Stability of dioctahedral 2:1 phyllosilicate edge structures based on pyrophyllite models

Molecular dynamics simulations of cesium adsorption on illite nanoparticles

“…The "Al O AOH 2 bond is distinct from other AlAO(H) bonds, with the charge neutral OH 2 ligand attracted to the aluminum by van der Waals interaction with the permanent OH 2 dipole. These findings are consistent with previous DFT calculations with small pyrophyllite clusters showing that the AlAOH 2 bond is readily broken by thermal motion [59,50]. To account for the weakness of the "Al O AOH 2 bond, we slightly modified the partial charge distribution in the AOH 2 group formed by Oe3 atoms to match that of the SPC/E water model.…”

“…Edge surfaces were created by cleaving the crystal structure along the so-called AC bond chain identified by periodic bond chain theory [103], the most stable or one of the most stable cleavage planes according to quantum mechanical calculations [19,50,49]. Because of the periodic boundary conditions, the resulting nanoparticle is effectively an infinite needle elongated parallel to the crystallographic b-axis and cleaved along the AC plane.…”

Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential

“…Effects of the sheet stacking structure on the pyrophyllite morphology have not yet been explored with DFT studies. However, 2-D planar habits have been predicted through Wulff constructions (Wulff, 1901) based on calculated surface excess energies; euhedral crystals would take on a pseudohexagonal or rhombohedral shape depending on the surface coverage of water (Churakov, 2006;Lavikainen et al, 2015). Wulff constructions with our calculated surface free energies that include the vibrational component demonstrate that the equilibrium morphology of pyrophyllite crystals tend to be influenced by temperature and vapor pressure (Fig.…”

“…Compared with the atomistic structure of surfaces, the surface stability at different temperature and humidity conditions has been little investigated, although the AC edge surface appears to be more stable than the B edge surface. The surface excess energies of hydrated pyrophyllite edges were reported in previous DFT studies (Churakov, 2006;Lavikainen et al, 2015;Martins et al, 2014). The calculated energies were relatively small and differed little amongst the surfaces considered, but the AC edge surface generally possessed a slightly lower surface energy than the B edge surface; equilibrium morphologies for pyrophyllite crystals were also predicted based on the calculated energies.…”

Identification of montmorillonite particle edge orientations by atomic-force microscopy

“…Cleavage energies (ΔE) and corresponding Gibbs free energies (ΔG) for edge surfaces predicted by density functional theory (DFT) are also in agreement with these findings. For example, Lavikainen at al. (2015) calculated that the ratio of (110), (010) and (100) edge surfaces of pyrophillite, an uncharged clay mineral with a layer structure similar to montmorillonite, is 69%, 29%, and 2%, respectively, while the (130) edge surface represents less than 1% of the total surface area.…”