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1.
The kinetics of formation of copper adlayer, three-dimensional nucleation, and the deposit growth on polycrystalline platinum and glassy carbon in the 0.5 M H2SO4 + 10 mM CuSO4 + (0–2) M acetonitrile (AcN) solutions at the cathodic overvoltages is studied using the methods of cyclic voltammetry and potentiostatic current transients on a ring-disc electrode. At [AcN] = 2 M, the process of formation of copper adatoms on platinum is significantly retarded. In the solutions with high contents of AcN, the processes of Cu+ ion production, the formation of their complexes with acetonitrile, hydrogen evolution, copper nucleation, and the deposit growth proceed in parallel. The contribution of any process to the overall current depends on the amount of adsorbed AcN at the surface of substrate and copper deposit and on the electrode potential. At [AcN] = 2 M, an increase in the cathodic overvoltage to 0.32 V leads to an abnormal increase in the current of Cu+ ion production on platinum, which is caused by insufficiently rapid formation of copper atoms in the reduction of Cu+(AcN) x complexes.  相似文献   

2.
The recrystallization of ultradisperse copper chemically deposited onto a sulfo cation exchanger matrix was studied by the potentiometric method. The stationary value of the electrode potential of the copper-sulfo cation exchanger composite was established during a long period of time, which depended on the ionic form of the composite (H+, Cu2+, or Na+), solution composition (CuSO4, H2SO4, and Na2SO4), and solution concentration. Recrystallization was favored by copper(II) counterions, which entered the composite as a result of ion exchange, nonexchange absorption of copper sulfate, or preliminary composite transformation into the Cu2+ form. In the quasi-equilibrium state, the concentration of copper(II) counterions was maintained at a high level by the Donnan interfacial potential. At all the copper(II) sulfate concentrations used, the potential of the Cu2+/Cu ion—metal pair in the ion-exchange matrix remained at virtually the same level, which was indicative of the stable state of copper particles. In the absence of an external source of copper ions, recrystallization was significantly hindered; therefore, the potential exhibited only a slight drift. Copper ions formed in the solution of small crystals were localized in the vicinity of ionogenic matrix centers, which decreased the mobility of these particles as counterions; therefore, the dispersity of particles remained unchanged.  相似文献   

3.
LiMg0.5Mn1.5O4的合成及对Li+的离子交换选择性   总被引:8,自引:0,他引:8  
锂及其化合物在航空航天、化工、医药、空调、高能电池和热核反应等方面都有广泛应用,对锂及其化合物的需求与日俱增。我国液体锂资源非常丰富,开发利用其中的锂资源具有重要意义。从盐湖水、地下卤水、盐田母液、油气田水等咸水资源中提取锂的方法有碳酸盐沉淀法、离子交换法、萃取法等。离子  相似文献   

4.
Electrochemical reduction of molecular oxygen was studied on a [dispersed copper]-[macroporous KU-23 15/100S sulfocation exchanger with various metal concentrations] composite electrode. It was found that a high proton concentration in the ion-exchange matrix causes a decrease in the oxygen reaction overvoltage. The nanostructured state of copper particles causes stabilization of the intermediate product, i.e., hydrogen peroxide. Using the rotating disk electrode method, it was detected that the process is limited by external diffusion of oxygen to composite grains. The oxygen reaction is mostly concentrated on the grain surface and surface layers; oxygen is reduced in the bulk due to dispersed copper oxidation.  相似文献   

5.
Results are presented of a study of the electrochemical behavior of copper(II) and selenium(IV) ions and their joint reduction on a molybdenum electrode by cyclic voltammetry in a tartaric acid electrolyte. The potentiostatic deposition was used to obtain copper selenide deposits on Mo plates. The diffraction and energydispersive analyses demonstrated that a Cu2?xSe compound is formed with an admixture of the CuSe phase. A suggestion is made that the process of underpotential reduction affects the formation of copper selenide. Copper selenide films were deposited at a potential of ?0.6 V in the course of 30 min with a thickness of 0.43 μm and high adhesion to the substrate. At potentials in this range, an additional amount of the deposit may be formed due to the chemical reaction between Cu+ and Se2? ions. The p-type conduction was determined for films electrodeposited at various potentials.  相似文献   

