【作者】 洪勋；

【导师】 王冠中；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2010， 博士

【摘要】 电沉积是比较可控地制备纳米材料的一种方法。通过控制沉积电位、电解液浓度和表面剂等很多因素可以合成大量不同形貌的金属、半导体和导电聚合物等纳米结构。其中最具有代表性的是模板法电沉积一维纳米结构和非模板法电沉积多面体以及复杂纳米结构。这些电化学合成的纳米结构具有很多新颖的物理、化学特性,在光学、电学、磁学、传感器和催化等领域有着重要的应用。基于以上原因,本论文的工作将主要建立在使用模板法电化学沉积金属钯、铜及其二元金属的一维纳米结构,以及非模板法电沉积复杂的树枝状银纳米结构,并研究合成产物的性质和应用。论文的工作主要包括以下几方面的内容：1.树枝状和花状银纳米结构的合成及其表面增强拉曼性质在导电玻璃(FTO)衬底上,通过电沉积的方法可以制备银的树枝状纳米结构。并且这些合成的纳米结构有着很强的表面增强拉曼(SERS)性能。我们合成方法的特点是通过改变沉积电位、表面剂的种类以及硝酸银的浓度来控制银树枝状纳米结构的尺寸、形状和分枝密度。树枝状结构生长的一般趋势也得到了解释清楚。所以,我们可以准确的控制树枝状银产物颗粒间的距离,并且可以调节表面等离子体共振等去选择最适合做表面增强拉曼衬底的结构。其中,在PVP做表面剂的溶液中合成出来的尺寸60-100 nm、颗粒间距绝大部分在10 nm以下的树枝状银纳米结构的SERS灵敏度比在PVP／柠檬酸中合成出来的尺寸20-50 nm、颗粒间距大部分在10 nm以上的树枝状银纳米结构强很多。前者作为SERS衬底可以清楚的检测浓度低于10-10 M的若丹明6G分子。这种可控的合成方法也可以用来合成其他的金属和合金的树枝状纳米结构。除了树枝状Ag纳米结构,我们还合成了由树叶状的薄片堆积成的三维的花状结构。其生长模型可以用瞬时成核和扩散控制来解释。随着电沉积时间的延长,衬底上较少有新的核生成,仅仅是原来的核尺寸变大,这使其尺寸可以由沉积时间来控制。由于单个的银颗粒可以在显微镜下清晰的分辨出来,这种花状颗粒具有高的SERS灵敏度的同时有很好的可再现性。2.钯铜二元金属纳米管的合成以及其在硝酸根离子催化上的应用我们在氧化铝模板(AAO)中采用电沉积的方法一步合成了Pd/Cu二元金属纳米管和纳米线。所施加的电位决定着产物形貌是管还是线。在高的负电位下,沉积速率快,模板孔道内的离子被耗尽,沉积由扩散控制,形成纳米管结构。相反的,在较低的负电位下形成的是纳米线结构。纳米管是由几个纳米的Pd,Cu金属颗粒构成。电解液中的线性扫描伏安曲线测试说明了Pd和Cu。是分别沉积的,而且排除了因氢气析出而导致纳米管形成的可能性。在硝酸根离子的电催化实验中,相比于Pd/Cu薄膜,在低的电位下,纳米管受反应中间产物的吸附影响更大,催化性能相对较差；在有氢气析出的高电位时,纳米管的催化受氢气的影响相对较小。在空气中放置六个月后,Pd/Cu二元金属纳米管被氧化成均一的氧化物纳米管。3.超细氧化亚铜纳米线的合成我们利用PVP辅助的电沉积合成出来了尺寸10 nm以下的超细Cu2O纳米线。通过电位的控制,可以在一定尺度内控制超细纳米线的尺寸和长度。通过HRTEM和XPS以及吸收光谱表明这种合成的超细纳米线的结构是Cu2O的核和一层非常薄(～1 nm)的CuO壳。这层CuO的壳层使合成的纳米线结构非常稳定。从沉积条件(pH为2的酸性溶液)以及产物最初的HRTEM像判断出最初的产物是Cu纳米线,在去完模板清洗后在空气中自然氧化成Cu2O/CuO核壳纳米线结构。我们认为超细纳米线的形成是因为电解液中的PVP在电场的作用下在氧化铝模板中有序排列作为Cu沉积的软模板。这种有序排列是吸附阳离子的PVP链因为静电排斥作用展开成刷子状后在电场的作用下相互平行。铜离子和PVP的配位作用使沉积同时在PVP链上发生。对比实验也表明PVP是超细纳米线生长的必要条件。模板对于PVP的有序排列也很重要,在没有模板的情况下得不到超细纳米线的产物。这种超细的纳米线的生长也受电解液浓度的影响,高的浓度会导致颗粒的聚集而形成不了超细纳米线结构。这种10 nm以下的纳米线也表现出明显的量子限域效应,其吸收峰的蓝移非常明显。更多还原

