Preparation Of Hierarchical Porous Metal-Organic Framework And Its Application In Enzyme Immobilization And Adsorption

Metal-Organic Frameworks（MOFs）have attracted much attention from researchers because of their designable and easily tunable ordered structures,high porosity,and high specific surface area.However,the microporous structure of most MOFs is only suitable for the separation and adsorption of small guest molecules,hindering the diffusion of large molecules to the active site of MOFs.Therefore,the introduction of mesopores into microporous MOFs to form hierarchical porosity not only preserves a certain degree of microporous structure and ensures a high specific surface area,but also enlarges part of the pore size,which helps to provide the required accessibility space to molecular species and minimizes diffusion barriers and increases the adsorption capacity.Therefore,hierarchical porous MOFs combine the inherent properties of MOFs and the advantages of multistage pore materials,which can be applied in catalysis,adsorption,sensing,enzyme immobilization,etc.Based on this,two hollow hierarchical porous MOFs were synthesized to immobilize Candida rugosa lipase（CRL）and as biosensors for detecting nitrofen.And nickel metal-doped hierarchical porous MOFs were synthesized for the adsorption of tetracycline.The hollow MOFs have large internal voids to accommodate large molecule bioenzyme,and the hierarchical porous shell helped the entry of large molecules to achieve high loading rate,while the shell layer provided a microenvironment for the enzyme and can protect it.The hierarchical porous MOFs doped with metallic nickel not only add additional metal sites,but also the hierarchical porosity improved the active sites,and the combined effect of both improved the adsorption capacity of tetracycline.The specific results of the study were as follows:（1）Hollow hierarchical porous Ui O-66-NH₂（HH-Ui O-66-NH₂）was obtained by hydrothermal etching,and the composition structure,morphology,and pore size distribution of the sample were confirmed by a series of characterizations such as FT-IR and XRD.Then HH-Ui O-66-NH₂ was used to immobilize CRL,and the enzyme loading was significantly higher compared with the microporous original Ui O-66-NH₂.The enzyme loading obtained under optimal conditions was 263.62 mg·g^-1,and the V_max and K_m were calculated by the Michaelis equation to be 0.103 m M·min^-1 and 3.22 m M,respectively.The cycling experiments showed that the CRL immobilized in HH-Ui O-66-NH₂ was able to maintain its initial activity by 50%after the 8th cycle.As a biosensor for the detection of nitrofen,its linear range was（0-90μM）with a LOD of 1.04μM.（2）Using cuprous oxide as the template and providing metal source ions to synthesize the core-shell structure Cu₂O@Cu-BTC,and then the template was removed by etching to obtain the hollow hierarchical porous Cu-BTC（HH-Cu-BTC）.The composition structure,morphology,and pore size distribution of the sample were confirmed by a series of characterizations such as FT-IR and XRD;then HH-Cu-BTC was used to immobilize the lipase,and the optimum enzyme loading was obtained as 188.37 mg·g^-1.The V_max and K_mwere calculated by the Michaelis equation as 0.121 m M·min^-1 and 2.95 m M,respectively.In the stability experiments,the immobilized enzyme showed higher stability than the free enzyme;As a biosensor for the detection of nitrofen,its linear range was（0-78μM）and LOD was 1.15μM.（3）Ni（Ⅱ）-doped hierarchical porous Cu-BTC was synthesized using a template-free method and the introduction of metallic Ni（Ⅱ）.The successful synthesis of the material and the successful doping of Ni（Ⅱ）were demonstrated by XRD,FT-IR,EDS,etc.The Ni-HP-Cu-BTC was used for the adsorption of tetracycline,and the adsorption experiments showed that the adsorption capacity was up to 170 mg·g^-1 when the molar ratio of doping amount Ni:Cu was 1:2.and the adsorption kinetics and adsorption isotherms were in accordance with the quasi-secondary kinetic equation and Freundlich equation.