Electrocatalysis of redox reactions by metal nanoparticles on graphite electrodes

A selection of graphitic materials of both scientific as well as commercial importance has been modified by deposition of various metals at very low coverages under overpotential or underpotential conditions. Nanoparticles were found with some metals. The changes in the electrocatalytic activity of the supporting electrode by the metal modification were studied using electrochemical impedance measurements of a fast redox system. The carbon/solution interface was characterized with surface Raman spectroscopy, electrochemical impedance measurements, and cyclic voltammetry. Electronic Publication     

Study the Transition Metal and Semiconductor/Solution Interfaces by Confocal Microprobe Raman Spectroscopy

In the past two decades, practical application of surface Raman spectroscopy had been limited to a few metals, mainly,roughened Ag, Au and Cu, providing great surface enhanced Raman scattering (SERS) enhancement.     

Rh和Pt超薄层电极上的CO吸附行为(英文)

利用沉积在粗糙金电极上的过渡金属超薄层电极技术 ,我们获得了氢及一氧化碳在Rh和Pt表面上吸附的拉曼信号 ,并对两者之间的相互作用进行了分析 ..我们还进行了二氧化碳在这两种金属表面的还原行为的初步研究 ,以及对不同方式获得的一氧化碳吸附拉曼信号的特点进行了分析 .     

Raman spectroscopy on transition metals

Surface-enhanced Raman spectroscopy (SERS) has developed into one of the most important tools in analytical and surface sciences since its discovery in the mid-1970s. Recent work on the SERS of transition metals concluded that transition metals, other than Cu, Ag, and Au, can also generate surface enhancement as high as 4 orders of magnitude. The present article gives an overview of recent progresses in the field of Raman spectroscopy on transition metals, including experimental, theory, and applications. Experimental considerations of how to optimize the experimental conditions and calculate the surface enhancement factor are discussed first, followed by a very brief introduction of preparation of SERS-active transition metal substrates, including massive transition metal surfaces, aluminum-supported transition metal electrodes, and pure transition metal nanoparticle assembled electrodes. The advantages of using SERS in investigating surface bonding and reaction are illustrated for the adsorption and reaction of benzene on Pt and Rh electrodes. The electromagnetic enhancement, mainly lightning-rod effect, plays an essential role in the SERS of transition metals, and that the charge-transfer effect is also operative in some specific metal–molecule systems. An outlook for the field of Raman spectroscopy of transition metals is given in the last section, including the preparation of well-ordered or well-defined nanostructures, and core-shell nanoparticles for investigating species with extremely weak SERS signals, as well as some new emerging techniques, including tip-enhanced Raman spectroscopy and an in situ measuring technique. Figure Electric-field enhancement of a SERS-active Rh surface decorated with small nanohemispheres     

A Comparative Study on the Influence of Submonolayer Coverage Sn on SERS of Au and Pt Substrates

Since the discovery of the surface enhanced Raman scattering (SERS) in mid-1970's,great efforts have been devoted to understand the enhancement mechanism as well as to extend the SERS system and application. There has been a consensus that the electromagnetic enhancement (EM) and chemical enhancement are the two important SERS mechanisms but each of them can only explain some of experimental results^[1,2] The EM mechanism relies on the surface plasmon resonance under a proper incident laser excitation. Strong EM enhancement has been observed on metals such as Cu, Ag and Au but not on transition metals such as Pt. However, the surface electronic properties can be modulated through submonolayer quantity modification of foreign metal atoms, hi this paper, we report a comparative study on SERS of Au and Pt in the presence of underpotentially deposited (UPD) submonolayer Sn.     

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.     

用于电化学界面研究的共焦显微拉曼光谱技术(英文)

系统地介绍了将共焦显微拉曼光谱系统用于电化学界面研究的方法 ,包括铂电极的粗糙和电化学拉曼电解池的设计 .进行了铂上氢、氧和氯共吸附的拉曼光谱研究 .通过对甲醇氧化过程的现场跟踪 ,提出检测界面区溶液浓度变化和计算溶液 pH值的方法 .实验表明拉曼光谱技术可作为研究实际应用体系的重要工具 .     

