【作者】 秦军；

【导师】 赵玉宝；

【作者基本信息】 南华大学 ， 应用化学， 2010， 硕士

【摘要】 本文选择在光催化领域备受关注的二氧化钛为研究对象,以密度泛函理论为基础,利用第一性原理的计算软件CASTEP对单斜态相TiO2的能带、态密度等电子结构进行了模拟分析,为关联单斜态相TiO2的光学特性和催化性能的研究提供理论依据。实验研究中,以Ti(SO4)2为原料、30%的H2O2为络合剂、NaOH为沉淀剂,采用新颖简单的化学络合水热合成法制备了单斜态TiO2纳米管。确定了制备单斜TiO2纳米管的最佳工艺条件和参数；结合X-射线粉末衍射仪(XRD)、激光拉曼光谱仪(LPS)、X-射线光电子能谱仪(XPS)、氮吸附BET比表面积测试、透射电镜(TEM)、热重分析仪(TG-DSC)、红外光谱仪(FT-IR)等技术,对TiO2纳米管的结构、形貌、表面性能及晶相结构进行了表征和细致的分析；以甲基橙的降解为探针反应,研究了单斜态纳米TiO2催化降解甲基橙的性能。以期为把握多晶相材料的构效关系提供科学依据,同时为水体中有机污染物的高效降解提供理论指导与技术支持。第一章引言主要介绍纳米TiO2的研究现状,光催化基本原理,一维TiO2纳米管的主要制备方法,第一性原理模拟计算的理论基础,以及本文的选题意义和研究内容。第二章采用基于密度泛函理论的平面波超软赝势方法进行材料的模拟计算,使用第一性原理方法计算了锐钛矿相TiO2和单斜态TiO2(B)结构参数、能带、态密度。结果表明：与锐钛矿型TiO2相比,单斜态TiO2(B)结构中Ti-O键也呈现较强共价键特征,但其对称性降低,Ti-O键长及重叠布居数也发生了变化；单斜态TiO2的禁带变宽(Eg为2.875 eV),比实验值3.3 eV小些,理论预测光吸收波长可发生蓝移,计算结果与已有的实验数据符合较好。第三章采用基于密度泛函理论的平面波赝势方法,对Na0.2TiO2的能带结构、电子态密度和电荷密度进行了分析计算。结果表明,Na0.2TiO2属于一种间接带隙半导体,禁带宽度为2.81 eV；其电子态密度主要由Ti的3d层电子和O的2p层电子的能态密度决定；该材料对紫外线有较强的宽频吸收,拓展了光谱响应范围,提高太阳能利用转化率和光催化效率；Ti-O键比Na-O键结合的更紧密,Na原子与O原子形成的是离子性较强而共价键较弱的混合键,Ti-O键的共价作用要强于Na-O键。因此,可以通过阳离子交换来调变钛酸钠的键特性及稳定性。第四章以Ti(SO4)2为钛源,H2O2为络合剂,NaOH为沉淀剂水热反应制备出单斜态结构的TiO2(B)纳米管,经XRD、TEM、BET测试、XPS、TG-DSC等表征结果得知：呈现规整的中空管状,纳米管两端均为开口,管的外径为6 nm至25 nm不等,管的长度可达100 nm以上,并且样品的长径比很高；另外,钠离子主要覆盖在TiO2(B)产品的表面,经过去离子水多次洗涤样品后不含有钠离子。从TEM研究认为水热法制备TiO2(B)纳米管的过程在水热过程中形成的,即TiO2晶体与NaOH溶液反应生成二维薄板层状产物,然后薄板产物以[200]晶面为轴发生卷曲生成一维TiO2(B)纳米管,整个过程经历了从3-2-1D的过程。第五章根据实验结果及理论分析,优化出单斜态相TiO2纳米管暗处催化降解甲基橙的最佳条件：相对于锐钛矿和P25型TiO2,单斜态TiO2(B)纳米管具有独特的红外吸收峰,有较宽的带隙和较大的比表面积；单斜态纳米TiO2(B)不仅在光照条件下存在催化活性,而且在无光条件下也有极高的催化活性。在暗处降解5 h,降解率可达到99%,为了使TiO2(B)催化剂保持高的催化活性,H2O2的存在是必需的而不是光照,TiO2(B)与H2O2具有更好的协同作用；降解反应遵循一级反应动力学规律；催化剂稳定性能较好,有利于催化剂的多次利用,降低废水处理成本,具有较强的实际应用价值。因此,单斜态纳米TiO2独特的催化性能为纳米TiO2催化性能的研究开辟了一个新的方向,具有较好的学术价值和应用前景。更多还原

