H3PW12O40 inmovilizado sobre sílice mesoporosa como catalizadores sólidos ácidos en la síntesis de 1,5-benzodiazepinas

La catálisis a base de heteropoliácidos (HPAs) es un campo de gran interés y en crecimiento, ya que varios procesos industriales los utilizan como catalizadores en diversas reacciones

Síntesis de carbón activado mesoporoso a partir de residuos agroindustriales por activación química con H3PO4 y NaOH: estudio de optimización mediante un diseño experimental factorial DCC

En este trabajo se determinaron las condiciones óptimas para la síntesis de carbones activados mesoporosos (AC) usando cascaras de semilla de girasol (CSG) como precursor, siguiendo un diseño estadístico de experimentos de tipo factorial 22 de composición central - DCC

Inmovilización fotocatalítca de nanopartículas de TiO2 sobre películas de polietileno de baja densidad y su aplicación como superficies autolimpiantes fotoinducidas

Los procesos fotocatalíticos sobre TiO2 han emergido como una alternativa promisoria para ser aplicados como superficies autolimpiantes y antimicrobianas foto-inducidas

Tungsten Adsorption on to Alumina from Ammonium Meta- and Para-Tungstate Solutions — UV-Visible Spectra of the Solutions

The species in solutions used during tungsten adsorption on to alumina from ammonium meta- and para-tungstate solutions have been studied by UV-visible spectroscopy. For metatungstate, the spectra of the impregnant solution placed in contact with alumina and of the solutions corresponding to the dissolution pH and pH- were measured as a function of time. In all the cases, the intensity of the band corresponding to metatungstate decreased with time. The spectra of paratungstate B solutions placed in contact with alumina as a function of time were very different from those of paratungstate solutions maintained at the dissolution pH and at pH = 8.5. However, these latter spectra were similar to those obtained for metatungstate solution placed in contact with alumina. The decrease was more rapid for the solution which had been in contact with alumina relative to that to which ammonia had been added (pH = 9). In both cases, the variation in intensity with time was greater than that recorded for the metatungstate solution maintained at the dissolution pH. The observed fraction of metatungstate transformed depended not only on the solution pH but also on the presence of an additional effect due to the interaction of metatungstate ions and alumina. Only the monomeric species WO 2- 4 was present in a solution which had been placed in contact with alumina for 24 h. During impregnation of an alumina support with paratungstate B and ammonium metatungstate solution, the species adsorbed is the monomer while the metatungstate fraction which does not interact with alumina is slowly transformed to the WO 2- 4 species

Adsorption of Tungsten on Alumina from Sodium Tungstate Solutions. Estimation of Equilibrium and Kinetic Parameters

The tungsten adsorption isotherm from aqueous solutions of sodium tungstate on to alumina at 20°C has been studied. The isotherm shape was in agreement with that predicted by the classic Langmuir equation. This model was therefore fitted to the experimental data in order to determine the adsorption equilibrium constant and the total concentration of adsorption sites. Kinetic parameters of adsorption were also determined. To do so, a theoretical model that predicts the tungsten concentration profiles in impregnated thin layers was fitted to the experimental profiles. The diffuse reflectance spectra of dried samples used for isotherm determination and of thin alumina layers impregnated with tungsten solutions exhibit a band at 215 nm which is accompanied by a shoulder at 250 nm. For samples having a greater tungsten concentration, the shoulder develops and then transforms into a second band. The maximum at the lowest wavelength (first maximum) is assumed to correspond to tungsten in a tetrahedral coordination (monomeric species) while the second maximum is due to distortion in the tetrahedral symmetry caused by strong interactions between the support and the monomeric species

Parameters for the Adsorption of Tungsten from Metatungstate Solution on to Alumina

The adsorption of tungsten from aqueous solutions of ammonium metatungstate on to alumina has been studied, an adsorption isotherm at 20°C being obtained. The isotherm had a sigmoidal shape and reached a flat plateau region at an adsorbed concentration of 100 mg W/g Al2O3 within the range of initial concentrations used (up to 70,000 ppm W). A proposed relationship between the adsorbed concentration and the equilibrium solution concentration has enabled the adsorption equilibrium parameters to be estimated. Impregnation of flat thin layers of alumina with concentrated tungstate solutions (5,100, 31,200 and 72,800 ppm W) has also been studied. Fits between the experimental tungsten concentration profiles and those obtained via a theoretical model of the impregnation phenomena allowed the adsorption kinetic parameters to be obtained. These parameters are useful in predicting the concentration profiles resulting from the pore-filling impregnation of pellets provided a suitable theoretical model is employed

Chitosan films containing TiO2 nanoparticles modified with tungstophosphoric acid for the photobleaching of malachite green in solid-gas interfaces upon different wavelengths

Authors thank Lilian Osiglio and Mariela Theiller for their experimental collaboration. Financial support from CONICET (Project PIP 0449) and Universidad Nacional de La Plata (Project X-773 and X-732) is also acknowledged. J.A. Rengifo-Herrera thanks Universidad Nacional de San Agustin and CONCYTEC from Peru for the financial support of E. Mendoza-Portillo’s scientific stage.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte

A green and reusable catalytic system based on silicopolyoxotungstovanadates incorporated in a polymeric material for the selective oxidation of sulfides to sulfones

Two vanadium-containing Keggin silicopolyoxotungsto compounds K5SiVW11O40 and K6SiV2W10O40 were synthesized and characterized. They were incorporated in a superporous hydrogel constitute by prop-2-enamide and propenoic acid as initial monomers and bis-acrylamide as cross-linking moiety. Materials were characterized by several techniques. According to FTIR and 51V MAS-NMR, the (SiVxW12-xO40)(4+x)- anions are the main species present in the hybrid materials. Additionally, they do not decompose during the preparation of the composite. XRD and SEM-EDX results suggest that (SiVxW12-xO40)(4+x)- anions were well dispersed in the support or present as amorphous phases. These materials were evaluated as catalysts in the oxidation of sulfides to sulfones, using an eco-friendly oxidant and mild reaction conditions. The hybrid materials with higher content of the heteropoly compound displayed a remarkable catalytic behaviour in the oxidation of diphenyl sulfide. Materials also exhibited a stable catalytic performance through consecutive reuses. Optimum reaction parameters established were subsequently translated to the oxidation of a sulfide of interest (dapsone) due to its pharmacological activities. © 202