Repositório Institucional da Universidade de Aveiro
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Hydrothermal synthesis of boehmite in cellular alumina monoliths for catalytic and separation applications
No full textFor the first time, controlled hydrothermal functionalization was performed in porous cellular alpha-Al2O3 ceramics, targeting potential separation and catalytic processes for sustainable chemistry applications. Growth of micro-nano hierarchical structures of boehmite (gamma-AlOOH) with high aspect ratio was assessed by SEM/EDS/XRD/FTIR. The pH and precursors concentration determine the growth mechanism and final functionalization level. The obtained results anticipate strategies for promoting formation of boehmite at the pores surfaces and tuning its morphology, including pre-treatments of the cellular matrix to increase the concentration of the surface defects and preliminary saturation of the pores with appropriate precursors to achieve uniform functionalization. Thus grown boehmite structures can be easily converted to gamma-Al2O3 by thermal treatment while retaining the former distribution and aspect ratio, opening new possibilities for preparation of gamma-Al2O3 supported catalysts. (C) 2015 Elsevier Ltd. All rights reserved
Zirconia-doped nanoparticles: organic coating, polymeric entrapment and application as dual-imaging agents
No full textZirconia nanoparticles doped with Eu3+, Tb3+ and Gd3+ ions have been synthesized following the benzyl alcohol route. The nanoparticles were coated with N-hydroxydodecanamide and encapsulated in PLGA-b-PEG-COOH nanomicelles. The magnetic and fluorescent properties of these hybrid nanocarriers were investigated, proving them to be potential dual-imaging contrast agents
Characterization of Biocatalysts Prepared with Thermomyces lanuginosus Lipase and Different Silica Precursors, Dried using Aerogel and Xerogel Techniques
No full textThe use of lipases in industrial processes can result in products with high levels of purity and at the same time reduce pollutant generation and improve both selectivity and yields. In this work, lipase from Thermomyces lanuginosus was immobilized using two different techniques. The first involves the hydrolysis/polycondensation of a silica precursor (tetramethoxysilane (TMOS)) at neutral pH and ambient temperature, and the second one uses tetraethoxysilane (TEOS) as the silica precursor, involving the hydrolysis and polycondensation of the alkoxide in appropriate solvents. After immobilization, the enzymatic preparations were dried using the aerogel and xerogel techniques and then characterized in terms of their hydrolytic activities using a titrimetric method with olive oil and by the formation of 2-phenylethyl acetate in a transesterification reaction. The morphological properties of the materials were characterized using scanning electron microscopy, measurements of the surface area and pore size and volume, thermogravimetric analysis, and exploratory differential calorimetry. The results of the work indicate that the use of different silica precursors (TEOS or TMOS) and different drying techniques (aerogel or xerogel) can significantly affect the properties of the resulting biocatalyst. Drying with supercritical CO2 provided higher enzymatic activities and pore sizes and was therefore preferable to drying, using the xerogel technique. Thermogravimetric analysis and differential scanning calorimetry analyses revealed differences in behavior between the two biocatalyst preparations due to the compounds present
Crystal structure, magnetic and dielectric behavior of h-LuMnxO3 +/-delta ceramics (0.95 <= x <= 1.04)
No full textLattice constants, magnetic properties and dielectric behavior of h-LuMnxO3 +/-delta solid solution (0.95 <= x <= 1.04) of bulk ceramic samples prepared by the solid state reaction method were studied to determine the role of stoichiometry changes on the crystalline structure and magneto-electric coupling. It is found that increasing of Mn content results in reduction of cell volume of h-LuMnxO3 +/-delta ceramics mostly due to shrinkage of a-axis length. The antiferromagnetic interactions of Mn3+ ions weaken with cell volume contraction. A weak ferromagnetic contribution appeared in all samples and extends up to the Neel temperature, T-N. Irreversibility in temperature dependent