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1.
Using 1-ethyl-2-methylimidazolium trifluoroacetate (EMImTfa) as the supporting electrolyte, a couple of well-defined and reversible redox peaks of Myb could be observed at the basal plane graphite (BPG) electrode through direct electron transfer between the protein and the BPG electrode, whose anodic and cathodic peak potentials were at −0.098 V and −0.144 V vs. Ag | AgCl, respectively. Both anodic and cathodic peak currents increased linearly with the potential scan rates. Compared with the supporting electrolyte of phosphate buffer solution, EMImTfa played an important role for the direct electron transfer between Myb and the BPG electrode. Further investigation suggested that Myb was adsorbed tightly on the surface of the BPG electrode in the presence of EMImTfa to form a stable, approximate monolayer Myb film. Myb adsorbed on the BPG electrode surface could retain its biological activity and showed a remarkable electrocatalytic activity for the reduction of H2O2 in an EMImTfa aqueous solution. Based on these, a third-generation biosensor could be constructed to directly detect the concentration of H2O2 in EMImTfa aqueous solution with a limit of detection of 3.24 × 10−8 M. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 3, pp. 363–368. The text was submitted by the authors in English.  相似文献   

2.
Osmotic coefficients of binary mixtures containing an ionic liquid, (1-butyl-3-methylimidazolium tetrafluoroborate, [BMIm]BF4, 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIm]ES, and 1-butyl-3-methylimidazolium methyl sulfate, [BMIm]MS) with water were measured until about 3 molal concentrations using vapor pressure osmometry method (VPO) at temperature ranges 298.15–328.15 K and modeled using different electrolyte excess Gibbs free energy models including electrolyte non-random two liquids (NRTL), modified NRTL (MNRTL), mean spherical approximation NRTL (MSA-NRTL), non random factor (NRF), and extended Wilson models. The results show that osmotic coefficient data increase with increasing temperature. The calculated standard deviations of the studied systems show that the applicability of these models for the correlation of VLE properties of ionic liquid solutions. The average standard deviations for the models have the order σ(?) MNRTL < σ(?) Wilson < σ(?) NRTL < σ(?) MSA-NRTL < σ(?)NRF. The results show MNRTL model is able to reproduce experimental osmotic coefficients of aqueous solution of studied ionic liquids with good precision.  相似文献   

3.
A biodegradable gel polymer electrolyte system based on chitosan/magnesium trifluoromethanesulfonate/1-ethyl-3-methylimidazolium trifluoromethanesulfonate (CA/Mg (Tf)2/EMITf) is developed. The structure, thermal performance, mechanical properties, ionic conductivity, relaxation time, electrochemical stability and ionic transport number of the membranes are analyzed by various techniques. The ion migration mainly depends on the complexation and decomplexation of Mg2+ with amine band (NH2) in chitosan. The 90CA-10Mg (Tf)2 system plasticized with 10% EMITf (relative to the amount of 90CA-10Mg (Tf)2) is identified as the optimum one and the temperature dependence of ionic conductivity obeys the Arrhenius rule. Moreover, the relaxation time of the electrolyte is very short, being just 1.25 × 10−6 s, and its electrochemical stability window is quite wide, being up to 4.15 V. The anodic oxidation and cathodic reduction of Mg at the Mg-electrode/electrolyte interface is facile, and the ionic transference number of this electrolyte is 0.985, indicating that it could be a potential electrolyte candidate for Mg-ion devices.  相似文献   

4.
90Y was separated from 90Sr using an extraction chromatographic resin consisting of 4, 4′(5′)-bis-t-butylcyclohexano-18-crown-6 (DtBuCH18C6), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide (C2mimNTf2), and a polymer (Amberlite XAD-7). Ionic liquid was introduced into the column to improve the separation efficiency. The column showed an excellent performance for the separation of Y from Sr. After the separation, the ratio of 90Sr/90Y was <2.0 × 10?5; the column was recycled for >18 times. This study provides preliminary results on columns to produce 90Y with a high purity in radiopharmaceuticals.  相似文献   

