Extraction kinetics of rare earth elements with sec-octylphenoxy acetic acid

The kinetics of RE (La, Gd, Er, Yb and Y) extraction with sec-octylphenoxy acetic acid was investigated using a constant interfacial area cell with laminar flow at 303 K. The natures of the extracted complexes have some effect on the extraction rate which is controlled by the reaction rate of M(III) and extractant molecules at two-phase interface for Er(III), Yb(III) and Y(III), by a mixed chemical reaction-diffusion for Gd(III) and a diffusion for La( III). The extractant molecules tend to adsorb at the interface. So an interfacial extraction reaction model was derived.

Promoter effects of rare earth ions on electrocatalytic oxidation of methanol

The promoter effects of rare earth ions on the electrocatalytic oxidation of methanol at the Pt electrode were studied using the cyclic voltammetry and stable polarization techniques. It was found for the first time that Eu, Ho, Dy ions could accelerate the electrocatalytic oxidation of methanol at the Pt electrode, while Lu, Pr, Yb, Sm ions showed inhibitor effects.

Synthesis, properties and structural characterization of an intermolecular photosensitive complex: (HGly-Gly)(3)PMo12O40 center dot 4H(2)O

The first heteropoly acid-dipeptide complex, (HGly-Gly)(3)PMo12O40.4H(2)O, was synthesized and characterized by elemental analysis, IR, UV, H-1 NMR and single crystal X-ray diffraction. The X-ray crystallographic study showed that the crystal structure was constructed from N-H...O and O-H...O hydrogen bonds among the (HGly-Gly)(+), H2O and PMo12O403- units. This structure represents a model interaction between polyoxometalates and proteins. The complex has photosensitivity under irradiation by sunlight. The fluorescent activity of this compound is also reported.

UV-Vis and surface photovoltage spectra of Fe2O3/polystyrene composite microspheres

Fe2O3 sol with the particle diameter of 3-5 nm was flocculated by the addition of SDS, and the flocculate formed was redispersed by the further addition of that surfactant. Thus the surfactant bilayer was formed on the surface of Fe2O3. The emulsion polymerization of styrene (St) adsolubilized oil the surfactant adsorbed bilayer was carried out by initiator potassium persulfate (KPS). The UV-Vis and surface photovoltage spectra (SPS) indicate that the Fe2O3 particles were encapsulated in polystyrene(PSt) successfully.

Chemical bond parameters in Sr3MRhO6 (M=rare earth)

Chemical bond parameters, that is, bond covalency, bond valence, macroscopic linear susceptibility, and oxidation states of elements in Sr3MRhO6 (M=Sm, Eu, Tb, Dy, Ho, Er, Yb) have been calculated. The results indicate that the bond covalency of M-O decreases sharply with the decrease of ionic radius of M3+ from Sm to Yb, while no obvious trend has been found for Rh-O and Sr-O bonds. The global instability index indicates that the crystal structures of Sr(3)MrhO(6) (M = Sm, Eu, Tb, Dy, Ho) have strained bonds.

Synthesis and thermotropic liquid crystalline behaviour of novel poly(aryl ether ketone)s with a lateral methoxy group

Novel poly(aryl ether ketone)s containing a lateral methoxy group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and methoxyhydroquinone with 1,4-bis(4-fluorobenzoyl)benzene in a sulfolane solvent in the presence of anhydrous potassium carbonate. Their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques, e.g. differential scanning calorimetry (DSC), polarized light microscopy and temperature-dependent FTIR. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 30-80 mol-% mexthoxyhydroquinone. Both melting (T-m) and isotropization (T-i) transitions appeared in the DSC curves. The polarized light microscopy study of the liquid crystalline copolymers suggested their ordered smectic structures. As expected, the copolymers had lower melting transitions than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer methoxyhydroquinone.

