Tetragonal-cubic phase boundary in nanocrystalline ZrO(2)-Y(2)O(3) solid solutions synthesized by gel-combustion

By means of synchrotron X-ray powder diffraction (SXPD) and Raman spectroscopy, we have detected, in a series of nanocrystalline and compositionally homogeneous ZrO(2)-Y(2)O(3) solid solutions, the presence at room temperature of three different phases depending on Y(2)O(3) content, namely two tetragonal forms and the cubic phase. The studied materials, with average crystallite sizes within the range 7-10 nm, were synthesized by a nitrate-citrate gel-combustion process. The crystal structure of these phases was also investigated by SXPD. The results presented here indicate that the studied nanocrystalline ZrO(2)-Y(2)O(3) solid solutions exhibit the same phases reported in the literature for compositionally homogeneous materials containing larger (micro)crystals. The compositional boundaries between both tetragonal forms and between tetragonal and cubic phases were also determined. (C) 2011 Elsevier B.V. All rights reserved.

Characterization, photoluminescence, thermally stimulated luminescence and electron spin resonance studies of Eu(3+) doped LaAlO(3) phosphor

Europium-doped lanthanum aluminate (LaAlO(3)) powder was prepared by using a combustion method. The crystallization, surface morphology, specific surface area and luminescence properties of the samples have been investigated. Photoluminescence studies of Eu doped LaAlO(3) showed orange-reddish emission due to Eu(3+) ions. LaAlO(3):Eu(3+) exhibits one thermally stimulated luminescence (TSL) peak around 400 degrees C. Room temperature electron spin resonance spectrum of irradiated phosphor appears to be a superposition of two centres. One of them (centre I) with principal g-value 2.017 is identified as an O(-) centre while centre II with an isotropic g-value 2.011 is assigned to an F(+) centre (singly ionized oxygen vacancy). An additional defect centre observed during thermal annealing around 300 degrees C grows with the annealing temperature. This centre (assigned to F(+) centre) originates from an F-centre (oxygen vacancy with two electrons) and the F-centre along with the associated F(+) centre appear to correlate with the observed TSL peak in LaAlO(3):Eu(3+) phosphor. The activation energy for this peak has been determined to be 1.54 eV from TSL data. (C) 2010 Elsevier Masson SAS. All rights reserved.

Luminescence and defect centres in Tb(3+) doped LaMgAl(11)O(19) phosphors

Terbium (Tb) doped LaMgAl(11)O(19) phosphors have been prepared by the combustion of corresponding metal nitrates (oxidizer) and urea (fuel) at furnace temperature as low as 500 C Combustion synthesized powder phosphor was characterized by X-ray diffraction and field emission scanning electron microscopy techniques LaMgAl(11)O(19) doped with trivalent terbium ions emit weakly in blue and orange light region and strongly in green light region when excited by the ultraviolet light of 261 nm Electron Spin Resonance (ESR) studies were carried out to study the defect centres Induced in the phosphor by gamma irradiation and also to identify the defect centres responsible for the thermally stimulated luminescence (TSL) process Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least two defect centres One of the centres (centre I) with principal g-values g(parallel to) = 2 0417 and g(perpendicular to) = 2 0041 is identified as O(2)(-) ion while centre II with an axially symmetric g-tensor with principal values g(parallel to) = 19698 and g(perpendicular to) = 1 9653 is assigned to an F(+) centre (singly ionized oxygen vacancy) An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F(+) centre) seems to originate from an F centre (oxygen vacancy with two electrons) The F centre and also the F+ centre appear to correlate with the observed high temperature TSL peak in LaMgAl(11)O(19) Tb phosphor (C) 2010 Elsevier Masson SAS All rights reserved

Electronic structure and optical properties of BaMoO(4) powders

Barium molybdate (BaMoO(4)) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 degrees C for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm(-1), which is associated to the Mo-O antisymmetric stretching vibrations into the [MoO(4)] clusters. UV-vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap. (C) 2009 Elsevier B.V. All rights reserved.

