Synthesis of Mesoporous, Nanocrystalline Lanthanum Phosphate in the Presence of Citric Acid and Stearic Acid

Lanthanum phosphate was prepared in the presence of citric acid and stearic acid under methanolic conditions at pH 4.5 and pH 7, respectively. The samples obtained were intensively characterized using X-ray diffraction, nitrogen adsorption-desorption isotherm study, transmission electron microscopy （TEM）, thermal gravimetric and differential thermal analysis, and Fourier transform infrared （FTIR） analysis . The as-synthesized samples prepared at pH 4.5 showed lamellar mesostruroned form with high crystallinity. Results showed that the pore size and pore volume changed when the materials were prepared under different pH conditions. Morphology of the samples was observed by using TEM, which showed that the samples possessed relatively small particles closely packed together. The as-synthesized samples were investigated using FTIR, and the mesopore formation mechanism was discussed.

Conduction properties of condensed lanthanum phosphates:La(PO_3)_3 and LaP_5O_(14)

Single crystals of LaP3O9·3H2O were prepared using a classical method of aqueous chemistry whereas those of the ultraphosphate LaP5O14 were obtained by flux method.Thermal treatment of LaP3O9·3H2O up to 700 °C allowed us to obtain the lanthanum polyphosphate La(PO3)3.The conductivity as well as the vibrational study of the lanthanum ultraphosphate and polyphosphate were analysed in order to explain the mechanism of conduction.Activation energies of 0.45 and 0.84 eV,deduced from the Arrhenius relation,were r...

Synthesis of Mesoporous Lanthanum Phosphate and Its Use as a Novel Sorbent

Mesoporous lanthanum phosphate was synthesized by supramolecular self-assembly of cetyltrimethylammonium bromide and lanthanum nitrate following digestion in phosphoric acid. TGA-DTA, XRD and SEM were employed to study the uncalcined and calcined materials. Sorption behavior of Cr（Ⅲ）, Mn（Ⅱ）, Fe（Ⅲ）, Co（Ⅱ）, Ni（Ⅱ）, Cu（Ⅱ）, Zn（Ⅱ）, Cd（Ⅱ）, Ba（Ⅱ）, Hg（Ⅱ） and Pb（Ⅱ） cations was studied on such materials in water, 3 mol·L^-1 ammonia, 0.01 mol·L^-1 potassium ferrocyanide and 0.01 mol·L^-1 potassium ferricyanide solutions.

Lanthanum chloride or citrate is absorbed mainly via M cells in gastrointestinal tracts with lanthanum phosphates as the transformed species

In the present study, we investigated the transformed species and the absorptive mechanism of rare earth elements（REEs） in gastrointestinal（GI） tract, using La Cl3 and La Cit as representative compounds. Artificial gastric and intestinal fluids were used to simulate the environment of the digestive tract in vivo. The inductively coupled plasma mass spectrometry（ICP-MS） result showed that more than 99.9% of La Cl3 and La Cit formed precipitation in artificial intestinal fluid, with the average size distribution of 200 nm（2-h incubation） increasing to 600 nm（24-h incubation） determined by dynamic light scattering（DLS）, indicating the aggregation of the particles. The Fourier transform infrared spectroscopy（FTIR） analysis demonstrated that the constituents of these particles were mainly in the form of lanthanum phosphates. To explore the transport mechanism of REEs in GI tract, the mice Peyer＇s patches（PPs） and intestinal epithelium were separated to evaluate the content of lanthanum by ICP-MS following oral administration with 2 or 100 mg/kg/day of La Cit for 7 d. The results showed that the amount of lanthanum phosphate particles absorbed by PPs was significantly greater than that of intestinal epithelium, indicating that lanthanum particles might be phagocytosed mainly by M cells located in the follicle-associated epithelium（FAE） overlying PPs. Furthermore, Caco-2 cell monoculture and Caco-2/Raji B cell coculture models were established to simulate intestinal epithelial cells and FAE, respectively. The result showed that the transport of lanthanum in Caco-2/Raji B coculture model was significantly higher than that in Caco-2 monoculture model（about 60 times higher）, and the level of lanthanum in the basal compartment of Caco-2 monoculture model was very low, supporting that M cells were the main route for lanthanum phosphate particles to be transported and absorbed. Taken together, these data suggested that La Cl3 and La Cit in GI tract were absorbed mainly via M cells with lanthanum phosphates as transformed species. The obtained results would provide the theoretical basis for the rational application of REEs in agriculture and medicine.

