Alkali salts of heteropoly tungstates: Efficient catalysts for the synthesis of biodiesel from edible and non-edible oils

Alkali salts of tungsten based heteropoly acids with different central atom such as P, Si and Co were prepared and evaluated for transes- terification of both edible and non-edible oils to their corresponding fatty acid methyl esters. The catalyst of sodium salt of tungstic acid with Co as central atom （Na5CoW12O40） showed optimum activity towards transesterification compared with other heteropoly tungstates. The catalysts activities were correlated with the observed physico-chemical characteristics derived from FT-infrared （FT-IR）, X-ray diffraction （XRD）, temperature-programmed desorption of ammonia （NH3-TPD） and carbon dioxide （CO2-TPD）. The Na5CoW12O40 catalyst exhibiting high activity even at 65 ℃ is due to the presence of strong acidic as well as basic sites. The disclosed catalyst is tolerable towards water and free fatty acids present in the oils. The influence of catalyst loading, reaction time and reaction temperature is studied to optimize the reaction parameters.

New cadmium and rare earth metal tungstates with the scheelite type structure

New cadmium and rare earth metal tungstates with the formula Cd0.25RE0.50 0.25WO4 （RE=Nd, Sin, Eu, Gd, D-statistical distrib- uted vacancies in cation sublattice） were synthesized by the solid-state reaction between CdWO4 and corresponding RE2W209. The obtained phases crystallize in the scheelite type structure. The Cd0.25RE0.5 0.25WO4 compounds were characterized by X-ray diffractometer （XRD）, （DTA-TG）, infrared （IR） and EPR methods.

Complete degradation of high-loaded phenol using tungstate-based ionic liquids with long chain substituent at mild conditions

Phenol in waste water threatens human health and is difficultly to be decomposed by nature.Efficient degradation of high-loaded phenol in water under mild condition is still a great challenge.Herein,ionic liquids with tungstate anion were designed and prepared.It was found that dodecyltrimethylammonium tungstate could catalyzed degradation of phenol into gases and water thoroughly at 323 k in 8 h.Tungstate anion revealed good catalytic oxidative activity and long carbon chain group connecting with cation of ionic liquids enriched phenol around catalysts,which induced the complete degradation of phenol at mild conditions.Increasing the amounts of hydrogen peroxide benefited to the total degradation of phenol.In addition,the ionic liquid could be reused for its excellent thermal stability.Our work provided a different strategy to treat waste water containing phenol efficiently.

Nanostructured Ternary Metal Tungstate-Based Photocatalysts for Environmental Purification and Solar Water Splitting:A Review

Visible-light-responsive ternary metal tungstate(MWO_4) photocatalysts are being increasingly investigated for energy conversion and environmental purification applications owing to their striking features, including low cost,eco-friendliness, and high stability under acidic and oxidative conditions. However, rapid recombination of photoinduced electron–hole pairs and a narrow light response range to the solar spectrum lead to low photocatalytic activity of MWO_4-based materials, thus significantly hampering their wide usage in practice. To enable their widespread practical usage, significant efforts have been devoted, by developing new concepts and innovative strategies. In this review, we aim to provide an integrated overview of the fundamentals and recent progress of MWO_4-based photocatalysts. Furthermore, different strategies, including morphological control, surface modification, heteroatom doping, and heterojunction fabrication, which are employed to promote the photocatalyticactivities of MWO_4-based materials, are systematically summarized and discussed. Finally, existing challenges and a future perspective are also provided to shed light on the development of highly efficient MWO_4-based photocatalysts.

Synthesis,structure and luminescence properties of KEu_(0.01)Gd_(0.19)Yb_(0.8)(WO_4)_2 powder

The synthesis of co-doped KEu0.01Gd0.19Yb0.8（WO4）2 was achieved by a modified Pechini method at 750℃. The structure of obtained compound was confirmed using X-ray diffraction measurement and Raman spectroscopy. The Scherrer＇s formula was used to confirm the grain sizes visualized by TEM technique. The grain sizes of about 100 nm of monoclinic KGW were successfully obtained by this meth- odology. In order to study spectroscopic properties of the prepared system the emission spectra were measured. The effective down- and up-conversion processes in non-resonant system were investigated.

