Area de Quimica Fisica

Sevilla, Spain

Area de Quimica Fisica

Sevilla, Spain
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Romero J.M.,Area de Quimica Fisica | Jorge N.L.,Area de Quimica Fisica | Grand A.,CEA Grenoble | Grand A.,Autonomous University of Chile | And 2 more authors.
Chemical Physics Letters | Year: 2015

The degradation of the 2,4-dichlorophenoxyacetic acid in aqueous solution is an hydrolysis reaction. Two products are identified: 2,4-dichlorophenol and glycolic acid. Reaction is investigated as a function of pH and temperature, and it is first-order kinetics and pH-dependent. Reaction is modeled in gas phase, where a proton catalyses the reaction. Critical points of PES are calculated at B3LYP/6-311++G(3df,2p), and aug-cc-pvqz//6-311++G(3df,2p) levels plus ZPE at 6-311++G(3df,2p) level. The activation barrier is 21.2 kcal/mol. Theoretical results agree with the experimental results. A second mechanism related with a Cl2Ph-O-CH2-COOH...H2O complex is found, but with a rate limiting step of 38.4 kcal/mol. © 2015 Elsevier B.V. All rights reserved.

Navas J.,University of Cádiz | Alcantara R.,University of Cádiz | Fernandez-Lorenzo C.,University of Cádiz | Anta J.-A.,Area de Quimica Fisica | And 2 more authors.
Measurement Science and Technology | Year: 2010

The photocurrent response of dye-sensitized solar cells (DSSCs) to light excitation from focused and non-focused laser beams is investigated. We observe that part of the photocurrent is produced by the activation of the irradiated area, whereas another part is generated by the previously photoexcited area. A mathematical algorithm has been devised to describe the rise and decay processes. The application of this algorithm leads to a significant improvement in the surface photoresponse and quantum yield measurements in DSSCs by means of the laser beam-induced current (LBIC) technique. This algorithm enhances the quality and definition of the LBIC images and opens the way to use this technique to cope with the biphasic features of these photovoltaic devices and extracting key properties for device performance such as internal quantum efficiencies and electron diffusion lengths. © 2010 IOP Publishing Ltd.

Almandoz M.C.,Area de Quimica Fisica | Pagliero C.L.,CONICET | Ochoa N.A.,National University of San Luis | Marchese J.,National University of San Luis
Ceramics International | Year: 2015

This work concerns to the development and characterisation of support, active layer and tubular composite membranes (CM) from natural aluminosilicates as principal components (clay, bentonite, feldspar, quartz, alumina). The selection of these raw materials was primarily based on their low cost and they are locally produced. In the substrates preparation, the effect of materials compositions, additives, particle sizes, paste rheological properties, and drying-sintering temperatures was investigated. The consolidated ceramic substrates were characterised by SEM, DTA-TG, X-Ray diffraction, Hg intrusion, mechanical resistance, and water flux measurements. Extrusion has been used as the forming process of tubular support. The CM was fabricated depositing a thin active layer by slip-casting method on the support. The CM sintered at 1200 °C showed the best structural characteristics, porosities of 50%, active layer pore size between 0.08 and 0.55 μm. The CM hydraulic permeabilities (10-274 L/h m2 kPa) were comparable and greater than several inorganic commercial membranes and CM obtained from other researches. The CM microfiltration effectiveness was tested with different substances from food industry, i.e. slaughterhouse wastewater treatment and goat milk pasteurisation. The obtained results, insoluble residue rejections (100%) and high bacterial removal (87-99%), make the ceramic CM suitable for microfiltration processes. © 2015 Elsevier Ltd and Techna Group S.r.l.

Profeta M.I.,Area de Quimica Fisica | Romero J.M.,Area de Quimica Fisica | Jorge N.L.,Area de Quimica Fisica | Grand A.,Laboratoire Lesions des Acides Nucleiques | And 2 more authors.
Journal of Molecular Modeling | Year: 2014

Cyclic organic peroxides are a broad and highly sought-after class of peroxide compounds that present high reactivity and even explosive character. The unusually high reactivity of these peroxides can generally be attributed to the rupture of O-O bonds. Cyclic diperoxides are a very interesting series of substituted compounds in which tetroxane is the most prominent member. Gas-phase thermolysis of the simplest substituted member of the series [3-methyl-1,2,4,5-tetroxane or methylformaldehyde diperoxide (MFDP)] has been observed to yield one acetaldehyde, one formaldehyde, and one oxygen molecule as reaction products. DFT at the 6-311+G**level of theory using the BHANDHLYP correlation-exchange functional was applied via the Gaussian09 program to calculate the critical points of the potential energy surface (PES) of this reaction. Equatorial and axial isomers were studied. The singlet state PES of MFDP was calculated, and an open diradical structure was found to be the first intermediate in a stepwise reaction. Two PESs were subsequently obtained: singlet state (S) and triplet state (T) PESs. After that, two alternative stepwise reactions were found to be possible: 1) one in which either an acetaldehyde, or 2) formaldehyde molecule is initially formed. For second one, exothermic reactions were observed for both the S and T PESs. The reaction products include a oxygenmolecule in either S or T state, with the T reaction being the most exothermic. When calculations were performed at the CASSCF(10,10)/6-311+ G**level, spin-orbit coupling permitted S to Tcrossing at the open diradical intermediate stage, a non-adiabatic reaction was observed, and lower activation energies and higher exothermicity were generally seen for the T PES than for the S PES. These results were compared with the corresponding results for tetroxane. The spin-orbit coupling of MFDP and tetroxane yielded identical values, so it appears that the methyl substituent does not have any effect on this coupling. © Springer-Verlag 2014.

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