Biological effects of anionic meso-tetrakis (para-sulfonatophenyl) porphyrins modulated by the metal center. Studies in rat liver mitochondria

In this paper, we present a study about the influence of the porphyrin metal center and mesa ligands on the biological effects of meso-tetrakis porphyrins. Different from the cationic meso-tetrakis 4-N-methyl pyridinium (Mn(III)TMPyP), the anionic Mn(III) meso-tetrakis (para-sulfonatophenyl) porphyrin (Mn(III)TPPS4) exhibited no protector effect against Fe(citrate)-induced lipid oxidation. Mn(III)TPPS4 did not protect mitochondria against endogenous hydrogen peroxide and only delayed the swelling caused by tert-BuOOH and Ca(2+). Fe(III)TPPS4 exacerbated the effect of the tert-BuOOH, and both porphyrins did not significantly affect Fe(II)citrate-induced swelling. Consistently, Fe(III)TPPS4 predominantly promotes the homolytic cleavage of peroxides and exhibits catalytic efficiency ten-fold higher than Mn(III)TPPS4. For Mn(III)TPPS4, the microenvironment of rat liver mitochondria favors the heterolytic cleavage of peroxides and increases the catalytic efficiency of the manganese porphyrin due to the availability of axial ligands for the metal center and reducing agents such as glutathione (GSH) and proteins necessary for Compound II (oxomanganese IV) recycling to the initial Mn(III) form. The use of thiol reducing agents for the recycling of Mn(III)TPPS4 leads to GSH depletion and protein oxidation and consequent damages in the organelle. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

CeO(2)-catalyzed ozonation of phenol

Three different cerium citrate-based precursors were used for synthesizing CeO(2) through thermal treatment. Three morphological types of CeO(2) were obtained. Characterization of these oxides was carried out by XRD patterns, SEM microscopy, N(2) adsorption isotherms, Raman spectroscopy, zeta potential, and UV/Vis luminescence. Ozonation of phenol catalyzed by CeO(2) was studied as a representative reaction of environmental interest. The differences on the catalytic activity showed by these three oxides could be correlated to amounts of Ce(3+) on CeO(2) surface and, consequently, to the demand for oxygen needed to burn each precursor.

Preparation and characterization of the novels terpolymers of poly-{trans-[RuCl(2)(vpy)(4)]-styrene-divinylbenzene} and styrene-divinylbenzene-vinylpiridine impregnated with silver nanoparticles

This paper reports the preparation and characterization of poly-{trans-[RuCl(2)(vpy)(4)]-styrene-divinylbenzene} and styrene-divinylbenzene-vinylpiridine filled with nanosilver. Theses materials were synthesized by non aqueous polymerization through a chemical reaction using benzoyl peroxide as the initiator. The nanosilver was obtained from chemical reduction using NaBH(4) as reducing agent and sodium citrate as stabilizer. The nanometric dimension of nanosilver was monitored by UV-visible and confirmed through TEM. The morphology was characterized by SEM and the thermal properties were done by TGA and DSC. The antimicrobial action of the polymers impregnated with nanosilver was evaluated using both microorganisms, Staphylococcus aureus and Escherichia coli. The antimicrobial activity of the poly-{trans-[RuCl(2)(vpy)(4)]-styrene-divinylbenzene} filled with nanosilver was confirmed by the presence of an inhibition halo of the bacterial growth in seeded culture media, but was not confirmed to the styrene-divinylbenzene-vinylpiridine. The present work suggest that trans - [RuCl(2)(vpy)(4)] complex facilitate the release of silver ion from the media.

Supramolecular Approach to Gold Nanoparticle/Triruthenium Cluster Hybrid Materials and Interfaces

