【作者】 印会鸣；

【导师】 丁轶；

【作者基本信息】 山东大学 ， 物理化学， 2010， 博士

【摘要】 利用脱合金法制备纳米多孔金属并对其物理、化学性能,如力学、光学、催化等特性进行研究是纳米材料领域的一个新兴研究方向,而将脱合金法这一简单易行的制备方法进行拓宽,合成其他功能纳米材料亦具有重要意义。本论文即以脱合金过程为基础,进行了以下三方面的研究。一、超低Au含量Au-Ag合金的脱合金化过程研究炼制了不同原子比例的金银合金(Au1Ag(99),Au5Ag(95)和Au(10)A(90)),并且研究了合金成分、腐蚀方法、腐蚀介质和反应条件对产物纳米多孔金形貌结构的影响。实验结果表明,直接在硝酸中进行自由腐蚀时,对于低Au含量合金,硝酸浓度越低越有利于形成三维网状纳米多孔结构,但是浓度降低到1 M左右腐蚀反应基本停止,所得纳米多孔Au的壁厚在30 nm左右；采用电化学腐蚀方法,在硝酸和高氯酸溶液中均可制得结构均匀的纳米多孔金,壁厚约5nm；在中性的硝酸钾溶液中得到的是Ag2O粉末,但是在硝酸和硝酸钾的混合溶液中也可获得尺寸匀称的纳米多孔金结构；特别的是,通过在稀硝酸中加入氟化铵进行电化学腐蚀可得到孔壁尺寸仅有2 nm左右但形貌结构均匀的纳米多孔金。二、纳米多孔金在葡萄糖氧化反应中的催化活性研究通过简单的脱合金化方法制备了不同尺寸和不同含Ag量的纳米多孔金催化剂。实验结果表明,即使是孔壁尺寸大于10 nm时,这种无负载的纳米多孔金催化剂对葡萄糖氧化生成葡萄糖酸的反应都具有良好的催化活性和催化选择性。孔壁尺寸为6 nm的纳米多孔金表现出最高的催化活性而且不容易失活；30 nm的纳米多孔金表现出良好的结构稳定性。研究还发现,纳米多孔金催化剂中的残留Ag并没有提高其对葡萄糖氧化反应的催化活性。基于上述研究结果,我们认为纳米多孔金中边、角处的Au原子是纳米多孔金的反应活性位。葡萄糖氧化反应的反应动力学研究说明,在纳米多孔金表面发生的葡萄糖氧化反应的速控步骤是孔中葡萄糖分子的内部扩散和葡萄糖分子在催化剂表面的吸附。总的来说,由于完全不同的催化剂结构和反应进程,纳米多孔金的催化活性无法和纳米金颗粒相媲美,但是纳米多孔金却具有作为催化剂的独特的优势,如易于制备、回收和循环利用；催化剂材料结构上的连续性和良好的导电性使其表面容易功能化修饰上其他材料并以此来设计和开发新型器件,如适合工业应用的薄膜反应器等。三、贵金属掺杂纳米多孔TiO2的制备及其催化性能研究开发了一条新颖的合成路线,以金属间化合物TiAl3、Ti(1-x)AuxAl3、Ti(1-x)PtxAl3和Ti(1-x)PdxAl3作为源材料,通过碱腐蚀-酸处理-高温退火这一途径成功制备了贵金属Au、Pt、Pd掺杂的纳米多孔TiO2。实验结果表明,用浓碱液对金属间化合物进行腐蚀后,必须将产物进行酸化-退火处理才能得到纳米多孔的锐钛矿TiO2。以脱合金化过程为基础的这一制备方法可以推广到其他金属氧化物或复合氧化物的合成领域。对所得产物的光催化活性进行研究发现,掺杂Au、Pt、Pd可有效提高纳米多孔TiO2的光催化活性,说明采用脱合金这一简单方法可以制备贵金属掺杂的TiO2光催化剂,并达到提高其光催化活性的目的。本文还研究了Au掺杂Tio2对CO氧化反应的催化活性,结果表明所制备出的Au掺杂的TiO2对CO氧化反应有很好的催化作用。更多还原

【Abstract】 A newly emerging research direction that preparing nanoporous metals by dealloying method and investigating their physical and chemical properties such as mechanical, optical, catalytical properties has been attracted a number of scientists. Furthermore, it is also very important to extend the facile dealloying method to prepare other functional materials. The content of this thesis contains three parts based on the dealloying process.i) Dealloying of Au-Ag alloy with ultra low Au contentsAu-Ag alloys with different Au/Ag molar ratios (Au1Ag99, Au5Ag95, and Au10A90) were made and the effects of alloy composition, etching method and electrolyte on the structure and morphology of nanoporous gold were investigated. The experimental results indicated that, the lower concentration of the nitric acid, the more uniform of the nanoporous gold while the alloy with ultra-low Au content (1%) was free dealloyed in nitric acid. When the Au-Ag alloy was electrochemically dealloyed in nitric acid and perchloric acid respectively, the products both were homogeneous nanoporous structure with ligament size about 5 nm. Furthermore, nanoporous gold with ultra-small ligament size 2 nm could be obtained in dilute nitric acid added ammonium fluoride by electrochemical dealloying method.ii) Aerobic oxidation of D-glucose on unsupported nanoporous goldNPG catalysts were fabricated by a simple dealloying method with different ligament sizes and Ag residual contents. This unsupported Au was found to be active and highly selective for the aerobic oxidation of D-glucose to D-gluconic acid, even when the ligament sizes are larger than 10 nm. NPG catalyst with a ligament size of 6 nm exhibits the highest catalytic activity and is more resistant to deactivation. Additionally, the 30 nm sample was found to have better structure stability during the whole catalytic process, while keeping decent catalytic activity. The presence of residual Ag atoms does not seem to contribute to the activity of NPG for glucose oxidation. On the basis of the above results, we suggest that the active sites of NPG are Au atoms on the corners and step edges. The investigation on reaction kinetics suggests that internal diffusion in pores as well as the adsorption of glucose molecules etermine the overall reaction rate on NPG. Finally, although the catalytic activity of NPG can not match that of Au nanoparticles due to their completely different structures and reaction configurations, NPG holds additional advantages as a catalyst, in a way that it can be easily prepared, recovered, and recycled. Their structural continuity and excellent electric conductivity also allow surface functionalization with other materials to design and develop novel devices such as membrane reactors for industrial applications.iii) Preparation of noble metal doped nanoporous TiO2 by dealloying method and their catalytic propertiesA novel synthesis route, originated from dealloying of intermetallic compound (TiAl3, Ti1-xAuxAl3, Ti1-xPtxAl3 and Ti1-xPdxAl3) to acidic treatment and thermal treatment, has been developed for the preparation of noble metal (Au, Pt, Pd) doped nanoporous TiO2. The experimental results indicated the important process of acidic treatment for the preparation of nanoporous TiO2 and furthermore, this route can be extended to fabricate other metal oxides or composite metal oxides. The doped TiO2 was applied in photodegradation of methyl orange and the results showed the greatly enhanced photocatalytic acitivity by noble metal doping. The Au doped nanoporous TiO2 was used in CO oxidation reaction. The resuts exhibited an effective catalytic activity of the sample and the good stability under 400℃.更多还原