Repositório Institucional da Universidade de Aveiro
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Ceria-based substrates for CO2 separation membranes
No full textComposites based on Gd-doped ceria and alkaline carbonates were produced in different manners to identify key compositional and microstructural features determining their mixed oxide and carbonate-ion conductivity. Co-firing of fine powder precursors yielded composites with delicate ceramic skeletons. After impregnation with alkaline carbonates, pre-sintered ceramic substrates produced from coarsened ceramic powders showed better densification and performance with respect to oxide-ion conduction. Microstructural analysis combined with low temperature impedance data obtained with ceramic substrates and composites confirmed the potential of impedance spectroscopy to infer on the oxide phase contribution to charge transport. (C) 2013 Elsevier B.V. All rights reserved
Thermophysical properties of sulfonium- and ammonium-based ionic liquids
No full textExperimental data for the density, viscosity, refractive index, and surface tension of four sulfonium- and ammonium-based ionic liquids (ILs) with the common bis(trifluoromethylsulfonyl)imide anion were measured in the temperature range between 288.15 and 353.15K and at atmospheric pressure. The ILs considered include butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, [N-4111][NTf2], tributyl-methylammonium bis(trifluoromethylsulfonyl)imide, [N-4441][NTf2], diethylmethylsulfonium bis(trifluoromethylsulfonyl)imide, [S-221] [NTf2], and triethylsulfonium bis(trifluoromethylsulfonyl)imide, [S-222][NTf2]. Based on the gathered results and on data taken from literature, the impact of the cation isomerism and of the size of the aliphatic tails, as well as the effect resulting from the substitution of a nitrogen by a sulfur atom as the cation central atom, on the thermophysical properties of sulfonium- and ammonium-based Its is discussed here. Remarkably, more symmetric cations present a lower viscosity for the same, and sometimes even for higher, alkyl chain lengths at the cation. Additional derivative properties, such as the isobaric thermal expansion coefficient, the surface thermodynamic properties and the critical temperature for the investigated ILs were also estimated and are presented and discussed. (C) 2014 Elsevier B.V. All rights reserved
Multiwall Carbon Nanotubes / Porcelain Stoneware Composites: a view under the microscope
No full textSupercritical fluid extraction of vegetable matrices: Applications, trends and future perspectives of a convincing green technology
No full textAlong more than a decade, R\&D on supercritical fluid extraction (SFE) of vegetable matrices has been increasingly reported in the literature. Aiming at portraying the current state of this field and its evolution in terms of raw materials, products, modes of operation, optimization, modeling techniques, and closeness to industrial application, a large compilation of almost 600 essays from 2000 to 2013 has been deeply analyzed in order to unveil those indicators and their trends. Furthermore, strengths and weaknesses are identified, and some remarks that may drive upcoming research are provided. Globally, more than 300 species are reported in the literature, with prevalence of the extraction of seeds (28% of works) and leaves (17%). The main families of extracted compounds, cosolvents and operating conditions adopted are critically examined, being possible to conclude that researchers investigate many times working regions far from the optimum due to practical limitations or absence of experimental optimization. Current phenomenological, statistical and semi-empirical approaches are reviewed, along with scale-up studies, and economic analysis. In the whole, the most comprehensive picture over SFE of vegetable matrices is provided in this review, highlighting pertinent aspects and opportunities that may further consolidate the convincing route of this technology for the next years. (C) 2014 Elsevier B.V. All rights reserved
Tris(pyrazolyl)methane molybdenum tricarbonyl complexes as catalyst precursors for olefin epoxidation
No full textThe molybdenum tricarbonyl complexes [Mo(CO)(3)(HC(3,5-Me(2)pz)(3))] (1) and [Mo(CO)(3)(HC(pz)(3))] (2) (HC(3,5-Me(2)pz)(3) = tris(3,5-dimethyl-1-pyrazolyl)methane, HC(pz)(3) = tris(1-pyrazolyl)methane) were obtained in good yields by the microwave-assisted reaction of Mo(CO)(6) with the respective organic ligand. Complete oxidative decarbonylation of 1 and 2 was achieved by reaction with excess tert-butylhydroperoxide (TBHP) in 1,2-dichloroethane at 55 degrees C. For complex 1, the (mu(2)-oxo)bis[dioxomolybdenum(VI)] hexamolybdate of composition [{MoO2(HC(3,5-Me(2)pz)(3))}(2)(mu(2)-O)][Mo6O19] (3) was obtained in good yield, and its structure was determined by single crystal X-ray diffraction. The compound (4) obtained by oxidative decarbonylation of 2 was not unambiguously identified, but may be chemically analogous to 3. Compounds 1-4 were examined for the first time as homogeneous (pre)catalysts for the epoxidation of olefins with TBHP, using different types of cosolvents at 55 degrees C. During the catalytic reactions 1 and 2 transform in situ into 3 and 4, respectively, and the latter two are fairly stable catalysts. Catalytic tests and characterization studies of the recovered catalysts were carried out in an attempt to understand the kinetic differences observed between the compounds prepared in situ during the catalytic reaction and those prepared prior to the catalytic reaction, from the same precursor complex. (c) 2013 Elsevier B.V. All rights reserved
