【作者】 童天中；

【导师】 张金龙；

【作者基本信息】 华东理工大学 ， 应用化学， 2010， 博士

【摘要】 开发高效实用的光催化材料是光催化研究的核心目标,纳米Ti02以其廉价、化学性质稳定、无毒无害,优越的物理化学特性,在环境污染物降解方面等领域显示出广阔的应用前景。论文从纳米Ti02制备入手,通过合成条件的选择,控制纳米二氧化钛粒子的晶型和形貌,从而获得高光催化活性；通过过渡金属离子和稀土金属离子的掺杂,有效地抑制光生电子和空穴的复合,提高Ti02的光催化效率；改变光激发路径,拓展Ti02对可见光的光谱响应范围。相关研究有利于提高Ti02光催化技术的实用性。利用溶胶凝胶和水热法制备纳米Ti02,通过调节晶化过程中酸的种类、酸浓度和水热温度,分别制备出纯金红石相(R),锐钛矿(A)和板钛矿(B)两相混晶,以及不同比例的R、A和B三相混晶,对样品分别进行XRD、TEM等表征；盐酸和硝酸溶液中水热晶化过程可以通过酸浓度和水热温度的调节控制混晶的比例,混晶的比例主要由不同晶相热力学和动力学稳定性决定,酸浓度的影响主要体现在水解路线不同和晶核表面吸附电荷多少上；硫酸溶液中,水热晶化得到的晶体都是由A和B两种晶型组成的混晶,并且混晶的比例与硫酸浓度和水热晶化温度无关。硫酸根离子的存在通过空间位阻和晶核表面同性电荷相斥作用进而生成更多晶核,抑制晶核长大,阻止R相生成。通过超声状态下酯化原位水解和水热晶化相结合,制备出具有球形形貌的纯锐钛矿型纳米Ti02微球,采用XRD、TEM、XPS、EPR、AAS、FT-IR、DRS和N2吸附-解吸等手段分别对制备的样品进行了测试和表征；该微球具有不规则孔道和介孔结构。多孔和介孔结构的形成可能与超声下的原位缓慢水解有关,而锐钛矿的形成与硫酸根离子的存在有关。在球形形貌锐钛矿纳米Ti02制备基础上,制备了Fe3+掺杂纳米Ti02光催化剂,并对制备的样品进行XRD、TEM、XPS、EPR、AAS、UV-vis DRS和N2吸附-解吸等表征。相关表征结果证明：Fe3+离子能取代Ti4+离子进入Ti02晶体结构形成新的Ti-O-Fe键；掺杂纳米Ti02保持了纯锐钛矿晶型和有孔结构的球形团聚体形貌。掺杂进入的Fe3+/Fe4+能级高于TiO2价带能级,而Fe3+/Fe2+能级低于TiO2导带能级,Fe3+能同时捕获光生电子和空穴,阻止它们复合几率,提高催化剂光催化活性,但掺杂量过大反而可能形成复合中心,降低催化活性；掺杂后样品对可见光区域的吸收增强,可能来源于光生电子从掺杂能级(Fe3+/Fe4+)到二氧化钛导带的电子激发迁移所致。在球形形貌锐钛矿纳米Ti02制备基础上,制备了稀土元素Ce4+掺杂纳米Ti02光催化剂,并对样品进行了XRD、UV-vis DRS、SEM-EDS、AAS和XPS等测试和表征。结果表明：Ce4+离子可能没有取代Ti4+离子进入Ti02晶体结构中,而是以Ce02和Ce203等形式掺杂在Ti02八面体的间隙,或者仅仅吸附在Ti02晶体的表面；改性纳米Ti02保持着掺杂前纯锐钛矿晶型和有孔结构的球形团聚体形貌,但晶体平均粒径有所减小,表面积有所增大。掺杂改性增强了纳米Ti02在紫外光和可见光下光催化活性,可见光下,电子可以直接从掺杂Ti02的价带激发到Ce 4f能级上,或者电子从Ce203基态被激发到Ce 4f能级上；紫外光下,Ce4+掺杂不仅促进了过氧自由基的生成,也因为对光生电子的捕获,降低了光生电子和空穴的复合几率,提高了半导体光量子效率。更多还原

