Modelling Electrolyte Adsorption in Nanoporous Materials
Miha Lukšièa, Vojko Vlachya*, and Orest Piziob
aFaculty of Chemistry and Chemical Technology,University of
Ljubljana, Aškerèeva 5, 1000 Ljubljana, Slovenia
bInstituto de Química de la UNAM, Circuito Exterior, Coyoacán 04510,
México D.F.
Absrtract
The structural and thermodynamic
properties of a model electrolyte solution confined in disordered matrices with
charged obstacles were studied by means of the grand canonical Monte Carlo
simulation. A disordered nanoporous medium was modelled as i) an equilibrium
distribution of ions in a +1:-1 primitive model electrolyte; ii) a system of
dipolar hard spheres; iii) a collection of chainlike molecules with alternating
charge on the beads (polyampholyte); and iv) as a system of charged chainlike
molecules (oligoelectrolyte) with the pertaining counterions. The confined
electrolyte was assumed to be in thermodynamic equilibrium with the obstacles
forming the nanoporous matrix and an external electrolyte of the same chemical
composition. The solvent in all these cases was treated as a dielectric
continuum. In the present study we were interested in effects of the
distribution of charged obstacles on the mean activity coefficient of the
confined electrolyte. The computer simulations were performed for a set of
values of the model parameters such as the concentration of matrix ions and of
the annealed electrolyte, pre-quenching conditions and the conditions of
observation. The results confirmed our previous findings that the properties of
an annealed electrolyte depend strongly on the conditions of observation
(temperature and dielectric constant of solvent), as well as on the
concentrations of all components. The effect of the matrix-charge distribution,
investigated in this work, was found to be significant and more important for
higher Coulomb couplings.
Key words: nanoporous
material, adsorption, electrolyte, Monte Carlo simulation