| Acid treated carbon nanotubes (CNTs) was used to modify glassy carbon electrode(GCE).DNA modified CNTs/GCE was fabricated.The Fe3O4-CNTs complex wassynthesized by layer-by-layer assembling.Transmission Electron Microscope (TEM),scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR),ultraviolet-visible spectroscopy (UV-vis) analysis, and electroanalysis were employed tostudy the morphology structure and the electrochemical performances of modifiedelectrodes.Series of environmental organics were detected based on the CNTs'characteristics of favorable electron transmission, high catalysing activity, and large ratiosurface.The CNTs-based electrode offered sensitive, fast, and low cost determination methodsfor environmental analysis.The main contents are listed as following:(1) Diameter of purified CNTs was about 20 nm and multi-wall obtained by TEM.CNTs enhanced greatly the capacitance of GCE, the electron transfer kinetics of[Fe(CN)6]3-/[Fe(CN)6]4 on the CNTs/GCE was 53.5 fold than that obtained on GCE,indicating that the CNTs accelerated greatly the electron transfer.The electrode process ofCNTs/GCE in blank buffer solution was diffusion-controlled.The potential window of theCNTs/GCE was wider than those of bare gold, bare platinum and bare glassy carbonelectrodes, and it was broader in neutral solution than in acidic or alkaline solutions.(2) CNTs/GCE catalyzed greatly the Trp oxidation.The electrode process of Trpoxidation is diffusion-controlled.The relationship between potential and pH indicated thatproton participated in the reaction, and equal electron and proton were involved in theoxidation process.The current of Trp was linear with the temperature in the range of16～35℃with temperature coefficient 0.695μA/℃.The peak current is linearlyproportional to the concentration of Trp in the range from 1.0×10-6～1.0×10-4 mol/L with aregression coefficient of 0.995.Via changing pH, selective detection of Trp at presence ofTyr was achieved.The method was applied to the detection of Trp in 17AA compoundamino acid injection.The result was consistent with the tagged value.Recoveryexperiment proved the accuracy of the method.(3) The oxidation of oxalic acid was greatly improved at the CNTs/GCE as comparedwith the bare GCE.Dispercant and amount of CNTs affected the response of oxalic acid. The inflection point of the plot between oxidation potential and pH was near pH 4.5,which was consistent with the pKa (4.2).The irreversible oxidation process of oxalic acidwas diffusion-controlled.Two electrons and two protons were involved in the process.Thesurface concentration and diffusion coefficient of oxalic acid at the CNTs/GCE wereestimated to be 7.17×10-9 mol/cm2 and 1.16×10-4 cm/s by chronocoulometry.ThisCNTs/GCE presented a wide linear response range from 5.0×10-5～1.5×10-2 mol/L foroxalic acid.The method was applied to detect the oxalic acid content in spinach, the resultwas 3.24±0.19 mg/g close to the 3.45±0.22 mg/g obtained by the potassium permanganatetitration.(4) The electrochemical behaviors of 2,4-DNP, p-CP and p-cresol on CNTs/GCEwere all strengtherned as compared with those on GCE.After 2 min the adsorptionreached saturation.A linear relationship existed between the potential and pH in the rangeof pH 3.6～9.5.The oxidation processes were all adsorption-controlled.The currents wereproportional with the concerntrations of the three phenols in some ranges.Theelectrochemical behavior of BTA and TTA on CNTs/GCE were investigated.The activearea of CNT/GCE and GCE were evaluated respectively 0.0235 cm2 and 0.0113 cm2 viaelectron probe experiment.The reduction current of BTA on CNTs/GCE was 15.5 foldthan that obtained on GCE and potential shifted positively.The adsorption of BTA byCNTs played an important role.The current reached the maximum with 3μL CNTs and 2min adsorption.The current was larger in acidic buffer than those at neutral and alkalineconditions, which was due to the different protonation degree.The reduction process wasdiffusion-controlled.The surface concentration and diffusion coefficient of BTA on theCNTs/GCE were estimated to be 2.05×10-8 mol/cm2 and 2.67×10-2 cm/s.Theelectrochemical properties and reaction mechanism of TTA were same with those of BTA.The currents were linearly proportional with the concerntrations in the range of3.0×10-6～1.6×10-4 mol/L for BTA and 5.0×10-6～7.5×10-5 mol/L for TTA.The UV-Vis wasdifferent at various pH.There were two adsorption peaks under neutral and acidicconditions and only one under alkaline conditions, the possible reason was that BTAprotonates easily in acidic solution, which results in a new adsorption peak, whereas itcouldn't happen in alkaline conditions.(5) The DNA was electrostaticly and physically adsorbed onto the CNTs/GCE,denoted as DNA/CNTs/GCE.The preparation conditions for the DNA sensor were studied,results indicated that the optimal preparation conditions were: 20μL CNTs, 0.3 mg/mLDNA solution, 0.25 mol/L HAC-NaAC buffer (pH4.8), applied potential of 0.3 V for 5 min, among which the amount of CNTs enfluenced most.The interactions between phenol,m-cresol or catechol with DNA sensor were analyzed, results indicated that the threephenols damaged DNA.The direct oxidation peaks of DNA were decreased linearly withthe phenols concemtrations.R%D50 values showed that the m-cresol damnified DNA mosteasily.(6)The CNTs-Fe3O4 compound was fabricated by LBL assembling and in situchemical deposition methods.TEM indicated that the particle diameter of Fe3O4 wasabout in the range of 6 nm～11 nm.The Fe3O4 nanoparticle adhered compactly on CNTsmade by LBL assembling, the binding force was stronger than that obtained by in situdeposition.The capacitances of Fe3O4-CNTs and Fe3O4 modified GCE were 1.686 mF/cm2and 1.286 mF/cm2.Due to the good adsorption of p-CP and p-cresol on CNTs, thesimultaneous solid phase extraction and electrochemical detection of them on theCNTs-Fe3O4 and Fe3O4 were investigated.The result indicated that the adsorption anddetection result of Fe3O4-CNTs was better than that of Fe3O4, due to the enhancement ofadsorption and electrocatalysis by CNTs.The effects of the adsorbant amount, CTABamount, pH and time on the adsorption of p-CP and p-cresol were studied by voltammetry.The oxidation currents were linearly proportional with the concerntrations in the rangefrom 5.0×10(-6)～1.1×10(-4) mol/L for p-CP and from 5.0×10(-6)～7.5×10(-5) mol/L for p-cresol.
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