In-situ Electrosynthesis And Characterization Of Molecularly Imprinted Polymers

Molecularly imprinted polymers (MIPs) are an important class of synthetic materials mimicking molecular recognition by natural receptors.The general principle of molecular imprinting is based on such a process where functional and cross-linking monomers are copolymerized in the presence of a target analyte which acts as a template. Upon removal of the molecular template, the material retains its moulded shape to fit and coincide with that of the template molecules.Thus, MIPs can selectively bind to molecules of interest.Due to the nano sizes and unobvious structure characteristics of bare metal ions, MIPs imprinted with metal inos are usually synthesized through a process where functional monomer forms a complex with the target metal ion through coordination bonding followed by the copolymerization between the functional and cross-linking monomers. Some metal ions exhibit high electroactivities, so it's inappropriate to synthesize metal ion imprinted polymers with electrochemical method. In this work, we use ethylenediamintetraacetate (EDTA) to chelate with metal ions to form metal-EDTA chelates, which act as the templates. In this respect, the electroactivities of the metal ions are inhibited by the chelation. Then, o-phenylenediamine (o-PD) is initiated to polymerize by cyclic voltammetry in the presence of the template. The resultant polymer exhibits high binding specificity to the template, and is believed to have potential applications in heavy metal ions detection.The main results are summarized as follows:1. Optimization on the electropolymerization of o-phenylenediamine The electropolymerization of o-PD was investigated in solutions with different pH values. The resultant polymer films and soluble oligomers were characterized by UV-Vis. The UV-Vis analysis results demonstrate that higher degree poly-o-phenylenediamine (PoPD) will be obtained from the solution with pH≥5.0.2. Electrosynthesis of metal-EDTA imprinted PoPD on the Au electrode of quartz crystalMetal-EDTA imprinted PoPD was electrosynthesized on the Au electrode of quartz crystal. The resultant polymers were characterized by UV-Vis,XPS,FT-IR and SEM. The results demonstrate successful embedding of Metal-EDTA chelate in the PoPD film, and deduce hydrogen bonding as a major interaction between the template and PoPD film. Differential pulse voltammetry (DPV) analysis confirms successful removal of the template from the PoPD film.3. Evaluation of binding specificity of the metal-EDTA imprinted PoPDThe binding specificity of Cu(II)-EDTA,Zn(II)-EDTA,Fe(III)-EDTA and Cd(II)-EDTA imprinted PoPD films were investigated via the frequency response of the quartz crystal microbalance (QCM) to the adsorption of the templates and their analogs. The results show that these metal-EDTA imprinted polymers exhibit obvious binding specificity to their templates, respectively. Linear relationships are observed between the frequency shift and the concentration of the templates over a typical range of ~10-6 to ~10-4 mol·L-1. The association constants of metal-EDTA imprinted polymers to the templates were calculated. The results also suggest no significant correlation between binding specificity and the ionic (or atomic) radius of the investigated metal ions. The observed specificity is qualitatively attributed to the overall conformational difference of the metal-EDTA complexes resulting from their difference in both ionic radius and electronic structures.