Adsorption of phenol from dilute and concentrated aqueous solutions by activated carbons

Combined calorimetric and adsorption techniques show that in the case of phenol adsorption from either dilute or concentrated aqueous solutions, water is always adsorbed preferentially by the oxygen-containing surface groups of the carbon. This reduces the surface and/or the micropore volume accessible to the phenol molecule and quantitatively explains the decrease in the limiting adsorption of phenol on a given carbon after oxidation. In the case of dilute solutions, as established earlier, the mechanism corresponds to the coating of the total surface (external surface and micropore walls) by a monolayer of phenol. On the other hand, for concentrated solutions (15-25% of water), one observes a process of micropore filling by phenol. Both mechanisms can be described in the framework of Dubinin's theory, which allows predictions based on simple physical and structural parameters.