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 LiClO_4. Two typical SERS features observed at 475−490 and 2055−2080 cm^(-1) are attributed to the platinum−CO (ν_(Pt-C)) and intramolecular C−O (ν_(C-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 positive and moderately negative potentials (−0.2 to 0.6 V), the Pt−C and CO intramolecular bands exhibit opposite frequency changes with decreasing potential, with Stark tuning rate being −6 and 24 cm^(-1)/V, respectively. At more negative potentials, both ν_(Pt-C) and ν_(CO) exhibit nonmonotonic potential dependences. The gradually decreasing slope for ν_(Pt-C) can be explained in terms of the nearly offsetting contributions from the π-back-donation and σ-bonding, along with increasing steric repulsion from negatively charged surfaces. The nearly potential-invariant frequencies for ν_(CO) were observed at potentials more negative than −1.0 V, indicating the key role of increasing concentration of H^+ in the inner double layer, possibly weakening the electron density back-donated from platinum to CO 2π^* orbitals

Theoretical and experimental studies on the adsorption behavior of thiophenol on gold nanoparticles

FT-Raman spectra were obtained for thiophenol UP) and TP on gold nanoparticles. All vibrational fundamentals for the TP molecule are assigned on the basis of the scaled quantum force field procedure. Three model systems are studied and compared for the interactions of TP with the Au atom: (1) TP with a Au atom, C6H5SH-Au; (2) TP anion with a Au atom, C6H5S--Au; and (3) TP with a Au atom and subsequent formation of thiophenylate, C6H5SAu. The equilibrium structures and Raman spectra were calculated for the model systems using density functional theory (DFT) with the B3LYP functionals and the mixed basis set 6-311+G** (for C, S, H) and LANL2DZ (for Au), and theoretical Raman wavenumbers of C6H5SAu and C6H5S--Au were assigned according to potential energy distributions. The third model system is shown to be preferred over the other two. The calculated binding energies are also shown to support the third model system. It is suggested that a simple model, such as the one used in the present study, is reasonable to describe surface-enhanced Raman spectroscopy of thiophenol adsorbed on gold nanoparticles. Copyright (C) 2007 John Wiley & Sons, Ltd

Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate

Self-assembly of metal nanoparticles has attracted considerable attention because of its unique applications in technologies such as plasmonics, surface-enhanced optics, sensors, and catalysts. However, fabrication of ordered nanoparticle structures remains a significant challenge. Thus, developing an efficient approach for the assembly of large-scale Au nanoparticles films for theoretical studies and for various applications is highly desired. In this paper, a facial approach for fabricating a monolayer film of Au nanoparticles was developed successfully. Using the surfactant polyvinyl­pyrrolidone (PVP), a large-scale monolayer film of well-ordered, uniform-sized Au nanoparticles was fabricated at the air/water interface. The film exhibited a two-dimensional (2D) hexagonal close-packed (HCP) structure having interparticle gaps smaller than 2 nm. These gaps generated numerous uniform “hot spots” for surface-enhanced Raman scattering (SERS) activity. The as-prepared monolayer film could be transferred to a solid substrate for use as a suitable SERS substrate with high activity, high uniformity, and high stability. The low spot-to-spot and substrate-to-substrate variations of intensity (<10%), the large surface enhancement factor (∼10⁶), and the high stability (∼45 days) make the substrate suitable for SERS measurements. Transfer of the monolayer film onto a glassy carbon electrode produced an Au electrode with clean, well-defined nanostructure suitable for electrochemical SERS measurements. The adsorption process of ionic liquids on the electrode with the monolayer film is similar to that on bulk metal electrodes. The present strategy provides an effective way for self-assembly of Au nanoparticles into well-defined nanostructures that may form optimal reproducible SERS substrates for quantitative analysis. It also provides an electrode with clean, well-defined nanostructure for electrochemical investigations

Stacking faults enriched silver nanowires: Facile synthesis, catalysis and SERS investigations

NSFC [20973120, 21073128, 21173155]; Natural Science Foundation of Jiangsu Province [BK2012187]; Natural Science Fundamental Research Project of Jiangsu Colleges and Universities [12KJD150011]; Soochow university; priority academic program development of Jiangsu higher education institutions; State Key Laboratory for Physical Chemistry of Solid Surfaces, Xiamen UniversityA facile approach based on seed-mediated method for synthesis of stacking faults enriched Ag nanowires (SFEANWs) was successfully developed. SFEANWs were formed and attached onto the seed (alpha-Fe2O3/Au) surfaces through the reduction of AgNO3 by ascorbic acid (AA) in the presence of sodium polyacrylate (PAANa). Their length can be tuned with different concentrations of AgNO3 or PAANa. According to the effects of seeds and PAANa, the plausible growth mechanism of SFEANWs was discussed. The catalytic activity of SFEANWs comparing with.fivefold twinned Ag nanowires (FFTANWs) was evaluated through reducing p-nitrophenol by NaBH4. The activation energy of the classical reaction catalyzed by SFEANWs was calculated through the Arrhenius equation. In addition, these SFEANWs exhibited excellent surface enhanced Raman scattering (SERS) activities due to the hot spots located in the cross of the twist wires. The detection limit of by SERS for 1,4-benzenedithiol (1,4-BDT) was estimated about 10(-7) mol/L. (C) 2013 Elsevier Inc. All rights reserved

Adsorption and corrosion inhibition behavior of imidazole on cobalt electrodes studied by SERS and electrochemical methods

The interaction of imidazole with Co electrodes in an electrochemical system was studied by surface-enhanced Raman scattering (SERS) and electrochemical methods. The SER spectra of Cc in an imidazole solution as a function of the applied potential were analyzed and the assignment of the Raman bands was made. It was found that there were three kinds of surface species on the Co surface in different potential regions and they were interchangeable depending on the potential. In a relatively negative potential region (-1.2 to -0.9 V), imidazole was adsorbed on the surface and its orientation might change from a vertical configuration via the N-end of the pyridine ring to a tilted configuration via the C2=N3 double bond. In a more positive potential region (-0.8 to -0.7 V), the SERS signal from the adsorbed imidazole weakened and finally disappeared, meanwhile the signal from the Co and imidazole complex strengthened gradually. At the open circuit potential (-0.6 V), we detected very strong bands from the Co oxides. By comparing the Tafel curves of the Co electrode in the solution without and with imidazole, we found that imidazole has a marked effect on the corrosion inhibition of the Cc electrode. This result demonstrates that we may be able to reveal the complicated interaction of surface species with metal surface at the molecular level by combining the SERS and electrochemical methods