【作者】 陈敏；

【导师】 赵素玲；

【作者基本信息】 武汉理工大学 ， 材料学， 2012， 硕士

【摘要】 利用太阳能光催化分解水制氢技术因其节能环保的优点,已成为未来解决能源与环境问题的理想途径之一。Ta205及多数钽酸盐具有较高的导带位置,其光生电子具有较强的还原能力,因而在高效光解水制氢方面有重要应用潜力。但其较宽的带隙限制它们只能吸收紫外光,大大影响其产氢效率。催化剂的带隙、晶粒尺寸、比表面积等是影响光催化制氢活性的重要因素,本课题以氧化钽(Ta2O5)、氮化钽(Ta3N5)和钽酸铋(BiTaO4)纳米纤维为研究对象,对其结构、组成进行控制,考察了其在甲醇水溶液中的光催化制氢活性并讨论其影响因素。具体研究内容如下：(1)采用静电纺丝法结合退火工艺,以PVP为结构导向剂,通过改变升温速率制备了具有不同结构特征的Ta205纳米纤维,并测试比较了它们的光催化制氢性能。发现随退火工艺中升温速率的增加,样品的晶粒尺寸减小,介孔性和比表面积出现最大值。这主要是由有机物分解行为和无机物的结晶反应共同导致。随着升温速率的增加,纤维内形成较多Ta205晶核；同时,纤维迅速达到PVP的分解和Ta205的结晶温度,表面的Ta205迅速结晶成型,PVP的断链分解带动纤维以结晶部分为骨架定向收缩并分解挥发,从而在纤维内部留下孔洞形成介孔纤维结构。然而升温速率过快,PVP的剧烈燃烧挥发和Ta205的迅速结晶一定程度上阻碍了颗粒间的连结成型,造成孔洞坍塌形成粒子堆积使纤维比表面积减小。光催化制氢活性显示,样品的光催化产氢速率随比表面积的增大而增加,但不仅仅取决于比表面积,还与晶粒尺寸密切相关。(2)采用程序升温氨解法制备出了氮化钽纳米纤维,研究了Ta205纳米纤维前驱物的结构、组成和氮化时间等对氮化过程的影响。发现在相同的氮化方式下,无定形态的Ta2O5比晶态的Ta205更容易被氮化,且得到的氮化产物晶粒尺寸较小,纤维表面较光滑；但后者更容易得到结构稳定、具有明显多孔结构的氮化产物。无定形态多孔Ta2O5纳米纤维在700℃氨解2h即可产生氮化钽。随着氮化时间的延长和氮化温度的提高,产物的氮化程度提高,光吸收带边红移程度增大。以晶态Ta205纳米纤维为前驱体在800℃氮化4h得到的产物具有最高的产氢速率,这可归因于其具有良好的结晶性和多孔结构,能较强的吸收可见光。(3)发展了一种制备多元金属氧化物纳米纤维的简便方法,采用静电纺丝法制备了BiTaO4多孔纳米纤维。研究了退火温度对BiTaO4纳米纤维的晶型、吸光性质和可见光催化制氢性能的影响。结果表明,采用静电纺丝法可在较低的退火温度下得到BiTaO4多孔纳米纤维,其大约在700℃发生从正交晶型向三斜晶型的转变。退火温度对制备的样品的吸收带边影响不明显,均在430nm左右。随退火温度的升高,在750℃下退火的三斜晶型的BiTaO4表现出最好的光催化活性：16.6μmol/h。这与催化剂较好的结晶性和晶型有关。更多还原

【Abstract】 In order to preserve the fossil energy and protect the environment, people are trying their best to seek clean, renewable and affordable alternative energy. Water splitting for hydrogen production by solar energy has become an ideal way to solve the question of energy and environment. Ta2O5and tantalates have the relatively higher conduction band and its photo-induced electrons have strong reducibility, so they are more suitable for water splitting for hydrogen production. However, the wider band gap limits its visible light absorption. The grain size and the specific surface area of photocatalysts are the most important factors influencing photocatalytic hydrogen production activities. In this thesis, we focus on controlling structures and compositions of Ta2O5, Ta3N5and BiTaO4nano fibers, and investigating their properties of water splitting for hydrogen production.(1) Ta2O5nanofibers were prepared by electrospining method. By changing the heating rate we got different structural characteristics samples. The grain size, surface area, mesoporous properties and photocatalytic hydrogen production activities were investigated as a function of heating rate. We found that with the heating rate increase, the grain size of samples decreases, the mesoporous and the specific surface area have a maximum value. This is mainly due to the decomposition of organic matter and crystallization of inorganic matter. The faster the heating rate was, the more the crystal nucleus generated in the fibers; Ta2O5nanoparticles on the fibers’surface crystallized firstly, and the chain scission and decomposition of PVP drived fiber directed contraction to the crystalline on the surface, then the decomposition of PVP left the holes in the fibers. But if the heating rate was too rapid, the combustion of PVP and the fast crystallization of Ta2O5hindered the connection of the particles to some extent, result in holes collapse and specific surface decrease. Photocatalytic hydrogen production rate of as-prepared samples depended on not only the specific surface area, but also the grain size.(2) Tantalum nitride porous nanofibers were prepared by the mothod of temperature programmed aminolysis. The influence of the precursor composition of Ta2O5nanofibers, nitridation time as well as nitridation temperature on optical absorption properties and the photocatalytic activities of the as-prepared samples were studied. We found that the amorphous Ta2O5was more easily nitride than the crystalline Ta2O5in the same way of nitridation, and had the smaller grain size and relatively smooth surface. But the later one was apt to obtain the nitride product with structural stability and porous structure. As nitriding temperature rising and time increasing, the products had a significant red shift of optical absorption band edge. The nitride products which used crystalline Ta2O5nanofibers as precursor and nitrided at800℃for4h showed the highest activity, and this was due to its well crystallization and porous structure as well as the strong absorption of visible light.(3) A convenient method for synthetizing multi-metal oxide nanofibers was developed. BiTaO4nanofibers were prepared by electrospinning, the influence of the annealing temperature on the structure, optical absorption and photocatalytic hydrogen production activities of the nanofibers was researched. We found that the products began to change from orthorhombic crystal to triclinic crystal at about700℃, and crystal transformation completed when annealing temprature rose to750℃. UV-Vis results showed that the annealing temperature had slight effect on the optical absorption band-edge of BiTaO4nanofibers, which were all about430nm. The sample annealed at750℃had the best hydrogen production rate of16.6μmol/h. This is related to its good crystallinity.更多还原