Influence of impregnation of chitosan beads with cetyl trimethyl ammonium bromide on their structure and adsorption of congo red from aqueous solutions

The effect of impregnation of chitosan (CS) beads with cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant, on the structural organization of the beads was investigated using various techniques such as infrared spectroscopy, zeta potential, X-ray diffraction, transmission electron microscopy and scanning electron microscopy equipped with energy dispersive X-ray. Impregnation of chitosan beads with this surfactant (CTAB) significantly increased adsorption capacity from 178.32 (0 wt% CTAB) to 373.29 mg/g (0.05 wt% CTAB) for adsorption of congo red (CR) from an initial concentration of 1000 mg/l. The results of zeta potential analysis of CS beads impregnated with various CTAB concentrations indicated that zeta potential was not significantly increased by CTAB impregnation up to 0.1%. Based on different characterization results, enhanced adsorption of CR onto CTAB-impregnated CS beads not only involves electrostatic interactions between CR molecules, and multiple functional groups of CS and positively charged head group of CTAB molecules, but also involves significant hydrophobic interactions between the hydrophobic tail of CTAB and hydrophobic moieties of CR molecules. (C) 2009 Elsevier B.V. All rights reserved.