【作者】 郑燕琼；

【导师】 杨昌柱； 张敬东；

【作者基本信息】 华中科技大学 ， 环境工程， 2009， 博士

【摘要】 利用混酸纯化处理后的碳纳米管（CNTs）修饰玻碳电极（GCE），并在CNTs／GCE基础上构建了DNA修饰电极，和用层层组装技术（LBL）制备磁性Fe₃O₄-CNTs纳米复合物。对所制备的修饰电极用透射电镜（TEM）、扫描电镜（SEM）、傅利叶红外光谱（FTIR）、紫外-可见光谱分析（UV-Vis）、电化学分析等各种方法进行表面形貌、结构以及电化学性能表征研究。并利用CNTs良好的电子传输性能、高催化活性和大比表面等特性将这些CNTs及其复合物修饰电极成功地用于环境有机物的分析检测，为环境分析提供了灵敏、快速、低成本的检测方法。主要研究结果如下：（1）TEM结果表明纯化后的CNTs直径为20nm左右，且此纳米管为多壁结构。CNTs的存在大大增强了GC电极的电容，[Fe（CN）₆]^3-／[Fe（CN）₆]^4-在CNTs／GCE表面的电子传递速率是裸GCE的54.5倍，CNTs极大地促进了电子传递速率。CNTs／GCE在空白缓冲溶液中的电化学反应为表面控制过程。CNTs／GCE比裸金电极、裸铂电极和玻碳电极的电位窗口更宽，且中性条件下的电位窗口比酸性和碱性条件下的更宽。（2）CNTs／GCE对色氨酸（L-Trp）的氧化反应表现出显著的电催化活性。L-Trp的氧化过程受扩散步骤控制，氧化峰与pH的关系表明有质子参与反应，且参与反应的质子数和电子数相等；温度在16～35℃范围内，色氨酸在CNTs／GCE上的响应电流与温度成线性关系，温度系数为0.695μA／℃。氧化峰电流与Trp浓度在1.0×10^-6～1.0×10^-4mol／L范围内呈良好线性关系。通过改变电解质的酸度，实现了在酪氨酸（Tyr）存在下色氨酸（Trp）的选择性检测。并对复方氨基酸注射液中的色氨酸进行了检测，所测结果与标示值很接近。回收实验说明了此方法的准确性。（3）相对于GCE，草酸在CNTs／GCE上有更好的电流响应。分散剂和CNTs的量对草酸的响应有一定的影响。电位与pH的关系曲线的拐点在4.5附近，这和草酸的pKa（4.2）较接近。草酸在CNTs／GCE上的电极过程为扩散控制的不可逆过程。根据峰电位和扫描速率之间的关系可知在此氧化过程中有2个电子和2个质子参与。通过计时电量法测得草酸在电极表面的覆盖率为7.17×10^-9mol／cm，在溶液中的扩散系数为1.16×10^-4cm／s。氧化峰电流和草酸的浓度在5.0×10^-5～1.5×10^-2mol／L范围内呈良好的线性关系。将此方法用于检测菠菜中的草酸，测得草酸浓度为3.24±0.19mg／g。而用高锰酸钾滴定法得到的结果为3.45±0.22mg／g，两种方法得出的结果很接近。（4）CNTs／GCE对2，4-DNP、对氯酚和对甲酚的电化学行为均有增敏效果。富集2min时吸附基本达到饱和。在pH3.6～9.5范围内，这三种酚的氧化电位与pH呈线性关系。三种酚在修饰电极上的氧化过程均为吸附控制过程。在一定浓度范围内，3种酚的氧化峰电流与其浓度呈线性关系。另外又研究了苯骈三氮唑（BTA）及甲基苯骈三氮唑（TTA）在修饰电极上的还原行为。电子探针实验可估算出CNT／GCE和GCE的电活性面积分别为0.0235cm²和0.0113cm²。相对于GC电极，BTA在CNTs／GCE上的还原电位正移，电流为GC电极上的15.5倍。其中CNTs对BTA的吸附起了很大的作用。CNTs的量为3μL和吸附2min时，BTA的电流基本稳定。pH的影响最显著，酸性条件下的电流响应明显比中性和碱性条件下的大，这可能归因于BTA质子化的程度不同。BTA的还原过程受扩散控制。BTA在电极表面的覆盖率为2.05×10^-8mol／cm，扩散系数为2.67×10^-2 cm／s。还原电流与其浓度在3.0×10^-6～1.6×10^-4mol／L范围内呈线性关系。甲基衍生物TTA与BTA的电化学性质相似，反应机理是一致的。TTA的还原电流与浓度在5.0×10^-6～7.5×10^-5mol／L范围内呈线性关系。不同pH条件下的紫外吸收光谱差别较大，酸性和中性条件下出现2个吸收峰，而碱性条件下只有一个较强的吸收峰，可能原因是酸性和中性条件下质子化BTA导致新的吸收峰出现，而碱性条件下不能质子化因此只有一个吸收峰。（5）通过静电吸附和物理吸附将DNA固定于CNTs／GCE上，得到DNA生物传感器。研究了此传感器制备过程中的各种条件对DNA直接电化学行为的影响；制备传感器的最佳条件为：CNTs的量为20μL，DNA溶液的浓度为0.3mg／mL，缓冲溶液采用0.25mol／L醋酸-醋酸钠（pH4.8），吸附电位选择0.3V，电吸附时间为5min，其中CNTs的量影响显著。研究了苯酚、间甲酚和邻苯二酚与DNA的作用，结果表明其对DNA有损伤作用，且存在剂量效应关系，一定浓度范围内，DNA的峰电流与酚的浓度呈线性下降关系。R％D₅₀值分析结果表明这三种酚污染物中间甲酚最容易损伤DNA。（6）采用层层组装（LBL）和原位化学沉积法制备了负载Fe₃O₄磁性粒子的CNTs（Fe₃O₄-CNTs），TEM结果表明Fe₃O₄粒径为6nm～11nm之间，且LBL法制备的复合物上Fe₃O₄沿着CNTs致密地分布，结合力比原位沉积法得到的复合物强得多。Fe₃O₄-CNTs和Fe₃O₄修饰玻碳电极的电容分别为1.69mF／cm²和1.29mF／cm²。以在复合物上吸附性能较好的对氯酚和对甲酚为模型物，将磁性复合物用于对溶液中的两种酚进行固相萃取和电化学检测，由于CNTs的存在增强了Fe₃O₄对酚的吸附和电催化氧化，因此Fe₃O₄-CNTs复合物的吸附检测效果比Fe₃O₄的检测效果好。通过伏安法研究了吸附剂的量、CTAB的量、pH和时间对吸附效果的影响。对氯酚的氧化电流与其浓度在5.0×10^-6～1.1×10^-4mol／L范围内呈线性关系，对甲酚的氧化电流与其浓度在5.0×10^-6～7.5×10^-5mol／L范围内呈线性关系。更多还原

【Abstract】 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.更多还原