Preparation Of Mesoporous Metal-organic Frameworks And Its Application In Enzyme Immobilization

Enzymes are“chips”in green biomanufacturing.As biocatalysts,enzymes can synthesize various chemicals.Compared with chemical catalysts,enzymes have the advantages of high selectivity,high specificity,and operation under mild conditions.However,due to the fragility of the enzymes,it is easily to be denatured or deactivated inactivated influenced by the environment.As a result,it is highly desirable to explore efficient solid carriers that can maintain the enzyme activity,enhance its operational stability,and facilitate its separation and reuse for industrial applications.Metal-organic frameworks（MOFs）which feature high specific surface area and tunable pore structure,have broad applications as solid carriers for enzyme immobilization.However,most of the current MOFs have microporous channels（<2 nm）,and enzyme molecules usually have large dimensions of at least 3-5 nm.So the direct immobilizaion of enzymes into MOFs still remains a big challenge.In this thesis,we have designed and synthesized metal-organic frameworks with mesoporous structure.Inspired by molecular imprinting technology,a new“physical imprinting”method was develped for the preparation of mesoporous MOFs that were suitable for enzyme immobilization.The main research results of this thesis include:（1）Preparation of mesoporous metal-organic frameworks.Proteins with different molecular weights,cytochrome c（Cyt c）,horseradish peroxidase（HRP）,lipase,and bovine serum albumin（BSA）were selected as the template molecules.The proteins were encapsulated as a template during the co-precipatation synthesis of ZIF-8.Then,the protein template was removed by calcination to generate mesopores in ZIF-8.Scanning electron microscopy images revealed that ZIF-8 had the same morphology before and after calcination,which was rhombic regular dodecahedron.Transmission electron microscopy images and pore size distributions confirmed that the resultant mesoporous MOFs had an average pore size of 10.32-20.15 nm.（2）Study of enzymatic catalysis performances of enzymes immobilized in mesoporous MOFs.Mesoporous MOFs were used as solid carriers to immobilize enzymes.Energy-dispersive X-ray analysis showed the uniform distribution of sulphur element in MOFs,confirming the successful immobilization of the enzymes in mesopores.The immobilization capacity of enzymes in HZIF-8_[Enzyme]is about twice of that immobilized in HZIF-8_[BSA],indicating the selectivity of mesopores towards its template.By comparing the enzymatic activities of the immobilized enzymes and free enzymes,it is observed that mesoporous MOF can enhance its operational stability and improve the enzymatic activity to some extent due to the confinement effect of the mesopores.For example,the enzymatic activities of Cyt c and lipase after immobilization were increased by about 16.7-and1.9-times compared with free enzymes.The catalytic efficiency of immobilized enzymes was also significantly improved by 20-and 21-fold.At the same time,the enzymes immobilized in mesoporous MOFs showed exceptional stability in strong acid and alkaline,and high temperature conditions.The residual enzyme activity was still 80%after 18 cycles of repeated use.