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- On the influence of imidazolium ionic liquids on cellulose derived polymersPublication . Paiva, Tiago; Echeverria Zabala, Coro; Godinho, Maria Helena; Almeida, Pedro L.; Corvo, Marta C.The demand for better cellulose solvents has driven the search for new and improved materials to enable the processing of this polysaccharide. Ionic liquids have been debated for a long time as interesting alternatives, but the molecular details on the solubilization mechanism have been a matter of controversy. Herein, for the first time, the structure and dynamics of hydroxypropylcellulose (HPC) liquid crystal solutions were probed in the presence of imidazolium ionic liquids (ILs), conjugating rheological measurements with magnetic resonance spectroscopy. This study provides a characterization of the solutions macroscopic behaviour, where the liquid crystalline (LC) properties were maintained. Using ILs with different side chain lengths, the influence of the hydrophobic IL domain in the solvation abilities of ILs towards a cellulose derived polymer was accessed, providing experimental evidence on these interactions.
- Tuning the 1H NMR paramagnetic relaxation enhancement and local order of [Aliquat]+-based systems mixed with DMSOPublication . Cordeiro, Rui; Beira, Maria; Cruz, Carlos; Figueirinhas, João; Corvo, Marta C.; Almeida, Pedro L.; Rosatella, Andreia; Mateus Afonso, Carlos Alberto; Daniel, Carla; Sebastião, PedroUnderstanding the behavior of a chemical compound at a molecular level is fundamental, not only to explain its macroscopic properties, but also to enable the control and optimization of these properties. The present work aims to characterize a set of systems based on the ionic liquids [Aliquat][Cl] and [Aliquat][FeCl4] and on mixtures of these with different concentrations of DMSO by means of H-1 NMR relaxometry, diffusometry and X-ray diffractometry. Without DMSO, the compounds reveal locally ordered domains, which are large enough to induce order fluctuation as a significant relaxation pathway, and present paramagnetic relaxation enhancement for the [Aliquat][Cl] and [Aliquat][FeCl4] mixture. The addition of DMSO provides a way of tuning both the local order of these systems and the relaxation enhancement produced by the tetrachloroferrate anion. Very small DMSO volume concentrations (at least up to 1%) lead to enhanced paramagnetic relaxation without compromising the locally ordered domains. Larger DMSO concentrations gradually destroy these domains and reduce the effect of paramagnetic relaxation, while solvating the ions present in the mixtures. The paramagnetic relaxation was explained as a correlated combination of inner and outer-sphere mechanisms, in line with the size and structure differences between cation and anion. This study presents a robust method of characterizing paramagnetic ionic systems and obtaining a consistent analysis for a large set of samples having different co-solvent concentrations.
- Desulfurization process conciliating heterogeneous oxidation and liquid extraction: Organic solvent or centrifugation/water?Publication . Ribeiro, Susana O.; Nogueira, Lucie S.; Gago, Sandra; Almeida, Pedro L.; Corvo, Marta C.; De Castro, Baltazar; Granadeiro, Carlos; Balula, SaleteThe present work presents a strategic oxidative desulfurization system able to efficiently operate under sustainable conditions, i.e. using an eco-friendly oxidant and without the need of extractive organic solvents. The catalytic performance of Eu(PW11O39)2@aptesSBA-15 was evaluated for the oxidative desulfurization of a multicomponent model diesel using a solvent-free or biphasic systems. The results reveal its remarkable desulfurization performance achieving complete desulfurization after just 2 h of reaction. Moreover, the composite has shown a high recycling ability without loss of catalytic activity for ten consecutive ODS cycles. Interestingly, under solvent-free conditions it was possible to maintain the desulfurization efficiency of the biphasic system while being able to avoid the use of harmful organic solvents. In this case, a successful extraction of oxidized sulfur compounds was found conciliating centrifugation and water as extraction solvent. Therefore, this work reports an important step towards the development of novel eco-sustainable desulfurization systems with high industrial interest.
