A computational study of electrolyte adsorption in a simple model for intercalated clays

Abstract

A pillared interlayered clay is represented by a two-dimensional quenched charged disordered medium, in which the pillar configuration is produced by the quench of a two-dimensional electrolyte and the subsequent removal of the anions (that act as a template). The cation charge is counterbalanced by a neutralizing background that is an ideal representation of the layer's negative charge in the experimental system. In this paper we investigate the adsorption of electrolyte particles in this charged disordered medium resorting both to the use of the replica Ornstein-Zernike equation in the hypernetted chain approximation and grand canonical Monte Carlo simulations. The theoretical approach qualitatively reproduces the simulated behavior of the adsorbed fluids. Theoretical estimates of the material porosities obtained for various types of pillar distributions are in good agreement with the simulation. We investigate the influence of the matrix on correlation functions and adsorption isotherms.

A three dimensional integral equation approach for fluids under confinement: Argon in zeolites

“…This we have done on a 2048 point grid with a grid size of 0.02σ ArAr using standard procedures. 29 As mentioned, as input data our calculations require the knowledge of the structure factor. Since the zeolite structures are well-known, the structure factors can be accurately determined.…”

“…The explicit procedure for the solution of the ROZ equations can be found in Ref. 29, and we briefly sketch here its main points for completeness.…”

Explicit spatial description of fluid inclusions in porous matrices in terms of an inhomogeneous integral equation

“…The explicit procedure to build and solve the ROZ equations for our system of interest can be found in Ref. 16, and we briefly sketch here its main points for completion.…”

“…From the theoretical perspective, the advent of the Replica Ornstein Zernike (ROZ) approach in the early nineties 1-3 provided a powerful alternative to direct molecular simulation for the description of fluid inclusions in disordered porous systems. Since then, the ROZ approximation has been much exploited to describe templated 4-7 and sponge-like materials 8,9 , and a large variety of inclusions, such as simple binary mixtures 10 illustrating their phase behavior 11 , colloid/polymer mixtures 12 , electrolytes [13][14][15][16] , and associating fluids 17,18 . This approach yields average thermodynamic properties, fluid-fluid, and fluid-matrix correlations, but if one is interested in the explicit spatial distribution of the fluid/adsorbate for a given configuration of the matrix an alternative approach is needed, aside from resorting to molecular simulation.…”

“…Now, with the purpose of providing a sensible approximation for the fluid-fluid direct correlation under confinement required within the formalism, we have resorted to a ROZ equation with an HNC closure for a templated matrix 5,16 (ROZ-HNC). This approach furnishes fluid-fluid correlations averaged over matrix disorder, and these will be seen to represent a better approximation for our adsorbed fluid than the corresponding bulk counterparts.…”