Joel C. Rubim

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.

Surface enhanced Raman spectra of benzotriazole adsorbed on a copper electrode

Abstract The surface-enhanced Raman spectra of benzotriazole adsorbed on a silver electrode have been investigated in order to study the formation of complexes at the electrode surface as a function of the applied potential, the pH and the type of halide in the electrolyte solution. The use of a pseudo-halide, SCN−, in the electrolyte (KNO3) solution allowed the simultaneous adsorption of SCN− and benzotriazole to be followed.

Determination of methyl ester contents in biodiesel blends by FTIR-ATR and FTNIR spectroscopies.

Partial last square regression (PLS) and artificial neural network (ANN) combined to FTIR-ATR and FTNIR spectroscopies have been used to design calibration models for the determination of methyl ester content (%, w/w) in biodiesel blends (methyl ester+diesel). Methyl esters were obtained by the methanolysis of soybean, babassu, dende, and soybean fried oils. Two sets of samples have been used: Group I, binary mixtures (diesel+one kind of methyl ester), corresponding to 96 biodiesel blends (0-100%, w/w), and Group II, quaternary mixtures (diesel+three types of methyl esters), corresponding to 60 biodiesel blends (0-100%, w/w). The PLS results have shown that the FTNIR model for Group I is more precise and accurate (+/-0.02 and +/-0.06%, w/w). In the case of Group II the PLS models (FTIR-ATR and FTNIR) have shown the same accuracies, while the ANN/FTNIR models has presented better performance than the ANN/FTIR-ATR models. The best accuracy was achieved by the ANN/FTNIR model for diesel determination (0.14%, w/w) while the worthiest was that of dende ANN/FTIR-ATR model (0.6%, w/w). Precisions in Group II analysis ranged from 0.06 to 0.53% (w/w) and coefficients of variation were better than 3% indicating that these models are suitable for the determination of diesel-biodiesel blends composed of methyl esters derived from different vegetable oils.

Determination of ethanol in fuel ethanol and beverages by Fourier transform (FT)-near infrared and FT-Raman spectrometries

Fourier transform-near infrared (FT-NIR) and FT-Raman spectrometries have been used to design partial least squares (PLS) calibration models for the determination of the ethanol content of ethanol fuel and alcoholic beverages. In the FT-NIR measurements the spectra were obtained using air as reference, and the spectral region for PLS modeling were selected based on the spectral distribution of the relative standard deviation in concentration. In the FT-Raman measurements hexachloro-1,3-butadiene (HCBD) has been used as an external standard. In the PLS/FT-NIR modeling for ethanol fuel analysis 50 ethanol fuel standards (84.9–100% (w/w)) were used (25 in the calibration, 25 in the validation). In the PLS/FT-Raman modeling 25 standards were used (13 in the calibration, 12 in the validation). The PLS/FT-NIR and FT-Raman models for beverage analysis made use of 24 standards (0–100% (v/v)). Twelve of them contained sugars (1–5% (w/w)), one-half was used in the calibration and the other half in the validation. Different spectral pre-processing were used in the PLS modeling, depending on the type of sample investigated. In the ethanol fuel analysis the FT-NIR pre-processing was a 17 points smoothed first derivative and for beverages no spectral pre-processing was used. The FT-Raman spectra were pre-processed by vector normalization in the ethanol fuel analysis and by a second derivative (17 points smoothing) in the beverage analysis. The PLS models were used in the analysis of real ethanol fuel and beverage samples. A t-test has shown that the FT-NIR model has an accuracy equivalent to that of the reference method (ASTM D4052) in the analysis of ethanol fuel, while in the analysis of beverages, the FT-Raman model presents an accuracy equivalent to the reference method. The limits of detection for NIR and Raman calibration models were 0.05 and 0.2% (w/w), respectively. It has also been shown that both techniques, present better results than gas chromatography (GC) in evaluating the ethanol content of beverages.

