Study of Physical and Chemical Properties of the Sodium Montmorillonite Compound through First Principles Calculations

The montmorillonite (MMT) M_xAl₃Si₈O₂₄H₄Na (M_x: Mg²⁺, Fe²⁺) clay is a lamellar silicate mineral that is found in nature or synthesized in order to create structures, such as polymer matrix nanocomposites. These materials have several remarkable physicochemical properties, opening up a wide variety of industrial applications. Each lamella of anhydrous or hydrated MMT consists of two tetrahedral layers involving an octahedral one. The aluminum Al³⁺ in the octahedral layer may optionally be substituted by other cations generating negative charges, and to keep electroneutrality a cation is added between the lamellae. As sodium cations are present between the lamellae the clay is called sodium montmorillonite (MMT-Na⁺). This work shows results of investigation through ab initio calculations of the physicochemical properties of MMT-Na⁺ isomorphically replaced by Mg²⁺ and Fe²⁺. The electronic properties were obtained by calculating the band structures and density of states, and a comparison is made with experimental results from visible and ultraviolet spectroscopy of the natural MMT-Na⁺ (Cloisite®). Our results pave the way for understanding the behavior of MMT nanocomposites upon chemical and structural changes due to inclusions.