Effects of the surface chemistry of carbon materials on the adsorption of phenol–aniline mixtures from water Original Research Article

The adsorption behavior of phenol, aniline and phenol–aniline mixtures in water over carbonaceous material surfaces has been studied. The adsorbents used were: a mesoporous high surface area graphite (HSAG) and a microporous activated carbon (AC). Aliquots of AC were treated with HCl and H2F2 to remove inorganic surface impurities. Furthermore, samples of HSAG and AC were subjected at 1173 K, to inert He flow, in order to eliminate surface oxygen groups. Apparent surface areas, surface oxygen groups and, zero point of charge of the adsorbent surfaces have been determined. All the adsorption isotherms of phenol and aniline on HSAGs are adequately fitted by Freundlich type isotherms, while on ACs, the extended Langmuir equation provides a better description of the experimental results. This fact reveals the importance of the textural characteristics (i.e., pore sizes) on the adsorption behavior. The presence of oxygen surface groups affects the adsorption behavior. Their effect depends on the amount of these groups that are present on the adsorbent surface and on the nature of the adsorbate molecule. In the case of HSAG, aniline is adsorbed to a larger extent than phenol for all the studied phenol–aniline mixtures. The opposite trend was found for ACs. Elimination of oxygen groups, originally present in larger amounts on the HSAG surface than on AC, produces an inversion in the selectivity adsorption of the mixtures. That is, more phenol than aniline is adsorbed on the surface of heat-treated HSAG (HSAGT).