Adsorption Geometry of Alizarin on Silver Nanoparticles: A Computational and Spectroscopic Study (original) (raw)
Related papers
Journal of Raman Spectroscopy, 2004
FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behavior of the highly fluorescent anthraquinone dye alizarin on Ag colloids prepared by chemical reduction with hydroxylamine hydrochloride. The SERS spectra were obtained at different conditions of pH, excitation wavelength and pigment concentration in order to deduce the adsorption mechanism of this molecule. On the basis of the results found we propose an adsorption model for alizarin, which has a different acidic behavior on the metal surface to that in solution. On the metal the deprotonation order of the OH groups changes with respect to the aqueous solution, the OH in position 1 being the first to be ionized instead of that in position 2 as occurs in solution. The two main alizarin forms identified on the metal surface correspond to the mono-and dianionic alizarin species.
Chemical Physics, 2006
The adsorption of biologically important 2-amino-6-methylbenzothiazole (2A-6MBT) molecule on silver colloids has been investigated by Surface Enhanced Raman Scattering (SERS) study. The SERS spectra of 2A-6MBT at different adsorbate concentrations are compared with its Fourier transform infrared spectrum and normal Raman spectrum in varied environments. Concentration-dependent SERS spectra of the molecule reveal the existence of two types of adsorbed species on colloidal silver particles, whose relative population varies with adsorbate concentrations. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using density functional theory calculations. The appearance of Ag–N stretching mode at around 212 cm−1 in the SERS spectra along with theoretically calculated atomic charge density, force us to believe that the molecules are adsorbed through the lone pair electrons of the nitrogen (N9 and N10) atoms with the molecular plane tilted or remain pendant on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory.
Vibrational Spectroscopy, 2002
Surface-enhanced Raman scattering (SERS) spectroscopy is applied in this work to the study of the adsorption of naphthazarin (NZ) on Ag nanoparticles. Spectra recorded at different excitation wavelengths and pHs revealed that this molecule is adsorbed on the metal through several mechanisms. Two main types of adsorbed molecules can be identified that correspond to neutral and ionized NZ, which may be physisorbed or chemisorbed on the metal. The existence of these different forms can be due to different binding sites on the surface or to the formation of a multilayer architecture on the metal surface giving rise to different adsorbate states. Although the amount of the ionized molecule attached on the surface is higher at neutral pH, the neutral molecule may also exist even at very high pH. The amount of neutral NZ increases with the time and also as the NZ concentration is raised or as the dimethylsulfoxide (DMSO) concentration existing in the medium is increased. #
Vibrational Spectroscopy, 2016
Surface-enhanced Raman scattering (SERS) was used to obtain adsorption isotherms for two types of SERS-active substrates: silver nanoparticles (AgNPs) dispersed in water (AgNP/sol); and AgNPs dispersed in agarose gel (AgNP/Agar). Rodhamine 6G (R6G) was chosen as the probe molecule to evaluate the two substrates. R6G adsorbs on both substrates following Langmuir isotherms with very similar adsorption constants. The SERS from R6G in AgNP/Agar is ca. 10 times more intense than in AgNP/sol due to the confinement of the R6G molecules within the gel matrix. The AgNP/Agar was further evaluated for the adsorption of methylene blue (MB), crystal violet (CV) and benzotriazole (BTA). The results showed that, for lower surface coverages (u < 0.1), the observed SERS (or SERRS) spectra corresponded to single molecule events. In this case, each single spectrum presented different relative intensities than from the ensemble averaged spectrum. On the other hand, for higher coverages (u % 1), the relative intensities of a single spectrum were quite similar to those of the ensemble average. Single molecule SERRS events were well identified for MB, because the spectra of the monomer and of the aggregated state differ considerably for this dye. The results also indicate that R6G and CV adsorb on the SERS-active sites forming ion pairs with the adsorbed chloride, while MB and BTA form covalent bonds with Ag atoms on the AgNP surface. In all cases the Gibbs free energy of adsorption were below À30 kJ mol À1 , characterizing chemical adsorption.
Journal of Raman Spectroscopy, 2003
The normal Raman and surface-enhanced Raman spectra of acridine derivative lucigenin were analysed on Ag colloid. The effect of different anions on the adsorption mechanism of this molecule was also investigated under different experimental conditions, i.e. excitation wavelength and adsorbate concentration, in order to study the different adsorption of the molecule on the metal under different conditions. The adsorption of lucigenin, which is under the dicationic form, changes depending on the anion added to the surface: in the presence of chloride the molecule forms an ion pair, with a predominant perpendicular orientation, whereas in the presence of sulphate and nitrate, the adsorption is weak and the dication seems to adopt a different orientation with respect to the surface.
Indian Journal of Physics, 2011
The comparative study of normal Raman spectrum with the SERS along with the DFT calculations predicts the adsorption geometry of plumbagin on silver surface. The surface geometry of plumbagin molecule was studied by analysis of the SERS spectra adsorbed on silver colloid surfaces. The large enhancement of inplane ring stretching and C-H in-plane bending modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a stand-on orientation of PLBN on a silver surface.
Surface-enhanced Raman scattering study of alizarin red S
Vibrational Spectroscopy, 2010
This paper presents the application of surface-enhanced resonance Raman spectroscopy (SERRS) for the structural study of alizarin red S (ARS) and the nature of its interaction with silver nanoparticles. SERRS data for ARS over nanostructured silver electrodes suggest a surface-induced reaction of the adsorbed dye and the formation of an ion stabilized by the dye and alkali ions adsorbed at the metal surface. We found that precoating the SERS active substrate with 1-propanethiol inhibits the surface-induced modification of ARS. In addition to preventing structural modifications of ARS, the coating also concentrates the hydrophobic dye close enough to the SERS active interface enabling the observation of excellent Raman spectra of ARS in aqueous environment at ppm levels. The influence of resonance Raman effect and of the pH on the SERS spectra of ARS was also investigated.
The Journal of Physical Chemistry B, 2006
In this work piperazine-1-carbodithioic acid (PZCDT) and piperazine-1,4-dicarbodithioic acid (PZbCDT) were synthesized. These analytes PZCDT and PZbCDT have chair conformations, which is expected to give specific surface-enhanced Raman scattering (SERS) effects on individual bands. SERS, UV-Visible, TEM and DFT methods have proved that the dithiocarbamate moiety is a potential and suitable functional group for silver and ZnO nanoparticles (AgNPs and ZnONPs). The enhancement mechanism and enhancement factors in both SERS@AgNPs and SERS@ZnONPs are also discussed. Two new strong bands appear at 1630, 1286 cm À1 with very large intensity in SERS@AgNPs, which signifies the conversion of the C-N bond of the dithiocarbamate moiety into C]N bonds. The SERS signatures that are observed are quite different in SERS@AgNPs and SERS@ZnONPs. PAPER adenine, benzenethiol derivatives etc. The -N site of the PZ ring (aer removal of H atom) is associated to the -dithiocarbamate moiety.
Vibrational Spectroscopy, 2004
Surface-enhanced Raman scattering (SERS) spectroscopy was used for the vibrational characterization of the highly fluorescent anthraquinone molecules danthron and quinizarin, by using Ag nanoparticles prepared by citrate reduction. The adsorption of these two molecules is studied in this work on the basis of the results found by varying the pH of the medium, and the excitation wavelength. On the other hand, interesting structural findings where deduced by comparing the SERS results reported here with those found for the parent molecules emodin and naphtazarin which could be of interest in the assessment of the biological activity of these important drugs. #