Repositório Institucional da Universidade de Aveiro
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Intercalation of a molybdenum(0)-tetracarbonyl-bipyridine complex in a layered double hydroxide
No full textA Zn,Al layered double hydroxide (LDH) intercalated by cis-[Mo(CO)(4)(bpdc)](2-) anions (bpdc - 2,2'-bipyridine-5,5'-dicarboxylate) has been prepared by ion exchange of a Zn,Al-NO3 LDH precursor, and characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), FT-IR, FT-Raman and UV-Vis spectroscopies. The ion exchange method gives rise to a highly organized intercalate with up to six (00l) basal reflections in the powder XRD pattern. The interlayer spacing of 18.0 angstrom indicates that the material contains a monolayer of guest anions positioned in such a way that the bpdc ligands are arranged with their longest dimension roughly perpendicular to the hydroxide layers of the host. Spectroscopic studies confirm the presence of structurally intact cis-[Mo(CO)(4)(bpdc)](2-) anions in the freshly prepared material, while also showing that the guest anions undergo slow decarbonylation over a period of several days, which is accelerated upon exposure of the material to light and air. The oxidative decarbonylation can be performed rapidly by reaction of the LDH containing intercalated tetracarbonyl complexes with tert-butylhydroperoxide, leading to intercalated molybdenum oxide/bipyridine species, which may be polymeric species of the type [MoO3(bpdc)](2-). Catalytic tests for the epoxidation of olefins and the oxidative dehydrogenation of alcohols were carried out for this material. (C) 2013 Elsevier B.V. All rights reserved
Fast detection of nitroaromatics using phosphonate pyrene motifs as dual chemosensors
No full textA new class of dual fluorescent chemosensors for nitroaromatic compounds (NACs) based on phosphonated pyrene derivatives is reported, showing high selectivity towards trinitrotoluene (TNT). The strong intermolecular interactions (pi-pi stacking and hydrogen bonding) allow high fluorescence quenching with visual detection in short response times
Development of bilayer glass-ceramic SOFC sealants via optimizing the chemical composition of glasses-a review
No full textGlasses and glass-ceramics (GCs), in particular alkaline-earth alumino silicate-based compositions, are becoming the most common sealing materials for gas-tight sealing applications in solid oxide fuel cells (SOFCs). The present review aims at reporting the systematic procedures put forward developing a novel concept of diopside-based bilayer GC seal, which contains a rigid GC and a self-healing (SH) GC. The concept behind the bilayer GCs is (i) a small gradient in the coefficient of thermal expansion (CTE) will lead to lower thermal expansion mismatch between the sealing layers and other SOFC components, thus providing enhanced mechanical reliability for the stack; and (ii) cracks produced due to minor thermal stresses in the rigid GC layer can be healed by the SH GC layer due to sufficient amorphous content. In general, at high temperature, highly crystallized glass behaves as a rigid glass. On the other hand, due to low viscosity behavior, partially crystallized glass provides a SH behavior. Various glasses in the field of diopside crystalline materials have been systematically designed by varying the chemical composition of glass to achieve desired combination of functional properties for the rigid and SH GC layers. The glass Sr-0.3 where Sr replaced 30 % of Ca was revealed as a highly reliable rigid GC seal for high-temperature electrochemical applications. On the other hand, SH features have been achieved in 30 % Sr-containing diopside-based glass with Gd2O3 for MgO + SiO2 substitution (denoted as Gd-0.3). These GCs exhibit similar thermal properties and excellent thermal stability along a period of 1000 h, while differing in their amorphous fractions, and revealed excellent thermal stability along a period of 1000 h. The bilayered GC synthesized from Sr-0.3 and Gd-0.3 showed good wetting and bonding ability to the SOFC metallic Crofer22APU components. The results revealed superior performance for the newly proposed bilayer GCs in comparison to single-layer sealants
Generating Ionic Liquids from Ionic Solids: An Investigation of the Melting Behavior of Binary Mixtures of Ionic Liquids
