Preparation Of Molecularly Imprinted Membranes And Their Application Study Of The Membrane Chromatography

Molecularly imprinted membranes (MIMs) are a kind of membrane which contain or are composed of molecularly imprinted polymers. Molecular imprinting is a promising technology for separating polymers with predetermined selectivity and high affinity, while membrane technology is a traditional method for separation with high stability and good continuity. MIMs have the advantages of both molecular imprinting and membrane technology and have been widely used in the fields of separation, catalysis and sensor technology. In the thesis, fourier transform infrared spectroscopy (FTIR) was used to determine the binding constant between the momoner and the template moleculars in the pre-organization solution. poly(vinylidene fluoride) (PVDF) membrane was used as supporting membrane, and free radical polymerization method or atom transfer radical polymerization (ATRP) polymerization method were used to prepare the imprinting layer. Then modules were assembled to evaluate the MIMs'separation performance. The main results were summarized as follows:Firstly, the binding constant (K) for the formation of monomer-template adduct in S-naproxen system was determined as 13.8 M-1 by means of FTIR analysis and nonlinear least-squares method. The molecularly imprinted polymers were prepared by free radical polymerization and the optimal conditions were determined as 4 mmol 4-vinylpyridine (4-VPY),20 mmol ethylene glycol dimethacrylate (EDMA),20 mL chloroform under 60℃for 48h. Then MIMs for selective binding and permeation of S-naproxen (S-Nap) were synthesized on the PVDF supporting membrane. Scanning electron microscopy (SEM) was used to visualize the surface and cross-sections of the membranes. The separation property of the imprinted membrane was determined by on-line high performance liquid chromatography (HPLC) membrane separation technology. And the result showed that there were two peaks at 5.1 min and 10.1 min in the HPLC chromatogram, corresponding to different enantiomers of the R-naproxen. The separation mechanism of the S-naproxen imprinted membrane can be defined as facilitated permeation mechanism.Secondly, Ultraviolet (UV) and FTIR titration were firstly used and the binding constant (K) for the formation of monomer-template adduct were 140 M-1 for theophylline and 83 M-1 for caffeine respectively. Molecularly imprinted composite membranes for selective binding of theophylline were then synthesized using free radical polymerization method with methacrylic acid (MAA) as functional monomers and EDMA as cross-linkers. Ultrsonic washing was used to remove the template moleculars. FTIR, SEM and dynamic contact angle analysis showed that there was an imprinted layer deposited on PVDF support membranes. The optimum condition for preparing the molecular imprinted composite membranes was obtained by batch-wise guest-binding experiments and the selectivity factor of theophylline to caffeine was found to be 1.56. Meanwhile, ATRP was used to covalently immobilize the molecularly imprinted layer on PVDF substrate membranes. Both FTIR and UV results showed that the PVDF membrane can directly initiate the polymerization of MAA, EDMA and theophylline when using CuCl/DMDP as catalyst/ligand in acetonitrile. SEM, AFM and contact angle characterizations further confirmed the successful preparation of theophylline molecularly imprinted membranes. The adsorptive selectivity ofα=2.14 between theophylline and caffeine showed a good specific affinity of the MIMs to theophylline. It is expected that the application of ATRP as a living/controlling technique provide a method to prepare the PVDF-based MIMs.Then, theophylline-MIMs were prepared by thermal initiated free radical polymerization on the surface of PVDF hollow fiber membranes. SEM was used to analyze the surface morphology of the membranes before and after polymerization. The polymeric layer in the MIMs was proved by SEM and methanol flux experiments. The modules were assembled to detect the MIMs'separation performance for THO and TB. The concentrations of the filtration were determined by HPLC. The optimum HPLC conditions for determining the concentrations of THO and TB in the methanol solution were obtained, with Symmetry C18 as column, acetonitrile-water (1:9) as the fluid phase,275nm as the determining wavelength and 1mL/min as the flow rate. The linear regression equation for high concentration were Y=3.186×106X-1.025×105 (r=0.9999, injection amount 0.09-1.35μg) for THO and Y=3.011×106X-4.092×104 (r=0.9998, injection amount 0.036-0.36μg) for TB. The linear regression equation for low concentration were Y=2.634×106X+7627.7 (r=0.999, injection amount 0.01-0.2μg) for THO and Y=3.13×106X-5511.29 (r=0.999, injection amount 0.01-0.2μg) for TB. Meanwhile, the effect of concentration and acetic acid content in extraction solution on the filtration results was discussed. And it showed that the selectivity of the MIMs decreased with the increase of the concentration of the initial solution and the acetic acid content in extraction solution.Finally, the separation effect of Cu(Ⅱ) and MIMs was studied and the results showed that the existence of Cu(Ⅱ) could effectively increased the separation effeciency and complete separation of THO and TB could be achieved. Cu(Ⅱ) complex interation was more stronger than hydrogen bond. Under the existence of Cu(Ⅱ), PVDF supporting membrane can also separate THO and TB. The combination of Cu(Ⅱ) complex effect and PVDF supporting effect combined to separate THO and TB has industrial application potential.