A systematic and comprehensive study of the interaction of citrate-stabilized gold nanoparticles with triruthenium cluster complexes of general formula [Ru(3)(CH(3)COO)(6)(L)](+) [L = 4-cyanopyridine (4-CNpy), 4,4`-bipyridine (4,4`-bpy) or 4,4`-bis(pyridyl)ethylene (bpe)] has been carried out. The cluster-nanoparticle interaction in solution and the construction of thin films of the hybrid materials were investigated in detail by electronic and surface plasmon resonance (SPR) spectroscopy, Raman scattering spectroscopy and scanning electron microscopy (SEM). Citrate-stabilized gold nanoparticles readily interacted with [Ru(3)O(CH(3)COO)(6)(L)(3)](+) complexes to generate functionalized nanoparticles that tend to aggregate according to rates and extents that depend on the bond strength defined by the characteristics of the cluster L ligands following the sequence bpe > 4,4`-bpy >> 4-CNpy. The formation of compact thin films of hybrid AuNP/[Ru(3)O(CH(3)COO)(6)(L)(3)](+) derivatives with L = bpe and 4,4`-bpy indicated that the stability/lability of AuNP-cluster bonds as well as their solubility are important parameters that influence the film contruction process. Fluorine-doped tin oxide electrodes modified with thin films of these nanomaterials exhibited similar electrocatalytic activity but much higher sensitivity than a conventional gold electrode in the oxidation of nitrite ion to nitrate depending on the bridging cluster complex, demonstrating the high potential for the development of amperometric sensors.

Spectroscopic Characterization of Oligoaniline Microspheres Obtained by an Aniline-Persulfate Approach

This paper investigates the structure of the pro; ducts obtained from the polymerization of aniline with ammonium persulfate in a citrate/phosphate buffer solution at pH 3 by resonance Raman, NMR, FTIR, and UV-vis-NIR spectroscopies. All the spectroscopic data showed that the major product presented segments that were formed by a 1,4-Michael reaction between aniline and p-benzoquinone monoimine, ruling out the formation of polyazane structure that has been recently proposed. The characterization of samples obtained at different stages of the reaction indicated that, as the reaction progressed, phenazine units were formed and 1,4-Michael-type adducts were hydrolyzed/oxidized to yield benzoquinone. Raman mapping data suggested that phenazine-like segments could be related to the formation of the microspheres morphology.

La(2-x)Ce(x)Cu(1-y)Zn(y)O(4) perovskites for high temperature water-gas shift reaction

The performance of La(2-x)Ce(x)Cu(1-y)Zn(y)O(4) perovskites as catalysts for the high temperature water-gas shift reaction (H T-W G S R) was investigated. The catalysts were characterized by EDS, XRD, BET surface area, TPR, and XANES. The results showed that all the perovskites exhibited the La(2)CuO(4) orthorhombic structure, so the Pechini method is suitable for the preparation of pure perovskite. However, the La(1.90)Ce(0.10)CuO(4) perovskite alone, when calcined at 350/700 degrees C, also showed a (La(0.935)Ce(0.065))(2)CuO(4) perovskite with tetragonal structure, which produced a surface area higher than the other perovskites. The perovskites that exhibited the best catalytic performance were those calcined at 350/700 degrees C and, among these, La(1.90)Ce(0.10)CuO(4) was outstanding, probably because of the high surface area associated with the presence of the (La(0.935)Ce(0.065))(2)CuO(4) perovskite with tetragonal structure and orthorhombic La(2)CuO(4) phase.

Hydrogen production by steam reforming of ethanol over Ni-based catalysts promoted with noble metals

The catalytic activity of Ni/La(2)O(3)-Al(2)O(3) Catalysts modified with noble metals(Pt and Pd) was investigated in the steam reforming of ethanol. The catalysts were characterized by ICP, S(BFT), X-ray diffraction, temperature-programmed reduction, UV-vis diffuse reflectance spectroscopy and X-ray absorption fine structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of La(2)O(3) dispersed on the alumina. The promoting effect of noble metals included a marked decrease in the reduction temperatures of NiO species interacting with the support. due to the hydrogen spillover effect, facilitating greatly the reduction of the promoted catalysts. it was seen that the addition of noble metal stabilized the Ni sites in the reduced state throughout the reaction, increasing ethanol conversion and decreasing coke formation, irrespective of the nature or loading of the noble metal. (C) 2009 Elsevier B.V. All rights reserved.

