Showing papers on "Lanthanum published in 2017"

Enhanced Phosphorus Locking by Novel Lanthanum/Aluminum–Hydroxide Composite: Implications for Eutrophication Control

Abstract: Lanthanum (La) bearing materials have been widely used to remove phosphorus (P) in water treatment. However, it remains a challenge to enhance phosphate (PO4) adsorption capacity and La usage efficiency. In this study, La was coprecipitated with aluminum (Al) to obtain a La/Al–hydroxide composite (LAH) for P adsorption. The maximum PO4 adsorption capacities of LAH (5.3% La) were 76.3 and 45.3 mg P g–1 at pH 4.0 and 8.5, which were 8.5 and 5.3 times higher than those of commercially available La-modified bentonite (Phoslock, 5.6% La), respectively. P K-edge X-ray absorption near edge structure analysis showed that PO4 was preferentially bonded with Al under weakly acid conditions (pH 4.0), while tended to associate with La under alkaline conditions (pH 8.5). La LIII-edge extended X-ray absorption fine structure analysis indicated that PO4 was bonded on La sites by forming inner sphere bidentate-binuclear complexes and oxygen defects exhibited on LAH surfaces, which could be active adsorption sites for PO4....

Removal Mechanisms of Phosphate by Lanthanum Hydroxide Nanorods: Investigations using EXAFS, ATR-FTIR, DFT, and Surface Complexation Modeling Approaches.

Abstract: Lanthanum-based materials are effective for sequestering phosphate in water, however, their removal mechanisms remain unclear, and the effects of environmentally relevant factors have not yet been studied. Hereby, this study explored the mechanisms of phosphate removal using La(OH)3 by employing extended X-ray absorption spectroscopy (EXAFS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), density functional theory (DFT) and chemical equilibrium modeling. The results showed that surface complexation was the primary mechanism for phosphate removal and in binary phosphate configurations, namely diprotonated bidentate mononuclear (BM-H2) and bidentate binuclear (BB-H2), coexisting on La(OH)3 in acidic conditions. By increasing the pH to 7, BM-H1 and BB-H2 were the two major configurations governing phosphate adsorption on La(OH)3, whereas BB-H1 was the dominant configuration of phosphate adsorption at pH 9. With increasing phosphate loading, the phosphate configuration of on ...

Key factors in Sr-doped LaBO3 (B = Co or Mn) perovskites for NO oxidation in efficient diesel exhaust purification

Abstract: Perovskites have attracted attention in recent years as an economic alternative to noble metals in oxidation processes. Synthesis conditions of LaCoO3 and LaMnO3 perovskites have been studied varying citrate to nitrate molar ratio in the starting solution, pH and calcination protocol, with the aim of obtaining high purity perovskites, absence of impurities, and with enhanced textural properties. Once synthesis conditions were established, strontium was incorporated in the perovskite lattice as a textural and structural promoter, by substituting lanthanum with different doping levels, i.e. La0.9Sr0.1BO3, La0.8Sr0.2BO3, La0.7Sr0.3BO3, La0.6Sr0.4BO3 and La0.5Sr0.5BO3 with B = Co or Mn. The prepared solids were characterized in terms of crystalline phase identification (XRD), specific surface area (N2 adsorption–desorption at −196 °C), reducibility and oxidation state of transition metal ions (H2-TPR), quantification of adsorbed oxygen species (O2-TPD) and surface elemental composition (XPS). Charge imbalance associated to strontium (Sr2+) incorporation in the perovskite lattice in substitution of lanthanum (La3+) was preferentially balanced by Mn4+ promotion in La1−xSrxMnO3 perovskites, whereas formation of oxygen vacancies seems to be the mechanism for charge compensation in La1−xSrxCoO3 perovskites, where Co ions remained as Co3+ ions. Strontium doped perovskites further improved NO conversion compared to the non-substituted formulations. The best NO oxidation performance was obtained with La0.7Sr0.3CoO3 and La0.9Sr0.1MnO3 samples, achieving maximum NO conversion of 83 and 65% at 300 and 325 °C, respectively. Higher oxidation capacity of La0.7Sr0.3CoO3 sample was associated to the higher oxygen mobility and exchange capacity between oxygen in the lattice and gas phase oxygen. It is worth noting that prepared perovskites presented far higher NO oxidation capacity than platinum-based NSR model catalysts, confirming perovskites as an economic alternative to catalyze NO oxidation reactions in automotive catalysis.

