Showing papers on "Lanthanum published in 2010"

Effects of Single Metal-Ion Doping on the Visible-Light Photoreactivity of TiO2

Abstract: Titanium dioxide (M-TiO2), which was doped with 13 different metal ions (ie, silver (Ag+), rubidium (Rb+), nickel (Ni2+), cobalt (Co2+), copper (Cu2+), vanadium (V3+), ruthenium (Ru3+), iron (Fe3+), osmium (Os3+), yttrium (Y3+), lanthanum (La3+), platinum (Pt4+, Pt2+), and chromium (Cr3+, Cr6+)) at doping levels ranging from 01 to 10 at %, was synthesized by standard sol−gel methods and characterized by X-ray diffraction, BET surface area measurement, SEM, and UV−vis diffuse reflectance spectroscopy Doping with Pt(IV/II), Cr(III), V(III), and Fe(III) resulted in a lower anatase to rutile phase transformation (A−R phase transformation) temperature for the resultant TiO2 particles, while doping with Ru(III) inhibited the A−R phase transformation Metal-ion doping also resulted in a red shift of the photophysical response of TiO2 that was reflected in an extended absorption in the visible region between 400 and 700 nm In contrast, doping with Ag(I), Rb(I), Y(III), and La(III) did not result in a red s

Doped nanosized ceria solid solutions for low temperature soot oxidation: Zirconium versus lanthanum promoters

Abstract: The relative efficacies of zirconium and lanthanum promoters in ceria solid solutions were investigated systematically for low temperature soot oxidation. Thus nanosized CeO 2 –ZrO 2 (CZ, 1:1) and CeO 2 –La 2 O 3 (CL, 8:2) solid solutions, and a reference CeO 2 (C) were synthesized and investigated by means of various characterization techniques namely, XRD, TEM, BET surface area, XPS, UV–vis DRS, Raman and TPR. The catalytic efficiency for oxygen storage/release capacity (OSC) and soot oxidation were evaluated by a thermogravimetric (TG) method. The XRD results suggested formation of solid solutions and TEM studies confirmed nanosized nature of the particles. Raman and XPS measurements disclosed the presence of oxygen vacancies and lattice defects in both CZ and CL samples and these were more prominent in the case of CL sample. XPS studies revealed existence of both Ce 3+ and Ce 4+ (confirming redox nature), and the concentration of former is relatively higher in CL sample. The CL solid solution exhibited high intense and more resolved O 2− → Ce 3+ charge transfer transition band compared to CZ in the UV–vis DRS study. TPR measurements indicated a facile reduction of ceria after La 3+ incorporation. Activity studies revealed that La 3+ doped ceria accelerates the oxidation rate of soot compared to pure ceria and Zr 4+ doped ceria. An attempt has been made to explain the enhanced activity of CL sample in terms of active oxygen formation provoked by defective structure of ceria due to the presence of La 3+ .

Nickel- and Ruthenium-Doped Lanthanum Chromite Anodes: Effects of Nanoscale Metal Precipitation on Solid Oxide Fuel Cell Performance

Abstract: This paper compares the effects of Ni and Ru dopants in lanthanum chromite anodes by correlating structural characterization and electrochemical measurements in solid oxide fuel cells (SOFCs). Transmission electron microscope observations showed that nanoclusters of Ni or Ru metal precipitated onto lanthanum chromite (La 0.8 Sr 0.2 Cr 1-y X y O 3-δ , X = Ni,Ru) surfaces, respectively, after exposure to hydrogen at 750-800°C. Ni nanoclusters were typically ∼10 nm in diameter immediately after reduction and coarsened to ~50 nm over ~300 h at 800°C. In contrast, Ru cluster size was stable at ≤5 nm, and the cluster density was > 10 times larger. SOFC tests were done with the doped lanthanum chromite anodes on La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ electrolyte-supported cells. Ni nanocluster nucleation improved cell performance and reduced anode polarization resistance compared to cells with undoped (La 0.8 Sr 0.2 CrO 3-δ ) anodes, but the improvement was much less than that for Ru. This comparison suggests that the smaller size of the Ru nanoclusters played an important role in enhancing anode electrochemical kinetics.

