Adsorption of antiviral drug, acyclovir from aqueous solution on powdered activated charcoal: kinetics, equilibrium, and thermodynamic studies

The adsorption capacity of commercial powdered activated charcoal (PAC) was investigated for the removal of acyclovir from aqueous solutions. The effects of the initial acyclovir concentration (100-400 mg/L), pH (3-11), contact time, temperature (25-45 degrees C), and PAC dose (1-4 g/L) on the removal of acyclovir have been studied. The maximum removal was found to be 98% for 100 mg/L of acyclovir solution with 4 g/L of PAC dose at 45 degrees C. The results indicate that basic pH from 7 to 11 of acyclovir solution favored the adsorption on PAC. Moreover, the results showed that the adsorption kinetics can be represented by a pseudo-first-order model. The adsorption experimental data fitted in the order of decreasing accuracy as Freundlich, Redlich-Peterson, Temkin, Langmuir, and Dubinin-Radushkevich models. The Freundlich model was found the best to describe the equilibrium isotherm data of acyclovir adsorption on PAC. The maximum adsorption capacity of acyclovir determined from the Freundlich model was found to be 20.2 mg/g. The heat of adsorption was positive indicating endothermic nature and its low values (<70 kJ/mol) confirmed physisorption.