Oxygen-induced Decrease in the Equilibrium Adsorptive Capacities of Activated Carbons

Special attention was paid in this work to the role of surface chemistry in the adsorption of phenol and salicylic acid onto activated carbons. To this end, two commercial activated carbons (granular and powdered) were oxidised using ammonium peroxodisulphate [(NH4)2S2O8] and nitric acid in different concentrations. The structural and chemical properties of the oxidised adsorbents were characterised via nitrogen adsorption isotherms measured at –196°C and Boehm titrations. Phenol adsorption from solution at low concentration was studied at room temperature without specific pH control of the solution. The results showed a significant reduction in the adsorptive capacities towards phenol of the activated carbons as the oxygen content of the latter increased. However, very little effect was observed towards the retention of salicylic acid. The decrease in adsorptive capacity depended not only on the amount of oxygen per unit mass of activated carbon, but also on the textural properties of the latter.