Au单晶表面氟表面活性剂FSN自组装膜的电化学行为

研究Au(111)和Au(100)表面非离子型氟表面活性剂FSN自组装膜的电化学行为.电化学扫描隧道显微术和循环伏安法测试表明,在0～0.8 V电位区间,FSN自组装膜未发生氧化还原,均一性好,可稳定地存在于电极表面,并显著抑制硫酸根离子在电极表面的吸附和Au单晶表面的重构.在FSN自组装膜Au单晶电极的初始氧化阶段,Au(111)表面有少量突起,而Au(100)表面呈现台阶剧烈变化,但FSN自组装膜的吸附结构没有改变.与Au(100)表面相比,Au(111)表面形成的FSN自组装膜可更有效地抑制Au表面的氧化.     

Sb在Au电极上不可逆吸附的电化学过程

用电化学循环伏安法和电化学石英晶体微天平(EQCM)技术研究了Sb在Au电极上不可逆吸附的电化学过程. 研究结果表明, 在-0.25 V到0.18 V(vs SCE)范围内, Sb可在Au电极上稳定吸附, 并且在0.15 V附近出现特征氧化还原峰. 根据EQCM实验数据, 在电位0.18 V时, Sb在Au电极上的氧化产物是Sb2O3; 同时Sb的吸附阻止了电解液中阴离子和水在Au电极上的吸附. 当电极电位超过0.20 V时, Sb2O3会被进一步氧化成Sb5+化合物, 同时逐渐从Au电极表面脱附.     

碱基腺嘌呤与胸腺嘧啶在Au(111)电极上的共吸附

用循环伏安法(CV)和电化学扫描隧道显微镜(ECSTM)在HClO4溶液中研究了配对碱基腺嘌呤(Adenine,A)与胸腺嘧啶(Thymine,T)在Au(111)电极上的共吸附行为.CV曲线表明,A和T的电化学共吸附行为更接近于A的电化学吸附行为.高分辨STM图像显示,在物理吸附区域碱基A和T分子之间通过氢键作用形成一种不同于单组分的网络结构.根据STM图像提出一个可能的模型,并给出了在Au(111)电极上共吸附时A和T分子之间可能的氢键作用方式.     

Sb在Au单晶电极上结构敏感吸附行为的比较

本文研究比较Sb(III)在Au(111)和Au(100)电极上的不可逆吸附与还原和Sb的欠电位沉积行为及其相互影响.现场扫描隧道显微镜和循环伏安法测试结果表明,基底表面结构不仅影响阴离子的吸附行为和Sb的吸附结构,而且还影响其自身结构的稳定性.在Au(111)表面,致密无序膜的SbO+不可逆吸附层还原后基本保持原有的无序结构;而在Au(100)表面,由于SO42-的共吸附,不可逆吸附物种还原后形成(2×2)有序结构.在Au(111)表面上,Sb的欠电位沉积伴随显著的合金化,且因表面有序结构的破坏而形成沟道状二维结构;但对Au(100)表面,由于其晶格和尺寸与稳定的AuSb2合金之(100)面有较好的匹配性,使Au与Sb得以形成有序的表面化合物,从而避免了欠电位沉积过程中的表面合金化问题,进一步体现基底结构的敏感性和重要性.     

半冠醚配体在Au(111)电极表面上的有序阵列的原位STM研究

利用电化学扫描隧道显微术(ECSTM)和循环伏安法, 研究了三个半冠醚配体在Au(111)表面上的吸附结构. 虽然配体分子的几何结构复杂、对称性较差, 但在Au(111)电极表面, 均形成了有序的阵列, 这是分子-分子间相互作用与分子-基底间相互作用平衡的结果. 高分辨率STM图像揭示了有序阵列中分子的内部结构、取向、排列方式等. 该研究为通过过渡金属调控的纳米结构制备提供了实验依据.     

Au单晶电极上H2O2的氧化反应研究

本文利用旋转圆盘电极系统研究了酸性介质中H₂O₂在Au(100)和Au(111)电极表面的电化学行为. 实验发现在Au电极上H₂O₂难以发生还原,但是当电位稍微正于H₂O₂氧化为O₂的平衡电势时即可发生氧化. 在Au(111)上H₂O₂氧化的起始电位比在Au(100)正0.1 V左右. Au(100)上的双桥位位点能增强反应中间体*OOH的吸附,可能是导致Au(100)上H₂O₂氧化反应超电势比Au(111)低的主要原因. 在较正电位区(E>1.2 V), 当电极表面被氧物种覆盖时,H₂O₂在两个电极上的氧化都会受到一定程度的抑制,这种影响在Au(111)上比Au(100)上更加明显,这与Au(111)上氧物种的生成与逆向还原可逆性差的趋势一致. 最后还将Au与Pt单晶电极上H₂O₂氧化的行为进行了对比分析.     

