Influence of surface acidic functional groups on activated carbons for adsorption and desorption kinetics of phenol from aqueous solutions

Adsorption and desorption kinetics of phenol onto activated carbons with and without surface acidic oxygen functional groups were examined in aqueous solutions. Aniline was also used to compare with phenol. The surface oxygen groups was introduced by nitric acid oxidation after de-ashing, and completely removed by out-gassing, respectively. Langmuir isotherms could be successfully employed for both activated carbons. Application of Langmuir kinetic equation was limited to the oxidized carbons, whereas it was not fitted very well for the out-gassed carbons. For desorption experiments from the pre-adsorbed out-gassed carbons, first rapid desorption and consecutive slow re-adsorption was clearly observed for phenol and aniline, while only rapid desorption was measured from the oxidized carbons. Based on the results, for the oxidized carbons the adsorption was progressed by collision control kinetics between phenol and adsorption sites on the external carbon surface and meso- and macro-pore on the one hand, not only collision control but also diffusion control kinetics was included for the out-gassed carbons on the other hand. From the results of the temperature dependence of adsorption capacity and the aniline adsorption kinetics, coupling reaction accompanied by dehydration would be taken place on the out-gassed carbons simultaneously with the adsorption process.