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 ac...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.展开更多
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...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.展开更多
The leaching of sulfuric acid converted product of scheelite in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammoni...The leaching of sulfuric acid converted product of scheelite in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammonium paratungstate production.The results showed that the WO_(3)leaching efficiency was about 99%under optimal conditions of 350 r/min,liquid-to-solid ratio of 3 mL/g,1 mol/L NH_(4)HCO_(3),4 mol/L NH_(3)·H_(2)O,25℃,and 15 min.During the leaching,CaSO_(4)almost had no change and was still in a banding or rod-like shape in short leaching time,while conglobate CaCO_(3)was gradually formed on the CaSO_(4)surface.A secondary reaction might occur between CaSO_(4)and WO_(4)^(2−),which could be restrained by a certain amount of CO_(3)^(2−)in the solution.There was no CaCO_(3)phase determined by XRD in leaching residue of converted product for scheelite concentrate under optimal conditions,which was different from that for synthetic scheelite.The leaching process could be explained by neutralization reaction of H_(2)WO_(4)and solid transformation of CaSO_(4)in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution.展开更多
Bismuth-doped antimony tungstate(Bi-doped Sb_(2)WO_(6))microspheres were synthesized via a novel hydrothermal synthesis approach.These microspheres were then used as active layers in gas sensors for the detection of c...Bismuth-doped antimony tungstate(Bi-doped Sb_(2)WO_(6))microspheres were synthesized via a novel hydrothermal synthesis approach.These microspheres were then used as active layers in gas sensors for the detection of carbon dioxide(CO_(2)),a significant greenhouse gas and a critical parameter for evaluating air quality.The incorporation of bismuth significantly enhances the gas-sensing performance of the Sb_(2)WO_(6)microspheres,with the 4%Bidoped sensing active layer achieving a remarkable response value of 15 when exposed to 200 ppm of CO_(2),outperforming the undoped Sb_(2)WO_(6).Furthermore,the selectivity of the 4%Bi-Sb_(2)WO_(6)sensor toward CO_(2)gas was enhanced relative to the Sb_(2)WO_(6)sensor.The fundamental mechanisms of gas sensing and the factors contributing to the improved CO_(2)response of 4%Bi-Sb_(2)WO_(6)micro spheres were investigated using density functional theory.Bi-doped Sb_(2)WO_(6)materials exhibit significant advantages in gas-sensing applications,including improved conductivity,enhanced gas adsorption capacity,increased reaction rates,good chemical stability,excellent selectivity,and the ability to adjust electron density.These characteristics enable Bi-doped Sb_(2)WO_(6)to demonstrate higher sensitivity and rapid response capabilities in gas sensors,making it suitable for practical applications.展开更多
The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from ...The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from the tungstate solution by magnesium salt precipitation were obtained. The results show that when the concentration of total magnesium increases from 0.01 mol/L to 1.0 mol/L, the optimal pH for the phosphorus removal by magnesium phosphate decreases from 9.8 to 8.8. The residual concentration of total phosphorus almost keeps the level of 4.0×10-6 mol/L in the system. MgHPO4, Mg3（PO4）2 and the mixture of Mg3（PO4）2 and Mg（OH）2 are stabilized in these system, respectively. However, increasing the total concentration of magnesium has little effect on phosphorus removal by magnesium ammonium phosphate, while it is helpful for phosphorus removal by increasing the total ammonia concentration. The calculated results demonstrate that the residual concentration of total phosphorus can decrease to 5.0×10-7 mol/L as the total concentration of ammonia reaches 5.0 mol/L and the optimal pH value is 9-10. Finally, verification experiments were conducted with home-made ammonium tungstate solution containing 50 g/L WO3 and 13 g/L P. The results show that when the dosage of MgCl2 is 1.1 times of the theoretical amount, the optimum pH for removing phosphorus is 9.5, which matches with the results of the theoretical calculation exactly.展开更多