magnetic measurements already reported for stoichiometric compositions of hexagonal RMnO3 oxides appears for all h-LuMnxO3 +/-delta samples right below Neel ordering transition. An increase of magnetic coercive field and magnetization on cooling below T-N in samples is observed in field dependent magnetization and rises as x increases. In addition to the antiferromagnetic ordering transition at T-N, two anomalies of the temperature dependent magnetic susceptibility and dielectric constant are identified below T-N, centered at 69 K and 31 K respectively, being probably due to inhomogeneity of the crystalline structure inside ceramic grains. Changes of the dielectric constant at T-N can be attributed to magneto-electric coupling in the off-stoichiometric hexagonal LuMnxO3+delta lattice. The behavior of the dielectric relaxation follows a thermally activated mechanism with activation energy values characteristic of polaron hoping. (C) 2015 Elsevier B.V. All rights reserve
Synthesis of hexaphyrins and N-fused pentaphyrins bearing pyridin-4-ylsulfanyl groups
No full textIn recent years much attention has been devoted to expanded macrocyclic chemistry. Nevertheless, while several advancements were achieved in the synthesis of novel expanded porphyrin architectures, not much has been developed in the functionalization of these macrocycles. This report shows the selective replacement of the p-fluorine atoms of meso-pentakis(pentafluorophenyl) N-fused [22]pentaphyrin and meso-hexakis(pentafluorophenyl) [26]hexaphyrin with 4-mercaptopyridine moieties, thus increasing their potential as ligands for coordination chemistry and catalysis or electronic transfer applications striving new synthetic methodologies and a new set of specific applications for this type of compounds
Di-ureasil Hybrid Electrolytes Incorporating a New Proton Ionic Liquid
No full textThe protic ionic liquid (PIL) N-butylimidazolium trifluoromethanesulfonate ([BIm][TfO]) was obtained for the first time and incorporated into a sol-gel-derived di-ureasil matrix with a concentration of X=5, 10, and 30%, where X is the ratio of the mass of PIL per mass of poly(oxyethylene). Four years after their synthesis, the resulting quasi-anhydrous electrolytes remained amorphous, homogeneous, flexible, and thermally stable below 200 degrees C. SEM/EDS data revealed the presence of the PIL at the surface of the xerogels with X>5%, demonstrating that this type of morphological characterization is mandatory to avoid misleading ionic conductivity values. The highest ionic conductivity was produced in the washed sample with X=30% (3.5 x 10(-5) and 2.1 x 10(-3) Scm(-1) at 25 and 170 degrees C, respectively). The present family of electrolytes yielded higher conductivities than the N-ethylimidazolium trifluoromethane-sulfonate-based analogues introduced earlier by our group and may thus be considered as promising candidates for applications in fuel cells
Crystal Structure and Catalytic Behavior in Olefin Epoxidation of a One-Dimensional Tungsten Oxide/Bipyridine Hybrid
No full textThe tungsten oxide/2,2'-bipyridine hybrid material [WO3(2,2'-bpy)]center dot nH(2)O (n = 1-2) (1) has been prepared in near quantitative yield by the reaction of H2WO4, 2,2'-bpy, and H2O in the mole ratio of ca. 1:2:700 at 160 degrees C for 98 h in a rotating Teflon-lined digestion bomb. The solid-state structure of 1 was solved and refined through Rietveld analysis of high-resolution synchrotron X-ray diffraction data collected for the microcrystalline powder. The material, crystallizing in the orthorhombic space group Iba2, is composed of a one-dimensional organic-inorganic hybrid polymer, (1)(infinity)[WO3(2,2'-bpy)], topologically identical to that found in the previously reported anhydrous phases [MO3(2,2'-bpy)] (M = Mo, W). While in the latter the N,N'-chelated 2,2'-bpy ligands of adjacent corner-shared {MO4N2} octahedra are positioned on the same side of the 1D chain, in 1 the 2,2'-bpy ligands alternate above and below the chain. The catalytic behavior of compound 1 for the epoxidation of cis-cyclooctene was compared with that for several other tungsten- or molybdenum-based (pre)catalysts, including the hybrid polymer [MoO3(2,2'-bpy)]. While the latter exhibits superior performance when tert-butyl hydropercndde (TBHP) is used as the oxidant, compound 1 is superior when aqueous hydrogen peroxide is used, allowing near-quantitative conversion of the olefin to the epoxide. With H2O2, compounds 1 and [MoO3(2,2'-bpy)] act as sources of soluble active species, namely, the oxodiperoxo complex [MO(O-2)(2)(2,2'-bpy)], which is formed in situ. Compounds 1 and [WO(O-2)(2)(2,2'-bpy)] (2) were further tested in the epoxidation of cydododecene, trans-2-octene, 1-octene, (R)-limonene, and styrene. The structure of 2 was determined by single-crystal X-ray diffraction and found to be isotypical with the molybdenum analogue
