Surface-enhanced Raman Spectroscopy Study Research Articles

Surface-Enhanced Raman Spectroscopy Studies on the Adsorption and Electrooxidation of Carbon Monoxide at the Platinum−Formic Acid Interface

The vibrational spectrum of carbon monoxide, exerted by dissociation of formic aid, has been investigated at the platinum electrode as a function of applied potential by using the surface-enhanced Raman spectroscopy (SERS) technique. The electrolyte is 0.1 M LiClO4. Two typical SERS features observed at 475−490 and 2055−2080 cm-1 are attributed to the platinum−CO (νPt-C) and intramolecular C−O (νC-O) stretching vibration, respectively, indicating linearly adsorbed CO on platinum. Comparisons of the present data with previous studies in aqueous solutions show that solution components, particularly the dielectric in the inner double layer, may significantly influence the interaction of CO with platinum, especially the CO intramolecular mode. Electrooxidation of CO was observed to occur at potentials more positive than 0.6 V, being slightly negative relative to previous studies for CO on smooth platinum, suggestive of a higher electrocatalytic activity for the present highly roughened platinum surface. At po...

Surface enhanced Raman spectroscopic studies of surface orientation of pyrazine adsorbed on rhodium electrode

Surface enhanced Raman spectroscopic studies of surface orientation of pyrazine adsorbed on rhodium electrode

Electrochemical and Surface-Enhanced Raman Spectroscopic Studies on the Adsorption and Electrooxidation of C1 Molecules on a Roughened Rh Electrode

By using the previously developed roughening method for producing SERS-active Rh electrode, and assisted by the highly sensitive confocal microprobe Raman system, we carried out a detailed SERS study on the dissociation and electrooxidation of C1 molecules on a Rh surface. The SERS spectra obtained in a wide frequency region provide not only the vibrations reflecting the internal bonding of CO (at ca. 2000 cm-1) but also the bonding between CO or O with Rh (at ca. 450 cm-1). A complementary electrochemical study was also performed on the roughened Rh surface in order to correlate the electrochemical and vibrational information. Both electrochemical and SERS studies show that Rh has no discernible activity toward the electrooxidation or dissociation of methanol in acidic solutions. Rh becomes active and its activity increases with the decrease of the solution acidity. For HCHO and HCOOH, the electrooxidation activity of Rh increases with increasing pH. On the basis of the result of the model CO system, dis...

Raman spectroscopy, surface‐enhanced Raman spectroscopy and density functional theory studies of 2‐formylfuran

AbstractThe Raman spectrum of 2‐formylfuran in the liquid phase shows pairs of bands whose temperature and solvent dependence behavior can be interpreted in terms of cis–trans conformational equilibrium. Density functional theory (DFT) calculations performed at the BPW91/6–311+G* and B3LYP/6–311+G* theoretical levels show that the trans‐isomer is more stable than the cis‐isomer by 2.81 and 3.12 kJ mol−1, respectively. The theoretical ΔH values obtained at these theoretical levels [2.99 kJ mol−1 (BPW91) and 3.2 kJ mol−1 (B3LYP)] are very close to the experimental value ΔH = 2.52 kJ mol−1 determined from the plots of logarithmic relative intensities of the band pairs 1673/1692, 1477/1465 and 1396/1371 cm−1 of these isomers against reciprocal temperature. The surface‐enhanced Raman spectrum of 2‐formylfuran in silver colloid suggests the chemisorption of this molecular species on the silver surface both through the ring oxygen and the oxygen atom of the substituent group, the cis‐form being preferred in the adsorption state. The adsorbed molecules are oriented perpendicular or least tilted with respect to the silver surface. Copyright © 2003 John Wiley & Sons, Ltd.

Surface enhanced Raman spectroscopy study of the potential dependence of thymine on silver electrodes

The potential-induced changes in thymine coordination on polycrystalline silver electrodes are studied by surface enhanced Raman spectroscopy (SERS) for potentials positive to the potential of zero charge up to the end of the double layer range. Two distinct sets of spectra could be obtained in the range of potentials studied. Both states correspond to chemisorbed phases of thymine on silver, where a distinct heteroatom is deemed responsible for the bond with the surface. At less positive potentials, one of the ring oxygen atoms is responsible for the chemical bond and the molecule assumes a tilted position. At more positive potentials, one of the ring nitrogen atoms, possibly deprotonated, establishes a new bond with the surface, aligning the molecule's axis closer to the surface normal.

