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Several lanthanum hydroxides (28-146 m/g) were prepared by different procedures involving precipitation and hydrothermal methods by conventional heating or with microwaves. The use of ultrasounds during precipitation led to the formation of additional crystalline phases whereas the aging treatment with microwaves decreased the temperature needed to form the lanthanum oxide phase when compared with the samples aged by conventional heating. After calcination, LaO samples showed similar BET surface areas (3-5 m/g) but different particle sizes ranging from 150 to 600 nm depending on the La(OH) preparation method, as observed by TEM. LaO samples were completely rehydroxylated after 80 h of exposure to atmospheric air at controlled humidity conditions recovering only partially the surface areas of the La(OH) precursors (14-18 m/g). The progress of rehydroxylation with time occurred in several steps at different rates. Rehydroxylation rate mainly depended on the particle size and surface area of the lanthanum oxide sample. Therefore, the method used to prepare the initial lanthanum hydroxide affects the surface and rehydroxylation properties of the subsequent lanthanum oxide sample. [ABSTRACT FROM AUTHOR]

Abstract: Europium-doped La2O3 nanocrystalline powders with sizes ranging from 4nm to 300nm have been obtained by the modified Pechini, hydrothermal with conventional furnace, hydrothermal with microwave furnace, and precipitation with ultrasonic bath methods. X-ray diffraction techniques were used to study the evolution of the prepared gels towards the desired crystalline phase. We determined the size and the morphology of the nanoparticles by electronic microscopy. Finally, we studied and analyzed the luminescence properties of the trivalent europium in the hexagonal La2O3 nanocrystals by photoluminescence and cathodoluminescence. [Copyright &y& Elsevier]

Shape controlled metal nanoparticles were studied in the epoxidation of olefins. PVP mediated polyol processes were employed to generate silver nanowires/rods, nanocubes and nanopolyhedra. Spherical copper nanoparticles were also obtained by the polyol process. The mean diameter of the silver nanoparticles was around 150 nm. Furthermore, Cu nanoparticles were synthesized in an ethanol solution using CTAB as surfactant and as reducing agent. Additionally Au nanoparticles were synthesized by a phase-transfer system irradiated with 254 nm UV light. The mean diameter of these Au and Cu nanoparticles was around 10 nm. The catalytic activity of these nanoparticles on several supports such as α-Al2O3, CaCO3 and spherical particles of TiO2 obtained by the Stöber method was investigated in the epoxidation of a no-allylic olefin such as styrene, as well as for an allylic olefin, such as propene, using molecular oxygen and N2O as oxidants. The effect of Cs promotion in the styrene epoxidation was also investigated. The type of metal, the particle size, the support and the oxidant, as well as the addition of promoters such as Cs, showed a strong influence towards the formation of selective oxidation products. The metal nanoparticles were characterized employing various techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), UV-visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ICP-AES. [ABSTRACT FROM AUTHOR]

We have studied the preparation of silver-gold alloy nanoparticles based on the phase transfer of metal precursors from aqueous phase to organic solution by a fatty amine at room temperature. Silver-gold nanoparticles were synthesized with different molar ratios (2:1, 1:1, 1:2). Ultraviolet-visible absorption spectra suggested the formation of alloy phases. The elemental Ag:Au ratios in the bimetallic nanoparticles determined by energy dispersive x-ray analysis (EDX) were consistent with the Ag:Au molar ratios used in the feeding solution. Transmission electron microscopy (TEM) revealed the formation of a uniform size distribution of Ag:Au nanoparticles (around 5 nm). X-ray photoelectron spectroscopy (XPS) showed that the composition in the outer part of the Ag:Au nanoparticles was similar to that obtained by EDX analysis, which indicates the formation of homogeneous silver-gold nanoparticles. Silver-gold alloy nanoparticles on a gram scale can be obtained with this method. [ABSTRACT FROM AUTHOR]

Abstract: Europium-doped La2O3 nanocrystalline powders with sizes in the range of 50–200nm have been obtained by the modified sol–gel Pechini method. These nanocrystals have been deagglomerated using sonication for 3h and have been dispersed into a semiconductor P3HT polymeric matrix. We studied and analysed the spectroscopic properties of the trivalent europium in the hexagonal La2O3 nanocrystals dispersed in the polymer. The luminescence spectrum of Eu3+ in these nanocrystals is dominated by the 5D0 → 7F2 transition with a maximum intensity peak located at 626nm. We observed that P3HT absorbs part of the light emitted by the nanoparticles. These properties look promising for using this material as a down-converter material in solar cells. [Copyright &y& Elsevier]

Abstract: Europium-doped La2O3 nanocrystalline powders with sizes in the range of 50–200nm have been obtained by the modified sol–gel Pechini method. Differential thermal analysis, thermogravimetric analysis, infrared spectroscopy and X-ray diffraction were used to study the evolution of the precursor powders towards the desired crystalline phase. We determined the size and the morphology of the nanoparticles by electronic microscopy. Finally, we studied and analyzed the luminescence properties of the trivalent europium in the hexagonal La2O3 nanocrystals by photoluminescence and cathodoluminescence. The luminescence spectrum of Eu3+ in these nanocrystals is dominated by the 5D0 → 7F2 transition with its maximum intensity peak located at 626nm, which makes of these nanocrystals promising nanophosphors emitting in the red region of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

Abstract: The increasing pollution of natural sources of drinking water encourages the development of new emerging technologies and processes for water remediation. This work deals with the study of catalytic reduction of contaminated waters containing nitrates (60ppm) in a continuous reactor working at room temperature and atmospheric pressure and using hydrogen as reducing agent. Optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found. Besides, novel catalysts obtained from copper nanoparticles doped with Pd or Pt and supported on activated carbon, have also been studied. For all catalysts the Pt-Cu pair seems to be more selective in the transformation of the nitrates ions to nitrogen compared to Pd-Cu pair. Furthermore, considering the noble metal amount, the bimetallic nanosphere catalysts are more active (between 20 and 50) than the impregnated ones. The catalysts have been characterized by hydrogen chemisorption, BET, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. During the reaction, a considerable amount of the noble metal in its oxidised form has been detected. Based on this result an additional step to the generally accepted reaction mechanism of the nitrate reduction has been proposed. [Copyright &y& Elsevier]

Abstract: This study shows how different morphologies of silver nanoparticles affect the selective oxidation of styrene in the gas phase using oxygen as oxidant. Silver nanoparticles (nanowires and nanopolyhedra), prepared using the polyol process, were supported on α-Al2O3. For comparison, a conventional catalyst obtained by wet impregnation was also prepared. Phenylacetaldehyde (Phe) and styrene oxide (SO) were the main products for nanoparticles catalysts. The promotion effect on the catalytic activity of potassium and cesium on the silver nanowires catalysts was also studied. At 573K, the styrene conversion and selectivity to styrene oxide with the silver nanowires catalyst were 57.6 and 42.5%, respectively. Silver nanopolyhedra catalyst showed 57.5% conversion and 30.8% selectivity to styrene oxide. The promotion by cesium played an important role in improving the epoxidation of styrene. The samples were structurally characterized using X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were applied to characterize the oxygen species detected (Oβ, Oγ) on the silver surface. [Copyright &y& Elsevier]