Successive projections algorithm improving the multivariate simultaneous direct spectrophotometric determination of five phenolic compounds in sea water

This paper proposes an analytical method to determine directly and simultaneously five phenolic compounds (4-nitrophenol, 2-nitrophenol, phenol, 2,4,6-trichlorophenol and 4-chlorophenol) in sea water (Ria de Bahía Blanca, Argentine). The advantages of this method is that only requires spectrophotometric measurements (separation steps and derivatization reagents are avoided) and chemometric modelling (PLS and MLR–SPA).The statistical comparison between PLS — a well established multivariate method — and MLR–SPA — a recently presented chemometric modelling — demonstrated better analytical performance for the later one. This fact is indicative of the potentiality of MLR–SPA for solving complex analytical problems.     

Comparison between experimental and theoretical values of effectiveness factor in cephalosporin C production process with immobilized cells

Cells ofCephalosporium acretnonium ATCC 48272 immobilized in calcium alginate beads were utilized for cephalosporin C production and the results were compared with those obtained with free cells. The experiments were performed with synthetic medium containing glucose and sucrose as carbon and energy sources. Experimental effectiveness factor values were obtained at various cell and dissolved-oxygen concentrations, considering Monod kinetics for the respiration rate, and were compared with the values calculated with zero-order kinetics in spherical bioparticle. The results showed that the assumption of oxygen limitation by diffusion in the bioparticle was correct, and that cephalosporin C production with immobilized cells is perfectly viable, although a slightly lower rate than that obtained in the free cell process was observed.     

New pi-complexation adsorbents for propane-propylene separation

New adsorbents were prepared and tested for the separation of propane-propylene mixtures by adsorption. The ordered mesoporous material SBA-15 was used as the starting material for silver-ion deposition for pi-complexation with propylene. Two different loadings of silver were evaluated. Adsorption equilibrium and kinetic measurements of propane and propylene in the matrix (pure SBA-15) and the silver-modified adsorbents were performed at 323, 343, and 373 K. In this temperature range, the selectivity of propylene in one of the materials (Ag/SBA-15 = 0.5) is in the range 13-22 because the amount of propane adsorbed is very small, 0.095 mmol/g of propane versus 1.12 mmol/g of propylene at 100 kPa and 343 K. The diffusivity of both hydrocarbons is not seriously affected by the introduction of silver into the mesoporous structure.     

Zero shear viscosity in miscible polymer blends of polystyrene and poly(2,6-dimethylphenylene ether)

The dynamic viscosities of blends of high molecular weight, narrowmolecular-weight distributed polystyrene and poly(2, 6-dimethylphenylene ether) are studied. The zero shear viscosity η_o depends on the weight average molecular weight M̄_w and on the average entanglement molecular weight M̄_e in the blend according to η_o ≈︁ M̄^3.4 _w(blend)/M̄^2.4_e(blend).     

DFT calculations on the cyclic ethers hydrogen-bonded complexes: molecular parameters and the non-linearity of the hydrogen bond

B3LYP/6-311+G(d,p) calculations were used to explore the geometry, intermolecular energy and the vibrational harmonic spectrum of heterocyclic complexes formed between 2,5-dihydrofuran and thiophene cyclic ethers and the HCl and HF acids. The simulated structures of these hydrogen complexes are discussed in terms of the linearity deviation of the n...HX hydrogen bond. Theoretical results are satisfactory as compared to the experimental equilibrium structure. The energies of the hydrogen bonds were determinate through the difference between the complex and its correspondent isolated monomers. Moreover, to obtain the correct energies of the hydrogen bonds, it was included the values of the zero point vibrational energy and the basis set superposition error. The infrared spectra reveal the direct relationship between the distance of the hydrogen bond and its stretching frequencies, as well as a good interpretation of the bathochromic effect of the HCl and HF stretching modes from intermolecular charge transfer.     

Electrochemical growth of CuInSe<Subscript>2</Subscript> thin film on different substrates from alkaline medium. Characterization of the films

The simultaneous electrodeposition of the system Cu–In–Se was investigated. The study was carried out at pH 8.5 using diethylentriamine as complexing agent for the Cu⁺² ion. The synthesis of CuInSe₂ semiconductor thin films was carried out by electrodeposition on different substrates [indium–tin oxide (ITO) on glass, aluminum and type 304 steel]. The simultaneous codeposition of the Cu, In, and Se was achieved by constant potential electrolysis technique in aqueous solutions containing the elements that conform this material. The deposits of CuInSe₂ were about 4 μm thick, which is thick enough for the photovoltaic effect to take place. The as-deposited films were characterized by atomic emission spectroscopy with inductive coupling plasm (AES-ICP) and scanning electronic microscopy (SEM). Annealed films were characterized X-ray diffraction, optical NIR spectroscopy, and photoelectrochemical studies The films were obtained with a well-defined composition, very close to the expected one. Homogeneous deposit with chalcopyrite structure was produced. A In₂O₃ phase was also observed. Annealing of the film improved the crystallinity of the films. Good photo response, an appropriate absorption coefficient, and a band gap of 1.09 eV were obtained.     

Fenton’s reagent-mediated degradation of residual Kraft black liquor

In this work, the effect of Fento’s reagent on the degradation of residual Kraft black liquor was investigated. The effect of Fenton’s reagent on the black liquor degradation was dependent on the concentration of H₂O₂. At low concentrations (5 and 15 mM) of H₂O₂, Fenton’s reagent caused the degradation of phenolic groups (6.8 and 44.8%, respectively), the reduction of reaction medium pH (18.2%), and the polymerization of black liquor lignin. At a high concentration (60 mM) of H₂O₂, Fenton’s reagent induced an extensive degradation of lignin (95–100%) and discoloration of the black liquor. In the presence of traces of iron, the addition of H₂O₂ alone induced mainly lignin fragmentation. In conclusion, Fenton’s reagent and H₂O₂ alone can degrade residual Kraft black liquor under acidic conditions at room temperature.     

Optical studies of carbon nanotubes and nanographites

Resonance Raman and photoluminescence excitation (PLE) spectroscopies are used to study the optical properties of different types of carbon nanostructures such as carbon nanotube, nanoribbons, nanographites and graphite edges. In the resonance Raman experiments of carbon nanotubes, the (n,m) assignment is obtained by comparing the experimental and theoretical diameter and chirality dependence of the optical transitions. The influence of the environment on the optical transitions of the nanotubes is also obtained in the Raman experiments. The PLE measurements in different samples of carbon nanotubes show both direct and phonon-assisted optical transitions, and the results give new evidences that the optical transitions in nanotubes have an excitonic character, which is very strong for the low energy transitions. We also analyze the Raman spectra of nanoribbons and nanographites, showing that this technique is an important tool for defect characterization in graphitic materials, and can be used to distinguish the atomic structure of the graphite edges.