Recent progress in the studies of endohedral metallofullerenes

This overview presents the recent progress in the area of endohedral metallofullerenes in the past several years. The important results have been summarized as follows: (1) Many metals including Group 3 metals, most of the lanthanide series elements, and Group 2 metals have been encapsulated into a fullerene cage to form mono-, di-, and trimetallofullerenes by using the arc-evaporation technique. (2) Some endohedral metallofullerenes such as Group 3 metals, most of the lanthanide series elements, Group 2 metals, and some of their isomers have been successfully isolated and purified by a two-step or several-step HPLC technique. By using high-temperature and high-pressure extraction with pyridine, Ln@C-80, Ln@C-82, and Ln2@C-80 for most rare-earth metals have been selectively extracted in high yield (about 1% of the saw soot) from fullerenes and other size metallofullerenes. (3) The endohedral nature of metallofullerenes such as Y@C-82, Sc2@C-84, and Sc@C-82 has been finally confirmed by synchrotron X-ray powder diffraction. The symmetries and the structures of metallofullerenes such as Ca@C-82(III), La-2@C-80(I-h), Sc-2@C-84(D-2d), and Sc-2@C-84(C-s) have been confirmed by NMR measurements. (Lb) The information on the electronic structures and properties of endohedral metallofullerenes has been obtained by various spectrometric means Such as EPR, W-vis-MR, XPS, CV. It is generally accepted that three-electron transfer is favorable when M = Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Lu but Sc, Eu, Sm, Yb, Tm, Ca, Sr, Ba prefer to donate two electrons to the fullerene cages. (5) Several chemical reactions of endohedral metallofullerenes have been reported in which reagents are disilacyclopropane, digermacyclopropane, diphenyldiazomethane, and trifluoroacetic acid. (6) Mass spectrometry provided the crucial evidence that led to the discovery of metallofullerenes in 1985 and has always played a key role in their identification and characterization, Ion-mobility measurements of gas-phase ions have obtained the information of structures and the formation mechanism of endohedral metallofullerenes. till Theoretical calculations on the endohedral metallofullerenes have made an important contribution to the studies on the symmetry of the cage, the position of metal atom(s) inside the cage, the number of electronic transfer between metal atom(s) and fullerene cage, etc. (C) 2000 Elsevier Science S.A. All rights reserved.

Effect on the property of the photoinduced carrier transport of CdS as sensitizer for TiO2 nanoparticulate thin films

The TiO2 nanoparticle thin films have been sensitized in situ with CdS nanoparticles. The SPS measurement showed that large surface state density was present on the TiO2 nanoparticles and the surface state can be efficiently decreased by sensitization as well as selecting suitable heat treatment, Both the photocurrent response and the charge recombination kinetics in TiO2 thin films were strongly influenced by trapping/detrapping of surface states. The slow photocurrent response of TiO2 nanoparticulate thin films upon the illumination was attributed to the trap saturation effects, The semiconductor sensitization made the slow photoresponse disappeared and the steady-state photocurrent value increased drastically, which suggested that the sensitization of TiO2 thin films with CdS could get a better charge separation and provide a simple alternative to minimize the effect of surface state on the photocurrent response.

Structure characteristics and valence state study for La1-xNaxTiO3 synthesized under high-pressure and high-temperature conditions

By using a novel high-pressure, high-temperature method, perovskite oxides of La1-xNaxTiO3 (x = 0.05, 0.1-0.8) with mixed valence state were synthesized. XRD analysis shows a cubic cell for the samples. Cell volumes of the samples with 0.1 less than or equal to x less than or equal to 0.5 decreases as x increases, and the cell Volume for x = 0.05 is smaller than that for x = 0.1. XPS of surface and EPR measurements indicate that Ti ions are of mixed valence of +3 and +4 and that A-cations vacancies exist in the samples. As x increases, the amount of Ti3+ ions decreases and the amount of A-cations vacancies increases. The valence state of Ti ions can be altered by changing both pressure and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

High-pressure and-temperature synthesis and characterization of mixed valence perovskite oxides LaTi1-xMgxO3

Perovskite oxides LaTi1-xMgxO3 (x = 0.25, 0.5) were synthesized using high-pressure and-temperature method. LaTi0.75Mg0.25O3 is a new compound. This new synthesis route has some advantages. XRD analysis showed that the x = 0.25 sample belongs to cubic perovskite-type structure and the a = 0.5 sample belongs to orthorhombic perovskite-type structure. EPR measurement indicated that Ti ions were in mixed valence state of +3 and +4. IR measurement indicated that the vibration frequency and width of BO6 octahedron stretching vibration absorption band decreases with the increasing of x. The valence state of Ti ions can be altered by high-pressure and-temperature. (C) 2000 Elsevier Science S.A. All rights reserved.