Remarkable catalytic properties of rare-earth doped nickel ferrites synthesized by sol-gel auto-combustion with maleic acid as fuel for CWPO of dyes

Abstract: NiFe1.98RE0.02O4 (where RE = La, Sm, Gd and Dy) spinel ferrites were synthesized by sol–gel autocombustion method using maleic acid as fuel. The effect of rare-earth cations (RE) doping on structural, magnetic and catalytic properties of nickel ferrite is reported. XRD and FT-IR analysis revealed the successful insertion of the rare-earth cations into the spinel matrix in all samples. We observed a decreasing of crystallite and particle sizes (estimated from XRD patterns and TEM micrographs, respectively) as well as the magnetization value in the presence of lanthanide ions into the spinel structure. Additionally, these ferrites were employed as heterogeneous catalysts for catalytic wet hydrogen peroxide oxidation (CWPO) of Orange II azo-dye. The color removal efficiency was boosted from 30.6% for undoped nickel ferrite to 90.6% for the lanthanum doped nickel ferrite, after only 15 min of reaction. The decolorization of Orange II solution followed the pseudo-first-order kinetics and was achieved via decay reaction as demonstrated by Langmuir-Hinshelwood model. The remarkable increase in catalytic performance of doped nickel ferrites with a very small amount of rare-earth cations was correlated with the size factor, expressed as the ratio between particle and crystallite size. The desirability function approach enabled to identify the optimal material (NiFe1.98La0.02O4) with the best catalytic performance; the smallest size factor and appropriate magnetic properties.

Influence of La3+ Substitution on Structure, Morphology and Magnetic Properties of Nanocrystalline Ni-Zn Ferrite.

Abstract: Lanthanum substituted Ni-Zn ferrite nanoparticles (Ni0.5Zn0.5LaxFe1-xO4; 0.00 ≤x≤ 1.00) synthesized by sol-gel method were presented. X-ray diffraction patterns reveal the typical single phase spinel cubic ferrite structure, with the traces of secondary phase for lanthanum substituted nanocrystals. In addition, the structural analysis also demonstrates that the average crystallite size varied in the range of 21-25 nm. FTIR spectra present the two prominent absorption bands in the range of 400 to 600 cm-1 which are the fingerprint region of all ferrites. Surface morphology of both substituted and unsubstituted Ni-Zn ferrite nanoparticle samples was studied using FESEM technique and it indicates a significant increase in the size of spherical shaped particles with La3+ substitution. Magnetic properties of all samples were analyzed using vibrating sample magnetometer (VSM). The results revealed that saturation magnetization (Ms) and coercivity (Hc) of La3+ substituted samples has decreased as compared to the Ni-Zn ferrite samples. Hence, the observed results affirm that the lanthanum ion substitution has greatly influenced the structural, morphology and magnetic properties of Ni-Zn ferrite nanoparticles.

Facile preparation and characterization of lanthanum-loaded carboxylated multi-walled carbon nanotubes and their application for the adsorption of phosphate ions

Abstract: A new carboxylated multi-walled carbon nanotubes adsorbent modified with lanthanum hydroxide (MWCNTs-COOH-La) was prepared, characterized and investigated for phosphate removal in batch experiments. The maximum adsorption capacity of the MWCNTs-COOH-La was 48.02 mg P g−1 according to Langmuir model. Structural characterizations demonstrated that the MWCNTs-COOH-La was successfully synthesized and La species was present in the form of La(OH)3. Batch experiments were performed under various conditions (e.g., initial concentrations, temperature, pH, co-existing ions) to investigate the removal of phosphate by MWCNTs-COOH-La. Equilibrium data agreed very well with the Langmuir model, suggesting that the adsorption feature was monolayer. The adsorption behaviors of phosphate were described better by the pseudo-second-order, indicating that the adsorption behaviors were mainly ascribed to chemic-sorption. Phosphate adsorption varied slightly at pH 3–7, but decreased significantly at higher pH values. Phosphate adsorption was slightly influenced by solution ionic strength. A high selectivity of phosphate was also observed in the presence of co-existing anions (except CO3 2−). The underlying mechanism for the specific adsorption of phosphate by MWCNTs-COOH-La was fully analyzed by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy technologies. The above results revealed that the hydroxyl groups were involved in the sorption of phosphate and LaPO4 was formed during the adsorption process. This study implied that MWCNTs-COOH-La might be an alternatively viable and promising adsorbent for removal of phosphate from aqueous solution.

