Repositório Institucional da Universidade de Aveiro
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Accurate Model for Predicting Adsorption of Olefins and Paraffins on MOFs with Open Metal Sites
No full textMetal-organic frameworks (MOFs) have shown tremendous potential for challenging gas separation applications, an example of which is the separation of olefins from paraffins. Some of the most promising MOFs show enhanced selectivity for the olefins due to the presence of coordinatively unsaturated metal sites, but accurate predictive models for such systems are still lacking. In this paper, we present results of a combined experimental and theoretical study on adsorption of propane, propylene, ethane, and ethylene in CuBTC, a MOF with open metal sites. We first propose a simple procedure to correct for impurities present in real materials, which in most cases makes experimental data from different sources consistent with each other and with molecular simulation results. By applying a novel molecular modeling approach based on a combination of quantum mechanical density functional theory and classical grand canonical Monte Carlo simulations, we are able to achieve excellent predictions of olefin adsorption, in much better agreement with experiment than traditional, mostly empirical, molecular models. Such an improvement in predictive ability relies on a correct representation of the attractive energy of the unsaturated metal for the carboncarbon double bond present in alkenes. This approach has the potential to be generally applicable to other gas separations that involve specific coordination-type bonds between adsorbates and adsorbents
Synthesis, characterizations and structure of orthometallated Pt(II) and Pt(IV) complexes: Oxidative addition to C,N,N,O coordinated Pt(II) complexes
No full textReactions of 2-(arylazo)-1-N-salicylidene phenylamine, H2L, 1, [H represents the dissociable protons upon complexation], with K2PtCl4 afforded orthometallated complexes of composition [Pt(L)], 2 where the Pt(II) is coordinated by the tetradentate (C,N,N,O) ligand, L2-. Reaction of the precursor complex [Pt(L)] with I-2 afforded octahedral complexes of composition [PtI2(L)], 3. All the complexes were characterized unequivocally. X-ray crystal structure of [Pt(L-1)] and [Pt I-2(L-1)] have been determined. (C) 2014 Published by Elsevier Ltd
A biocompatible hybrid material with simultaneous calcium and strontium release capability for bone tissue repair
No full textThe increasing interest in the effect of strontium in bone tissue repair has promoted the development of bioactive materials with strontium release capability. According to literature, hybrid materials based on the system PDMS-SiO2 have been considered a plausible alternative as they present a mechanical behavior similar to the one of the human bone. The main purpose of this study was to obtain a biocompatible hybrid material with simultaneous calcium and strontium release capability. A hybrid material, in the system PDMS-SiO2-CaO-SrO, was prepared with the incorporation of 0.05 mol of titanium per mol of SiO2. Calcium and strontium were added using the respective acetates as sources, following a sol-gel technique previously developed by the present authors. The obtained samples were characterized by FT-IR, solid-state NMR, and SAXS, and surface roughness was analyzed by 3D optical profilometry. In vitro studies were performed by immersion of the samples in Kokubo's SBF for different periods of time, in order to determine the bioactive potential of these hybrids. Surfaces of the immersed samples were observed by SEM, EDS and PIXE, showing the formation of calcium phosphate precipitates. Supernatants were analyzed by ICP, revealing the capability of the material to simultaneously fix phosphorus ions and to release calcium and strontium, in a concentration range within the values reported as suitable for the induction of the bone tissue repair. The material demonstrated to be cytocompatible when tested with MG63 osteoblastic cells, exhibiting an inductive effect on cell proliferation and alkaline phosphatase activity. (C) 2016 Elsevier B.V. All rights reserved
Visible-Light Excited Luminescent Thermometer Based on Single Lanthanide Organic Frameworks