Hydrothermal Synthesis,Crystal Structure and Spectral Characterization of a New Copper Isopolytungstate: [Cu(phen)_3][W_6O_(19)]

An unusual inorganic-organic hybrid hexatungstate complex [Cu（phen）3][W6O19] 1 （C36H24 CuN6O19W6, Mr= 2011.20） was hydrothermally synthesized and characterized by singlecrystal X-ray diffraction, IR spectrum, UV-VIS spectrum and elemental analyses. This compound crystallizes in the monoclinic system, space group C2/c with a = 19.1005（11）, b = 11.2585（11）, c = 20.2867（15） A, β= 102.177（2）°, V= 4264.4 A^ 3, μ（MoKa） = 16.691 mm^-1, Dc = 3.133 g/cm^3, Z = 4, F（000） = 3628, the final R = 0.0338 and wR = 0.0798 for 4090 observed reflections with I 〉 2σ（I）. The result of structure determination shows that the crystal structure is constructed from [W6O19]^2- cluster anions and [Cu（phen）3]^2＋ complex fragments, which are held together into a three-dimensional network through hydrogen-bonding interactions.

Crystal structure and negative thermal expansion of solid solution Lu_2W_(3-x)Mo_xO_(12)

A new series of solid solutions Lu2W3-xMoxO12 （0.5≤r≤2.5） were successfully synthesized by the solid-state method. Their crystal structure and negative thermal expansion properties were studied using high-temperature X-ray powder diffraction and the Rietveld method. All samples of rare-earth ttmgstates and molybdates are found to crystallize in the same orthorhombic structure with space group Pnca and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients （TEC） of Lu2W3_xMoxO12 are determined as -20.0× 10^-6 K^-1 for x=0.5 and -16.1×10^-6 K^-1 for x=2.5 but -18.6× 10^-6 and -16.9× 10^-6K^-1 for unsubstituted Lu2W3012 and Lu2M03012 in the identical temperature range of 200 to 800℃. High-temperature X-ray diffraction （XRD） data and bond length analysis suggest that the difference between W-O and Mo-O bond is responsible for the change of TECs after the element substitution in this series of solid solutions.

Studies on NaLn(WO_4)_2 Single Crystals(Ln=La,Pr,Nd)

The crystals of NaLn(WO4)_2(Ln=La,Pr,Nd)are grown from a melt of LiCl-Na_2WO_4 flux by slow cooling method.The chemical analysis data show that the crystals are NaLa(WO_4)_2,NaPr(WO4)_2 and NaNd(WO_4)_2 respectively.The structures of the crystals are ascertained that they belong to scheelite structure of the tetragonal system with a space group of 14_1/a.The lattice parameters of the crystals have been calculated.It is found that the cell volume of NaLn(WO_4)_2 crystals decrease with a decrease of Ln^(3+)radius. The bond distances and their angles in NaLa(WO_4)_2 and NaNd(WO_4)_2 are given.It is found that in accordance with the decrease of ionic radii of Ln^(3+)due to increase of atomic number,the bond distances between Ln-O,Ln-Ln and W-O decrease regularly.The infrared spectra of NaLn(WO_4)_2 are measured.The tetrahedra characteristic absorptions of WO_4^(2-)are shown.The sensitization of host lattice is observed from the excitation and fluorescent spectra of NaLa(WO_4)_2 and NaPr(WO_4)_2.

Growth and characterization of Nd:Sr_(0.95)Ba_(0.05)WO_4 single crystal

Synthesis of polycrystalline Nd：Sr0.95Ba0.05WO4 by means of liquid-and solid-phase reaction was reported.X-ray powder diffraction results showed that the as-grown Sr0.95Ba0.05WO4 and Nd：Sr0.95Ba0.05WO4 single crystals belonged to tetragonal system and I41/a space group.Transparent Nd：Sr0.95Ba0.05WO4 single crystal could be obtained along c-axis by Czochralski method from the synthesized polycrys-talline material.As the transmittance of Sr0.95Ba.005WO4 single crystal could reach 80%, Nd3＋ ion was adopted to be doped into the single crystal.Spontaneous Raman spectrums of polycrystalline material and single crystal were measured by RERKZN-ELMER2000 and JY-HR800.By using X-ray fluorescence method, the effective segregation coefficients of Nd, Ba, Sr, and W elements in Sr0.95Ba.005WO4 single crystal were estimated as 0.844（0.745）, 0.44, 1.09, and 0.95, respectively.The segregation coefficients of Nd in Sr0.95Ba0.05WO4 were higher than that in BaWO4, and this is as better as a Raman laser crystal.