Linear Optical Properties of Zinc Borotellurite Glass Doped with Lanthanum Oxide Nanoparticles for Optoelectronic and Photonic Application

Abstract: Enhancing the optical properties of glasses for the sake of optical application in various fields is an ongoing challenge in materials science and technology. Thus, the optical properties of zinc borotellurite glass doped with lanthanum oxide nanoparticles (La2O3 NPs) with the chemical composition of {[(TeO2)0.7(B2O3)0.3]0.7(ZnO)0.3}1−x (La2O3 NPs)x, where = 0.01, 0.02, 0.03, 0.04, and 0.05 molar fraction, have been investigated. Characterization techniques such as x-ray diffraction, Fourier Transform Infrared Spectroscopy, and Ultraviolet-Visible Spectroscopy are employed to yield the structural properties and optical parameter of the glass. The amorphous nature of the fabricated glasses is confirmed with the presence of a broad hump via XRD diffraction pattern. The decreasing amount of high polarizable nonbridging oxygen as the concentration of La2O3 NPs increases has contributed to the increasing trend of energy band gap in the range of 2.70 to 3.52 eV and decreasing value of refractive index between 2.34 and 2.48. The fabricated glasses that have a higher refractive index than the widely used fiber material, pure silica glass, indicate that zinc borotellurite glass doped with lanthanum nanoparticles is a promising material to be applied as optical fibers.

High-κ Lanthanum Zirconium Oxide Thin Film Dielectrics from Aqueous Solution Precursors.

Abstract: Metal oxide thin films are critical components in modern electronic applications. In particular, high-κ dielectrics are of interest for reducing power consumption in metal–insulator–semiconductor (MIS) field-effect transistors. Although thin-film materials are typically produced via vacuum-based methods, solution deposition offers a scalable and cost-efficient alternative. We report an all-inorganic aqueous solution route to amorphous lanthanum zirconium oxide (La2Zr2O7, LZO) dielectric thin films. LZO films were spin-cast from aqueous solutions of metal nitrates and annealed at temperatures between 300 and 600 °C to produce dense, defect-free, and smooth films with subnanometer roughness. Dielectric constants of 12.2–16.4 and loss tangents <0.6% were obtained for MIS devices utilizing LZO as the dielectric layer (1 kHz). Leakage currents <10–7 A cm–2 at 4 MV cm–1 were measured for samples annealed at 600 °C. The excellent surface morphology, high dielectric constants, and low leakage current densities ma...

Optical, electrical and magnetic properties of lanthanum strontium manganite La1-xSrxMnO3 synthesized through the citrate combustion method.

Abstract: Generally, strontium-doped lanthanum manganites (LSM) are materials connected ordinarily as cathodes in the solid oxide fuel cell (SOFC). In this study, the structural, optical, electrical and magnetic properties of La1−xSrxMnO3 (x = 0.2, 0.5, 0.8) synthesized using an organic acid precursor strategy were investigated, based on using citric acid as a fuel. Evidently, the results disclosed that a pure single monoclinic LSM phase was obtained from the thermally treated precursors annealed at 1000 °C with an annealing time of 2 h. The microstructure of the formed sample relied on the Sr2+ ion content. Moreover, a good optical transparency of 45–60% in a wide range of wavelengths between 800 and 1800 nm for all samples substituted by Sr2+ ions was performed. The optical band gap energy was increased from 2.09 to 2.76 eV by increasing the Sr2+ ion molar ratios. The trend in the calculated refractive index, the high frequency dielectric constant (eα) and the static dielectric constant (e0) of all the produced samples can be linked to an increase in the Sr2+ ion concentration. Moreover, the magnetic properties were enhanced with increasing Sr2+ ion content.

Fabrication of lanthanum doped BaTiO3 fine-grained ceramics with a high dielectric constant and temperature-stable dielectric properties using hydro-phase method at atmospheric pressure

Abstract: Lanthanum doped BaTiO3 powders were synthesized by the hydro-phase method at atmospheric pressure, which controls the uniformity and particle size of the ceramic powders. The effects of La3+ ions concentration on the microstructure and dielectric properties of BaTiO3 ceramics were studied. The results suggested that both the average grain size and dielectric constants (er and emax) of the ceramics decreased as the concentration of La3+ increased. The ceramic met the X8R specifications: La3+ ions concentration of 3 mol%, a permittivity of 2322, low dielectric loss of less than 0.6% at room temperature, and average grain size of about 260 nm.