Preparation Of Mesoporous Zr-based MOF Based On Biomimetic Mineralization And Its Application In Enzyme Immobilization

Global catalyst industry worth nearly$20 billion,nearly 80 percent of consumer goods production stage requires a catalyst,the catalyst demand growing steadily in recent decades,and it is expected to continue growing in the future.Laccase,horseradish peroxidase,cellulase distributed as widely on earth,and have good catalytic efficiency of the catalyst,it has already been applied to many fields.But there can not be duplicate natural enzymes catalyze,over-reliance on the environment and other shortcomings,its application has been hampered.A number of strategies have been developed in recent years to improve enzyme stability and its catalytic properties.Among them,metal organic frameworks（MOFs）have been extensively studied as enzyme immobilization supports.How to obtain a MOF-enzyme biocomposite catalyst with high catalytic efficiency,low operating cost and high stability is of great significance.This article is based on physical adsorption method to immobilize laccase,horseradish peroxidase and cellulase on mesoporous MOF in order to improve the catalytic activity and stability of the enzyme.Specific studies are as follows:（1）In the experiment,natural polymer polysaccharide（dextran 1500）was used as template agent,and the mesoporous Zr-MOFs carrier material with appropriate pore size was constructed by biomineralization method,which was successfully used to enhance the adsorption strength of PVP modified cellulase on the carrier surface,and greatly improving the stability of the immobilized enzyme.The surface area of the mesoporous CD-UIO-66-Zr was 633.89 m² g^-1 and the pore size was 4.617 nm.The short axis of cellulase（3.7 nm）can be partially inserted into the pores of CD-UIO-66-Zr which enhance the adsorption strength of cellulase on the surface of CD-UIO-66-Zr.Under optimized conditions,the maximum adsorption capacity of PVP-cellulase@CD-UIO-66-Zr was 265 mg g^-1.The"encapsulation"of PVP on cellulase was beneficial to enhance the anchoring effect of cellulase on CD-UIO-66-Zr.Compared with free cellulase,PVP-cellulase@CD-UIO-66-Zr had great p H stability,thermal stability,storage stability,cycle stability and catalytic efficiency.PVP-cellulase@CD-UIO-66-Zr was incubated at p H 8.0 or 80℃for 1 hour,and 80%of the enzyme activity can be retained.When PVP-cellulase@CD-UIO-66-Zr was stored at 4℃for 30 days,the enzyme activity retention rate was 63%;after 8 cycles,the enzyme activity was remained 83%.In addition,the catalytic efficiency of PVP-cellulase@CD-UIO-66-Zr was 1.79 times higher than that of the free enzyme.（2）In the experiment,three different graded mesoporous CB-UIO-66-Zr（6.46 nm,7.55 nm,10.80 nm）materials were prepared by altering the amount of BSA template to immobilize laccase,horseradish peroxidase and cellulase respectively.Experiments have founded that when the enzymes were immobilized on three carrier materials with different pore sizes,as the size of the enzyme increased,the amount of enzyme immobilized gradually decreased.Compared with the other two carrier materials,CB_0.5-UIO-66-Zr had the highest adsorption capacity for the three enzymes.In addition,the p H stability,thermal stability,and organic solution tolerance of the three immobilized enzymes have been significantly improved.laccase@CB-UIO-66-Zr,HRP@CB-UIO-66-Zr and cellulase@CB-UIO-66-Zr can respectively retain 70%,81%and 77%of the original enzyme activity after 10,8 and 10 cycles.Through the study of catalytic reaction kinetics,it was found that the catalytic efficiency of laccase@CB-UIO-66-Zr was equivalent to the free laccase;the substrate affinity of HRP@CB-UIO-66-Zr and cellulase@CB-UIO-66-Zr was increased.At the same time,the catalytic efficiency of HRP@CB-UIO-66-Zr and cellulase@CB-UIO-66-Zr was respectively1.96 times and 1.57 times higher than the corresponding free enzymes.And it was founded that the adsorption of CB-UIO-66-Zr to laccase,horseradish peroxidase and cellulase were all spontaneous adsorption processes.The laccase@CB-UIO-66-Zr was highly consistent with the pseudo-first order adsorption kinetic model,HRP@CB-UIO-66-Zr mainly followed the kinetic model of diffusion adsorption inparticles,and the cellulase@CB-UIO-66-Zr’s major adsorption rate was mainly affected by the adsorption steps.