Ione Maluf Baibich

The interaction of encapsulated pharmaceutical drugs with a silica matrix.

A series of seven drugs, namely, fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline, were encapsulated. The encapsulated systems were characterized using a series of complementary techniques: Fourier-transform infrared spectroscopy (FT-IR), diffusive reflectance spectroscopy in the UV-vis region (DRS) and X-ray photoelectron spectroscopy (XPS). According to the DRS spectra, most of the encapsulated systems showed a band shift of the maximum absorption when compared with the corresponding bare pharmaceutical. Additionally, after encapsulation, the drugs exhibited infrared band shifts toward higher wavenumbers, which in turn provided insight into potential sites for interaction with the silica framework. The amine group showed a band shift in the spectra of almost all the drugs (except nifedipine and tetracycline). This finding indicates the possibility of a hydrogen bonding interaction between the drug and the silica via electron donation from the amine group to the silica framework. XPS confirmed this interaction between the pharmaceuticals and the silica through the amine group. A correlation was observed between the textural characteristics of the solids and the spectroscopic data, suggesting that the amine groups from the pharmaceuticals were more perturbed upon encapsulation.

Infrared and Raman spectroscopic characterization of some organic substituted hybrid silicas

Nine hybrid silicas bearing the organic substituent groups methyl, octyl, octadecyl, vinyl, phenyl, mercaptopropyl, isocyanatopropyl, chloropropyl and glycidoxypropyl were synthesized by an acid-catalyzed, hydrolytic sol-gel process. The resulting solid materials were characterized by their absorbance and attenuated total reflection (ATR) IR and Raman spectra. The latter technique proved to be particularly useful in the identification of the organic moieties in the hybrid silicas. The effect of the presence of the organic groups on the silica networks was also investigated - there were increases observed in both the SiOSi bond angles and bond lengths. Moreover, deconvolution of the IR-active antisymmetric SiOSi stretching bands permitted detection of the four- and six-membered siloxane rings present in the silicas. There proved to be a greater number of four-membered rings on the surfaces of the particles. Both IR and Raman spectroscopy proved to be invaluable in the characterization of these hybrid materials.

Preparation and characterization of alumina supported Pd-W and Pd-Mo catalysts photogenerated from group VI metal carbonyls

Abstract Tungsten and molybdenum were introduced in γ-Al 2 O 3 and Pd/γ-Al 2 O 3 using metalcarbonyls [W(CO) 6 and Mo(CO) 6 ] photoactivation. DRIFTS FT-IR spectra of the surfaces prior to thermal decomposition reveal the presence of unstable metalsubcarbonyl species, in contrast with the ones found previously, when the photoactivation was performed in the presence of triphenylphosphine. The ν (CO) band intensities did not reflect the tungsten and molybdenum uptakes determined by AAS, the loadings being higher in the presence of palladium. After thermal treatment, the catalysts were further characterized by hydrogen chemisorption and FT-IR spectra of adsorbed CO and NO. The results showed that a reaction between the hexacarbonyls and the supported palladium particles takes place leading to bimetallic catalysts, with clear palladium–tungsten and palladium–molybdenum interactions. Pd + Mo ( CO ) 6 ⇒ uv Pd + Mo ( CO ) 6−x ⇒ Pd - Mo ( CO ) 6−x ⇒ uv Pd - Mo . Both group VI metals strongly modify the chemisorption properties of palladium, while molybdenum seems to be present in a reduced state in close association with palladium.

Evidências da formação de monocamada de óxido de alumínio sobre sílica, através de reações de enxerto

Aluminum oxide was dispersed on a commercial silica gel surface, using successive grafting reactions. The reaction products were characterized by N2 adsorption-desorption isotherms, scanning electron microscopy and infrared spectroscopy. The progressive incorporation of aluminum, up to 5.5% (w/w), does not produce agglomeration of alumina, since changes in the original pore size distribution of the silica matrix were not observed. The aluminum oxide covers homogeneously the silica surface.

Synthesis and characterization of SiO2–CrO3, SiO2–MoO3, and SiO2–WO3 mixed oxides produced using the non-hydrolytic sol–gel process

Silica-based mixed oxide xerogels, namely SiO2–CrO3, SiO2–MoO3, and SiO2–WO3, were prepared using the non-hydrolytic sol–gel process. The materials were synthesized using metal chloride:tetraethoxysilane (TEOS) molar ratios of 0.1:2; 0.2:2 and 0.4:2 for each metal chloride and 1:2 SiCl4:TEOS molar ratio. All of the xerogels containing Cr, Mo or W had considerably greater surface areas than that of SiO2. The small angle X-ray scattering experiments suggest that the surface roughness of the aggregates in SiO2–CrO3 is less than that of SiO2–MoO3 and SiO2–WO3. The morphological characteristics of the silica-based mixed oxide xerogels were not affected by the nature and amount of metal chloride employed in the synthesis. An irregular morphology was observed for SiO2–CrO3, SiO2–MoO3 and SiO2–WO3, but a lamellar structure was observed for SiO2. X-ray photoelectron spectroscopy analysis suggests that tungsten species were preferentially distributed on the outmost part of the grain. The resulting particle diameter was shown to be lower for the mixed oxides compared to that of bare silica. Furthermore, the presence of metals (Cr, Mo and W) on silica caused a decrease in the size of the particles as the atomic radii of these metals increased. According to the Fourier transform infrared spectroscopy and Raman, Cr, Mo and W were incorporated within the silica framework.

