模板法合成聚吡咯纳米材料和器件及其电化学性质研究

【作者】 刘玲；

【导师】 江志裕；

【作者基本信息】 复旦大学 ， 物理化学， 2005， 博士

【摘要】 纳米材料的有序微阵列体系的制备对于规模化功能器件例如微探针、传感器和动力元件等的研制具有特别重要的意义。氧化铝有序阵列模板具有高度有序、制备工艺简单、且易于工业化生产等特点。采用氧化铝模板合成纳米材料已被视为制备纳米材料有序阵列体系最有前途的方法之一。导电高聚物优异的物理化学性能使其在能源（太阳能电池，二次电池）、光电子器件、电磁屏蔽、隐身技术、传感器、金属防腐、分子器件和生命科学等技术领域都有广泛的应用前景。作为一种重要的导电聚合物，聚吡咯材料具有优良的电化学可逆性，对环境稳定性高等优点，因此具有重要的应用价值。本文采用电沉积、化学沉积等方法结合模板技术合成聚吡咯纳米材料的有序微阵列，研究了它们的电化学性能。首次制备了纳米电容器、生物传感器阵列电极，研究了纳米聚吡咯阵列电极的光电化学性质，研究了纳米聚毗咯二极管的制备和性质，以及吡咯在纳米孔中的生长机理。所获得的主要结果和结论如下：1、采用二次电化学阳极氧化的方法，优化合成工艺，在草酸溶液中制备了孔径为60～80nm的厚度可控的高度有序氧化铝阵列模板。模板厚度可通过控制阳极氧化时间和在酸溶液中的浸泡时间加以控制，并探讨了孔的生长机理。2、利用交流电沉积的方法制备了有序聚吡咯纳米管阵列，研究结果表明：聚吡咯纳米管首先沿着管壁生长，在氧化铝模板的孔中填充是不均匀的，有的管的内径减小至10nm，有些管顶部被生长的聚吡咯所堵塞。有的即使提高电压和增加电沉积时间也不能将孔完全填满。电化学交流沉积是合成较短的纳米管状聚吡咯材料的一种好的方法。3、采用电化学恒电位沉积的方法在氧化铝有序阵列模板中制备了聚吡咯纳米线阵列。并研究其在模板纳米孔中的生长机理，分为成核、一维生长、二维生长和三维生长四阶段。由不同扫描速度下的循环伏安图可以发现，阴极峰电流与扫描速度呈线性关系，说明聚吡咯纳米线的电化学行为符合薄层电极的特征：0.2V以上的电位扫描区域体现了双电层电容的充放过程。通过测定不同电极电位下的交流阻抗图谱，计算出了0.4V电位下的扩散系数，ClO₄^-在聚吡咯纳米线中的扩散远高于在平面聚吡咯膜中的扩散，其反应电阻则小于平面聚毗咯电极的，提高了聚吡咯纳米线的氧化还原动力学过程。4、纳米聚吡咯器件的制备及表征。第一类，将恒电位电沉积制备的纳米聚吡咯线进行碱处理。碱处理使纳米聚吡咯线阵列电极的反应电流下降，材料结构发生变化。ITO／非活性纳米PPy的Ⅰ-Ⅴ特性曲线，显示了PPy电导率随所加电压的升高而增加的特点，可望用作纳米电子开关。第二类，先在氧化铝模板的孔中沉积金，再继续电沉积聚吡咯。Au／PPy和Au／非活性PPy的Ⅰ-Ⅴ特性曲线表明均显示了整流效应，可作为纳米整流器。该整流效应是由于纳米p型聚吡咯与金之间形成的异质结所引起的。5、采用电沉积和化学沉积的方法，用二氧化钛作隔膜成功地制备了聚吡咯纳米线阵列超电容。第一步，在AAO纳米孔的底部电沉积聚吡咯作为一个电极；第二步，继续电沉积二氧化钛作为隔膜；第三步，以过硫酸胺为氧化剂化学沉积聚吡咯作为另一个电极，制成纳米尺寸的PPy／TiO₂／PPy超电容。用钨针尖作探头，检测了纳米电容器的充放电性能。从充放曲线也证明纳米电容器组装成功，其电容值为3.5nF，且具有较好的充放电性能。6、纳米聚吡咯阵列电极的光电化学性质研究。在测定纳米聚吡咯阵列电极在-0.7～0.5V范围内的光电化学性质时，发现纳米聚吡咯阵列电极在此电位范围内存在明显的阴极光电流，该电流可由聚吡咯的p型半导体的性质来解释。光电流与厚度有密切的关系。存在最佳厚度，当厚度在40nm～50hm之间，有最大光电流。当厚度增加时，光电流响应减小。这是由于在厚膜中光生电子和空穴易于复合猝灭的缘故。实验还发现由于AAO模板对聚吡咯纳米线的隔离散热作用，未测到聚吡咯的阳极光电流。聚吡咯纳米线可作为纳电子线路中的纳米光电器件。7、用两步法在氧化铝模板中制备了聚吡咯葡萄糖生物传感器纳米阵列电极。第一步，在恒电位0.5V（vs.SCE）下，pH=6.86的含有1.5mg／ml的葡萄糖氧化酶的磷酸缓冲溶液中，将葡萄糖氧化酶电吸附进入氧化铝模板的孔中。第二步，在含有吡咯单体和葡萄糖氧化酶的溶液中共沉积形成聚吡咯葡萄糖生物传感器纳米阵列。该纳米聚吡咯葡萄糖生物传感器阵列电极对过氧化氢有好的渗透性，且使氧化电位下降至0.2V。红外光谱和TEM研究证实了葡萄糖氧化酶成功地固定在聚吡咯纳米线上，主要嵌入在聚吡咯纳米线的表面区域。两步固定法能大大提高酶在氧化铝模板孔中的固载量。聚吡咯葡萄糖生物传感器纳米阵列电极对葡萄糖的响应迅速（＜15s）。随着葡萄糖检测浓度的增加，电流～葡萄糖浓度标准曲线符合Michaelis-Menten特征，米氏表观常数是5.7mM，低于普通的葡萄糖氧化酶传感器的。表明固定的葡萄糖氧化酶有更高的生物活性，对葡萄糖有更高的亲和性。在pH=6.86的磷酸缓冲溶液经过两个月的保存，生物活性仍保持在原有活性的80％。更多还原