纳米金膜电极上CN~-吸附的电化学和原位红外反射光谱研究

应用循环伏安(CV)和原位红外反射光谱(in situFTIRS)研究碱性介质中氰(CN-)在纳米金膜电极(nm-Au/GC)上的吸附行为.结果显示,当研究电极电位低于0.0 V时,CN-可稳定吸附在nm-Au/GC电极表面,高于0.0 V,则发生氧化脱附.发现nm-Au/GC表面具有异常红外效应(AIREs),即吸附态CN-谱峰呈现出与本体Au电极不同的方向倒反、红外吸收增强(39.2倍)以及半峰宽增加的异常光谱特征.本研究将纳米薄膜材料的这一AIREs从过渡金属拓展到币族金属,进一步证明AIREs是迄今研究的金属及合金纳米材料的普遍特性.     

四氮杂杯芳烃三嗪衍生物在Au(111)表面的自组装结构的电化学STM研究

利用电化学扫描隧道显微镜和循环伏安法研究了一种新型的杂杯杂芳烃四氮杂杯芳烃三嗪衍生物在Au(111)表面的自组装结构. 高分辨的STM图像表明, 该杂杯杂芳烃可以在Au(111)表面形成长程有序的单层膜. 此外, 分子以1,3-交替构象吸附, 两个三嗪环平躺在表面, 而苯环倾斜吸附在基底上, 这是分子间与分子-基底间相互作用平衡的结果.     

细胞色素c在自组装纳米膜电极上的有效固定及直接电化学

采用自组装方法将壳聚糖-纳米金(Chi-Nano Au)修饰到金(Au)电极上,并经进一步自组装细胞色素c(Cyt c),制得自组装膜电极Cyt c/Chi-Nano Au/Au.测定了自组装膜电极的循环伏安曲线(CV)及稳定性.结果表明,利用自组装膜电极Chi-Nano Au/Au可以有效地固定Cyt c,并实现直接电子转移反应.Cyt c在0.13～0.28V(vs Ag/AgCl)之间显示一对明显的可逆氧化还原峰;峰电流与扫描速度呈现良好的线性关系,线性方程为Ipc=0.063 64+0.003 51υ,线性相关系数为r=0.997 2,这表明该电极过程受吸附控制.此外,所制备的膜电极稳定性良好.     

阴离子特性吸附和Pt(111)电极表面结构对乙二醇解离吸附动力学的影响

运用电化学循环伏安和程序电位阶跃方法研究了阴离子特性吸附和Pt(111)电极表面结构对乙二醇解离吸附反应动力学的影响. 结果表明, 阴离子特性吸附显著影响乙二醇的解离吸附, 在高氯酸介质中(无特性吸附)测得乙二醇解离吸附反应的初始速率vi以及解离吸附物种(DA)的饱和覆盖度均明显大于硫酸溶液(发生SO2-4/HSO-4特性吸附)中的相应值; 其平均速率v随电极电位的变化呈类似火山型分布, 最大值位于0.22 V(vs SCE)附近. 还发现通过不同处理获得的Pt(111)电极的不同表面结构对这一表面过程也具有显著的影响.     

Differential capacity and chronocoulometry studies of a quaternary ammonium surfactant adsorbed on Au(111)

The adsorption of a model quaternary ammonium surfactant, octyltrimethylammonium triflate, on Au(111) has been studied using capacity and chronoculometry methods. The surfactant adsorbs on the metal surface as a non‐dissociated ion pair at moderate potentials but can be desorbed by either positive or negative polarization. Within the adsorption region, two states are observed which correspond to a horizontal monolayer and a higher coverage vertically oriented film. Measurements of capacity transients upon potential steps reveal a slow organization of the molecular film. Although it is possible to equate the transients to known surfactant film aggregate geometries, the results are in disagreement with thermodynamic results. In comparison with other studies, the results indicate that the states of surfactant adsorption depend on surfactant chain length and electrode crystallography. Copyright © 2013 John Wiley & Sons, Ltd.     

