Synthesis, crystal structure, and thermal property of a novel supramolecular assembly: (NH42810424)(CHNO) O-[H(V)O(]2H)4(10)28(2), constructed from decavanadate and caffeine

A novel 3D supramolecular assembly constructed from decavanadate and caffeine building blocks, (NH4)(2)(C8H10N4O2)(4)[H4V10O28].2H(2)O (1), has been synthesized in aqueous solution and characterized by elemental analysis, IR, H-1 NMR, V-51 NMR, TG-DTA, and single crystal X-Ray diffraction. The compound 1 crystallizes in monoclinic system, space group P2(1)/n, a = 15.801(1) Angstrom, b = 12.914(1) Angstrom, c = 15.913(2) Angstrom, beta = 113.55degrees, V = 2976.4 (5) Angstrom(3), Z = 2, R = 0.0498 with 6818 reflections. Water molecules, ammonium ions, and caffeine act as "cement" linking the polyanions into 1D chain along the c-axis by hydrogen bonding. In compound 1, extensive hydrogen-bond contacts and strong pi-pi interactions lead to an ordered 3D supramolecular framework. TG-DTA curves indicate that the weight loss of the complex can be divided into three stages.

Preparation of nanocrystalline NiZnCu ferrite particles by sol-gel method and their magnetic properties

Polyvinyl alcohol (PVA) was first used as chelating agent and metal nitrates as precursor of ferrite in the fabrication of nanocrystalline Ni0.65Zn0.35Cu0.1Fe1.9O4 particles by the sol-gel method. The thermal decomposition process of dried gel was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of resultant particles were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Mossbauer spectroscopy. The dependence of the decomposition of dried gel, the formation of spinel structured NiZnCu ferrite, the sizes of annealed particles, the saturation magnetization and coercivity of annealed particles on annealing temperature is presented.

Rapid synthesis of Mn0.65Zn0.35Fe2O4/SiO2 homogeneous nanocomposites by modified sol-gel auto-combustion method

MnZn-ferrite/SiO2 nanocomposites with different silica content were successfully fabricated by a novel modified sol-gel auto-combustion method using citric acid as a chelating agent and tetraethyl orthosilicate (TEOS) as the source of silica matrix. The auto-combustion nature of the dried gel was studied by X-ray diffraction (XRD), Infrared spectra (IR), thermogravimetry (TG) and differential thermal analysis (DTA). Transmission electron microscope (TEM) observation shows that the MnZn-ferrite particles are homogeneously dispersed in silica matrix after auto-combustion of the dried gels. The magnetic properties vary with the silica content. The transition from the ferromagnetic to paramagnetic state is observed by Mossbauer spectra measurement with the increasing silica content. Vibrating sample magnetometer (VSM) shows that the magnetic properties of Mn0.65Zn0.35Fe2O4/SiO2 nanocomposites strongly depend on the silica content.

Sol-ogel deposition and luminescence properties of lanthanide ion-doped Y2(1-x)Gd2xSiWO8 (0 <= x <= 1) phosphor films

Y2(1-x) Gd2xSiWO8 : A ( 0 <= x <= 1; A= Eu3+, Dy3+, Sm3+, Er3+) phosphor films have been prepared on silica glass substrates through the sol - gel dip-coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscope (AFM), scanning electron microscopy (SEM) and photoluminescence spectra as well as lifetimes were used to characterize the resulting films. The results of the XRD indicated that the films began to crystallize at 800 degrees C and crystallized completely at 1000 degrees C. The AFM and SEM study revealed that the phosphor films, which mainly consisted of closely packed grains with an average size of 90 - 120 nm with a thickness of 660 nm, were uniform and crack free. Owing to an efficient energy transfer from the WO42- groups to the activators, the doped lanthanide ion ( A) showed its characteristic f - f transition emissions in crystalline Y2(1-x) Gd2xSiWO8 (0 <= x <= 1) films. The optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 21, 5, 3 and 7 mol% of Y3+ in Y2SiWO8 films, respectively.

Citrate-gel synthesis and luminescent properties of alpha-Zn-3(PO4)(2) doped with Eu3+

By using inorganic salts as raw materials and citric acid as complexing agent, alpha-Zn-3(PO4)(2) and Eu3+ doped alpha-Zn-3(PO4)(2) phosphor powders were prepared by a citrate-gel process. X-ray diffraction, (XRD), TG - DTA, FT - IR and luminescence excitation and emission spectra were used to characterize the resulting products. The results of XRD reveal that the powders begin to crystallize at 500 degreesC and pure alpha-Zn-3(PO4)(2) phase is obtained at 800 degreesC. And the results of XRD reveal that Eu3+ exists Lis EoPO(4) ill the powder. In the phosphor powders, the Eu3+ shows its characteristic red-orange (592 nm, D-5(0) - F-7(1)) emission and has no quenching concentration.

