The modification of activated carbon cloth by alumina deposition

Abstract

The impregnation of mesoporous carbon cloth with alumina has been studied. The most successful method of impregnation resulted from preparation of the alumina phase by a sol/gel route. This method involves a boehmite intermediate, and the heating environment for the thermal transition of boehmite to the final alumina was investigated. Heat treatment of the boehmite intermediate under flowing N2, flowing air and vacuum was found to give a different pore size distribution for the final alumina than did still air heat treatment. For the former environments the transition from boehmite to alumina was not accompanied by the usual increase in pore size. Alumina/carbon composites were made by dipping pieces of mesoporous carbon cloth in a boehmite sol. The distribution of boehmite about the carbon cloth was found to be improved by pre-wetting the carbon cloth and by the use of ultrasonic dispersion during boehmite impregnation. Dried boehmite/carbon composites, with loading levels of up to 180wt.%, were heated under vacuum to 5000 C. In this manner alumina/carbon composites of up to 60wt.% alumina were fabricated. The distribution of the alumina phase about the carbon cloth was investigated by electron microscopy and by gas adsorption techniques. Nitrogen isotherm data indicated that the mesopores of the carbon cloth were not blocked by the deposited alumina, rather the pore volume of the carbon cloth was increased by the clustering of porous alumina about the pore entrances of the carbon cloth. Water isotherms were determined for the composite materials. The water activity of the composite, particularly at low relative pressures, was found to be significantly greater than that of the carbon cloth as a result of the presence of alumina. CO2 activity of the composites was investigated by a gas chromatographic technique. The CO2 activity of the composite material was found to be up to 500 times greater than that of virgin carbon cloth.