Adsorption behavior of phosphate on Lanthanum(III) doped mesoporous silicates material.

Abstract: A series of lanthanum doped meosoporous MCM-41 (LaxM41, x is Si/La molar ratio) was prepared by sol-gel method The surface structure of the materials was investigated with X-ray diffraction and N2 adsorption/desorption technique The content of La in the materials was determined by ICP It was found that the La content of La25M41, La50M41 and La100M41 was 753%, 389% and 232%, respectively The phosphate adsorption capacities increased with increasing amount of La incorporation With 040 g La25M41 997% phosphate could be removed The effects of Si/La molar ratio, LaxM41 dose, pH, initial concentration of phosphate solution, co-ions on phosphate adsorption were also evaluated The phosphate adsorption kinetics of LaxM41 could be well-described by the pseudo second-order model, and Langmuir isotherm fit equilibrium data much better than the Freundlich isotherm

Lanthanum titanate and lithium lanthanum titanate thin films grown by atomic layer deposition

Abstract: Thin films of lanthanum titanate and lithium lanthanum titanate (LLT) have been grown by atomic layer deposition (ALD). Studies on the growth of lanthanum titanates showed that the lanthanum deposition rate is reduced when the titanium oxide and lanthanum oxide processes are combined, leading to higher titanium contents in the films. The precursor systems used for deposition of lanthanum titanates were TiCl4 + water and La(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) + ozone. Lithium was introduced into the material in order to deposit LLT by using lithium tert-butoxide (LiOtBu) and water as precursors. The deposited films were analyzed by time-of-flight elastic recoil detection analysis (TOF-ERDA), secondary ion mass spectrometry (SIMS), X-ray fluorescence (XRF), X-ray reflectivity (XRR) and X-ray diffraction (XRD). TOF-ERDA gave the film composition of Li0.32La0.30TiOz at saturation conditions.

Enhancement of ferromagnetic and dielectric properties in lanthanum doped BiFeO3 by hydrothermal synthesis

Abstract: Multiferroic Bi 1- x1 La x FeO 3 ( x = 0.0, 0.1, 0.2, and 0.3) micro-particles were successfully synthesized by a hydrothermal technique. All the samples were phase pure crystallizing in a perovskite structure with a space group of R 3 c . XRD refinement revealed that the lattice parameters increased along with increase of La content, while the Fe–O octahedra became more distorted. It was found that the morphologies of as-obtained micron-sized particles turned from spheroidal to octahedral according to different doping levels. The dielectric constant of Bi 1- x1 La x FeO 3 sample increased after La doping, and reached the largest value for the sample of x = 0.2, both in low and high frequency range at room temperature. All the as-prepared samples exhibited magnetic moments starting above room temperature. It was found that the magnetic moment was significantly enhanced from 0.264 emu/g of BiFeO 3 to 0.658 emu/g of Bi 0.9 La 0.1 FeO 3 in a field of 3 T at 77 K. Both enhancements of ferromagnetic and dielectric properties possibly attribute to the changes of lattice parameters and Fe–O bond lengths caused by lanthanum substitution.

Nature of N-N bonding within high-pressure noble-metal pernitrides and the prediction of lanthanum pernitride.

Abstract: The nature of nitrogen-nitrogen bonding and the metal oxidation states within late-noble-metal pernitrides have been determined by a series of density-functional electronic-structure calculations. In contrast to alkaline-earth pernitrides such as BaN(2) which contain quasi-molecular double-bonded N(2)(2-) units, compounds such as PtN(2) incorporate a tetravalent metal and a N(2)(4-) species with a N-N single bond due to four surplus electrons within the antibonding 1pi(g)* molecular orbital. This fact is the source of the huge bulk moduli of PtN(2) and related materials such as OsN(2) and IrN(2). The crystal structure of lanthanum pernitride, LaN(2) La(3+) + N(2)(2-) + e(-), yet to be made, has been predicted, and its electronic structure is compared with a likewise hypothetical LaN(2) which consists of both N(2)(2-) and N(2)(4-) pernitride units together with a trivalent lanthanum cation. Finite-temperature DFT calculations predict a very moderate reaction pressure toward LaN(2) starting from LaN and elemental nitrogen of less than 2 GPa at 300 K.