Use of Raman micro-spectroscopy in the characterization of MIIFe2O4 (M = Fe, Zn) electric double layer ferrofluids

MIIFe2O4 (M = Fe, Zn) electric double layer ferrofluids (edl-ferrofluids) were investigated and characterized by Raman micro-spectroscopy as solids (powder) or in solution forming magnetic fluids. The Raman spectra showed that the nanoparticles forming the magnetic fluids have different compositions depending on the MII ion used in their preparation. In the case of FeFe2O4 edl-ferrofluid, maghemite, magnetite, an amorphous non-stoichiometric oxyhydroxide [FeOx(OH)3 − 2x, x<1] and Fe(OH)3 phases are present. In the case of the ZnFe2O4 edl-ferrofluid, a magnetite-like structure where the FeII centers were replaced by the ZnII ions is present. A model of the distribution of the different chemical phases on the nanoparticles is presented. The Raman spectrum of the FeFe2O4 edl-ferrofluid excited close to an absorption band of the sample at 650 nm presents several Raman features above 900 cm−1 that are not observed for the ZnFe2O4 edl-ferrofluid sample. These results have been interpreted considering the resonant excitation of the density of phonon states with k ≠ 0 due to quantum size effects. Copyright

Biocompatible magnetic fluid precursors based on aspartic and glutamic acid modified maghemite nanostructures

Abstract Biocompatible magnetic fluid precursors based on chemically modified maghemite nanostructures (γ-Fe 2 O 3 ) are able to chemisorb aspartic and glutamic acids, as shown by conductometric measurements. The amino acids adsorb onto the maghemite surface following an adsorption isotherm. The modified nanoparticles formed a stable colloidal solution at a pH of 5–8. Raman and FTIR spectroscopy directly showed that the investigated amino acids adsorb on the maghemite surface in the form of their respective salts, glutamate and aspartate.

New heterogeneous metal-oxides based catalyst for vegetable oil trans-esterification

The preparation of new materials obtained from the co-precipitation of aluminum, tin and zinc oxides and their use as catalytic system activities for vegetable oils alcoholysis are reported herein. It was observed that these metal-oxides of the type (Al2O3)X(SnO)Y(ZnO) Z are active for soybean oil alcoholysis, uzing several alcohols, including branched ones. Best result was achieved using methanol, with conversion yields up to 80% in 4 h. It was also possible to recycle the catalysts without apparent loss of activity.

Electrochemical and spectroelectrochemical (SERS) studies of the reduction of methylene blue on a silver electrode

The electrochemical behavior of methylene blue (MB+) on a silver electrode has been investigated by cyclic voltammetry, the rotating disk electrode technique, chronoamperometry and surface-enhanced Raman spectroscopy (SERS). The electrochemical results have shown that MB+ is reduced in two one-electron steps and that these two reduction processes are, at least partially, controlled by mass transport. The electrochemical measurements have also shown that the reduction of MB+ on the surface of a silver electrode promotes the formation of two different films. The SERS spectra have shown the presence of distinct species on the electrode surface as the potential is made more negative. Such a dependence on the potential allowed the characterization of the chemical species associated with the first and second film formation. They are, respectively, the radical cation (HMB+) and leucomethylene blue (LMB).

Enhanced Raman scattering from passive films on silver-coated iron electrodes

Abstract The passivation of an iron electrode in 0.5 M H 2 SO 4 , borate buffer (pH 8.4) and in carbonate/bicarbonate buffer (pH 8.9) solutions has been investigated by in situ Raman spectroscopy. Raman spectra were obtained before and after the electrochemical deposition of a silver film on the passivated iron electrode. After the silver deposition, the background intensity was enhanced by a factor of 10 and Raman signals of the passive film could then be observed. The enhanced Raman spectra of the different passive films showed a common feature at ca. 544 cm −1 , which has been assigned tentatively to the presence of Fe(OH) 2 on the passive film. Raman signals of iron(III) hydroxides were also observed. Raman signals characteristic of δ-FeOOH and Fe(OH) 3 were observed. In the carbonate/bicarbonate buffer solution, the presence of an iron(II) carbonate in the passive film was also confirmed. SEM micrographs and cyclic voltammograms of the silver-coated iron electrode showed that the silver film is discontinuous.

Fabrication of glycine-functionalized maghemite nanoparticles for magnetic removal of copper from wastewater

Maghemite nanoparticles (MNPs) were functionalized with glycine, by a cost-effective and environmentally friendly procedure, as an alternative route to typical amine-functionalized polymeric coatings, for highly efficient removal of copper ions from water. MNPs were synthesized by co-precipitation method and adsorption of glycine was investigated as a function of ligand concentration and pH. The efficiency of these functionalized nanoparticles for removal of Cu(2+) from water has been explored and showed that adsorption is highly dependent of pH and that it occurs either by forming chelate complexes and/or by electrostatic interaction. The adsorption process, which reaches equilibrium in few minutes and fits a pseudo second-order model, follows the Langmuir adsorption model with a very high maximum adsorption capacity for Cu(2+) of 625mg/g. Furthermore, these nanoadsorbents can be used as highly efficient separable and reusable materials for removal of toxic metal ions.