Expanding generality of surface-enhanced Raman spectroscopy with borrowing SERS activity strategy

Surface-enhanced Raman scattering (SERS) was discovered three decades ago and has gone through a tortuous pathway to develop into a powerful diagnostic technique. Recently, the lack of substrate, surface and molecular generalities of SERS has been circumvented to a large extent by devising and utilizing various nanostructures by many groups including ours. This article aims to present our recent approaches of utilizing the borrowing SERS activity strategy mainly through constructing two types of nanostructures. The first nanostructure is chemically synthesized Au nanoparticles coated with ultra-thin shells (ca. one to ten atomic layers) of various transition metals, e.g., Pt, Pd, Ni and Co, respectively. Boosted by the long-range effect of the enhanced electromagnetic (EM) field generated by the highly SERS-active Au core, the originally low surface enhancement of the transition metal can be substantially improved giving total enhancement factors up to 10(4)-10(5). It allows us to obtain the Raman spectra of surface water, having small Raman cross-section, on several transition metals for the first time. To expand the surface generality of SERS, tip-enhanced Raman spectroscopy (TERS) has been employed. With TERS, a nanogap can be formed controllably between an atomically flat metal surface and the tip with an optimized shape, within which the enhanced EM field from the tip can be coupled (borrowed) effectively. Therefore, one can obtain surface Raman signals (TERS signals) from adsorbed species at Au(110), Au(111) and, more importantly, Pt(l10) surfaces. The enhancement factor achieved on these single crystal surfaces can be up to 106, especially with a very high spatial resolution down to about 14 nm. To fully accomplish the borrowing strategy from different nanostructures and to explain the experimental observations, a three-dimensional finite-difference time-domain method was used to calculate and evaluate the local EM field on the core-shell nanoparticle surfaces and the TERS tips. Finally, prospects and further developments of this valuable strategy are briefly discussed with emphasis on the emerging experimental methodologies.     

Photon-driven charge transfer and Herzberg-Teller vibronic coupling mechanism in surface-enhanced Raman scattering of p-aminothiophenol adsorbed on coinage metal surfaces: a density functional theory study

The chemical enhancement effects in surface-enhanced Raman scattering of p-aminothiophenol (PATP, it is also called p-mercaptoaniline or p-aminobenzenthiol) adsorbed on coinage metal surfaces with single thiol end or trapped into metal-molecule-metal junctions with both thiol and amino groups have been studied by density functional theory (DFT). We focus on the influence of photon-driven charge transfer (PDCT) and chemical bonding interaction (ground-state charge transfer) on the intensity enhancement and frequency shift in the surface Raman spectra of PATP. For comparison, the electronic structures and transitions of free PATP are studied first. The simulated pre-resonance UV Raman spectra illustrate that b(2) modes can be selectively enhanced via vibronic coupling. The fundamentals of all the b(2) modes in the frequency range of 1000 to 1650 cm(-1) are assigned in detail. For PATP adsorbed on coinage metals, the time-dependent-DFT calculations indicate that the low-lying CT excited state arises from the π bonding orbital of molecule to the antibonding s orbital of metallic clusters. Our results further show that the PDCT resonance-like Raman scattering mechanism enhances the totally symmetric vibrational modes and the NH(2) wagging vibration. Finally, the effect of chemical bonding interaction is also investigated. The amino group binding to metals gives a characteristic band of the NH(2) wagging mode with the large blueshift frequency and an intense Raman signal.     

等离子体金属纳米结构在SERS传感及可穿戴应力传感中的应用

等离子体金属(金、银)纳米结构因其特有的理化性能,被广泛应用于表面增强拉曼散射(Surface-enhanced Raman scattering,SERS)传感及可穿戴应力传感领域.其中,SERS是一种应用贵金属纳米材料增强拉曼散射信号的检测技术,该技术灵敏度高、特异性强,已被广泛用于生物医学、环境监测、食品药品检测...     

