【作者】 张国权；

【导师】 杨凤林；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 博士

【摘要】 聚吡咯（PPy）作为典型的导电聚合物，具有无毒无害、制备简便、高的导电性、优良的电催化活性和环境稳定性等特点。在吡咯（Py）单体聚合的过程中可以将不同的阴离子基团掺杂进PPy膜内，从而得到具有掺杂阴离子特性的导电聚合物薄膜。利用掺杂阴离子的电化学性质可以实现修饰电极的电催化和电分析等功能。由于氧电极在燃料电池和金属-空气电池上的广泛应用，电催化氧还原一直是备受瞩目的研究领域。此外，醌及其衍生物因能促进氧还原为过氧化氢（H₂O₂）的反应速率而使醌及其衍生物修饰电极电催化氧还原备受关注。然而，以自然吸附和共价键合两种方式修饰在电极表面的单层醌及其衍生物经长时间使用后容易脱落，造成修饰电极环境稳定性和电催化活性的降低甚至消失。为了提高修饰电极的稳定性和电催化活性，并利用醌型化合物和PPy膜的优点，本研究中用电化学的方法在水溶液中制备了掺杂蒽醌双磺酸盐（AQDS）的PPy膜（AQDS／PPy）修饰电极。本文采用循环伏安（CV）法研究了不同pH缓冲溶液中，扩散相和掺杂相AQDS的电化学行为以及AQDS／PPy复合膜修饰电极的稳定性。结果表明，水溶液介质条件下扩散相和掺杂相AQDS均表现出准可逆的氧化还原行为，两种状态AQDS均经历一步两电子的还原过程。扩散相AQDS的氧化还原过程受扩散传质控制，而掺杂相AQDS的氧化还原是非扩散控制的过程。在较宽的pH范围内，AQDS／PPy复合膜具有良好的电化学活性，扩散相和掺杂相AQDS的氢醌／氢醌阴离子（H₂AQ／HAQ^-）氧化还原对的电离常数pK_a分别为7．6和9．5。PPy膜的存在不仅增大了电极的比表面积，增强了复合膜修饰电极的电化学稳定性，而且促进了掺杂相和扩散相AQDS在PPy膜修饰电极上的电化学反应，增大了AQDS的氧化和还原峰电流，降低了氧化和还原峰电位差。本文以醌及其衍生物修饰电极电催化氧还原的理论为基础，利用循环伏安（CV）、旋转圆盘电极（RDE）、计时安培／计时库仑和Tafel极化等技术研究了扩散相和掺杂相AQDS对氧还原反应的电催化性能和电极过程动力学，确定了氧还原反应的扩散和反应动力学参数以及AQDS媒介电催化氧还原的反应机理。结果表明，扩散相和掺杂相AQDS电催化氧还原反应的最佳介质条件为pH=5．5-7．0。不同pH缓冲溶液中，AQDS媒介电催化氧还原主要是两电子还原为H₂O₂的不可逆过程。在酸性和碱性溶液介质中，氢醌（H₂AQ）和半醌基阴离子(AQ^·-)分别对氧还原反应起主要的电催化作用，催化机理符合电化学-化学机制（EC机制），氧还原过程受溶解氧的扩散传质-催化反应动力学混合控制，而PPy膜只起到电子传递和增强修饰电极稳定性的作用。AQDS／PPy复合膜内AQDS与PPy链结合牢固，具有良好的电化学重现性。在氧饱和的缓冲溶液中长时间工作后，在氮气饱和的相同缓冲溶液中其循环伏安峰电流和峰电位仅有微小的降低（<15％）。本文分别以AQDS／PPy复合膜修饰的石墨（AQDS／PPy／Graphite）和裸石墨作为电解池的阴极，向电解液中通入氧气和投加Fe²⁺或者Fe³⁺盐，原位电生成Fenton试剂氧化降解苋菜红偶氮染料。考察了溶液pH、阴极电位、Fe²⁺和Fe³⁺浓度以及AQDS／PPy复合膜内AQDS掺杂浓度等因素对电Fenton氧化降解偶氮染料效率（染料脱色率和TOC去除率）的影响，确定了电Fenton过程的最佳工艺条件。此外，考察了AQDS／PPy／Graphite复合膜电极和裸石墨电极作为阴极时，溶液pH、阴极电位、氧气流率和PPy膜内AQDS的掺杂浓度等不同实验条件对H₂O₂形成和Fe²⁺再生的影响。实验结果表明：（1）H₂O₂的形成和Fe²⁺的再生依赖于所使用的阴极材料，AQDS／PPy／Graphite复合膜电极具有氧扩散阴极的性质，对溶解氧的两电子还原为H₂O₂的反应具有良好的电催化能力；（2）裸电极对Fe²⁺的再生具有优良的电催化性能；（3）合适的Fe²⁺和Fe³⁺浓度是实现电Fenton过程氧化降解能力和效率的先决条件。循环伏安（CV）和傅立叶变换红外光谱（FT-IR）技术表明，在电Fenton系统中使用过的AQDS／PPy／Graphite复合膜电极具有良好的电化学重现性，掺杂的AQDS与PPy链结合牢固，没有从PPy聚合体中脱出。但AQDS／PPy复合膜的电催化能力有所降低。更多还原