No full textIsostructural lanthanide organic frameworks (Me2NH2)(3)[Ln(3)(FDC)(4)(NO3)(4)]center dot 4H(2)O (Ln = Eu (1), Gd (2), Tb (3), H2FDC = 9-fluorenone-2,7-dicarboxylic acid), synthesized under solvothermal conditions, feature a Ln-O-C rod-packing 3D framework. Time-resolved luminescence studies show that in 1 the energy difference between the H2FDC triplet excited state (17794 cm(-1)) and the D-5(0) Eu3+ level (17241 cm(-1)) is small enough to allow a strong thermally activated ion-to-ligand back energy transfer. Whereas the emission of the ligand is essentially constant the D-5(0)-> F-7(2) intensity is quenched when the temperature increases from 12 to 320 K, rendering 1 the first single-lanthanide organic framework ratiometric luminescent thermometer based on ion-to-ligand back energy transfer. More importantly, this material is also the first example of a metal organic framework thermometer operative over a wide temperature range including the physiological (12-320 K), upon excitation with visible light (450 nm)
High pressure density and solubility for the CO2+1-ethyl-3-methylimidazolium ethylsulfate system
No full textThe solubility and density of the CO2 + 1-ethyl-3-methylimidazolium ethylsulfate system were investigated. The carbon dioxide solubility in the IL was measured in the temperature range 273-413 K, for pressure up to 5 MPa and CO2 mole fractions ranging from 0.02 to 0.5 using the isochoric method, while the system density was carried out at temperatures ranging from 278.15 K to 398.15 K, pressures from 10 MPa to 120 MPa and 0.2, 0.4, 0.7 and 0.8 CO2 mole fractions. Similar to what was previously observed for phosphonate-based ILs, the ionic liquid high polarity leads to positive deviations from ideality resulting from unfavorable interactions with the CO2. The results from the density and solubility derived properties show that the system presents important negative excess molar volumes, over the whole range of compositions and temperatures, and a negative entropy of solvation that suggests an increase in ordering of the solvent molecules surrounding the solute. The observed negative excess molar volumes result from the large difference between the molecular volumes of the species involved, with the small carbon dioxide molecules occupying the empty spaces between the larger IL ions, supporting the notion that the carbon dioxide, upon dissolution, occupies essentially the bulk free volume since the IL does not significantly expand upon gas absorption. These results portray ionic liquids as a porous media, like a soft sponge, with a huge free volume in which large amounts of carbon dioxide are able to accommodate during the dissolution process. (C) 2014 Elsevier B.V. All rights reserved
Influence of Mg doping on dielectric and optical properties of ZnO nano-plates prepared by wet chemical method
No full textMg-doped ZnO nano-plates were successfully prepared by the low cost wet chemical method. X-ray diffraction (XRD) pattern revealed a polycrystalline pure hexagonal wurtzite structure. Scanning electron microscopy (SEM) was used to study the morphology of the synthesized samples. Further, Energy-dispersive X-ray spectroscopy (EDS) measurement confirmed the presence of Mg elements in the ZnO matrix. The UV-visible reflectance spectroscopy was applied to study the effect of dopant on band gap of pure ZnO. The result showed a slight decrease in the band gap with Mg doping. In addition, the dielectric analyses of the obtained samples were done in a wide frequency range and electronic properties of the pure and doped samples were analyzed using various theoretical models. These results suggested that the Mg-doped ZnO nano-plates have potential applications in the optoelectronic devices. The results were analyzed in derail. (C) 2014 Elsevier Ltd. All rights reserved
Solid phase microextraction method for characterizing the organic fraction of an industrial brine stream
No full textThe manufacturing process of DOW Chemical Company in Portugal produces a brine stream containing organic contaminants. For recovering the sodium chloride by-product, it is necessary to fully characterize this brine stream. With this purpose, a direct immersion-solid phase microextraction-gas chromatograph (SPME-GC) analytical method was successfully optimized and implemented, being possible to quantify accurately, with reproducibility, the organic fraction at ppb levels. The effects of salt content, extraction time, temperature, and pH were investigated, and the SPME experimental conditions optimized. For the poly(dimethylsyloxane-co-divinylbenzene) fiber utilized, the resulting parameters were: 25% (wt.) of NaCl, 30min, 20 degrees C, and pH 11. The fiber desorption was performed at 250 degrees C for 15min. The calibration curves of the representative organics of the brine (benzenamine, cyclohexanamine, 2-methylbenzenamine, N-cyclohexylcyclohexanamine, cyclohexyl alcohol, nitrobenzene, cyclohexanone, and 4-phenylcyclohexylamine) presented good correlation coefficients (0.991R(2)0.997). The detection limits of the method were determined for each species for the optimized analytical conditions; the detection limits vary from 0.21 to 3.22ppb, respectively for N-cyclohexylcyclohexanamine and benzenamine, the, precision ranged from 4.4 to 8.7% RSD and the validation criteria was obeyed for all analytes. The industrial brine stream was then characterized during several days to register the concentration history of contaminants. Independently of the stream composition fluctuations, the SPME methodology developed and optimized in this work was able to assess accurately their concentrations at ppb levels
