Enhanced and normal Raman scattering from pyridine adsorbed on rough and smooth silver electrodes

A multiplex spectrograph has been used to record potential difference and modulation Raman spectra of pyridine adsorbed on silver electrodes in an electrochemical cell. Spectra have been obtained from rough silver surfaces which give SERS and from surfaces where SERS has been diminished by prolonged cathodic polarisation (DSERS). Raman scattering from pyridine at smooth silver surfaces in potassium perchlorate and fluoride solutions has been distinguished from solution scatter by a potential modulation technique. The results show that the enhanced scattering caused by silver atom or cluster sites is respresentative of the surface as a whole as similar Raman spectra are obtained on smooth surfaces at a count rate as low as ?1.4 photons s^?1 (incident laser power 500 mW).Correlation of simultaneous differential capacitance data and “snapshot” SER spectra indicate that pyridine molecules in aqueous chloride ion solutions adsorb on silver in a flat π-bonded configuration at potentials markedly positive to the point of zero charge and exhibit specific reorientation at ?0.3 V and ?0.45 V (vs. SCE) to become N-bonded, perpendicular to the surface. Results also show that the adsorption behaviour of pyridine in chloride and fluoride ion solutions is largely similar.     

Raman spectroscopy of adsorbates on thin film electrodes deposited on silver substrates

Is is shown that enhanced Raman spectra can be detected for CN⁻ absorbed on thin Ni, Co, Cu and Zn layers deposited from cyanide plating baths onto silver substrate electrodes roughened in a preceding controlled oxidation-reduction cycle; adsorption of CN⁻ on Ag stabilises the roughened substrate structure during the electroplating step. Mechanisms for the generation of enhanced spectra at such composite layered electrodes are discussed briefly.     

Surface-enhanced Raman scattering measurements on silver nanoparticles covered with differently formed platinum films

Gold and silver electromagnetic nanoresonators covered by a thin layer of platinum are often used to study adsorption of various molecules on “model platinum surfaces” with surface-enhanced Raman scattering (SERS) spectroscopy. In this contribution spectra of pyridine adsorbed on films formed from core–shell Ag@Pt and Ag@Ag–Pt nanoparticles and pure Pt or Ag nanoparticles were measured using a confocal Raman microscope. The SERS spectra of pyridine adsorbed on alloy Ag@Ag–Pt nanoparticles could not be obtained as a linear combination of spectra measured on pure Ag and Pt surfaces. In other words, for silver electromagnetic nanoresonators covered by platinum there is no simple correlation between the “quality” of the deposited Pt layer and the relative intensity of SERS bands characteristic for adsorbate interacting with silver. The SERS spectra accumulated from various places of a film formed from Ag@Pt or Ag@Ag–Pt nanoclusters may differ significantly. Using Ag@Pt nanoparticles with practically negligible amount of Ag on the surface (as per the stripping measurement), it is possible to record SERS spectrum in which the contribution characteristic for pyridine adsorbed on the Ag surface is well visible. It means that, even for macroscopic samples of core–shell Ag–Pt nanoparticles, averaging of many spectra measured at various locations of the sample should be carried out to characterize reliably their properties.     

粗糙镍电极上吡啶和二巯基嘧啶的表面拉曼光谱

粗糙镍电极上吡啶和二巯基嘧啶的表面拉曼光谱①黄群健高劲松蔡雄伟毛秉伟郑明森田中群＊（厦门大学化学系，固体表面物理化学国家重点实验室，厦门３６１００５）自从人们发现和认知表面增强拉曼散射（ＳＥＲＳ）效应以来［１］，ＳＥＲＳ技术以其极高的表面灵敏度为电极...     

