Study On The Preparation Of Functional Nanofibers And Their Applications For Enzyme Immobilization

Nanofibers have gained a great deal of attention in recent years due to such properties as high surfacearea per unit mass, remarkable high porosity. The expanding applications of nanofibers include drugdelivery, filtration, tissue engineering and so on. In order to improve the load amount of enzyme andpromote the catalytic character of immobilized enzyme, functional nanofibers were obtained by regulatingthe structures and chemical composition of electrospun nanofibers, which were used as carrier for enzymeimmobilization in this work. In addition, novel enzyme membrane reactor （EMR） was formed on the baseof above work. It was expected that the EMR can integrate the process of biocatalysis and membraneseparation.Amidoxime polyacryonitrile （AOPAN） nanofibrous membranes were generated by the reactionbetween electrospun polyacryonitrile （PAN） nanofibrous membranes and hydroxylamine hydrochloride,which were used as the matrix for metal ions chelation. FTIR spectra of the PAN nanofibers and AOPANnanofibers were recorded for analysis of the surface chemical structures, the surface morphologies of thenanofibers were observed by scanning electronic microscope （SEM）. FTIR spectrum indicated theconversion of the nitrile to the amidoxime group, and the SEM images revealed that the diameter ofAOPAN nanofibers did not change substantially, and the fibrous structures was not distorted obviously onthe optimal condition. According to the results of dynamic contact angle measurement, the wettability ofAOPAN nanofibers have remarkably improved. Chelated amounts of metal ions were calculated byatomic absorption spectrometry （AAS）. Results indicated that the chelated capacities of AOPAN nanofibersto Cd²⁺、Cu²⁺and Fe3+ions were higher than that of AOPAN conventional fibers. Many isothermal modelswere used to analyze the experimental data, the chelated isothermal processes of AOPAN nanofibers werefound to be in conformity with Langmuir model. Adsorption processes of AOPAN nanifibers to metal ionswere confirmed as chemical adsorption in accordance with average adsorption energies. The mechanismsof adsorption processes were described as metal ions were chelated with amidoxime group on the surfaceof AOPAN nanofibrous membrane by coordinate bond.Fe（Ⅲ）-AOPAN nanofibrous membranes were used as carrier for catalases immobilization withcoordination bond. Surface morphologies of the nanofibrous membranes and immobilized catalases wereobserved by fluorescence microscopy and SEM. Enzyme molecules were successfully immobilized on thesurface of Fe（Ⅲ）-AOPAN nanofibrous membranes with coordination bond. Kinetic parameters Vmaxand Kmwere analyzed for both immobilized and free catalases., the results indicated that the immobilized catalaseshad a high affinity with the support. The immobilized catalases showed better resistance to pH andtemperature change than that of free catalases. The storage stability was significantly improved and thereusability was very high after catalases were immobilized onto the surface of Fe（III）-AOPAN nanofibrousmembranes.PVA/PA6composite nanofibers were formed by electrospinning. Cu（Ⅱ）-PVA/PA6metal chelated nanofibers were prepared by reaction between PVA/PA6composite nanofibers and Cu2+solution, whichwere used as the support for catalases immobilization. The result of experiments showed that PVA/PA6composite nanofibers have excellent chelation capacity for Cu2+ions. At the same time, the structures ofnanofibers had not been distorted obviously during the reaction with Cu2+solution. The immobilizedcatalases showed better resistance to pH and temperature inactivation than that of free form, and the storagestabilities，reusability of immobilized catalases were significantly improved. The half-lives of free andimmobilized catalases were8d and24d repectively. Besides, the epoxy PVA/PA6nanofibers weregenerated by epoxidation reaction for catalases immobilization. Comparing the experimental data, theimmobilized catalases on matrix of Cu（Ⅱ）-PVA/PA6nanofibers presented higher activities thanimmobilized catalases on the surface of epoxy PVA/PA6nanofibers.On the base of Fe（Ⅲ）-AOPAN metal chelated nanofibrous membrane and Cu（Ⅱ）-PVA/PA6metalchelated nanofibrous membrane, the EMRs were assembled. The relationships among operating pressure,membrane flux, and conversion ratio of H2O2were investigated, and results showed that the EMRs weresteady, efficient and repeatable.