Evaluating the toxicity of biomass derived platform chemicals
No full textFurans and their derivatives are well-known chemical building blocks common in plant biomass, and are abundantly used in food, medicines and industrial processes. As a bio-renewable resource, obtainable from the abundant and inexpensive lignocellulosic biomass, there is a growing interest in their study, physico-chemical characterization and application. Due to their biological origin, there is a presumption of low toxicity and high biodegradability for these compounds, which makes them \"green\" solvents, and thus potential substitutes of the classical organic solvents or oil derived commodities. Surprisingly, their ecotoxicity is poorly characterized. The few studies dealing with the toxicity of furans, namely towards animals, have presented contradictory results. In this work, the toxicity of eighteen furans and their derivatives was evaluated by the Microtox toxicity assay, using the marine bacterium Vibrio fischeri. Different levels of toxicity were observed among the furan derivatives investigated. The results obtained suggest that it might not be adequate to consider furans and their derivatives as \"green\" solvents as, in general, furans are more toxic than the classical solvents. Nevertheless, more data and studies across more trophic levels are necessary to fully understand the effects of furans on the environment as well as their biodegradability
Experimental measurements and modeling of CO2 solubility in sunflower, castor and rapeseed oils
No full textIn this work solubility measurements of CO2 in three vegetable oils, a high oleic sunflower oil (HOSO), a castor oil and a rapeseed oil, for mole fractions ranging from 0.32 to 0.93 in the temperature range 298-363 K and up to 75 MPa were performed. Moreover, the densities and viscosities of these oils are reported from 278.15 to 373.15 K at atmospheric pressure. These data were used to evaluate the predictive ability of the fragment based approach. Solubility data were modeled by means of the SRK EoS and predicted employing the Carvalho and Coutinho correlation. Global average deviations inferior to 6% in CO2 mole fraction composition were achieved with the SRK EoS and maximum percentage absolute average deviations of 13% in pressure were obtained using the Carvalho and Coutinho correlation. (C) 2013 Elsevier B.V. All rights reserved
SDS-PAGE and IR spectroscopy to evaluate modifications in the viral protein profile induced by a cationic porphyrinic photosensitizer
No full textReactive oxygen species can be responsible for microbial photodynamic inactivation due to its toxic effects, which include severe damage to proteins, lipids and nucleic acids. In this study, the photo-oxidative modifications of the proteins of a non-enveloped T4-like bacteriophage, induced by the cationic porphyrin 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide were evaluated. Two methods were used: sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and infrared spectroscopy. SDS-PAGE analysis showed that the phage protein profile was considerably altered after photodynamic treatment. Seven protein bands putatively corresponding to capsid and tail tube proteins were attenuated and two other were enhanced. Infrared spectroscopy confirmed the time-dependent alteration on the phage protein profile detected by SDS-PAGE, indicative of a response to oxidative damage. Infrared analysis showed to be a promising and rapid screening approach for the analysis of the modifications induced on viral proteins by photosensitization. In fact, one single infrared spectrum can highlight the changes induced to all viral molecular structures, overcoming the delays and complex protocols of the conventional methods, in a much simple and cost effective way