氯离子吸附单层对Au(111)电极表面应力的贡献

以Cl-为例,应用格子气模型,建立了阴离子吸附层对Au(111)表面应力贡献的统计热力学理论,计算了吸附层Cl-离子间相互作用能、表面应力贡献和二维体积弹性模量.计算结果表明, Cl-吸附层对表面应力贡献的大小,与实验值相近;在Cl-低覆盖度时,经验包括ClO4-贡献,计算了表面应力变化-电荷密度曲线,近似呈线性关系;对于Cl-/Au(111)体系,表面应力与表面张力之差与表面应力同量级,两者差别不可忽略.较好地解释了有关的实验事实.     

Quaternary ammonium bromide surfactant adsorption on low-index surfaces of gold. 1. Au(111)

The coadsorption of the anionic and cationic components of a model quaternary ammonium bromide surfactant on Au(111) has been measured using the thermodynamics of an ideally polarized electrode. The results indicate that both bromide and trimethyloctylammonium (OTA(+)) ions are coadsorbed over a broad range of the electrical state of the gold surface. At negative polarizations, the Gibbs surface excess of the cationic surfactant is largely unperturbed by the presence of bromide ions in solution. However, when the Au(111) surface is weakly charged the existence of a low-coverage, gaslike phase of adsorbed halide induces an appreciable (~25%) enhancement of the interfacial concentration of the cationic surfactant ion. At more positive polarizations, the coadsorbed OTA(+)/Br(-) layer undergoes at least one phase transition which appears to be concomitant with the lifting of the Au(111) reconstruction and the formation of a densely packed bromide adlayer. In the absence of coadsorbed halide, the OTA(+) ions are completely desorbed from the Au(111) surface at the most positive electrode polarizations studied. However, with NaBr present in the electrolyte, a high surface excess of bromide species leads to the stabilization of adsorbed OTA(+) at such positive potentials (or equivalent charge densities).     

Ordered molecular assemblies of substituted bis(phthalocyaninato) rare earth complexes on Au(111): in situ scanning tunneling microscopy and electrochemical studies

Substituted bis(phthalocyaninato) rare earth complexes ML2 (M = Y and Ce; L = [Pc(OC8H17)8]2, where Pc = phthalocyaninato) were adsorbed onto single crystalline Au(111) electrodes from benzene saturated with either YL2 or CeL2 complex at room temperature. In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to examine the structures and the redox reactions of these admolecules on Au(111) electrodes in 0.1 mol dm(-3) HClO4. The CVs obtained with YL2- and CeL2-coated Au(111) electrodes respectively contained two and three pairs of redox peaks between 0 and 1.0 V (versus reversible hydrogen electrode). STM molecular resolution revealed that YL2 and CeL2 admolecules were imaged as spherical protrusions separated by 2.3 nm, which suggests that they were oriented with their molecular planes parallel to the unreconstructed Au(111)-(1 x 1). Both molecules when adsorbing from approximately micromolar benzene dosing solutions produced mainly ordered arrays characterized as (8 x 5 radical3)rect (theta = 0.0125). The redox reactions occurring between 0.2 and 1.0 V caused no change in the adlayer, but they were desorbed or oxidized at the negative and positive potential limits. The processes of adsorption and desorption at the negative potentials were reversible to the modulation of potential. Electrochemical impedance spectroscopy (EIS) and CV measurements showed that YL2 and CeL2 adlayers could block the adsorption of perchlorate anions and mediating electron transfer at the Au(111) electrode, leading to the enhancement of charge transfer for the ferro/ferricyanide redox couple.     

In situ STM evidence for the adsorption geometry of three N-heteroaromatic thiols on Au(111)

The electrochemical behavior of three heteroaromatic thiols (MBs) (2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzoxazole (MBO)) on a Au(111) surface has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV) in 0.1 M HClO(4) solution. All three thiols form oriented molecular cluster lines along the reconstruction line direction at 0.55 V. With the electrode potential shifting negatively, the molecules undergo a disordered-ordered structural transition. Molecularly resolved STM images show that all three molecules form striped adlayers in the desorption region on the Au(111) surface. The different heteroatoms in the heteroaromatic rings result in different electrochemical behavior of the MB self-assembled monolayers (SAMs). MBI, MBT, and MBO are proposed to interact with the substrate via the S-Au bonds from thiol group and the coordination interaction of N, S, and O with the substrate from the heteroaromatic ring, respectively. These results provide direct evidence of the electrochemical behavior and the adlayer structures of MB SAMs on the Au electrode.     