In situ SERS study of the adsorption of inhibitors of carbon dioxide corrosion

AbstractA specially designed electrochemical cell incorporating a rotating disc electrode has been used for in situ surface‐enhanced Raman spectroscopy (SERS) studies of the adsorption of inhibitors of carbon dioxide corrosion onto silver‐coated mild steel electrodes. It is shown that SERS‐active inhibitors comprising aromatic moieties may be detected using the SERS technique. Furthermore, the efficacy of adsorption of corrosion inhibitors employed in the present study is optimal near the open cell or corrosion potential, demonstrating that electrode polarization induces electrostatic forces of repulsion that retard the adsorption of the inhibitor to the corroding steel surface. Copyright © 2003 John Wiley & Sons, Ltd.

Surface-Enhanced Raman Spectroscopy Studies on the Interaction of Imidazole with a Silver Electrode in Acetonitrile Solution

Surface-enhanced Raman scattering (SERS) spectrum of imidazole adsorbed at a silver electrode in nonaqueous acetonitrile solution has been investigated as a function of applied potential. The electrolyte is 0.1 M LiClO4. Results show that imidazole adsorbs on silver as a neutral molecule via the pyridine nitrogen atom. Coadsorption of perchlorate anion with imidazole, possibly by forming intermolecular hydrogen bonding, is also suggested by the enhancement of the ClO4- band at 933 cm-1. An edge-on orientation of imidazole at more positive potentials is proposed by the observation of the increase in frequency of the ring breathing modes, along with the enhancement of most of the in-plane modes of imidazole. When the potential is made more negative, particularly near −0.5 V, the imidazole ring may change from vertical to be slightly inclined to the silver surface at an intermediate angle from the surface normal. At the same time, a slight rotation of the imidazole ring plane may occur, evidenced by the observation of the changes in relative intensity of ν(C2H) to asymmetric ν(HCCH) vibration. In addition, the decomposition reaction of the solvent acetonitrile at the silver surface is also assumed by the appearance of a characteristic band of cyanide ion at ca. 2110 cm-1. Competitive adsorption of imidazole at more positive potentials inhibits significantly the decomposition of acetonitrile.

Theoretical and pH dependent surface enhanced Raman spectroscopy study on caffeine.

The surface enhanced Raman spectroscopy (SERS) spectrum of caffeine is recorded on a silver colloid at different pH values. It is discussed on the basis of the SERS "surface selection rules" in order to characterize its vibrational behavior on such a biological artificial model. To improve the previous assignments in the Raman spectrum and for a reliable, detailed analysis of SERS spectra, density functional theory calculations (structural parameters, harmonic vibrational wavenumbers, total electron density, and natural population analysis of the molecule) are performed for the anhydrous form of caffeine and the results are discussed. The predicted geometry and vibrational Raman spectra are in good agreement with the experimental data. The flat orientation of the mainly chemisorbed caffeine attached through the pi electrons and the lone pair of nonmethylated N atoms of the imidazole ring are proposed to occur at neutral and basic pH values. At acid pH values caffeine is probably adsorbed on the Ag surface through one or both oxygen atoms, more probably through the O atom of the conjugated carbonyl group with an end-on orientation. However, the changes in the overall SERS spectral pattern seem to indicate the electromagnetic mechanism as being the dominant one.

A SERS study of self-assembled (4-methylmercapto)benzaldehyde thin films

A Surface-Enhanced Raman Spectroscopy (SERS) study on self-assembled mercapto-aldehyde derivative—4-(methylmercapto)benzaldehyde (SBZA)—is reported. This molecule was adsorbed onto silver surface, previously roughened to give SERS effect. The spectroscopic characterization of the adsorbed layer has shown a complete chemisorption of each molecule along with the presence of free aldehydic functionality. It is a group able to interact in several different reactions. In this connection, we have also discussed a condensation reaction between the aldehyde group of SBZA, adsorbed onto silver, with pyrrole. These dipyrroil derivatives immobilized in thin films have been recently found to be active coatings in chemical recognition of alcohol vapours.

