Selective adsorption of Zn²⁺ on surface ion-imprinted polymer

Abstract

A new type of Zn²⁺ ion-imprinted polymer (Zn²⁺-IIP) was synthesized on the surface of attapulgite, displaying high affinity and selectivity to Zn²⁺. Fourier transform infrared spectra (FTIR) revealed Zn²⁺-IIP to be an organic–inorganic hybrid polymer, with Zn²⁺ imprinted cavities formed by CTS groups and connected to the surface of the attapulgite by A-187 cross-linked network. The adsorption kinetic investigation showed that the adsorption of Zn²⁺on Zn²⁺-IIP was a pseudo-second-order process. The maximum adsorption capacities of Zn²⁺ were 0.536, 0.665, 0.715, and 0.722 meq/g at 288, 298, 308, and 318 K, respectively, where the activation energy, E_a, was evaluated as 23.8 kJ/mol. By thermodynamic study, ΔH° and ΔS° of the adsorption were determined as 30.862 kJ/mol and 108.664 J/mol K, respectively, while the negative ΔG° decreased with rising temperatures, indicating that the adsorption process was feasible and spontaneous. The adsorption selectivity of the Zn²⁺-IIP was also investigated via competitive adsorption of Zn²⁺, Cd²⁺, Cs⁺, Co²⁺, Ba²⁺, Sr²⁺, and Pb²⁺ from a mixture, demonstrating that Zn²⁺-IIP had the capability of recognizing Zn²⁺ with high affinity and selectivity. The study of multi adsorption–desorption cycles showed that the Zn²⁺-IIP can be reused many times without a significant decrease in the adsorption capacity.

Keywords:

• Adsorption
• Zn²⁺
• Ion-imprinted polymer