Paola Corio

Effect of sodium dodecylsulfate on copper corrosion in sulfuric acid media in the absence and presence of benzotriazole

The effect of sodium dodecylsulfate (SDS) on the copper corrosion in 0.5 mol dm−3 H2SO4 solution has been studied by electrochemical and in situ Raman spectroscopic measurements. It has been shown that SDS is a corrosion inhibitor for copper on the entire range of potentials studied and presents a synergetic effect on the inhibitive action of benzotriazole (BTAH). It has been also observed that SDS inhibits the H+/H2 reaction on the copper electrode below or above the cmc. The surfactant film, at −750 mV (SCE) obeys a Langmuir adsorption isotherm considering 1.2 surface sites for each adsorbed SDS molecule, when [SDS]<cmc. The equilibrium adsorption constant, K=1.7×103 mol dm−3, suggests the presence of a chemical adsorption. The spectroscopic results have shown that the SDS adsorbs on the copper surface with both moieties, the hydrophobic and hydrophilic, interacting with the copper surface. The in situ spectroelectrochemical results have also shown that SDS co-adsorbs on the copper surface in the presence of BTAH and that the structure of the co-adsorbed SDS molecules is different from that observed in the absence of BTAH.

Chemical analysis of polycyclic aromatic hydrocarbons by surface-enhanced Raman spectroscopy.

The use of surface-enhanced Raman spectroscopy (SERS) for trace determination of polycyclic aromatic hydrocarbons (PAHs) is described. This paper focuses on the development of SERS-active substrates that are specific for the characterization and spectroscopic study of PAHs. The SERS-active substrates are based on thin gold films evaporated on a glass surface previously treated with a mercaptoalkylsilane. SERS of PAHs was investigated over uncoated gold island films and over such films coated with a self-assembled monolayer (SAM) of 1-propanethiol. Adsorption of PAHs on a plain SERS-active Au-film led to a surface-induced decomposition of PAHs, due to catalytic properties of nanostructured gold. Thus, the functionalization of the SERS-active substrates by means of SAM was done aiming at a specific chemical interaction toward PAHs. Thus, in addition to preventing decomposition of the PAHs, the coating also concentrates the hydrophobic PAHs close enough to the SERS-active interface. Results show that high sensitivity, SERS-active nanostructured gold substrates that show selectivity towards PAHs were obtained, with the following properties: strong intensification of the Raman signal, reproducibility, and stability over time. The employed methodology enables the observation of excellent Raman spectra of PAHs in aqueous environment at ppm levels.

High performance gold nanorods and silver nanocubes in surface-enhanced Raman spectroscopy of pesticides.

The behavior of Au nanorods and Ag nanocubes as analytical sensors was evaluated for three different classes of herbicides. The use of such anisotropic nanoparticles in surface-enhanced Raman scattering (SERS) experiments allows the one to obtain the spectrum of crystal violet dye in the single molecule regime, as well as the pesticides dichlorophenoxyacetic acid (2,4-D), trichlorfon and ametryn. Such metallic substrates show high SERS performance at low analyte concentrations making them adequate for use as analytical sensors. Density functional theory (DFT) calculations of the geometries and vibrational wavenumbers of the adsorbates in the presence of silver or gold atoms were used to elucidate the nature of adsorbate-nanostructure bonding in each case and support the enhancement patterns observed in each SERS spectrum.

Evolution of the molecular structure of metallic and semiconducting carbon nanotubes under laser irradiation

The temperature dependence of the morphology of single wall carbon nanotubes (SWNTs) has been studied by Raman spectroscopy at different temperatures by changing the incident laser power. It is shown that a high power laser irradiation treatment of as-grown samples anneals the SWNTs, improving their structural order and perhaps also removing adsorbed gases. As a result, a significant increase in the Raman cross-section of the nanotubes upon laser irradiation can be observed, for both metallic or semiconducting tubes. The investigation of the power level dependence of the Raman spectra also reveals that smaller diameter nanotubes are burned off first, increasing the mean diameter of the nanotubes in the sample.

Silver–gold nanotubes containing hot spots on their surface: facile synthesis and surface-enhanced Raman scattering investigations

We report the synthesis of silver–gold nanotubes containing hot spots along their surface. The Ag–Au nanotubes exhibited exceptional SERS properties compared to silver nanowires, enabling the detection of crystal violet in the 10−10 M regime, as well as 9-nitroanthracene and benzo[a]pyrene at 3.3 × 10−7 M.