Cr3 + -Doped Lanthanum Gallogermanate Phosphors with Long Persistent IR Emission

Abstract: Lanthanum gallogermanate co-doped with chromium (La 3 Ga 5 GeO 14 :Cr 3+ ,M, where M = Li, Pb 2+ , Zn 2+ , Eu 3+ , Tm 3+ , and Dy 3+ ) samples have been prepared using a solid-state chemical reaction method. The phosphor with Dy 3+ is observed to have a persistent IR emission for more than 8 h, which is recorded using a spectrometer. The wavelength of the major IR emission is in the range from 700 to 1100 nm. The intensity of the phosphorescence and persistent time can be modified by co-doping proper trapping centers.

La–Mn perovskite-type oxide prepared by combustion method: Catalytic activity in ethanol oxidation

Abstract: The present work deals with the use of the combustion method to synthesize a series of lanthanum manganite (LM) and to study their physico-chemical and catalytic properties in ethanol deep oxidation. Some synthesis parameters such as chemical nature of the fuel molecules (glycine and citric acid) and additional thermal treatment were used and their effects on the powder characteristics were studied. XRD patterns showed a single phase perovskite-type oxide for all studied samples. Additional lanthanum oxocarbonate was observed on powder patterns of samples obtained with citric acid. The presence of chemisorbed carbonate species was studied by IR spectra analysis in the 2000–500 cm −1 , XRD and XPS analyses of the C1s and O1s levels. Their concentration was higher on surface samples prepared with citric acid than on those prepared with glycine. From XPS results, the use of glycine as gelling agent rather than citric acid and additional thermal treatment resulted in a decrease in superficial La/Mn atomic ratio and carbonate content and in an increase in relative content of the surface O 2 2− /O − species. These preparation parameters determined the best catalytic activity of the studied LM materials. Our results indicated that the catalytic activity in deep oxidation of ethanol over lanthanum manganite may be described as a synergetic effect of lanthanum and manganese. Ethanol activation was favoured by the strong basicity of lanthanum oxide at the surface of perovskite-structure and deep oxidation to CO 2 was enhanced by the activation of oxygen species on manganese site through a redox cycle.

Lanthanum doped multiferroic DyFeO3: Structural and magnetic properties

Abstract: Lanthanum doped multiferroic DyFeO3 was synthesized by solid state reaction. X-ray diffraction and refinement show that the lattice parameters of Dy1−xLaxFeO3 increase linearly with the La content. Raman spectroscopy reveals that the short-range force constant in Dy1−xLaxFeO3 is decreased by La3+ ion substitution. The spin reorientation phase transition temperature (TSRPT) is observed to decrease along with the doping level. The antiferromagnetic ordering temperature TN of Fe3+ ions is depressed with increasing doping level. Both decreasing TSRPT and decreasing TN indicate that Fe–Dy and Fe–Fe interactions are weakened by La substitution. It is found that the electron configuration of Fe3+ is high spin state and not affected by the La doping in all the samples above TN.

