Preparation And Characterization Of Bisphenol A Molecular Imprinted Polymers On The Surface Of Mulit-Walled Carbon Nanotubes

Bisphenol A (BPA) is a kind of environment estrogen that has strong biotoxicities and endocrine disruptions. It can enter into the environment through various channels, and finally accumulate in the human body, interfere with the body’s endocrine system and cause many diseases. BPA can be easily adsorbed by complex sample matrix owing to its strong polarity, which brings about many difficulties to the separation and determination of BPA. Therefore, it is very important for us to figure out a selective and specific method for the separation and detection of BPA from complex environment medium.Surface molecular imprinting technique is a newly developed molecular imprinting technique after the traditional embedding method. In this method, the reaction between template and functional monomer can occur on the substrate surface owing to the introduction of the substrate to the prepolymerization solution. The molecular recognition sites are completely exposed on the the substrate surface, leading to small space steric hindrance for the template molecules.Therefore, the template molecules can freely in and out of the specific recognition sites immobilized on surface of the polymer substrate. Accordingly, the selective absorption ability of the molecularly imprinted materials is improved.It is very important to choose a favorable functional monomer and substrate material for the preparation of surface molecularly imprinted polymers. Ionic liquid, developed in recent years, is a kind of new material with good application prospect. It has been widely used in separation field due to its special physical and chemical properties. If ionic liquid is used as the functional monomer, a molecularly imprinted polymer with selective recognition is expected to be obtained through the strong electrostatic interaction, hydrogen bonding and π-πn interaction between the temple and the functional monomer. Carbon nanotube is a kind of seamless hollow-pipe that consists of graphite flake with layered structure. It can be an ideal substrate material for the preparation of surface molecular imprinted polymers owing to its large surface area, high mechanical strength and easy-to-modify feature. In this work, two acrylamide modified carbon nanotubes with different sizes were obtained by the covalent modification of the carboxylation carbon nanotube. A BPA molecular imprinted polymer was synthesized on the surface of carbon nanotubes through the free radical polymerization and suface molecular imprinting technique by using acrylamide modified carbon nanotube as substrate material, BPA as temple molecule, and allyl-functionalized ionic liquid as function monomer. The synthesis conditions of the BPA molecularly imprinted polymer were optimized, the formation process was characterized and the selective or specific adsorption properties were evaluated comprehensively. The main results are as follow:1. The adsorption ability of BPA molecular imprinted polymers were mainly affected by the amount of the crosslinking agent, the ratio of functional monomer to template molecule, and the ratio of the solid to the liquid. The optimal conditions were as follows:60mg temple BPA, the molar ration of temple to functional monomer1:1.26,90ml acetonitrile solution,1.5ml EGDMA and20mg acrylamide modified carbon nanotube. The reaction solution was stirred for24h in60℃after removing oxygen by30minutes of nitrogen purging.2. The molecular imprinted polymers obtained by using [AMIM][PF6] as functional monomer showed better adsorption properties than that obtained by using [AMIM][N(SO2CF3)2]. This can be explained by the fact that the polarity of the functional monomer is stronger, the interaction between template molecule and functional monomer is stronger, and thus the selectivity of the molecular imprinted polymer is better. Therefore, we can choose [AMIM][C1] as functional monomer to improve the selectivity of the molecular imprinted polymer.3. The selectivity of the molecular imprinted polymer was not affected by the small change in size of acrylamide modified carbon nanotube when it was used as the substrate material. Because the substrates are same and they are all at the nanoscale, so there is no big change in the property of substrates and the surface morphology of the molecular imprinted polymer when the size of substrate change in the small rage of nanoscale. Accordingly, the selectivity of the molecularly imprinted materials for BPA doesn’t change much.4. First, the there kinds of molecular imprinted polymers have better adsorption properties when compared with non-imprinted polymers. The synthesized molecular imprinted polymers did not have obvious selectivity to phenol because phenol is smaller than BPA and only has one hydroxyl in its structure. It showed similar adsorption selectivity to BPA and bisphenol AF because these two compounds has very alike structure and molecular size. Hydroquinone has two hydroxyls in its structure, so the synthesized molecular imprinted polymers also showed some selectivity to it. Moreover, the adsorption of BPA on the molecular imprinted polymers can reach equilibrium very quickly because the imprinted sites were distributed on the surface of carbon nanotube. Finally, the adsorption of BPA on the molecular imprinted polymers is invertible, so the synthesized molecular imprinted polymers can be used repeatly.5. The adsorption mechanism of BPA on the molecularly imprinted polymer was as follows:there are two kinds of acting forces between BPA and the molecularly imprinted polymer, one is nonspecific physical adsorption force, the other is specific adsorption force that related to imprinted sites, and the main acting force is the specific adsorption force.