【作者】 许元妹；

【导师】 张正国；

【作者基本信息】 华南理工大学 ， 化学工程， 2010， 博士

【摘要】 TiO2纳米晶是重要的多功能纳米材料,在光催化、气体传感器、光学材料以及染料敏化太阳电池等诸多领域具有广阔的应用。具有高效率和低成本特点的染料敏化太阳电池被誉为是传统硅太阳电池的有力替代者。探索晶型与形貌可控可调、工艺简单易控且收率高的TiO2纳米晶的制备途径,不仅具有理论研究价值,而且也是大规模推广应用TiO2纳米晶的关键。将特性优良的TiO2纳米晶和取向薄膜应用于染料敏化太阳电池,有利于提高染料敏化太阳电池的光电转换效率,推进其商品化进程。本论文的第一部分工作是研究强碱性水热法制得的钛酸盐纳米管和纳米棒向晶相组成和形貌各异的TiO2纳米晶的水热转化,采用XRD、TEM以及HRTEM对产物的晶相和微观形貌进行了表征。系统研究了钛酸盐纳米管水热转化中钠离子含量、水热体系pH值和水热温度等工艺条件对所得产物的晶相组成和形貌的影响,并结合HRTEM提出了钛酸盐纳米管向TiO2纳米晶的水热转化机制。结果表明：在pH≥1.0的体系中,钛酸盐纳米管水热转化为以锐钛矿相为主的TiO2纳米晶；在pH≤0.5的体系中则转化为两头为锥形结构的单晶金红石相纳米棒。钛酸盐纳米管中钠离子含量对其水热转化所得TiO2产物的相组成、形貌和尺寸都有明显的影响。在水热处理过程中,钛酸盐纳米管首先转化为尺寸约为3 nm的锐钛矿相纳米晶,再通过这些细小纳米晶的生长,最终得到晶相组成和形貌各异的TiO2纳米晶,这种生长过程涉及质子化、定向附着和Oswald熟化。研究了钛酸盐纳米棒的水热过程中体系的pH值和温度对产物晶相组成和形貌的影响。在pH为0的体系中制得了金红石相和板钛矿相两种晶相共存的纳米棒和纳米颗粒混合产物；在其它pH值为2、4、和7的条件下,均得到了纯锐钛矿相TiO2纳米棒；当二次水热温度低于180℃时,纳米棒前驱体没有转化完全,所得产物为前驱体与锐钛矿相TiO2共存的纳米棒；当水热温度为180℃和210℃时,产物为纯锐钛矿相纳米棒。通过钛酸盐一维纳米材料的水热转化来制备TiO2纳米晶具有产物晶相组成和形貌可控、收率高以及工艺易于控制的特点。本论文的第二部分研究工作是采用低温溶液法沉积取向性金红石TiO2膜。用XRD、SEM以及TEM对TiO2膜的晶相和微观形貌进行了表征。结果表明所沉积的金红石TiO2膜为取向性薄膜,且结晶度很好,垂直于衬底表面,在[001]方向择优生长。考察了反应时间,酞酸丁酯体积,四氯化钛浓度以及盐酸用量等工艺条件对TiO2薄膜厚度及形貌的影响,用SEM和TEM观察TiO2膜的微观结构,测定了薄膜的吸收光谱和荧光光谱,并用接触角测定仪表征了薄膜的超亲水性。结果表明：反应时间、前驱体酞酸丁酯体积和四氯化钛浓度以及盐酸体积改变时,TiO2材料的形貌和膜的厚度均发生改变；紫外可见漫反射光谱表明所合成的TiO2材料的最大吸收在波长374nm处,禁带宽度为3.06ev；不同条件下制备的TiO2膜的荧光锋位置和形状几乎相似,但峰强度不同；所合成的TiO2膜用紫外光照射3 min表现出良好的超亲水性。第三部分工作是将钛酸盐纳米管水热转化制得的双锥形锐钛矿相纳米晶和用低温溶液沉积法制得的金红石取向性薄膜用作染料敏化太阳电池的光阳极。在基于锐钛矿Ti02纳米晶的染料敏化太阳电池的研究中,制备了不同厚度的TiO2纳米晶多孔膜,采用SEM观测了多孔膜的微观形貌,测定了多孔膜的BET比表面积；测试染料敏化太阳电池的I-V特性,考察膜厚对电池的开路光电压、短路光电流密度、填充因子以及光电转化效率等性能参数的影响,并与基于P25纳米TiO2粉的染料敏化太阳电池进行性能对比。结果表明：(1)用水热法制备的纳米晶Ti02结晶度好,为纯的单晶锐钛矿。与P25粉相比,纳米晶多孔膜的比表面积大。(2)纳米晶TiO2膜的染料吸附量高于P25膜。(3)由纳米晶TiO2组成的染料敏化太阳电池的光捕获效率(LHE)高,导致其光电流密度和转换效率都明显高于用P25组成的DSSC。在基于金红石取向性薄膜的染料敏化太阳电池的初步研究中,测试了电池I-V特性,得到电池光电流密度Jsc为7.9mA/cm2,开路电压Voc为731mV,填充因子FF为59%,电池的总的转换效率η为3.41%。更多还原