【Abstract】 The fabrication of ordered array nano structures are particularly important for obtaining scaled-up functional devices such as probes, sensors and micromechanical devices. One of strategies is to use Nanoporous alumina membranes with highly ordered nanochannel as template to prepare such structures on a large scale.Conducting polymers could be extensively used in the field of energy （photoelectrochemical cells, battery）, photoelectronic device, electromagnetism materials, shield technique, sensors, corrosion-resistance of metal, molecular devices and biology science for their excellent physical properties. As one of the most important conducting polymers, PPy is reversible in electrochemical behavior and stable to environment and it can be used in many fields.Preparation of uniform and ordered nano-sized material make the use of the new material possible, which attracts the attention of the chemical、 physical and material science. In the paper, anodic aluminum oxide （AAO） films were used as the templates. The PPy nano-sized materials were prepared in the pores of the template through ac and dc electrochemical methods. Nano devices such as diode, supercapacitor, biosensor based on PPy nanofibers were fabricated and their electronic and electrochemical properties were studied via electrochemical methods. The main results and conclusion can be summarized as following:1. The anodic aluminum oxide （AAO） template with the ordered straight nano-channel has been prepared by two-step anodizing process. The length and the pore diameter ranging from 60 to 80 nm of the AAO membrane can be adjusted in oxalic acid solutions by controlling the anodizing time and dipping time in acid solution.2. This work demonstrates the preparation of polypyrrole nano-tubules using AAO membranes as the template by electrochemical ac method which is an easy route to proceed. The presence of hollow tubules suggests that PPy initially deposits on the surface of the inner pore walls. The relative surface coverage of the filled pores is not uniform. The diameters of some nano-pores reduced to 10nm. Some nano-poreswere not filled completely and PPy did not stick out of membrane even by increasing the synthesis time and voltage.3. Polypyrrole nanofibers have been prepared by electrochemical dc method in AAO templates. The cyclic voltammgrams of a PPy nano-fiber arrays electrode at different scan rate were tested. The linear relationship between cathodic current peak and the potential sweeping rate reflects the electrochemical characteristic of thin film electrode. In the potential region higher than 0.2V the anodic current curves are paralleled with the cathodic current curves with relative high margins between. The behavior indicates that the charge and discharge of double layer capacity are the main processes in this region. The AC impedance spectrums of PPy nanofibers at different potential were also tested. The AC impedance spectrum at more positive potential accorded with the Ho model. The diffusion coefficient D of PPy nanofiber was calculated to be 2.38 × 10^-9cm²s^-1 much higher than 1.13 × 10^-11cm²s^-1 of PPy film.4. PPy nanofiber devices have been fabricated within two-step oxidized AAO membrane. Their electrical properties were measured using a simple way, in which an external power source and a very sharp Pt tip was used for measuring the I—V curves. The ITO/PPy nanofiber device presents a common resistance behavior. But after an alkaline treatment the ITO/ inactive PPy nanofiber device shows unusual behavior, at high voltage its conductivity becomes high. It might be used for nano-fiber switching diode. The Au/PPy or Au/ inactive PPy nanofiber devices demonstrate a rectifying behavior and might be used as nano-fiber rectifiers.5. The nano-supercapacitor consisted of electropolymerized PPy electrode / porous TiO₂ separator / chemical polymerized PPy electrode was fabricated in the array pores of two-step anodizing aluminum oxide （AAO） membrane, based upon layer-by-layer synthetic strategy. It performs typical electrochemical supercapacitor behavior with good charge-discharge ability, and presents the smallest capacity of 3.5nF right now. The nano devices could be useful for the development of nano electronic devices and microelectromechanical systems （MEMS）.6. Photoelectrochemical behavior of PPy nanofiber array electrode has been studied. The cathodic photocurrent response of PPy nanofiber array electrode hasbeen observed due to the semiconductor properties of PPy nanofiber. It was found that the thickness of PPy nanofiber array electrode was very important factor. There was an optimism thickness for photocurrent response. When the length of PPy fibers was more than 1.4 μ m, no photocurrent appeared. It could be explained that for thick PPy film the photoinduced electrons and holes were easy to recombine. No anodic photocurrent was observed.7. Novel glucose oxidase （GOx） sensor arrays with nanoelectrode population densities of up to 1×10¹⁰ / cm² nanoelectrodes was reported. The nanoelectrode sensors, were fabricated by first electroadsorping GOD followed by electrochemical codepositing PPy and GOx within the nanopores of anodic aluminum oxide （AAO） membrane electrodes. FTIR spectrum and TEM images show that GOx enzyme clusters were intercalated in PPy nanofiber, mainly in the region close to nanofiber surface. Due to the small size of the nanofiber sensor, the sensor gave very fast response （<15 s）. With the increase in glucose concentration, the response curve tends to be level off, featuring Michaelis-Menten characteristics. These features make the nanofiber sensor potentially useful for in vivo detection of glucose. The biosensor arrays also showed good stability. Amperometric measurements of lmM glucose were conducted over two monthes still with 80% of original sensitivity.更多还原