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.Centro de Investigación y Desarrollo en Ciencias Aplicada

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.Centro de Investigación y Desarrollo en Ciencias Aplicada

Aplicación de la pirólisis rápida para el tratamiento de biomasa de desecho proveniente de La Plata y el gran La Plata

Se desarrollarán catalizadores ácidos a partir de la inmovilización de heteropoliácidos con estructura tipo Keggin en zirconia bajo la metodología de hidrólisis controlada de n-propóxido de zirconio con estructura porosa multimodal generada mediante la adición de formadores de macro y meso poros. Luego se les realizará una caracterización mediante técnicas que permitan identificar las propiedades texturales, fisicoquímicas, estabilidad térmica y de composición del sólido resultante.Centro de Investigación y Desarrollo en Ciencias Aplicada

Green catalytic synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes using recyclable mesoporous zirconia modified with tungstophosphoric acid

A simple and efficient procedure has been developed for the preparation of aryl-14H-dibenzo[a,j]xanthenes by a one-pot condensation of 2-naphthol and aryl aldehydes, in the presence of mesoporous zirconia modified with tungstophosphoric acid (ZrTPA60BT100), to be used as a heterogeneous catalyst in a solvent-free medium using conventional heating. The present approach offers the advantages of clean reaction, simple methodology, short reaction time, and high yield. The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions without appreciable loss of the catalytic activity.Centro de Investigación y Desarrollo en Ciencias Aplicada

Tungstophosphoric acid heterogenized onto NH₄ZSM5 as an efficient and recyclable catalyst for the photocatalytic degradation of dyes

Materials based on tungstophosphoric acid (TPA) immobilized on NH4ZSM5 zeolite were prepared by wet impregnation of the zeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and 30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, 31P MAS-NMR, TGA.-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (SBET) decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH4)3PW12O40. According to the Fourier transform infrared and 31P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW12O40]3- anion, which was partially transformed into the [P2W21O71]6- anion during the synthesis and drying steps. The thermal stability of the NH4ZSM5TPA materials was similar to that of their parent zeolites. Moreover, the samples with the highest TPA content exhibited band gap energy values similar to those reported for TiO2. The immobilization of TPA on NH4ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 °C. These can be reused at least three times without any significant decrease in degree of degradation.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Ciencias Aplicada

Green catalytic synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes using recyclable mesoporous zirconia modified with tungstophosphoric acid

A simple and efficient procedure has been developed for the preparation of aryl-14H-dibenzo[a,j]xanthenes by a one-pot condensation of 2-naphthol and aryl aldehydes, in the presence of mesoporous zirconia modified with tungstophosphoric acid (ZrTPA60BT100), to be used as a heterogeneous catalyst in a solvent-free medium using conventional heating. The present approach offers the advantages of clean reaction, simple methodology, short reaction time, and high yield. The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions without appreciable loss of the catalytic activity.Centro de Investigación y Desarrollo en Ciencias Aplicada

Tungstophosphoric acid heterogenized onto NH₄ZSM5 as an efficient and recyclable catalyst for the photocatalytic degradation of dyes

Materials based on tungstophosphoric acid (TPA) immobilized on NH4ZSM5 zeolite were prepared by wet impregnation of the zeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and 30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, 31P MAS-NMR, TGA.-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (SBET) decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH4)3PW12O40. According to the Fourier transform infrared and 31P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW12O40]3- anion, which was partially transformed into the [P2W21O71]6- anion during the synthesis and drying steps. The thermal stability of the NH4ZSM5TPA materials was similar to that of their parent zeolites. Moreover, the samples with the highest TPA content exhibited band gap energy values similar to those reported for TiO2. The immobilization of TPA on NH4ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 °C. These can be reused at least three times without any significant decrease in degree of degradation.Facultad de Ciencias ExactasCentro de Investigación y Desarrollo en Ciencias Aplicada

Nanoesferas mesoporosas de sílice modificadas con ácido tungstofosfórico

Se prepararon nanoesferas de sílice mesoporosa (MSN) en fase acuosa/orgánica usando el método de plantillas de micelas. Los materiales obtenidos presentaron una alta área superficial, distribución de poros (DTP) estrecha y un tamaño de esferas regulables. Se observó que la variación de la concentración de estireno (EST) llevó principalmente a una modificación del diámetro medio de poros, mientras que la variación de la concentración de octano (OCT) implicó un cambio del tamaño de partícula. La impregnación de las MSN con ácido tungstofosfórico (TPA) no condujo a variación de las características morfológicas de los materiales, observándose que el TPA se encuentra bien distribuido sobre la superficie del soporte y que se mantiene su estructura Keggin intacta. Esto conduce a sólidos con características ácidas muy fuertes, aptos para su empleo futuro como catalizadores en reacciones ácidas.Facultad de Ciencias Agrarias y Forestale

Síntesis de bajo impacto ambiental de moléculas análogas a monastrol y nifedipina a través de reacciones multicomponente empleando catalizadores compuestos de heteropoliácidos soportados en óxidos mesoporosos

En este trabajo se sintetizarán catalizadores de ácido tungstofosfórico (H3PW12O40) y tungstosilísico (H4SiW12O40) inmovilizados en matrices de zirconia-sílice. La caracterización de estos materiales se llevará a cabo mediante técnicas de difracción de rayos X, microscopía electrónica de transmisión y barrido, espectroscopía fotoelectrónica de rayos X, IR y RMN, fisisorción de N2, TGA, DSC y titulación potenciométrica.Centro de Investigación y Desarrollo en Ciencias Aplicada

Síntesis de heterociclos mediante nanoparticulas de sílice mesoporosa modificadas con ácido tungstofosforico

Los heterociclos contienen N, O u otros átomos en sus anillos cíclicos carbonados. Estos compuestos están presentes en la mayoría de productos naturales bioactivos, drogas sintéticas, ciencia de los materiales, entre otras. Las aminas heterocíclicas son sustancias en las que el nitrógeno se encuentra como parte de un anillo, son muy comunes y tienen muchas propiedades biológicas importantes.Centro de Investigación y Desarrollo en Ciencias Aplicada