GAS VAPOR ADSORPTION IN IMOGOLITE - A MICROPOROUS TUBULAR ALUMINOSILICATE

Imogolite is a structurally microporous tubular aluminosilicate with o ne-dimensional pore channels of a single diameter that may be varied b etween 0.6 and 1.0 nm depending on composition. With proper processing , imogolite tubes may be synthesized and aligned into macroscopic, den sely-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 concentrat ions of amorphous (nontubular) impurities as compared to purified natu ral imogolite. The microporous structure of natural and synthetic imog olite has been investigated by nitrogen adsorption at 77 K as a functi on 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 t he pressure range of 0-800 Torr and uptake is influenced by tube diame ter even though the surface area of the two synthetic samples is simil ar.