Additive synthesis by sol-gel method for its use as antimicrobial

The antimicrobial activity of silver nanoparticles makes this chemical element attractive for their incorporation in different materials. Additionally, heteropolyacids (HPAs) have advantages as catalysts which make them environmentally very interesting. The objective of this work is to incorporate in a silica matrix obtained by sol-gel an HPA together with Ag, for their use as fillers in paints or adhesives. Six samples were synthesized, using tetraethoxysilane, methyltrimethoxysilane, acetic acid, molybdophosphoric acid and silver acetate. The silicas were characterized by potentiometric titration, XRD, SEM, TEM, SBET and FT-IR. When HPA is used instead of acetic acid, a variation on the final acidity is produced. The specific surface area decreases when HPA is incorporated into the silica synthesized using tetraethoxysilane as precursor, noticing a slight increase when Ag is added because a different distribution of HPA in the matrix. By SEM, it was observed that the particle size is bigger when the silicas are synthesized with TEOS-HPA, but it still shows the characteristic morphology of bulk silica. Additionally, preliminary test to evaluate the antimicrobial properties of the solids were carried out with fungi as Chaetomium globosum and Alternaria alternate, isolated from contaminated paints, and the first results are encouraging to continue with the development of these materials.Fil: Arreche, Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; ArgentinaFil: Hernández, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; ArgentinaFil: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; Argentin

Synthesis and characterization of hollow silica spheres

The synthesis and characterization of mono-dispersed silica hollow spheres using polystyrene (PS) spheres as template from the hydrolysis and condensation of tetraethylorthosilicate (TEOS) is presented. Successive washing steps with toluene and subsequent calcination at different temperatures were performed, in order to remove the PS template. Furthermore, the PS core removal was studied using different calcination temperatures, but without the prior washing with toluene. The morphology of the materials was studied by scanning electron microscopy and by transmission electron microscopy. A shell formed by silica nanoparticles with 50 nm diameter, being the layer of 100 nm thickness, was observed when using a low concentration of catalyst in the sol-gel reaction. The textural properties of the silica coating, obtained from N2 adsorption-desorption isotherms, depend on the catalyst amount added for the TEOS hydrolysis. From the Fourier transform infrared spectra and the results of the thermogravimetric analyses, it was found that the almost complete removal of the polystyrene core can be directly achieved by calcining at 500 °C, without the need of carrying out any washing and minimizing the formation of cracks in the silica hollow spheres.Fil: Gorsd, Marina Noelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin

Synthesis of Polystyrene Microspheres to be Used as Template in the Preparation of Hollow Spherical Materials: Study of the Operative Variables

Mono-disperse polystyrene (PS) spheres were synthesized. The styrene polymerization was carried out using 4,4´-azobis 4-cyanovaleric acid (ACVA) or potassium persulfate (KPS) as initiators in the presence of polyvinyl pyrrolidone (PVP) as surfactant or stabilizing agent. Size measurement and its distribution were followed by scanning electron microscopy. A very narrow size distribution was obtained by controlling the synthesis temperature. For both initiators, it was observed that smaller PS particles are obtained when PVP amount increases. Besides, the ssphere size decreased when KPS amount increased at a fixed PVP concentration. Similar results were obtained for the polystyrene spheres synthesized using ACVA as initiator. On the other hand, the influence of a co-monomer addition in the sphere size was also analyzed. The suitable selection of the initiator type and its concentration, as well as the surfactant agent amount, led to a controlled obtainment of the polystyrene microspheres, appropriate to be used as template in the synthesis of hollow spherical materials.Fil: Gorsd, Marina Noelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin

Biomass derivative valorization using nano core-shell magnetic materials based on keggin-heteropolyacids: Levulinic acid esterification kinetic study with n-butanol