Microwave assisted N-alkylation of amine functionalized crystal-like mesoporous phenylene-silica
No full textN-Alkylation reaction of amine functionalized phenylene moieties in crystal-like mesoporous silica is successfully achieved with about 87% of conversion in two reaction cycles. A potassium iodide catalyzed method commonly used for the selective N-monoalkylation of aniline is adapted and optimized to the N-monoalkylation reactions of the amine functionalized periodic mesoporous phenylene-silica (NH2-PMO) under microwave irradiation with preservation of the ordered mesostructure and of the crystal-like molecular scale periodicity of the material. This functionalization opens an avenue for the preparation of new materials with different amino-alkyl groups specially designed for a desired application, namely on the adsorption or catalytic fields
Bioprospecting for lipophilic-like components of five Phaeophyta macroalgae from the Portuguese coast
No full textLipophilic compounds present in dichloromethane extracts of five brown macroalgae from the Portuguese coast were analyzed by gas chromatography-mass spectrometry (GC-MS). Their dicarboxylic acids, long-chain aliphatic alcohols, and monoglyceride profile are reported for the first time. Additionally, other new compounds were also first reported: 24-methylene-cholesterol in Himanthalia elongata, Laminaria ochroleuca, and Undaria pinnatifida; desmosterol and brassicasterol in H. elongata, L. ochroleuca, Sargassum muticum, and U. pinnatifida; fucosterol and campesterol in S. muticum; and cholest-5-en-3-ol-(3 beta)-3-phenyl-2-propenoate in Cystoseira tamariscifolia. Brown macroalgae dichloromethane extracts are mainly composed of fatty acids (463.4-3089.0 mg kg(-1) of dry material) and sterols (75.5-442.7 mg kg(-1) of dry material). High amounts of polyunsaturated fatty acids were found, with the omega-6/omega-3 ratios of all species lower than 3. Cystoseira tamariscifolia, H. elongata, and S. muticum showed to be also promising sources of fucosterol. These results seem to uphold the incorporation of these macroalgae in a more balanced diet, as well as their use in the nutraceutical industry, as long as they are coupled with sustainable management of these natural resources
Pyrazolyl Pd(II) complexes containing triphenylphosphine: Synthesis and antimycobacterial activity
No full textComplexes of the type trans-[PdCl2(HL)(PPh3)], where HL = pyrazole (1); 3,5-dimethylpyrazole (2); 4-nitropyrazole (3); 4-iodopyrazole (4) and PPh3 = triphenylphosphine, were synthesized and characterized by elemental analyses, infrared and H-1 NMR spectroscopies. Single-crystal X-ray diffraction determination on 3.0.9 CHCl3 and 4 showed that the coordination geometry around Pd(II) is nearly square-planar, with the chloro ligands in a trans configuration. In vitro antimycobacterial evaluation demonstrated that compound 4 displayed a minimum inhibitory concentration (MIC) of 7.61 +/- 2.18 mu M, being superior to the values observed for some commonly used antituberculosis drugs and other metal-based complexes. (C) 2015 Elsevier Ltd. All rights reserved
Ionic liquid recovery alternatives in ionic liquid-based three-phase partitioning (ILTPP)
No full textIonic liquid-based three-phase partitioning (ILTPP) is a promising technique to recover high-added value proteins at the liquid-liquid interface. Its economic and environmental performance highly depends on the net ionic liquid consumption. Alternatives to maximize the fraction of ionic liquid that can be recycled are studied. It is demonstrated that the addition of extra salt, previously proposed in literature, has a very limited effect on ionic liquid recovery for relatively high protein concentrations in the feed stream, and that it may even lead to an increase of the ionic liquid losses under certain conditions. However, small additions of salt are shown to be effective and profitable from an economic point of view. Vacuum evaporation is shown to allow for the complete ionic liquid and salt recovery, reinforcing the sustainability and viability of ILTPP processes. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 3577-3586, 201
REVIEW ON RECENT ADVANCES IN ENVIRONMENTAL REMEDIATION AND RELATED TOXICITY OF ENGINEERED NANOPARTICLES
No full textProduction and utilization of engineered nanoparticles (ENPs), which are smart materials with ability of sensing and destroying chemical contaminants, is growing rapidly. However, these materials seem to have some ecological and health adverse effects. Hence, the main goal of this review study is to give a brief description about the recent developments of the commercial available engineered nano particles in the environmental remediation and also to note the current state of findings about the toxic effects of such advanced materials. The key references revealed the potential in vitro and/or in vivo toxic effects of some ENPs which are commonly used in environmental remediation. However, with respect to highly potential physicochemical and biochemical properties of ENPs, the studies which have been carried out till now are not ample to obtain satisfactory exposure data for both human beings and the environment. Therefore, more surveys should be done in this field to fill the gap of high quality data and to develop new engineered nanoparticles with minimum toxicity