5.
《Electroanalysis》2005,17(19):1734-1739
In the present study anodic oxidation of iridium layer formed thermally on a gold‐sputtered quartz crystal electrode has been investigated by electrochemical quartz crystal microgravimetry (EQCM) in the solutions of 0.5 M H2SO4 and 0.1 M KOH. The emphasis here has been put on the microgravimetric behavior of iridium as a metal, because a few previous EQCM studies reported in literature have been devoted to iridium oxide films (IROFs). The objective pursued here has been to elucidate the nature of the main voltammetric peaks, which occur at different ranges of potential in the solutions investigated. It has been found that anodic oxidation of iridium electrode in 0.5 M H2SO4 and 0.1 M KOH solutions is accompanied by irregular fluctuations of the electrode mass at 0.4 V<E<0.8 V followed by regular increase in mass at 0.8 V<E<1.2 V. The cathodic process initially, at 1.2 V>E>0.9 V, proceeds without any or with slight increase in electrode mass, whereas at E<0.8 V a regular decrease in mass is observed. It has been found that mass to charge ratio characterizing the processes of interest is 2 to 3 g F?1in acidic medium, whereas in the case of alkaline one it is 4 to 6 g F?1. The main pair of peaks seen in the voltammograms of Ir electrode in alkaline medium at E<0.8 V is attributable to redox transition Ir(0)→Ir(III), whereas those observed in the case of acidic medium at E>0.8 V should be related to the redox process Ir(0)→Ir(IV) going via intermediate stage of Ir(III) formation. As a consequence of these redox transitions, the gel‐like surface layer consisting of Ir(III) or Ir(IV) hydrous oxides forms on the electrode surface.  相似文献   

6.
The Randles–Sev?ik relationship has been applied to evaluate atomic hydrogen diffusivity in massive LaNi5 intermetallic compound. The electrode was cathodically hydrogenated in 6 M KOH solution (22 °C), and then voltammetry measurements were carried out at various, very slow potential scan rates (υ?=?0.01–0.1 mV?·?s?1). At potentials more noble than the equilibrium potential of the H2O/H2 system, the anodic peaks were registered as a consequence of oxidation of hydrogen absorbed in cathodic range. The peak potentials linearly increase with the logarithm of the scan rate with a slope of 0.059 V. The slope testifies to a symmetric charge transfer process with symmetry factor α?=?½. The peak currents linearly increase with the square root of the potential scan rate, and the straight line runs through the origin of the coordinate system. The slope of the I a (peak) ?=?f(υ 1/2) straight line is a measure of the atomic hydrogen diffusion coefficient. Assuming the hydrogen concentration in the LaNi5 material after cathodic exposure to be C 0,H?=?0.071 mol?·?cm?3 (63 % of theoretical value), the hydrogen diffusion coefficient equals D H?=?2.0?·?10?9 cm2s?1. Extrapolation of rectilinear segments of potentiodynamic polarization curves with Tafel slopes of 0.12 V and linear polarization dependencies from voltammetry tests allowed the exchange current densities of the H2O/H2 system on the tested material to be determined. The exchange current densities on initially hydrogenated LaNi5 alloy are close to 1 mA?·?cm?2, irrespective of the electrode potential scan rate.  相似文献   

7.
The electrochemical polymerization of methylene green has been carried out using cyclic voltammetry. The electrolytic solution consisted of 4° 10?3 mol/L methylene green, 0.1 mol/L NaNO3 and 1 × 10?2 mol/L sodium tetraborate with pH 11.0. The temperature for polymerization is controlled at 60°C. The scan potential is set between ?0.2 and 1.2 V (vs. Ag/AgCl with saturated KCl solution). There are an anodic peak and a cathodic peak on the cyclic voltammogram of poly (methylene green) at pH≤3.8. Both peak potentials shift towards negative potentials with increasing pH value, and their peak currents decrease with increasing pH value. Poly (methylene green) has a good electrochemical activity and stability in aqueous solutions with pH≤3.8. The UV‐Visible spectrum and FTIR spectrum of poly (methylene green) are different from those of methylene green.  相似文献   

