Preparstion Of Metal-organic Framework-enzyme Integrated Nanocatalys And Their Performance In Degradation Of Organophosphate Nerve Agents

Metal-Organic Frameworks(MOFs)have received much attention in the field of enzymes immobilization thanks to their extremely large surface area,appropriate micro-porous pores,and highly ordered crystal structures.However,the pores of MOFs generally belong to micropores,and most of the enzyme molecules are larger than 2 nm in diameter,so the microporous structure is one of the problems that restrict the MOFs material as the universal enzyme support.Meanwhile,MOFs as a kind of highly efficient inorganic catalyst with uniform and confined catalytic sites,size-,shape-and enantioselectivities have high research value in the synthesis and degradation of complex macromolecules.In this paper,a series of integrated nanocatalysts were constructed by using biocatalysts and MOFs catalysts,and applied to the degradation of organophosphate nerve agents.The main contents were descried as follows:Firstly,the core-shell magnetic hierarchically porous Zr-MOF(HP-UIO-66@C/Fe2O3)was synthesized with strong acid-resistant magnetic porous carbon(C/Fe2O3)as magnetic core and dodecanoic acid as soft template.The prepared HP-UIO-66@C/Fe2O3 are monodisperse spherical particles with a diameter of about 180 nm,an average pore size of 5.5 nm,a specific surface area of 386 m~2/g,and a saturated magnetic property of 40.2 emu/g,respectively.The immobilization of organophosphorus hydrolase(OPH)was achieved by physical adsorption,and the immobilized OPH(OPH@HP-UIO-66@C/Fe2O3)was applied to the degradation of organophosphorus nerve agents,namely organophosphate nerve agents(Methyl parathion as the substrate mimetic)were degraded into p-nitrophenol.Compared to free OPH,OPH@HP-UIO-66@C/Fe2O3 presented much wider p H scope,better stability and better tolerance environmental tolerance.Meanwhile,OPH@HP-UIO-66@C/Fe2O3 can be recycled and reused by using external magnetic field.Secondly,the integrated nanocatalyst(OPH@MIL-100(Fe))was constructed by covalently immobilizing OPH onto MIL-100(Fe).This nanocatalyst can degrade the organophosphate nerve agents into p-aminophenol by cascade reaction.Compared with p-nitrophenol,p-aminophenol presented lower toxicity.In OPH@MIL-100(Fe),OPH hydrolyzes methyl parathion into p-nitrophenol first,and then MIL-100(Fe)hydrogenates p-nitrophenol into p-aminophenol in the presence of sodium borohydride.MIL-100(Fe)can also act as support for OPH immobilization,which makes separation and reuse of OPH easy.The morphology,structure and composition of OPH@MIL-100(Fe)were characterized by confocal laser scanning microscopy,scanning electron microscopy and X-ray diffraction.The results showed that OPH@MIL-100(Fe)was synthesized successfully and the OPH was immobilized by covalent binding.On this basis,the effects of the ratio of the two catalysts and the immobilization time on the catalytic rate were further explored.The results showed that when the immobilization time was 4 h and the ratio of OPH to MIL-100(Fe)was0.053:1,the catalytic rate of the nonocatalyst was the highest,which was 1.5mmol/min/g.Finally,0.75 mmol/ml substrate concentration,40 ~oC,p H 9 and 30mg/ml sodium borohydride concentration were selected as the optimum catalytic conditions.OPH@MIL-100(Fe)also showed good reusability,stability and substrate universality.Lastly,ZIF-67 was prepared by hydrothermal synthesis,and then the magnetic porous carbon material(C/Co)containing Co was synthesized by pyrolysis of ZIF-67under nitrogen atmosphere.After modifying C/Co with glutaraldehyde,OPH was immobilized covalently into C/Co to obtain magnetic integrated nanocatalyst(OPH@C/Co).The results show that the maximum catalytic rate of OPH@C/Co was46-fold that of OPH@MIL-100(Fe).The magnetic properties of C/Co itself allow OPH@C/Co to be easily separated by external magnetic forces rather than costly filtration or centrifugation.The feasibility of the cascade reaction was explored using the separate experiment.Moreover,the results show that the addition of sodium borohydride after the completion of the first step of the cascade reaction can make OPH@C/Co exhibit the higher degradation rate and degradation rate.OPH@C/Co exhibits better reusability and stability than OPH@MIL-100(Fe).