Showing papers on "Lanthanum published in 2015"

Thermoelectric power generation from lanthanum strontium titanium oxide at room temperature through the addition of graphene

Abstract: The applications of strontium titanium oxide based thermoelectric materials are currently limited by their high operating temperatures of >700 °C. Herein, we show that the thermal operating window of lanthanum strontium titanium oxide (LSTO) can be reduced to room temperature by the addition of a small amount of graphene. This increase in operating performance will enable future applications such as generators in vehicles and other sectors. The LSTO composites incorporated one percent or less of graphene and were sintered under an argon/hydrogen atmosphere. The resultant materials were reduced and possessed a multiphase structure with nanosized grains. The thermal conductivity of the nanocomposites decreased upon the addition of graphene, whereas the electrical conductivity and power factor both increased significantly. These factors, together with a moderate Seebeck coefficient, meant that a high power factor of ∼2500 μWm–1 K–2 was reached at room temperature at a loading of 0.6 wt % graphene. The highes...

Lanthanum Manganite Perovskites with Ca/Sr A‐site and Al B‐site Doping as Effective Oxygen Exchange Materials for Solar Thermochemical Fuel Production

Abstract: Perovskite oxides have recently been proposed as promising redox intermediates for solar thermochemical splitting of H2O and CO2, offering the benefit of significantly reduced operating temperatures. We present a systematic experimental screening of doped lanthanum manganites within the composition space La1−x(Ca,Sr)xMn1−yAlyO3 and identify several promising redox materials. In particular, La0.6Sr0.4Mn0.6Al0.4O3 and La0.6Ca0.4Mn0.6Al0.4O3 boast a five- to thirteen-fold improvement in the reduction extent compared to the state-of-the-art material CeO2 in the temperature range 1200–1400 °C. The materials are shown to be capable of splitting CO2 into CO fuel when isothermally cycled between low-pO2 and high-pCO2 environments at 1240 °C and to approach full reoxidation in CO2 with temperature swings as low as 200 °C, with mass-specific fuel yields up to ten times that of CeO2. The underlying material thermodynamics are investigated and used to explain the favorable redox behavior.

A microporous lanthanum metal-organic framework as a bi-functional chemosensor for the detection of picric acid and Fe(3+) ions.

Abstract: A microporous lanthanum metal–organic framework [La(TPT)(DMSO)2]·H2O (La-MOF (1)), has been synthesized using a rigid unsymmetrical tricarboxylate ligand of p-terphenyl-3,4′′,5-tricarboxylic acid (H3TPT). The structure of 1 is constructed by bi-nuclear lanthanum clusters and fully deprotonated TPT3− ligands, which can be simplified into a 3,6-connected flu-3,6-C2/c topology with a point symbol of (44·6)2(4·62·87·102). The π-electron rich ligand H3TPT enables 1 to have blue luminescence when excited at 342 nm at ambient temperature. Meanwhile, 1 exhibits the selective detection of picric acid (PA) and Fe3+ ions in ethanol solution over other nitroaromatic compounds and metal ions. The high quenching efficiency and selectivity of 1 makes it a potential bi-functional chemosensor for both PA and Fe3+ ions.

Characterization of phosphate sequestration by a lanthanum modified bentonite clay: a solid-state NMR, EXAFS, and PXRD study.

Abstract: Phosphate (Pi) sequestration by a lanthanum (La) exchanged clay mineral (La-Bentonite), which is extensively used in chemical lake restoration, was investigated on the molecular level using a combination of 31P and 139La solid state NMR spectroscopy (SSNMR), extended X-ray absorption spectroscopy (EXAFS), powder X-ray diffraction (PXRD) and sorption studies. 31P SSNMR show that all Pi was immobilized as rhabdophane (LaPO4·n H2O, n ≤ 3), which was further supported by 139La SSNMR and EXAFS. However, PXRD results were ambiguous with respect to rhabdophane and monazite (LaPO4). Adsorption studies showed that at dissolved organic carbon (DOC) concentration above ca. 250 μM the binding capacity was only 50% of the theoretical value or even less. No other La or Pi phases were detected by SSNMR and EXAFS indicating the effect of DOC is kinetic. Moreover, 31P SSNMR showed that rhabdophane formed upon Pi sequestration is in close proximity to the clay matrix.

