First-principle calculations of sulfur dioxide adsorption on the Ca-montmorillonite.

According to the serious problem of sulfur dioxide pollution, montmorillonite is one of the effective ways in gas pollution control because of its excellent absorption properties. One of the fundamental questions is to fully understand sulfur dioxide absorption mechanism of montmorillonite. In this study, using the first-principle methods, we studied the adsorption characteristics of Ca-montmorillonite in the presence of [Formula: see text]. The adsorption energy and elasticity constants as a function of the adsorption capacity were also studied. The calculated results show that bridge site is the most stable adsorption site for [Formula: see text] with the adsorption energy of - 140 meV. As adsorbent, Ca-montmorillonite is a clay with layer-structure, most of bond lengths(such as Al-O, Mg-O, Si-O, and H-O) does not obviously change. As adsorbed gas, the O-S-O bond angle of adsorbed [Formula: see text] change from [Formula: see text] to [Formula: see text]. The volume and adsorption energies of Ca-montmorillonite almost increase linearly with increasing [Formula: see text] adsorption. By calculating the montmorillonite elasticity constants under different adsorption capacity, we found that the elasticity constant C33 which perpendicular to the crystal face, with the maximum changes from 450 to 326 GPa. In addition, Young's modulus,bulk modulus and shear modulus significantly decrease with the increasing adsorption. The calculated results will not only help to understand the physical and chemical of montmorillonite but may also provide theoretical guidance for dealing with the problem of gas pollution.