Thermodynamic studies on the adsorption of phenol from aqueous solution by coffee husk activated carbon

Activated carbons (ACs) obtained from coffee husk by KOH activation at 650 (ACK-650) and 750 degrees C (ACK-750), were used as an adsorbent for the adsorption of phenol from aqueous solution. The ACs was characterized by SEM, EDX, BET, and Boehm titration techniques. The experimental equilibrium data of phenol adsorption was analyzed by eight isotherm models, which are four two-parameter equations (Langmuir, Freundlich, Elovich, and Temkin) and four three-parameter equations (Redlich-Peterson, Sips, Radke-Prausnitz, and Toth). The results reveal that in general, three-parameter isotherms can provide better prediction than two- parameter isotherms. The best fit for ACK-650 sample is Sips isotherm, while for ACK-750 sample is Redlich-Peterson isotherm. Isosteric heat and thermodynamic parameters Delta G degrees, Delta H degrees, and Delta S degrees of the adsorption were determined, and the results showed that the adsorption of phenol was exothermic and physical in nature. A scale-up of a batch system is designed for 2 to 10 L phenol with an initial concentration of 100 mg L-1.