【Abstract】 Polypyrrole （PPy）, as a typical conducting polymer, has many advantages such as harmlessness, simple and convenient preparation, high conductivity, electrocatalytic activity and high environmental stability. In seeking to functionalize films with the desired electrochemical properties such as electrocatalysis and electroanalysis, a wide variety of anionic functional groups were incorporated into PPy matrix during the polymerization process of pyrrole （Py） monomer. The electrochemical reduction of oxygen has been received much attention because of the wide use of oxygen reduction electrodes in fuel cells and metal-air batteries. Moreover, the electrochemical reduction of oxygen has also been widely studied on quinones and their various derivatives modified electrodes, since the surface modification of electrodes with quinones greatly increase the rate of oxygen reduction to hydrogen peroxide （H₂O₂）. However, quinones and their various derivatives which are grafted as spontaneously adsorbed or covalently bound monolayer on the electrode surface, tend to desorb from the surface during the long-term operation, leading to a loss of electrocatalytic ability and stability of the working electrodes. Therefore, aimed at improving the stability and the electrocatalytic activity of electrocatalyst, and taking advantage of both PPy film and quinonoid compounds, anthraquinonedisulphonate （AQDS） was incorporated into PPy matrix using the electrochemical method during the preparation of the modified electrode.The electrochemical behaviors of AQDS dissolved in solution and incorporated into PPy matrix as doping species at PPy film modified glassy carbon （GC） electrode were investigated in various pH buffered solutions, also examined was the stability of the AQDS/PPy composite film （AQDS in doping phase）. It was found that the redox process of AQDS in solution and doping phase both exhibit quasi-reversible behavior and pH dependence. For AQDS in solution phase, the reduction of AQDS is diffusion-controlled adsorption process, while for AQDS in doping phase the reduction of AQDS is non-diffusion-controlled process. The value of ionization constant pKa for the H₂AQ/HAQ^- couple increases obviously from 7.6 in solution phase to 9.5 when AQDS is incorporated into PPy matrix. The immobilized and diffusive AQDS both proceed a single two-electron reduction step in aqueous solution. The PPy matrix not only increases the specific surface area of electrode and lowers the redox peak potential separation of AQDS, but also increases the redox peak currents. In addition, the AQDS/PPy composite film modified electrode exhibited a good electrochemical stability.In view of the earlier works which have been done on the electrocatalytic effect of quinonoid compounds on O₂/O₂^2- redox reaction, the electrocatalytic activity of the immobilized and diffusive AQDS towards the electroreduction of oxygen was investigated using cyclic voltammetry （CV）, rotating disc electrode （RDE）, chronoamperometric/chronocoulometric and Tafel polarization technique. The diffusive and reactive kinetic parameters were also determined using these electrochemical approaches and the probable mechanism for oxygen reduction catalyzed by AQDS operating in various pH buffered solutions were proposed. It was found that the pH range of 5.5-7.0 buffered solution is a more suitable medium for oxygen reduction catalyzed by the immobilized and diffusive AQDS. In various pH buffered solutions, the electrocatalytic reduction of oxygen mediated by AQDS establishes a pathway of irreversible two-electron reduction to form H₂O₂. The dihydroanthraquinone （H2AQ） and semiquinone radical anion （AQ^-） are responsible for the extraordinary catalytic activity to the oxygen reduction reaction in acidic and alkaline media, respectively. The catalytic reaction occurred in the presence of AQDS and O₂ is in agreement with an electrochemical-chemical （EC） mechanism, and the electrocatalytic current is under mixed diffusion-reaction kinetic control. The AQDS/PPy composite film exhibits reproducible characteristic. After performing repetitive CVs in an O₂-saturated buffer solution, there was a slightly decrease （< 15%） in the corresponding voltammograms in the same N₂-saturated solution.The degradation of amaranth azo dye was investigated by in-situ electrogenerated Fenton’s reagent using the bare graphite and the AQDS/PPy composite film modified graphite （AQDS/PPy/Graphite） as cathodes and Fe²⁺ or Fe³⁺ as catalyst. The H₂O₂ was produced by electrochemical reduction of oxygen on cathode and the Fe²⁺ was also regenerated by cathodic reduction of Fe³⁺. The influence of various operational parameters such as solution pH, cathode potential, Fe³⁺ and Fe²⁺ concentration, and AQDS doping concentration on amaranth azo dye degradation efficiency （color fading and total organic carbon （TOC） removal） were studied and the best experiment conditions for dye degradation was established. In addition, the electrocatalytic activities of the bare graphite and the AQDS/PPy/graphite cathodes towards oxygen reduction and Fe²⁺ regeneration were studied using CV and cathodic polarization technologies, and the effects of various operational parameters such as solution pH, cathodic potential, oxygen flow rate and AQDS doping concentration on H₂O₂ accumulation and current efficiency were investigated systematically. The results show that H₂O₂ generation and Fe²⁺ regeneration mainly depend on the cathode materials utilized. The AQDS/PPy/Graphite composite film electrode exhibits the characteristic of gas diffusion cathode and is highly efficient for H₂O₂ electrogeneration with high generation rate and current efficiency, while the bare graphite electrode exhibits better electrocatalytic activity for Fe²⁺ regeneration. The suitable Fe²⁺ and Fe³⁺ concentration is an important and crucial factor for electro-Fenton oxidation ability and efficiency. The CV and fourier transfer infrared （FT-IR） analyses confirm that the bulk AQDS strongly interacts with PPy matrix and cannot be expelled from the polymer after use in electro-Fenton process, but there is a slight decrease in the electrocatalytic activity of AQDS/PPy composite film.更多还原