(2)(-) have closer contacts to the hydrogen atoms in BMPip(+) than the fluorine atoms, indicative of their stronger basicity.

Microstructure and structural transition in coconut oil microemulsion using semidifferential electroanalysis

The microemulsification in coconut oil/octadecyltrimethylammonium bromide/iso-pentanol/water system is investigated. The effect of iso-pentanol concentrations on the size of single-phase microemulsion region is discussed. It is found that the maximum microemulsion domain is obtained when cosurfactant (iso-pentanol)-to-surfactant (octadecyltrimethylammonium bromide) mass ratio is 1.5. The diffusion coefficients of ferrocene (electroactive probe) in microemulsion microenvironment are measured by semidifferential electroanalysis. The microstructure and structural transition from water-in-oil to oil-in-water microemulsions through a bicontinuous structure is examined. The results are found to be in agreement with that of conductivity measurements.

Diffusion coefficient of ferrocene in 1-butyl-3-methylimidazolium tetrafluoroborate – concentration dependence and solvent purity

The ionic liquid l-butyl-3-methylimidazolium tetrafluoroborate is used as electrolyte in the electrochemical determination of the diffusion coefficient of ferrocene as a function of concentration by cyclic voltammetry and chronoamperometry. An improved synthesis of the room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate is described, which yields a product of high purity suitable for electrochemical purposes. A qualitative color test is discussed which allows the simple detection of silver ion contaminations. The diffusion coefficient of ferrocene appears to be concentration dependent in the solvent chosen.

Determination of Viscosity, Ionic Conductivity, and Diffusion Coefficients in Some Binary Systems: Ionic Liquids + Molecular Solvents

Experimental data for viscosities, diffusion coefficients of ferrocene, and conductivities were obtained for three ionic liquid mixtures: 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (bmpyNTf2), and N-methyl-N-hexylpyrrolidinium bis(trifluoromethylsulfonyl)imide (hmpyNTf2) + dimethylformamide (DMF) or + 3-picoline as cosolvents, in the range of temperature T = (295.2 to 325.2) K. At a given temperature, the viscosity decreases exponentially with the mole fraction of the added cosolvent, and the variation of the diffusion coefficient agrees with the Stokes−Einstein law. Concerning the conductivity, addition of the polar solvent dimethylformamide produces an increase much greater than the addition of 3-picoline. The viscosity, diffusion coefficient, and conductivity follow the Arrhenius model in the explored temperature range. Consequently, moderate heating and addition of a cosolvent are two good means for obtaining conditions well adapted to electrosynthetic applications in ionic liquids.

The electrochemical redox reactions in silica sol–gel glass monoliths and films with embedded organic electrolyte

The electrochemical redox reaction of ferrocene and Co(II)tris(bipyridine) has been studied in silica sol–gel glass with embedded organic electrolyte. This material has been prepared by acid catalysed hydrolysis of the tetraalkylorthosilicate sol mixed with salt solution in organic polar solvent. Tetramethyl- or tetraethylorthosilicate was used as precursor. Lithium or tetraalkylammonium perchlorate solution in propylene carbonate or sulpholane was used as modifier. Sol–gel glass has been prepared in the form of a monolith or film. The electrochemical behaviour of the redox probe was studied by cyclic voltammetry and chronoamperometry on ultramicroelectrodes in the absence of macroscopic liquid phase. The accessible potential window in solid material is more narrow than in analogous liquid organic electrolyte. The shape of the cyclic voltammograms corresponding to the electrochemical redox reaction in sol–gel monolith is similar to that obtained in liquid electrolyte and does not depend on gel ageing. On the other hand, the current substantially decreases during the first few days after gelation, and later becomes weakly dependent on ageing. The precursor, salt, solvent and redox probe affect the motion rate of the redox probe. The latter is five times slower in electrolyte made of tetraethylorthosilicate in comparison to that obtained using the tetramethyl derivative. The diffusion coefficient of ferrocene is larger in the gel obtained in the presence of the large tetraalkylammonium cations. The electro-oxidation of ferrocene was also studied in films made from tetraethylorthosilicate, cast on the surface of the electrode assembly. The magnitude of the current is similar to that obtained in a glass monolith made of the same material.

Diffusion Coefficients of Ferrocene and Ferricinium Ion in Tetraethylammonium Perchlorate Acetonitrile Solutions, as Determined by Chronoamperometry

Diffusion Coefficients of Ferrocene and Ferricinium Ion in Tetraethylammonium Perchlorate Acetonitrile Solutions, as Determined by Chronoamperometry

Electrochemical probing of the sol–gel–xerogel evolution

Chronoamperometry has been performed on ferrocene embedded in silica and zirconia gels. The diffusion coefficient of ferrocene was measured along the sol–gel–xerogel transformations. Such electrochemical measurements are a sensitive probe of the structural and textural changes occurring in the sol–gel process.

Electrochemistry in near-critical and supercritical fluids: Part 8. Methyl viologen, decamethylferrocene, Os(bpy) 32+ and ferrocene in acetonitrile and the effect of pressure on diffusion coefficients under supercritical conditions

The cyclic voltammetry (CV) of methyl viologen (MV 2+), decamethylferrocene (DMFc), Os(bpy) 3 2+ (bpy = 2,2'-bipyridine) and ferrocene (Fc) was studied at high temperatures and pressures in a small cell (7.5 ml) where the pressure and temperature could be varied independently. While the CV of MV 2+ and Os(bpy) 3 3+ remained well-behaved with reversible or quasi-reversible waves only into the near-critical region (up to ca. 230° C), Fc and DMFc showed well-defined behavior under supercritical conditions. The diffusion coefficient of ferrocene was measured at a supercritical temperature (280° C) as a function of pressure, and the experimental results were correlated to values calculated by the Stokes-Einstein relation.