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     

Adsorption of 4-aminopyridine on Co and Ag electrodes probed by SERS

The adsorption of 4-aminopyridine (4-AP) on Co and Ag electrodes in acid or alkaline solutions of KCl and KI electrolyte salts were monitored by the Surface-enhanced Raman Spectroscopy (SERS) technique. The SERS intensity for the Ag electrode was in 2 orders of magnitude higher than for the Co electrode, due to the enhancement of the Raman cross-section on Ag by the surface-plasmon excitation. In acidic chloride medium (pH 4), the SERS results for Ag electrodes indicate that the protonated form of 4-AP (4-APH⁺) adsorbs in the potential range of −0.1 to −0.6 V (Ag|AgCl|KCl sat) through hydrogen-bonding between 4-APH⁺ and Cl⁻ adsorbed on the electrode surface; at more negative potentials the neutral form 4-AP is the predominant adsorbed species. For Co electrode in the same medium, only bands due to neutral 4-AP were observed in the spectra at −0.8 and −0.9 V. For more negative potentials bands assigned to both 4-AP and 4-AP surface complex are observed, with the lasts being enhanced, as the potentials are turned more negative. In alkaline chloride medium (pH 13), for less negative potentials the bands assigned to free 4-AP were observed in the spectra of both Ag and Co surfaces. For more negative potentials, only bands assigned to the 4-AP surface complex were observed. For 0.1 mol L⁻¹ KI acidic or alkaline solutions, bands assigned to 4-AP and 4-APH⁺ were observed in a wider potential range than in chloride solutions. An adsorption scheme of 4-AP on Ag and Co is proposed for acidic and alkaline solutions.     

Raman spectroscopy as a probe of adsorption on rhodium particles

Raman spectroscopy has been used as a probe of the adsorption of pyridine onto small particles of rhodium. The band energies of the surface phase correspond with those found on roughened silver electrodes. Chemical experiments indicate that the pyridine is stronyly chemisorbed. The similarity with the spectrum of pyridine on Ag presumably means that the predominant surface species is the same on each metal. This work represents the first report of an enhanced Raman spectrum on metallic rhodium.     

Potential-dependant SERS interaction of ortho-substituted N-benzylamino(boronphenyl)methylphosphonic acid with Ag,Au, and Cu electrode surfaces

In this study we present surface-enhanced Raman spectroscopy (SERS) investigations of ortho-substituted N-benzylamino(boronphenyl)methylphosphonic acid (N-benzylamino-(2-boronphenyl)-R-methylphosphonic acid; o-PhR) adsorbed onto a roughened in oxidation–reduction cycles (ORC) Ag, Au, and Cu electrode surfaces at different applied electrode potentials. Based on the spectral changes in bandwidth and wavenumber of selected bands upon the alternation of the applied electrodes potential the manner and differences in the interaction of o-PhR with the Ag, Au, and Cu electrode surfaces were determined. Briefly, the spectral patterns on Ag and Au suggest that, generally, the both aromatic rings are involved in the o-PhR/electrode interaction, whereas the boronophenyl ring only interacts with Cu. Also, the boronic acid and phosphonic acid groups participate in the o-PhR interaction with all the types of electrodes. However, the type of the used electrode material and the applied electrode potential have influence onto the mode of adsorption.     

过渡金属表面α-吡啶基的振动光谱学判据

基于簇模型采用密度泛函理论在B3LYP/6-311+G^**/LANL2DZ(metal)基组水平上计算了吡啶及α-吡啶基吸附于Pt、Pd、Rh、Ni四种金属表面的红外和拉曼光谱. 通过详细地分析和比较计算结果与文献报道的实验谱图, 提出了以N端吸附的吡啶分子和α-吡啶基这两种表面物种各自存在的谱学判据. 计算结果表明在以上四种金属表面, α-吡啶基的拉曼活性比吡啶的小, 而特征谱峰的红外强度与吡啶相当. 该结果表明红外光谱是检测金属表面α-吡啶基的有效手段, 也解释了采用表面增强拉曼光谱和红外光谱研究吡啶吸附在金属表面得出不同结构的原因.     

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     

Binding interactions and Raman spectral properties of pyridine interacting with bimetallic silver-gold clusters.

The binding interactions between pyridine and bimetallic silver-gold clusters are investigated using density functional theory (DFT). The binding energies of pyridine-bimetallic cluster complexes indicate that the bonding depends strongly on the binding site (Au or Ag atom) and bonding molecular orbitals in a given configuration. The donation of the lone-pair electrons of the nitrogen of pyridine to an appropriate unoccupied orbital of each metal cluster plays an important role. The low-lying excited states and charge-transfer states of four stable complexes of interest are calculated on the basis of a time-dependent DFT method. In nonresonance Raman scattering processes, the influence of binding interactions on the relative Raman intensity of totally symmetric pyridine vibrational modes is discussed. These calculated relative Raman intensities are compared with observed surface-enhanced Raman spectra of pyridine adsorbed on silver-gold alloy surfaces.     

