Showing papers on "Supporting electrolyte published in 1995"

Characterizing trace metal adsorption on kaolinite

Abstract: Summary Adsorption of Cu(II), Zn(II), Co(II) and Cd(II) on kaolinite has been investigated at 25°C as a function of pH, concentration of the substrate, and the nature and concentration of the supporting electrolyte. The adsorption edges for three metals (Zn(II), Co(II) and Cd(II)) showed clear evidence of two distinct adsorption processes. As the pH was increased adsorption began at pH 4.5 for all metals, but the fraction of metal adsorbed at the completion of the first stage differed, the order being Zn(II)>Co(II)∼Cd(II). The second stage of adsorption had characteristics similar to those for adsorption of the metals on alumina and silica. Type 1 adsorption (the first stage) probably occurs on the permanent negatively charged kaolinite faces, while Type 2 (the second stage) is associated with the variable-charge surfaces. Increasing the concentration of supporting electrolyte (KNO3 or NaCl) dramatically reduced the extent of Type 1 adsorption: at 0.1 m no evidence of this process existed. At intermediate concentrations electrolytes containing K+ suppressed Type 1 adsorption more than those containing Na+.

Polarography and Voltammetry of Aqueous Colloidal SnO2 Solutions

Abstract: In acidic aqueous solutions the protonated TiO 2 colloid undergoes a complex process ofelectroreduction. It starts by reduction of protons on the surface of the particles ; in cyclic voltammetry with a fast scan rate this reaction is reversible. In the absence of an excess of a supporting electrolyte the particles, deprived of the stabilizing positive charge in the electroreduction process, aggregate and adsorb at the electrode and hinder the electrode reaction. Added electrolyte removes this hindrance and produces an increase of the electrolytic current. The hydrogen atoms generated at the TiO 2 surface are able to reduce Ti(IV) to Ti(III). At more negative potentials a direct reduction of surface hydroxo complexes of Ti(IV) takes place. The mechanism and the potential ofelectroreduction of TiO 2 colloids are strongly affected by ligands which form complexes with titanium atoms on the particle surface.

Capillary Electrophoretic Chiral Separations Using a Sulfated β-Cyclodextrin-Containing Electrolyte

Abstract: Sulfated β-cyclodextrin (SO3-β-CD) was utilized as a chiral additive for capillary zone electrophoresis (CZE). Chiral separations of several uhcharged enantiomers, such as phensuximide, indapamide, etc., which are difficult to separate using neutral CDs, were achieved. The effects of SO3-β-CD concentration and the pH and ionic strength of the supporting electrolyte as well as the presence of an organic modifier, methanol, were discussed.

Electrochemical properties of iron phthalocyanine immobilized on titanium(IV) oxide coated on silica gel surface

Abstract: Electrochemical studies of iron tetrasulfonated phthalocyanine (FeTsPc) immobilized on silica gel modified with titanium(IV)oxide were carried out in aqueous solutions. Cyclic voltammograms recorded in different supporting electrolyte solutions presented a redox process that became better defined under acidification. The position of the peak potentials (0.35-0.45 V vs SCE) and their invariance with solution pH indicated that these processes can be assigned to the Fe II TSPc/Fe III TsPc redox couple, with characteristics similar to those observed for FeTsPc adsorbed on graphite surfaces. The nature of the supporting cation in solution does not shift the midpoint potential (E m ) of the redox process, when Li + , Na + , K + , and NH 4 + are used. In contrast, the supporting anion has a strong effect, i.e., the E m shifts toward more positive values in the order ClO 4 - >NO 3 - >Cl - >SO 4 = . Preliminary experiments indicated that the modified electrode presents catalytic activity for hydrazine oxidation in neutral solution.

Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25°C

Abstract: Potentiometric titrations of uranyl(VI) solutions were conducted using a standard glasslcalomel electrode combination over the pH range 3 to 12 at 0.1 molkg−1 ionic strength with tetramethylammonium trifluoromethanesulfonate as the supporting electrolyte. The electrodes were calibrated directly on the hydrogen ion concentration scale during the initial stage of each titration. The species, UO 2 2+ , (UO2)2(OH) 2 2+ , (UO2)3(OH) 5 + , (UO2)3(OH) 7 − , (UO2)3(OH) 8 2− , and (UO2)3(OH) 10 4− identified in an earlier Raman study were compatible with the analysis of the titration data. Based on this analysis and application of the extended Debye-Huckel treatment, the polynuclear species indicated above were assigned overall formation constants at 25°C and at infinite dilution of −5.51±0.04, −15.3±0.1, −27.77±0.09, −37.65±0.14, and −62.4±0.3, respectively. The results are discussed in reference to hydrolysis quotients reported in the literature for the first three species. Formation quotients for the last two species have not been reported previously.

Electrochemical reduction of metal salts as a method of preparing highly dispersed metal colloids and substrate fixed metal clusters by electrochemical reduction of metal salts

Abstract: The object of the invention is a method for the electrochemical preparation of metal colloids with particle sizes of less than 30 nm, characterized in that one or more salts of one or more metals of groups Ib, IIb, III, IV, V, VI, VIIb, VIII, lanthanoides, and/or actinoides of the periodic table are cathodically reduced in the presence of a stabilizer, optionally with a supporting electrolyte being added, in organic solvents or in solvent mixtures of organic solvents and/or water within a temperature range of between -78° C and +120° C to form metal colloidal solutions or redispersible metal colloid powders, optionally in the presence of inert substrates and/or soluble metal salts of the respective metals The invention further relates to soluble or redispersible colloids as well as application on substrates and immobilization thereof, in particular for the preparation of catalysts

Cation determination in aqueous solution using the methyl viologen-doped zeolite-modified carbon paste electrode

Abstract: Methyl viologen (MV2+) initially exchanged in a zeolite Y modified carbon paste electrode (ZMCPE) is reduced after being exchanged for the supporting electrolyte cation. The use of an electrolyte cation that cannot enter zeolite channels to a great extent does not give rise to appreciable currents while a non-size-excluded cation allows liberating MV2+ from zeolite particles and their subsequent reduction at the electrode–solution interface. Following those observations, the MV2+-based ZMCPE has been used for the constant potential (−0.85 V) amperometric detection of nonreducible:, non-size-excluded cations in aqueous medium. The performance of this electrode was investigated in both batch injection analysis (BIA) and flow injection analysis (FIA). The great advantage of BIA coupled to the amperometric detection is the ability to use electrolyte-free sample solutions. For FIA experiments, dissolved oxygen was eliminated by using an electrochemical scrubber containing porous carbon electrodes. With the MV2+-doped ZMCPE, alkali and alkali-metal cations can be detected at the submillimolar level for both batch and flow injection analysis.

Voltammetry of metals at mercury film microelectrodes in the absence and the presence of varying concentrations of supporting electrolyte

Abstract: The steady-state limiting current for reduction of mono and divalent metal cations to amalgam in solution without supporting electrolyte depends on both the charge of the cation and the charge of the associated anion. The ratio of limiting current in the absence of supporting electrolyte (i i o ) to diffusional current (i d ) was found to agree well with theoretical predictions (for reduction of M + , 2 and 3/2 for X - and X 2- , respectively, and for M 2+ , 3 and 2 for X - and X 2- , respectively). The reduction current of metal cation depends on the type and concentration of supporting electrolyte. The diffusional current is reached at a lower electrolyte ratio when the cation of the electrolyte is divalent than when it is monovalent in solutions without supporting electrolyte, the limiting current for reduction of a cation having a large negative reduction potential was found to increase in the presence of a cation reducing at a less negative potential. This phenomenon was observed for thallium ion with hydrogen ion and for lead ion with hydrogen ion. The increase of the current is due to the increased rate of transport of the more easily reduced cation at potentials where both reductions are transport-controlled

