Kinetics of adsorption of disperse dyes by polyepicholorohydrin-dimethylamine cationic polymer/bentonite

The characterization of polyepicholorohydrin-dimethylaminelbentonite and the kinetics of adsorption of four disperse dyes, namely, Disperse Yellow Brown S-2RFL (DYB S-2RFL), Disperse Red S-R (DR S-R), Disperse Blue SBL (DB SBL) and Disperse Yellow (DY SE-6GFL) onto organophilic bentonite (polyepicholorohydrin-dimethylamineibentonite) have been studied at various solution concentrations and temperatures. The adsorption kinetics was studied in terms of a two-step first-order kinetic rate equation and intra-particle diffusion model. The adsorption process has been found to follow with two different rate constants (k(1) and k(2)) for two-step first-order kinetic rate equation and also two different intra-particle diffusion rate constants (k(int1) and k(int2)) for intra-particle diffusion model. For both the kinetic steps, the energies of activation of adsorption (E-a1 and E-a2) and other thermodynamic parameters (Delta H-1* and Delta H-2*, Delta S-1* and Delta S-2*, Delta G(1)* and Delta G(2)*) have been calculated using Arrhenius's and Eyring's equation, respectively. It has been found that or both the adsorption kinetic steps, E-a1 and E-a2 are corresponding to the values of k(1) and k(2) and Delta H-1* < -T-av Delta S-1*, Delta H-2* < -T-av Delta S-2* and Delta G* > 0, which means that the influence of entropy is more remarkable than enthalpy in activation reaction and the adsorption process is not spontaneous. (c) 2006 Elsevier B.V. All rights reserved.