In-Situ Growth Of Au@WO₃ And Study Of Their Peroxidase-like Activity

As an important reaction intermediate,hydrogen peroxide is very important.Till now,some methods have developed to sensing H2O2,such as fluorescence analysis,polarographic analysis,spectro photometry and so on.Because H2O2 can be oxidized using peroxidase by which we can determine the concentration of H2O2.However,natural enzymes bear some drawbacks.For example,the catalytic activity of enzyme is very sensitive to the environmental changes,and leads to a poor operational stability due to their denaturation and digestion,as well as the high costs in preparation and purification limit their application.A solution to this problem is offered by the rapidly advanced nanotechnology,from which lots of artificial complexes have emerged as mimic enzyme due to their high surface energies and large surface-to-volume ratios.In comparison with natural enzymes,nanomaterials based mimic enzyme exhibits high stability against harsh reaction conditions.Meanwhile,they possess additional advantages of controlled preparation at low cost,flexibility in structure design and composition,and tunable catalytic activities.The artificial simulation enzyme instead of natural enzyme can solve the above problem very well.Based on the above analysis,this work studies the preparation of Au nanoparticles decorated WO3(Au@WO3),and its application in the hydrogen peroxide catalytic as superoxide simulated enzyme.The first chapter gives a brief describe for the concept,properties and applications of nano-tungsten oxide and Au nanoparticles,and introduce how to prepare and apply the above materials.In the end,we give a brief summary for the significance and goals of this study.In the second chapter,noble metal/WO3 nanocomposite is prepared and characterized.In this work,we applied a one-step solution-phase method to prepare tungsten oxide.In this method,WCl6 was dissolved in ethanol and heated at 180℃ for 24 h in a teflon-lined stainless-steel autoclave,and a dark blue urchin-like WO2.72 nanostructure was successfully formed.Based on the weak reducing property of WO2.72,noble metal can be reduced on the surface through an in-situ redox reaction between WO2.72 and the noble metal salt precursors in aqueous solution to form Au@WO3 nanocomposite.The as-resulted Au@WO3 nanocomposite keeps the urchin-like morphology.The advantage of this work is no additional reducing agents or stabilizing agents is required,thus can avoide the introduction of impurities and ensure the purity of metal/WO3 interface。The samples were characteristics by XRD,SEM,TEM and UV-vis analysis methods to show crystal phase,surface morphology and optical absorption properties.In the third chapter,the Au@WO3 nanocomposite was applied as artificial mimic enzyme and its catalytic kinetics were studied in detail.Firstly,qualitatively studies showed that only Au@WO3 had good peroxidase-like activity based on the color reaction of TMB as the chromogenic reagent.However,the nanostructured WO3 and WO2.72 didn’t show any peroxidase-like activity.Then,the influences of pH and operation temperature on the catalytic activity of Au@WO3 were optimized.The peroxidase-like activity of Au@WO3 nanocomposite was further studied.The obtained data were then fitted to the michaelis-Menten model and Lineweaver-Burk plot,by which the catalytic parameters Km and Vm were calculated accordingly.The above work extends the application potentials of Au@WO3,and provides a good direction for the preparation and application of noble/WO3 nanocomposites.