Mechanisms of para-chlorophenol adsorption onto activated carbons having different textural and chemical properties

The present study describes the adsorption behavior, mechanisms governing the process and thermodynamics of the separation of p-chlorophenol (4-CP) from aqueous solutions by several granular activated carbons (ACs). The main contribution of this work consists in bringing more insight onto the proper selection of sorbents based on the affinity between them and a specific sorbate with a special regard onto the textural and chemical characteristics of sorbents. Batch tests were conducted in order to evaluate the kinetics, equilibrium and thermodynamics of each considered adsorption system. Equilibrium data were fitted to Langmuir, Freundlich, Sips, Redlich–Peterson and Radke–Prausnitz isotherms in order to elucidate the mechanisms governing the adsorption processes. Also, the kinetics data were analyzed by means of pseudo-first-order, pseudo-second-order, and intraparticle diffusion models The best-fitted adsorption isotherm models were found to be in the order Sips > Redlich– Peterson > Freundlich > Radke–Prausnitz > Langmuir, and the pseudo-second-order model described best the behavior of the adsorption of 4-CP onto each of the five investigated ACs. The adsorption capacity of the AC was found to decrease with temperature. The process of 4-CP adsorption onto AC was spontaneous, and physical in nature and thermodynamically feasible.