Ion-imprinted polyvinylimidazole-silica hybrid copolymer for selective extraction of Pb(II): Characterization and metal adsorption kinetic and thermodynamic studies

The current paper presents a synthesis of a novel ion-imprinted hybrid copolymer (IIHC) [poly(1-vinylimidazole)-co-(3-(trimethoxysilyl)propyl methacrylate) and its application to selective adsorption of Pb2+ ions. The hybrid copolymer was prepared by coupling free radical addition and sol-gel processing, using tetraethoxysilane (TEOS) as cross-linker. Thermogravimetry (TG), FT-IR, X-ray diffraction, specific surface area (BET) and scanning electron microscopy (SEM) were used to characterize the copolymers. The equilibrium data obtained were fitted very well to the non-linear Langmuir-Freundlich isotherm model, as compared to other models, and the maximum adsorption uptake was found to be 7.6 mg g−1. The thermodynamic parameters, including Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) of the adsorption process, were found to be −16.23 kJ mol−1, −10.37 kmol−1 and −19.42 J K−1 mol−1, respectively. These results demonstrate that the adsorption of Pb2+ onto the hybrid copolymer takes place by a spontaneous and exothermic process with further decrease in the degree of freedom without disordering at the solid-solution interface due to the negative ΔS° value. Furthermore, the pseudo-first-order and pseudo-second-order models were used to describe the kinetic data. The experimental data were fitted well to the pseudo-first-order kinetics. Under competitive adsorption conditions, the ion-imprinted hybrid copolymer was 8.8, 64.9 and 16 times more selective when compared to the blank copolymer (NIC - non-imprinted copolymer) for Pb2+/Cu2+, Pb2+/Cd2+, and Pb2+/Zn2+ systems.