Electrochemical and Surface-Enhanced Raman Spectroscopy Studies on Inhibition of Iron Corrosion by Benzotriazole

The different initial interactions of benzotriazole (BTAH) with iron in both 0.5 M H2SO4 and simulated saline water (3.4% NaCl) have been investigated systematically by using a confocal microprobe Raman system, surface-enhanced Raman spectroscopy (SERS), and electrochemical potentiodynamic polarization curves. The SERS spectra of BTAH at the bare iron electrodes in both 0.5 M H2SO4 and simulated saline water have been obtained successfully for the first time. Electrochemical measurements show that the inhibition efficiency of BTAH is higher in saline water than that in acid solution, which is in accordance with the identification of the surface interaction on the basis of the SERS data. BTAH may be physisorbed onto the iron surface through its neutral molecule form or protonated BTAH2+ ions. While in saline water, the formation of the surface coordination compound characterized as Fe(II)−BTA may contribute to the outstanding spectral features. A cleavage of the NH bond is believed to occur while adsorptio...

Surface-Enhanced Raman Spectroscopic Studies of Dissociative Adsorption of Amino Acids on Platinum and Gold Electrodes in Alkaline Solutions

The dissociative adsorption of amino acids on Pt and Au electrodes in 0.1 M NaOH solutions was studied by cyclic voltammetry and surface-enhanced Raman spectroscopy (SERS). The intermediate species has been determined as adsorbed cyanide, which is designated by a potential-dependent vibration band around 2110 cm-1 on both Pt and Au surfaces. The dissociation of glycine can be observed on Pt surface in a wide potential region to form cyanide, while the dissociation of serine and threonine occurs at relatively high potentials along with the oxidation of their functional groups. The onset potential of dissociation of amino acids on the Pt surface increases in the order glycine < threonine < serine. It has been revealed that the self-inhibition of amino acid oxidation is originated from the strongly adsorbed cyanide, which is oxidized at potentials above 0.2 V vs SCE. On gold surfaces, cyanide species can be formed only from anodic oxidation of amino acids. The present study reveals characteristic interaction...

Surface-enhanced Raman spectroscopy studies of platinum surfaces in acetonitrile solutions

Surface-enhanced Raman spectroscopy (SERS) studies have been successfully extended to Pt electrodes in a nonaqueous solution. The acetonitrile decomposition in 0.1 M LiClO 4+CH 3CN and the adsorption behavior of the resulting cyanide ions at a Pt electrode surface have been studied as a function of applied potential by using the SERS technique. Results show that acetonitrile decomposition occurs at a certain more negative potential by the appearance of the 2115 and 2147 cm −1 bands assigned to CN stretching modes. Evidence is presented to suggest that a photoelectrochemical reduction of acetonitrile may occur. By adding water or pyridine to CH 3CN, the decomposition reduction occurs at more negative potentials, suggesting a competitive adsorption at the Pt electrode surface. Two different adsorption configurations of the resulting cyanide ions: the types CN −⋯Li + and CN −⋯CH 3CN, are proposed to explain the spectral features and changes with potential.

Surface-enhanced Raman spectroscopy study on the structure changes of 4-mercaptopyridine adsorbed on silver substrates and silver colloids

Surface-enhanced Raman scattering (SERS) of 4-mercaptopyridine (4-mpy) adsorbed on HNO 3 etched silver foil, chemically deposited silver films (silver mirror) and silver colloids were measured. The SERS study has revealed that 4-mpy was adsorbed onto the three kinds of silver surfaces by a sulfur–silver bond with the plane of pyridine ring being normal to the silver substrates. The structure of 4-mpy adsorbed on the silver surfaces depends largely on the pH values of environment. When the pH values of the environment are changed, the structure of 4-mpy adsorbed on silver surfaces can easily be altered through a protonation or deprotonation reaction occurring on the N atom of the pyridine ring, and the modified structure shows unique characters on the SERS spectrum. Owing to the remarkable enhancement ability of SERS technique and characteristic spectrum of different species, a monolayer of 4-mpy assembled on a silver mirror holds potential as a H + sensor for highly sensitive detection of the proton concentration in an aqueous solution.

Electrochemical and surface-enhanced Raman spectroscopy studies of 4-phenylpyridine adsorption at the gold/solution interface

The adsorption of 4-phenylpyridine (4-PhPy) on the Au electrode was examined using conventional electrochemical techniques: cyclic voltammetry and impedance measurements and also by surface enhanced Raman spectroscopy (SERS) in a wide range of electrode potentials. Electrochemical results indicate the strong adsorption of 4-Phpy molecules, particularly at the positively charged Au electrode. The wide shoulder of capacity close to the pzc suggests that the composition and/or the structure of 4-Phpy monolayer change with the sign of the surface charge on the electrode. Investigation of integrity of adsorbed layer, however, indicates that adsorbed molecules do not form tight, compact monolayer even in the case of adsorption from saturated solution. SERS spectra provided evidence for gradual, potential-induced reorientation of the molecular plane with respect to the surface, from nearly vertical in the negatively charged electrode, to more flat at the positively charged metal surface.

