Dehydration, dehydroxylation, and rehydroxylation of single-walled aluminosilicate nanotubes.

Abstract

Single-walled metal oxide (aluminosilicate) nanotubes are excellent candidates for addressing the long-standing issue of functionalizing nanotube interiors, due to their high surface reactivity and controllable dimensions. However, functionalization of the nanotube interior is impeded by its high surface silanol density (9.1 -OH/nm(2)) and resulting hydrophilicity. Controlled dehydration of the nanotubes is critical for the success of functionalization efforts. We employ a range of solid-state characterization tools to elucidate dehydration and dehydroxylation phenomena in the nanotubes as a function of heat treatment up to 450 degrees C. Vibrational spectroscopy (Fourier transform infrared, FT-IR), thermogravimetric analysis-mass spectrometry (TGA-MS), nitrogen physisorption, solid-state NMR, and X-ray diffraction (XRD) reveal that a completely dehydrated condition is achieved at 250 degrees C under vacuum and that the maximum pore volume is achieved at 300 degrees C under vacuum due to partial dehydroxylation of the dehydrated nanotube. Beyond 300 degrees C, further dehydroxylation partially disorders the nanotube wall structure. However, a unique rehydroxylation mechanism can partially reverse these structural changes upon re-exposure to water vapor. Finally, detailed XRD simulations and experiments allow further insight into the nanotube packing, the dimensions, and the dependence of nanotube XRD patterns on the water content.

• Authors: Dun-Yen Kang, Ji Zang, Elizabeth R Wright, Arthur L McCanna, Christopher W Jones, Sankar Nair
• Journal: ACS nano (ACS Nano) Vol. 4 Issue 8 Pg. 4897-907 (Aug 24 2010) ISSN: 1936-086X [Electronic] United States
• PMID: 20684571 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)