【作者】 肖鹏；

【导师】 王新强；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2008， 博士

【摘要】 TiO₂纳米管是典型的一维纳米材料,拥有丰富的物理化学性质以及低的制备成本,因此蕴藏着更广阔的应用前景。特别是近年的研究表明,由于具有大的比表面积及纳米尺寸效应,与其它纳米结构形式相比,TiO₂纳米管在光催化、传感、太阳能电池等领域展现了巨大的开发潜力,已成为目前国际上纳米材料的研究热点之一。本论文工作以此为契机,探索制备出高度定向的TiO₂纳米管阵列,深入探讨了退火条件对其形貌及晶型结构的影响,系统研究了TiO₂纳米管阵列的电化学性质,并尝试开发其在介体型酶电极、锂离子电池电极等领域的应用。主要研究工作及内容概括如下:1)系统地研究了阳极氧化制备TiO₂纳米管的方法,探讨了不同电解液体系中TiO₂纳米管的制备条件,并通过阳极氧化自组装模型分析了TiO₂纳米管的生长机理。在HF电解液体系中,制备出的纳米管管径为40¹10nm,管长度为100⁵00nm。在KF电解液体系中,当电解液的pH值在3～5时,制备出的纳米管管径在40nm～110nm之间,管长在500nm～2μm。在有机电解液体系中,阳极氧化电压工作范围在20V～60V,制备出超长的TiO₂纳米管,最大管长度为60μm。XRD测试表明,制备出的TiO₂纳米管为非晶态。2)另外,在有机电解液体系中,我们成功制备出以FTO为衬底的TiO₂纳米管薄膜,管孔径为90nm,管长度为5μm。在450℃空气中退火处理后,纳米管由非晶态转变为锐钛矿相。TiO₂纳米管薄膜由退火前的不透明转变为退火后的透明,紫外-可见光谱分析表明在400nm处有一明显吸收峰。这一研究工作为开发基于TiO₂纳米管的太阳能电池奠定了基础。3)对制备的TiO₂纳米管分别进行空气及氮气气氛中的退火处理,详细研究了退火温度、退火气氛对TiO₂纳米管的形貌及晶型结构的影响。发现在空气中当退火温度大于800℃时,纳米管结构开始塌陷,且锐钛矿向金红石转变的温度在750℃。而在氮气中退火处理后明显观察到纳米管的收缩效应,700℃时,纳米管结构开始塌陷,锐钛矿向金红石转变的温度为650℃。基于上述实验现象,我们进一步分析了TiO₂纳米管在退火过程中的相变模型及相变机理,指出在氮气中退火,影响其结构的变化及相变过程的主要因素存在于两个方面,一是氧空位的产生;二是Ti3+离子的参杂效应。这在前人的工作中还未见报道。4)结合循环伏安法及交流阻抗谱法,深入研究了TiO₂纳米管的电化学性质,并从非化学计量化合物角度及缺陷反应方程式推导出氧空位的形成是氮气气氛中退火处理后TiO₂纳米管电极电导率提高的主要原因。研究发现,非晶态TiO₂纳米管电极的伏安响应为不可逆电子传递反应;空气中退火处理后的TiO₂纳米管电极的循环伏安响应为有表面吸附的不可逆反应;而氮气中退火处理后的TiO₂纳米管电极的循环响应表现出了较好的伏安曲线,氧化峰与还原峰电位分离ΔEp为0.18V,满足准可逆反应的标准,电极上的电子转移速度常数k 0 = 1 .87×10?3cm/s。交流阻抗谱模拟表明,氮气中退火的纳米管,其电极表面电荷转移电阻Rct的值比非晶态及空气中退火处理的纳米管电极小70%～80%。这项研究工作是本论文的主要创新之处。5)通过共吸附法将辣根过氧化酵素（HRP）及电子介体硫堇（Th）修饰在TiO₂纳米管电极上,制备出TiO₂纳米管介体型酶电极。通过循环伏安法及安培法探讨了TiO₂纳米管酶电极对不同浓度的H2O2的催化效应,推导出响应电流与H2O2浓度的线性拟和关系,对于氮气退火处理后的酶电极,响应范围为0.5×10-5 3.6×10-3 mol/L,灵敏度为89μA/mM,是非晶态酶电极的4-7倍,检测下限为0.5×10-6 mol/L,这是本论文的一项创新之处。6)研究了氮气气氛中不同温度下退火处理的TiO₂纳米管的电化学嵌锂性能,通过循环伏安法探讨了锂离子在纳米管电极表面的嵌入/脱嵌过程,通过计时电位法研究它的充放电容量及稳定性。结果表明,在每个放电周期中,300℃退火样品的放电容量是最大的;而从充/放电的循环性能表明,400℃退火样品放电容量的稳定性是最好的。将TiO₂纳米管电极的电化学嵌锂性能与MnO2薄膜电极进行比较,发现前者的放电容量的稳定性要远远高于后者,这为开发高度定向型纳米管锂离子电池电极奠定了实验基础,进一步的工作还有待继续开展,这是本论文的又一创新之处。更多还原

