Surface characterization of polyethyleneterephthalate (PET) based activated carbon and the effect of pH on its adsorption capacity from aqueous phenol and 2,3,4-trichlorophenol solutions Original Research Article

A predominantly microporous activated carbon produced from polyethyleneterephthalate (PET) by physical activation (burn-off 50%) has a BET surface area of 1170 m2/g and a total pore volume of 0.625 cm3/g. Its surface possesses an amphoteric nature due to the oxygen functionalities present, however, the majority of the groups are basic. The adsorption of phenol and 2,3,4-trichlorophenol has been studied from aqueous solution of different pH (pH=3, 11 and unbuffered) on this carbon. The adsorption mechanism depends both on the pH of the solutions and the pKa of the phenols, as the former influences the surface chemistry of the carbon as well. In the case of the phenol, a competitive adsorption takes place, as the interactions are weak in all three media investigated. The triple chlorine substitution in the 2,3,4-trichlorophenol significantly increases the strength of the interactions in comparison with phenol. Due to its smaller pKa value, in unbuffered medium ionic interaction occurs, as has been concluded from the shape of the isotherm and the outstandingly high value of the adsorption equilibrium constant. Competitive adsorption takes place only in the basic media, where the adsorption of the 2,3,4-trichlorophenol is hindered by electrostatic repulsion.