Two-dimensional beta-NaLuF4 hexagonal microplates

A simple hydrothermal method has been developed to synthesize monodisperse beta-NaLuF4 microplates in a large scale. The microcrystals have a perfect hexagonal shape with a diameter of about 5.2 mu m and a thickness of 300 nm. Trisodium citrate (Cit(3-)), which is introduced into the reaction mixture and acts as the chelating agent and shape modifier, plays a key role in fine-tuning the microstructures. The dominant adsorption of Cit(3-) onto the {0001} facets lowers the surface energy of these facets.

Controlled Synthesis of Ln(3+) (Ln = Tb, Eu, Dy) and V5+ Ion-Doped YPO4 Nano-/Microstructures with Tunable Luminescent Colors

YPO4 nano/microcrystals with multiform crystal phases and morphologies, such as hexagonal nano/submicroprisms, spherical-like nanoparticles, and nanorods with different length/diameter ratios as well as tetragonal nanospindles, have been synthesized via a facile hydrothermal route. A series of controlled experiments indicate that the pH values in the initial solution, phosphorus sources, and the organic additive trisodium citrate (Cit(3-)) are responsible for crystal phase and shape determination of final products. It is found that Cit(3-) as a ligand and shape modifier has the dynamic effect by adjusting the growth rate of different facets under different experimental conditions, resulting in the formation of various geometries of the final products. The possible formation mechanisms for products with diverse architectures have been presented.

LaF3, CeF3, CeF3 : Tb3+, and CeF3 : Tb3+@LaF3 (core-shell) nanoplates: Hydrothermal synthesis and luminescence properties

LaF3. CeF3, CeF3:Tb3+, and CeF3:Tb3+ @LaF3 (core-shell) 2D nanoplates have been successfully synthesized by a facile and effective hydrothermal process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. The experimental results indicate that the organic additive, trisodium citrate (Cit(3-)), as a shape modifier has the dynamic effect by adjusting the growth rate of different crystal facets, resulting in forming the anisotropic geometries of the final products. The possible formation mechanisms for different products have been presented. The CeF3, CeF3:Tb3+, and CeF3:Tb3+ @LaF3 (core/shell) nanoplates show characteristic emission of Ce3+ (5d-4f) and Tb3+ (f-f), respectively.

Facile Hydrothermal Synthesis and Luminescent Properties of Large-Scale GdVO4:Eu3+ Nanowires

Large-scale GdVO4:Eu3+ nanowires with diameters of about 15 nm and lengths of several micrometers were achieved by a facile hydrothermal method in the presence of disodium ethylenediamine tetraacetate (Na2H2L). The influences of several parameters, such as pH value, reaction temperature, and molar ratio of Na2H2L to Gd3+ on the final products were investigated. The formation mechanism of the as-obtained GdVO4:Eu3+ nanowires is proposed on the basis of time-dependent experiments. It is found that the organic additive Na2H2L, which acts as a shape modifier, has a dynamic effect by adjusting the growth rates of different facets, resulting in the formation of the GdVO4:Eu3+ nanowires. The luminescent spectrum of GdVO4:Eu3+ nanowires shows the strong characteristic dominant emission of the Eu3+ ions at 614 nm.

Different microstructures of ss-NaYF4 fabricated by hydrothermal process: Effects of pH values and fluoride sources

beta-NaYF4 microcrystals with a variety of morphologies, such as microrod, hexagonal microprism, and octadecahedron, have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra were used to characterize the samples. The intrinsic structural feature of beta-NaYF4 seeds and two important external factors, namely, the pH values in the initial reaction solution and fluoride sources, are responsible for shape determination of beta-NaYF4 microcrystals. It is found that the organic additive trisodium citrate (Cit(3-)) as a shape modifier has the dynamic effect by adjusting the growth rate of different facets under different experimental conditions, resulting in the formation of the anisotropic geometries of various beta-NaYF4 microcrystals. The possible formation mechanisms for products with various architectures have been presented. A systematic study on the photoluminescence of Tb3+-doped beta-NaYF4 samples with rod, prism, and octadecahedral shapes has shown that the optical properties of these phosphors are strongly dependent on their morphologies and sizes.

