Comparative adsorption of levodopa from aqueous solution on different activated carbons

Adsorption on activated carbon has been successfully used in wastewater and drinking water treatment plants for the removal of various pollutants. Among them, pharmaceutical compounds have become a growing issue. The present study has focused on levodopa molecule, which is one of the drugs used to treat symptoms of Parkinson's disease. The adsorption of levodopa onto three activated carbons from different source materials is reported for the first time and analyzed according to both textural and surface chemical properties of the carbons. The activated carbons are characterized using low temperature nitrogen adsorption, thermogravimetry analysis and Boehm titration. The equilibrium isotherms are measured at 25 degrees C and five models (Langmuir, Jovanovic, Freundlich, Redlich-Peterson and Khan) are evaluated to fit the experimental data. The characteristic parameters of each isotherm model are optimized and the selection of the most adequate one is performed using statistical regression criteria. For two of the studied carbons the adsorption process can be well described by Freundlich model with an average relative error of 5%, while for the last carbon only three-parameter models gives good fitting. (C) 2009 Elsevier B.V. All rights reserved.