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- Biodegradable polyesters reinforced with mesoporous silica particlesPublication . Campos, João M.; Ribeiro, M. R.; Deffieux, A.; Péruch, F.; Lourenço, J. P.; Cerrada, María L.In recent years, the development of mechanically reinforced nanocomposites based on biodegradable polyester matrices has gained a strong incentive due to their potential use as biomaterials and to growing worldwide environmental concerns.
- Hafnocene catalyst for polyethylene and its nanocomposites with SBA-15 by in situ polymerization: immobilization approaches, catalytic behavior and properties evaluationPublication . Ferreira, Ana E.; Cerrada, María L.; Pérez, Ernesto; Lorenzo, Vicente; Cramail, Henri; Lourenço, J. P.; Quijada, Raul; Ribeiro, M. RosárioA hafnocene catalyst combined with methylaluminoxane (MAO) has been used as catalytic complex for the preparation of a set of polyethylene homopolymers by in situ polymerization under homogenous conditions and of different nanocomposites with mesoporous SBA- 15 particles, the latter playing the dual role of catalyst support and nanofiller. Distinct immobilization approaches have been explored for obtainment of these nanocomposites. Moreover, catalytic features, thermal stability, melting and crystallization transitions and mechanical behavior have been evaluated for those materials.
- Structure analysis of the novel microporous aluminophosphate IST-1 using synchrotron powder diffraction data and HETCOR MAS NMRPublication . Jordá, J. L.; McCusker, L. B.; Baerlocher, C.; Morais, C. M.; Rocha, J.; Fernandez, C.; Borges, C.; Lourenço, J. P.; Ribeiro, M. F.; Gabelica, Z.A combination of advanced powder diffraction and NMR techniques have allowed the structure of the novel microporous aluminophosphate IST-1 (|(CH3NH2)4(CH3NHþ 3 )4(OH )4|½Al12P12O48 ) to be elucidated. The framework structure was determined in the non-centrosymmetric space group Pca21 (a ¼ 9:61523ð1Þ AA, b ¼ 8:67024ð1Þ AA, c ¼ 16:21957ð2Þ AA) from high-resolution synchrotron powder diffraction data using the program FOCUS. Extra framework species were then located on difference electron density maps. A hydroxyl group was found to bridge between two of the framework Al atoms, and one methylamine species, presumably protonated, could be located in the channels where it H-bonds to three framework oxygens. The most unusual feature of the structure is the second methylamine molecule, which bonds directly to a framework Al atom. The structure is entirely consistent with 31P and 27Al MAS NMR studies, which showed there to be three P (all 4-coordinate) and three Al (one 4-, one 5- and one 6-coordinate) sites, and with 13C MAS NMR, which showed there to be two different types of methylamine species in equal amounts. Assignment of the 31P, 27Al and 13C MAS NMR signals could be deduced from the crystallographic data,31P-27Al HETCOR spectra and ab initio calculations.
- Disproportionation of ethylbenzene over SAPO-40Publication . Lourenço, J. P.; Ribeiro, M. F.; Ramôa Ribeiro, F.; Rocha, J.; Gabelica, Z.SAPO-40 exhibits strong acid sites, which catalyse the reaction of disproportionation of ethylbenzene. The distribution of diethylbenzene isomers suggests a high void volume in the structure of this molecular sieve.
- Synthesis and characterization of new CoAPSO-40 and ZnAPSO-40 molecular sieves. Influence of the composition on the thermal and hydrothermal stability of AlPO4-40 -based materialsPublication . Lourenço, J. P.; Ribeiro, M. F.; Borges, C.; Rocha, J.; Onida, B.; Garrone, E.; Gabelica, Z.Highly crystalline CoAPSO-40 and ZnAPSO-40 have been synthesized and characterized by powder XRD, TG/ DSC, SEM, EDX, 27Al, 31P and 29Si solid-state NMR, di use re¯ectance UV±VIS spectroscopy, FT IR and catalytic tests using the m-xylene isomerization and n-heptane cracking as model reactions. The simultaneous incorporation of silicon and a divalent metal in the framework of the AFR structure results in the generation of Brùnsted acid sites similar to those found in SAPO-40 and MeAPO-40. The catalytic activity of the samples for acid catalyzed reactions is higher than that of SAPO-40 with a homogeneous framework silicon distribution. The framework incorporation of cobalt or zinc results in a decrease of the thermal and hydrothermal stability of the metal bearing AFR framework, when compared with AlPO4-40 and SAPO-40.