Versatile Nickel–Lanthanum(III) Catalyst for Direct Conversion of Cellulose to Glycols

Abstract: Using cellulosic biomass to synthesize bulk quantities of high-value chemicals is of great interest for developing a sustainable biobased society. Especially, direct catalytic conversion of cellulose to glycols, important building blocks for polymers, remains a grand challenge. Herein, we report the development of a versatile binary nickel–lanthanum(III) catalyst for the conversion of cellulose to both ethylene glycol (EG) and propylene glycol (1,2-PG) in a yield of 63.7%, which is one of the best performances reported for this catalytic reaction. Especially, lanthanum(III) exhibited a high level of activity toward the degradation of cellulose (TON = 339) at a very low concentration (0.2 mmol/L). On the basis of density functional theory calculations and experimental analyses, we addressed a dual route for this catalytic mechanism: a major route involving the selective cracking of sugars into C2 molecules and a minor route involving the hydrogenolysis of sugar alcohols. Lanthanum(III) catalyzes the cleava...

Biosorption of lanthanum and cerium from aqueous solutions by grapefruit peel: equilibrium, kinetic and thermodynamic studies

Abstract: The biosorption characteristics of lanthanum and cerium ions from aqueous solution by grapefruit peel have been investigated as a function of pH, biosorbent dosage, contact time, and temperature. The pH was found to be significantly affecting the biosorption performance: pH 5.0 was found to be an optimum pH for favorable biosorption of lanthanum and cerium ions. The experimental isotherm data were analyzed using Langmuir and Freundlich equations. The Langmuir model fits the equilibrium data better than the Freundlich model. According to the Langmuir equation, the maximum uptake for La(III) and Ce(III) ions were 171.20 and 159.30 mg/g, respectively. Pseudo-first-order and pseudo-second-order models were used to represent the kinetics of the process. The results show that the pseudo-second-order model is the one that best describes the kinetics of the biosorption of both metal ions. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) show that the biosorption process is feasible, spontaneous, and endothermic at 20–50 °C. FTIR analysis demonstrates that carboxyl and hydroxyl groups are involved in the biosorption of the metal ions. This study shows that grapefruit peel has the potential of application as an efficient biosorbent for the removal of lanthanide elements from aqueous solutions.

Lanthanum chromite based perovskites for oxygen transport membrane

Abstract: Judicious selection of mixed ionic–electronic conducting (MIEC) perovskite oxide as oxygen transport membrane (OTM) offers the potential to enhance overall process economics and systems performance for a wide variety of industrial applications ranging from clean and efficient energy conversion (oxy-combustion) to selective gas separation (high purity oxygen production) and value added chemicals (syngas and liquid fuel) production with near-zero greenhouse gas emissions. Doped lanthanum chromite perovskites have been considered as promising material of choice for oxygen transport membrane (OTM) due to their superior thermo-chemical stability in aggressive environment (800–1000 °C, 0.21–10−20 P O 2 ) than the other mixed ionic–electronic conducting (MIEC) perovskites such as ferrites and cobaltite's. Thermo-physical properties of the lanthanum chromite, required for optimum oxygen transport can be tuned by modifying the crystal structure, chemical bonding, and ionic and electronic transport properties through selection of dopant's type and level. A perspective on the development of lanthanum chromite-based oxygen transport membranes is presented with an insight based on the pertinent literature and data analysis. The role of various A- and B-site dopants on the crystal structure, densification, thermal expansion, electrical transport, oxygen permeation, mechanical properties, and thermochemical stability of lanthanum chromite is discussed to enlighten ‘composition–structure–property’ correlations. It has been found that: the preferred dopants are strontium at A-site and manganese, nickel, iron, and titanium at B-site to obtain the desired thermo–chemo–electro–mechano properties. Challenges for long term performance and structural stability of doped lanthanum chromite as an oxygen transport membrane are outlined for the applications under ‘real system’ exposure conditions.

Mesoporous Mn- and La-Doped Cerium Oxide/Cobalt Oxide Mixed Metal Catalysts for Methane Oxidation

Abstract: New precious-metal-free mesoporous materials were investigated as catalysts for the complete oxidation of methane to carbon dioxide. Mesoporous cobalt oxide was first synthesized using KIT-6 mesoporous silica as a hard template. After removal of the silica, the cobalt oxide was itself used as a hard template to construct cerium oxide/cobalt oxide composite materials. Furthermore, cerium oxide/cobalt oxide composite materials doped with manganese and lanthanum were also prepared. All of the new composite materials retained the hierarchical long-range order of the original KIT-6 template. Temperature-programmed oxidation measurements showed that these cerium oxide/cobalt oxide and doped cerium oxide/cobalt oxide materials are effective catalysts for the total oxidation of methane, with a light-off temperature (T50%) of ∼400 °C observed for all of the nanostructured materials.

