Adsorptive Removal of Phenol by Coffee Residue Activated Carbon and Commercial Activated Carbon: Equilibrium, Kinetics, and Thermodynamics

Carbons were prepared from coffee residue using chemical activation with ZnCl2. Among five carbons prepared by varying the activating agent ratio (mass of ZnCl2/mass of coffee residue) from 0 % to 100 %, the one with an activation ratio equal to 25 % (AC 25 %) was the most effective sorbent showing the maximum phenol uptake (68 %). Consequently, all the adsorption experiments were achieved with the carbon having an activation ratio equal to 25 %. A comparative study of prepared activated carbon (AC 25 %) and a commercial activated carbon (CAC) was undertaken to determine their capacities for phenol removal. For each adsorbent-phenol system, a pseudosecond-order kinetic model described the adsorption kinetics accurately at all concentrations and temperatures for the two systems. The thermodynamics of the phenol-CAC and phenol-AC 25 % systems indicate an exothermic process. Phenol adsorption isotherms onto the prepared and commercial activated carbons have been studied. They display two plateaus. The degree of coverage of the surface of two carbons by the phenol molecules was calculated, and it was revealed that the second plateau, appearing at high concentrations, is assigned to the desorption of water molecules fixed on the surface oxygen groups of the activated carbons and the occupation of these sites by phenol molecules in excess in the treated solutions. The Langmuir, Freundlich, and Elovich models were tested.