(591c) Computational Evaluation of Separations with Single-Walled Aluminosilicate Nanotubes

Single-walled metal oxide nanotubes are attractive candidates for molecular separations as they present a well-defined solid-state structure, precisely tunable length and diameter, and hydrophilic and functionalizable interiors for obtaining transport and adsorption selectivity. Unlike the situation for carbon nanotubes, little is currently known about molecular separation in metal oxide nanotubes. Recent studies on transport properties of hydrogen-bonding liquids (water, methanol and ethanol) through single-walled aluminosilicate nanotubes have shown that the hydrogen bond network associated with water makes its diffusion behavior different from methanol and ethanol. And mixtures of water and methanol show segregation in the nanotube, with water located closer to the tube wall and the alcohol molecules localized near the center of the nanotube. Here, we study the adsorption and diffusion of water/methanol and CH₄/CO₂ in aluminosilicate nanotubes using Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to investigate the effects of competitive transport of different chemical species. We show that the flexibility of inner surface hydroxyl groups play an important role in adsorption of hydrogen-bonding liquids. Both self- and corrected diffusivity for water (CH₄) are higher than those of methanol (CO₂) at high molecule loadings. By using the adsorption isotherm and transport coefficients of molecules in aluminosilicate nanotubes as input parameters into a continuum model, we examine the possibility of selective transport of molecular species in the present nanotubes. Furthermore, we investigate the effect of organic functionalization of tube interiors on CH₄/CO₂ separation and discuss the possibility of tuning the transport properties of the nanotubes.