CHARACTERIZATION OF THE SURFACE CHEMISTRY OF ACTIVATED CARBON USING MULTICOMPONENT ADSORPTION: SPECIFIC ADSORPTION OF BENZYL ALCOHOL.
K A Alkhamis1 , D E Wurster2 , L E Matheson3
1Jordan University of Science and Technology, College of Pharmacy, Irbid, Jordan, Jordan 2University of Iowa, College of Pharmacy, Iowa City, IA, 3University of Iowa, College of Pharmacy, Iowa City, IA,
To characterize the surface of an activated carbon (Norit B SupraÒ), and to study the specificity of interactions using multicomponent adsorption.
Methods. The competition between phenobarbital and benzyl alcohol was studied by conducting multicomponent adsorption experiments. Benzyl alcohol and phenobarbital were combined to form a bisolute system. The adsorption of the bisolute system from simulated intestinal fluid (without pancreatin) by activated carbon was studied using the rotating bottle method. The concentrations, both before and after the attainment of equilibrium, were determined with the aid of an HPLC system.
Results. The modified competitive Langmuir-like model was fit to the data. A good correlation was obtained between the experimental and the calculated data (slopes are close to one, with intercepts close to zero). This result indicates that benzyl alcohol and phenobarbital are competing for the same binding sites. This interaction is mainly with the hydroxyl groups on the activated carbon surface. This result was not expected, since Norit B SupraÒ has several oxygen-containing functional groups including the carbonyl group. Therefore, the highest energy site for the adsorption of benzyl alcohol by activated carbon was expected to be the carbonyl group.
Conclusions. Firstly, the good correlation between the experimental and the calculated data suggests that benzyl alcohol and phenobarbital are competing for the same binding site. Secondly, the unexpected competition between benzyl alcohol and phenobarbital suggests that benzyl alcohol is not interacting with the highest energy site due to the blockage of this site by the solvent (water). Thirdly, although the activated carbon surface is heterogeneous and contains several different oxygen functional groups, the phenolic group is likely to be the most important group for benzyl alcohol when the adsorption occurs from aqueous solution.