Highly uniform and monodisperse beta-NaYF4 : Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprism crystals: Hydrothermal synthesis and luminescent properties

beta-NaYF4:Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb3+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu(3+) (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to D-5(0-3) -> F-7(J) (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively.

(R,R)-DPEN-modified Ru/gamma-Al2O3 - An efficient heterogeneous catalyst for enantioselective hydrogenation of acetophenone

An efficient enantioselective catalyst of 5 wt.% Ru/-gamma-Al2O3 modified with R,R-1,2-diphenylethylene-diamine ((R,R)-DPEN) for the hydrogenation of a non-activated aromatic ketone of acetophenone has been investigated, a relatively high enantiomeric excess (ee) of 60.5% was obtained at both the conversion and selectivity larger than 99%, it was about three times higher than the ee values reported up to now for acetophenone hydrogenation with the supported transition metal catalysts modified by chiral reagents. The influences of some reaction parameters such as phosphine ligand, substrate/catalyst/modifier molar ratios, base, solvent, pressure and reaction temperature have been discussed. The chiral modifier of (R,R)-DPEN was very important in controlling the enantioselectivity through adsorption competing with other substrates on the surface of active metal species. The phosphine ligand and base were also important and indispensable in the present reaction.

Extraction and separation of yttrium from the rare earths with sec-octylphenoxy acetic acid in chloride media

Extraction and separation of yttrium from the rare earths in chloride medium using sec-octylphenoxy acetic acid (CA-12), tri-n-butyl phosphate (TBP) as modifier, in kerosene has been investigated. The separation coefficients, beta, were obtained and the extraction selectivity has been enhanced when compared with that of naphthenic acid. The experimental results indicated that CA-12-TBP system could be employed to separate yttrium, from rare earths. Fractional extraction (15 stages for extraction and 10 stages for scrubbing) was studied, the raffinate of the first stage was abundant in purity yttrium of 99.5%, with a yield of > 95%, percentage of yttrium in the mixture rare earths was less than 5% in the loaded organic phase of the 25th stage and loaded capability was about 0.2 mol/L.

An investigation on the dispersion of montmorillonite (MMT) primary particles in PP matrix

A novel path of preparing PP/o-MMT nanocomposites, which pay attention to the breaking up of MMT original agglomerates and dispersing of its primary particles, rather than the intercalation or exfoliation degree of o-MMT, was reported. The method of predispersing the o-MMT particles into a polar poly(vinyl alcohol) (PVA) matrix and then melt blending the pre-treated PVA/o-MMT hybrids with PP was studied. 3-isopropenyl-alpha,alpha-dimethylbenzene-isocyanate (TMI) was used as a modifier of PVA to improve the compatibility between PVA and PP matrix. Pre-disperse o-MMT with TMI modified PVA was proved to be an effective way to get a composite with fine o-MMT particles dispersion. But the method, which is pre-dispersing o-MMT with non modified PVA and then using TMI to modify such PVA/o-MMT hybrid, would largely reduce the reaction degree between TMI and PVA because of the relatively lower reaction temperature. Although the latter method also can obtain finer dispersion composites than that with using PP-g-MAH as compatibilizer, the relatively higher degradation degree of PP matrix in this method will limit the use of this nanocomposite.

Morphology evolutions of organically modified montmorillonite/polyamide 12 nanocomposites

Organically modified montmorillonites (OMMTs) by octadecylammonium chloride with two adsorption levels were dispersed in polyamide 12 (PA12) matrices with two molecular weights for different melt mixing times in order to investigate morphology evolutions and factors influencing fabrication of PA12 nanocomposites. Different adsorption levels of the modifier in the OMMTs provide different environments for diffusion of polymer chains and different attractions between MMT layers. Wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and gas permeability were used to characterize morphologies of the nanocomposites. Both OMMTs can be exfoliated in the PA12 matrix with higher molecular weight, but only OMMT with lower adsorption level can be exfoliated in the PA12 matrix with lower molecular weight. It was attributed to the differences in the levels of shear stress and molecular diffusion in the nanocomposites. The exfoliation of OMMT platelets results from a combination of molecular diffusion and shear. After intercalation of PA12 into interlayer of OMMT in the initial period of mixing, further dispersion of OMMTs in PA12 matrices is controlled by a slippage process of MMT layers during fabricating PA12 nanocomposites with exfoliated structure.

