Preparation Of Molecularly Imprinted Membrane And Studies On Characteristic Of Its Molecule Recognition And Performance Of Permeability

Membrane separation technology as a new type of science and industrialtechnology has been widely used in many fields. However, current commercialmembranes are all based on screening and unable to achieve selective separation forspecific substance from the perspective of material separation. Molecule imprintedmembrane(MIM) combine the specific recognition of MIPs to template with thecharacteristics of continuous operation of membrane separation, providing an effectiveroute for selective separation for specific substance. Through the idea of moleculedesign, we have synthesized molecularly imprinted graft-membrane(MIGM) with thetemplate cytisine and matrine based on polysulfone(PSF), using the new surfaceimprinted technology established by our research group. The binding characteristic ofthe MIGM membrane for the template molecule and the performance of permeationand separation of the MIGM membrane as well as the permeation mechanism weremainly examined and investigated. The MIGM we have prepared is a new kind ofimprinted membrane which has good performance in osmotic permeation for templatemolecule. It has both the characteristic of high permeation and excellent mechanicalproperties of molecularly imprinted composite membrane, and the advantage of stablechemical property of molecular imprinted monolithic membrane. The results of thispaper have important scientific significance and applicable value for the promotion ofthe development of MIM technology and the standard of separation and purificationtechnology for alkaloids.Polysulfone was first chloromethylated with the chloromethylation reagent1,4-dichloromethoxybutane(BCMB), resulting in chloromethylated polysulfone (CMPSF). The casting solution of CMPSF was formed withN,N-dimethylacetamide(DMAc) as solvent, and PEG-400as pore-foaming agent wasadded. The asymmetric porous membrane CMPSF was formed by phase inversion. Thefilm consist of a dense skin layer which have rich nanopores and large poroussupporting structure. And then the amination (AM) membrane AMPSF was obtainedvia the substitution reaction between the chloromethyl group on CMPSF membrane andethanediamine(EDA). After that, with the initiator (NH4)2S2O8the radical wereproduced on and the graft-polymerization of methacrylic acid (MAA) was carried outby the initiating of the surface-initiating system of-NH2/S2O82-, obtaining the graftedfunctional membrane PSF-g-PMAA. The effects of main factors on thegraft-polymerization of MAA were investigated, and the reaction conditions wereoptimized. The grafted membrane of PSF-g-PMAA was characterized by infraredspectroscopy (FT-IR) and optical microscope(OM) as well as weighing method. Finally,the adsorption character of the grafted membrane of PSF-g-PMAA for two alkaloids,oxymatrine and cytisine, was examined. The experimental results showed that by usingsurface-initiating system of amino group/peroxysulphate, the graft-polymerization ofMAA on the surface of the aminated membrane, AMPSF membrane, can smoothlycarried out, and the grafting degree of PMAA increases with the content of aminogroup on the basement membrane AMPSF. The suitable temperature for thegraft-polymerization of MAA is50℃, and the appropriate concentration of theinitiator peroxysulphate in the solution is1.0%of the monomer mass. Under theoptimum conditions, the grafted membrane PSF-g-PMAA with a PMAA graftingdegree of4.62mg/cm2can be gained. The functional grafted membrane PSF-g-PMAAcan produce strong adsorption action for alkaloid compounds. By right of thesynergism of electrostatic interaction and hydrogen bonding, and in neutral solution,the adsorption capacities of the functional grafted membrane PSF-g-PMAA can reach2.03mg/cm2for oxymatrine and1.35mg/cm2for cytisine, respectively. This laid agood foundation for carrying molecular imprinting of alkaloids on the surface of the grafted membrane PSF-g-PMAA.Based on the above research, the polysulfone-based molecularly imprintedmembrane with graft-type MIGM was prepared with cytisine as template molecule andwith ethylene glycol diglycidyl ether (EGDE) as crosslinker. By right of the ringopening reaction between the epoxy group of the crosslinker and the carboxyl ofPMAA, the chains of PMAA are cross-linked and the surface molecular imprinting ofcytosine was realized. The graft-type MIGM was prepared after template was removed.On the basis of characterizing the pore structure of MIGM membrane with scanningelectron microscope and the chemical composition with the FT-IR, the bindingcharacteristic of the MIGM membrane for the template molecule and the performanceof permeation and separation of the MIGM membrane were mainly examined andinvestigated. The investigation results show that the imprinted membrane MIGM hasspecific recognition selectivity and excellent binding affinity for the template cytisinemolecule, and relative to the contrast alkaloids, oxymatrine and matrine, thecoefficients of selectivity of membrane MIGM towards cytisine are6.92and5.17,respectively. The imprinted membrane MIGM can produce fine “gate effect”, whichcomes from its structural characteristics, and exhibits higher permeation selectivity forthe template molecule. For a mixed solution of cytisine and oxymatrine, the separationfactor of the imprinted membrane MIGM for cytisine gets up to8.3.The graft-type MIGM for matrine was also investigated in the same way. MIGMwas prepared with matrine as template molecule and with ethylene glycol diglycidylether (EGDE) as crosslinker. By right of the ring opening reaction between the epoxygroup of the crosslinker and the carboxyl of PMAA, the chains of PMAA arecross-linked and the surface molecular imprinting of cytosine was realized. Thegraft-type MIGM was gained after template was removed. The membrane wascharacterized by FT-IR, OM and SEM. the binding characteristic of the MIGMmembrane for the template molecule and the performance of permeation and separationof the MIGM membrane were mainly examined and investigated. The investigation results show that the imprinted membrane MIGM has specific recognition selectivityand excellent binding affinity for the template cytisine molecule, and relative to thecontrast alkaloids, cytisine, the coefficients of selectivity of membrane MIGM towardsmatine is3.62. The imprinted membrane MIGM can produce fine “gate effect”, whichcomes from its structural characteristics, and exhibits higher permeation selectivity forthe template molecule. For a mixed solution of cytisine and matrine, the separationfactor of the imprinted membrane MIGM for matrine gets up to8.3.