Surface-enhanced Raman spectroscopy studies of phenylpyridines interacting with a copper electrode surface

Surface-enhanced Raman scattering (SERS) spectra serve as a valuable source of information about the organic adsorbates at the surface and about the nature of the oxide films of monolayer thickness. In this study, interactions of 2-phenylpyridine and 3-phenylpyridine with copper surface were investigated by means of SERS spectroscopy and cyclic voltammetry and compared with 4-phenylpyridine. A strong dependence of the spectral pattern on the applied potential was observed for all phenylpyridines. Experimental spectra were compared with ab initio calculations in order to better understand the spectral effects. The SERS results were interpreted in terms of reorientation of the molecular plane with respect to the Cu surface.

Surface Raman spectroscopic studies on the adsorption of pyridine at bare iron electrodes

Surface-enhanced Raman spectroscopic (SERS) studies have been extended successfully to iron electrodes by using a highly sensitive confocal microprobe Raman system. Several surface roughening procedures were attempted to obtain high-quality surface Raman spectra of pyridine on iron electrodes. Results show that proper surface roughness factor can not only increase the surface area, but also induce a weak SERS effect. Potential-dependent surface Raman spectra of pyridine in neutral solution suggest that the pyridine molecule may be adsorbed onto the iron electrode through the nitrogen atom by a coordination bond of FeN in an end-on configuration (or slightly tilting). Decreasing the solution pH value to ca. 2.0 did not affect the adsorption of pyridine and the pyridinium ion may dissociate before its adsorption onto the iron surface.

Surface enhanced Raman spectroscopic studies of 1H-indazole on silver sols

The SER spectra of 1H-indazole adsorbed on silver hydrosol were recorded in the 1800–100 cm −1 and in the 3200–2800 cm −1 regions. The SERS data were interpreted on the basis of previous vibrational assignments, with the help of the results of DFT calculations carried out using the 6-31G** basis. From the comparison of SER and normal Raman spectra it can be deduced that 1H-indazole is non-dissociatively adsorbed on metal surface and that it interacts with silver sol via nitrogen atoms and ring π-system. The molecular plane assumes a tilted orientation with respect to the silver surface. The effect of varying the concentration of adsorbate was also evaluated. The observed changes of the relative intensities of some enhanced bands suggest that the molecule assumes a more tilted orientation upon lowering the concentration of the adsorbate.

Origin of the Breit-Wigner-Fano lineshape of the tangentialG-band feature of metallic carbon nanotubes

A detailed line-shape analysis of the tangential G-band feature attributable to metallic single-walled carbon nanotubes is presented. Only two components are needed to account for the entire G-band feature for metallic nanotubes. The higher-frequency component has a Lorentzian line shape, and the lower one has a Breit-Wigner-Fano (BWF) line shape. Through comparisons of the Raman tangential G-band spectra from three different diameter distributions of carbon nanotubes, we find that both the frequency and linewidth of the BWF component are diameter dependent and show functional forms consistent with theory. The nanotube curvature is responsible for both the frequency differences between the two components of the characteristic metallic G-band spectrum and the BWF coupling of the lower-frequency component. Surface-enhanced Raman spectroscopy studies provide supporting evidence that the phonon BWF coupling is to an electronic continuum.

Pre-resonance Raman and surface-enhanced Raman spectroscopy study of the complex of the antiviral and antiparkinsonian drug amantadine with histidine

UV-pre-resonance Raman spectroscopy (PRS) and surface-enhanced Raman spectroscopy (SERS) were applied to study the interaction of the antiviral and antiparkinsonian agent amantadine with histidine. The binding sites of amantadine and histidine molecules were identified in the complex. In this model, (i) the amino group of amantadine and the N1H group of histidine are included in the complex formation, (ii) the creation of the complex is mediated via formation of an H-bond between the nitrogen of the amantadine amino group and the hydrogen of the histidine N1H group. This model of the amantadine–histidine complex formation is discussed in the relation to a possible mode of interaction of the M2 protein transmembrane region with amantadine.

Surface-enhanced Raman spectroscopy study on adsorption of an emulsion stabilizer (4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene) on a silver surface

Adsorption of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene (TAI) on a silver surface has been investigated by means of surface-enhanced Raman spectroscopy (SERS). The basic principles of the technique are presented. The relationship between the intensities of SERS and oxidation/reduction cycles (ORCs) was also investigated.