【Abstract】 TiO2, as one of the most welcome material in catalytic field, is concerned in the present research. In this paper, based on the density functional theory(DFT), the band gap, density of states of monoclinic TiO2(B) were simulated by using the calculation software CASTEP of first principles to discuss the relationship of the monoclinic phase TiO2 between its optical properties and catalytic activity. A noble and simple chemical peroxide-complex-hydrothermal method for the preparation of monoclinic TiO2(B) nanotubes from a precursor based on Ti(SO4)2, hydrogen peroxide and different base was reported. The influence of the H2O2/Ti molar ratio, the calcination temperature and acid treatment on structure and property of products were studied, and some excellent reference data were gained. The morphology, crystal structure, thermal stability, component and surface properties were intensively investigated by TEM, XRD, LRS, TG-DSC, XPS, BET and FT-IR techniques. And the catalytic degradation of methyl orange was used as model reaction to study the catalytic properties of monoclinic TiO2(B) nanotubes under different conditions. The effects of preparation and reaction conditions on the catalytic performances are studied. Meanwhile, nanostructure TiO2 with single crystal phase, anatase and rutile, were prepared by homogeneous precipitation and microemulsion-hydrothermal methods, and to study their catalytic activity. The following is the main aspects of the present research.In chapter 1, the research status of TiO2, photocatalytic principles, the main preparation methods of one-dimensional TiO2 nanotubes, the basic theory of first principles simulation, as well as significance and content of topics were introduced In chapter 2, with the density functional theory(DFT), the band gap, density of states of anatase TiO2 and monoclinic TiO2(B) were simulated by using the plane wave pseudo potentials(PWPP). The calculation showed that compared to anatase, Ti-O bonds of TiO2(B) have been changed by tomic population analysis; the band gap of monoclinic TiO2(B) was wider, which was smaller than the experimental result.The results of theoretical simulation were in accordance with experimental results.In chapter 3, the band gap, density of states, electron density of monoclinic Nao.2Ti02 were simulated by using the plane wave pseudo potentials (PWPP) based on the density functional theory (DFT). Calculated results show that Na0.2TiO2 is an indirect semiconductor with the band gap of 2.81 eV. The density of states is mainly made up of Ti 3d and O 2p. The material has strong broadband UV absorption, extends the range of spectral response and increases utilization rate of solar energy and photocatalytic efficiency. While the Na and O atoms is connected by a strong ionic and weak covalent mixed bond, the Ti-O bond is shorter and has more covlent component than Na-0 bond. This work may provides a theoretical guid for the molecular design and applications of Na0.2TiO2 and related materials. Therefore, the bond-characteristics and stability of Sodium Titanate can be changed by Cation-exchange.In chapter 4, a new approach, to synthesize TiO2(B) nanotubes by peroxide-complex-hydrothermal treatment in concentrated NaOH solution, was presented. The as-prepared nanotubes were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption-desorption isotherm measurements (BET). The diameter of the nanotube was from 6 to 25 nm. In addition, the sodium ions covering the surface of the TiO2(B), were not presence after washing with the deionized water, repeated. It was suggested that the nanotubes TiO2(B) were formed during the hydrothermal process from the TEM, which two-dimensional thin layer fromTiO2 crystal and NaOH solution, generated one-dimensional TiO2(B) nanotube by the axis of crystal plane [200], with the whole process through 3-2-ID. In chapter 5, TiO2(B)has been used for the first time as a hydrogen peroxide catalyst and showed remarkable activity for the removal of MO in aqueous solution at darkness. The experiment compares the photocatalysts of monocline TiO2 (B) and anatase TiO2 in stationary MO solution both in absence and presence of H2O2 under Hg lamp, the results have shown that the presence of H2O2 obviously improved the activity of TiO2 catalyst(the degradation ratio 99%) and accelerated the decomposition of MO, and H2O2 must be necessary to achieve high MO decomposition especially for TiO2 (B). At the same time, we found that TiO2 (B) exhibited excellent repetitive-use performance; degradation reaction followed the first order kinetics; the better stability catalyst was conducive to strong practical applications value and Cutting down costs of wastewater treatment with repeated use. Therefore, the unique catalytic properties of nano-TiO2/H2O2 have opened up a new direction for conventional catalytic research, with a certain degree of academic values and application prospects.更多还原