Ryszard Sprycha

Electrical double layer at alumina/electrolyte interface. I: Surface charge and zeta potential

Surface charge and zeta potential of γ-Al2O3 in different 1:1 electrolytes were determined. The solutions of NaCl, CsCl, and NaI of concentrations ranging from 0.0001 to 1.0 M were used. The potentiometric titration method was used to determine the surface charge of alumina. Zeta potential was calculated from electrophoretic mobilities of alumina particles. The data are described in terms of the site-binding model of the electrical double layer. Surface ionization constants, pKa1,a2int, of -A1OH groups were determined by double extrapolation methods using zeta potential and surface charge data for the sample. Using electrokinetic data for the sample and knowing surface ionization constants, surface potential and -A1OH2+ and -A1O− components, as a function of pH of the solution, were evaluated for different ionic strengths.

Surface charge and adsorption of background electrolyte ions at anatase/electrolyte interface

Abstract Attempt of estimation of C 1 and C 2 capacities of the compact layer and distribution of potentials within the electrical double layer at the TiO 2 (anatase)-electrolyte interface is presented in this paper taking into consideration the potentiometric titration, adsorption of swamping electrolyte ions, and electrokinetic data for this system. The ionization and complexation constants of surface groups are determined as well. The measurements were performed in LiCl, NaCl, KCI, CsCl, NaBr, and NaI solutions of different concentrations—from 0.001 to 0.1 M . The adsorption densities were determined by use of radiometric technique. New methods of surface ionization and complexation constants determination have been used. The limited applicability of the ionization-complexation model of the electrical double layer to the system studied has been ascertained.

Electrical double layer at alumina/electrolyte interface: II. Adsorption of supporting electrolyte ions

Abstract Adsorption densities of supporting electrolyte ions onto γ-Al2O3 were measured using a radioisotopic method. The measurements were performed in NaCl, CsCl, and NaI solutions of concentrations ranging from 0.0001 to 1.0 M. The isotopes 22Na, 137Cs, 36Cl, and 131I were used. The surface complexation constants of anion and cation were estimated: p ∗ K Na + int = 8.6, p ∗ K Cl int = 7.5 , and ΔpKcomplex = 1.1. The potential distribution within the electrical double layer and C2 capacity were also evaluated using potentiometric titration and electrokinetic data. It was found that the complete results are inconsistent if ΔpKa = 6.2. It was presumed that hitherto existing methods of determination of surface ionization constants can be the reason for this inconsistency. The new concept of pKa1,a2int determination from adsorption measurements is presented in detail. It was estimated that pKa1int ⩾ 6.0 ± 0.2, pKa2int ⩽ 10.2 ± 0.2, and ΔpKa ⩽ 4.2 ± 0.4. Using ΔpKa = 4.2 the surface potential and ionic components of surface charge were determined vs pH. The capacitances C1 and C2 were also estimated for differing ionic strengths as a function of pH.

Estimation of surface ionization constants from electrokinetic data

A modified double extrapolation technique of surface ionization constants estimation from electrokinetic data for oxides is described. The pKa1int and pKa2int constants determined by the above method for SiO2, Al2O3, TiO2, and FeOOH are compared with those determined by double extrapolation technique using potentiometric titration data.

Zeta potential and surface charge of monodispersed colloidal yttrium(III) oxide and basic carbonate

Abstract Zeta potentials of yttrium oxide and basic carbonate dispersions of narrow size distribution were determined by the microelectrophoresis method as a function of the pH and the ionic strength. The isoelectric point (iep) changed with the temperature of calcination and was found to be at pH = 8.6 for YOHCO 3 and 9.1 for Y 2 O 3 calcined at 900°C, and it was independent of the concentration of sodium perchlorate. Net electrical surface charge was determined by potentiometric titrations using two different experimental techniques described in the literature. One of them takes into account the solubility reactions in calculating the real surface charge from potentiometric titration data, while the other does not. The value of the point of zero charge (pzc) was also dependent on the temperature of calcination of yttrium basic carbonate and changed from 7.7 for YOHCO 3 to 9.1 for yttrium oxide calcined at 900°C. The dissociation constants of surface — YOH groups were calculated.

Zeta potential and surface charge components at anatase/electrolyte interface

Abstract Zeta potential vs pH for the TiO 2 (anatase)/electrolyte system was measured for NaCl, CsCl, and NaI solutions of concentrations ranging from 0.0001 to 0.01 M . Surface ionization constants of anatase as well as [SO − ] and [SOH 2 + ] concentrations vs pH were determined from electrokinetic data. Surface charge components were determined taking into account adsorption of background electrolyte ions and electrokinetic data for the system studied.

Attempt to estimate σβ charge components on oxides from anion and cation adsorption measurements

Abstract The method of estimation of σβ charge components on γ-Al2O3 by use of cation and anion, of supporting electrolyte, adsorption data is described. The surface complexation constants calculated from adsorption densities of cation and anion at pzc with those determined by extrapolation techniques are compared.

Ionic components of charge on oxides

Abstract Esin-Markov coefficients (β) were determined for different oxides and electrolyte concentrations using literature potentiometric titration data. The problem of ionic components of charge is discussed using Lyklemas approach as well as experimental adsorption data for oxides. The adsorption data show that the contributions of cations and anions to the surface charge at the point of zero charge are different from zero. This finding can be explained by introducing the site-binding model of the electrical double layer to Lyklemas approach of determination of ionic components of charge on the basis of Esin-Markov coefficients.

Electrochemical Aspects Of Sodium Dodecyl Sulfate Adsorption At The Zn0/Electrolyte Interface

The results of investigations of adsorption phenomena in the ZnO-SDS-phosphate system are described. Surface charge of the ZnO in phosphate solutions of different concentrations was determined using the potentiometric titration technique and taking into account corrections for solubility of zinc oxide. Potentiometric titrations were performed in the presence and absence of sodium dodecyl sulfate.

Adsorption Of Surfactants On Modified Controlled Porosity Glasses (CPG’s)

Controlled porosity glasses (CPG’s) are very often used as catalysts, adsorbents, ion exchangers and supports of adhesively or chemically bonded stationary phases. Their strong adsorption properties result from the presence of boron atoms on the surface and the siliceous structure as well. Surface hydroxyl groups and small amounts of surface sodium ions are responsible for ion exchange properties of the CPG.