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Au Surface (au + surface)
Selected AbstractsSERS study of hydrogen peroxide electroreduction on a Pb-modified Au electrodeJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2005Xiao Li Abstract The mechanism of the electroreduction of H2O2 on a Pb-modified Au surface was examined by surface-enhanced Raman spectroscopy. The measurements show the presence of lead peroxide, PbOOH+, with the maximum intensity at potential just positive of underpotentially deposited Pb, and bimetallic dihydroxide, AuPb(OH)2, at potential just positive of that where peroxide is reduced and Pb islands maximally formed on the surface. All the modes for these two species decay rapidly and even disappear as the reduction current flows. Both species are absent in solutions not containing either Pb2+ or H2O2. The edge of Pb islands on the Au surface is thus shown to be the active site for this catalysis process. These results further underscore the important role of MOH species in the peroxide electroreduction reaction. Copyright © 2005 John Wiley & Sons, Ltd. [source] Role of Capping Ligands on the Nanoparticles in the Modulation of Properties of a Hybrid Matrix of Nanoparticles in a 2D Film and in a Supramolecular OrganogelCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2009Asish Pal Dr. Abstract We incorporate various gold nanoparticles (AuNPs) capped with different ligands in two-dimensional films and three-dimensional aggregates derived from N -stearoyl- L -alanine and N -lauroyl- L -alanine, respectively. The assemblies of N -stearoyl- L -alanine afforded stable films at the air,water interface. More compact assemblies were formed upon incorporation of AuNPs in the air,water interface of N -stearoyl- L -alanine. We then examined the effects of incorporation of various AuNPs functionalized with different capping ligands in three-dimensional assemblies of N -lauroyl- L -alanine, a compound that formed a gel in hydrocarbons. The profound influence of nanoparticle incorporation into physical gels was evident from evaluation of various microscopic and bulk properties. The interaction of AuNPs with the gelator assembly was found to depend critically on the capping ligands protecting the Au surface of the gold nanoparticles. Transmission electron microscopy (TEM) showed a long-range directional assembly of certain AuNPs along the gel fibers. Scanning electron microscopy (SEM) images of the freeze-dried gels and nanocomposites indicate that the morphological transformation in the composite microstructures depends significantly on the capping agent of the nanoparticles. Differential scanning calorimetry (DSC) showed that gel formation from sol occurred at a lower temperature upon incorporation of AuNPs having capping ligands that were able to align and noncovalently interact with the gel fibers. Rheological studies indicate that the gel,nanoparticle composites exhibit significantly greater viscoelasticity compared to the native gel alone when the capping ligands are able to interact through interdigitation into the gelator assembly. Thus, it was possible to define a clear relationship between the materials and the molecular-level properties by means of manipulation of the information inscribed on the NP surface. [source] Adsorption of 4,4,-biphenyl diisocyanide on gold nanoparticle surfaces investigated by surface-enhanced Raman scatteringJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2003Sang-Woo Joo Abstract We investigated the spectral features of the ,(NC) bands when 4,4,-biphenyl diisocyanide (BPDNC) is adsorbed on gold nanoparticle surfaces by surface-enhanced Raman scattering (SERS). The mode of adsorption of BPDNC on gold nanoparticles was found to change with the bulk concentration. At low concentrations of BPDNC, only the ,(NC)bound band was conspicuous at ,2185 cm,1 and the free NC stretching band was barely detected in the SERS spectra. When the bulk concentration was increased, the ,(NC)free band became prominent at ,2123 cm,1. BPDNC was assumed to bridge two different gold particles at low concentrations, but as the concentration was increased, the bridge appeared to be broken and bonded to the gold particle only via one of the two isocyanide groups. On the basis of the electromagnetic surface selection rule, we attempted to explain the orientation of the adsorbate on Au surfaces by determining the relative enhancement factor of each vibrational band. Copyright © 2003 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman scattering of 4,4,-dicyanobiphenyl on gold and silver nanoparticle surfacesJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2002Chung-ro Lee The adsorption behavior of 4,4,-dicyanobiphenyl (DCBP) on Ag and Au nanoparticle surfaces was studied by surface-enhanced Raman scattering (SERS). The absence of the ring CH band denoted a flat orientation of the biphenyl ring on Ag and Au. The red shift of the ,8a band indicated a direct ring ,-orbital interaction with the surfaces. The two benzene rings of DCBP appeared to lie on the same plane with a ,-type interaction upon adsorption on the surfaces. The ,(CN) bands were blue shifted in the Ag and Au SERS spectra by 2 and 22 cm,1, respectively from the ordinary Raman spectrum. The orientation of DCBP on the Ag and Au surfaces was analyzed by the relative enhancement factors of the vibrational bands based on the electromagnetic SERS selection rule. Copyright © 2002 John Wiley & Sons, Ltd. [source] Adsorption of 1,3-Benzenedithiol and 1,3-Benzenedimethanethiol on Gold Surfaces,CHEMPHYSCHEM, Issue 12 2008Jong Kuk Lim Dr. Abstract The adsorption characteristics of 1,3-benzenedithiol (1,3-BDT) and 1,3-benzenedimethanethiol (1,3-BDMT) on Au surfaces are investigated by means of surface-enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3-BDMT is found to adsorb via two S,Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3-BDT is found to adsorb by forming two S,Au linkages, regardless of concentration, based on the disappearance of the ,(SH)free stretching band. Because of the absence of the methylene unit, 1,3-BDT appeares not to self-assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self-assembled monolayers of 1,3-BDT and 1,3-BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au8 cluster are performed to better understand the nature of the adsorption characteristics of 1,3-BDT and 1,3-BDMT on Au surfaces. [source] | ||||||||||