- MCM-41 as Nanofiller in Polyethylene Hybrid MaterialsPublication . Ribeiro, M. R.; Campos, João M.; Bento, A.; Lourenço, J. P.; Pérez, Ernesto; Cerrada, María L.Mesoporous MCM-41 exhibits a stable framework structure, well-defined nanopores and a large surface area. When combined with metallocene polymerisation catalyst, these mesoporous materials, provide a unique route for preparing polyolefin-based nanocomposites by in situ polymerisation.
- Self-reinforced hybrid polyethylene/MCM-41 nanocomposites: in-situ polymerisation and effect of MCM-41 content on rigidityPublication . Campos, João M.; Ribeiro, M. R.; Lourenço, J. P.; Pérez, Ernesto; Cerrada, María L.The synthesis of self-reinforced polyethylene-based materials prepared by in-situ polymerisation is described. The methodology developed uses MCM-41 mesoporous material in a triple role: as catalyst carrier for ethylene polymerisation within its pores and channels in a first stage, as nanofiller of the formed polyethylene matrixdur ing its useful lifetime and, finally, as promoter for long-term waste disposal. As evidenced by FTIR analysis, when the polymer is formed under these confined conditions different interactions between the MCM-41 material and the polyethylene matrix occur, when compared to simple blends. The influence of the filler content on the rigidity of the resulting nanocomposites is analysed by microhardness measurements and corroborated by the storage modulus values: a significant increase in rigidity is observed as the filler contents rises. In addition, thermogravimetric studies show interesting features concerning the degradability of these materials. The catalytic action of MCM-41 during degradation involves a reduction of the energetic requirements for their cracking and, therefore, a positive environmental impact.
- Microencapsulation of selenium by spray-drying as a tool to improve bioaccessibility in food matrixPublication . Grenha, Ana; Guerreiro, Filipa; Lourenço, João P.; Lopes, João Almeida; Cámara-Martos, FernandoSe in the form of sodium selenite was microencapsulated by spray - drying and added to a food matrix (yogurt) to study the potential improvement of its bioaccessibility. Yogurt samples were also supplemented with Se in free salt form. Se-loaded microparticles were successfully prepared by spray-drying with production yields above 70%. The supplementation of yogurt with Se in the form of free sodium selenite had a low effect on improving the bioaccessibility of this micronutrient (1%). In turn, Se microencapsulation with mannitol or mannitol/gastro-resistant polymer (Eudragit (R)) had a strong impact on bioaccessibility results. After the gastric phase, Se bio-accessibility reached values of 21 and 40% for the microencapsulated formulations, respectively. This percentage rose to 55% at the end of intestinal phase, showing no differences between both formulations. Our results show the relevance of microencapsulation as an effective tool to improve the bioaccessibility of micronutrients when they are used in food supplementation.
- Charged pullulan derivatives for the development of nanocarriers by polyelectrolyte complexationPublication . Dionísio, Marita; Braz, L.; Corvo, M.; Lourenço, J. P.; Grenha, Ana; Costa, Ana M. Rosa daPullulan, a neutral polysaccharide, was chemically modified in order to obtain two charged derivatives: reaction with SO3(.)DMF complex afforded a sulfate derivative (SP), while reaction with glycidyltrimethylammonium chloride gave a quaternary ammonium salt (AP). The presence of the charged groups was confirmed by FTIR. Assessment of the positions where the reaction took place was based on (1)H- and (13)C NMR (COSY, HSQC-TOCSY, HSQC-DEPT, and HMBC) experiments. Estimation of the degree of substitution (DS) was made from elemental analysis data, and further confirmed by NMR peak areas in the case of AP. These new derivatives showed the capability to condense with each other, forming nanoparticles with the ability to associate a model protein (BSA) and displaying adequate size for drug delivery applications, therefore making them good candidates for the production of pullulan-based nanocarriers by polyelectrolyte complexation.
- Spectroscopic characterization of the hydroxyl groups in SAPO-40. Part II: interaction with CO and N2Publication . Onida, B.; Gabelica, Z.; Lourenço, J. P.; Ribeiro, M. F.; Garrone, E.SAPO-40 exhibits five main OH species, describable as high-frequency ones (HF, at 3737, 3730, and 3724 cm-1) and low-frequency ones (LF1 and LF2, at 3559 and 3528 cm-1, respectively), the former probably sitting in 12-member-ring channels and the latter either in side pockets or eight-member-ring channels of the AFR structure. The low-temperature interaction of such OH species with CO shows that HF species have strictly similar acidity (comparable to that of HY zeolites), in contrast with previous results concerning H-transfer to NH3. The ease of interaction and the spectral features are in accord with the location in large cavities. The vibration of H-bonded hydroxyl has a noticeable structure with subbands. The interaction of CO with LF1 and LF2 species occurs with difficulty and yields nonlinear complexes because of the steric hindrance brought about by small cavities. Adsorption of N2 follows similar patterns.