- Designing silica xerogels containing RTIL for CO2 capture and CO2/CH4 separation: Influence of ILs anion, cation and cation side alkyl chain length and ramificationPublication . Dos Santos, Leonardo; Bernard, Franciele L.; Polesso, Barbara B.; Pinto, Ingrid S.; Frankenberg, Claudio C.; Corvo, Marta C.; Almeida, Pedro L.; Cabrita, Eurico J; Einloft, SandraCO2 separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO2 capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO2 sorption, reusability and CO2/CH4 selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO2 capture processes including higher CO2 sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO2 over CH4. The best performance was obtained by SX- [bmim] [TF2N] (223.4 mg CO2/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF2N] showed higher CO2 sorption capacity as compared to other reported sorbents. CO2 sorption and CO2/CH4 selectivity results were submitted to an analysis of variance and the means compared using Tukey's test (5%).
- H-1 NMR relaxometry and diffusometry study of magnetic and nonmagnetic ionic liquid-based solutions: cosolvent and temperature effectsPublication . Beira, Maria; Daniel, Carla; Almeida, Pedro L.; Corvo, Marta C.; Rosatella, Andreia; Afonso, Carlos A. M.; Sebastião, PedroIn this work, H-1 NMR relaxometry and diffusometry as well as viscometry experiments were carried out as a means to study the molecular dynamics of magnetic and nonmagnetic ionic liquid-based systems. In order to evaluate the effect of a cosolvent on the superparamagnetic properties observed for Aliquat-iron-based magnetic ionic liquids, mixtures comprising different concentrations, 1% and 10% (v/v), of DMSO-d6 were prepared and studied. The results for both magnetic and nonmagnetic systems were consistently analyzed an suggest that, when at low concentrations, DMSO-d6 promotes more structured ionic arrangements, thus enhancing these superparamagnetic properties. Furthermore, the analysis of temperature and water concentration effects allowed to conclude that neither one of these variables significantly affected the superparamagnetic properties of the studied magnetic ionic liquids.
- Efficient heterogeneous polyoxometalate-hybrid catalysts for the oxidative desulfurization of fuelsPublication . Mirante, Fátima; Dias, Luís; Silva, Mariana; Ribeiro, Susana; Corvo, Marta C.; De Castro, Baltazar; Granadeiro, Carlos; Balula, SaleteThe heterogenization of the highly active monovacant polyoxotungstate ([PW11O39](7-), abbreviated as PW11) was achieved by preparing the corresponding long chain quaternary ammonium salt (ODA(7)PW(11), ODA = CH3(CH2)(17)(CH3)(3)N). The complete cation exchange confers total heterogeneity to the monovacant catalyst while keeping its oxidative catalytic activity. In fact, the heterogeneous catalyst allowed for the complete desulfurization of a multicomponent model diesel (2000 ppm S) after 40 min of reaction, conciliating extraction (using BMIMPF6 solvent) and oxidation (ECODS process using H2O2 oxidant). The heterogeneous catalyst has shown a superior desulfurization performance when compared with the homogeneous quaternary ammonium TBAPW(11) catalyst (TBA = (C4H9)(4) N). Both hybrid catalysts have been successfully reused in consecutive ECODS cycles. Additionally, the long carbon chain cations provide a protective environment around the polyoxometalate allowing for ODA(7)PW(11) to retain its heterogeneity and structure after the ECODS process.
- Molecular order and dynamics of water in hybrid cellulose acetate-silica asymmetric membranesPublication . Beira, Maria Jardim; Condesso, Miguel; Pereira Da Silva, Miguel; Cosme, Pedro; Almeida, Pedro L.; Corvo, Marta C.; Sebastião, Pedro J.; Figueirinhas, João; De Pinho, Maria NorbertaIn this work 2H NMR spectroscopy and 1H NMR relaxometry and diffusometry were used to characterise water order and dynamics in cellulose acetate/silica asymmetric membranes. Two hydrated membranes were characterised allowing the identification of extra ordering of the water molecules and the presence in each membrane of up to two spectral components with different degrees of order and different T1 values. The mechanism behind this order increase was ascribed to the rapid exchange of the water molecules between the pore walls and its interior. T1 relaxometry dispersions allowed for the identification of the relevant mechanisms of pore-confined water motion, with rotations mediated by translational displacements (RMTD) as the dominant mechanism in the low frequency region. Using the RMTD low cut off frequency along with the in situ directly measured diffusion constant it was possible do determine characteristic lengths of correlated water motion in both membranes studied, which fall in ranges compatible with typical pore dimensions in similar membranes.
