Электростатическая теория селективности ионообменников

Vladimir A. Shaposhnik

doi:10.17308/sorpchrom.2020.20/2379

Vladimir A. Shaposhnik Voronezh State University, Voronezh

DOI: https://doi.org/10.17308/sorpchrom.2020.20/2379

Keywords: ion exchange, selectivity, electrostatic interactions, hydrogen bonds, energy of activation, quantum chemistry.

Abstract

Ion exchangers are supramolecular substances that combine strong covalent bonds (hard chemistry)
with weak ionic and hydrogen bonds (soft chemistry). Ionic bonds in ion exchangers are weakened by the
hydration of counter-ions and fixed ions. Hydrogen bonds are formed between their hydrate molecules. The elementary transport act of ion exchange involves the breaking of weak bonds. The purpose of this work was to determine the type of bond that defines the selectivity of ion exchangers.
The integral form of Coulomb's law was used to calculate the energy of ion bonds. Using Pauley's
assumptions, the electrostatic interaction energies of fixed ions with counter-ions were calculated. It has been established that the retention time of alkali metal cations is a positive exponential function of the energy of the electrostatic attraction of counter-ions by fixed ions. Correction of the parameters of the electrostatic interaction of ions was performed using non-empirical methods of quantum chemistry.
To determine the total energy of breaking the bonds of counter-ions with fixed ions (activation energy),
the temperature dependence of the electrical conductivity of ion-exchange membranes was measured
using the contact-difference method. The hydrogen bond energies were calculated from the difference between the activation energies and the electrostatic attraction energies of counter-ions by fixed ions. As a result, it was found that the energies of the elementary transport act in ion exchangers for single-charged ions are determined mainly by hydrogen bonds, while ion bonds, in addition to hydrogen bonds, play a significant role for counter-ions of a higher charge number. The main result of the study is confirming the determining role of the electrostatic interaction (ionic bonds) in the selectivity of ion exchangers.

References
1. Tswett M., Selected Works, M., Science, 2013. 679 p.
2. Shpigun O.A., Zolotov Yu.A., Ionic Chromatography, Moscow Univ., 1990, 199 p.3. Pauley J.L., J.Amer. Chem. Soc., 1954, Vol. 76, pp. 1422-1425.
4. Debye P., Polar molecules, N.Y., 1929. 172 p.
5. Shaposhnik V.A., Emel’anov D.E., Drobysheva I.V., Colloid. J., 1984, Vol. 46, No 6, pp.
1116-1119.
6. Wang J.H., Robinson C.V., Edelman I.S., J. Amer. Chem. Soc., 1953, Vol. 75, p. 466.
7. Shaposhnik V.A., Rus. J. Electrochem., 1994, Vol.30, No 5, pp. 638-643.
8. Butyrskaya E.V., Shaposhnik V.A., J. Structural Chem., 2003, Vol. 44, No 6, pp. 1180-1185.
9. Badessa T.S., Shaposhnik V.A., J. Membrane Science, 2016, Vol. 498, pp. 86-93.