Effect of pore size and heterogeneous surface on the adsorption of CO2, N2, O2, and Ar on carbon aerogel, RF aerogel, and activated carbons

Abstract

Aerogels are porous super materials that have many desirable properties including high surface areas which cause them to have significant gas adsorption. In this study, carbon aerogel and resorcinol-formaldehyde (RF) aerogel are compared with six commercial activated carbons (Derived from wood, coconut shells, polymers, and bituminous coal). This study investigates many intrinsic properties of these carbons including surface area, pore size, presence and type of surface groups, as well as ash content and determines their influence on the adsorption of CO 2 , N 2 , O 2 , and Ar using pure gas adsorption isotherms. This study noted that there was no trend for ash content but a strong correlation existed between the adsorption capacity and the pore size in the higher pressure region according to Dubinin's micropore volume filling theory. In the lower pressure range, the heterogeneous nature of the surface dominates the adsorption particularly for CO 2 which has the strongest polarizability and quadrupole moment of the probe molecules investigated. The two aerogel samples were then further investigated by determining their adsorption in the presence of air using the temperature dependant Toth model with N 2 and O 2 being adsorbed significantly more than CO 2 and Ar at ambient conditions, due to their much higher compositions in the air. • Isotherms of CO 2 , N 2 , O 2 , and Argon with 8 Carbon materials were determined. • Effects of pore size, surface area, % oxidation and ash content were studied. • No trend for ash content, but pore size affected adsorption at high pressures. • Relationship between adsorption capacity and thermal properties were discussed.