铂和钌纳米薄膜电极的全湿法制备及表面增强红外效应

金属纳米薄膜的合理制备是衰减全反射表面增强红外光谱法(ATR-SEIRAS)成功应用的关键. 通过简便可控的全湿法镀膜, 即先在红外窗口硅面上化学镀金膜, 而后再电沉积铂或钌, 制得具有极强表面增强红外效应、吸收峰向正常且几乎“无针孔”的铂或钌纳米薄膜电极, 从而可使ATR-SEIRAS技术广泛应用于研究铂、钌电极表面的吸附与反应.     

Extending in situ attenuated-total-reflection surface-enhanced infrared absorption spectroscopy to ni electrodes

Surface-enhanced infrared absorption spectroscopy (SEIRAS) in the attenuated-total-reflection configuration (ATR-SEIRAS) has been applied for the first time to Ni electrodes. SEIRA-active Ni electrodes were obtained through initial chemical deposition of a 60-nm-thick Au underlayer on the reflecting plane of an ATR Si prism followed by potentiostatic electrodeposition of a 40-nm-thick Ni overlayer in a modified Watt's electrolyte. The Ni nanoparticle film thus obtained exhibited exceptionally enhanced IR absorption for the surface probe molecule CO while maintaining unipolar and normally directed bands. With the advantages of ATR-SEIRAS, free H2O molecules coadsorbed with CO at the Ni electrode were revealed, and their role in the electrooxidation of the CO adlayer at the Ni electrode is discussed. In addition, the conversion of bridge to linearly bonded CO at Ni electrode in a neutral solution was clearly identified upon electrooxidation of the CO adlayer. ATR-SEIRAS was also used to characterize the adsorption configuration of a pyridine adlayer at the Ni electrode. Both A1 and B1 modes of adsorbed pyridine were detected with comparably large intensities, essentially maintaining the spectral feature of pyridine molecules rather than that of "alpha-pyridyl species", which strongly suggests an "edge-tilted pyridine" configuration present at the Ni electrode, a configuration intermediate between the "end-on pyridine" and "edge-on alpha-pyridyl" adsorption modes reported in the literature.     

镉电极上的衰减全反射表面增强红外光谱

利用两步“湿法镀膜”方法将ATR-SEIRAS的研究进一步拓展到ⅡB族Cd电极上. 选择吡啶(Py)作为模型分子, 初步比较了Py在不同金属电极表面上的吸附构型.     

Ubiquitous strategy for probing ATR surface-enhanced infrared absorption at platinum group metal-electrolyte interfaces

A versatile two-step wet process to fabricate Pt, Pd, Rh, and Ru nanoparticle films (simplified as nanofilms hereafter) for in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) study of electrochemical interfaces is presented, which incorporates an initial chemical deposition of a gold nanofilm on the basal plane of a silicon prism with the subsequent electrodepostion of desired platinum group metal overlayers. Galvanostatic electrodeposition of Pt, Rh, and Pd from phosphate or perchloric acid electrolytes, or potentiostatic electrodeposition of Ru from a sulfuric acid electrolyte, yields sufficiently "pinhole-free" overlayers as evidenced by electrochemical and spectroscopic characterizations. The Pt group metal nanofilms thus obtained exhibit strongly enhanced IR absorption. In contrast to the corresponding metal films electrochemically deposited directly on glassy carbon and bulk metal electrodes, the observed enhanced absorption for the probe molecule CO exhibits normal unipolar band shapes. Scanning tunneling microscopic (STM) images reveal that fine nanoparticles of Pt group metals are deposited around wavy and stepped bunches of Au nanoparticles of relatively large sizes. This ubiquitous strategy is expected to open a wide avenue for extending ATR surface-enhanced IR absorption spectroscopy to explore molecular adsorption and reactions on technologically important transition metals, as exemplified by successful real-time spectroscopic and electrochemical monitoring of the oxidation of CO at Pd and that of methanol at Pt nanofilm electrodes. The spectral features of free water molecules coadsorbed with CO on Pt, Pd, Rh, and Ru are also discussed.     

Melting Mechanism and Structure Evolution of Au Nanofilms Explored by Molecular Dynamics Simulations

The melting mechanism and structure evolution of two-dimensional Au nanofilms with different thicknesses have been investigated in detail by using classical molecular dynamics simulations. The simulation results demonstrate that all Au nanofilms display a two-stage melting behavior of surface premelting and homogenous melting. Furthermore, the premelting behavior only occurs in the outermost layers but the other inner layers always keep a stable solid state until the corresponding melting point, which is different from the premelting behavior from surface into the interior in zero-dimensional Au nanocluster and one-dimensional Au nanowire. Meanwhile, the increase of nanofilm thickness can lead to an increase of melting point. During the premelting process, the surface reconstruction fromthe f100g plane to the f111g plane has directly been observed at a atomic level for all Au nanofilms. However even for the thinnest L2 nanofilm, the surface stress can't induce such surface reconstruction until temperature is up to 500 K, while similar surface reconstruction induced by surface stress can be observed at much lower temperature for the Au nanowire due to its higher surface-to-volume ratios compared to the Au nanofilm. In addition, our simulation results show that the thinnest Au nanofilm with two atomic layers can be broken into independent one-dimensional nanowires when the temperature reaches a certain value.     