The effects of the underpotential and overpotential deposition of lead and thallium on silver on the Raman spectra of adsorbates

It is shown that the underpotential deposition (UPD) and dissolution of monolayers of Pb and Tl onto Ag surfaces roughened in a controlled oxidation-reduction cycle produces a Ag surface which shows diminished surface enhanced Raman scattering (DSERS). Significantly enhanced Raman spectra can still be obtained from electrodes covered by complete UPD and overpotential deposited (OPD) layers of the metals. Correct choice of electrolytes for the UPD of the metal reduces the loss of enhanced Raman scattering; chloride ions, constituents of many electrolytes used in the investigation of surface enhanced Raman scattering (SERS), are shown to be especially active in causing the loss of SERS.     

Pigment identification in artwork using graphite furnace atomic absorption spectrometry

The use of a sampling technique is described for the identification of metals from inorganic pigments in paint. The sampling technique involves gently contacting a cotton swab with the painted surface to physically remove a minute quantity (∼1-2 μg) of pigment. The amount of material removed from the painted surface is invisible to the unaided eye and does not cause any visible effect to the painted surface. The cotton swab was then placed in a 1.5 ml polystyrene beaker containing HNO₃ to extract pigment metals prior to analysis using graphite furnace atomic absorption spectrometry (GFAAS). GFAAS is well suited for identifying pigment metals since it requires small samples and many pigments consist of main group elements (e.g. Al) as well as transition metals (e.g. Zn, Fe and Cd). Using Cd (cadmium red) as the test element, the reproducibility of sampling a paint surface with the cotton swab was approximately 13% in either a water or oil medium. To test the feasibility of cotton sampling for pigment identification, samples were obtained from paintings (watercolour and oil) of a local collection. Raman spectra provided complementary information to the GFAAS, which together are essential for positive identification of some pigments. For example, GFAAS indicated the presence of Cu, but the Raman spectra positively identified the modern copper pigment phthalocyanine green (Cu(C₃₂Cl₁₆N₈). Both Raman spectroscopy and GFAAS were useful for identifying ZnO as a white pigment.     

SERS,AFM and Electrochemical Characterization of Metal Nanorod and Nanowire Arrays

Metal nanowires (nanorods) have novel properties and potential applications in a wide field^[1]. Many two-dimensional nanowire arrays of semiconductors and metals with different diameter and length have been made using template synthesis method^[2]. The nanorod arrays of various metals (e.g., Cu, Ag,Au, Ni and Co) with different diameters from about 15 nm to 130 nm were fabricated by electrodeposition of the metals into the highly ordered nanochannel arrays in alumina film followed by partial removal of the film in phosphoric acid or sodium hydroxide. In the present work, surface-enhanced Raman spectroscopy (SERS), AFM and electrochemical methods have been used to characterize the metal nanorod (nanowire) arrays. Tapping mode AFM and SERS were performed on Nanoscope Ⅲa (Digital Instruments) and on confocal Raman microscopy (LabRam I,Dilor) respectively.     

The influence of selected metals and halogens on the electronic system of benzoic acid

The influence of halogens and metals on the electronic system of the aromatic ring in lithium, sodium and potassium complexes with p-halogenobenzoic acids has been investigated by means of ¹³C and ¹H NMR, IR and Raman spectroscopy and semi-empirical calculations. It has been shown that ionic potentials and electronegativities of halogens and metals are the main factors responsible for perturbations of the electronic charge distribution in the ring.     

The influence of selected metals and halogens on the electronic system of benzoic acid

The influence of halogens and metals on the electronic system of the aromatic ring in lithium, sodium and potassium complexes with p-halogenobenzoic acids has been investigated by means of ¹³C and ¹H NMR, IR and Raman spectroscopy and semi-empirical calculations. It has been shown that ionic potentials and electronegativities of halogens and metals are the main factors responsible for perturbations of the electronic charge distribution in the ring.     

