【作者】 周舟；

【导师】 李国希； 何德良；

【作者基本信息】 湖南大学 ， 应用化学， 2009， 博士

【摘要】 导电聚合物是近年来的研究热点,它在电化学催化、传感、电容器等领域的成功应用引来了越来越多关注的目光。室温离子液体作为一类新型的环境友好的绿色溶剂拥有许多优异的物理、化学性能,它的出现为绿色化学开辟了一条崭新的道路。本论文分别采用电化学聚合法、化学聚合法、光诱导聚合法在室温离子液体溶液以及室温离子液体与水形成的微乳液体系中制备了具有纳米尺寸的导电聚合物材料以及导电聚合物复合材料,并通过扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X射线能量色散谱（EDS）、X射线衍射谱（XRD）、红外光谱（IR）、紫外光谱（UV-vis）、电化学循环伏安扫描（CV）、电化学阻抗谱（EIS）等分析测试技术对制得的纳米材料的形貌、结构、物理化学性质及应用进行了详细研究。本论文的主要研究工作如下:（1）通过两步法制得三种室温离子液体1-乙基-3-甲基咪唑六氟磷酸盐[emim]PF₆、1-丁基-3-甲基咪唑六氟磷酸盐[bmim]PF₆、1-辛基-3-甲基咪唑六氟磷酸盐[omim]PF₆,使用CV扫描对三者的电化学稳定性进行考察,发现三者在铂电极上的电化学窗口分别为4.14 V、3.40 V、3.28 V。通过向三种室温离子液体中添加一系列定量的杂质,发现随着室温离子液体阳离子取代基碳链的增长,三种室温离子液体电化学稳定性受杂质影响的程度有所减弱。（2）采用循环伏安法研究了氯化亚钴在室温离子液体[bmim]PF₆中的电化学行为。虽然[bmim]PF₆中Co²⁺/Co³⁺氧化还原电对在玻碳电极上的氧化还原峰电位差大于59 mV,但是通过对峰电流与扫描速度以及峰电流与峰电位的拟合分析还是可以证明该电化学反应仍然为一个可逆过程。通过不同温度下循环伏安法峰值电流与扫描速率之间的关系拟合得出[bmim]PF₆中Co²⁺的扩散系数D在10^-11 m²·s^-1数量级,且随温度的升高而增加,进而推导得出[bmim]PF₆中Co²⁺的扩散活化能ED为23.4 kJ·mol^-1,这同时说明[bmim]PF₆是一种性能优良的电化学反应介质。（3）在含有醋酸的室温离子液体[bmim]PF₆溶液中采用循环伏安法和计时电位法研究了苯并三氮唑在金电极上的电化学聚合过程,并在硫酸溶液中考察了所制备的聚苯并三氮唑膜电极的电化学性能。通过计时电位法研究发现苯并三氮唑在电化学氧化初期生长方式遵循3D瞬时成核模型。SEM照片显示聚苯并三氮唑膜表面致密、平滑,IR光谱分析证明聚合物的主链是通过不饱和的氮原子耦合连接而成。对聚苯并三氮唑膜电极进一步的循环伏安扫描后发现该聚合物膜具有良好的电化学活性,并且在0.9 V（相对于Ag/AgCl电极）的电位附近表现出稳定的准可逆的氧化还原特性。（4）由室温离子液体与其它溶剂组成的微乳液是一种可以用于制备纳米材料的新型绿色介质。采用循环伏安法在室温离子液体[bmim]PF₆和水组成的微乳液（IL/W型）中成功制得了导电聚苯胺（PAN）,在这样的介质环境中制得的PAN的电化学性能与在常规水溶液中制备的PAN的性能有明显的差别,而且采用循环伏安法聚合时的聚合圈数对制得的PAN的电化学性能（如比电容）存在一定影响,通过电流密度为2 mA·cm^-2的冲放电实验检测发现在室温离子液体型微乳液中经过50圈循环伏安扫描制得的PAN的比电容可以达到334 F·g^-1,这样的PAN是一种性能优越的超级电容器电极材料。同时SEM照片显示制得的PAN拥有花菜状的微观形貌,而且EDS元素分析检测结果可以证明聚合物存在SO42-和PF₆-的共掺杂。（5）采用计时电位法分别在室温离子液体[bmim]PF₆和水组成的W/IL型与IL/W型微乳液中制备得到了PAN-Ag纳米复合材料。通过SEM、TEM和XRD分析了不同介质环境中制得的PAN-Ag纳米复合材料在形貌与结构上的差别,结果证明在W/IL型微乳液中制得的PAN-Ag纳米复合材料为纤维状结构,粒径5 nm左右的Ag纳米颗粒均匀的分布在其中,而在IL/W型微乳液中制得的PAN-Ag纳米复合材料为树枝状结构,其中的Ag纳米颗粒的粒径大约50-100 nm。采用CV和EIS技术进一步研究了不同微乳液类型以及电化学合成条件对PAN-Ag纳米复合材料电化学性能的影响,并通过与纯PAN材料的比较,发现具有特殊形貌特征的PAN-Ag纳米复合材料拥有更优越的电化学性能。（6）在由室温离子液体与水组成的微乳液体系（IL/W型）中,采用化学氧化法制得了[bmim]PF₆和十二烷基苯磺酸（DBSA）或盐酸（HCl）共掺杂的PAN纳米材料。室温离子液体在制备过程中既是溶解苯胺单体的油相,又起到了对阴离子掺杂的作用。通过研究发现,不同对阴离子的掺杂对PAN产物的物理、化学性质存在较大影响。在三种PAN产物中,[bmim]PF₆与DBSA共掺杂的PAN拥有最大的分子量(81104 g·mol^-1),最高的电导率(1.85 S·cm^-1),最低的玻璃化温度（181℃）以及最高的电化学氧化还原电流;[bmim]PF₆单掺杂的PAN表现出的电导率和电化学氧化还原电流最低;[bmim]PF₆与HCl共掺杂的PAN也展现出较高的电导率。而且,三种PAN在中性条件下都拥有良好的电化学反应活性以及充放电稳定性。这都可以证明,在酸性条件下通过不同对阴离子共掺杂可以改善PAN产物的氧化程度,从而提高PAN的导电性能以及电化学性能。（7）首次采用光诱导聚合法在室温离子液体溶液介质中制备得到了PAN纳米颗粒。在聚合反应过程中,光子和具有光化学活性的室温离子液体阳离子取代了传统的化学氧化剂和金属络合物促使苯胺单体发生氧化。通过SEM观察证实所制得的PAN颗粒粒径在纳米级范围内。随着室温离子液体溶液介质中质子酸含量的增加,PAN产物的产率和电导率都有所上升,紫外吸收也有所增强,而且部分吸收峰发生蓝移。进一步对室温离子液体作为反应介质的重复使用性进行考察发现,在重复使用5次后,室温离子液体对于光诱导聚合苯胺的催化活性并没有明显的降低。本方法为直接使用太阳能制备纳米导电聚合物开创了一条崭新的道路。更多还原

【Abstract】 Conducting polymers have attracted considerable attention because of their application in electrochemical catalysis, sensor, capacitor, etc.“Green solvent”room temperature ionic liquids are environmentally benign, and exhibit many excellent physical and chemical properties. They play an important part in green chemistry. This dissertation is concentrated on the preparations of nano-sized conducting polymers and conducting polymer composites by using electrochemical, chemical and photo-induced polymerization in room temperature ionic liquid solutions or microemulsions composed of room temperature ionic liquid and water. Their micrographs, structure, properties and applications have been investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, infrared absorption spectra （IR）, ultraviolet visible absorption spectra （UV–vis）, cyclic voltammetry （CV）, and electrochemical impedance spectroscopy （EIS）, etc. The main points of this dissertation are summarized as follows:（1） Three room temperature ionic liquids 1-ethyl-3-methylimidazolium hexafluorophosphate （ [emim]PF₆ ） , 1-butyl-3-methylimidazolium hexafluorophosphate （ [bmim]PF₆ ） and 1-octyl-3-methylimidazolium hexafluorophosphate （[omim]PF₆） were prepared. Their electrochemical stabilities were investigated by CV, and corresponding electrochemical windows was 4.14 V, 3.40 V, and 3.28 V, respectively. Longer the substituted group on room temperature ionic liquid cation is, weaker the effect of impurities on the electrochemical stability of room temperature ionic liquids is.（2） The electrochemical behavior of CoCl₂ in [bmim]PF₆ was investigated by CV. The well-defined cyclic voltammograms were obtained from electrochemical measurement under different temperatures, and the reversible behavior for Co²⁺/Co³⁺ redox couple on glassy carbon electrode in [bmim]PF₆ was confirmed by the characteristic of the peak currents. The diffusion coefficients (about 10^-11 m²·s^-1) of Co²⁺ in [bmim]PF₆ under different temperatures were evaluated from the dependence of the peak current density on the potential scan rates in cyclic voltammograms. It is found that the diffusion coefficient increases with increasing temperature. Diffusion activation energy of Co²⁺ in [bmim]PF₆ is also calculated to be 23.4 kJ?mol-1 according to the relationship between diffusion coefficient and temperature. It is confirmed that [bmim]PF₆ is a good solvent for electrochemical reactions.（3） The electropolymerization of benzotriazole on an Au electrode was investigated via CV and chronoamperometry in a room temperature ionic liquid medium, [bmim]PF₆ containing glacial acetic acid. The chronoamperometric investigation revealed that the instantaneous nucleation predominated the potentiostatic electropolymerization of benzotriazole at the oxidation peak potential. SEM image indicated that the polymer film was compact and relatively smooth and IR result suggested the polymer chains were formed mainly via coupling of the unsaturated nitrogen atoms. The polymer was found to be highly electroactive, showing a quasi-reversible and stable pair of redox peaks centering at 0.9 V versus Ag/AgCl in 0.1 mol?L-1 H2SO4 solution.（4） Room temperature ionic liquid microemulsion, a new way to synthesize the controllable size and shape of nano-scale materials, has received increasing attention. Polyaniline （PAN） has been prepared by CV in room temperature ionic liquid-in-water （IL/W） microemulsion. The electrochemical properties of the PAN prepared in IL/W microemulsion were compared with that of the PAN polymerized in conventional acidic aqueous solution. Also, the effects of the potential cycle number on the specific capacitance and electrochemical characteristics of the PANI film electrode were discussed in detail. The result shows that the specific capacitance of the PAN film obtained by 50-cycle electropolymerization is 334 F·g^-1 at the charge-discharge current density of 2 mA·cm^-2. The SEM image indicates that the PAN film presented cauliflower like morphology, and the EDS elemental analysis result suggests the polymer were co-doped with SO₄^2- and PF₆^-.