8.
CrIII Phthalocyaninates: Synthesis and Spectroscopical Properties of Di(halo)phthalocyaninato(2 –)chromates(III) [Cr(H2O)2Pc2?]+ reacts in acetone with (nBu4N)X to yield less soluble tetra(n-butyl)ammonium di(halo)phthalocyaninato(2 –)chromate(III), (nBu4N)[Cr(X)2Pc2?] (X = F, Cl, Br, I). In the differential pulse voltammograms the first ring oxidation is observed at 0,80 V, the ring reduction at ?1,48 V and the metal reduction (Cr(III)/Cr(II)) at ?0,80 V (averaged potentials). The last is followed by a partial dissociation of one of the halo ligands. In the UV-VIS-NIR spectra there are three weakly absorbing spin-allowed trip-quarter(TQ) transitions (TQ1 (8,4) < TQ2 (11,5) < TQ3 (20,6); averaged values (av) in 103 cm?1), a (Pc + X)-CrCT transition (31,3; av in 103 cm?1) and the characteristic π-π* transitions of the Pc2? ligand (B (14,5) < Q1 (24,5) < Q2 (29,2) < N (36,0) < L (41,0); av in 103 cm?1). Q1 and (Pc + X)-CrCT depend strongly on the halo ligands. Prominent luminescence spectra are obtained by excitation within the TQ1 region, in which the spin-forbidden trip-sextet transition (8330 (X = F), 7680 (Cl), 7460 (Br) 7450 cm?1 (I)) dominates at low temperatures (T < 50 K). The vibrational spectra are discussed. In coincidence of the excitation lines with TQ3, vs(Cr? X) at 458 (X = F) < 246 (Cl) < 157 (Br) < 107 cm?1 ( I ) is selectively resonance Raman enhanced. vas(Cr? X) is observed in the FIR spectrum at 522 (X = F) < 283/326 (Cl) < 227 (Br) < 205 cm?1 ( I ).  相似文献   

9.
A new kind of secondarily formed peaks was found in cyclic and stripping voltammetry in neutral sulphate, perchlorate and nitrate supporting electrolytes containing some divalent cations and a substance (for example O2), the reduction of which gives as a by-product OH? ions. The hydroxides deposited in the vicinity of the mercury electrode, in the course of a cathodic scan, react during the anodic scan according to the reaction Hg+Me(OH)2=Hg(OH)2+Me2++2e forming a new, separate anodic peak.It was found that silver exerts a catalytic effect on the reduction of NO3? ions on the mercury electrode. In neutral nitrate supporting electrolyte containing Ag+ ions the hydroxides of some cations (Cd2+, Zn2+, Mn2+, Co2+ and Ni2+) were deposited during the cathodic scan or during the preelectrolysis. Afterwards, in the course of the anodic scan, a new peak, of the kind described above, was observed. The same effect was formerly interpreted, for Zn2+ and Cd2+, as evidence for the formation of intermetallic compounds, AgZn and AgCd.  相似文献   

10.
The cyclic voltammetry responses and the redox switching dynamics of poly(3,4-ethylenedioxythiophene) (PEDOT) in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMImTf2N), were investigated. The shape of the cyclic voltammograms showed two anodic and two cathodic peaks. These peak currents varied linearly with the scan rate indicating a thin-layer behaviour. No memory effects were observed during the cyclic voltammetry experiments in this ionic liquid. On the other hand, the redox switching dynamics of PEDOT were studied by means of potential step experiments. The analysis of chronocoulograms in term of RC-circuits indicated that the time dependence of the charge transferred during the potential step showed two time constants. These results were consistent with the postulated structure or morphology of the PEDOT film which contained two types of coexisting zones: a compact and an open structures.  相似文献   

11.
A facile, rapid and ultra‐sensitive method for the determination of vitamin B12 (cyanocobalamin) at the sub‐nanomolar concentration range by using low‐cost, disposable graphite screen‐printed electrodes is described. The method is based on the cathodic preconcentration of square planar vitamin B12s, as occurred due to the electro reduction of Co(III) center in vitamin B12a to Co(I), at ?1.3 V versus Ag/AgCl/3 M KCl for 40 s. Then, an anodic square wave scan was applied and the height of the peak appeared at ca. ?0.73 V versus Ag/AgCl/3 M KCl, due to the oxidation of Co(I) to Co(II) in the adsorbed molecule, was related to the concentration of the vitamin B12 in the sample. EDTA was found to serve as a key‐component of the electrolyte by eliminating the background signal caused by metal cations impurities contained in the electrolyte (0.1 M phosphate buffer in 0.1 M KCl, pH 3). It also blocks trace metals contained in real samples, thus eliminating their interference effect. The method was optimized to various working parameters and under the selected conditions the calibration curve was linear over the range 1×10?10–8×10?9 mol L?1 vitamin B12 (R2=0.994), while the limit of detection for a signal‐to‐noise ratio of 3 (7×10?11 mol L?1 vitamin B12) is the lowest value of any reported in the literature for the electrochemical determination of vitamin B12. The sensors were successfully applied to the determination of vitamin B12 in pharmaceutical products.  相似文献   

12.
Herein the structure of the interfacial layer between the air- and water-stable ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM]FAP) and Au(111) is investigated using in situ scanning tunneling microscopy (STM), distance tunneling spectroscopy (DTS) and cyclic voltammetry (CV) measurements. The in situ STM measurements reveal that structured interfacial layers can be probed in both cathodic and anodic regimes at the IL/Au(111) interface. The structure of these layers is dependent on the applied electrode potential, the number of subsequent STM scans and the scan rate. Furthermore, first DTS results show that the tunneling barrier during the 1st STM scan does not seem to change significantly in the cathodic potential regime between the ocp (-0.2 V) and -2.0 V.  相似文献   

13.
The anodic oxidation of a dropping copper amalgam electrode in presence of dilute solutions of glycine in 0.50 M NaClO4 has been studied. An anodic wave at ?0.28V (SCE) is observed, yielded by diffusion of glycinate anion in the solution towards the electrode surface. The wave-heights increase with the glycinate concentration (function of glycine concentration and pH value) until the anodic oxidation is controlled by the metal diffusion into mercury. The effect of pH is interpreted by attributing it to the depolarizer effects at glycinate anion even though the zwitterion is present in much larger concentrations. The applicability of anodic oxidation of a dropping copper amalgam electrode in the determination of glycine in the range of concentrations 10?4–10?2M with a rigorous control of pH (8.0<pH<10.5) is shown. The standard deviation of the proposed method is 4.1% and the minimum concentration determinable is in the 1×10?4M range.  相似文献   

14.
The electrode behavior and microstructure of freshly prepared (La0.8Sr0.2)0.9MnO3 (LSM) electrodes were investigated under various polarization conditions. The original, large agglomerates in freshly prepared LSM electrodes were broken down into sphere-shaped grains when exposed to cathodic or anodic current passage of 200 mA cm–2 at 800 °C in air for 3 h. Microstructural changes under cathodic polarization could be related to the pronounced diffusion and migration of oxygen vacancies and Mn ions on the LSM surface and lattice expansion, while lattice shrinkage under oxidation conditions most likely contributes to the structural changes under anodic polarization. Such morphological changes were irreversible and were found to be beneficial to the performance of freshly prepared LSM electrodes. Freshly prepared LSM electrodes behaved very differently with respect to the cathodic and anodic current passage treatment.  相似文献   

15.
The electrochemistry of a single-component redox flow battery employing vanadium(III) acetylacetonate in acetonitrile and tetraethylammonium tetrafluoroborate has been investigated. The electrode kinetics of the anodic and cathodic reactions were studied using cyclic voltammetry. The V(II)/V(III) and V(III)/V(IV) couples were quasi-reversible and together yielded a cell potential of 2.2 V. The diffusion coefficient for vanadium acetylacetonate was estimated to be in the range of 1.8–2.9 × 10?6 cm2 s?1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell, and coulombic efficiencies near 50% were achieved.  相似文献   

16.
7Li-NMR spectroscopy was used to study the complexation of Li+ ion with 12C4, 15C5, C222, C221, C211 in acetonitrile (AN) and its 50% (wt/wt) mixtures with two new room temperature ionic liquids, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMim PF6) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMim BF4) at 298 K. Excluding the cases of Li+-C211 in all solvents and Li+-C221 in AN and 50% (wt/wt) AN-EMim PF6, in other cases, the exchange between free and 1:1 complexed Li+ was fast on the NMR time scale and only a single population average 7Li signal was observed. Formation constants of the resulting 1:1 complexes were evaluated by computer fitting of the chemical shift-mole ratio data and integration of two 7Li signals. All complexes in EMim PF6 were found to be more stable than those in EMim BF4. 7Li-NMR line-shape analysis was used to determine the kinetic parameters and the mechanism for the chemical exchange of Li+ between the free and 1:1 complex with C221 in 50% (wt/wt) AN-EMim PF6 mixtures solution. By comparing our study with the previous one, it is derived that, increasing the percentage of ion liquid in acetonitrile, changes the mechanism and decrease the exchange rate constant of Li+ ion between free and complex sites.  相似文献   