- Enhancement of CO2/N2 selectivity and CO2 uptake by tuning concentration and chemical structure of imidazolium-based ILs immobilized in mesoporous silicaPublication . Duczinski, Rafael; Polesso, Barbara B.; Bernard, Franciele L.; Ferrari, Henrique Z.; Almeida, Pedro L.; Corvo, Marta C.; Cabrita, Eurico J; Menezes, Sónia; Einloft, SandraImidazolium-based ionic liquids (ILs) with different cation alkyl chain ([i-C5mim] or [C4mim]) and inorganic anions ([Cl−], [Tf2N−], [PF6−] and [DCA−]) were synthesized and immobilized in commercial mesoporous silica. The synthesized supported ILs (SILs) were characterized using NMR, FTIR, TGA, BET, SEM and TEM. CO2 sorption capacity, reusability and CO2/N2 selectivity were assessed by the pressure-decay technique. The effects of IL concentration, cation and anion chemical structure in CO2 sorption capacity and CO2/N2 separation performance wereevaluated. Tests evidencedthatthe presenceofbranching on thecation alkylsidechainincreases CO2/N2 selectivity. The immobilization of the IL [i-C5TPIm][Cl] on mesoporous silica in different concentrations (50, 20, 10 and 5 %) revealed that lower IL concentration results in higher CO2 sorption capacity. Immobilization of ILs containing fluorinated anions at low concentrations in the mesoporous silica support may promote the improvement of the CO2/N2 selectivity without interfering on CO2 sorption capacity of the original support. CO2 sorption capacity value shown by sample SIL-5 % - [i-C5TPIm][Tf2N] (79.50 ± 0.70mg CO2 g-1) was close to the value obtained for the pristine mesoporous silica (81.70 ± 2.20mg CO2g-1) and the selectivity (4.30 ± 0.70) was more than twice of the one obtained for the support alone (2.32 ± 0.4). Recycle tests demonstrated that the ILs immobilized in mesoporous silica samples are stable, providing a new option to be used in CO2 capture processes.
- Waterborne polyurethane/Fe3O4-synthetic talc composites: synthesis, characterization, and magnetic propertiesPublication . Dos Santos, Leonardo; Ligabue, Rosane; Dumas, Angela; Le Roux, Christophe; Micoud, Pierre; Meunier, Jean-François; Martin, François; Corvo, Marta C.; Almeida, Pedro L.; Einloft, SandraNano-Fe3O4-synthetic talc gel was used as filler in the synthesis of waterborne polyurethane/Fe3O4-synthetic talc nanocomposites. This filler presents numerous edges (Si-O and Mg-O) and OH groups easily forming hydrogen bonds and polar interaction with water conferring hydrophilic character, consequently improving filler dispersion within a water-based matrix. Yet, the use of waterborne polyurethane (WPU) as matrix must be highlighted due to its environmentally friendly characteristics and low toxicity compared to solvent-based product. Fe3O4-synthetic talc-nanofillers were well dispersed into the polyurethane matrix even at high filler content as supported by XRD and TEM analyses. NMR indicates the interaction of filler OH groups with the matrix. For all nanocomposites, one can see a typical ferromagnetic behavior below Curie temperature (about 120 K) and a superparamagnetic behavior above this temperature. The use of Fe3O4-synthetic talc for obtaining magnetic nanocomposites resulted in improved materials with superior mechanical properties compared to solvent-based nanocomposites.
- Influence of chain length of prepolymers in permanent memory effect of PDLC assessed by solid-state NMRPublication . Mouquinho, Ana; Corvo, Marta C.; Almeida, Pedro L.; Feio, Gabriel; Sotomayor, JoaoThe relationship between linear chain (ethylene oxide units) length of polymerisable monomers with morphology, electro-optical properties and C-13 nuclear magnetic resonance (NMR) spectroscopy of the corresponding polymer-dispersed liquid crystal (PDLC) films was investigated. The preferred liquid crystal molecule alignment and permanent memory effect of PDLC were greatly influenced by the length of the molecular chain of prepolymers to be incorporated as a polymer matrix. By increasing the number of ethylene oxide in prepolymer chain and maintaining the number of functionalities (polymerisable groups in each monomer molecule), the permanent memory effect of PDLC increased, as proved by solid-state C-13 NMR spectroscopy.