6.
EPR was used to establish the structure of Cu2+ coordination centers in macroporous cross-linked polyvinylpyridines in the presence of Ag+ ions. The influence of a change in the hydrophilic nature of the polymer matrix, of the concentration of sorbed copper and silver ions, and of the moisture content of the samples on the formation and distribution of different forms of copper complexes has been determined. It has been shown that in the case of competition between Ag+ and Cu2+ for the ligand groups of the ion exchanger the formation of Ag+ coordination centers predominates. The coordination centers of copper are partially destroyed by forming hydrate and solvate complexes which are easily removed from the ion-exchanger matrix. The analysis of the integral intensities of the EPR spectra has given a quantitative estimation of the change in the content of Cu2+ coordination centers in the ion-exchanger matrix.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 462–468, July–August, 1990.  相似文献   

7.
The ion-exchanger LiAlTiO4 of spinel type was prepared by the common precipitation/hydrothermal crystallization method, and was acid-modified. Its ion-exchange properties for alkali ions such as saturation capacity of exchange, distribution coefficient and pH titration curve were determined. LiAlTiO4 was characterized by the X-ray diffraction method. The acid treatment of LiAlTiO4 caused Li+ extraction ratio to change from 28% to 72%, while the dissolution of Al is less than 6.8%. This inorganic ion-exchanger (LiAlTiO4-700) has a higher saturation capacity of exchange for Li than for other alkali ions, the saturation capacity of exchange for Li+ reaches 4.29 mmol/g (30.03 mg/g); LiAlTiO4-700(H) has a higher selectivity of ion exchange for Li+ than for other alkali ions. These results show LiAlTiO4-700(H) has better memory and selectivity of ion exchange, and higher capacity of ion exchange for Li+. It is a kind of prospective ionic sieve for Li+. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22 (7) (in Chinese)  相似文献   

8.
The formation of an adatom layer on polycrystalline platinum and the three-dimensional nucleation of copper in a copper perchlorate solution are studied by cyclic voltammetry at 0.1 V s–1 while varying potential ranges and by recording potentiostatic current transients. About 0.6 monolayers of copper adatoms are deposited when cycling with anodic limit E a = 1.35 V, the process is slower than that in an acid sulfate solution. Decreasing E a accelerates the process (nearly one monolayer forms for E a = 0.80–0.95 V in a cathodic scan) due to an increased number of active centers (metastable copper oxides) and, probably, to a change in the platinum surface microstructure. Oxygen for copper oxides is presumably supplied by water molecules adsorbed on a monolayer of copper adsorbed atoms and by subsurface oxygen (Oss), which appears on the platinum surface after the destruction of complexes Oss–Pt n –ClO4. Both the copper nucleation and the deposit growth accelerate at higher concentrations of copper oxides, which form at low E a. High cathodic overvoltages decrease the number of active crystallization centers due to reduction or removal of copper oxides.  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.
Potentiostatic measurements are used to show that, depending on the overvoltage sign, either electrochemical deposition or dissolution of copper occurs at the Cu/Cu4RbCl3I2 interface at overvoltages η > 8–10 mV. At η = 10–100 mV, the reaction rate is limited by the formation and expansion of dissolution centers at the copper surface during anodic polarization and crystallization centers, during cathodic polarization. At η > 120 mV, the reaction rate is limited by charge transfer; the exchange current density is 2.7 mA cm?2 and the anodic transfer coefficient is ~0.45. Under anodic polarization, formation of electron holes in the electrolyte occurs in parallel with the copper anodic dissolution. Therefore, nonstoichiometry of the electrolyte emerges in the near-electrode layer and divalent copper accumulates there.  相似文献   