【Abstract】 TiO2 nanocrystals are well-known as important multifunctional nanomaterials, and have been widely used in many fields, such as photocatalysts, gas sensors, optical materials and dye-sensitized solar cells. Dye-sensitized solar cells that possess the properties of high conversion efficiency and low cost are considered as a promising alternative for conventional silicon solar cells.To explore a route with simple process and high production yield for synthesis of TiO2 with controllable phase composition and morphology, not only is of significance for scientific research, but also is the key step to promote the large-scale application of TiO2 nanocrystals.In the first part of this dissertation, we studied hydrothermal transformation from titanate one-dimensional nanotubes and nanorods produced by the alkaline hydrothermal method into TiO2 nanocrystals with different phase composition and morphology. The obtained products were characterized by XRD,TEM and HRTEM. For the hydrothermal transition of titanate nanotubes, the effects of the sodium content in titanate nanotubes, the pH value and the hydrothermal temperature on the phase composition and morphologies of TiO2 nanomaterials were investigated. Based on the HRTEM images, the transformation mechanisms from titanate nanotubes to TiO2 nanocrystals were presented. It was shown that, the pH value of the titanate nanotube suspension had a significant influence on the phase composition and morphology of TiO2 nanocrystals.The H-titanate nanotubes were predominately transformed into anatase nanoparticle with rhombic shape when the pH value was greater than or equal to 1.0, whereas primarily turned into rutile nanorod with pyramidal ends at the pH value less than or equal to 0.5.We propose a possible mechanism for hydrothermal transformation of H-titanate nanotubes into single-crystalline TiO2 nanomaterials. While the H-titanate nanotubes transform into tiny anatase nanocrystallites of ca.3 nm in size, the formed nanocrystallites as an intermediate grow into the TiO2 nanomaterials with controlled phase composition and morphology. This growth process involves the steps of protonation, oriented attachment, and Ostwald ripening. The sodium content of titanate nanotubes also has an effect on the phase composition and morphology of the obtained TiO2 nanomaterials. For the hydrothermal transformation of titanate nanorods, a mixture of nanoparticles and nanorods with the phase composition of rutile and anatase coexisting was obtained under the condition of pH 0; the anatase nanorods were produced under the condition of pH 2,4 and 7; when the hydrothermal temperaure was low than 180℃, the titanate nanorods have not completely been transformed to TiO2;when the hydrothermal temperaure was 180℃and 200℃, anatase nanorods were obtained.In the second part of this dissertation, oriented rutile TiO2 films were deposited by low-temperature solution method. The obtained TiO2 films were characterized by XRD,TEM and HRTEM. The results indicates that the TiO2 film is well crystallized and grows perpendicular to the substrate, and a preferential orientation in the [001]direction. The effects of process conditions including the growth time,the amount of tetrabutyl titanate, the concentration of titanium tetrachloride, and the amount of hydrochloric acid on the thickness and morphology of films were investigated. The microstructure of TiO2 films were characterization by SEM, TEM and HRTEM. The UV-vis and photoluminescence spetra of the oriented films were measured. The super-hydrophilic properties of the oriented films were characterized by measuring the contact angles. The results indicated that the morphology and thickness of rutile TiO2 film varied by changing the growth time, initial titanium precursor concentration of tetrabutyl titanate and titanium tetrachloride,and the amount of hydrochloric acid. The diffuse reflectance UV-Vis spectra of the rutile TiO2 film indicated that the maximum absorbance was at 374nm and the band gap Eg for the rutile TiO2 is about 3.06 eV. The line shapes in the PL spectra from all the samples are similar, but the intensities of the features in the PL spectra are different from each other. Rutile TiO2 films show super-hydrophobic feature after UV illumination only for 3 min.In the third part of this dissertation, the single-crystalline anatase nanoparticles prepared by the hydrothermal transformation of titanate nanotubes and the oriented rutile TiO2 films prepaed by the low-temperature solution method were used as the photoanodes of dye-sensitized solar cells (DSSCs).Porous TiO2 films with different thickness were fabricated by using the bipyramidal anatase nanocrystals, and their microstructures and specific surface area were characterized by SEM and N2 adsorption. The I-V curves of the DSSCs, including the open voltage, photocurrent density and conversion efficiency were evaluated as compared with the DSSCs based on the commercially available P25 TiO2 nanopowder. The results indicated that:(1)TiO2 nanocrystalline was pure anatase with good crystallinity, and had larger specific surface area, thus exhibited stronger optical absorption as compared with P25 powder. (2) The mesoporous film made from the nanocrystalline TiO2 absorbed more dye molecules as compared with the film made from P25.(3)The mesoporous film made from the nanocrystalline TiO2 exhibited higher light harvesting efficiency (LHE), thus the photocurrent densities and conversion efficiencies were obviously superior over those of the cells based on the P25 films.DSSCs based on oriented rutile thin films.The I-V properties of the DSSCs were evaluated and photocurrent density Jsc (7.9mA/cm2), open voltage Voc (731mV), fill factor FF (59%) and overall conversion efficiencies of the dye-sensitized solar cellsη(3.41%) were obtained.更多还原