Fabrication And Investigation Of Nanostructured Cupric Oxide Composites As Electrode Materials For Non-enzymatic Glucose Sensing

Glucose sensor has always been a hot topic in the field of chemical and biological sensor.Particularly, the non-enzymatic glucose sensor for the direct electrochemical oxidation of glucose with the favorable features of lifetime stability and low cost has attracted more and more attentions, recently. Particularly, the electrode materials of non-enzymatic glucose sensors based on the transition metal oxides with special electronic structure of unfilled d-track and unpaired d-electron have demonstrated excellent electrochemical catalytic activity,which have been widely designed and used for enzyme-free glucose sensor, such as Co3O4,NiO, CuO, etc. Among these metal oxides, CuO as a common semiconductor material not only presents excellent electrical catalytic activity but also possesses the properties of cheapness, non-toxic, easy to produce, etc, therefore, widely investigating as electrode materials for non-enzyme glucose sensor. It is well known that the redox ability, mass transfer rate, structure size as well as conductivity of CuO will have a large influence on the catalytic activity. Notably, reducing the size of CuO to prepare nanostructured CuO can effectively improve the specific surface areas and greatly shorten the ion diffusion length. This can increase the accessible surface areas of the electrode materials with glucose solution to improve the electrochemical catalytic activity. Taking these above into account, this paper pays most focus on the preparation of different nanostructured CuO composites,morphological/structural control as well as mechanism investigation as the following aspects.（1） Ultra-long one-dimensional CuO/Cu₂ O composite nanofibers have been fabricated successfully by the electrospinning technique and hydrothermal reduced reactions. The as-prepared CuO/Cu₂ O composite nanofibers presented the properties of multiple oxidation states of Cu（II）/Cu（I）, large length to radius ratio, and ultra-long one-dimensional nanostructures, the synergistic effects of which could facilitate the redox reactions, increase the accessible surface areas, shorten the ion diffusion length, and achieve rapid charge transfer along the longitude direction, contributing to the electrochemical activity. Thus, the CuO/Cu₂ O composite nanofibers as electrode materials for non-enzymatic glucose sensor have demonstrated high sensitivity, strong anti-interference as well as wide detected range for glucose.（2） CuO/Cu₂ O nano/micro-porous structures have been facilely prepared by combining the vacuum freeze-drying technology and calcination method. It can be seen that the CuO/Cu₂ O nano/micro-porous structures exhibited three-dimensional open and well-interconnected hierarchical porous structures as well as high specific surface areas. As we know, the well-designed porous structures could facilitate the fast solution flow and reduce the ion diffusion length contributing to improve the sensitivity. Moreover, the hierarchical structures could also enhance the accessible surface area and provide abundant electrical catalytic sites, both of which would facilitate the catalytic activity. Notably, in orderto further improve the electrical catalytic ability of the 3D morphology/structure, the CuO/Cu₂ O electrode materials have been optimized by adjusting the concentration of the polymer in precursor solution. It also should be noted that the optimized CuO/Cu₂ O nano/micro-porous structure as template could also be partially reduced by glucose by using hydrothermal method, the products of which with the Cu（II）/Cu（I） multiple oxidation state and hierarchical structures have demonstrated enhanced electrocatalytic activity. Thus, the CuO/Cu₂ O as electrode materials was very promising for high sensitivity for the enzyme-free glucose biosensor.（3） The CuO/N-CNFs composites have been facilely and effectively constructed by carbonizing PAN@PANI core-shell nanofibers and hydrothermal reactions. The obtained nitrogen doped hierarchical porous carbon nanofibers（N-CNFs） by carbonizing PAN@PANI nanofibers retained high nitrogen content. As known, the high nitrogen retention would change the chemical characteristics of the surface and result in large accessible surface areas,abundant active sites and high charge transfer rate on the surface of N-CNFs. Furthermore,the good porosity and high specific surface areas could also effectively shorten the ion diffusion length. And the ultra-long one-dimensional nanostructure with good conductivity of N-CNFs could achieve fast electron transport and collect, contributing to the sensitivity. Thus,by decorating the N-CNFs with CuO, the prepared CuO/N-CNFs composites as electrode materials benefiting from the synergistic effects would be beneficial to achieve desirable electrocatalytic activity for non-enzyme glucose biosensor.