Resonant Raman scattering characterization of carbon nanotubes grown with different catalysts

Single-walled carbon nanotube samples produced in the presence of different combinations of metal catalysts have been studied by resonant Raman spectroscopy. The diameter distribution of different samples has been determined by analysis of the laser excitation energy dependence of the tangential modes associated with metallic nanotubes. These modes are resonantly enhanced over a narrow range of the exciting energies, which shifts for different samples. The Raman cross-section expression has been used to fit the experimental Raman excitation profiles. This procedure was used to determine the mean value and the width of the distribution of diameters within each sample.

Characterization of the [Ru(CN)5(pyS)]4− ion complex adsorbed on gold, silver and copper substrates by surface-enhanced Raman spectroscopy

Abstract The adsorption of the [Ru(CN) 5 (pyS)] 4− (pyS=4-mercaptopyridine) ion complex on gold, silver and copper surfaces has been studied by surface-enhanced Raman spectroscopy (SERS). The influence of the nature of the metallic substrates in the adsorption geometry of the complex is reflected in a strong variation of the SERS spectra, particularly, the relative intensities of characteristic vibrational modes of pyS and CN ligands, which is likely to result from changes in specific chemical interactions involving both ligands and the surface. The effect of the surface modification procedure on the properties of the adsorbed monolayers has also been investigated for the gold surface. Surface modification has been performed by self-assembly or under an electrochemical potential. The spectroscopic results have shown that, according to the modification procedure, the modifier can be bound to the surface via sulfur atom or via CN nitrogen atoms. The ability to control the orientation of the adsorbed monolayer permits control over the properties of the interface, as demonstrated by the study of the electrochemistry of cytochrome- c (cyt- c ) on the differently prepared surfaces. A reversible electrochemical response of the metalloprotein is only observed on the self-assembly prepared surface, where CN moieties of the surface modifier are available to interact with the protein molecule.

The effects of solvent and electrolyte in the surface enhanced Raman spectrum of iron(II)bis(1,10 phenanthroline)dicyano: evidence for the formation of strong ion-pairs

Abstract The SERS (surface-enhanced Raman scattering) and SERRS (surface-enhanced resonant Raman scattering) spectra of Fe(phen)2(CN)2 adsorbed on a silver electrode were investigated in different solvents and in the presence of different electrolytes. The remarkable solvatochromism and ionochromism of the complex is reflected by an outstanding dependence of the SERS spectrum on the solvent and electrolyte, particularly the relative intensity of the CN and phenanthroline modes. All evidence points to a strong interaction involving the CN moiety and the acidic protons of the solvents, besides a strong ion-pair interaction involving such moiety and cations as Li+ and Mg2+. Excitation of the SERS spectrum of Fe(phen)2(CN)2 close to resonance with the high energy shoulder of the MLCT transition indicates the presence of a second charge transfer transition involving the CN moiety.

Rhodium Nanoparticles as Precursors for the Preparation of an Efficient and Recyclable Hydroformylation Catalyst

Despite all the advances in the application of nanoparticle (NP) catalysts, they have received little attention in relation to the hydroformylation reaction. Herein, we present the preparation of a hydroformylation catalyst through the immobilization of air‐stable rhodium NPs onto a magnetic support functionalized with chelating phosphine ligands, which serves as an alternative to air‐sensitive precursors. The catalyst was active in hydroformylation and could be used in successive reactions with negligible metal leaching. The interaction between the rhodium NPs and the diphenylphosphine ligand was evidenced by an enhancement in the Raman spectrum of the ligand. Changes occurred in the Raman spectrum of the catalyst recovered after the reaction, which suggests that the rhodium NPs are precursors of active molecular species that are formed in situ. The supported catalyst was active for successive reactions even after it was exposed to air during the recycling runs and was easily recovered through magnetic separation.

Aplicação de espectroscopias raman e infravermelho na identificação e quantificação de plastificantes em filmes comerciais de PVC esticável

This paper reports the use of Raman and infrared techniques for the qualitative and quantitative analysis of plasticizers in polyvinylchloride (PVC) commercial films. FT-Raman marker bands were indentified for di-2-ethyl-hexyl adipate (DEHA) and di-2-ethyl-hexyl phthalate (DEHP), allowing for the rapid identification of these species in the commercial film. Quantitative analysis by FT-IR resulted in plasticizers concentrations ranging from 11 to 27% (w/w). Considering the little sample preparation and the low cost of the techniques, FT-IR and FT-Raman are viable techniques for a first assessment of plasticizers in commercial samples.