The influence of core-shell structured modifiers on the toughness of poly (vinyl chloride)

The core-shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core-shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix.

Isolation and extraction of total flavonoids from Epimedium Koreanum Nakai by supercritical fluid extraction

In the present paper is reported the method for the isolation and extraction of total flavonoids of Epimedium Koreanum Nakai by means of supercritical fluid extraction (SFE). By examining pressure, temperature. amounts of modifier and extraction time, the optimized condition of SFE is confirmed as 30 MPa and 60 degreesC. with 70% ethanol as the modifier. The samples were statically extracted for 30 min, followed by dynamic extraction for 120 min at a flow rate of 6 mL/min. The quantitative analysis of total flavonoids was performed by UV-Vis spectrophotometry. Compared with the conventional method, the SFE method is more efficient. more rapid and more friendly environmentally.

Synthesis of novel maleimide-terminated thioetherimide oligomer and its bulk copolymerization with reactive solvents

This paper reports the synthesis of a novel maleimide-terminated thioetherimide oligomer and its copolymefization with reactive solvents bearing vinyl. Starting from 3-chlorophthalic anhydride and 4-chlorophthalic anhydride, 2,2',3,3'-thiodiphenyl tertracaboxylic dianhydride (3,3'-TDPA) and 3,3',4,4'-thiodiphenyl tertracaboxylic dianhydride (4,4'-TDPA) were synthesized. Thereby, a novel maleimide-terminated thioetherimide oligomer was prepared from. 3,3-TDPA, 4,4'-TDPA, 3,3'-dimethyl-4,4-diaminodiphenylmethane (DMMDA) and maleic anhydride. Binary and ternary copolymer resin were derived from corresponding binary and ternary homogeous solution consisting of thioetherimide oligomer, reactive solvent N-vinylpyrrolidone (NVP) or N,N'-dimethylacrylamide (DMAA) and divinylbenzene (DVB) as modifier, initiated either by gamma ray irradiation or by benzoyl peroxide (BPO). Thermal and mechanical properties of copolymer resin are determined and compared in terms of the kind of reactive solvent, addition of modifier DVB. The effect of initiation approach on property of final copolymer resin were studied. Phase separation and sub-transition of ternary copolymer resin induced by BPO are observed, which could be accounted for by thermal movement of DMAA molecules during thermal initiation.

The influence of arrangement of St in MBS on the properties of PVC/MBS blends

Three series of MBS core-shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle-ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding.

Synthesis and characterization of hyperbranched aromatic poly(ether imide)s

The four AB(2) monomers, N-[3- or 4-bis(4-hydroxyphenyl)toluoyl]-4-chlorophthalimide and N-{3- or 4-[1,1-bis(4-hydroxyphenyl)]ethylphenyl}-4-chlorophthalimides, were prepared and used for synthesis of hyperbranched poly(ether imide)s bearing hydroxyl end groups. These hyperbranched poly(ether imide)s had moderate molecular weights with broad distributions and showed glass-transition temperatures (Tgs) between 177 and 230 degreesC. The thermogravimetric analytic measurement revealed the decomposition temperature at 5% weight-loss temperatures (T-d(5%)) ranging from 240 to 281 degreesC. Analysis using H-1 NMR spectroscopy revealed the four types of hyperbranched poly(ether imide)s to have similar degrees of branching (ca. 60%). These polymers were modified by acylation or nucleophilic substitution reaction at the hydroxyl end groups. The conversion effectiveness depended on the type of modification reaction, modifier, and reaction conditions. The thermal stability and solubility of hyperbranched poly(ether imide)s were improved by the modification of the end groups.