Role of surface chemistry in adsorption of phenol on activated carbons

Two samples of activated carbon of wood origin were oxidized using ammonium persulfate. The structural properties and surface chemistry of the samples and their oxidized counterparts were characterized using sorption of nitrogen and Boehm titration, respectively. Phenol adsorption from solution (at trace concentrations) was studied at temperatures close to ambient without maintaining a specific pH of the solution. The results showed, as expected, that the phenol uptake is dependent on both the porosity and surface chemistry of the carbons. Furthermore, phenol adsorption showed a strong dependence on the number of carboxylic groups due to two factors: (1) phenol reacts with carboxylic groups on the carbon surface, forming an ester bond, and (2) carboxylic groups on the carbon surface remove the π-electron from the activated carbon aromatic ring matrix, causing a decrease in the strength of interactions between the benzene ring of phenol and the carbon's basal planes, which decreases the uptake of phenol.