Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

Abstract

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO3)3 and Cr(NO3)3 solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al3+ ions in 10–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al3+ adsorption and membrane charge reversal at Al3+ concentration in a solution higher than 10–6 M. The dependences of the ion selectivity ϕ on pH and Al3+ concentration C Al in a solution are similar. At pH 10–6 M, the ϕ1–2 > ϕ1–1 > ϕ2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the ϕ2–1 > ϕ1–1 > ϕ1–2 series characteristic of positively charged membranes.