Stable ordered mesoporous silica materials templated by high-temperature stable surfactant micelle in alkaline media

Ordered hexagonal mesoporous silica material (JLU-30) has been successfully synthesized in alkaline media at high temperature (> 160 degreesC, using cationic (1,3-dimethyl-2-imidazolidin-2-ylidene)hexadecylmethyl-ammonium bromide (DIHAB) as a template, and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, differential thermal analysis (DTA), and thermogravimetric analysis (TG), as well as Al-27 and Si-29 nuclear magnetic resonance (NMR) spectroscopy. Mesoporous JLU-30 shows much higher hydrothermal stability than MCM-41. Si-29 NMR spectra indicate that the pore walls of JLU-30 samples synthesized at high temperature (160 degreesC) are fully condensed, giving a Q(4)/Q(3) ratio as high as 6.2. In contrast, MCM-41 synthesized at relatively low temperature (100 degreesC) shows the Q(4)/Q(3) + Q(2) ratio at 1.1. Such unique structural feature might be responsible for the observed highly hydrothermal stability of the mesoporous silica materials (JLU-30).

New proton exchange membranes based on poly (vinyl alcohol) for DMFCs

A series of new composite proton exchange membranes for direct methanol fuel cells (DMFCs) based on poly (vinyl alcohol) (PVA), phosphotungstic acid (PWA) and silica were prepared. The highest proton conductivity (a) of these membranes is 0.017 S/cm at ambient temperature. The methanol permeability (D) of these composite membranes ranges from 10(-7) to 10(-8) cm(2)/S. From the ratios of sigma/D, it was found that the optimal weight composition of the PVA/PWA/SiO2 membrane is PVA/PWA/SiO2=0.40:0.40:0.20 wt. Infrared (IR) spectrographic measurements indicate that the Keggin structure characteristics of the PW12O403- anion is present in the composite membranes. Cyclic voltammetry shows that the electrochemical stability window of the complex membrane is from -0.5 to 1.5 V vs. Ag/AgCl electrode. The results of differential scanning calorimetry (DSC) show that silica can improve the thermal stability of the complexes and the single Tg of the membrane indicates that the membrane is homogeneous. The complexes behave as X-ray amorphous.

Preparation and luminescence properties of in situ formed lanthanide complexes covalently grafted to a silica network

Lanthanide-doped sol-gel-derived materials are an attractive type of luminescent materials that can be processed at ambient temperatures. However, the solubility of the lanthanide complexes in the matrix is a problem and it is difficult to obtain a uniform distribution of the complexes. Fortunately, these problems can be solved by covalently linking the lanthanide complex to the sol-gel-derived matrix. In this study, luminescent Eu3+ and Tb3+ bipyridine complexes were immobilized on sol-gel-derived silica. FT-IR, DTA-TG and luminescence spectra, as well as luminescence decay analysis, were used to characterize the obtained hybrid materials. The organic groups from the bipyridine-Si moiety were mostly destroyed between 220 and 600 degreesC. The luminescence properties of lanthanide bipyridine complexes anchored to the backbone of the silica network and the corresponding pure complexes were comparatively investigated, which indicates that the lanthanide bipyridine complex was formed during the hydrolysis and co-condensation of TEOS and modified bipyridine. Excitation at the ligand absorption wavelength (336 nm for the hybrid materials and 350 nm for the pure complexes) resulted in strong emission of the lanthanide ions: Eu3+ D-5(0)-F-7(J) (J = 0, 1, 2, 3, 4) and Tb3+ D-5(4)-F-7(J) (J = 6, 5, 4, 3) emission lines due to efficient energy transfer from the ligands to the lanthanide ions.

Thermal and crystalline properties of random copolymer of CL and DTC prepared by La(OAr)(3)

Thermal and crystalline properties of random copolymer of epsilon-caprolactone (CL) and 2,2-dimethyl trimethylene carbonate (DTC) prepared by lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) (La(OAr)(3)) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and wide-angle X-ray diffraction (WAXD). Fox equation interprets the relationship between glass transition temperature (T-g) and copolymer compositions. T-g decreases from PDTC (16.7degreesC) to PCL (-65.1degreesC), reflecting the internal plasticizing effect of CL units on DTC units in the copolymers. The introduction of CL units to PDTC can effectively improve its heat resistance. Small amount of DTC (5% molar) in PCL chain improves the mechanical properties of the polymer, which had elongation of 1000, much higher than that of PCL (8.8).

