Polyol synthesis of platinum nanostructures: Control of morphology through the manipulation of reduction kinetics
Polyol synthesis of platinum nanostructures: Control of morphology through the manipulation of reduction kinetics
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DOI：
10.1002/anie.200462668
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Xia, YN
中科院分区：
文献类型：
--
作者：
Chen, JY;Herricks, T;Xia, YN
大量的努力已经指向具有良好控制的形态的纳米结构的合成。[1]通常接受的是，纳米结构的形态（包括维度和形状）可以允许调节，其与调节尺寸一样强大，用于定制功能材料的电子、光学、磁性和催化性质。在这里，我们报告了一个案例研究中，铂纳米结构的形态可以很容易地控制通过操纵还原动力学的多元醇合成。更具体地说，铂纳米结构的形式的球体，星形颗粒，分支多脚，和均匀的纳米线已成功地合成通过耦合的多元醇还原的铂前体与FeII/FeIII氧化还原对和吸附的氧气和氮气。铂在许多工业应用中起着重要作用。[2]例如，它在减少汽车排放的污染气体、硝酸合成、石油裂解和质子交换膜（PEM）燃料电池中用作催化剂。[3]所有这些应用都需要使用作为细颗粒的Pt。还已经确定，Pt纳米结构在催化反应中的反应性和选择性都高度依赖于形态，因此依赖于暴露在纳米颗粒表面上的晶面。[4]由于这些原因，许多努力已经投入到生产的Pt纳米结构与单分散的大小和明确的形态。然而，这些研究中的大多数仅限于可以通过使用各种化学方法容易地合成的Pt纳米颗粒。[5]通常，这种合成涉及在聚合物稳定剂存在下通过使用还原剂如醇、硼氢化钠或氢气还原PtIV或PtII前体。虽然所得的纳米颗粒可以被认为在尺寸上是单分散的，但它们通常是球形的或缺乏明确限定的小面。良好刻面的纳米颗粒的形成仅在有限数量的实施例中得到证实，其中氢气用作还原剂，聚丙烯酸钠用作稳定剂。[6]另一种产生多面Pt纳米颗粒的化学方法是基于在0 ° C下在水中用硼氢化钠还原PtIV前体，然后将还原的物质相转移到有机溶剂中。[7]负责形成这些多面纳米颗粒的机制尚未阐明。在不同的方法中，多晶Pt的纳米棒和纳米管已经通过对多孔材料中的通道进行模板化来制造[8]，以及Ag或Se纳米线。[9]Kijima等人也证明了通过采用表面活性剂的自组装结构作为模板来合成Pt纳米管。[10]虽然基于模板的合成已被证明是简单和通用的，但它们受到许多缺点的限制，这些缺点包括需要去除模板以获得纯产物、形态变化的有限范围以及通常与产物相关的多晶性。在最近的一项研究中，[11]我们发现，向多元醇工艺中添加微量的铁物质（FeII或FeIII）可以显著改变Pt纳米结构的生长动力学，从而诱导Pt纳米线的形成。这些纳米线的特征在于均匀的直径和相对高的纵横比。在这里，我们证明，还原动力学可以进一步操纵，以获得其他几种形态，如分支多脚。根据紫外/维斯光谱和X射线光电子能谱的结果，
A great deal of effort has been directed towards the synthesis of nanostructures that have well-controlled morphology.[1] It is generally accepted that the morphology (including dimensionality and shape) of a nanostructure may allow tuning that is as powerful as tuning with size for tailoring the electronic, optical, magnetic, and catalytic properties of a functional material. Herein we report a case study in which the morphology of Pt nanostructures could be readily controlled by manipulating the reduction kinetics of a polyol synthesis. More specifically, Pt nanostructures in the form of spheres, star-shaped particles, branched multipods, and uniform nanowires have been successfully synthesized by coupling the polyol reduction of a platinum precursor with the FeII/FeIII redox pair and the adsorption of oxygen and nitrogen gases. Platinum plays an important role in many industrial applications.[2] For example, it serves as a catalyst in the reduction of pollutant gases emitted from automobiles, the synthesis of nitric acid, oil cracking, and proton-exchange membrane (PEM) fuel cells.[3] All of these applications require the use of Pt as fine particles. It has also been established that both the reactivity and selectivity of Pt nanostructures in a catalytic reaction are highly dependent on the morphology and therefore on the crystallographic planes exposed on the surface of the nanoparticles.[4] For these reasons, much effort has been devoted to the production of Pt nanostructures with monodispersed sizes and well-defined morphologies. Most of these studies, however, have been limited to Pt nanoparticles that could be easily synthesized by using a variety of chemical methods.[5] In general, such a synthesis involves the reduction of a PtIV or PtII precursor in the presence of a polymeric stabilizer by using reducing agents such as alcohol, sodium borohydride, or hydrogen gas. While the resultant nanoparticles may be considered monodisperse in size, they are often spherical or lack well-defined facets. The formation of well-faceted nanoparticles has only been demonstrated in a limited number of examples in which hydrogen gas was used as the reducing agent and sodium polyacrylate as the stabilizer.[6] Another chemical method of generating faceted Pt nanoparticles is based on the reduction of a PtIV precursor with sodium borohydride in water at 08C, followed by phase transfer of the reduced species to an organic solvent.[7] The mechanism responsible for the formation of these faceted nanoparticles has yet to be elucidated. In a different approach, nanorods and nanotubes of polycrystalline Pt have been fabricated by templating against channels in porous materials,[8] as well as Ag or Se nanowires.[9] Kijima et al. have also demonstrated the synthesis of Pt nanotubes by employing self-assembled structures of surfactants as the template.[10] Although template-based syntheses have proven to be straightforward and versatile, they are restricted by a number of drawbacks that include the requirement of template removal to obtain a pure product, the limited scope of morphological variation, and the polycrystallinity often associated with the product. In a recent study,[11] we discovered that the addition of a trace amount of iron species (FeII or FeIII) to a polyol process could significantly alter the growth kinetics of Pt nanostructures and thus induce the formation of Pt nanowires. These nanowires are characterized by uniform diameters and relatively high aspect ratios. Herein we demonstrate that the reduction kinetics can be further manipulated to obtain several other morphologies such as branched multipods. On the basis of our results from UV/Vis and X-ray photoelectron …