First-Principles Calculations Investigation on Different Coverage of H2o Adsorption on the Mg-Montmorillonite (010) Edge Surface

Abstract

Clay minerals are often the source of deformation in soft rock tunnel engineering, resulting in safety issues. Mg-montmorillonite (Mg-MMT) with good adsorbability is one of the most prevalent elements in clay minerals. In this paper, the density functional theory was employed to clarify the adsorption mechanism of H2O on the Mg-MMT (010) surface at the molecular level. And the adsorption energies and structures of H2O molecules on the Mg-MMT (010) surface were investigated with coverages ranging from 0 to 1.0 monolayer (ML). The interlayer-bridge site was the most favorable, and followed by the hollow, bridge, and top adsorption sites. When the coverage was 0.5 ML, the maximum adsorption energies for above adsorption sites was 0.71, 0.62, 0.61, and 0.44 eV, respectively. In 0 < Θ ≤ 0.5 ML, the adsorption energy increased with the increasing coverage for water molecules, while decreased with the coverage range of 0.5 < Θ ≤ 1.0 ML. The above results suggested that water molecules could be easily adsorbed on the Mg-MMT (010) surface. Besides, other properties of the H2O/Mg-MMT (010) surface system, including the atomic structures, bonding analyses, density of electronic states and charge distribution were also studied for different coverages.

Keywords: Mg-montmorillonite H2O molecules Adsorption First-principles calculations