（5） Chronopotentiometry was employed to prepare polyaniline-silver （PAN-Ag） nanocomposite films in water-in-room temperature ionic liquid （W/IL） microemulsion and room temperature ionic liquid-in-water （IL/W） microemulsion. The resulted nanocomposites were characterized by SEM, TEM, HRTEM, and XRD. It is demonstrated that the PAN-Ag nanocomposite prepared in W/IL microemulsion is nanofibrous and the Ag nanocrystals with 5 nm diameter are dispersed homogeneously, whereas the morphology of the PAN-Ag nanocomposite prepared in IL/W microemulsion exhibits dendritic structure and the diameter of Ag nanocrystals is 50-100 nm. Further, the effects of different microemulsion systems and electrochemical synthesis conditions on the electrochemical properties of the nanocomposite films were studied by CV and EIS. The pure PAN films were also made for comparative purpose. It is found that the special structures of the PAN-Ag nanocomposite result in more excellent electrochemical activity than that of the pure PAN.（6） Three nano-sized PAN powders doped with room temperature ionic liquid [bmim]PF₆ and dodecyl benzene sulfonic acid （DBSA） or hydrochloric acid （HCl） have been prepared in room temperature ionic liquid-in-water microemulsion system. The oil-phase room temperature ionic liquid was used as both monomer solvent and doped counterion. The effects of different counterions on the properties （molecular weight, electrical conductivity, glass transition temperature, electrochemical activity） of PAN were investigated. The PAN co-doped with [bmim]PF₆ and DBSA shows the highest molecular weight (81104 g·mol^–1), the highest electrical conductivity (1.85 S·cm^–1) the lowest glass transition temperature （181°C） and the highest redox reaction current density, while the PAN doped with [bmim]PF₆ only exhibits the lowest conductivity (0.018 S·cm^–1) and lower redox reaction current density. The PAN co-doped with [bmim]PF₆ and HCl shows higher conductivity. Also they exhibit good electrochemical stability and charge/discharge performance in neutral medium. These indicate that co-doping of different counterions under acidic condition could improve oxidation degree and doping ratio of PAN, and results in high electrical conductivity and good electrochemical properties.（7） Photo-induced polymerization was employed to prepare PAN nanoparticles in room temperature ionic liquid for the first time. Photons and photoactive room temperature ionic liquid cations replaced conventional oxidants and metal complexes to promote the polymerization of aniline monomer. The diameter of the resulted PAN is confirmed in nano-scale by SEM. With increase of protonic acid in medium, the yield of the PAN increased, the UV absorption of the PAN strengthened, and a blue shift of the p-polaron absorption was observed. And the conductivity of the PAN also increased with the acid content in medium. The potential mechanism of photo-induced polymerization of aniline was proposed. Moreover, after the room temperature ionic liquid was separated from the reaction mixture and reused for five times, no obvious decrease in catalytic activity could be found in photo-induced polymerization of aniline. The method may open a new pathway to prepare nano-scale conducting polymers with sunlight.更多还原