Extensive lanthanum deposition in the gastric mucosa: the first histopathological report.

Abstract: Lanthanum carbonate is one of the new phosphate binders used for the treatment of hyperphosphatemia in patients with chronic kidney disease. It is poorly absorbed from the gastrointestinal tract, forms insoluble complexes within the lumen, and prevents the absorption of dietary phosphate. A 63-year-old female with a 7-year history of peritoneal dialysis, who was treated with lanthanum carbonate for four years, underwent endoscopic submucosal dissection for intramucosal gastric cancer. Resected specimens showed massive accumulation of macrophages containing fine, granular, brown material in the lamina propria. This was confirmed as lanthanum deposition by scanning electron microscopy with energy dispersive x-ray spectroscopy. Although lanthanum may be poorly absorbed, increased tissue accumulation of lanthanum, particularly in the liver and bone, has been reported in animals with chronic kidney disease. This report indicates enhanced gastrointestinal absorption of lanthanum in some patients or conditions, although its clinical significance awaits further studies.

The Effect of Temperature and Support on the Reduction of Cobalt Oxide: An in Situ X-ray Diffraction Study

Abstract: In situ X-ray diffraction was used to study the reduction of unsupported CoO, and Co3O4 under different conditions of time and temperature, and the effect of lanthanum, ruthenium, or zinc doping of γ-alumina on the reduction of supported cobalt oxide. The reduction of unsupported cobalt oxide (Co3O4) produced CoO, then hexagonal close-packed Co (Co(hcp)) and at temperatures above 400 °C, only face-centered cubic Co (Co(fcc)) was obtained. However, it was possible to obtain a mixture of Co(hcp) and Co(fcc) at 450 °C only when the reduction was performed stepwise. Metallic Co(fcc) was obtained after reduction at 350 °C of supported Co3O4 on doped alumina; however, the reduction of unsupported CoO under the same conditions produced Co(hcp). Doping alumina with ruthenium oxide favors the reduction of Co3O4 to CoO and then to metallic Co(fcc). The crystal size apparently affects the phase of metallic cobalt obtained.

Raman and X-ray Studies of Uranium–Lanthanum-Mixed Oxides Before and After Air Oxidation

Abstract: UO2 samples doped with 6, 11, 22 mol% lanthanum were examined before and after air oxidation. To verify the formation of uranium–lanthanum-mixed oxide solid solutions, powder X-ray diffraction (XRD) analyses of the crystalline phases in the materials were carried out. The presence of oxygen vacancies in the La-doped UO2 samples was identified by Raman spectrometry. It was evidenced by changes induced in the Raman spectra by air oxidation. This latter was carried out either by increasing the Raman laser power or by thermally treating the samples at 500 K for 370 h. In addition, oxidation behavior differences of pure and La-doped UO2 samples were reported by comparing XRD and Raman results of the samples before and after air oxidation. It was shown that the concentration of the M4O9 (M: U, La) phase increased with increasing content of La, whereas inhibition for the formation of M3O8 phase was observed.

Synthesis and support composition effects on CH4 partial oxidation over Ni–CeLa oxides

Abstract: Two series of Ni (6 wt%) catalysts supported over CeO 2 , La 2 O 3 and mixed CeO 2 –La 2 O 3 were prepared by co-precipitation and by wet-impregnation. The effect of the two Ni loading procedures on the catalyst structural properties was investigated by XRD, TPR and XPS. The catalytic behavior of the catalysts was tested in the methane partial oxidation reaction performed at 1 atm in a temperature range of 400–800 °C using dilute feed gas mixture with CH 4 /O 2 = 2 and gas hourly space velocity of 60,000 ml g −1 h −1 . Total methane combustion was observed within the 450 °C ≤ T ≤ 650 °C temperature range. Above 650 °C partial oxidation of methane started to occur, reaching at 800 °C a CO selectivity close to 90%. The lanthanum containing catalysts prepared by wet impregnation exhibited higher CPO activity at lower temperature as compared to the co-precipitated ones. Opposite behavior was observed with the Ni–CeO 2 catalysts. During the stability test at high temperature, carbon formed only over the single oxide supported catalysts, Ni–CeO 2 and Ni–La 2 O 3 . According to the characterization results carbon was not responsible for catalyst deactivation but it prevented the sintering of the nickel particle. The interplay of the crystallite sizes and the formation of various nickel–lanthanum oxide species with different Ni oxidation states were responsible for the differences in the CPO performance.

