Yang Liu, Chen Ting, Wang Dong, Wan Li-Jun
Institute of Chemistry Chinese Academy of Sciences, Beijing National Laboratory for Molecular Sciences, Beijing 100190, China.
J Nanosci Nanotechnol. 2011 Jun;11(6):4800-5. doi: 10.1166/jnn.2011.4196.
The adsorption and adlayer structure of p-nitrobenzoic acid (pNBA) on a Au(111) surface in 0.1 M HCIO4 are investigated by in-situ scanning tunneling microscopy (STM) and cyclic voltammetry. The pNBA adlayer is prepared by dipping Au(111) into a saturated pNBA aqueous solution. The cyclic voltammogram (CV) of the so-prepared Au(111) electrode shows an irreversible cathodic peak at 0.24 V, which corresponds to the electro-reduction reaction from pNBA to hydroxylamine, and a pair of reversible peaks at ca. 0.7 V, corresponding to redox reaction of hydroxylamine to nitrosobenzoic acid. STM is employed to investigate the pNBA adlayer structure. The molecules form ordered adlayers in (16 x 2 square root of 3), (7 x 4 square root of 3) and (9 x 6 square root of 3) structures at the double layer potential region. High resolution STM image reveals the details of the molecular arrangement in the adlayers. On the basis of the STM image and the chemical structure of pNBA, structural models for three adlayers are proposed. In all three structures, pNBA molecules adsorb perpendicularly with the carboxylic groups contacting with the Au(111) substrate. The effect of dipping time on the adlayer formation is investigated. Upon shifting the electrode potentials in negative direction to induce the electroreduction reaction, the bright dots corresponding to the molecular aggregations start emerging on the surface and selectively locate at the elbow position along Au(111) reconstruction lines. The results provide direct evidence for the adsorption and electrochemical behavior of nitro-benzene derivatives.
采用原位扫描隧道显微镜（STM）和循环伏安法研究了对硝基苯甲酸（pNBA）在0.1 M高氯酸溶液中Au(111)表面的吸附及吸附层结构。通过将Au(111)浸入饱和pNBA水溶液中来制备pNBA吸附层。如此制备的Au(111)电极的循环伏安图（CV）在0.24 V处显示出一个不可逆的阴极峰，该峰对应于pNBA到羟胺的电还原反应，在约0.7 V处有一对可逆峰，对应于羟胺到亚硝基苯甲酸的氧化还原反应。利用STM研究pNBA吸附层结构。在双层电位区域，分子形成了(16×2√3)、(7×4√3)和(9×6√3)结构的有序吸附层。高分辨率STM图像揭示了吸附层中分子排列的细节。基于STM图像和pNBA的化学结构，提出了三种吸附层的结构模型。在所有三种结构中，pNBA分子均垂直吸附，羧基与Au(111)基底接触。研究了浸渍时间对吸附层形成的影响。当将电极电位向负方向移动以诱导电还原反应时，对应于分子聚集体的亮点开始出现在表面，并选择性地位于沿Au(111)重构线的肘部位置。这些结果为硝基苯衍生物的吸附和电化学行为提供了直接证据。
