Electrochemical Sensor Based On Novel Metal Nanowire Arrays And Graphene Composite System

Nanomaterials have provoked considerable interest in recent year owing to their novel optical, electronic, catalytic and magnetic properties and potential applications. Particularly, metal-based nanoelectroanalytical chemistry as a rising interdisciplinary field has become one of the most exciting topics. This is because that metal nanomaterials modified electrochemical interfaces will provide a very high electrochemically active area and thereby lead to high detection sensitivity. And they can also act as enhanced elements for effectively accelerating the electron transfer between electrode and probe molecules, which will lead to a rapid current response and meantime reduce the over-potential of electrochemical reactions.In this experiment, nanomaterials (nanoparticles, nanowires, and nanoparticle modified graphene) are fabricated via a variety of preparative strategies and modified on the surface of glassy carbon electrodes for the preparation of different electrochemal sensors. The developed for formaldehyde, H2O2and NO2-sensors have well liner range, lower detection limit and fast response time. The details are summarized as follows:(1) The Pd NW arrays were obtained via the direct electrodeposition of Pd on a glassy carbon electrode within the pores of an anodized aluminum oxide membrane (AAO). The AAO was adopted in preparation with nanowire owing to uniform pore dimension, intensive pore quantity and the simplicity of operation. The procedure may represent a promising route for the synthesis of other materials with well-defined structures. Electrodeposition method was applied because of simple operation, methods maturity and high throughout. The morphology of AAO and Pd NW arrays were investigated by SEM:the porous alumina structure consisted of cylindrical hexagonal cells with an average diameter of approximately50nm; the straw shape of the Pd NW arrays had a good orientation, which was perpendicular to the surface of the substrate. The diameters of the Pd NW arrays were approximately50nm, retaining the size and near cylinder shape of the pores of the AAO template. Nanowire can accelerate electron-trasfer and improve the sensitivity of sensors duing to high surface-to-volume ratio.The electrocatalytic activity of Pd NW array electrodes for formaldehyde detection in alkaline media has been studied by a series of electrochemical measurements.It can be found that the Pd NW array electrodes,at lower potential of+0.05V, show a very high catalytic activity for formaldehyde.The current on Pd NW array electrodes is3times larger than Pd NPs electrodes.The experimental data further reveal that the electro-oxidation of formaldehyde inhibits the formation of the poisonous intermediate carbon monoxide.The oxidation current has a linear relationship with formaldehyde concentration in the range of2×10-6～1×10-3mol·L-1(R=0.9982).The detection limit was5×10-7mol.L-1(S/N=3).In addition,the prepared sensor has long-term stability.(2)The Ag NW arrays was obtained according to the methods of(1).The morphology of Ag NW arrays were investigated by SEM:nanowires are uniform, parallel to one another and sranding vertically to the electrode surface.The average length of the nanowires is10μm and the diamerer of nanowire is50nm.Adjacent nallowire has slight aggregation effect.Noble Ag may facilitate more efficient electron transfer than other metal,since Ag exhibit the highest conductivity among all metals.Nanowire modified electrochemical interfaces,can accelerate electron-trasfer and improve the sensitivity of sensors duing to high surface-to-volume ratio.In pH7PBS solution,at the potential-0.4V,the sensor show a good catalytic activity for H2O2,with a linear range of1×10-5～7.5×10-4mol·L-1(R=0.999)and the detection limit of5×10-6mol·L-1(S/N=3).Moreover,the sensor has long-term stability,relative good anti-interference.(3)Graphene was researched widely in the past years owing to high chemical, thermal stability and a fast electron-transfer rate.The noble nanoparticle(NPs)exhibit superior catalytic activity, high surface-to-volume ratio and more active site. Immobilizing NPs on graphene may generate synergistic reaction and enhance the sellsitivity of the sensor.In this chapter,grapheme oxide wan prepared according to Hummers methods.The preparation grapheme oxide was dispersed in HAuCl4solution,and then sodium citrate was added to reduce AuCl4-to form Au nanopartcle. The morphology of Au NPs/graphene was investigated by TEM:graphene has a transparent flakelike shape with wrinkles, Au NPs were dispersed the surface of graphene uniformity. It can be observed that the average diameter of Au NPs is about15nm. Au NPs/graphene electrode was employed to investigate catalytic activity of NO2-. In pH3Na2HPO4-sodium citrate solution, at a potential+0.85V, the sensor show high catalytic activity for NO2-, with a linear range of2.5×10-5～1.0×10-3mol·L-1(R=0.999)and the detection limit of8×10-6mol·L-1(S/N=3). Furthermore, the sensor exhibits good stability, relative good anti-interference and can be applied in sample analysis. The preparation AuNPs/Graphene/GC provides an effective development platform for other nanostructured electrochemical sensors or biosensors.