Portugal
Portugal

Time filter

Source Type

Caiado M.,University of Évora | MacHado A.,New University of Lisbon | Santos R.N.,New University of Lisbon | Matos I.,New University of Lisbon | And 5 more authors.
Applied Catalysis A: General | Year: 2013

Silica-occluded tungstophosphoric acid (PW-Ssg) was used as an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase alkoxylation of camphene into their more valuable alkyl isobornyl ether, which is used as perfume and cosmetic products, in the pharmaceutical industry, as well as in the food industry. The alkoxylation of camphene with C 1-C4 alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol) to alkyl isobornyl ether was studied in the presence of PW-Ssg (4.2% w/w) at 60-80 °C. Different linear and branched alcohols are compared in relation to their activity for the alkoxylation of camphene. The catalytic activity decreased with the increase of number of carbon atoms in the chain alcohol, which can be explained due to the presence of sterical hindrance and diffusion limitations inside the porous system of the catalyst. High selectivity of PW-Ssg catalyst for the alkyl isobornyl ether was observed. The effect of various parameters, such as catalysts loading, initial concentration of camphene and temperature were studied to optimise the ethoxylation of camphene. The catalytic stability of PW-S sg in the ethoxylation of camphene was studied by performing consecutive batch runs with the same catalyst sample at the same conditions. After the third run, the catalytic activity stabilized. The catalyst can be recovered and reused without significant leaching of PW. The catalytic activity of PW-Ssg was compared with the activity of tungstophosphoric acid immobilized on silica by impregnation method (PW-Sim). The activity of PW-Ssg is higher than that of PW-Sim catalyst. After reaction, the PW-Sim sample lost 20% of its heteropolyacid. © 2012 Elsevier B.V.


Figueiredo A.B.,CICECO | Evtuguin D.V.,CICECO | Monteiro J.,University of Aveiro | Cardoso E.F.,SONAE Industria de Revestimentos | And 2 more authors.
Industrial and Engineering Chemistry Research | Year: 2011

The structural features of four different kraft papers were related to their surface properties and to the response upon industrial impregnation with phenol-formaldehyde (PF) resin. The chemical composition and the structure of paper were suggested to be important factors determining the interaction with PF resin, which was assessed by contact angle measurements and surface energy analysis. The presence of fatty matter (extractives) and inorganic fillers together with structural anisotropy of paper confers the difference in affinity of the face and backside of papers toward PF resin. This affects the resin distribution in impregnated precured kraft papers as revealed by microfluorescence spectroscopic analysis of transversal cuts. © 2011 American Chemical Society.


Mateus P.,New University of Lisbon | Delgado R.,New University of Lisbon | Groves P.,New University of Lisbon | Campos S.R.R.,New University of Lisbon | And 3 more authors.
Journal of Organic Chemistry | Year: 2012

A new heteroditopic macrobicyclic compound (t2pN 5O3) containing two separate polyoxa and polyaza compartments was synthesized in good yield through a [1 + 1] "tripod-tripod coupling" strategy. The X-ray crystal structure of H3t 2pN5O3 3+ revealed the presence of one encapsulated water molecule accepting two hydrogen bonds from two protonated secondary amines and donating a hydrogen bond to one amino group. The acid-base behavior of the compound was studied by potentiometry at 298.2 K in aqueous solution and at ionic strength 0.10 M in KCl. The results revealed unusual protonation behavior, namely a surprisingly low fourth protonation constant contrary to what was expected for the compound. 1H NMR and DOSY experiments, as well as molecular modeling studies, showed that the water encapsulation and the conformation observed in the solid state are retained in solution. The strong binding of the encapsulated water molecule, reinforced by the cooperative occurrence of a trifurcated hydrogen bond at the polyether compartment of the macrobicycle, account for the very low log K4 H value obtained. © 2012 American Chemical Society.


Santos L.M.N.B.F.,University of Porto | Rocha M.A.A.,University of Porto | Gomes L.R.,Fernando Pessoa University | Gomes L.R.,University of Porto | And 2 more authors.
Journal of Chemical and Engineering Data | Year: 2010

