Single-Walled Aluminosilicate Nanotubes with Organic-Modified Interiors

A methodology for modifying the interior of single-walled metal oxide (aluminosilicate) nanotubes by covalently immobilizing organic functional entities on the interior surface of the nanotube structure is reported. Characterization of the modified nanotubes by a range of solid-state characterization techniquesincluding nitrogen physisorption, thermogravimetric analysis, transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and solid-state NMRstrongly indicates that the organic entities are immobilized on the inner surface of the nanotubes by reaction with the silanol groups on the interior wall. The resulting organic-modified single-walled nanotubes (SWNTs) show higher hydrophobicity than bare nanotubes based upon water adsorption measurements. Furthermore, a mechanistic understanding of water adsorption in the modified SWNTs is developed, by interpretation of the water adsorption data with a multilayer adsorption model. The degree of interior surface silanol substitution is estimated, with up to 35% of the silanols being substituted through the present modification chemistry. This methodology of immobilizing various functional entities at the inner wall of aluminosilicate nanotubes opens up a range of previously inaccessible “molecular recognition”-based applications for nanotube materials in areas such as catalysis, molecular encapsulation, sensing, and separation.