DECOMPOSIÇÃO CATALÍTICA DE ÓXIDOS DE NITROGÊNIO

Contaminant gases in the atmosphere constitute an important problem to be solved in the world. The NOx gases produced as a consequence of engine high temperatures are deleterious to environment and human health, as they promote acid rain and can act in the same way as freons in the destruction of the ozone layer in the stratosphere. In this review, three way and selective reduction catalysts for decomposition of these contaminant gases are described. Details about conditions and problems, such as catalyst poisoning, and the search for new catalysts are shown.

Preparation and characterization of W/γ-Al2O3 and Pd–W/γ-Al2O3 catalysts from organometallic precursors. The catalytic activity for NO decomposition

Abstract The photochemical reaction of W(CO)6 with triphenylphosphine (PPh3) in the presence of γ-Al2O3 and Pd/γ-Al2O3 has been used to prepare W/γ-Al2O3 and Pd–W/γ-Al2O3 catalysts. Adsorbed mono- and disubstituted W species have been identified by FTIR spectroscopy. There is evidence of the adsorption of W(CO)6−x Lx species on both the alumina and the Pd surface. After thermal decomposition and reduction at 573 K the catalysts have been characterized by FTIR spectroscopy of adsorbed NH3, CO and NO. The retention of W and P suppresses the Lewis acidity of the alumina support. On Pd–W/γ-Al2O3, the W is present in a partially reduced state in close association with Pd. This interaction modifies the chemisorptive properties of NO relative to those of the monometallic Pd and W catalysts. In line with these observations the Pd–W/γ-Al2O3 catalyst presents an enhanced activity for NO decomposition at 473 K.

Green synthesis of Pt and Ag nanoparticles and their use towards nitric oxide abatement

Pt and Ag nanoparticles (NPs) were synthesized by eco-friendly room-temperature chemical reduction routes based on trisodium citrate and L-ascorbic acid (for Pt NPs) and on gelatin and trisodium citrate (for Ag NPs). The as-prepared NPs were characterized by UV-visible absorption spectroscopy and transmission electron microscopy analyses, which confirmed the formation of sub-10 nm metal particles. Then, the colloidal solutions were used to obtain activated carbon-supported catalysts (metal/AC) for direct NO decomposition. X-ray photoelectron spectroscopy and x-ray diffraction measurements proved that the NPs hosted on the support surface were present in the metallic chemical state. In situ infrared absorption spectroscopy investigations during NO reduction catalytic reactions showed that the Pt/AC and Ag/AC catalysts were highly active at 373 K. At 573 K, we observed different behaviors for each catalyst. While Ag/AC performed similarly to the reaction at 373 K, Pt/AC was found to participate in a redox mechanism, where the catalysts active sites were oxidized by NO and reduced by carbon, thus emitting CO2 and enhancing its catalytic activity, an effect that we have also observed in carbon-supported Pd NPs.

Selective reduction of NOx by propylene over silver catalyst under oxidative conditions

Neste trabalho foram estudados catalisadores Ag/Al2O3 e Ag/Al2O3/Corderita, preparados por um metodo de impregnacao convencional, na reacao de reducao de NO utilizando propeno como agente redutor. Os catalisadores foram caracterizados por reducao a temperatura programada (RTP), quimissorcao de oxigenio e area superficial, pelo metodo BET. A atividade catalitica foi determinada utilizando uma mistura reacional contendo 100 ppm de NO, 250 ppm de C3H6 e 2% de oxigenio e uma velocidade espacial de 100000 h-1. Os produtos da reacao foram estudados por FTIR. Os resultados dos testes cataliticos mostraram 56% de conversao de NO para o catalisador 2,22%Ag/Al2O3 a 723 K. Os catalisadores de cordierita apresentaram um comportamento semelhante, mas a temperatura de maxima conversao de NO deslocou-se para temperaturas menores.

Photogeneration and characterization of group 6 metal carbonyl derivatives on alumina

Abstract The photochemically-induced CO substitution reactions of [M (CO) 6 ] (M = Cr, Mo, W) have been investigated in the presence of triphenylphosphine (PPh 3 ) and γ-alumina. The metal loading was determined by Rutherford backscattering spectrometry (RBS) and the generated species were analysed by Fourier transform IR spectroscopy (FT-IR) and 13 C NMR spectroscopy. The metal loading on alumina surface was seen to increase with the irradiation time reaching 0.6, 0.8 and 3.4% for Cr, W and Mo, respectively. The ligand cone angle plays an important role in the case of Cr, where only the trans disubstituted species was found on the alumina surface. However, it is less important for the two other metals, where the cis compound was formed preferentially and the electronic cis -labilization factor seems more important. After grafting, only the disubstituted species was seen to remain on alumina evidencing a stronger interaction with the support than in the case of the monosubstituted and the hexacarbonyl compounds.