11.
A simple system for controlled potential electrodeposition on to a graphite probe electrode is described. Totally pyrolytic graphite was found to be better for electrodeposition than microporous glassy carbon or electrographite coated with pyrolytic graphite. Lead can be deposited by anodic and cathodic processes as PbO2 and Pb, respectively. Potentials of + 1.2 to + 2.0 V were best for anodic deposition and – 0.8 to– 2.0 V were best for cathodic deposition. With an electrodeposition time of 120 s, AAS sensitivity gains of × 9 and × 3.5 were achieved for anodic and cathodic deposition, respectively, in comparison with the results obtained by direct injection of 20 1 sample volumes on to the probe. The lead cathodic process was unaffected by NaCl concentrations up to 10–2 M, but only 10–3 M NaCl could be tolerated by anodic deposition.  相似文献   

12.
Aluminum containing silica spherical MCM-41 was synthesized and modified with copper by the template ion-exchange method (TIE) and its modified version, including treatment of the samples with ammonia solution directly after template ion-exchange (TIE-NH3). The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low temperature N2 sorption), morphology (SEM-EDS), form and aggregation of deposited copper species (UV-vis DRS), reducibility of copper species (H2-TPR), and surface acidity (NH3-TPD). The deposition of copper by the TIE-NH3 method resulted in much better dispersion of this metal on the MCM-41 surface comparing to copper introduced by TIE method. It was shown that such highly dispersed copper species, mainly monomeric Cu2+ cations, deposited on aluminum containing silica spheres of MCM-41, are significantly more catalytically effective in the NH3-SCR process than analogous catalysts containing aggregated copper oxide species. The catalysts obtained by the TIE-NH3 method effectively operated in much broader temperature and were less active in the side process of direct ammonia oxidation by oxygen.  相似文献   

13.
Initial stages of copper electrocrystallization on platinum rotating and stationary ring-disk electrodes are studied in sulfate electrolytes of different acidities by cyclic voltammetry with a variable cathodic limit. In a weakly acid sodium sulfate solution of pH 3.7, copper deposition occurs at a higher rate than in a sulfuric acid electrolyte, which is due to an acceleration of the discharge of copper ions caused by local electrostatic effects that occur during the specific adsorption of sulfate anions and hydroxyl ions and to alterating nature of electroactive species. The mechanism of the formation of intermediate species (ions Cu+) during the deposition and dissolution of copper in solutions of different acidities is established.  相似文献   

14.
The characteristics of the copper deposition process from electrochemical cells using a solution of Cu(CF3SO3)2 in low molecular weight poly(ethylene glycol), PEG, have been investigated by cyclic voltammetry, potential steps and impedance spectroscopy. The results suggest that under non-equilibrium at the cathodic side the process mainly involves the reduction of Cu(II) ions to copper metal while at the anodic side a chemical reaction competes with the electrochemical dissolution.  相似文献   

15.
In this paper pH sensors based on tetra-metal oxide system (TMOF) film was synthesized by branched cathodic electrodeposition technique. Four different metal oxides mainly IrO2, RuO2, SnO2, and TiO2 used to form a film, which coated on various substrates such as titanium, steel, tin, and copper. The fabricated pH sensors underwent characterization and evaluation sensing performance. Characterizations results have indicated that titanium and steel substrates outperform alternative metal substrates Tin and copper. Nernstian performance of Steel and Titanium substrate with pH sensitivity ∼59 mV/pH remain the same, as well as tin and copper which are behaved as super-Nernstian with sensitivity ∼65 mV/pH. Fast response time ranged from 1 to 3 s were obtained. Perfect selectivity obtained using Na+, K+, Li+ and Mg2+ ions vs. primary one H+.  相似文献   