Factors Affecting Lanthanum and Cerium Biosorption on Pinus brutia Leaf Powder

Abstract: The biosorption behavior of lanthanum and cerium ions from aqueous solution by leaf powder of Pinus brutia was separately studied in a batch system as a function of initial pH, contact time, initial metal ion concentration, temperature, and adsorbent amount. The uptake of lanthanum and cerium was increased when the initial pH of the solution was increased. Thermodynamic parameters such as standard enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were calculated and the results indicated that biosorption was endothermic and spontaneous in nature. The biosorption of lanthanum and cerium on powdered leaf of Pinus brutia was investigated by the Freundlich, Langmuir, and D-R isotherms. The results show that lanthanum and cerium adsorption can be explained by the Langmuir isotherm model and monolayer capacity was found as 22.94 mg g−1 for lanthanum and 17.24 mg g−1 for cerium. Desorption of lanthanum and cerium was studied using 0.5 M HNO3 solution. The results suggested that powdered leaf of Pinus brutia ma...

Facile synthesis, growth mechanism and luminescence properties of uniform La(OH)3 : Ho3+/Yb3+ and La2O3 : Ho3+/Yb3+ nanorods

Abstract: One-dimensional (1D) La2O3 and La2O3 : Ln3+ (Ln = Ho/Yb) nanorods have been successfully synthesized at a mild condition via a facile homogenous precipitation method followed a heat treatment of their corresponding hydroxides. It can be found that the type of alkali and dosage of urea play crucial roles in the formation of uniform lanthanum hydroxide nanorods. The lanthanum hydroxide nanorods are morphology-formative intermediate for the formation of lanthanum oxides nanorods. The possible formation processes of 1-D lanthanum hydroxide and oxide nanorods were investigated. Under ultraviolet light and low-voltage electron beam excitation, the as-prepared Ho3+-doped La2O3 nanorods show a strong green emission corresponding to 5S2 → 5I8 transition of Ho3+ ions, which possesses sharper transition lines in the green region and higher color purity than that of commercial ZnO : Zn phosphor. At the same time, La2O3 : Ho3+ nanorods have higher luminescence intensity than its bulk samples under the same excitation condition. Furthermore, green and red up-conversion emissions originating from two-photon ESA and ET are also observed from the La2O3 : Yb3+, Ho3+ nanorod samples.

Fractional factorial design for the optimization of hydrothermal synthesis of lanthanum oxide nanoparticles under supercritical water condition

Abstract: In this research, synthesis of lanthanum oxide nanoparticles using supercritical water as a reaction medium in batch type reactor was studied. The crystallographic identity and morphology of the synthesized nanoparticles were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns indicate that the well-crystallized lanthanum oxide nanocrystals can be easily obtained under the current synthetic conditions. The effect of four parameters includes temperature, reaction time; primary concentration of aqueous solution of lanthanum (III) nitrate and pH of starting solution on reaction efficiency, particle size and the BET surface area were investigated using 2 4−1 fractional factorial design. Finally, by employing a regression analysis a model based on effect of significant main variables and their binary interactions was proposed which can predict the percentage of reaction efficiency with acceptable confidence.

Isobutane alkylation with solid catalysts based on beta zeolite

Abstract: The isobutane alkylation with butenes is a reaction in which the substitution of mineral acids, such as sulphuric and hydrofluoric acids, by solid acid catalysts is highly desirable. Solid catalysts with good activity and selectivity for this reaction have been previously reported. However, bad stability is a major drawback in most cases. In this work, catalysts based on beta zeolite, exchanged with lanthanum were studied. It was found that these catalysts have lower activity than the Y zeolite both, in the protonic form, or with lanthanum in replacement of protons. EDX analyses showed that lanthanum is practically fully removed from the zeolite structure during an exchange with ammonium nitrate, even though the catalyst was precalcined. The total acidity as measured by pyridine temperature-programmed desorption is similar in the beta and the Y zeolites. However, the former zeolite has stronger acid sites, and because of this, the deactivation process occurs faster. Pulses of 1-butene at different temperatures can be used as a technique to predict the catalytic behavior of acid catalysts in the alkylation reaction. Using this technique, it was possible to determine that the beta zeolite is deactivated during the alkylation reaction by pore mouth plugging. The addition of platinum to the beta zeolite is useful in order to regenerate the catalyst using hydrogen at 80 °C, although long times are needed to accomplish this regeneration.