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

The characterization of polyepicholorohydrin-dimethylamine/bentonite 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-dimethylamine/bentonite) 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 (k1 and k2) for two-step first-order kinetic rate equation and also two different intra-particle diffusion rate constants (kint1 and kint2) for intra-particle diffusion model. For both the kinetic steps, the energies of activation of adsorption (Ea1 and Ea2) and other thermodynamic parameters (ΔH1* and ΔH2*, ΔS1* and ΔS2*, ΔG1* and ΔG2*) have been calculated using Arrhenius's and Eyring's equation, respectively. It has been found that for both the adsorption kinetic steps, Ea1 and Ea2 are corresponding to the values of k1 and k2 and ΔH1*<−Tav ΔS1*, ΔH2*<−Tav ΔS2* and ΔG* > 0, which means that the influence of entropy is more remarkable than enthalpy in activation reaction and the adsorption process is not spontaneous.