Pt-Ru合金薄膜的电沉积制备及其电化学表面增强红外吸收光谱

在1mmol·L-1H2PtCl6+1mmol·L-1RuCl3+0.1mol·L-1H2SO4镀液中采用电沉积法在化学镀金膜的红外窗口Si反射面上制备Pt50Ru50合金电极.利用原子力显微镜(AFM)可以观察到制备的Pt50Ru50合金电极形貌呈现出100-200nm大小的颗粒.常规电化学分析方法得出该电极具有典型的合金特征,对CO和CH3OH具有很好的催化氧化作用.应用电化学现场衰减全反射表面增强红外光谱法(ATR-SEIRAS)可以观察到该电极上Pt位和Ru位上CO的振动谱峰,且表现出Pt-Ru二元金属良好的协同催化性能.     

铂电极上吸附芳香分子的表面增强红外光谱研究

应用衰减全反射表面增强红外吸收光谱法分别研究了0.1 mol•L^－1 HClO₄中对硝基苯甲酸(PNBA)和0.1 mol•L^－1 KClO₄中吡啶(Py)在铂电极上的吸脱附. 结果表明在较高电位下(0.3～0.7 V vs. SCE) PNBA是通过其羧基脱质子后羧酸根的两个氧原子等位吸附在Pt电极表面, 而随着电位的负移, 除PNBA逐步脱附外, 还呈现出单个氧原子吸附的谱学特征. 光谱强度与电位的关系表明PNBA在铂电极表面吸脱附的中间电位约为0.2 V vs. SCE. 吡啶的吸附主要是通过氮原子的孤对电子及脱氢后的α碳原子与Pt电极表面键合. 在较宽的电位区间(0.4～－0.4 V vs. SCE)吡啶的吸附方式和取向基本维持不变.     

Ru膜上Pt层的自发沉积及其在电化学表面增强红外光谱中的应用

采用自发沉积法在Ru膜上生成超薄Pt层(简称Ru/Pt膜), 即在开路状态下将电化学还原后的Ru膜浸于除去氧的H2PtCl6溶液中进行自发沉积. 电化学伏安法测量表明, 随着电还原-自发沉积循环次数的增加, 该Ru/Pt膜电极所含Pt组分增加, 且CO吸附层的电氧化峰电位较Pt膜电极上的明显负移. 应用现场衰减全反射表面增强红外光谱法(ATR-SEIRAS)可轻易检测到在该膜电极Pt和Ru位上吸附CO的振动谱峰. 所制Ru/Pt膜电极不仅对CO的电催化氧化具有协同效应, 还可应用于现场ATR-SEIRAS的研究中.     

Spectroelectrochemical examination of the interaction between bacterial cells and gold electrodes

The interaction between bacterial cells of Pseudomonas fluorescens (ATCC 17552) and gold electrodes was analyzed by cyclic voltammetry (CV) and attenuated total reflection-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The voltammetric evaluation of cell adsorption showed a decrease in the double-layer capacitance of polyoriented single-crystal gold electrodes with cell adhesion. As followed by IR spectroscopy in the ATR configuration, the adsorption of bacterial cells onto thin-film gold electrodes was mainly indicated by the increase in intensity with time of amide I and amide II protein-related bands at 1664 and 1549 cm(-1), respectively. Bands at 1448 and 2900 cm(-1) corresponding to the scissoring and the stretching bands of CH2 were also detected, together with a minor peak at 1407 cm(-1) due to the vs COO- stretching. Weak signals at 1237 cm(-1) were due to amide III, and a broad band between 1100 and 1200 cm(-1) indicated the presence of alcohol groups. Bacteria were found to displace water molecules and anions coadsorbed on the surface in order to interact with the electrode intimately. This fact was evidenced in the SEIRAS spectra by the negative features appearing at 3450 and 3575 cm-1, corresponding to interfacial water directly interacting with the electrode and water associated with chloride ions adsorbed on the electrode, respectively. Experiments in deuterated water confirmed these assignments and allowed a better estimation of amide absorption bands. In CV experiments, an oxidation process was observed at potentials higher than 0.4 V that was dependent on the exposure time of electrodes in concentrated bacterial suspensions. Adsorbed bacterial cells were found to get closer to the gold surface during oxidation, as indicated by the concomitant increment in the main IR bacterial signals including amide I, a sharp band at 1240 cm(-1), and a broad one at 1120 cm(-1) related to phosphate groups in the bacterial membranes. It is proposed to be due to the oxidation of lipopolysaccharides on the outermost bacterial surface.     