Tuning oxygen vacancy photoluminescence in monoclinic Y2WO6 by selectively occupying yttrium sites using lanthanum

Abstract: The effect of isovalent lanthanum (La) doping on the monoclinic Y2WO6 photoluminescence was studied. Introducing the non-activated La3+ into Y2WO6 brings new excitation bands from violet to visible regions and strong near-infrared emission, while the bands position and intensity depend on the doping concentration. It is interesting to find that doping La3+ into Y2WO6 promotes the oxygen vacancy formation according to the first-principle calculation, Raman spectrum, and synchrotron radiation analysis. Through the Rietveld refinement and X-ray photoelectron spectroscopy results, La3+ is found to mainly occupy the Y2 (2f) site in low-concentration doped samples. With increasing doping concentration, the La3+ occupation number at the Y3 (4g) site increases faster than those at the Y1 (2e) and Y2 (2f) sites. When La3+ occupies different Y sites, the localized energy states caused by the oxygen vacancy pair change their position in the forbidden band, inducing the variation of the excitation and emission bands. This research proposes a feasible method to tune the oxygen vacancy emission, eliminating the challenge of precisely controlling the calcination atmosphere.

Synthesis, characterization and study of lanthanum phosphates as light alcohols dehydration catalysts

Abstract: Four preparation methods have been developed for the synthesis of lanthanum orthophosphate catalysts, which are shown to be active and selective catalysts for the dehydration of light alcohols (C2 to C4). Their crystallinity, surface area, surface composition and acid–base properties appear to differ according to the preparation method used. The most important parameter influencing their catalytic properties appears to be their surface composition since this has a direct influence on their surface acidity. All of the solids presented weak and moderately strong Bronsted and Lewis acid sites, and only weak basic sites in low quantities. These acid–base properties resulted in the prevalence of an E1-type mechanism for 1-butanol dehydration. Bronsted acid sites, which appear as the most efficient sites, are associated with the presence of an excess of phosphorus at their surface and from spectroscopic data this is attributed to (H2PO4)−3+n (n = 1 or 2) species from spectroscopic data. The prevalence of these species and their optimum surface distribution make them extraordinarily efficient and ultra-selective for the dehydration of several alcohols.

Investigations On Multiferroic, Optical And Photocatalytic Properties Of Lanthanum Doped Bismuth Ferrite Nanoparticles

Abstract: Single phase Bi1-xLaxFeO3 nanoparticles have been successfully synthesized with varied concentration (0.0 ≤ x ≤ 0.2) for the photocatalytic degradation of an industrial dye. The room temperature X-ray diffraction (XRD) pattern of La 3+ doped BiFeO3 nanoparticles reveals the structural phase transition from rhombohedral (R3c) to orthorhombic (Pnma) at x=0.1, which is further analyzed via Rietveld refinement. The La 3+ doped BiFeO3 nanoparticles have much negative enthalpy of formation (ΔHf) than undoped BiFeO3. The particle size gradually decreases from ~132 to ~68 nm with La 3+ doping. Magnetic and ferroelectric transition temperatures are found to be slightly shifted towards room temperature upto x= 0.1 and then higher temperature side which could be attribute to the particle size effect. All compositions presented weak ferromagnetic ordering, which indicates that the La 3+ substitution in the BiFeO3 matrix released the latent magnetization. The increase in the energy band gap from 2.045 to 2.658 eV with cutoff wavelengths 639.58 and 513.061 nm for x=0.0 and 0.2 respectively, increases the visible light efficiency of photocatalytic activity in La 3+ doped BiFeO3 samples. The photodegradation efficiency of La 3+ doped BiFeO3 for azo-dye RB-5 is observed to be ~27% higher as compared to the undoped BiFeO3 (43% photodegradation efficiency), which makes it suitable for visible-light responsive photocatalysis for photocatalytic applications. Copyright © 2015 VBRI Press.