The gaseous phase heat capacity of benzoic acid (BA) was proven using the experimental technique called the "in vacuum sublimation/vaporization Calvet microcalorimetry drop method". To overcome known experimental shortfalls, the gaseous phase heat capacity of BA monomer was estimated by ab initio calculations and compared with experimental results. Gaseous phase heat capacities of BA were directly derived via calculated harmonic frequencies obtained by density functional theory (DFT) (B3LYP, BLYP, BP86, with 6-311++G(d,p), TZVP, cc-pVTZ basis sets) and the second-order Møller-Plesset theory, MP2/6-311++G(d,p). To increase the accuracy of estimation of the thermal properties, a procedure based on the calculation of the heat capacity from quantum chemical calculations in combination with a heat capacity balance of isodesmic reactions is described and applied to calculate the gaseous phase heat capacity, Cp,m, of the monomeric species over the temperature range of (298.15 to 600) K. The gaseous phase thermodynamic properties of the monomeric form of the BA were also derived from the assignment of the fundamental vibrational frequencies using experimental IR spectra. An excellent agreement among the experimental gaseous phase heat capacities, the results obtained using the proposed ab initio procedure, and the results derived from the assignment of fundamental vibrational frequencies was found. The results for the monomeric form of the BA, directly or indirectly obtained, and conclusions of this work strongly support the thesis that the gaseous phase heat capacity data as currently found in the literature are underestimated to the order of 20 %. © 2010 American Chemical Society.


Ferreira A.S.,University of Aveiro | Nunes C.,University of Aveiro | Castro A.,CICECO | Ferreira P.,CICECO | Coimbra M.A.,University of Aveiro
Carbohydrate Polymers | Year: 2014

Chitosan has been studied as a renewable polymer to form edible films allowing the incorporation of functional compounds. The aim of this work was to evaluate the effects in the chitosan films properties of the incorporation of grape pomace extracts: 0.15% of hot water extract (mainly polysaccharides), 0.15 and 0.3% of chloroform extract (wax), and 0.3 and 0.75% of n-hexane extract (oil). The evaluation of the surface morphology revealed that the films with the aqueous extract had the most homogeneous and smoother topography. The incorporation of higher proportion of wax and oil led to changes in mechanical properties of the films, namely lower resistance and stiffness. The chitosan-based films with 0.75% oil demonstrated a 75% decrease of solubility in water, due to their hydrophobicity, as confirmed by the contact angle and surface free energy measurements. The hydrophobic films showed higher antioxidant capacity in organic medium (ABTS and DPPH assays) whereas the most hydrophilic films showed an improvement in FRAP and reducing power assays. Therefore, all the chitosan-based films prepared by incorporation of these grape pomace extracts are promising for food shelf life extension. © 2014 Elsevier Ltd.


Wack J.,University of Bayreuth | Siegel R.,University of Bayreuth | Ahnfeldt T.,University of Bayreuth | Ahnfeldt T.,University of Kiel | And 3 more authors.
Journal of Physical Chemistry C | Year: 2013

We present a study analyzing the selectivity of host-guest interactions in a series of functionalized Al-MIL-53-X metal-organic frameworks with X = H, NH2, and NHCHO using acetone, ethanol, and water as probe molecules. While the amino group introduces additional hydrogen bond donor centers the NHCHO anchors function as donor and acceptor. The guests were chosen due to their ability to act solely as an acceptor in the case of acetone, whereas ethanol and water provide acceptor and donor qualities with a gradual decrease of the acceptor strength toward ethanol. The characterization of the host-guest interactions includes a comprehensive solid-state NMR spectroscopic study based on a full assignment of 1H and 13C high-resolution spectra using CRAMPS decoupling schemes to enhance 1H resolution combined with advanced 2D HETCOR (1H-13C, 1H- 27Al, and 1H-14N) spectra at high magnetic fields. In spite of a pronounced dynamical disorder of the guests, we could identify a preferred binding of the acetone via a NH···OC hydrogen bond for the NH2 and the NHCHO anchor groups by analyzing trends in the 13C isotropic chemical shifts. At the same time 1H-1H through-space connectivities reveal a close vicinity of the acetone methyl groups to the benzene rings of the linkers. In contrast, for ethanol and water, the interaction with the anchor groups is too weak to compete with the thermal disorder at room temperature. © 2013 American Chemical Society.


Kumar M.V.V.,Sri Krishnadevaraya University | Gopal K.R.,Sri Krishnadevaraya University | Reddy R.R.,Sri Krishnadevaraya University | Reddy G.V.L.,Government Degree College | And 2 more authors.
Journal of Non-Crystalline Solids | Year: 2013

Praseodymium doped lead telluroborate (PTBPr) glasses were prepared by conventional melt quenching method. The absorption spectra have been analyzed to evaluate the intensity parameters applying the standard and the modified Judd-Ofelt theories. The emission spectra under 3P2 level excitation (λex = 447 nm) were investigated to estimate the laser characteristic parameters. These emission measurements together with Judd-Ofelt intensity parameters (λ = 2,4,6) have been used to calculate the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of the transitions from 3P0 and 1D2 levels to their lower lying levels. The quenching of fluorescence intensity and experimental lifetime with the increase of Pr 3 + concentration and the shift of 1D2 → 3H4 emission peak towards longer wavelengths was discussed. The non-radiative losses due to multiphonon and energy transfer relaxations were also explained. The Commission Internationale de I'Eclairage (CIE) coordinates, color purity and optical band gap energy values were evaluated. Some of the basic laser characteristics such as stimulated emission cross-section, optical and bandwidth gain parameters and fluorescence quantum efficiency were also reported. © 2012 Elsevier B.V.