Surface-enhanced Raman scattering of pyridine on platinum and nickel electrodes in nonaqueous solutions

Surface-enhanced Raman scattering (SERS) spectra of pyridine adsorbed onto bare platinum and nickel electrodes in nonaqueous solutions are reported in this Letter. There are similarities and differences between the SERS from aqueous and nonaqueous solutions. The surface enhancement factor for platinum in acetonitrile solution has been calculated to decrease by a factor of ca. 10 compared with that in the aqueous media. The double-band character for the ring breathing mode is observed at 1009 and 1019 cm⁻¹. Two adsorption modes of pyridine on the platinum surface were assumed. Part of the pyridine molecules may be chemisorbed onto the surface, with the ring plane oriented vertical to the surface; other pyridine molecules may co-adsorb with lithium cations onto the surface.     

First Principles Calculations Toward Understanding SERS of 2,2′-Bipyridyl Adsorbed on Au,Ag, and Au–Ag Nanoalloy

First principles electrodyanmics and quantum chemical simulations are performed to gain insights into the underlying mechanisms of the surface enhanced Raman spectra of 22BPY adsorbed on pure Au and Ag as well as on Au–Ag alloy nanodiscs. Experimental SERS spectra from Au and Ag nanodiscs show similar peaks, whereas those from Au–Ag alloy reveal new spectral features. The physical enhancement factors due to surface nano-texture were considered by numerical FDTD simulations of light intensity distribution for the nano-textured Au, Ag, and Au–Ag alloy and compared with experimental results. For the chemical insights of the enhancement, the DFT calculations with the dispersion interaction were performed using Au₂₀, Ag₂₀, and Au₁₀Ag₁₀ clusters of a pyramidal structure for SERS modeling. Binding of 22BPY to the clusters was simulated by considering possible arrangements of vertex and planar physical as well as chemical adsorption models. The DFT results indicate that 22BPY prefers a coplanar adsorption on a (111) face with trans-conformation having close energy difference to cis-conformation. Binding to pure Au cluster is stronger than to pure Ag or Au–Ag alloy clusters and adsorption onto the alloy surface can deform the surface. The computed Raman spectra are compared with experimental data and assignments for pure Au and Ag models are well matching, indicating the need of dispersion interaction to reproduce strong Raman signal at around 800 cm^–1. This work provides insight into 3D character of SERS on nanorough surfaces due to different binding energies and bond length of nanoalloys. © 2018 Wiley Periodicals, Inc.     

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.     

钛酸盐纳米管与二硫化碳修饰钛酸盐纳米管的合成、表征及其去除重金属离子性能

在水热法制备钛酸盐纳米管的基础上, 通过形成黄原酸基反应合成了CS2修饰的钛氧纳米管. 采用粉末X射线衍射(XRD)、透射电镜(TEM)、红外光谱(FTIR)和拉曼光谱(Raman)等技术对产物进行了表征. 以水溶液中铅离子、铜离子和银离子作为目标重金属离子, 分别用纯钛酸盐纳米管和CS2修饰后的钛氧纳米管对其进行反应和吸附, 通过一系列对比性实验, 评价了不同形式纳米管去除重金属的能力. 实验结果表明, 与文献报道的吸附剂对重金属离子的吸附量相比, 纯钛酸盐纳米管和CS2修饰的钛氧纳米管吸附重金属离子的容量非常大, 尤其是经CS2修饰后的钛氧纳米管去除铅离子的能力明显增强, 它们去除重金属离子的能力还与重金属盐的阴离子、溶液的pH值相关. 在相同的pH条件下, 钛酸盐纳米管去除铅离子、铜离子和银离子的能力分别为599.37, 163.22和474.73 mg/g; CS2修饰的钛氧纳米管去除铅离子、铜离子和银离子的能力分别为663.37, 160.21和423.05 mg/g.     

A resonance Raman,surface-enhanced resonance Raman,IR, and ab initio vibrational spectroscopic study of nickel(II) tetraazaannulene complexes

The IR and resonance Raman spectra of the nickel(II) complexes of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) and 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TMTAA) have been measured and compared with ab initio calculations of the vibrational wavenumbers at the B3-LYP level using the LanL2DZ basis set. An excellent fit is found between the experimental and calculated data, enabling precise vibrational assignments to be made. Surface-enhanced resonance Raman spectra were obtained following adsorption on Ag electrodes, with potentials in the range -0.1 to -1.1 V vs Ag/AgCl. There is evidence for contributions from both the electromagnetic and charge transfer (CT) surface enhancement mechanisms. The data indicate that variations in band intensities with electrode potential can be interpreted in terms of the CT mechanism.     

