【作者】 薛红星；

【导师】 吴进明；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2011， 硕士

【摘要】 本文利用双氧水溶液直接氧化钛金属制备二氧化钛(TiO2)纳米线和空心多面体,研究其生长机理和光催化性能。以H2O2和冷轧纯钛片为反应物,通过向H2O2中加入三聚氰胺及浓硝酸,调整工艺参数,控制TiO2薄膜的低温生长,成功获得TiO2纳米线阵列薄膜；通过向H2O2中加入NaF及浓硝酸,辅以适当的后续热处理和水洗处理,成功获得TiO2多面体；双氧水溶液中同时添加NaF、三聚氰胺和HNO3,经后续热处理后则直接获得TiO2空心多面体。利用场发射扫描电子显微镜、高分辨透射电子显微镜、X射线衍射、紫外-可见漫反射、激光拉曼光谱、X射线光电子谱、热重分析、低温N2吸附等测试手段分析纳米结构TiO2的形态、结构及其光响应行为,探讨其生长机理,研究其辅助降解水中若丹明B (RhB)染料的能力。论文取得主要结果如下：1.TiO2纳米线：研发了一种在金属钛基体上制备TiO2纳米线阵列的技术,过程简单易工业化,重复性好,不需要模板和催化剂。80℃反应温度下,钛金属被H2O2腐蚀氧化,在金属表面形成非晶结构TiO2多孔薄膜的同时,向溶液中释放水合Ti(Ⅳ)离子。溶液中水合Ti(Ⅳ)离子浓度达到一临界值后,在金属表面TiO2多孔薄膜处非均匀形核析出TiO2。另一方面,在较强的酸性环境下,溶液中的三聚氰胺分解为三聚氰酸,并通过-OH的桥梁作用吸附在TiO2纳米晶表面。由于不同晶面-OH密度的差异,三聚氰酸可以在TiO2纳米晶表面实现选择性吸附,最终导致从溶液中析出的TiO2纳米晶(尽管结晶度较差)以“定向融合”机制自组装形成平均直径为25nm,长径比大约为40的纳米线阵列。后续450℃空气中热处理显著提高TiO2纳米线阵列的结晶程度。光催化性能测试结果表明,锐钛矿TiO2纳米线阵列光催化降解水中若丹明B的能力显著优于商业P25 TiO2纳米粉。2.TiO2(空心)多面体：在Ti和H2O2反应体系中添加NaF和HNO3,80℃温度下反应10 min～96 h,在钛金属表面生成Na3TiF6多面体。反应进行到30 min时,主要生成立方体；随着反应的继续进行,立方体八个顶点被截去,逐渐演化为八面体结构。后续热处理过程中,大部分Na3TiF6多面体在209℃开始发生氧化反应,分解为TiO2和NaF,其中的TiO2为厚度约20 nm的薄片,垂直交叉构成多面体。经进一步水洗去除NaF和残留的Na3TiF6后,获得TiO2多面体,其比表面积为196.3m2/g,间接禁带宽度为3.11 eV,具有明显的光催化效果。双氧水溶液中同时添加NaF、三聚氰胺和HNO3,80℃反应72 h,经后续热处理后可以直接获得TiO2空心多面体。更多还原

【Abstract】 In this thesis, titania nanowire arrays and hollow polyhedra were fabricated sucessfuly through direct oxidation of metallic titanium by hydrogen peroxide solutions. The related growing procedure was disclosed and the photocatalytic activity of the resultant nanostructured titania was evaluated.Titania nanowire arrays were deposited on Ti substrates by the interactions of Ti and H2O2 solutions with the additives of melamine and nitric acid, through controlling the low-temperature growth via adjusting carefully the reaction parameters. Titania polyhedra were fabricated by the reactions between metallic Ti and and H2O2 solutions containing NaF and nitric acid, followed by calcination and water-washing. Hollow titania polyhedra were achieved directly by oxidation of Ti with H2O2 solutions containing melamine, NaF and nitric acid, followed by a subsequent calcination. The structure, morphology and photon-induced property of the achieved titania were investigated in detail with various techniques of field emission scanning electron microscope (FE-SEM), high-resolution transmission electron microscope (HR-TEM), X-ray diffaraction (XRD), UV-Vis diffuse reflectance spectra (UV-Vis DRS), Raman spectra, X-ray photoelectron spectra (XPS), differential thermogravimetric (DTG) and N2 adsorption. The photocatalytic activity of the achieved titania was evaluated by photodegradation of rhodamine B in water.Follows are the main results obtained:1. Titania nanowire arrays. An approach to fabricate titania nanowire arrays on Ti substrates was developed succesffuly. The method is simple and can be scaled-up easily, with good reproducibility and involves no templates or catalysts. Under the low temperature of 80℃, metallic Ti was oxidized by H2O2 to form a porous amorphous titania film on the surface. Hydrated Ti(Ⅳ) ions were released to the solution at the same time. Once the Ti(Ⅳ) ions in the solution reached a critical concentration, titania precipitated from the solution, predominantly through heterogeneous nucleation on the titania film formed previously on the Ti substrates. On the other hand, the melamine in the acidic solution decomposed to from cyanuric acid, which was adsorbed on the precipitated titania nanocrystals through bridging by-OH groups. Because of the various densities of-OH groups on different planes of the titania nanocrystals, the selective absorption of cyanuric acid is possible. As a result, the precipitated titania nanocrystals, although poorly-crystallized, self-assembled to form nanowires with an average diameter of 25 nm and an aspect ration of ca.40, through the "oriented attachment" mechanism. The crystallinity of the nanowires was improved significantly by a subsequent calcination in air at 450℃The nanowire arrays possessed an activity to assist photodegradation of rhodamine B in water higher than that of the P25 counterpart.2. Titania (hollow) polyhedra. With the additives of certain amounts of NaF and nitric acid in the H2O2 solution, polyhedra mainly consisted of Na3TiF6 were achieved on the Ti surface while maintaining at 80℃for 10 min to 96 h. The initial reaction for 30 min resulted in cubes, which evolved to octahedron with the prolonged reaction duration. Most of Na3TiF6 decomposed to NaF and TiO2, which inititated at 209℃, during the subsequent calcination. The later was titania thin plates with a thickness of ca.20 nm that interlocked with each other to form a polyhedron. After a further water-washing to remove NaF and the remained Na3TiF6, phase pure TiO2 can be achieved. The titania polyhedra, which exhibited an indirect band gap of 3.11 eV, possessed a high specific surface area of 196.3 m2/g. The remarkable photocatalytic activity was confirmed by photodegradation of rhodamine B in water. Hollow titania polyhedra were achieved directly by oxidation of Ti at 80℃for 72 h, with H2O2 solutions containing melamine, NaF and nitric acid, followed by a subsequent calcination.更多还原