SPR银金电极上光电化学反应和EC-SERS理论研究

随着纳米科学的发展,人们再次关注到金属电极上的光电化学研究. 这主要得益于币族金属纳米结构具有强的表面等离激元共振（SPR）效应,它能有效地将光从远场光转化为近场光,汇聚光能到金属表面区域,可以在表面产生强的光电场效应,或产生较长寿命的热电子-空穴载流子效应,或是更长时间尺度的热效应. 因此,SPR效应不仅产生了表面增强拉曼散射(SERS)效应,用于表征吸附分子,而且可能诱发表面化学反应,为在电化学界面实现光与电协同调控化学反应提供新思路. 本文首先回顾了金属电极上光电流理论的发展,然后总结了本研究组近年来将量子化学计算用于光电化学反应和SERS光谱研究的工作,并以在银金纳米结构电极上水合质子还原和芳香胺氧化为例,比较了热电子和热空穴参与光电化学反应的特点,揭示了SPR参与光电化学反应的本质.     

金、铜金属纳米棒或纳米线的AFM和SERS的研究(英文)

通过电化学氧化法制备具有不同孔径氧化铝模板 ,利用交流电镀的方法在模板中沉积金属 ,再用酸溶解模板可以得到相应尺度的金属纳米线或纳米棒的阵列 .本文利用原子力显微镜和表面增强拉曼技术分别表征了金和铜两种金属纳米线阵列 .研究结果表明 ,作为探针分子的硫氰(SCN )在金属纳米线上的碳氮三键的振动频率随纳米线直径的增大而蓝移 .这一现象可能是因为尺寸效应对纳米线的费米能级造成影响 ,使不同直径的金属纳米线电子结构存在微小的差别 .     

Investigation the Corrosion Process of the Co Electrode by Surface Raman Spectroscopy

Due to its special magnetic property, Co has become a very important material in surface science. Furthermore, its unique high catalytic activity has made it an important catalyst for syngas in the catalytic industries. On the other hand, in electrochemistry, Co and its oxides are wide-used electrode materials in the Ni battery and alloy electrodes for hydrogen storage. Thus it is very important to perform the study on the surface process on the Co surface. Raman Spectroscopy is a powerful technique in characterizing the surface species, however Co has been considered as not a suitable material for creating enormous surface enhanced Raman process. Theoretically, it has been reported that Co with suitable particle size could be able to generate weak surface enhancement, but no experimental evidence is available. In this study,we developed a method to roughen the Co surface to create possible enhancement in the Raman signal. Based on that, the oxidation process of the Co surface (or the etching process of the Co surface in electrolytes) was studied. Benzotriazole(BTA), a very typical corrosion inhibitor, was added to the electrolyte to study its effect on the corrosion of the Co electrode.     

电化学界面SERS光谱的密度泛函理论研究

运用量子化学密度泛函DFT理论和拉曼光谱研究了吡啶在过渡金属(Ⅷ族)和币族金属(IB族)表面吸附的成键机理及其拉曼光谱的变化规律.总结了作者研究组有关吡啶-金属SERS体系的研究,并从化学成键机理和光驱电荷转移机理两个方面探讨了电化学界面SERS谱峰的频率位移和增强效应,解释了实验观测到的SERS光谱随金属电极材料、激发光波长以及电极电位变化的现象.     

Synthesis and optical properties of three-dimensional porous core-shell nanoarchitectures

Three-dimensional porous core-shell nanostructures consisting of gold skeletons and silver shells were fabricated by controllable electroless plating. Optical properties of the 3D nanocomposite with a heterogeneous interface exhibit a significant shell-thickness dependence. The porous core-shell structure with an optimized shell thickness of approximately 3-5 nm exhibits a considerable improvement in surface-enhanced Raman scattering. This study has important implications in the functionalization of nanoporous metals by surface modification.