Co/Mg/Al hydrotalcite-type precursor, promoted with La and Ce, studied by XPS and applied to methane steam reforming reactions

Catalysts` precursor of Co/Mg/Al promoted with Ce and La were tested in the steam reforming of methane (SRM). The addition of promoters was made by anion-exchange. The oxides characterization was made by X-ray Photoelectron Spectroscopy (XPS) analysis that confirmed Co(2+) species in free form on surface and interacted with Mg and Al in the form of solid solution. In the SRM with high fed molar ratio of H(2)O:CH(4) = 4:1, the catalysts showed a great affinity with water and immediately deactivated by oxidation of the active sites. In the stoichiometric ratio of H(2)O:CH(4) = 2: 1 the catalysts were active and presented low carbon deposition during the time reaction tested. Also a test with low fed molar ratio H(2)O:CH(4) = 0.5:1 was carried out to evaluate the stability of the catalysts by CH(4) decomposition and all the catalysts were stable during 6 h of reaction. Promoted catalysts presented lower carbon deposition. (C) 2009 Elsevier B. V. All rights reserved.

Study of Water-Gas-Shift Reaction over La((1-y))Sr(y)Ni(x)Co((1-x))O(3) Perovskite as Precursors

The performance of La((1-y))Sr(y)Ni(x)Co((1-x))O(3) perovskites for the water gas shift reaction (WGSR) was investigated. The samples were prepared by the co- precipitation method and were performed by the BET method, XRD, TPR, and XPS. The catalytic tests were performed at 300 and 400 A degrees C and H(2)O(v)/CO = 2.3/1 (molar ratio). The sample with the highest surface area is La(0.70)Sr(0.30)NiO(3). The XRD results showed the formation of perovskite structure for all samples, and the La(0.70)Sr(0.30)NiO(3) sample also presented peaks corresponding to La(2)NiO(4) and NiO, indicating that the solubility limit of Sr in the perovskite lattice was surpassed. The replacement of Co by Ni favored the reduction of the species at lower temperatures, and the sample containing Sr presented the highest amount of reducible species, as identified by TPR results. All samples were active, the Sr containing perovskite appearing the most active due to the highest surface area, presence of the La(2)NiO(4) phase, and higher content of Cu in the surface, as detected by XPS. Among the samples containing Co, the most active one was that with x = 0.70 (60% of CO conversion).

Hydrogen purification for fuel cell using CuO/CeO(2)-Al(2)O(3) catalyst

CuO/CeO(2), CuO/Al(2)O(3) and CuO/CeO(2)-Al(2)O(3) catalysts, with CuO loading varying from 1 to 5 wt.%, were prepared by the citrate method and applied to the preferential oxidation of carbon monoxide in a reaction medium containing large amounts of hydrogen (PROX-CO). The compounds were characterized ex situ by X-ray diffraction, specific surface area measurements, temperature-programmed reduction and temperature-programmed reduction of oxidized surfaces; XANES-PROX in situ experiments were also carried out to study the copper oxidation state under PROX-CO conditions. These analyses showed that in the reaction medium the Cu(0) is present as dispersed particles. On the ceria, these metallic particles are smaller and more finely dispersed, resulting in a stronger metal-support interaction than in CuO/Al(2)O(3) or CuO/CeO(2)-Al(2)O(3) catalysts, providing higher PROX-CO activity and better selectivity in the conversion of CO to CO(2) despite the greater BET area presented by samples supported on alumina. It is also shown that the lower CuO content, the higher metal dispersion and consequently the catalytic activity. The redox properties of the ceria support also contributed to catalytic performance. (C) 2010 Elsevier B.V. All rights reserved.

Effects of adding La and Ce to hydrotalcite-type Ni/Mg/Al catalyst precursors on ethanol steam reforming reactions

Catalyst precursors composed of Ni/Mg/Al oxides with added La and Ce were tested in ethanol steam reforming (ESR) reactions. La and Ce were added by anion-exchange. The oxides were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) analysis. The catalyst precursors consist of a mixture of oxides, with the nickel in the form of NiO strongly interacting with the support Mg/Al. The XPS analysis showed a lanthanum-support interaction, but no interaction of Ce species with the support. The reaction data obtained with the active catalysts showed that the addition of Ce and La resulted in better H(2) production at 550 degrees C. The CeNi catalyst provided the higher ethanol conversion, with lower acetaldehyde production, possibly clue to a favoring of water adsorption on the weakly interacting clusters of CeO(2) on the surface. (C) 2010 Elsevier B.V. All rights reserved.