La_(0.5)R_(0.5)Ba_2Cu_3O_7,Pr_(0.5)R_(0.5)Ba_2Cu_3O_7以及RBa_2Cu_3O_7(R=稀土)的键共价性计算

使用复杂晶体化学键理论计算了La0 .5R0 .5Ba2 Cu3O7(R =Pr,Nd ,Sm ,Eu ,Gd ,Dy ,Y ,Ho,Er,Tm ,Yb ,Lu) (La-R12 3) ,Pr0 .5R0 .5Ba2 Cu3O7(R =La ,Nd ,Sm ,Eu ,Gd ,Dy ,Ho ,Y ,Er,Tm ,Yb ,Lu) (Pr -R12 3)以及RBa2 Cu3O7(R =La ,Pr,Nd ,Sm ,Eu ,Gd ,Dy ,Ho ,Y ,Er,Tm) (R12 3)中Cu—O键的键共价性 ,结果表明Pr-R12 3,La-R12 3,以及R12 3都应具有超导性 ,而实验结果是La0 .5Pr0 .5Ba2 Cu3O7,R0 .5Pr0 .5Ba2 Cu3O7(R =La,Nd ,Sm ,Eu ,Gd)无超导性 .产生这种矛盾的原因尚不明确 ,需要做进一步的研究.

恒电位电解法掺稀土对多孔硅光致发光性能的影响

研究了恒电位电解法掺稀土(Er、Nd与Yb)对多孔硅(PS)室温可见区光致发光性能的影响。结果表明:适当高浓度稀土的掺入可以提高PS的发光强度、使PS发光波长蓝移;掺入稀土浓度过高对PS的发光起猝灭作用。掺稀土可以缩短PS发光衰减的平均寿命,而不影响衰减曲线的形状。提出用“表面态辅助的量子限制效应”观点来解释PS和掺稀土多孔硅的光致发光。

Sol-gel deposition of calcium silicate red-emitting luminescent films doped with Eu3+

Eu3+-activated calcium silicate (CaO-SiO2:Eu3+) luminescent films were prepared by the sol-gel method. The structural evolution of the film was studied by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the luminescence properties of the phosphor films were investigated as a function of heat treatment temperature. The XRD study indicates that a kilchoanite phase forms in the film sintered at 800 degreesC, which is different from that in gel powder treated under the same conditions. The SEM results show that the film thickness decreases and the particles in the film become smaller with increasing heat treatment temperature. The CaO-SiO2:Eu film shows the characteristic emission of Eu3+ under UV excitation, with the Eu3+ D-5(0)-->F-7(2) band (616 nm) being the most prominent. A large difference in the Eu3+ lifetime is observed between the film samples treated at 500 and 700 degreesC (or above). Concentration quenching occurs when the Eu3+ doping concentration is above 6 mol% of Ca2+ in the film.

Photosensitization of TiO2 nanoparticulate thin film electrodes by CdS nanoparticles

Surface photovoltage spectra (SPS) measurements of TiO2 show that a large surface state density is present on the TiO2 nanoparticles and these surface states can be efficiently decreased by sensitization using US nanoparticles as well as by suitable heat treatment. The photoelectrochemical behavior of the bare TiO2 thin film indicates that the mechanism of photoelectron transport is controlled by the trapping/detrapping properties of surface states within the thin films, The slow photocurrent response upon the illumination can be explained by the trap saturation effect. For a TiO2 nanoparticulate thin film sensitized using US nanoparticles, the slow photocurrent response disappears and the steady-state photocurrent increases drastically, which suggests that photosensitization can decrease the effect of surface states on photocurrent response.

Synthesis and characterization of polynuclear half-sandwich lanthanoid complexes [Na(THF)(6)](2)[(Cp6Sm6Se13)-Sm-t] and [Li(LHF4](2)[Cp6Nd6Se13]

The half-sandwich tert-butyl cyclopentadienyl lanthanoid complexes {[Cp ' Ln(THF)](2)(mu (2)-Cl)(2)(mu (3)-Cl)(3)Na(THF)}(n) [Cp ' = eta (5)-' BuC5H4; Ln = Nd (1a), Sm (1b), Gd (1c), Yb (1d)] are prepared by the reaction of anhydrous lanthanoid trichloride, LnCl(3), with NaCp ' in THF solution. Complex 1b reacts with Na2Se5 to give hexanuclear samarium polyselenide complexes [Na(THF)(6)](2)[Cp-6' SM6(mu (6)-Se)(mu -Se-2)(6)] (2). An analogous cyclopentadienyl neodymium polyselenide complex [Li(THF)(4)](2)[Cp6Nd6(mu (6)-Se)(mu -Se-2)(6)] (3) is synthesized by the reaction of [CpNdCl2. 2LiCl . 5THF] with Na2Se5 in THF solution. The molecular structures of 1a and 2 were determined by X-ray crystal structure analysis. Complex 2 contains an interstitial selenium atom which is coordinated with six samarium atoms. (C) 2001 Elsevier Science BN. All rights reserved.