Preparation Of Graphene And Its Metal Nano-composite Materials By One-step Electrodeposition

Many methods have been proposed for graphene production in recent years,among which the chemical reduction of graphene oxide (GO) obtained from ultrasonicexfoliation of oxidized graphite is the most convenient way to yield large quantities ofgraphene sheets, which makes the method of graphene oxide reduction become amainstream method of preparation of graphene based composite materials. Whenelectrochemical methods were brought into graphene production, toxic chemicalreagents would never be used and materials are not polluted. The proposedelectrochemical methods are environmental friendly but with time consuming anduncontrollable yield. Therefore it is an important subject to simplify operation stepsand improve controllability.In this paper, a green and controllable method is proposed for one step synthesisof graphene and its nano composite materials. Structures and performances of thematerials are characterized by scan electronic microscopy and electrochemicaltechnologies, and application of the materials in sensors is investigated.Details are summarized as follows:(1) Preparation of graphene by direct electrodeposition from graphene oxide:graphene oxide was obtained by ultrasonic exfoliation of oxidized graphite that wassynthesized by modified Hummers method in phosphate buffer solution, from whichgraphene nanosheets were directly deposited onto a glassy carbon electrode throughcyclic voltammetric reduction of a GO colloidal solution. The cyclic voltammogram(CV) of GO electrolysis on a glassy carbon electrode (GCE) is analysed, one cathodicpeak at about1.2V is attributed to the reduction of graphene oxide, while theoxygen-containing groups on graphene are not reduced utterly. Electrolysis of the GOdispersions was carried out at different pHs and it was found that theelectrodeposition could occur in the pH range of2.0~10.0. The amount of deposit isincreased linearly in a certain range, and mechanism of the electrodeposition ofgraphene was deduced. Electrochemical technology is employed to surveyelectrochemical performances which show better performance than glass carbon.Relation between pH and potential of graphene was obtained by test of stability.Graphene would be oxidized to dissolve in high-pH solutions at high electrodepotentials. The graphene-modified electrodes can simultaneously determine ascorbic acid, dopamine and uric acid with higher sensitivity and selectivity.(2) Preparation of graphene/Au nano-composite material by directelectrodeposition: Chloroauric acid used as precursor was added in a GO solution aselectrolyte for carrying out the synthesis of graphene/Au nano particle compositematerials. SEM and TEM revealed the formation of layered graphene/Aunanocomposites. The mechanism of the layered structure was explored, for which twoessential conditions which are metal ions complex as precursors and appropriateconcentration in electrolyte are required. When the form of ions or its concentration ischanged, morphology of composite materials prepared is adjusted, in other words,morphology of composite materials can be controlled by adjusting the form and theconcentrate of metal ions. Electrochemical test of modified electrodes suggests thatthe charge current is higher than that of graphene alone, which confirms that thesurface area increased by coinstantaneous incorporation of Au nano-particles.Modified electrodes based on graphene/Au nano-particle composite materials cansimultaneously determine ascorbic acid, dopamine and uric acid with highersensitivity and selectivity than graphene alone.