No full textMixtures of ionic liquids (ILs) allow enlarging the plethora of the physical and chemical properties of these materials in addition to the well-known tunable character associated with pure compounds. It is shown here that mixtures also induce a significant decrease of the melting points of the mixture to values well below those of the original compounds allowing the tuning of the melting point of an ionic liquid mixture and the generation of novel ionic liquids from mesotherm salts. This work evaluates the melting behavior of mixtures of seven hexafluorophosphate-based compounds combined with imidazolium-, pyridinium-, pyrrolidinium-, piperidinium- ammonium-, or phosphonium-based cations. The solid-liquid equilibrium phase diagrams of nine of their binary mixtures were measured using optical microscopy and differential scanning calorimetry. The pure ILs' melting profile reveals the presence of polymorphs with highly energetic solid-solid transitions that are relevant for the evaluation of these systems. The phase diagrams reported here also allow an investigation on the nonideality of the mixtures of ionic liquids. A classical thermodynamic approach shows that while most of the mixtures investigated present an ideal liquid behavior, others show slight or even marked nonideal profiles. One particular system, [C(3)mpyr][PF6] (1-methyl-1-propylpyrrolidinium hexafluorophosphate) + [C(3)mpip][PF6] (1-methyl-1-propylpiperidinium hexafluorophosphate), displays a continuous solid solution as established by differential scanning calorimetry, powder X-ray diffraction, and crystallographic data being one of the few ionic liquid alloys ever reported
Rheological behaviour of cork-polymer composites for injection moulding
No full textThe incorporation of cork in synthetic polymers has become an effective approach to develop new sustainable materials. Cork-polypropylene composites (CPC) filled with three different cork granulometries were studied. Rheological analyses were performed to assess the processability of these CPC and a set of experiments was conducted keeping the same matrix/cork weight ratio, varying the cork granulometric distribution. The effect of three different cork granulometries, temperature and the effect of a coupling agent, polypropylene graft maleic anhydride (PPgMA), were analysed. All composites exhibited non-Newtonian, pseudoplastic behaviour. Related to neat PP, cork incorporation led to a viscosity increase. This increase is more significant in the CPC with the lowest powder cork granulometry used. On the other side, the addition of PPgMA resulted on a decrease of CPC viscosity. The experimental results were fitted to Cross-WLF Model through a viscosity master curve obtained by the time-temperature superposition principle (TTSP). This study showed that cork can be considered on the development of sustainable materials for injection moulding technology. (C) 2016 Elsevier Ltd. All rights reserved
Local bias induced ferroelectricity in manganites with competing charge and orbital order states
No full textPerovskite-type manganites, such as Pr1-xCaxMnO3, La1-xCaxMnO3 and La1-xSrxMnO3 solid solutions, are set forth as a case study of ferroelectricity formation mechanisms associated with the appearance of site- and bond- centered orbital ordering which breaks structural inversion symmetry. Even though the observation of macroscopic ferroelectricity may be hindered by the finite conductivity of manganites, polarization can still exist in nanoscale volumes. We use Piezoresponse Force Microscopy to probe local bias induced modifications of electrical and electromechanical properties at the manganite surface. Clear bias-induced piezocontrast and local hysteresis loops are observed for La0.89Sr0.11MnO3 and Pr0.60Ca0.40MnO3 compounds providing convincing evidence of the existence of locally induced polar states well above the transition temperature of the CO phase, while the reference samples without CO behavior show no ferroelectric-like response. Such coexistence of ferroelectricity and magnetism in manganites due to the charge ordering (CO) under locally applied electric field opens up a new pathway to expand the phase diagrams of such systems and to achieve spatially localized multiferroic effects with a potential to be used in a new generation of memory cells and data processing circuits
Hospital food waste and environmental and economic indicators - A Portuguese case study
No full textThis study presents a comprehensive characterization of plate waste (food served but not eaten) at an acute care hospital in Portugal and elaborates on possible waste reduction measures. Even though waste prevention is a priority in Europe, large amounts of food are still being wasted every day, with hospitals giving rise to two to three times more food waste than other foodservice sectors. For this work the plate waste arising at the ward level was audited during 8 weeks, covering almost 8000 meals, using a general hospital as case study. Weighing the food served to patients and that returned after the meal allowed calculating plate waste for the average meal, as well as for individual meal items. Comparison of food waste arising showed that differences exist among wards, with some generating more waste than others. On average each patient throws away 953 g of food each day, representing 35% of the food served. This equates to 8.7 thousand tonnes of food waste being thrown away each year at hospitals across Portugal. These tonnes of food transformed into waste represent economic losses and environmental impacts, being estimated that 16.4 thousand tonnes of CO2 (equivalent) and 35.3 million euros are the annual national indicators in Portugal. This means that 0.5% of the Portuguese National Health budget gets thrown away as food waste. Given the magnitude of the food problem five measures were suggested to reduce food waste, and their potential impact and ease of implementation were discussed. Even though food waste is unavoidable the results obtained in this work highlight the potential financial and environmental savings for Portuguese hospitals, providing a basis to establish future strategies to tackle food waste. (C) 2015 Elsevier Ltd. All rights reserved