【Abstract】 1. Controllable Electrochemical Synthesis of Silver Dendritic Nanostructures and Their SERS PropertiesAg dendritic nanostructures have been fabricated on FTO covered glass substrates by the electrodepositon method and have been used as SERS substrates which exhibit extremely high SERS activity. An advantage of the prepared method reported here is that the size, shape, and branch density of the silver dendrites can be varied by the applied potential, the surfactants and the concentration of AgN03. The general trends in the formation of the structures have been also identified. The dendrite surfaces can therefore be precisely tailored to tune the interparticle spacings and surface plasmon modes to match the requirements of the SERS experiment. The Ag dendrites prepared in PVP solution with diameter of 60-100 nm and many sub-10 nm interparticle spacings exhibit much better surface enhanced Raman scattering than those dendrites with diameter of 20-50 nm and interparticle spacings larger than 10 nm prepared in mixed PVP/citrate solution, which was able to clearly detect rhodamine 6G concentrations up to 10-10 M. Alloy or composite dendrites for further applications could also be prepared by this easy controlled electrodeposition method.3-D flower-like microstructure deposited at low driving force follows diffusion controlled growth and deposition occurs by an instantaneous mechanism. Once all of the nucleation sites are occupied, further increasing the deposition time would only increase the size of the nanocrystals and not their number density because no new nucleation sites are created. Individual flowerlike Ag particles were investigated by optical microscopy. Both sensitivity and reproducibility can be found at the same time.2. Electrodeposition Pd/Cu Bimetallic Nanotubes and Their Application in Nitrate Electroreduction.We have synthesized Pd/Cu bimetallic nanotubes and nanorods in AAO membranes by a one-step coelectrodeposition. Whether nanotubes or nanorods would be finally formed is determined by the applied potential. Fast deposition induced by a higher negative potential can deplete metal ions near the end of a tube in a channel of the membrane, thus the deposition is dominated by ions diffusing to the growth sites, which results in formation of nanotubes. Contrarily, the alloy nanorods are formed in a deposition-dominated process at a lower negative potential. The Pd/Cu nanotubes are formed by Pd and Cu nanoparticles. Electrochemical measurment demonstrated that the Pd/Cu bimetallic nanotube electrode is less sensitive to hydrogen poisoning compared to Pd/Cu films though the catalysis of films was better at the low potential. The Pd/Cu bimetallic nanotubes were oxidized to uniform PdxCu1-xO nanotubes after the bimetallic nanotubes exposed to air for six months.3. Synthesis of sub-10 nm Cu2O Nanowires by Poly(vinyl yrrolidone)-Assisted ElectrodepositionOrdered sub-10nm cuprous oxide nanowires were synthesized by electrodeposition in anodic aluminum oxide (AAO) membranes assisted with poly(vinyl pyrrolidone) (PVP) as soft templates. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy demonstrate that a nanowire has a core of Cu2O and a thin shell of CuO. The formation of the copper oxide was attributed to the oxidized process of Cu nanowires.The formation of ultrathin nanowires is attributed to the arrangement of the PVP in the channels of AAO membranes under an electric field. The diameter and the length of the nanowires depend on the applied potential in the electrodeposition. PVP is the key of the formation of ultrathin nanowires. The growth of the ultrathin nanowires also depends on the concentration of CuCl2·2H2O, and the confinement of the channels in the AAO membrane. UV-vis absorption spectroscopy shows the quantum confinement effect of the Cu2O nanowires.更多还原