Supercritical Fluid-Assisted Fabrication Of Metal Oxides Based On Polymer “Nanoreactors” For Its Performance Investigation As Nanozymes

Natural enzymes have the inherent effect of significantly accelerating the speed of specific chemical reactions in biological processes,thus play an indispensable role in social production,clothing,food,shelter,and other aspects.However,they are mainly made of protein or RNA,resulting in some inherent limitations of natural enzymes,such as high manufacturing and purification costs,difficulties in transportation and storage,and harsh application environment requirements.In order to avoid the barriers of using enzymes,the preparation of nanomaterials with catalytic activities of natural enzyme substrates as artificial enzymes（nanozymes）has become an emerging field of biomimetic chemistry,aiming to design functional nanomaterials that mimic various inherent properties of natural enzymes.This project aims to use the"nanoreactor"constructed by the solution enhanced dispersion（SEDS）method in the supercritical carbon dioxide fluid"nanoreactor"technology to regulate the production of polymer-based oxide nanozymes for the construction of glucose molecular biosensors.Supercritical carbon dioxide fluid technology can make up for the environmental pollution,the complex synthesis steps as well as the cumbersome separation process and other disadvantages in traditional chemical synthesis due to its advantages of lower cost,recyclability,non-toxicity,non-flammability,non-pollution,easy regulation of parameters and lower critical conditions（Tc=304.1 K,Pc=7.38MPa）.In addition,the crystal growth of metal oxides prepared by supercritical"nanoreactors"in the battery anode materials and liquid cell in situ transmission electron microscopy（LC-TEM）was also investigated to expand the application field of supercritical"nanoreactor"products.The specific work is as follows:1.Construction of hollow metal oxide nanoparticles precursor:Firstly,the methanol mixture of manganese（Ⅲ）acetylacetone（Mn（acac）₃）and Polyvinyl Pyrrolidone（PVP）were evenly mixed.Subsequently,the precursor salt nanoparticles were prepared by SEDS under constant pressure and temperature of 15 MPa and 45℃respectively.Field emission scanning electron microscopy（FE-SEM）test results showed that the PVP-coated Mn（acac）₃ nanoparticles prepared by supercritical"nanoreactor"had uniform morphology under these conditions,and the average particle size is 22±28 nm.Subsequently,X-ray powder diffraction（XRD）,Fourier infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）were used to determine the related structural properties of the precursor salts.2.Explore the properties and nanozymes performance of hollow metal oxide nanospheres:The metal oxide nanospheres were directly obtained by one-step calcination of PVP crosslinked Mn（acac）₃ nanoparticles.The hollow structure characteristics of the metal oxides were confirmed by transmission electron microscopy（TEM）.The physicochemical properties of the hollow oxide Mn₂O₃ nanospheres were determined by XRD,FT-IR and Raman spectroscopy.Then,with 3,3’,5,5’-tetramethylbenzidine（TMB）as the color base,the performance of hollow nanozyme simulation catalytic specific substrate,optimal pH and temperature catalytic conditions,enzymatic reaction kinetics,catalytic mechanism and its stability were studied through experimental design.The results showed that hollow Mn₂O₃ nanospheres have the best peroxidase-like catalytic activity at pH 3.5 and temperature 40℃,and follow Michaelis-Menten mechanism.3.Construction of carbon doped metal oxide nanoparticles precursor:Firstly,cobalt nitrate hexahydrate（Co（NO₃）₂·6H₂O）and poly-（methyl vinyl ether-co-maleic anhydride）（PVM/MA）formed a blend solution with acetone at an equal mass concentration gradient from 10%to 60%.Subsequently,the high-pressure vessel was maintained at a constant pressure and temperature of 12 MPa and 35℃using the SEDS method.The FE-SEM results showed that the morphology of these nanoparticles was relatively uniform.4.Explore the properties and nanozymes performance of carbon doped metal oxide nanoparticles:The crystal surface spacing and elemental composition of calcined nanoparticles were determined by TEM combined with element energy dispersive spectroscopy（EDS）.Subsequently,XRD test was used to verify that the calcined nanoparticles have C-doped structural characteristics.XPS test results confirmed the substitution doping form of C.In addition,the structural advantages of C-doped nanoparticles were analyzed by first principles density functional theory（DFT）.After the structural characteristics of C-doped Co₃O₄ nanoparticles were clarified,the performance of hollow nanozymes simulating horseradish peroxidase to catalyze specific substrates,the optimal pH and temperature catalytic conditions,the kinetics of enzymatic reaction,the catalytic mechanism and stability were studied through experimental design using TMB as the chromogenic substrate.Finally,the influence of C doping structure on the activity of peroxide-like enzymes was explored by first principles again.The results showed that C doping was beneficial to promote the catalytic activity of nanozymes.5.A glucose molecular biosensor using hollow metal oxide nanospheres or carbon doped metal oxide nanoparticles as nanozyme catalyst was constructed:The feasibility,anti-interference,stability,and detection limit of the glucose biosensor were studied through experimental design.The experimental results showed that both the hollow Mn₂O₃ nanozymes and the C-doped Co₃O₄ nanozymes could construct stable glucose biosensor with detection limits of 2.31μM and 3.86μM,respectively.In summary,this thesis made full use of the advantages of the supercritical solution forced dispersion"nanoreactor"to construct a nanozyme based on hollow Mn₂O₃ nanospheres and carbon-doped Co₃O₄ nanoparticles,and used these two nanozymes for glucose molecular biosensor.At the same time,the application of Co₃O₄ nanoparticles as seeds on the growth of nanowires in in-situ LC-TEM was preliminarily investigated.It is expected to provide a potential nanomaterial preparation technology and research idea for improving the application conditions of natural enzymes,enriching the construction types of biosensors,and helping to understand the multifunctional applications of supercritical"nanoreactor"products.