Gautam U.K.,Japan International Center for Materials Nanoarchitectonics | Costa P.M.F.J.,CICECO | Bando Y.,Japan International Center for Materials Nanoarchitectonics | Fang X.,Japan International Center for Materials Nanoarchitectonics | And 3 more authors.
Science and Technology of Advanced Materials | Year: 2010

Carbon nanotubes (CNTs) are a unique class of nanomaterials that can be imagined as rolled graphene sheets. The inner hollow of a CNT provides an extremely small, one-dimensional space for storage of materials. In the last decade, enormous effort has been spent to produce filled CNTs that combine the properties of both the host CNT and the guest filling material. CNTs filled with various inorganic materials such as metals, alloys, semiconductors and insulators have been obtained using different synthesis approaches including capillary filling and chemical vapor deposition. Recently, several potential applications have emerged for these materials, such as the measurement of temperature at the nanoscale, nano-spot welding, and the storage and delivery of extremely small quantities of materials. A clear distinction between this class of materials and other nanostructures is the existence of an enormous interfacial area between the CNT and the filling matter. Theoretical investigations have shown that the lattice mismatch and strong exchange interaction of CNTs with the guest material across the interface should result in reordering of the guest crystal structure and passivation of the surface dangling bonds and thus yielding new and interesting physical properties. Despite preliminary successes, there remain many challenges in realizing applications of CNTs filled with inorganic materials, such as a comprehensive understanding of their growth and physical properties and control of their structural parameters. In this article, we overview research on filled CNT nanomaterials with special emphasis on recent progress and key achievements. We also discuss the future scope and the key challenges emerging out of a decade of intensive research on these fascinating materials. © 2010 National Institute for Materials Science.


PubMed | CICECO and Japan International Center for Materials Nanoarchitectonics
Type: Review | Journal: Science and technology of advanced materials | Year: 2016

Carbon nanotubes (CNTs) are a unique class of nanomaterials that can be imagined as rolled graphene sheets. The inner hollow of a CNT provides an extremely small, one-dimensional space for storage of materials. In the last decade, enormous effort has been spent to produce filled CNTs that combine the properties of both the host CNT and the guest filling material. CNTs filled with various inorganic materials such as metals, alloys, semiconductors and insulators have been obtained using different synthesis approaches including capillary filling and chemical vapor deposition. Recently, several potential applications have emerged for these materials, such as the measurement of temperature at the nanoscale, nano-spot welding, and the storage and delivery of extremely small quantities of materials. A clear distinction between this class of materials and other nanostructures is the existence of an enormous interfacial area between the CNT and the filling matter. Theoretical investigations have shown that the lattice mismatch and strong exchange interaction of CNTs with the guest material across the interface should result in reordering of the guest crystal structure and passivation of the surface dangling bonds and thus yielding new and interesting physical properties. Despite preliminary successes, there remain many challenges in realizing applications of CNTs filled with inorganic materials, such as a comprehensive understanding of their growth and physical properties and control of their structural parameters. In this article, we overview research on filled CNT nanomaterials with special emphasis on recent progress and key achievements. We also discuss the future scope and the key challenges emerging out of a decade of intensive research on these fascinating materials.


PubMed | University of Aveiro and CICECO
Type: | Journal: Carbohydrate polymers | Year: 2014

Chitosan has been studied as a renewable polymer to form edible films allowing the incorporation of functional compounds. The aim of this work was to evaluate the effects in the chitosan films properties of the incorporation of grape pomace extracts: 0.15% of hot water extract (mainly polysaccharides), 0.15 and 0.3% of chloroform extract (wax), and 0.3 and 0.75% of n-hexane extract (oil). The evaluation of the surface morphology revealed that the films with the aqueous extract had the most homogeneous and smoother topography. The incorporation of higher proportion of wax and oil led to changes in mechanical properties of the films, namely lower resistance and stiffness. The chitosan-based films with 0.75% oil demonstrated a 75% decrease of solubility in water, due to their hydrophobicity, as confirmed by the contact angle and surface free energy measurements. The hydrophobic films showed higher antioxidant capacity in organic medium (ABTS and DPPH assays) whereas the most hydrophilic films showed an improvement in FRAP and reducing power assays. Therefore, all the chitosan-based films prepared by incorporation of these grape pomace extracts are promising for food shelf life extension.

Loading CICECO collaborators
Loading CICECO collaborators