Catalytic deposition of Pb on regenerated gold nanofilm surface and its application in selective determination of Pb2+

We report a simple method of catalytic deposition of Pb on a gold nanofilm substrate, which was in situ prepared and used as nanocrystal seeds. Due to the unique properties of gold nanocrystal seeds, Pb could be catalytically deposited on the surface of the gold nanofilm. Compared with the deposition of Pb on bare gold electrode, a larger amount of Pb was deposited on the gold nanofilm and the electrical response was amplified significantly. The catalytic deposition of Pb on the gold nanofilm was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. A stable and quasi-reversible redox couple was obtained in neutral solution and studied in detail. The surface of the gold nanofilm could be easily regenerated in 0.1 mol L(-1) nitric acid solution. Since the redox peaks of Pb could be effectively separated from those of other metals such as Cu, Cd, and Zn, a selective determination of Pb2+ was achieved. Linear sweep voltammetry (LSV) was used for the determination of Pb2+. The peak currents of Pb varies linearly with the concentration of Pb2+ in aqueous solution ranging from 1.0 to 10.0 micromol L(-1) (R=0.999), with a detection limit of 0.1 micromol L(-1). It is expected that the gold nanofilm will facilitate the appearance of heavy metal ion sensors with good performance.     

The role of electrochemical reactions during electrophoretic particle deposition

Platinum microelectrodes were fabricated on a sapphire substrate by lithographic patterning and used to manipulate 1.58 microm silica particles in the plane of the substrate. A digital video system captured the motion of particles far from the electrodes and their deposition onto the working electrode during application of a DC potential. The role of electrode reversibility was investigated by comparing as-deposited electrodes with electrodes modified by electrolytic plating of platinum. Particles were also observed adhering to the substrate before reaching the electrode. The zeta potential of the particles and substrate was measured. The differing surface chemistry of the two systems and a local reduction in pH due to the production of hydrogen ion at the anode can explain the adhesion phenomena. Force distance curves were recorded using a colloid probe atomic force microscopy technique to directly measure the interaction of the silica particles with the sapphire substrate. These data validated the observed adhesion at the electrode and provided further support for the temporal and spatial reduction in pH. The role of Faradaic processes and the diffusion of potential determining ions in electrophoretic deposition were also considered.     

The synthesis and adsorption properties of polyvinylchloride nanofilms with ligand groups

Polyvinylchloride (PVC) samples with a fairly developed surface were prepared by the spontaneous removal of the solvent (benzyl alcohol) from a polymer gel. The surface of the product was modified to obtain ethanolocyclame and sodium acetocyclame nanofilms. The structure and composition of the nanofilms were studied by IR Fourier spectroscopy. The adsorption of nitrogen vapor at ?196°C and benzene and water at 20°C on the nanofilms was investigated. Surface modification was shown to increase the stability of PVC in water and benzene and the specific surface area and volume of nanopores. The conclusion was drawn that nanofilm ligand groups could stoichiometrically interact with water and benzene molecules on PVC with a modified surface.     

SERS and FT-IR studies of CO adsorbed on underpotential deposited Ag/Pt electrodes

CO adsorbed on UPD and OPD (under- and overpotential deposited) Ag layers on a Pt electrode surface was studied by SERS and IRRAS in conjunction with cyclic voltammetry. Electrochemical activation of a uniform UPD Ag adlayer produced Ag clusters on the Pt electrode as well as bare Pt sites. The strong adsorption of CO on the UPD Ag/Pt electrode compared with a bulk Ag electrode is explained by the influence of the substrate Pt atoms. The degree of electron back-donation to CO increases the degree of lower frequency shifts of CO on the electrodes in the order Pt electrodes < monolayer Ag/Pt < multilayer Ag/Pt.     

原位衰减全反射表面增强红外光谱实验技术

介绍了原位研究电极,溶液界面反应的技术--衰减全反射表面增强红外光谱实验技术(ATR-SEIRAS)的产生背景和工作原理,重点描述了ATR-SEIRAS实验技术的关键:光谱电化学池的构造和薄膜电极的制备.与IRAS相比,ATR-SEIRAS技术可以更容易消除溶剂的背景吸收,获得较高的表面灵敏度,而且允许物质在电极表面自由扩散.与循环伏安相结合,利用ATR-SEIRAS技术可以实时监测电极,溶液界面问的反应.选择了利用ATR-SEIRAS实验技术原位研究功能表面的构造和性质、分子识别和反应中间体的形成等方面的应用实例,分析了ATR-SEIRAS实验技术的研究方向.     