Magnetic materials based on Keggin heteropolyacids immobilized on mesoporous silica-coated magnetite particles with a core-shell structure were synthesized. The activity of the catalyst was studied in the esterification reaction of levulinic acid with n-butanol, and its kinetics was studied by the systematic variation of several reaction parameters, such as stirring speed, catalyst loading, molar ratio of reactants, and temperature. It was also seen that the reaction was free from any external mass transfer as well as intraparticle diffusion limitations and was intrinsically kinetically controlled. A second-order kinetic equation was found to be consistent with the experimental data. Also, an experimental activation energy of 17 kcal/mol was found. A solvent-free condition for this reaction has also added the green chemistry perception to the reaction. In addition, the resulting catalyst can be used repeatedly without significant decrease in activity.Fil: Escobar Caicedo, Angélica María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Martínez, José J.. Universidad Pedagogica y Tecnológica de Colombia. Facultad de Ciencias. Escuela de Química; ColombiaFil: Cubillos, Jairo A.. Universidad Pedagogica y Tecnológica de Colombia. Facultad de Ciencias; ColombiaFil: Romanelli, Gustavo Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin

Riociguat treatment in patients with chronic thromboembolic pulmonary hypertension: Final safety data from the EXPERT registry

Objective: The soluble guanylate cyclase stimulator riociguat is approved for the treatment of adult patients with pulmonary arterial hypertension (PAH) and inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH) following Phase

A contribution to the physicochemical characterization of nonstoichiometric salts of tungstosilicic acid

Nonstoichiometric cesium and rubidium salts of tungstosilicic acid (TSA) were synthesized by precipitation. These solids are insoluble in water, due to the low solvation energy of large cations, have high specific surface area, and a mainly microporous structure. In turn, nonstoichiometric potassium salts prepared by solution evaporation have a low specific surface area and porosity, high solubility in water, and a negligible porosity. All the synthesized tungstosilicates presented a cubic structure, with a lattice parameter that slightly decreases in the order Cs+ > Rb+ ≅ K+ salts. The salts displayed the characteristic FT-IR bands of TSA, though the band assigned to the stretching of the W{double bond, long}O terminal bond presented a slight widening and a shoulder, and the band attributed to a bridged W{single bond}O{single bond}W bond was shifted to a lower wavenumber and showed a shoulder. Such effects are indicative of the interaction between the [SiW12O40]4- anion and the alkaline cations. Assuming that an increase in 1H MAS-NMR chemical shift is due to a higher acid strength, the cesium salts would have acid sites with higher acid strength than the others. The potassium salts, however, presented protons in different acid environments, with a low proportion of very strong acid sites. The acidity measurement by potentiometric titration with n-butylamine also showed that the cesium salts have acid sites with higher strength than those of rubidium. The same behavior was observed for the potassium salts, which exhibited an acid strength higher than expected. The number of protons determined by titration decreased in the order Cs+ > Rb+ ≅ K+ salts and also decreased for the more substituted salts. © 2007 Elsevier Inc. All rights reserved.Fil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin

Properties of mesoporous tungstosilicic acid/titania composites prepared by sol-gel method

The tungstosilicic acid/titania composites were prepared by the sol–gel method. Titanium isopropoxide was used as titania precursor, and urea as a low-cost template. The tungstosilicic acid (TSA) was added in the same step as that in which titania hydrogel is formed. The TSA-modified samples only showed the characteristic peaks of anatase phase of titanium oxide in the XRD patterns, indicating that the presence of TSA retarded the crystallization of the anatase phase and its transformation into the rutile phase. Spherical particles with sizes between 200 and 700 nm, formed by aggregation of nanoparticle aggregates (4–50 nm in size), were observed. The particle size increased when the TSA content was raised and also increased slightly with the thermal treatment temperature. Mesoporous materials were obtained, with a mean pore diameter higher than 3.1 nm. Both the increase of the TSA concentration in the solid and the calcination temperature led to a decrease in the specific surface area of the samples. The main heteropolyoxometallate species present in the composites is the [SiW12O40] 4 anion for the composites calcined up to 500 8C. The band gap energy decreased as a result of the introduction of TSA into the titania matrix, though it remained almost constant with the calcination temperature increase.Fil: Blanco, Mirta Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Pizzio, Luis Rene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin