【作者】 周婧；

【导师】 赵高凌；

【作者基本信息】 浙江大学 ， 材料学， 2012， 博士

【摘要】 二氧化钛(TiO2)纳米材料具有成本低廉、无毒无害、应用广泛等优势,在光催化和太阳能电池等领域已经受到了越来越多的关注。同时,纳米材料的维度和尺寸已成为材料制备和应用领域的关键因素。由TiO2纳米结构单元有序排列组成的结构具有特殊的拓扑结构和维度尺寸,因而在光催化和太阳能电池等领域极有可能带来新的优越性能。本论文在对相应领域进行文献普查的基础上,针对传统纳米粉末光催化剂容易团聚和纳米颗粒多晶薄膜光电转换效率受限的问题,展开三维二氧化钛纳米结构和二氧化钛纳米棒阵列薄膜的制备机理研究。用溶剂热法制备得到了不同微观结构的三维TiO2纳米结构和TiO2纳米棒阵列薄膜,在TiO2纳米棒阵列薄膜上沉积CdS纳米颗粒,并对样品的光催化和光电化学性能进行了研究。本文的主要研究结果如下：通过改变溶剂极性,在无需添加表面活性剂或其他添加剂的条件下,经过一步溶剂热法合成不同微观结构二氧化钛组装而成的三维纳米结构。在非极性溶剂中,金红石相TiO2纳米棒自组装形成三维蒲公英状二氧化钛结构,在低极性或者极性溶剂中,也就是两亲性溶剂中,锐钛矿相TiO2纳米粒子自组装形成微米球,以纯水为溶剂时,形成TiO2的块状团聚物。给出了不同溶剂中TiO2纳米结构的生长机理。揭示了在非极性溶剂体系中,酸性介质、反应温度和反应物浓度对TiO2纳米结构的微观结构、光学性质和光催化活性有着显著影响。以盐酸为酸性介质制备的样品为棒状金红石型TiO2组成的三维蒲公英状结构,以硝酸或醋酸为酸性介质得到的样品均为锐钛矿型TiO2纳米粒子组成的三维球形结构。纳米棒尖端具有锥形结构的TiO2比顶端为平面的纳米棒、纳米棒碎片或纳米颗粒球形结构具有更低的反射率、更高的光吸收强度和更好的光催化活性。阐述了三维TiO2纳米结构在不同生长条件下的生长机理。对TiO2纳米棒阵列薄膜的研究表明,纳米棒的几何形貌,特别是尖端结构是决定TiO2薄膜光电极光电化学性能的关键因素。采用溶剂热法在非极性溶剂中制备二氧化钛纳米棒阵列薄膜,通过控制反应物中的钛源浓度来调节纳米棒的几何形貌。具有锥形尖端形貌的二氧化钛单晶纳米棒阵列薄膜具有梯度折射率和内部散射效应,能够获得更低的反射率、更高的光捕获效率、更快的电荷-载流子分离和传输、更好的亲水性和后续的量子点组装。在TiO2纳米棒表面沉积CdS纳米颗粒进行敏化。具有锥形尖端结构的TiO2薄膜光电极经CdS量子点敏化后具有很好的光电化学性能,光电流密度为5.13 mA/cm2,是相应的未敏化样品的25.6倍,IPCE最大值约为22%,出现在400-500 nm的可见光区。更多还原

【Abstract】 Titanium dioxide (TiC2) nano-materials has attracted considerable attention due to its low-cost, nontoxicity and widespread applications. Meanwhile, dimensionality and size of the materials have been regarded as critical factors in the areas of material preparation and application. TiO2 ordered nanostructures has caused great interest and is expected to have potential applications in photocatalysts and solar cells due to its unique topological structure and dimensionality. Traditional nanometer-scale powders are likely to aggregate. The conversion efficiency of polycrystalline films is limited. In this work, three-dimensional (3D) TiO2 nanostructures with various microstructures and TiO2 nanorod array films have been successfully synthesized via a surfactant-free and single-step solvothermal route. CdS nanoparticles were deposited on the TiO2 nanorod array films. Growth mechanisms of the TiO2 nanostructures and films were discussed. The photocatalytic and photoelectrochemical properties of the samples were investigated. The main results are as follows.Three-dimensional TiO2 nanostructures with various microstructures have been successfully synthesized by altering the solvent via a surfactant-free and single-step solvothermal route.3D dandelion-like TiO2 structures self-assembled of nanorods were synthesized in non-polar solvent based on water-nonpolar solvent interface. Microspheres composed of nanoparticles are obtained using low polar or polar solvent, which are also amphiphilic solvents. Only bulky aggregated TiO2 nanoparticles were obtained when pure water is used as the solvent due to the fast hydrolysis of titanium precursor. Mechanisms of the self-assembly of 3D TiO2 structures indifferent solvents were proposed.Acid media, reaction temperatures and reactant concentrations have highly impact on the microstructure, optical properties and photocatalytic activity of the 3D TiO2 nanostructures.3D dandelion-like microspheres assembled of radial rutile nanorods are obtained in the sample prepared with HC1. For the products derived from either HNO3 or HAc,3D spheres composed of anatase nanoparticles are present.3D dandelion-like structures with tapered tips showed lower reflectance, more efficient light harvesting, higher surface area and consequently higher photocatalytic activity compared with those with flat tops and fragment of nanorod sectors. The growth mechanism of the 3D dandelion-like nanostructures under various preparation conditions was discussed.The results indicated that the rod geometries, especially the tip morphologies, of the TiO2 nanorod array films were found to be crucial to photoelectrochemical performance of the film electrodes. TiO2 nanorod array film electrodes with different rod geometries were fabricated via solvothermal route. By controlling the solution growth conditions, the rod geometries, especially tip structures, of TiO2 were tuned. The vertical aligned hierarchical nanorod array s possessed conically shaped tip geometry, which was favorable for film electrode due to the reduced reflectance, enhanced light harvesting, fast charge carrier separation and transfer, suppression of carrier recombination, sufficient electrolyte penetration and subsequent efficient quantum dot assembly. CdS quantum dots were deposited on the TiO2 nanorod array films. CdS quantum dots sensitized TiO2 film electrode with tapered tips exhibited an enhanced photoelectrochemical performance, a photocurrent intensity of 5.13 mA/cm2 at a potential of 0 V versus saturated calomel electrode and IPCE of 22%in the visible light region from 400 to 500 nm.更多还原