铂电极上自组装铁原卟啉单分子层的表面增强振动光谱初探(英文)

应用现场表面增强拉曼光谱和衰减全反射表面增强红外光谱初步研究了0.1mol·L-1HClO4溶液中Pt电极表面铁原卟啉(FePP)自组装单层的电化学和结构特性.以514nm波长为激发线,得到了增强因子约为40的粗糙Pt电极上FePP在不同电位下的表面增强拉曼光谱.分析0.5～-0.3V(SCE)区间内谱峰变化,得到近似的吸附等温式,由此可估算出Fe3+/Fe2+的式量电位大约为-0.2V.原位表面增强红外光谱的测试结果表明,FePP分子主要以斜立方式吸附在Pt膜电极表面,其中一个环外羧酸根与电极表面相接触,而另一羧酸基团以氢键与相邻的FePP分子相连.这样的吸附结构在-0.1～0.9V(SCE)的电位区间内并没有显著的变化.     

Silver‐Assisted Chemical Etching on Silicon with Polyvinylpyrrolidone‐Mediated Formation of Silver Dendrites

Metal‐assisted chemical etching (MaCE) on silicon (Si)—mediated by polyvinylpyrrolidone (PVP)—is systematically investigated herein. It is found that the morphologies and crystallographic natures of the grown silver (Ag) dendrites can be significantly modulated, with the presence of PVP in the MaCE process leading to the formation of faceted Ag dendrites preferentially along the (111) crystallographic phase, rather than along the (200) phase. Further explorations of the PVP‐mediated effect on Si etching are also revealed. In contrast to the aligned Si nanowires formed by MaCE without PVP addition, only distributed nanopores with sizes of 200 to 400 nm appear on the Si surfaces in the presence of PVP. The origin of surface polishing on Si in the PVP‐mediated MaCE process can be attributed to the distinct transport pathway of holes supplied by the Ag⁺ ions, where the holes are injected directly into the primary Ag seeds, rather than through Ag dendrites, thus leading to the isotropic etching of the Si surface.     

苯胺在银和金电极上的表面增强拉曼光谱

聚苯胺作为性能较好的导电高聚物有很大的应用潜力,有关其聚合和导电机理的研究受到广泛重视。表面增强拉曼光谱(SERS)能现场(in situ)检测表面吸附分子、提     

SnO_2TiO_2复合半导体纳米薄膜的研究进展

本文概述了SnO2TiO2复合半导体纳米薄膜的发展历史和研究现状,对比分析了“混合”、“核壳”和“叠层”3种复合薄膜的结构和性能特点,着重论述了叠层结构的SnO2/TiO2复合薄膜的光电化学和光催化特性。结合作者的研究工作,探讨了SnO2/TiO2双层复合薄膜上下层厚度对其光催化活性的影响,指出复合薄膜光催化活性的提高可归因于电子从TiO2向SnO2的迁移。最后对SnO2/TiO2复合薄膜的局限性和发展潜势做一简要分析,强调了该复合薄膜本身的应用特点。     

Comparative study of the interaction of pyridine with polycrystalline Ag and amorphous solid water

The interaction of pyridine (C5H5N) with polycrystalline Ag and amorphous solid water (D2O) is compared. Metastable impact electron spectroscopy (MIES) and reflection-absorption infrared spectroscopy (RAIRS) were utilized to obtain information on the structure of the pyridine-Ag and pyridine-water interfaces. On polycrystalline Ag, C5H5N adsorbs with its molecular axis perpendicular to the surface whereby a work function decrease of 1.5 eV takes place during the build up of the first layer. In the second layer the molecular axis is tilted with respect to the surface normal. On amorphous solid water, C5H5N is initially adsorbed on top with its ring plane oriented preferentially near parallel with respect to the surface, reflecting the contribution of two different interactions to the bonding, the formation of a pi-hydrogen bond, and competitive bonding via the nitrogen lone pair. Coverage-driven reorientation takes place during the completion of the first monolayer and increases the average tilt angle. We have followed the growth of pyridine films up to the third layer which, according to RAIRS, shows clear signs of condensation. No embedding of pyridine species into the underlying water film can be noticed when heating up to desorption. The exposure of a pyridine film at 124 K to D2O molecules does not lead to on top adsorption. Instead, D2O becomes initially embedded into the pyridine film, and RAIRS indicates solvation of the pyridine species.     

Anguler-resolved raman spectroscopy of pyridine on copper and gold electrodes

The surface enhanced Raman scattering from pyridine molecules adsorbed on smooth copper or gold electrodes exhibits a similar strong enhancement as for pyridine on Ag. The intensity is very sensitive to the angle of incidence, and the signal is detectable only in a narrow angular range, when only monolayer amounts of the metals have been dissolved and redeposited electrochemically.