Determination of trace amounts of zinc, lead and copper in sugar cane spirits by anodic stripping voltammetry

Abstract: Anodic stripping voltammetry with a hanging mercury drop electrode was used for the determination of trace amounts of Zn, Pb and Cu in sugar cane spirit from different sources: commercial, oak-cask matured and home-made. The measurements were made directly on the samples, without previous treatment and in the absence of a supporting electrolyte. After electrodeposition, linear-sweep voltammetry, with low scan rates, was used for current measurements. The procedure allowed the determination of metal ions in the µg l–1 concentration range and the method was compared with atomic absorption spectrometry.

Rotating microdisk voltammetry

Abstract: The influence of the supporting electrolyte concentration on the steady-state voltammetric behavior of a 12.5-μm-radius rotating Pt disk electrode (angular velocity, ω = 0-378 rad/s) has been investigated for several electrochemical reactions in acetonitrile solutions. The results demonstrate that the voltammetric response is a strong function of the ratio of the supporting electrolyte and redox concentrations (C elec /C redox ) as well as the charge of the reactant (z). For the oxidation or reduction of monovalent and divalent species (e.g., [(trimethylammonio)methyl]-ferrocene (z = +1) and methylviologen (z = +2)), the observed voltammetric limiting currents are found to increase linearly with ω 1/2 , independent of C elec /c redox . Voltammetric currents corresponding to the oxidation or reduction of neutral reactants (e.g., ferrocene and nitrobenzene (z = 0)) show a more complex dependence on C elec /C redox . In solutions containing an appreciable quantity of supporting electrolyte, C elec /c redox > 0.1, mass transport limited currents are found to increase linearly with ω 1/2 . However, for C elec /C redox < 0.1, the voltammetric currents decrease with increasing ω. The unusual behavior observed for neutral species in low ionic strength solution is interpreted in terms of the rate of migration of charge-balancing electrolyte ions to the electrode surface, relative to the rate of removal of the same ions by forced convection. In low ionic strength solutions, electrolyte ions are removed by forced convection more rapidly than they are replenished by migration, resulting in a decrease in the electrical driving force for electron transfer

A simple theoretical model for the self-enhancement of the cathodic voltammetric waves of weak acids

Abstract: Weak acids dissociate negligibly, but their reduction wave heights, in the absence of supporting electrolyte, are higher by a factor of 2 compared to the excess electrolyte case A simple theoretical model presented in this work supports the experimental findings The model is based on solving the set of equations which include the transport equation (diffusion and migration), the Nernst-Planck equation, the electroneutrality principle, and the dissociation equilibrium of the acid under consideration It was found that the concentration profiles of H + and A - in the absence of supporting electrolyte are substantially different from those obtained for excess supporting electrolyte Regarding the electroactive species, the gradient and the concentration of the hydrogen ion are apparently higher in the absence of supporting electrolyte and are responsible for the enhancement of the waves of weak acids by a factor of 2

Electrochemical reduction of nickel ions from dilute solutions

Abstract: Electrochemical reduction of nickel ions in dilute solution using a divided GBC-cell is of interest for purification of waste waters. A typical solution to be treated is the effluent from steel etching processes which contain low quantities of nickel, chromate and chromium ions. Reduction of chromate in a divided GBC-cell results in effluent containing Cr3+ ions. This paper examines the limitations to further treatment of the effluent by electrochemical reduction of nickel ions. Nickel current efficiency has been determined by varying temperature, pH, current density and concentration of supporting electrolyte. It was found that the presence of a complexing agent, e.g. NH4+ is necessary. To deposit nickel, complete removal of Cr3+ ions from the solution is inevitable. Optimum nickel current efficiencies are obtained at pH 5 and current density 10 mA cm−2.