Modeling Multicomponent Gas Adsorption in Nanoporous Materials with Two Versions of Nonlocal Classical Density Functional Theory

Abstract

Two versions of nonlocal classical density functional theory (cDFT) have been proposed to predict multicomponent gas adsorption in nanoporous materials by using the Lennard-Jones model for gas mixtures and the universal force field for the adsorbents. With the modified fundamental measure theory to describe short-range repulsions or volume-exclusion effects, one version of cDFT adopts the mean-field approximation for van der Waals attraction (here referred to as cDFT-MFA) as commonly used in porous material characterization, and the other version accounts for long-range correlations through a weighted-density approximation (cDFT-WDA). For a number of gas mixtures in MOF-5 (without sub-pores inaccessible to gas molecules), the adsorption isotherms predicted from cDFT-WDA are quantitatively consistent with results from grand canonical Monte Carlo simulation, while cDFT-MFA systematically underestimates the adsorption due to the neglect of correlation effects. Nevertheless, both versions of cDFT outperform the ideal adsorbed solution theory (IAST) at high pressure. Because IAST predicts mixture adsorption using only single-component data, it fails to capture the selective behavior arising from asymmetric interactions among different chemical species. The cDFT calculations are implemented with massively parallel GPU-accelerated algorithms to achieve rapid yet accurate predictions of multicomponent adsorption isotherms with full atomistic details of the adsorbent materials. This work thus provides a theoretical basis for the computational design of adsorption-based separation processes as well as for screening and data-driven inverse design of nanoporous materials.

Integrative studies of ionic liquid interface layers: bridging experiments, theoretical models and simulations

“…98 To present the layering structures and properties of the interfacial ILs, an external potential is needed to consider the strongly assymetruic interactions between ILs and the solid surface. 99 DFTs have been intensively developed to study the properties such as gas adsorption isotherms in metal organic frameworks, 100,101 partition and selectivity of IL mixtures in porous electrodes, 102 surfactant and polyelectrolyte on rock surface for selecting appropriate polyelectrolytes suitable for different reservoirs, 103 interfacial layering of ILs, 104 interfacial structure and differential capacitance of IL-graphite interface, 105 etc. Meanwhile, further development has been conducted and extended to the dimention more than one, as well as complex structures including the surface roughness and heterogeneity.…”