Thermal Properties of K(Y_(1-x)Yb_x)(WO_4)_2(x=0.098,0.196,0.294) Crystal

Thermal properties of pure KY（WO4）2 and K（Y1-xYbx）（WO4）2（x=0.098,0.196,0.294） crystals were investigated.The specific heat and thermal diffusivity of crystals were calculated at a range of 50～300 ℃.The calculated result shows that the specific heat and thermal diffusivity of K（Y1-xYbx）（WO4）2（x=0.098,0.196,0.294） crystals were slightly affected by the Yb3＋ concentration.The thermal expansion coefficient of K（Y0.804Yb0.196）（WO4）2 crystals along x,y and z axes were determined to be 13.51,4.474 and 16.60×10-6 K^-1,respectively. These results suggest the K（Y1-xYbx）（WrO4）2 （x = 0.098, 0.196, 0.294） crystal as a laser crystal of low-middle power.

Simultaneous determination of some trace metal impurities in high-purity sodium tungstate using coprecipitation and inductively coupled plasma atomic emission spectrometry

A method based on the combination of coprecipitation with inductively coupledplasma atomic emission spectrometry (ICP-AES) was developed for the determination of impurities inhigh-purity sodium tungstate. Six elements (Co, Cu, Fe, Mn, Ni, and Pb) were coprecipitated bylanthanum hydroxide so as to be concentrated and separated from the tungsten matrix. Effects of somefactors on the recoveries of the analytes and on the residual amount of sodium tungstate wereinvestigated, and the optimum conditions for the coprecipitation were proposed. Matrix-matchingcalibration curve method was used for the analysis. It is shown that the elements mentioned abovecan be quantitatively recovered. The detection limits for Co, Cu, Fe, Mn, Ni, and Pb are 0.07, 0.4,0.2, 0.1, 0.6, and 1.3 μg·g^(-1), respectively. The recoveries vary from 92.5% to 108%, and therelative standard deviations (RSDs) are in the range of 3.1%-5.5%.

Synthesis and Structure of One Novel Polyoxometalate Compound Connected via Cerium(III) Cation with Three-dimensional Framework H_2{[K(H_2O)_2]_2[Ce(H_2O)_5]_2(H_2Mo_(1.16)W_(10.84)O_(42))}·8H_2O

One novel polyoxometalate compound connected via trivalent cerium cation as bridge H2{ [K（H2O）212[Ce（H2O）5]2（H2Mo1.16W10.84O42）}.8H2O 1 was designed and synthesized in aqueous solution. X-ray diffraction analysis reveals that the structure of 1 is a three-dimensional framework assembled from the arrangement of H2Mo1.16W10.84O42 （named paradodecmetalate-B） and Ce（H2O）5^3＋ containing two planes, which are constructed through the unification of H2Mo1.16W10.84O42^10- and Ce（H2O）5^3＋ along the [100] and [001] directions. Crystal data： H96Ce4KaMo2.32O128W21.68, Mr = 7074.89, monoclinic, P21/n, a = 12.5037（17）, b = 17.002（2）, c = 12.7473（17）A, β = 105.966（2）°, V = 2605.4（6）A^3, Z = 1, Dc = 4.509 g/cm^3, F（000） = 3132,μ = 26.098 mm^-1, R = 0.0377 and wR = 0.0789 （I 〉 2σ（I））.

Effect of sodium tungstate on visual evoked potentials in diabetic rats

AIM： To evaluate the effect of sodium tungstate on visual evoked potentials（VEPs） in diabetic rats.· METHODS： Wistar rats were randomly divided into three groups as normal control, diabetic control and diabetic rats treated with sodium tungstate. Diabetes was induced by single intraperitoneal injection of streptozotocin（50 mg/kg）. Sodium tungstate [40 mg/（kg·d）]was administered for 12 wk and then VEPs were recorded.Additionally, thiobarbituric acid reactive substance（TBARS） levels were measured in brain tissues.·RESULTS： The latencies of P1, N1, P2, N2 and P3 waves were significantly prolonged in diabetic rats compared with control group. Diabetes mellitus caused an increase in the lipid peroxidation process that was accompanied by changes in VEPs. However, prolonged latencies of VEPs for all components returned to control levels in sodium tungstate-treated group. The treatment of sodium tungstate significantly decreased brain TBARS levels and depleted the prolonged latencies of VEP components compared with diabetic control group.· CONCLUSION： Sodium tungstate shows protective effects on visual pathway in diabetic rats, and it can be worthy of further study for potential use.