Statistical analysis of grain size distributions in pressure-assisted BaLa4Ti4O15 microstructures
No full text[No abstract available
Enhanced Photocatalytic Activity of MIL-125 by Post-Synthetic Modification with Cr-III and Ag Nanoparticles
No full textNH2-MIL-125, [Ti8O8(OH)(4)(bdc-NH2)(6)] (bdc(2-) = 1,4-benzene dicarboxylate) is a highly porous metal-organic framework (MOF) that has a band gap lying within the ultraviolet region at about 2.6 eV. The band gap may be reduced by a suitable post-synthetic modification of the nanochannels using conventional organic chemistry methods. Here, it is shown that the photocatalytic activity of NH2-MIL-125 in the degradation of methylene blue under visible light is remarkably augmented by post-synthetic modification with acetylacetone followed by Cr-III complexation. The latter metal ion extends the absorption from the ultraviolet to the visible light region (band gap 2.21 eV). The photogenerated holes migrate from the MOF's valence band to the Cr-III valence band, promoting the separation of holes and electrons and increasing the recombination time. Moreover, it is shown that the MOF's photocatalytic activity is also much improved by doping with Ag nanoparticles, formed in situ by the reduction of Ag+ with the acetylacetonate pendant groups (the resulting MOF band gap is 2.09 eV). Presumably, the Ag nanoparticles are able to accept the MOF's photogenerated electrons, thus avoiding electron-hole recombination. Both, the Cr-and Ag-bearing materials are stable under photocatalytic conditions. These findings open new avenues for improving the photocatalytic activity of MOFs
Interactions of bioactive molecules \& nanomaterials with Langmuir monolayers as cell membrane models
No full textLangmuir monolayers at the air/water interface have been used for decades to mimic cell membranes in attempts to determine the mechanisms behind the physiological action of biologically-relevant molecules. In this review, we analyze the vast literature in the area, with the contents organized according to the type of molecules and materials, including peptides, proteins, polysaccharides, a variety of pharmaceuticals, and nanomaterials. The focus is placed on the correlation between the effects induced on the monolayers and the biological activity of the molecules and nanomaterials. Effects observed from these interactions can be coupling or adsorption and penetration of the molecules into the monolayer, which can be expanded, condensed or even disrupted. Changes in monolayer mechanical properties, for example, may be crucial for the biological activity. Whenever possible, we try to identify the forces prevailing in the interaction, which has been made possible with a combination of experimental techniques, including surface-specific spectroscopies, microscopies and rheological techniques, in addition to the traditional surface pressure and surface potential measurements. Overall, the mechanisms are governed by ionic electrostatic forces and hydrophobic interactions. Correlation may be straightforward, as in the cases of positively charged peptides and polymers whose antimicrobial activity is ascribed to electrostatic attraction with the negatively charged microbial membranes. Also general is the importance of hydrophobic interactions for the penetration into the membrane, which can be required for the biological action of, for example, polysaccharides. In other cases, correlation between monolayer properties and the physiological activity cannot be established precisely, as the latter may depend on a multitude of parameters that have not been possible to simulate with a simplified model such as that of a Langmuir monolayer. For nanomaterials, the emphasis is in relating interaction with the monolayers and their possible toxicity. Owing to the relevance of electrostatic and hydrophobic interactions, the effects on monolayers (and indeed toxicity) are found to depend largely on the coating or functionalization of the nanomaterials. (C) 2015 Elsevier B.V. All rights reserved