EFFECT OF ELECTROLYTES ON ELECTROSURFACE PROPERTIES OF MICROCRYSTALLINE CELLU-LOSE PARTICLES

The electrical surface properties (specific surface charge of particles - σ0, point of zero charge – pHPZC, electrokinetic potential - ζ and position of isoelectric point - pHIEP) of dispersions of microcrystalline cellulose (MCC) in aqueous solutions of H2SO4, NaOH, Na2SO4 and TiOSO4 were investigated. Significant effects of specific adsorption of anions and cations on pHPZC and pHIEP have been demonstrated. The isoelectric point of the MCC particles in the H2SO4 solution is at pH 2.0, while the zero charge point in 5·10-4 M solution Na2SO4 at pH 5.6. An explanation of the observed effects is given. Possible schemes of the structure of the electrical double layer at different pH values, taking into account specific adsorption of ions in the Stern layer, are given. The introduction of TiOSO4 (10-5 mol/dm3) shifts the position of IEP to a less acidic region (pHIEP 4.5) due to the specific adsorption of positively charged TiOSO4 hydrolysis products particles.

Electrolyte ion adsorption and charge blocking effect at the hematite/aqueous solution interface: an electrochemical impedance study using multivariate data analysis

Specific adsorption of ions such as protonation determines the electrochemical activity of the hematite surface.

A practical approach to modeling the electrical double layer in the presence of specific adsorption of ions

Model calculations are presented that yield in a straightforward manner the quantitative dependence of the specific adsorption of ions at electrode surfaces on the applied electrode potential (electrode charge). Furthermore, the double-layer capacitance and the potential at the outer Helmholtz plane (ø2) are obtained. The derivation is based on Devanathan's three-capacitor model for the interfacial electric-potential distribution. A convenient correction function for the ø1 potential accounting for the discreteness-of-charge effect is derived, largely on the basis of recent work by Conway et al. The results are shown to be in very good agreement with published work by Lawrence and Parsons on the double layer between Br− electrolyte and the mercury electrode. Keywords: electrochemistry, specific adsorption, electric double layer, discreteness-of-charge effect.

Determination of single ion activities by relying on the electrical double layer model: NaF aqueous solutions

Single ion activity coefficients for aqueous solutions of NaF in the range m = 0.1 up to m = 0.9 mol kg−1 have been derived by measuring the potential difference of the cell Hg (σ = const)/NaF(m)/F−-selective electrode. The approach rests on the assumption that the electric potential drop across the Hg/solution interface is independent of the electrolyte concentration once the diffuse layer effects are accounted for by the Gouy–Chapman theory, provided specific adsorption of ions is absent. The derived γ− values have been compared with the "real" activity coefficients as determined by Rabinovich and Titov and with the predictions of the hydration theory of Bates and Robinson. It is shown that the latter do not agree with the present experimental observations. Possible reasons for this apparent discrepancy are discussed.