【Abstract】 Titania nanotubes （TNT）, which is a typical one dimension nanomaterial, possess unique combinations of physicochemical properties and relatively low synthesis costs than other nanomaterials. Several recent studies have indicated that titania nanotubes have improved properties compared to any other form of titania for application in photocatalysis, sensing, photoelectrolysis, and photovoltaics due to their high surface-to-volume ratios and sizedependent properties. In this paper,we fabricated highly-ordered tinatia nanotube arrays by anodization,investigated the changes of its morphology and crystallized structure at different annealing conditions,studied the electrochemical properties of TiO₂ nanotubes and its application in medium enzyme electrode and lithium battery electrode. We abstract the main content of this dissertation as following:1)Fabricate the TiO₂ nanotubes arrays by anodization in different electrolyte and investigate the electrochemical conditions. In HF-based electrolyte, uniform titania nanotube arrays of various pore sizes （40¹00nm）, lengths （100⁵00 nm） are grown by controlling the anodization potential between 10V²2V and the concentration of F—between 0.05 0.3mol/L. Based in KF and ethylene glycol + NH4F electrolytes respectively, the nanotube pore size is from 40nm to 110nm, the length is from 1μm to 60μm. The as-prepared TiO₂ nanotubes are amorphous, EDX and XPS spectra presented that the TiO₂ nanotubes consisted by O and Ti, also existing F & C traces.2)Fabricate the TiO₂ nanotubes film on FTO substrate. The TiO₂ nanotubes film was fabricated by anodization Ti film and annealed in air. The XRD analysis showed that anatase phase of TiO₂ nanotubes were formed and the film was transparent after annealing, Uv-vis spectra of the transparent TiO₂ nanotubes film presented an adsorption peak on 400nm wavelength.3)Investigate the electrochemical properties of TiO₂ nanotubes arrays by cyclic voltammetric and AC impedance spectra. For amorphous TiO₂ nanotubes, the electrode reaction shows an irreversible response. For TiO₂ nanotubes annealed in air, the peak current is linear to scan rate, showing a irreversible response with absorption. While for the TiO₂ nanotubes annealed in nitrogen, the CV results showed a quasi-reversible response with a potential separationΔEp 0.18V, the electron transformation constant is k 0 = 1 .87×10?3cm/s. The electrochemical impedance spectra showed that the electron transformation resistance Rct of TiO₂ nanotubes annealed in nitrogen was less 70% ⁸0% than the Rct of TiO₂ nanotubes annealed in air, this presented that the electrical conductivity of TiO₂ nanotubes annealed in nitrogen was much improved than TiO₂ nanotubes annealed in air.4)Coadsorbed of horseradish peroxidase （HRP） with thionine （Th） on TiO₂ nanotubes and fabricated the medium enzyme biosensor. The addition of H2O2 leads to the biocatalytic oxidation of the reduced thionine in the presence of HRP. The investigation of TiO₂ nanotubes biosensor for H2O2 presented that the sensitivity of TiO₂ nanotubes electrode annealed in nitrogen was 4-7 times higher than the sensitivity of as-grown TNT electrodes. This allows us to develop a novel H2O2 sensor with a detection range from 0.5×10-5M to 3.6×10-3M and the sensitivity 89μA/mM.5)Investigate the lithium ions intercalation for TiO₂ nanotubes annealed in nitrogen at different temperatures. The electrochemical measurement showed that 300°C annealed arrays exhibited the best performance with a high discharge capacity of 240 mAh/g in the first cycle at a high current density of 640 mA/g. Good cycling stability was also observed in 400°C annealed arrays: beginning with a discharge capacity of 163mAh/g, after 50 cycles, the capacity still remained at145 mAh/g. This great enhancement of discharge capacity and stability at high current density could be attributed to the large active surface area of the nanotube arrays, a short facile diffusion path for Li-ions and improved electrode charge transfer conductivity brought about by N2 annealing. MnO2 film was deposited by electrochemical method, the measurement of lithium ions intercalation was performed by CV and CP, the results were compared with the properties of TiO₂ nanotubes.更多还原