Preparation and Luminescent Characteristics of LaPO_4∶Eu Nanoparticles and Nanowires

Nanoparticles and nanowires of LaPO 4: Eu phosphors were synthesized by hydrothermal method. Their luminescent properties including electronic transition, surface effect, and temperature-dependent luminescent characteristics were systemically studied and compared to the bulk powders. It can be concluded that in comparison with the bulk powders, the fluorescence intensity decreases in nanoparticles and nanowires, while the lifetime increases, indicating that the radiative transition rate decreases. The nonradiative transition rate in nanowires decreases than that in nanoparticles due to its decreased surface to volume ratio. The temperature-dependent experiments indicate that the thermal quenching in nanopowders becomes weaker than that in the bulk powders.

Preparation of Machinable Y-TZP/LaPO_4 Composite Ceramics by Liquid Precursor Infiltration

A machinable Y TZP/LaPO 4 composite ceramic was prepared by infiltrating LaPO 4 liquid precursor into Y TZP porous ceramic. Sintered Y TZP ceramic preformed with 35% (volume fraction) open pore volume was made by adding graphite (30%, volume fraction). The Y TZP/LaPO 4 composite ceramics containing different LaPO 4 contents were obtained by infiltration and pyrolysis cycles. The machinability and mechanical properties of materials were investigated. The results show that the machinable Y TZP/LaPO 4 composite ceramics containing 2 3% to 7.5% (volume fraction) LaPO 4 has good machinability as well as outstanding mechanical properties.

Effect of LaPO_(4) Introduction as a Vanadium Trap for Preventing USY Zeolite Destruction

The use of lanthanum phosphate as a vanadium trap for preventing destruction of USY zeolite was studied.The effect of deposited vanadium on the hydrothermal destruction of zeolite was investigated by the solid-state NMR technique.LaPO4 species can inhibit the zeolite framework structure from being collapsed by vanadium after steaming treatment.The EPR results show the oxidation-reduction reaction in LaPO4 and V2O5 system and inhibition of zeolite destruction by V5+.The catalysts prepared from USY and LaPO-USY zeolites were also tested in the catalytic reactions of heavy oil.The assessment results indicated that the USY modified with LaPO4 could bring about remarkably high dehydrogenation ability.

Preparation and Luminescence Properties of Color-tunable Single-phased LaPO4：Eu3＋/Tb3＋ Phosphors

A novel series of color-tunable single-phased phosphors La1-x-yPO4：xEu3＋/yTb3＋（x=0, 0.01, 0.02, 0.03, 0.04, 0.05; y=0, 0.05, 0.10, 0.15, 0.20） was synthesized via microwave-assisted co-precipitation method with diammonium hydrogen phosphate as precipitant. The morphology, crystal structure and photoluminescence properties of the as-prepared samples were characterized by means of X-ray diffraction（XRD）, scanning electron microscopy（SEM） and fluorescence spectrophotometer. The results reveal that the as-synthesized samples calcined at 1100 ℃ display spherical morphology with uniform distribution. Upon excitation with 350 nm ultraviolet radiation, the LaPOa：Eu3＋/Tb3＋ phosphors showed a green light peaking at 543 nm assigned to the characteristic 5Da-7F5 emission of Tb3＋ and a red light peaking at 591 nm corresponding to the characteristic 5D0-7F1 emission of Eu3＋ simultaneously. For the Eu3＋/Tb3＋ co-activated phosphors, Tb3＋ acts as an efficient sensitizer to enhance the emission intensity of Eu3＋ ions. The energy transfer mechanism and the emission color tunability of LaPO4：Eu3＋/Tb3＋ have been studied. The results indicate that a color-tunable luminescence（from green to white to red） can be achieved by adjusting the Eu3＋/Tb3＋ doping ratio in the LaPO4 host matrix.

Influences of LaCl3 on the mineral phase transformation during osteoblast mineralization in vitro

Rat calvarial osteoblasts were treated with lanthanum chloride（LaCl3） to explore its effect on the mineral crystalline phase during the process of osteoblast calcification in uitro.The results confirmed that La was readily deposited in the mineral component of the matrix.Employing high-resolution transmission electron microscopy and Fourier transform infrared microspectroscopy techniques,we demonstrated that features comparable to dicalcium phosphate dihydrate（DCPD） and octacalcium phosphate,and hydroxyapatite（HAP） were detected in the mineral phases in uitro.Particularly,LaCl3 treatment retarded conversion from DCPD-like phase into HAP during mineralization.In addition,La was introduced in DCPD powder during wet chemical synthesis.When compared with that of La-free DCPD,the dissolution rate of La-incorporated DCPD was lower,thereby leading to a delayed DCPD-to-HAP phase transformation.Thus,it can be concluded that LaCl3 treatment influences the kinetics of inorganic phase transition by decreasing the dissolution rate of DCPD.