| The study of metallic nanoarrays has always been the focus of intensive research because of its attractive electrical, optical, magnetic, and thermal properties, which leads to potential applications in microelectronics, optoelectronics, magnetic manipulation, biotechnology, catalysis, and sensors, especially in the field of high density magnetic storage medium. The synthesis of solid templates (e.g., Anodized aluminum oxide (AAO) is simple, low-cost and scalable. And the as-prepared templates can easily achieve excellent long-range order. AAO membrane is one of the templates that are generally used to produce nanoarrays via methods of vapor-liquid-solid (VLS), pulsed laser deposition (PLD), Electro-deposition and Electroless-deposition. However, for the porous-template assisted electrodeposition, electric power is required, whereas for the conventional porous-template-assisted electroless deposition, metallic ions are typically reduced in the presence of organic surfactants, and pore walls of the template are usually modified via a complex sensitization-preactivation process. Therefore, the research about inventing a novel and facile approach to prepare metal nanoarrays is very important from the point of view of science and applications.The main objective of this dissertation is to develop a novel and facile way to synthesize magnetic, noble metal and their alloy nanoarrays, and investigate the relationship between their magnetic parameters and structures. Furthermore, the pratical applications of metal and alloy nanoarrys will be discussed. The main parts of the as-obtained results are summarized as fellow:1. By infiltrating aqueous solutions of metal chloride salts into native AAO templates and reduced by Al sheet on the backside of AAO template, high density single crystalline Ni (so does other metal, such as Co, Fe etc) nanowires with an excellent surface coverage can be prepared via a novel simple synthesis route, in which Ni2+ions were reduced by Al substrate of AAO. When a magnetic field was applied during the redox reaction, the Ni nanoarrays exhibit an enhanced magnetic anisotropy behavior due to the single crystalline nanostructure of Ni nanoarrays. It is shown that the coercivity field and squareness are distinct for different directions, especially the coercivity of AF//(300Oe) is much larger than AF(?)(20Oe). By this novel approach, the problem of large area preparation and magnetic anisotropy for HDMDS media might be solved effectively. This process has its advantages as follows:(1) metal nanowires whose electrode potential is greater than that of aluminum can be prepared;(2) the system is simple to set up, easy to operate, easy to repair, and durable for industrialization;(3) one-pot reaction process for preparation of large-area uniform nanostructure arrays;(4) single crystalline metal nanowires with high magnetic anisotropy can be prepared.2. Nanocatalysts enjoy several advantages such as excellent activity, great selectivity, and high stability over conventional catalyst systems; however, isolation and recovery of these tiny nanocatalysts from the reaction mixture are not easy and the activity of the catalyst is usually reduced due to agglomeration or leaching. We developed the previous method to prepare palladium nanowire array catalysts at macroscopic size. Suzuki coupling reaction and4-nitrophenol (4-NP) reduction reaction were employed to study the catalytic activity of the nanocatalysts. The nanocatalysts not only demonstrate good activity in both Suzuki reaction (up to96%yield after1h) and4-NP reduction (the rate constant k is determined to be6.5x10-3s-1), but also simultaneously addresses the separation, stability, reusability and leaching issues commonly encountered in nanocatalysts:(1) In our system, the catalysts can be easily separated/recovered simply by taken away from the solution with tweezers.(2) Ths catalysts demonstrated great thermal stability with high activity at elevated temperatures.(3) The AAO supported Pd nanowires can be reused several times with no obvious decrease of conversion rate and selectivity even at high temperatures. The reusability capability of the catalyst is maintained at150℃. Moreover, the kinetic studies of five cycles showed that the initial rates and the subsequent rates of each cycles were not reduced.(4) Finally, leaching of the catalysts into the reaction mixture was not observed. The Pd content in the filtrate after the first reaction as well as after five cycles were all determined to be lower than1ppm by ICP-AES, indicating<0.1%of Pd leaching even after five cycles.3. Nanostructured Co, Ni and their alloys are of great interest in the catalysis area considering their low cost and high activity in varieties of reactions. It is crucial to develop synthetic methods that produce metal or alloy nanocatalysts with tunable size, shape, and composition (for alloys) in order to improve their catalytic performance. A Ni-Co alloy nanoarray can also be derived from the same method. This method can generate metal alloy nanoarrays with excellently controlled elemental combinations and ratios by simply changing concentration of the metal salts solution. The Ni-Co alloy nanocatalysts demonstrated good activity even as much better noble nanocatalysts (for4-NP reductions, the rate constant k can be up to5.24×10-3s-1by Ni1Cos) due to the synergistic effects, which are subject to surface electronic states,of Ni-Co alloy, easy separation and excellent reusability (displays ca.92%activity after10cycles.) in both inorganic (the redox reaction of K3[Fe(CN)6]/Na2S2O3) and organic reactions (reduction of4-NP). Especially, the alloys of Ni5Co1and Co5Ni1exhibit better catalytic activity than others. |
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