【Abstract】 It is the key target of photocatalysis research to explore highly effective photocatalytic materials. Due to its low cost, chemical stability, non-toxicity, and favorable physical/chemical properties, nano-TiO2 has been considered to be a promising photocatalysts in the applications of photocatalysis, especially in the decomposition of environmental contaminants. In this thesis, high photocatalytic activity TiO2 were prepared by selecting appropriate preparation condition to control the crystalline phase and morphology of TiO. Then, metal and rare earth doping was used to not only restrain the recombination of photogenerated electrons and holes, but also extend the light response of TiO2 into the visible light region. Above mentioned relative study is favorable for the practical application of TiO2-based photocatalysis.Nano-TiO2 samples were prepared with sol-gel and hydrothermal methods. By changing the type and concentration of used acids as well as the hydrothermal temperature, pure rutile (R), bicrystalline mixture of anatase (A) and brookite (B), and tricrystalline mixture with different ratio of A, R, and B were prepared. The samples were characterized by the XRD and TEM. In the HCl and HNO3 aqueous solutions, the hydrothermal crystallization process can be controlled by changing the concentration of acid and the temperature of hydrothermal treatment. The proportion of different crystal phases are determined by the thermodynamic and kinetic stabilities of different crystal phases, while the concentration of acid can influence the route of hydrolysis and the amount of charges adsorbed on the surface of TiO2 crystal nuclei. In H2SO4 solution, the obtained samples consist of bicrystalline mixture of A and B, and the ratio of anatase and brookite is independent of the concentration of H2SO4 and the temperature of hydrothermal treatment. The presence of SO42- ions can increase the steric repulsion and electrostatic repulsion among different nuclei, consequently promoting the formation of more crystal, restraining its growth, and preventing the formation of rutile.Anatase TiO2 microspheres with porous frameworks have been prepared by controlled hydrolysis with water generated "in situ" via an esterification reaction under ultrasound irradiation, followed by hydrothermal treatment. The samples were characterized by XRD, TEM, XPS, EPR, AAS, FT-IR, DRS, and nitrogen adsorption-desorption methods. It was found that the obtained TiO2 microspheres consist of disordered wormhole-like porous and mesoporous structures. The formation of porous structure might be related to the slow ’in situ’ hydrolysis under ultrasound irradiation. The formation of unique anatase should be attributed to the presence of SO42- ions.On the basis of preparing anatase nano-TiO2 microspheres, a series of Fe-doped TiO2 catalysts were prepared, and characterized by XRD, TEM, XPS, EPR, AAS, UV-vis DRS, and nitrogen adsorption-desorption. The results indicated that Fe3+ ions can be incorporated into the crystal lattice of TiO2 to substitute Ti4+, leading to the formation Ti-O-Fe bond. Similar to the undoped TiO2, Fe-TiO2 also exhibits anatase phase, porous structure, and spherical shape. The energy level of Fe3+/Fe4+ is above the valence band edge of TiO2 and the energy level for Fe3+/Fe2+ is below the conduction band edge of TiO2. Therefore, Fe3+ ions, acting as both electrons and holes traps, can restrain the recombination of photo-generated electrons and holes, resulting in the increase of photocatalytic activity. However, when the doping amount of Fe3+ ions is too large, Fe3+ ions can act as the recombination centers of the photo-generated electrons and holes, resulting in the decrease of photocatalytic activity. The enhancement of light absorption of Fe-TiO2 in the visible region is resulted from the electronic transition from the dopant energy level (Fe3+/Fe4+) to the conduction band of TiO2.On the basis of preparing anatase nano-TiO2 microspheres, rare earth Ce-doped TiO2 catalysts were prepared, and characterized by XRD, UV-vis DRS, SEM-EDS, TEM, AAS, and XPS. The results revealed that Ce4+ ions did not substitute Ti4+ into the crystal lattice of TiO2, but were doped into the interstitial sites of TiO2 octahedra or adsorbed on the crystal faces of TiO2 crystallites. Similar to the undoped TiO2, Ce-TiO2 also remained anatase phase, porous structure, and spherical shape. However, Ce modification can decrease the crystallite size and increase the surface area of TiO2. Ce modification improves the photocatalytic activity of TiO2 under both UV and visible light irradiation. Under visible light irradiation, electrons can be excited from the valence band of Ce-TiO2 into Ce 4f level or be excited from the ground state of Ce2O3 into Ce 4f level. Under UV light irradiation, Ce4+ modification not only promotes the formation of hydroperoxy radicals but also restrains the recombination of electrons and holes by trapping the photogenerated electrons, resulting in the improvement of quantum yield.更多还原