Effect of Particle Diameter of Activated Carbon on Adsorption Rate-Controlling Step of Organic Compounds

The effect of particle diameter of coconut shell-based granular activated carbons on the adsorption and desorption of organic compounds from solutions was studied. The adsorption of phenol and benzothiophene was examined for different particle sizes (0.053-0.588 mm) at 298 K in aqueous and hexane solution, respectively. The adsorption isotherm of phenol was well represented by the Langmuir equation and the amount of maximum adsorption was not influenced by the particle size. For both phenol and benzothiophene, the adsorption kinetics became faster with decreasing particle size. The desorption of phenol began before the adsorption equilibrium was reached, showing that adsorbate was rapidly desorbed from outer surface and subsequently re-adsorbed into the inner surface of the activated carbon. Analysis of the kinetics data revealed that the adsorption was represented by a pseudo-first-order equation during the first stage of the experiment, while a pseudo-second-order equation was given a better fit as time advanced. The adsorption model suggested in this work is discussed in terms of the mechanisms of phenol and benzothiophene adsorption onto activated carbon.