Repositório Institucional da Universidade de Aveiro
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Functionalized Porphyrins as Red Fluorescent Probes for Metal Cations: Spectroscopic, MALDI-TOF Spectrometry, and Doped-Polymer Studies
No full textThe sensing ability of benzoporphyrins 1-5 and porphyrin-2-ylpyridines 6-10 towards different metal ions Na+, K+, Ca2+, Mg2+, Pb2+, Cu2+, Ni2+, Zn2+, Cd2+, Hg2+, and Cr3+ was explored in solution by absorption and fluorescence spectroscopy. Strong changes in the ground and excited state were detected only in the case of the soft metal ions Zn2+, Cd2+, Hg2+, and Cu2+. A one metal per ligand molar ratio was obtained in all cases for compounds1-5. In addition, a remarkable increase of the emission intensity for 1-5 was observed in the presence of Hg2+. In this series the highest association constant was obtained for compound1 (logK(ass)=(8.71 +/- 4.81)x10(-3)), which was able to quantify 32ppb of Hg2+. For compounds6-10 containing an additional pyridine unit, a metal-to-ligand stoichiometry of 1:2 was determined. The gas-phase detection abilities of compounds1-10 using MALDI-TOF-MS spectrometry confirmed that their sensorial ability and theoretical calculations are in accordance with the stoichiometry observed. Our preliminary studies show that some of the compounds supported in polymethylmethacrylate (PMMA) films can be used as promising metal-ion solid chemosensors; it was found that compound 1 in PMMA is able to distinguish between Zn2+ and Hg2+ in the solid phase
Is the ubiquitous presence of barium carbonate responsible for the poor aqueous processing ability of barium titanate?
No full textThe ubiquitous presence of barium carbonate (BaCO3 - BC) as an impurity in barium titanate (BaTiO3 - BT) has been pointed out as the main reason for the well-known difficulties found by many investigators when attempting to process BT powders in aqueous media. Different and controversial arguments have been put forward to justify the observed aqueous processing difficulties of BT, but a satisfactory explanation is still to be found. With this aim, a systematic study was here undertaken to shed further light on the solid/liquid interactions occurring at the surface of BC and BT particles and their impact on the dispersion ability of both powders, separately and mixed in certain proportions. Long term colloidal stability and high solid loadings (60 vol.%) were obtained for BC, while colloidal instability and a lower maximum content of solids (50 vol.%) could be achieved for BT. This responds to the question risen in the title. (C) 2013 Elsevier Ltd, All rights reserved
Voltage-dependent domain evolution in La0.89Sr0.11MnO3 single crystals by Piezoresponse Force Microscopy
No full textBias voltage dependent domain dynamics have been investigated on the surface of La0.89Sr0.11MnO3 (LSMO-0.11) single crystals by Piezoresponse Force Microscopy (PFM). The created domain size increases with both the amplitude and duration of the bias voltage pulse. It is observed that domain growth takes place following an activated process wherein the domain wall interacts with the defects (e.g. oxygen vacancies) resulting from the high electric field under the PFM tip. Fractal analysis, based on the interaction of the domain boundary with the defects, provides the Hausdorff fractal dimension value similar to 1.3, lower than that usually observed for solid-state crystalline ferroelectrics indicating a smaller correlation length value for LSMO-0.11 crystal. These studies reveal a clear potential of LSMO for new memory devices based on ferroelectric-like domain states in manganites. (C) 2013 Elsevier Ltd. All rights reserved
Superior biofunctionality of dental implant fixtures uniformly coated with durable bioglass films by magnetron sputtering
No full textBioactive glasses are currently considered the suitable candidates to stir the quest for a new generation of osseous implants with superior biological/functional performance. In congruence with this vision, this contribution aims to introduce a reliable technological recipe for coating fairly complex 3D-shaped implants (e.g. dental screws) with uniform and mechanical resistant bioactive glass films by the radio-frequency magnetron sputtering method. The mechanical reliability of the bioactive glass films applied to real Ti dental implant fixtures has been evaluated by a procedure comprised of \"cold\" implantation in pig mandibular bone from a dead animal, followed by immediate tension-free extraction tests. The effects of the complex mechanical strains occurring during implantation were analysed by scanning electron microscopy coupled with electron dispersive spectroscopy. Extensive biocompatibility assays (MTS, immunofluorescence, Western blot) revealed that the bioactive glass films stimulated strong cellular adhesion and proliferation of human dental pulp stem cells, without promoting their differentiation. The ability of the implant coatings to conserve a healthy stem cell pool is promising to further endorse the fabrication of new osseointegration implant designs with extended lifetime. (C) 2015 Elsevier Ltd. All rights reserved