NON-ISOTHERMAL KINETIC STUDY ON THE THERMAL DEHYDRATION OF SODIUM TUNGSTATE DIHYDRATE

１ＩＮＴＲＯＤＵＣＴＩＯＮＳｏｄｉｕｍｔｕｎｇｓｔａｔｅｄｉｈｙｄｒａｔｅｉｓｕｓｅｄｉｎｔｈｅｐｒｅｐａｒａｔｉｏｎｏｆｃｏａｔｅｄｅｌｅｃｔｒｏｄｅｓｆｏｒｅｌｅｃｔｒｏｃａｔａｌｙｓｉｓ［１］ａｎｄａｓｆｉｒｅｒｅｔａｒｄａｎｔｆｏｒｆａｂｒ...

Expanded Industrial Experiments of Free-alkali Recovery from Sodium Tungstate Solution by the Membrane Electrolysis Process

The expanded industrial experiments were conducted with practical industrial liquor to separate free alkali from sodium tungstate solution by electrolysis with cation-exchange membrane. Experimental results show that on the condition that the temperature is 50-55 degreesC and the current density is 1000 A/m(2), the single electrolysis cell is operated stably and 80% free-alkali in mass fraction is separated from the anode feed liquor of sodium tungstate, with electric efficiency up to more than 88% and the unit energy consumption E lower than 1900 kWh/t; while three electrolysis cells in series are operated, under the condition that the temperature is 60-65 degreesC and the current density is 1000 A/m(2), the electric efficiency can reach higher than 88% and the unit energy consumption E can be lower than 2250 kWh/t.

Growth,structure and spectral characteristics of KEr_(0.1)Yb_(0.9)(WO_4)_2 laser crystal

The 10 at.% Er3+-doped KYb(WO4)2(KEr0.1Yb0.9(WO4)2) laser crystal with dimensions up to 25 mm×15 mm×10 mm was grown by the Kyropoulos method.The crystal structure was identified as β-KEr0.1Yb0.9(WO4)2 by XRD analysis.Through TG-DTA curves,the melting point and transition point of the crystal were determined to be 1058 and 1031 °C,respectively.Infrared spectrum and Raman spectrum were measured,and the vibration frequencies of infrared and Raman active modes for the crystal were assigned.The absorption cross ...

Synthesis and thermal expansion of 4J36/ZrW_2O_8 composites

Gas atomized 4J36 alloy powder was milled for 72 h then mixed with ZrW2O8 powder and sintered at 600℃ for 4 h under argon atmosphere. 4J36/ZrW2O8 composites containing 10 vol.%, 20 vol.%, 30 vol.%, and 40 vol.% ZrW2Os were fabricated, the relative density of which ranged from 70% to 80%. Thermal expansion coefficients of the composites decreased as the amount of ZrW2O8 increased, in agreement with the rule of the mixture. The coefficient of thermal expansion of the 4J36/40 vol.%ZrW2O8 composite in 25-100℃ is 0.55 × 10^＋6/℃.

Mortar-Pestle and Microwave Assisted Regioselective Nitration of Aromatic Compounds in Presence of Certain Group V and VI Metal Salts under Solvent Free Conditions

Solvent – free Mortar-pestle (grinding) and microwave-assisted nitration reactions (MWANR’s) underwent smoothly in the presence of group V and VI metal salts with high regio-selectivity for anilides, moderately- and non-activated aro-matic compounds. The reactions were conducted under solvent-free conditions, which afforded good to excellent yields. The observed reaction times in MW assisted conditions are in the range of only few minutes.

Fluorescence properties of divalent and trivalent europium ions in CdWO_4 single crystals grown by the Bridgman method

Optical absorption,excitation,and fluorescence were investigated in Eu ion-doped CdWO4 single crystal grown by a modified Bridgman method.The results indicate that Eu^2＋ and Eu^3＋ ions coexist in CdWO4 crystal and an energy transfer occurs between these Eu^2＋ and Eu^3＋ ions.When the crystal is excited by 266-nm light,the energy corresponding to the 4f65d to 8S7/2 transition of Eu^2＋ ions results in the excitation of the Eu^3＋ ions to the 5DJ level.The effect on fluorescence of annealing in oxygen at various temperatures was investigated.The excitation intensity of Eu^2＋ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K,but it remains at a certain equilibrium level when the annealing temperature is further increased.

Influences of Co-Doping Cation on Properties of PWO∶F- Scintillating Crystal

Whereas the light yield of PWO crystal can be significantly improved by doping with either of F- and Sb3+, effects of heavily co-doping with by F-+Sb3+, F-+Ca2+, and F-+Ca2++Sb3+, respectively, on the properties of PWO scintillation crystals, including optical transmission, luminescence and light yield were studied. The result indicates that co-doping with three dopants, F-+Ca2++Sb3+, is a more effective measure than doping with single dopant F- for the improvement of scintillation properties of PWO crystals, including light yield.