Functionalized Graphene Modified Electrodes For The Determination Of Phenols

Graphene,a novel single layer two dimensional cystal,owning unique optical and electronic properties,has led to an explosion of interest in most fields.Graphene nanosheets(GNs)were prepared by liquid-phase exfoliation method in this thesis.Thereafter electrochemical enhancement effect of the obtained graphene nanosheets and graphene composite was further investigated,the response mechanism of the remarkably enhanced electrochemical signal was deeply explained,the different modified electrodes were proposed for the simultaneous determination of phenols with high sensitivity.The research work of this thesis mainly contains the following four parts:(1)GNs were facilely prepared through one-step liquid-phase exfoliation of graphite powder in N,N-dimethylformamide(DMF)with the assistance of copper(II)meso-tetra(4-carboxyphenyl)porphyrin(Na(CuTCPP)),and then employed to modify the surface of glassy carbon electrode(GCE)via solvent evaporation.The surface morphology of the modified electrode was characterized by scanning electron microscope(SEM),transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).Electrochemcial behaviors of acetaminophen(AC)and dopamine hydrochloride(DA)on GN/GCE were investigated with cyclic voltammetry(CV)and square wave voltammetry(SWV).The results indicated that such notable signal enhancement effects could be ascribed to the high specific surface area of graphene together with the hydrogen-bonding interactions between Na(CuTCPP)(-COO~-)and AC and DA(-OH).The electrochemical method was developed for the same determination of AC and DA.Under the optimized condition,the response peak currents of the modified electrodes were linear over ranges from0.004 to 7.6?M for AC and from 0.0024 to 3.6?M for DA and the detection limits were 0.8 and 0.7 nM for AC and DA(S/N=3).The electrochemical sensor for the detection of these pharmaceutical preparations analysis,and the results were in good agreement with those obtained from HPLC method.(2)GNs were easily prepared through one-step liquid-phase exfoliation of graphite powder in N,N-dimethylformamide(DMF)with the assistance of sodium gallate.The surface morphology of the modified electrode was characterized by SEM,TEM.Electrochemcial behaviors of guaiacol(GU)and vanillin(VA)on GN/GCE were investigated with CV and SWV.Notable signal enhancement effects could be ascribed to the high specific surface area of graphene.Under the optimized condition,the response peak currents of the modified electrodes were linear over ranges from0.02 to 11?M for VA and from 0.02 to 12?M for GU,the detection limits were 0.9and 1.0 nM for VA and GU(S/N=3).GU and VA in tap water samples was tested with the proposed film modified electrode by calibration method.(3)GNs were easily prepared through one-step liquid-phase exfoliation of graphite powder in N,N-dimethylformamide(DMF)with the assistance of sodium citrate,and employed to modify the surface of glassy carbon electrode(GCE).Then,the poly(mercaptoacetic acid)/graphene composite film modified electrode(pMA/GN/GCE)was fabricated by electrodeposition method.The surface morphology of the modified electrode was characterized by SEM,TEM,Atomic force microscopy(AFM),X-ray powder diffraction(XRD),Raman spectra(RS).The electrochemical behaviors of hydroquinone(HQ)and catechol(CC)on pMA/GCE,GN/GCE and MA/GN/GCE were studied by CV and SWV.The oxidation signals of HQ and CC further enhanced greatly on the surface of pMA/GN/GCE,showing strong synergetic enhancement effects.Under the optimized experimental conditions,the linear ranges for detecting HQ and CC was from 0.1 to 100?M,and the detection limits were 85 and 80 nM for HQ and CC(S/N=3).(4)The above-mentioned GN/GCE,the polypyrimidine/graphene composite film modified electrode(pAMP/GN/GCE)was fabricated by electrodeposition method.The surface morphology of the modified electrode was characterized by SEM.Electrochemcial behaviors of sunset yellow(SY)and tartrazine(TT)on pAMP/GN/GCE were investigated by CV(SWV).The oxidation signals of SY and TT further enhanced greatly on the surface of pAMP/GN/GCE,showing strong synergetic enhancement effects.Under the optimized experimental conditions,the linear ranges for detecting SY and TT were 0.002~2?M and 0.003~6?M.The detection limits were as low as 0.5 nM and 0.9 nM(S/N=3),respectively.This developed method can be used for the simultaneous determination of SY and TT in food.