Nanoparticle assemblies: "Rectified" quantized charging in aqueous media
Nanoparticle assemblies: "Rectified" quantized charging in aqueous media
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DOI：
10.1021/ja0016093
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发表时间：
2000-08-02
影响因子：
15
通讯作者：
Chen, SW
中科院分区：
文献类型：
--
作者：
Chen, SW
近年来，由于纳米粒子材料作为电子纳米器件/纳米电路的构建块具有很大的应用潜力，对纳米粒子材料有组织组装的研究得到了加强。其中，单层保护纳米团簇（MPCs）因其（亚）阿法拉分子电容器特性而受到特别关注。在环境条件下，单分散MPCs溶液和表面系综表现出向其双层量子化的电荷，表现出与经典库仑阶梯相似的特征。9,11先前的研究也表明，这些独特的电子转移现象对颗粒尺寸很敏感，随着颗粒尺寸的减小，可以观察到向分子氧化还原行为的转变。然而，必须指出的是，这些早期关于MPC量子化充电的电化学研究主要局限于有机介质9,11，而在水环境中没有报道。因此，几个问题立即出现：溶剂在这些新的界面电子转移过程中起什么作用？是否有可能在水介质中观察到这些？如何观察？为了回答其中的一些问题，并更好地理解这些人工分子中的电子转移化学，我们采用自组装方法构建了MPC表面组织层，并利用它们研究了溶剂介质对电化学量子化充电事件的影响。先前已经描述了MPC自组装的方案（方案1）。简单地说，将烷硫代酸保护的MPC溶解在己烷中，并通过表面交换反应将几个烷二硫醇拷贝纳入MPC保护单层，使所得到的MPC具有游离外周硫基的表面活性。过量的烷二硫醇和置换的烷硫酸酯，然后通过使用甲醇己烷系统的重复液体萃取去除。在整个过程中，颗粒保持在溶液中（以防止颗粒间交联），然后它们可以锚定在金电极表面，形成远距离有序的表面组装。这里我们以1-己硫代保护金（C6Au）粒子和1,6 -己二硫醇（C6 (SH) 2）为例。这些颗粒被部分分离，以缩小尺寸的分散性，平均核心尺寸为~ 2 nm，每个颗粒有~ 91个C6配体。根据C6Au和C6 (SH) 2的初始进料比，大约有10个二硫醇配体被交换成mpc保护单层。MPC分子在清洁的金电极上自组装的典型孵育时间约为24小时，然后用丰富的己烷彻底冲洗电极以去除松散结合的MPC，并在N2流中轻轻干燥，然后转移到电解质溶液中进行电化学测量。
Research efforts in organized assemblies of nanosized particle materials have been intensified lately, in part, due to their application potentialities as the building blocks for electronic nanodevices/nanocircuits. 1-9 Among these, monolayer-protected nanoclusters (MPCs) 10 have attracted particular attention thanks to the (sub) attofarad molecular-capacitor characteristics. Under ambient conditions, solutions and surface ensembles of monodisperse MPCs exhibit quantized charging to their double layers, showing analogous features to the classical Coulomb staircase. 9, 11 Previous studies have also shown that these unique electrontransfer phenomena are sensitive to the particle dimensions, where a transition to molecular redox behaviors can be observed with decreasing particle sizes. 11 However, it has to be noted that these earlier electrochemical studies of MPC quantized charging are primarily confined to organic media, 9, 11 whereas none has been reported in aqueous environments. Thus, several questions arise immediately: What role do solvents play in these novel interfacial electron-transfer processes? Is it possible to observe these in aqueous media and how?In an attempt to answer some of these questions and to have a better understanding of the electron-transfer chemistry involved in these artificial molecules, we employed self-assembling9 to construct MPC surface-organized layers and used them to investigate the effect of solvent media on the electrochemical quantized charging events. The protocol for the MPC selfassembling has been described previously (Scheme 1). 9 Briefly, alkanethiolate-protected MPCs are dissolved in hexane, and several copies of alkanedithiols are incorporated into the MPC-protecting monolayers by surface exchange reactions, rendering the resulting MPCs surface-active with free peripheral thiol groups. Excessive alkanedithiols and displaced alkanethiolates are then removed by repeated liquid-extraction using a methanolhexane system. The particles are kept in the solution during the entire procedure (to prevent interparticle cross-linking) and they can then anchor onto a gold electrode surface, forming long-range ordered surface assemblies. Here we take 1-hexanethiolateprotectedgold (C6Au) particlesand1, 6-hexanedithiols (C6 (SH) 2) as the illustrating example. The particles had been partially fractionated10 to narrow the size dispersity, with average core size of∼ 2 nm and∼ 91 C6 ligands per particle. On the basis of the initial feed ratios of C6Au and C6 (SH) 2, approximately 10 dithiol ligands were exchanged into the MPC-protecting monolayers. Typical incubation time for the self-assembling of MPC molecules onto a cleaned gold electrode was about 24 h, and the electrode was then rinsed thoroughly with copious hexane to remove loosely bound MPCs and dried gently in a N2 stream before being transferred to an electrolyte solution for electrochemical measurements.