17.
The volumetric properties of seven {water + ionic liquid} binary mixtures have been studied as a function of temperature from (293 to 343) K. The phase behaviour of the systems was first investigated using a nephelometric method and excess molar volumes were calculated from densities measured using an Anton Paar densimeter and fitted using a Redlich–Kister type equation. Two ionic liquids fully miscible with water (1-butyl-3-methylimidazolium tetrafluoroborate ([C1C4Im][BF4]) and 1-ethyl-3-methylimidazolium ethylsulfate ([C1C2Im][EtSO4])) and five ionic liquids only partially miscible with water (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C1C2Im][NTf2]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C1C4Im][NTf2]), 1-butyl-3-methylimidazolium hexafluorophosphate ([C1C4Im][PF6]), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C1C4Pyrro][NTf2]), and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N4111][NTf2])) were chosen. Small excess volumes (less than 0.5 cm3 · mol?1 at 298 K) are obtained compared with the molar volumes of the pure components (less than 0.3% of the molar volume of the pure ionic liquid). For all the considered systems, except for {[C1C2Im][EtSO4] + water}, positive excess molar volumes were calculated. Finally, an increase of the non-ideality character is observed for all the systems as temperature increases.  相似文献   

18.
Pulse polarography and cyclic voltammetry are employed in studies of the electrochemical behaviour of 5-ethyl-5'-(l-methylbutyl)-2-thiobarbituric acid (I), l-methyl-5-ethyl-5'-(l-methylpropyl)-2-thiobarbituric acid (II) and l,3-dimethyl-5-ethyl-5'-p-chlorophenyl)-2-thiobarbituric acid (III) in the pH range 4–12. All three compounds show anodic and cathodic waves or peaks in this pH range. Compounds (I) and (II) are oxidized at mercury indicator electrodes to produce mercury salts which can adsorb thereon and are thus amenable to cathodic stripping voltammetric analysis (c.s.v.) down to concentrations of the order of 10-6 M, which is superior to the sensitivities obtained by differential pulse polarography (d.p.p.) based on a reduction peak. Compound (III) oxidizes to produce sulphur which is subsequently plated as HgS. Again the sensitivity of the c.s.v. method is of the order of lO-6 M and analytically superior to d.p.p. The optimum pH for the three determinations is 8. The determination of (II) in the presence of its oxygenated analogue and metabolite, phemitone, and the effect of chloride ions are reported.  相似文献   

19.
《Electroanalysis》2003,15(19):1541-1553
Theoretical expressions for differential pulse polarography (DPP) for a reversible electron transfer coupled with an irreversible follow‐up first‐order chemical reaction (ErCi) is derived approximately. The peaks as given by the current expressions are analyzed in terms of several parameters such as a ratio of anodic‐to‐cathodic peak‐currents (ipa/ipc), a separation of peak‐potentials (Epc?Epa), and a ratio of anodic‐to‐cathodic half‐peak‐widths (W1/2a/W1/2c) in order to characterize the ErCi process and distinguish it from other types of electrode processes. The anodic peak is found to be more susceptible to the post kinetics than the cathodic peak. The new parameter of W1/2a/W1/2c ratio is much more sensitive to the post kinetics than the peak separation (Epc?Epa). The peak current ratio (ipa/ipc) and the peak‐width ratio (W1/2a/W1/2c) have comparable sensitivities to the kinetics. Hence, W1/2a/W1/2c ratio is a better diagnostic parameters than (Epc?Epa) which has a poor sensitivity. This phenomenon is different from cyclic voltammetry (CV) in which Epc?Epa is as sensitive as ipa/ipc. The new criteria for EC with DPV is tested and successfully applied to several Co(III) complex systems, including coenzyme B12. The homogeneous rate constant (k) for the follow‐up step is estimated from the measurements of the experimental values of the parameters. The present treatment is valid quantitatively at lower values of k, yielding relatively larger errors for higher k values (k>10 s?1).  相似文献   

20.
A simple adsorptive cathodic stripping voltammetry method has been developed for antimony (III and V) speciation using 4‐(2‐thiazolylazo) – resorcinol (TAR). The methodology involves controlled preconcentration at pH 5, during which antimony(III) – TAR complex is adsorbed onto a hanging mercury drop electrode followed by measuring the cathodic peak current (Ip,c) at ?0.39 V versus Ag/AgCl electrode. The plot of Ip,c versus antimony(III) concentration was linear in the range 1.35×10?9–9.53×10?8 mol L?1.The LOD and LOQ for Sb(III) were found 4.06×10?10 and 1.35×10?9 mol L?1, respectively. Antimony(V) species after reduction to antimony(III) with Na2SO3 were also determined. Analysis of antimony in environment water samples was applied satisfactorily.  相似文献   

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