Adsorption of N-Decyl-N,N,N-trimethylammonium triflate (DeTATf), a cationic surfactant, on the Au(111) electrode surface

The adsorption behavior of the cationic surfactant N-decyl-N,N,N-trimethylammonium triflate (DeTATf) on the Au(111) electrode surface was characterized using cyclic voltammetry, differential capacity, and chronocoulometry. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DeTATf has a multistate character. At low bulk DeTATf concentrations, the adsorption state is consistent with the formation of an adsorbed film of nearly flat molecules. At higher concentrations this film may represent a three-dimensional aggregated state. At negative potentials and charge densities close to 0 microC cm-2, the data suggest the formation of a film of tilted molecules oriented with the hydrocarbon tail toward the metal surface and the polar head toward the solution. A surprising result of this study is that DeTATf displays adsorption characteristics of a zwitterionic rather than a cationic surfactant. This behavior indicates that the adsorbed species is an ion pair.     

Characterization of mixed alcohol monolayers adsorbed onto a Au(111) electrode using electro-fluorescence microscopy

A single-crystal Au(111) electrode modified with an adsorbed layer of 1-octadecanol (C18OH) or oleyl alcohol (OLA) in pure or mixed composition was characterized using electrochemical and in situ fluorescence microscopy. Cyclic voltammetry and differential capacitance measurements revealed a repeatable, potential-induced adsorption/desorption process of the surfactant to/from the electrode surface while charge density and film pressure measurements indicated quasi-ideal mixing of the two adsorbed alcohols. A layer less defective than pure C18OH was created with incorporated OLA. Optical characterization was accomplished using epi-fluorescence microscopy combined with electrochemistry (electro-fluorescence microscopy) through the incorporation of two fluorescent probes into the adsorbed surfactant layer. Since molecular luminescence is quenched by a nearby metal, fluorescence was only observed when the fluorescent dye/alcohol layers were desorbed and therefore separated from the metal surface. When desorbed, the structure of the alcohol layers were similar in character, revealing aggregated features which did not change in morphology over numerous desorption/re-adsorption cycles. We have also used the electro-fluorescence technique to estimate the distance separating the metal and desorbed surfactant and believe that the molecules are displaced from the electrode surface by a distance not more than 40 nm.     

Enhancing the electrochemiluminescence of tris(2,2'-bipyridyl)ruthenium(II) by ionic surfactants

The dependence of the electrochemiluminescence of Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) with tri-n-propylamine as co-reactant on the anionic surfactant SDS (sodium dodecyl sulfate) and the cationic surfactants CTAX (CTA = cetyltrimethylammonium cation, X = bromide, chloride and hydrogensulfate) was studied. Both SDS and CTAX, at low surfactant concentrations below the critical micelle concentrations, enhance the electrochemiluminescence at a platinum working electrode. A further enhancement of the light emission intensity by bromide ions was observed when CTAB (B = bromide) was used-an overall 30-fold increase in electrochemiluminescence efficiency was obtained at a CTAB concentration of 0.08 mM. Voltammetric data support adsorption of surfactant molecules on the electrode surface as the cause of the enhancement of electrochemiluminescence by ionic surfactants.     

Interaction between NO and Na, O, S, Cl on Au and Pd(111) surfaces

NO co-adsorption with X (X = Na, O, S, and Cl) on Au and Pd(111) surfaces is studied using density functional theory (DFT) calculations to get a deeper insight into the extraordinary sulfur enhanced adsorption on the Au surface. It is found that both electronegative and electropositive adatoms can enhance NO adsorption on Au(111). In Na + NO/Au(111), the strong electrostatic attraction between Na and NO dominates and stabilizes NO adsorption, though Na-induced surface negative charging weakens NO adsorption. In (O, S, Cl) + NO/Au, the electronegative atoms would induce a slight surface distortion and enhance NO adsorption accordingly. NO adsorption on Pd(111) is enhanced by Na, but weakened by electronegative species. We suggest that the unique features of noble metals, i.e., the narrow DOS at the Fermi level (E(F)) and the deep buried d-band center, should play an important role in the promotion of NO adsorption on their surface as the CO case.