Preparation of TiO2 nanocrystallites by hydrolyzing with gaseous water and their photocatalytic activity

TiO2 nanocrystallites were prepared front precursors tetra-n-butyl titanate (Ti(OC4H9)(4)) and titanium tetrachloride (TiCl4). The precursors were hydrolyzed by gaseous water in autoclave, and then calcined at predetermined testing temperatures. The samples were characterized by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR), and UV-vis diffuse reflectance spectra (DRS). The photocatalytic activities of the samples were evaluated by the photobleaching of methylene blue (MB) in aqueous solution and the photocatalytic oxidation of propylene in gas phase at ambient temperature. The results showed that the anatase phase nanocrystalline TiO2 could be obtained at relatively low temperatures (for precursor Ti(OC4H9)4 at I I VC and for TiCl4 at 140 degrees C, respectively), and that the as prepared samples exhibited high photocatalytic activities to photobleach MB in aqueous solution. As the calcination temperatures increasing. the decolor ratio of MB increased and reached the maximum value of nearly 100% at 600 degrees C, and then decreased. The photobleaching of MB by all samples followed the pseudo-first-order kinetics with respect to MB concentration.

Synthesis and characterization of spherical Sr2CeO4 phosphors by spray pyrolysis for field emission displays

A blue emitting Sr2CeO4 phosphor with a one-dimensional structure has been prepared by a two-step spray pyrolysis (SP) method, starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives. The material is ultimately designed for field emission displays (FEDs). X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), field emission scanning electron microscope pictures (FE-SEM) as well as photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and lifetime measurements have been employed to characterize the samples. The morphology, PL and low voltage CL properties of Sr2CeO4 phosphors as-prepared using the SP method have been investigated by changing the concentration of the precursor solution, concentration of PEG, annealing temperature, acceleration voltage and filament current. The obtained Sr2CeO4 phosphor particles are spherical and of submicron size, 0.5-2 mu m. The emission spectrum of the phosphors shows a broad band with maximum at 467 nm (lifetime = 37.4 mu s; CIE chromaticity coordinates: x = 0.15 and y = 0.21), presumably due to a ligand-to-metal charge-transfer transition.

Synthesis of nanocrystalline Ba(CoxZn1-x)(2)Fe16O27 by sol-gel auto-combustion method

The synthesis of nanocrystalline W-type hexaferrites Ba(CoxZn1-x)(2)Fe16O27 powders by sol-gel auto-combustion method has been investigated. The thermal decomposition process of dried gel was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of resultant particles were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The results reveal that the dried gel exhibits auto-combustion behavior. After combustion, pure nanocrystalline W-type hexaferrite phase starts to appear at the calcination temperature of 800 degrees C. The crystallinity and the grain size increase at higher temperature. The saturation magnetization and coercivity clearly depend on calcination temperature and Co content X.

Lanthanum zirconate nanofibers with high sintering-resistance

The PVP/lanthanum nitrate/zirconium oxychloride (PVP-precursor) nanofiber was prepared by electrospinning technique. Lanthanum zirconate (La2Zr2O7, LZ) in the nanofiber is formed after calcination at 800 degrees C and the nanofiber with pyrochlore structure and a diameter of 100-500 nm can be obtained by calcination of the above precursor fiber at 1000 degrees C for 12 h. The surface of the fiber is rough but the continuous microstructure is still maintained after calcination. LZ fibers stack randomly, resulting in a structure with a low contact area between the fibers. This special structure makes the fiber to have a high resistance to sintering at elevated temperatures. The BET (Brunauer-Emmett-Teller) specific surface areas of the LZ fiber and powder calcined at different temperatures are shown in this paper, and the fiber was characterized by TG-DTA (thermal gravimetry-differential thermal analysis), XRD (X-ray diffraction), N-2 absorption-desorption porosimetry and SEM (scanning electron microscopy).

One-pot synthesis of polyetherimides from bis(chlorophthalimide) and dichlorodiphenylsulfone in diphenylsulfone

Polyetherimides and copolymers have been synthesized in one pot from bis(chlorophthalimide), dichlorodiphenylsulfone, and bisphenolate using diphenylsulfone as the solvent. The inherent viscosities of the obtained polyimides are in the range of 0.32-0.72 dL/g, and the structures of polyimides were confirmed by IR and elemental analyses. All of the polyimides have good solubility in common organic solvents. The 5% weight-loss temperatures of the polyimides were 429-507 C in air. The glass transition temperatures (T3) of 4,4'-(9-fluorenylidene) diphenol-based polyimides are in the range of 253-268 degrees C. The Tg of bisphenol A-based polyimides is in the range of 198204 degrees C, while the T-g change inconspicuously when the ratios of diphenylsulfone increase. The wide-angle X-ray diffraction showed that all polyimides prepared are amorphous.

Novel PPV-based light-emitting copolymers containing triazole moiety

Two new light-emitting PPV-based copolymers bearing electron-withdrawing triazole unit in the main chain have been synthesized by Wittig reaction between triazole diphosphonium salt and the corresponding dialdehyde monomers, respectively. Their optical and physical properties are characterized by UV-vis, photoluminescence (PL), TGA and DSC. The resulting copolymers are highly soluble in common organic solvents and have high Tg and Td values. They show blue-greenish fluorescence in solution (lambda(max) 502 and 508 nm) and green fluorescence in the solid state (lambda(max) 520 and 526 nm), respectively.