Study On The Construction Of3D Graphene Composite And Its Application In Sensor

Electrochemical sensors have become the hot field in analytical chemistry owing to itsadvantages of simple preparation, high sensitivity, easy miniaturization and so on. It is shownthat sensing material plays an important part in deciding the performance of electrochemicalsensor. Graphene, with unique electrical, magnetic and optical properties, is playing anincreasingly important role in electrochemical sensor. However, the inherent electrochemicalproperties of graphene are far from reflected because of the insufficient of graphene inelectronic conductivity and mass transfer rate. We realize the obvious improvement andfunctionalization in electronic conductivity and mass transfer rate successfully byconstructing the three-dimensional graphene and complexing with layered double hydroxides.The thesis relates to the preparation of materials, the study on electrochemical properties andthe application in electrochemical sensors.Graphite oxide was fabricated by oxidating and exfoliating natural graphite through animproved Hummers method. Graphite oxide and polystyrene colloidal microsphere (PS) weredispersed in deionized water with the help of ultrasonic wave to form a stable dispersion.Then the ammonia and hydrazine were added into the dispersion to reduce graphene oxideand form the PS wrapped with graphene nanosheet. The above product was further treated intoluene to remove PS, followed by alkali corrosion in6mol·L-1KOH and high temperaturepyrolysis, obtaining the three-dimensional graphene nanosheets (3D-GNS). Besides, westudied the specific surface area, conducticity and electrochemical properties. It was foundthat the agglomeration of graphene was avoided because of the3D structure, leading to thespecific surface area up to1526.6m2·g-1. The graphite oxide was fully reduced by hightemperature pyrolysis in reducing atmosphere which effectively improved the electronicconductivity, making the conducticity up to10650.8S·m-1. Potassium hydroxide activationled to the formation of many holes which greately increased the transmission rate ofelectrolyte ions.The3D-GNS was dispersed in deionized water by ultrasonic wave, then hydrothermalmethod was used to the formation of3D graphene/nickel-aluminium layered doublehydroxide (3D-GNS/Ni-Al LDH) nanocomposite, in which nickel nitrate, aluminum nitrateand urea were respectively used as nickel, aluminum and alkali sources. In oder to improvethe conditions of the synthesis of3D-GNS/Ni-Al LDH composite, electrochemical functiontests was used to obtain optimal reaction conditions by comparing3D-GNS/Ni-Al LDHsynthesized in different polarity media and with varying contents of3D-GNS. Infrared,Raman, X-ray diffraction, scanning electron microscopy, transmission electron microscopyand galvanostatic charge-discharge measurement were used to investigate the structure, morpholoy and electrochemical property, respectively. It was found that Ni-Al LDHnanoflakes were well dispersed in the wall of3D-GNS. When using90%ethanol and the3D-GNS content being10.56%, the composite provided the most excellent electrochemicalproperties. The3D-GNS/Ni-Al LDH as the electrode materials offered the specificcapacitance of2684.3F·g-1at the current density of1A·g-1, while the specific capacitanceremained1368.8F·g-1when the current density increased up to30A·g-1. The value wasabove95%of capacitance retention after1000cycles. The above-mentioned datas indicatedthat the composite was of high electrochemical activity, good conductivity and excellentelectrochemical stability.The aboved3D-GNS/Ni-Al LDH was used to decorate the surface of glassy carbonelectrode (GCE). The non-enzyme sensor was prepared using the redox reaction property ofNi-Al LDH. Cyclic voltammetry and differential pulse voltammetry were employed to detectthe hydrogen peroxide. It was found that3D-GNS/Ni-Al LDH had good response tohydrogen peroxide, and it had a linear relationship within the scope of5.0×10-7~5.0×10-5mol·L-1, the detection limit was1.7×10-7mol·L-1(S/N=3) and the recovery rate was between95.0%~105.0%. The hydrogen peroxide senor prepared in this method was simple withfavorable stability and repeatability.