Rare-Earth-Substituted Strontium Titanate: Insight into Local Oxygen-Rich Structures and Redox Kinetics
No full textLn-substituted SrTiO3 is a promising material for energy conversion technologies such as. thermoelectric generators and solid oxide fuel/electrolysis cells. In this study, formation of local structures enabling accommodation of excess oxygen in perovskite matrix of SrTiO3 and related redox behavior were assessed employing static lattice simulations in combination with experimental methods (XRD, SEM/EDS, XPS, TGA, and electrical measurements) using Sr(0.90-x)Ln(0.10)TiO(3 +/-delta) (Ln = Ce, Pr; x = 0-0.10) as model systems. Although strontium-vacancy formation is found to be a preferable mechanism for donor compensation in oxidized Sr(Ln)TiO3, oxygen excess still can be accommodated by extended defects quenched from high temperatures. Linear Ln(Sr)(3+)center dot center dot center dot O-i(2-) defect clusters and SrO shear planes characteristic of Ruddlesden Popper phases are found to be the most probable extended defects enabling the accommodation of excess oxygen in oxidized titanates with Sr(1-x)Ln(x)TiO(3+delta) cation stoichiometry. The presence of oxygen-rich local structures is shown to be strongly correlated with the faster redox kinetics and higher electrical conductivity critical for practical applications. Easy oxidation of reduced Sr(1-x)Ln(x)TiO(3+delta) (with electronic donor compensation) provide further evidence in favor of Ln(Sr)(3+)center dot center dot center dot O-i(2-) defect clusters as mechanism of excess oxygen accommodation
Coordination polymers based on a glycine-derivative ligand
No full textThe combination of the glycine-derivative supramolecular salt 4,6-bis(carboxymethylamino)-2-oxo-2,3-dihydro-1,3,5-triazin-1-ium chloride (H(2)bodt center dot HCl) and lanthanide(III) chloride hydrates under hydrothermal conditions (120 degrees C, 48 h) led to the formation of a family of isotypical materials formulated as [Ln(bodt)(Hbodt)] [where Ln(3+) = La3+ (1), (La0.95Eu0.05)(3+) (2) and (La0.95Tb0.05)(3+) (3)]. The synthesis of the novel precursor H(2)bodt center dot HCl is detailed. The structures of H(2)bodt center dot HCl and its intermediate compound were unveiled by single-crystal X-ray diffraction and characterized by standard liquid-state techniques. The crystallographic details of compound 1 were unveiled in the monoclinic P2/c space group by using single-crystal X-ray diffraction, with the crystal structure of 1 comprising a one-dimensional (1)(infinity)[La(bodt)(Hbodt)] coordination polymer. All polymeric materials were fully characterized by FT-IR, electron microscopy (SEM and EDS), powder X-ray diffraction, and elemental and thermogravimetric analyses. The photoluminescent properties of 1 and of the mixed-lanthanide materials 2 and 3 were investigated at ambient and low temperatures. An excited-state intermolecular proton transfer (ESPT) process, induced by intermolecular hydrogen-bonding interactions, is proposed to account for the observed anomalous emission and excitation spectra of 1. Aiming at providing an in-depth understanding of the emission (fluorescence and phosphorescence) properties of the ligand, time-dependent density functional theory (TD-DFT) calculations were also performed
Multi-color emission tunability and energy transfer studies of YAl3(BO3)(4):Eu3+/Tb3+ phosphors
No full textA series of YAB:Eu3+/Tb3+ co-activated phosphors of composition Y(1-x-y)Al3(BO3)(4)xEu(3+)/yTb(3+) (x=0, 0.3, 0.5, 1, 2% and y=0.5%) were prepared by solid-state reaction method and their photoluminescence properties were characterized. Eu3+/Tb3+ co-doped phosphors have shown their excellent luminescent properties in their respective emission regions. The YAB:2%Eu3+ phosphor under 395 nm excitation exhibited red luminescence with Commission International de I'Eclairagein chromaticity coordinates (x=0.627, y=0.334) which are close to an ideal red and commercial Y2O3:Eu3+ red phosphor chromaticity coordinates. The emission color of Eu3+/Tb3+ co-doped phosphors has been tuned from pale-green to white as a function of Eu3+/Tb3+ concentration. Moreover, the Tb3+ acts as an efficient sensitizer and enhances the luminescence of Eu3+ by transferring absorbed excitation energy. The overlapping F-7(0)-> D-5(3,2,1,0) (Eu3+); F-7(1)->>D-5(1,0)(Eu3+); F-7(2)-> D-5(1)(Eu3+) excitation and D-5(3)-> F-7(5,4,3) (Tb3+); D-5(4)-> F-7(5,4)(Tb3+) emission transitions revealed the transfer of energy from Tb3+ to Eu3+ through exchange interaction mechanism in Eu3+-Tb3+ clusters instead of from these ions randomly distributed in YAB lattice. The YAB:Eu3+/Tb3+ phosphors have potential in the field of display technology. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved
Alkali Niobate and Tantalate Perovskites as Alternative Photocatalysts
No full textAlkali tantalates and niobates are listed as important photocatalysts for the development of renewable energy technologies and environmental remediation. Herein, the photocatalytic degradation of methylene blue dye in aqueous solution by using highly crystalline particles with perovskite-like structures, LiTaO3, LiNbO3, NaTaO3, NaNbO3, KNbO3, and KTaO3, is investigated. It is demonstrated that ferroelectric KNbO3 is the most efficient photocatalyst of those tested because it combines an electronic band structure that can respond successfully to UVA light with a relatively high surface energy that enhances the catalytic properties. Additionally, the built-in electric field due to internal polarization of ferroelectric particles may contribute to the unique properties of this functional photocatalyst. This work provides an ideal platform for the rational design of more efficient ferroelectric-based photocatalytic devices
Pyrrolidine-fused chlorin photosensitizer immobilized on solid supports for the photoinactivation of Gram negative bacteria
No full textThe emergence of resistant microorganism to conventional therapeutics prompted us to search new and better antimicrobial treatment modalities. In this work was envisaged an economically viable and environmental friendly approach to allow successive recovery and removal of the photosensitizer agent after photodynamic treatment. The photodynamic inactivation of bioluminescent Escherichia coli in the presence of an immobilized cationic chlorin photosensitizer and its reusability are described. The chlorin photosensitizer (PS) was immobilized on two commercial materials: a 3-bromopropyl-functionalized silica and a Merrifield resin. The new photosensitising materials were characterized by UV-vis spectroscopy, SEM and EDX. Their singlet oxygen generation capacities were also assessed. Previous studies showed that there is a direct relationship between the photoinactivation efficiency and the number of positive charges on such PS molecules. Therefore the number of positive charges on the new prepared materials was further increased by treatment of the PS-immobilized materials with 1-methylimidazole and pyridine. The efficiency of photoinactivation against bioluminescent E. coli was evaluated in the presence of the non-immobilized chlorin (20 mu M) as well as in the presence of the new prepared materials positively charged or non-charged on the surface (20-200 mu M) with white light at an irradiance of 4.0 mW cm(-2). Overall, this study shows that the materials resulting from the immobilization of the chlorin on the silica surface and on the Merrifield resin, followed by further treatment with pyridine, have high potential as PS for the inactivation of Gram negative bacteria (3.0 log reductions) and are able to maintain its antimicrobial efficiency after at least 3 repeated cycles of photoinactivation. Their reusability, without loss of effectiveness, confirms a potential inexpensive and friendly application in clinic and environmental areas. (C) 2014 Elsevier Ltd. All rights reserved
Galvanic Replacement Reactions in Metal Oxide Nanocrystals
No full textGalvanic replacement reactions provide a simple and versatile route for producing hollow nanostructures with controllable pore structures and compositions. However, these reactions have previously been limited to the chemical transformation of metallic nanostructures. We demonstrated galvanic replacement reactions in metal oxide nanocrystats as well. When manganese oxide (Mn3O4) nanocrystals were reacted with iron(II) perchlorate, hollow box-shaped nanocrystats of Mn3O4/gamma-Fe2O3 (\"nanoboxes\") were produced. These nanoboxes ultimately transformed into hollow cagetike nanocrystats of gamma-Fe2O3 (\"nanocages\"). Because of their nonequihbrium compositions and hollow structures, these nanoboxes and nanocages exhibited good performance as anode materials for lithium ion batteries. The generality of this approach was demonstrated with other metal pairs, including Co3O4/SnO2 and Mn3O4/SnO2