Processing Effects on Properties of (Fe,Mg,Al)(3)O-4 Spinels as Potential Consumable Anodes for Pyroelectrolysis
No full textA promising concept of consumable anode materials for high-temperature pyroelectrolysis process, which is expected to overcome the environmental and economical impacts of classical extractive metallurgy, relies on substituted magnetite-based ferrospinels, presenting high electrical conductivity, appropriate refractoriness, and redox stability. The present work aims assessment of the processing effects on structural, redox, and electrical properties of Fe2.3Al0.2Mg0.5O4 spinel, prepared by conventional solid-state route (SSR) and laser floating zone (LFZ) method. The observed trends for high-temperature electrical conductivity behavior indicated that the electronic transport is only slightly affected by the preparation method, suggesting the minor effects from the grain boundaries. For scaled-up ferrospinel-based consumable anodes the impact of oxidation during thermal cycling on electrical properties and electrode integrity can be minimized even in air, by using relatively fast cooling/heating rates
Design of SrTiO3-Based Thermoelectrics by Tungsten Substitution
No full textAmong n-type oxide thermoelectrics, donor-substituted strontium titanates, prepared in highly reducing conditions, show a particularly attractive thermoelectric figure of merit. High electrical conductivity, combined with outstanding redox tolerance and perovskite-phase stability of these materials, also make them prospective candidates for solid oxide fuel cell (SOFC) anode components. This work represents a first attempt to process strontium titanate ceramics with significant W for Ti substitution and to assess their relevant defect chemistry-related aspects and electrical and thermal properties, seeking mainly highly performing oxide thermoelectrics. Combined XRD/XPS/SEM/EDS studies of SrTi1-xWxO3 +/-delta (x = 0.01-0.10), prepared by a conventional solid state route, demonstrated that the maximum solubility of tungsten corresponds to 3-5% mol, depending on firing conditions and other composition changes. Separation of tungsten-containing phases on a submicro- and nanoscale level and formation of core-shell microstructures were confirmed for x >= 0.06, suggesting possibilities for tuning the thermal and electrical conductivities. Titanium cations are substituted predominantly by W6+ and partially by W5+ . High electrical conductivity and the Seebeck coefficient resulted in a maximum power factor of similar to 0.5 mW x m(-1) x K-2 for SrTi0.99W0.01O3 +/-delta; maximum ZT values, observed in the case of x = 0.01-0.06, amounted to 0.18-0.24 at 1173-1273 K. Co-substitution in Sr(Ti,Nb,W)TiO3 +/-delta materials showed good prospects for boosting thermoelectric performance in titanates, predominantly by significant reduction of the thermal conductivity
Optical Properties of Hybrid Organic-Inorganic Materials and their Applications
No full textResearch on hybrid inorganic-organic materials has experienced an explosive growth since the 1980s, with the expansion of soft inorganic chemistry based processes. Indeed, mild synthetic conditions, low processing temperatures provided by \"chimie douce\" and the versatility of the colloidal state allow for the mixing of the organic and inorganic components at the nanometer scale in virtually any ratio to produce the so called hybrid materials. Today a high degree of control over both composition and nanostructure of these hybrids can be achieved allowing tunable structure-property relationships. This, in turn, makes it possible to tailor and fine-tune many properties (mechanical, optical, electronic, thermal, chemical.) in very broad ranges, and to design specific multifunctional systems for applications. In particular, the field of \"Hybrid-Optics\" has been very productive not only scientifically but also in terms of applications. Indeed, numerous optical devices based on hybrids are already in, or very close, to the market. This review describes most of the recent advances performed in this field. Emphasis will be given to luminescent, photochromic, NLO and plasmonic properties. As an outlook we show that the controlled coupling between plasmonics and luminescence is opening a land of opportunities in the field of \"Hybrid-Optics\"