Surface-enhanced Raman scattering and density functional theory calculation of uracil on gold and silver nanoparticle surfaces

The adsorption structure of uracil on gold and silver nanoparticle surfaces has been comparatively studied by means of surface-enhanced Raman scattering (SERS). Uracil appeared to assume a perpendicular orientation with respect to the surfaces. The presence of the nu(CH) band in the SERS spectra indicated a vertical orientation of the aromatic ring of uracil on Au and Ag. The density functional theory (DFT) calculation was performed at the levels of B3LYP and MP2 to estimate the energetic stability of the N3- and N1-deprotonated tautomers and their vibrational frequencies on the surfaces. Almost all the vibrational bands in the SERS spectra at high concentrations could be ascribed to the N3-deprotonated uracil. The N3-deprotonated tautomer was predicted to be more favorable on Au than on Ag from the DFT calculation. The metal-N bond distance was assumed to be shorter for Au than for Ag upon adsorption of uracil.     

Effect of Ag and Au nanoparticles on the SERS of 4-aminobenzenethiol assembled on powdered copper

Raman scattering measurements were conducted for 4-aminobenzenethiol (4-ABT) assembled on powdered copper substrates. Initially, very weak Raman peaks were detected, but upon attaching Ag nanoparticles probably via NH2 groups onto 4-ABT/Cu, distinct Raman spectra were observed. Considering the fact that no Raman peak was identified when Ag nanoparticles were adsorbed on 4-aminophenyl-derivatized silane monolayers assembled on silica powders, the Raman spectra observed for Ag@4-ABT/Cu should be surface-enhanced Raman scattering (SERS) spectra, occurring by an electromagnetic coupling of the localized surface plasmon of Ag nanoparticles with the surface plasmon polariton of Cu powders. The extra enhancement factor attainable by the attachment of a single Ag nanoparticle is estimated to be as large as 1.4 x 10(5) in the case when 632.8-nm radiation is used as the excitation source. When Au nanoparticles were attached onto 4-ABT/Cu, at least an order of magnitude weaker Raman spectra were obtained at all excitation wavelengths, however, indicating that the Au-to-Cu coupling should be far less effective than the Ag-to-Cu coupling for the induction of SERS.     

Reaction of metallotetraphenylporphyrins on hydroxyl-modified silver colloid and Ag2O colloid by surface-enhanced Raman scattering.

This paper reports a novel reaction of metallotetraphenylporphyrins on hydroxyl-modified silver colloid and Ag2O colloid. Surface-enhanced Raman spectra of Ag(II) and Cu(II) complexes of tetraphenylporphyrin (TPP) adsorbed on the hydroxyl-modified Ag colloid and Ag2O colloid have been studied. The time-dependent SERS spectra of MTPP (M = Ag, Cu) on hydroxyl-modified Ag colloid were recorded and dramatic change on SERS spectra was observed. The final spectra were found to be strikingly different from the corresponding normal Raman spectra (NRS), with the appearance of new Raman bands at 1614. 1417, 947, 674 and 292 cm(-1). The UV-visible absorption spectrum of MTPP on hydroxyl-modified Ag colloid exhibits a broad shoulder near 460 nm. Similar spectral phenomena were also observed for AgTPP and CuTPP adsorbed on Ag2O colloid. The observed spectral alterations were ascribed to new species formation due to the irreducible oxidation of MTPP on the colloids.     

ESR study of Cu(II) ion complexes adsorbed on interlamellar surfaces of montmorillonite

Oriented films of Cu(II)-montmorillonite before and after adsorption of pyridine, glycine and $\text{b}\text{?}$-alanine showed markedly orientation-dependent ESR spectra. Complex formation of Cu(II) ions with the adsorbates was indicated by changes in ESR parameters. The ESR spectra and parameters suggest that the complexes formed on the interlamellar surfaces of montmorillonite have planar or axially elongated tetragonal structures and that the symmetry axes of the complexes are oriented perpendicularly to the aluminosilicate layers of the clay.