One-pot Electrospun Precious Metal Nanoparticle-containing ZnO Nanofiber For Non-enzyme H₂O₂ Sensor

H₂O₂ detection is of great importance in the fields of bioanalysis,medical safety and environmental protection.The electrochemical method for H₂O₂ determination has the many advantages of high selectivity,good stability,high sensitivity,fast detection and low cost.However,the common enzyme electrode method limits the broad application due to the disadvantages such as easy deactivation,high cost,and thermal instability.Therefore,it is necessary to find a new type of non-enzyme sensing material to replace enzyme.As a non-enzyme electrocatalyst,ZnO nanomaterials have been widely studied for their high catalytic activity,good biocompatibility,strong anti-interference ability and good stability.Precious metal nanoparticles?Au,Ag and Pt,etc.?have the characteristics of large surface volume ratio,high electric conductivity,good biocompatibility,good catalytic performance and high surface reactivity.The preparation of nanocomposites with precious metals combined with ZnO can effectively enhance the conductivity and electron transfer ability of ZnO and improve the performance of electrochemical sensors.In recent years,the Au?Ag?-ZnO nanocomposites of different structures were synthesized such as nanosheets,nanorods,nanoparticles and nanofibers to improve the electrical conductivity and electrochemical performance of composites.Nanofibers have the unique characteristics of high aspect ratio,large specific surface area and good electrical conductivity,suitable for electrochemical sensing.Electrospinning technology is one of the simplest and most effective methods to prepare the composite nanofibers,because the composition of precursor solution can be adjusted flexibly.In this paper,a nanofiber precursor is obtained by one-pot electrospinning a mixture of polyacrylonitrile?PAN?,polyvinylpyrrolidine?PVP?,zinc acetate and silver nitrate?or chloroauric acid?,followed by high temperature calcination to obtain a precious metal-ZnO nanocomposites.By adjusting the metal-Zn molar ratio,the fiber configuration,morphology and conductivity characteristics were characterized by various techniques.As a non-enzyme sensing material,the composite nanofiber modified glassy carbon electrode was applied for the determination of H₂O₂.The main results and conclusions are as follows:Under the optimized electrospinning conditions,Ag-PAN-PVP-Zn?Ac?₂ precursor fiber was prepared in one pot by mixing polyacrylonitrile?PAN?,polyvinylpyrrolidine?PVP?,zinc acetate and silver nitrate;following the high temperature calcination,Ag-ZnO nanocomposite fibers with uniform particle distribution were obtained.Through scanning electron microscopy and transmission electron microscopy characterization,it was found that the Ag-ZnO nanostructures were much related to the Ag/Zn molar ratio in the precursor solution.When the Ag/ZnO molar ratio was 0.16,Ag-ZnO exhibits a uniform and continuous nanofiber structure with good fiber continuity,high aspect ratio,and uniform distribution of Ag nanoparticles.X-ray photoelectron spectroscopy and X-ray diffraction characterization prove that Ag particles in the Ag-ZnO nanocomposite fibers exists in a face-centered cubic crystal structure,while ZnO exists in a hexagonal wurtzite crystal structure.The Ag-ZnO modified glassy carbon electrode?Ag-ZnO/GCE?was prepared by drop-coating the dispersion of Ag-ZnO nanocomposite fiber.Cyclic voltammetry and electrochemical impedance analysis indicate that the Ag-ZnO nanofibers have good conductivity and electron transfer ability.The cyclic voltammetry and time current curves show that the corresponding Ag-ZnO/GCE?Ag/Zn molar ratio of 0.16?has a highly sensitive catalytic response to H₂O₂ reduction.Ag-ZnO nanofibers were used as sensing materials for H₂O₂ detection.In the concentration range of 1×10^-55 M⁴×10^-33 M,there is a good linear relationship between current and H₂O₂ concentration.The detection limit is 0.3×10^-66 M?S/N>3?.Chloroauric acid,as a starting material of noble metal nanomaterials instead of AgNO₃,was mixed with DMF solution containing polyacrylonitrile?PAN?,polyvinylpyrrolidine?PVP?and zinc acetate to obtain the electrospinning precursor solution.The Au-PAN-PVP-Zn?Ac?₂ nanofiber precursor was prepared by one-pot electrospinning,and following the calcination,the Au-ZnO nanocomposite fibers were fabricated.The Au/Zn molar ratio in the precursor solution was adjusted to study the effect of Au content on the fiber structure.Scanning electron microscopy and transmission electron microscopy reveal that when the Au/Zn molar ratio is 0.24,the corresponding Au-ZnO nanofibers maintain a uniform and continuous fiber structure with a fiber diameter of approximately 150 nm.The fiber is mainly composed of interlinked ZnO small crystals,which is much smaller than that those in Ag-ZnO and Au nanoparticles with the size of20 nm are aligned along the ZnO fiber.The TEM-EDX elemental mapping further confirms the even distribution of Au nanoparticles around the fiber surface.Compared with Ag-ZnO nanocomposite fibers,Au-ZnO has a longer aspect ratio and more uniform distribution of metal nanoparticles.The composition and crystal structure of Au-ZnO nanocomposite fiber samples were analyzed by X-ray photoelectron spectroscopy and X-ray diffraction.It proved that Au and ZnO in Au-ZnO nanocomposite samples were in the face-centered cubic crystal Au and hexagonal wurtzite ZnO crystals,respectively.The Au-ZnO modified electrode?Au-ZnO/GCE?was prepared by drop-coating the Au-ZnO nanocomposite dispersion.The cyclic voltammetry and electrochemical impedance analysis showed that Au-ZnO nanofibers has better conductivity and electron-transfer ability than Ag-ZnO nanocomposites.Cyclic voltammetry and current-time?I-t?curves demonstrate the catalytic response of Au-ZnO/GCE to H₂O₂ reduction is more sensitive than that Ag-ZnO/GCE.As a sensing device of H₂O₂ detection,it was found that there existed a good linear relationship between current response and H₂O₂ concentration in the H₂O₂concentration range of 1×10^-66 M⁶×10^-33 M,and the detection limit arrived at 0.1×10^-66 M?S/N>3?.It has a wider detection range and 3 times lower detection limit than that of the Ag-ZnO electrode.It demonstrates that the Au-ZnO nanocomposite fiber has higher ability to catalyze the reduction of H₂O₂ due to the more uniform distribution of Au nanoparticles along ZnO fibers.The electrode has good stability and strong anti-interference ability.It has great potential for the application of non-enzyme H₂O₂ sensor.