Study On Fabrication Of Metal Organic Framework/Polyvinylidene Fluoride Hybrid Membranes And Their Immobilization For Biological Enzymes

Enzyme immobilization with its activity finely preserved has attracted tremendous attention in the fields of biochemistry,biosensor,and biomedicine.Metal-organic frameworks(MOFs)have large specific surface area,ultra-high porosity,uniformity,adjustable frame and structure,and void size of MOFs,and polyvinylidene fluoride(PVDF)is an excellent polymer porous membrane with good biocompatibility.Therefore,combining MOFs with polymer porous membranes to fabricate new solid carries used in the immobilization of enzymes with maintained the catalytic activity and stability of biological enzymes has great significance in enzyme immobilization engineering.In this thesis,zeolitic imidazolate framework(ZIF-8)incorporated polyvinylidene fluoride(PVDF)hybrid membranes(denoted as ZIF-8/PVDF hybrid membranes)were successfully fabricated for effective enzyme immobilization.Three different hybridization methods,including mechanical blending method(A),self-assembly after amination(B),and self-assembly after ligand functionalization(C),were employed to fabricate ZIF-8/PVDF hybrid membranes with various loading amounts of ZIF-8 composites.The morphologies,phases,and constituents of the ZIF-8 nanoparticle functionalized hybrid membranes were investigated by field emission scanning electron microscope(FESEM),X-ray diffraction(XRD),Fourier-transform infrared spectroscopy(FT-IR)and Thermal gravity analysis(TG),respectively.The hydrophobic/hydrophilic properties of the hybrid membranes were also investigated through measuring the surface water contact angle.The immobilization tests of cellulase demonstrated that the equilibrium adsorption capacity of cellulase on the as-prepared ZIF-8/PVDF hybrid membranes is greatly improved in comparison to that of the pure pristine PVDF membrane.In addition,the adsorption capacity of cellulase on ZIF-8/PVDF is correlated with the synthetic method and the loading amount of ZIF-8 nanocrystals.Among them,the ZIF-8/PVDF(A-2)presented the best adsorption activity,which was almost 1.2 times as that of the property on pristine PVDF.Compared to free cellulose,the immobilized enzyme kept activity and meanwhile significantly improved the stability against pH values,temperature and storage days.MIL-101 is a chromium terephthalate-based mesoporous MOFs,which is also applied in the fabrication of MIL-101(Cr)/PVDF hybrid membranes through a physical belnding method,wich is then used in the adsorption of catalase.The adsorption conditions were optimized,and the maximum adsorption capacity was 81.13?g/cm2.The adsorption kinetics fitting results showed that the adsorption of catalase by MIL-101(Cr)/PVDF is more suitable for pseudo-second-order kinetics,and the isothermal adsorption model is more applicable with the Langmuir isotherm model.The activity tests of immobilized enzyme showed that the immobilized catalase maintained its catalytic activity,and meanwhile increases the stability of the catalase against the pH condition and elevated temperature.