Preparations And Catalytic Properties Of Nanoporous Metal And Metal Oxide By Dealloying Method

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℃.