Electrochemistry of porous glass membranes in electrolyte solutions

Abstract

A comparative study of the influence of pore radius, concentration, counter-ion (H +, Na +, K +, Ba 2+, La 3+) charge on electrochemical properties of porous glass (PG) membranes with pore radii 1.3–13.2 nm was carried out by the methods of potentiometric titration, streaming and membrane potential and conductance. “Secondary” silica was found in pores for all membranes except for PG-13.2. This showed up in a concentration dependence of structural resistance coefficient, a non constancy of liquid velocity at constant pressure and a difference between total and through porosity. It was shown that the surface charge of PGs increased with the growth of counter-ion charge, pH and electrolyte concentration. Surface reaction constants, calculated from adsorption data were within the range of values reported in the literature for silanol groups. Cation transport numbers and efficiency coefficients, which characterise the contribution of EDL, decreased with increase in electrolyte concentration, pore radius and cation charge. The PG specific surface conductance, was of the order of 10 −10 mhO. Electrokinetic potentials ζ ∗ of PG-13.2 calculated with correction for EDL overlapping showed a normal concentration dependence, and ζ ∗ was close to the ζ-potentials usually observed for flat glass surfaces.