Synthesis And Evaluation Of Surface Molecular Imprinted Micro-nano Composite Materials

Molecular Imprinting Technology (MIT) is a novel technique for producing polymer materials with high affinity and selectivity for target compound (template). The Molecularly Imprinted Polymer (MIP) prepared by MIT has highly tallied with template molecule in the spatial structures and functional groups arrangement. Thus, the MIP has acquired an ability of memory recognition for template molecules. To date, it has been extensively applied in the chromatography separation, solid phase extraction, catalysis, sensing and other fields. Recently, the more promising surface molecular imprinting technique (SMIT) has been developed to imprint template molecules on the surface of various supports in order to overcome the disadvantage of traditional imprinting technique. As a result, most of the imprinted sites are situated at the surface or in the proximity of surface, which greatly improve the binding capacity, kinetics and site accessibility of imprinted materials.The Gastrodin surface molecularly imprinted polymer (GAS-SMIP), p-hydroxybenzoic acid surface molecularly imprinted polymer (p-HB-SMIP) and Amitrole magnetic surface molecularly imprinted polymer (AMI-MMIP) were successfully prepared by using novel surface molecularly imprinted technique. The morphology of the prepared polymer was characterized, respectively. Moreover, the mechanism of imprinting, recognition, absorption and catalysis were discussed in detail. The main conclusions included the following items:1. Synthesis and recognition of molecularly imprinted polymer for gastrodin based on surface modified silica nanoparticles(1) Silica nanoparticles were modified with3-Methacryloxypropyltrimethoxysilane (KH-570) as a carrier material. Then the gastrodin molecular imprinting polymer based on the surface of modified silica (GAS-SMIP) was prepared by adopting the novel surface molecular imprinting technique with methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EDMA) as the crosslinker, azoisobutyronitrile (AIBN) as initiator and methanol as solvent. The structure, composition and morphology of GAS-SMIP were studied by various characterizations. The results suggested the integral structure of GAS-SMIP nanoparticles were loose, existing obvious gap among particles.(2) UV-Vis spectroscopy indicated the strong non-covalent interactions existed between MAA and GAS and formed stable host-guest complexes. The equilibrium adsorptive experiments indicated that GAS-SMIP had significantly higher affinity and adsorption selectivity for GAS. And the adsorption isotherm studies indicated that Langmuir model fitted the adsorption isotherm data well. Scatchard analysis revealed that two classes of binding sites were formed in GAS-SMIP with dissociation constants of1.02and7.28μmol/mL, and the affinity binding sites of17.82and83.11μmol/g, respectively. Kinetic binding study showed GAS-SMIP reached saturation adsorption at1h. The selectivity of GAS-SMIP suggested the selectivity coefficient of GAS-SMIP for GAS in respect to competition species obtained was over2, which revealed GAS-SMIP had excellent selectivity and site accessibility for GAS. Reusability experiments revealed GAS-SMIP had promising regeneration property.2. Preparation and adsorption performance of p-hydroxybenzoic acid surface molecularly imprinted polymer as well as the application of catalyzing toluene to para-chlorotoluene(1) The p-hydroxybenzoic acid surface molecularly imprinted polymer (p-HB-SMIP) using silica microspheres modified with3-Methacryloxypropyltrimethoxysilane (KH-570) as supporting matrix was prepared by adopting the surface molecular imprinting technique with p-hydroxybenzoic (p-HB) as template, acrylamide (AM) as functional monomer, ethylene glycol dimethacrylate (EGMA) as cross linker and azoisobutyronitrile (AIBN) as initiator and methanol as solvent. The p-HB-SMIP was characterized by SEM micrographs, FT-IR spectra and thermogravimetry, respectively. The results indicated that surface of p-HB-SMIP with average particle size of ca.5-6μm was rough, ruleless and good monodispersity with obvious core-shell structure.(2) The static adsorption experiments revealed that p-HB-SMIP had significantly higher affinity and adsorption selectivity for p-HB. Scatchard analysis revealed that two classes of binding sites were formed in p-HB-SMIP with dissociation constants of1.77and9.62μmol/mL, and the maximum apparent binding capacity were24.11and73.94μmol/g, respectively. The static adsorption experiments revealed that the Freundlich equation fitted the adsorption isotherm data well. The kinetic binding study showed that p-HB-SMIP adsorbed quickly in the first30minute and then reached saturation adsorption at about100min, and the pseudo-second-order model fitted the adsorption kinetics data. The adsorption thermodynamics experiments showed that binding system for p-HB-SMIP was endothermic and spontaneous. Selective experiments showed that the p-HB-SMIP had high affinity and excellent recognition selectivity for the template p-HB.(3) The catalytic reaction of toluene to para-chlorotoluene catalyzed by p-HB-SMIP was using sulfuryl chloride as chlorine source. The optimal catalytic conditions were as follows:reaction temperature,60℃; reaction time,60min; mole ratio of methyl cyanide and toluene,2:1. The conversion of toluene was85.5%and the mole ratio of para-chlorotoluene and o-chorotoluene (p/o) was1.63, higher than traditional catalysts.3. Synthesis, characterization and adsorption of Amitrole magnetic molecularly imprinted nano-material(1) Superparamagnetism AMI-MMIP was synthesized by using Fe3O4as magnetic substrate, tetraethoxysilane (TEOS) as silica base modifier,3-Methacryloxypropyltrimethoxysilane (KH-570) as silane coupling agent, AMI as template, methacrylic acid (MAA) as function monomer, ethylene glycol dimethacrylate (EDMA) as coupling agent, azoisobutyronitrile (AIBN) as initiator, via hydro-thermal method, whose structure, composition, morphology, magnetic property and stability were characterized. The structure of AMI-MMIP was nuclear shell structure, theaverage particle size was ca.200nm, and the thickness of imprinted polymer was ca.30nm.(2) AMI-MMIP presented superparamagnetism. The saturation magnetization of it was48.4emu/g. The equilibrium absorption of AMI-MMIP showed that AMI-MMIP had good affinity and selectivity toward AMI. Two classes of bounding site of AMI with different affinity strength existed in caves of AMI-MMIP, which displayed fast absorption rate and large absorption amount. Selective experiments revealed AMI-MMIP had more excellent selectivity for AMI in respect to competition species. Compared to AMI non-imprinted polymers (AMI-MNIP), AMI-MMIP had better kinetic performance, and the pseudo-second-order model fitted the adsorption kinetics data well. The adsorption thermodynamics experiments showed that binding system for AMI-MMIP was endothermic and spontaneous in the experimental temperature range. AMI-MMIP exhibited outstanding selectivity and magnetic separation performance.