Kinetic and equilibrium studies on the removal of cationic dyes from aqueous solution by adsorption onto a cyclodextrin polymer

Batch adsorption experiments were carried out for the removal of basic dyes, namely C.I. Basic Blue 3, Basic Violet 3 and Basic Violet 10, from aqueous solutions using a cyclodextrin polymer. Studies concerning the effects of contact time and initial dye concentration are presented and discussed. Results of batch experiments showed that this adsorbent exhibited high sorption capacities toward basic dyes. Experimental data were analyzed using pseudo-second order kinetics, mass transfer, and intraparticle diffusion models. It was found that kinetics followed a pseudo-second order equation, suggesting that the rate-limiting step may be chemisorption. Equilibrium isotherm data were analyzed according to Langmuir and Freundlich equations. The characteristic parameters for each model have been determined. The Freundlich isotherm gave the best correlation for the adsorption of basic dyes on CDP material. On the basis of the Langmuir analysis, the maximum adsorption capacities were determined to be 53.2, 42.4 and 35.8 mg of dye per gram of polymer for C.I. Basic Violet 3, C.I. Basic Blue 3, and Basic Violet 3, respectively. The differences in adsorption capacities may be due to the effect of dye structure. The negative value of free energy change indicated the spontaneous nature of adsorption.