Kinetics, isotherm, and thermodynamic study of adsorption of zinc ions from aqueous solution by use of polyamidoamine dendrimer starch

A polyamidoamine dendrimer starch (PSt) was prepared and used to adsorb zinc ions from aqueous solution. Conditions affecting the amount of zinc ion adsorbed, for example treatment time, initial concentration of zinc ions, and pH of the solution, were investigated, and the equilibrium, thermodynamics, and kinetics of the adsorption process were further researched. The results showed that the equilibrium data followed the Langmuir isotherm. The maximum adsorption capacities of G1PSt (first generation polyamidoamine dendrimer starch), G2PSt (second generation polyamidoamine dendrimer starch), and G4PSt (fourth generation polyamidoamine dendrimer starch) used in this study were 3.2841, 3.5249, and 4.016 mmol/g, respectively, for zinc ions at 30 °C. The adsorption results revealed that the equilibrium time was approximately 30 min, and the pseudo-second-order kinetic model was a very good fit to the dynamic adsorption behavior of zinc ions. When the pH of the solution was adjusted below 3.0, PSt was no longer an effective zinc ion-sequestering agent. Moreover, the thermodynamic investigation demonstrated that the adsorption process was endothermic, and the enthalpy change (∆Hθ), the entropy change (∆Sθ), and free energy change (∆Gθ) of the adsorption process were calculated by use of adsorption isotherm data and basic thermodynamic relationships.