16.
Craggs A  Moody GJ  Thomas JD  Willcox A 《Talanta》1976,23(11-12):799-804
Radiotracer studies with 45Ca and 36Cl demonstrate that PVC matrix membranes containing Orion 92-20-02 liquid calcium ion-exchanger are permselective to counter-cations. Diffusion coefficients are quoted for the migration of 45Ca between pairs of calcium solutions and are discussed in terms of solution concentration, membrane thickness and concentration level of sensor in the membrane. Migration of calcium ions from calcium chloride solution to a Group (II) metal chloride solution through a PVC membrane containing calcium liquid ion-exchanger is discussed in terms of solvent extraction and electrode selectivity coefficient parameters. Thus, magnesium, strontium and barium ions appear to inhibit migration through the membrane by their low affinity for the membrane liquid ion-exchanger sites, while the inhibition by beryllium ions is attributed to site blockage by the strong affinity of dialkylphosphate sites for beryllium.  相似文献   

17.
Mechanism of copper electrocrystallization on highly oriented pyrolytic graphite electrode from a solution of 1 mmol/L CuSO4 and 1.0 mol/L H2SO4 has been studied using cyclic voltammogram and chronoamperometry. The results show that in copper electrodeposition the charge-transfer step is fast and the rate of growth is controlled by the rate of mass transfer of copper ions to the growing centers. Reduction of Cu(Ⅱ) ions did not undergo underpotential deposition. The initial deposition kinetics of Cu electrocrystallization corresponds to a model including progressive nucleation and diffusion controlled growth. Copper nanocrystals with size of 75.6 nm and relative standard deviation of 9% can be obtained by modulation potential electrodeposition.  相似文献   

18.
The electrochemical behaviour of lanthanum fluoride dissolved in molten lithium fluoride and in eutectic mixture LiF-CaF2 was investigated by cyclic voltammetry and laboratory electrolysis. The cyclic voltammetry experiments were carried out at 900°C and 800°C, respectively, in a graphite crucible (counter electrode). Several types of working electrodes (Mo, W, Ni and Cu) were used. Ni/Ni(II) was used as a reference electrode. Laboratory electrolysis was carried out in the system LiF-CaF2-LaF3 at 800°C in galvanostatic (j c = −0.21 A cm−2) and potentiostatic (E = 0.87 V) regimes. In both cases, nickel served as the cathode and graphite as the anode. It was found that no new separate reduction peak occurred on the molybdenum or tungsten electrodes in the investigated systems. When copper or nickel electrodes were used, new peaks corresponding to the reduction of lanthanum(III) to lanthanum metal appeared. This can be explained by the formation of alloys or intermetallic compounds of lanthanum with copper or nickel. X-ray microanalysis showed that lanthanum was electrodeposited together with calcium under formation of intermetallic compounds with the electrode materials in the galvanostatic regime. In the potentiostatic regime, mainly lanthanum was deposited, which enabled its separation.  相似文献   

19.
Kinetic aspects of extraction of Ni(II) ions with KU-2–8 cation-exchange resin in the Na+ form from wash water produced in electroless nickel-plating were studied. The optimal conditions and parameters of ion-exchange purification and regeneration of the cation-exchanger were determined.  相似文献   

20.
The electrochemical deposition of carbon films on a nickel substrate was carried out through anodic oxidation of calcium acetylide dissolved in a LiCl–KCl–CaCl2 melt at 823 K. Continuous and tenacious carbon films were prepared by a two-stage anodically potentiostatic deposition at a fast rate, and characterized by SEM, Raman spectroscopy, XRD and XPS. The results show the carbon films composed of micron-sized particles with graphitized and amorphous phases containing a mixture of sp3 and sp2 carbon. The cyclic voltammetry behavior of acetylide anion on graphite and nickel electrodes indicated that C22  ions are oxidized more favorably on the nickel substrate due to the anodic depolarization from nickel carburization.  相似文献   

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