Single-Walled Aluminosilicate Nanotubes: Emerging Materials for Separations and Renewable Energy Technology

Abstract

Synthetic single-walled metal oxide (aluminosilicate) nanotubes (SWNTs) are emerging materials for a number of applications involving molecular transport and adsorption due to their unique pore structure, high surface reactivity, and controllable dimensions. In this talk, we discuss the potential for employing SWNTs in next generation separation platforms based upon recent progress on synthesis, interior modification, molecular adsorption and diffusion properties, and transport modeling of metal oxide SWNTs. First, we describe the structure, synthesis, and characterization of the SWNTs. Thereafter, chemical modification of the nanotube interior is described as a means for tuning the nanotube properties for molecular separations. Interior functionalization of SWNTs (e.g. carbon nanotubes and metal oxide nanotubes) is a long-standing grand challenge in nanomaterials science, and recent findings from our synthesis and characterization studies suggest that properly conditioned imogolite nanotubes are amenable to interior surface functionalization. Specifically, controlled dehydration and dehydroxylation of SWNTs provides access for reagents at reactive interior sites, allowing for modification of SWNTs’ inner surfaces. With an appropriate heat-treatment process for controlled dehydration of SWNTs, we demonstrate that the SWNT inner surface can then be functionalized with various organic groups of practical interest via solid-liquid heterogeneous reactions. We also present examples of experimental measurements (e.g. separation of ethanol from water) and computational predictions of the adsorption and transport properties of these materials. Finally, we describe a mass transport model, the KJN model, for composite membranes composed of SWNTs as fillers and matrix materials. Case studies, such as natural gas separation and biofuel dehydration, are evaluated by the KJN model to assess the performance of SWNTs in large-scale membrane separation platforms. This talk will give a comprehensive overview of the state-of-the-art of the use of SWNTs for potential separation applications from both a nanoscale and a macroscale point of view.