A study on the adsorption characteristics of an amphiphilic phenothiazine drug on activated charcoal in the presence of surfactants

In this paper the adsorption of amphiphilic phenothiazine drug Thioridazine hydrchloride (THCl) on Activated charcoal (AC) surface was studied in aqueous solutions The effects of different types of surfactants anionic sodium dodecylsulfate (SDS) and lithium dodecylsulfate (LIDS), cationic cetyltrimethyl ammonium bromide (CTAB) and nonionic TritonX-100 (TX-100) micelles on the adsorption were reported It was found that the Langmuir isotherm appears to fit the isotherm data better than the Freundlich isotherm The adsorption of THCl was reduced in the presence of cationic CTAB bearing the same charge as THCl while presence of SDS and LiDs did not change significantly adsorption capacity of THCl on AC except the shape of the isotherm The presence of TX-100 micelles significantly increased adsorption of THCl on AC. Kinetic measurements showed that the adsorption equilibrium of THCl was attained within 30 min in aqueous media while in the presence of 10 mM anionic micelles the adsorption equilibrium of THCl reached the equilibrium almost in 1 min The kinetics of adsorption in view of three kinetic models i.e. the first-order Lagergren model, the pseudo-second-order model and the intraparticle diffusion model has been discussed The adsorption rate constants of THCl onto AC in the presence of anionic micelles are higher than in aqueous media for both kinetics models and the second-order model provides the best correlation of data in the absence and presence of micelles In order to gain further insight into the adsorption mechanism of THCl on AC, association of THCl with surfactants was also studied by absorption spectra. Binding constants of THCl to micelles were calculated by means of Benesi-Hildebrand Equation to provide more precise comparison of the effect of surfactants on the adsorption of THCl. (C) 2009 Elsevier B V All rights reserved.