Characterisation of surface oxides on carbon and their influence on dynamic adsorption

Abstract

The aim of this work is to gain a better fundamental understanding of the nature of surface oxide sites present on carbon surfaces, and their role in the adsorption process. A number of model carbon substrates with different degrees of surface oxidation and similar textural properties were prepared using a wide range of solution and gaseous phase oxidation techniques. Some of the carbons were characterised using established techniques including flow microcalorimetry, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results showed that both carboxylic acid (–CO 2H) and ether/hydroxyl (C–O) surface oxygen complexes were introduced to all of these carbons as a result of the oxidation processes. The number, strength and thermal stability of the surface groups formed were dependent on the nature of the base material and the oxidation conditions employed. The dynamic adsorption performance of the carbons against hexane, under humid conditions, was found to be mainly determined by the quantity of acidic surface functional groups. However, the location, strength of interaction and availability of the surface oxygen complexes to the adsorbate molecules, are also thought to affect the breakthrough characteristics of the carbons used in this work.