GAS VAPOR ADSORPTION IN IMOGOLITE - A MICROPOROUS TUBULAR ALUMINOSILICATE

Imogolite is a structurally microporous tubular aluminosilicate with one-dimensional pore channels of a single diameter that may be varied between 0.6 and 1.0 nm depending on composition. With proper processing, imogolite tubes may be synthesized and aligned into macroscopic, densely-packed arrays yielding a porous solid exhibiting a high degree of microporosity which is oriented in a single dimension as demonstrated via SEM and TEM. Si-29 MAS NMR indicates that with proper synthesis, essentially pure tube bundles may be obtained with very low concentrations of amorphous (nontubular) impurities as compared to purified natural imogolite. The microporous structure of natural and synthetic imogolite has been investigated by nitrogen adsorption at 77 K as a function of out gassing temperature. For synthetic samples, pore volumes are approximately 0.2 cm3/g and the average pore diameter for the 100% Si sample is approximately 0.7 nm and is approximately 0.9 nm for the 50% Si/50% Ge sample. CO2 and CH4 adsorption at 273 K is measured over the pressure range of 0-800 Torr and uptake is influenced by tube diameter even though the surface area of the two synthetic samples is similar.