Adsorption of Water and Methanol on Highly Graphitized Thermal Carbon Black and Activated Carbon Fibre

Abstract

Adsorption of water and methanol on different carbonaceous solids was carried out to investigate the roles of porous structure and functional groups on the adsorption of associating fluids. A highly graphitized thermal carbon black, non-porous Carbopack F, was chosen to study the effects of functional groups and their concentration, and two samples of porous activated carbon fibre (ACF), microporous A-5 and micro-mesoporous A-15, were used to investigate the interplay between the functional groups and confinement. On Carbopack F, adsorption of water at 298 K is not experimentally detectable until the relative pressure reaches about 0.9, and the adsorption isotherm exhibits a large hysteresis loop spanning a very wide range of pressure; by contrast methanol adsorption at the same temperature shows an onset of adsorption at a lower relative pressure of 0.2 and the isotherm has a very small hysteresis loop. This early onset, compared with water, is due to the dispersion interaction between the methyl group and the graphene surface; an interaction which is absent in water. For the porous ACF samples, the onset of water uptake shifts from a relative pressure of 0.9; as observed for Carbopack F, to the much lower values, depending on pore size, of 0.3 for microporous A-5 and 0.5 for micro-mesoporous A-15.