Ag2S/Ag2WO4 composite microrods,with lengths of 0.2-1μm and diameters of 20-30 nm,were fabricated by a facile sonochemical route.The as-synthesized products were intensively investigated by a series of physicochemica...Ag2S/Ag2WO4 composite microrods,with lengths of 0.2-1μm and diameters of 20-30 nm,were fabricated by a facile sonochemical route.The as-synthesized products were intensively investigated by a series of physicochemical characterizations,such as N2 physical adsorption,X-ray diffraction,scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectroscopy,diffuser reflectance spectroscopy,X-ray photoelectron spectroscopy,photoluminescence spectroscopy and photocurrent response measurements.Ultrasonic irradiation yields an obvious improvement in the photocatalyst texture,for example,an increase in crystallinity and surface area.Moreover,sonochemically fabricated Ag2S/Ag2WO4 microrods display strong visible light absorption and a high transient photocurrent response.The produced intimate Ag2S/Ag2WO4interface between Ag2S and Ag2WO4 crystal phases largely promotes the separation of photogenerated holes and electrons.High photocatalytic activity and stability were obtained over Ag2S/Ag2WO4composite microrods.The dye degradation rate constant of Ag2S/Ag2WO4 was 4.7 times and 29.8times higher than that of bare Ag2WO4 and Ag2S,respectively.展开更多
Rod-shaped PbW O4 microcrystals of length 1 μm were fabricated by a hydrothermal route and subsequent calcination. Pt nanoparticles（NPs） of different contents（0.5 wt%,1 wt% and 2 wt%） were subsequently deposited ...Rod-shaped PbW O4 microcrystals of length 1 μm were fabricated by a hydrothermal route and subsequent calcination. Pt nanoparticles（NPs） of different contents（0.5 wt%,1 wt% and 2 wt%） were subsequently deposited on the PbW O4 microcrystals,producing robust Pt/PbW O4 composite microcrystals. The PbW O4 microcrystals and Pt/PbW O4 photocatalysts were characterized by X-ray diffraction,N2 sorption measurements,scanning electron microscopy,transmission electron microscopy,and X-ray photoelectron,photoluminescence,Fourier-transform infrared,and ultraviolet-visible diffuse reflectance spectroscopies. The photocatalytic performances of the catalysts were evaluated by the consecutive photocatalytic degradation of acid orange II dye. The Pt/PbW O4 composite microcrystals exhibited high photocatalytic activity and stability. The deposition of Pt NPs produced surface plasmon resonance（SPR）,which induced a large visible light absorption. A Pt NP content of 1-2 wt% resulted in an ~2 times increase in photocatalytic activity,compared with the activity of Pt/PbW O4. The crystal structure and high crystallinity of PbW O4 resulted in its favorable photocatalytic property,and the SPR effect of the Pt NPs promoted visible light harvesting. The Pt NPs also enhanced the separation of photo-generated electrons and holes,which further promoted the photocatalytic reaction.展开更多
Based on the difference in tendency to polymerize between tungsten and molybdenum, a new method using D309 resin was propounded. The batch tests indicate that the optimum pH value and contact time for the separation a...Based on the difference in tendency to polymerize between tungsten and molybdenum, a new method using D309 resin was propounded. The batch tests indicate that the optimum pH value and contact time for the separation are 7.0 and 4 h respectively, the maxium separation factor of W and Mo is 9.29. And the experimental resules show that isothermal absorbing tungsten and molybdenum belongs to Langmuir model and Freundlich model respectively, and the absorbing kinetics for tungsten is controlled by intra-particle diffusion. With a solution containing 70 g/L WO3 and 28.97 g/L Mo, the effluent with a mass ratio of Mo to WO3 of 76 and the eluate with a mass ratio of WO3 to Mo of 53.33 are obtained after column test.展开更多
An adsorbent, Na1.6Al0.6Ti1.4（PO4）3 （or NATP）, was prepared by controlled crystallization of glasses in the Na2O-Al2O3-CaO-TiO2-P2O5 system. The crystalline phases characterized by X-ray diffraction （XRD） show t...An adsorbent, Na1.6Al0.6Ti1.4（PO4）3 （or NATP）, was prepared by controlled crystallization of glasses in the Na2O-Al2O3-CaO-TiO2-P2O5 system. The crystalline phases characterized by X-ray diffraction （XRD） show that the sample glasses crystallizes into two phases, i.e. NATP and Ca9Al（PO4）7, while the Ca9Al（PO4）7 phase can be leached selectively with HCl, leaving a massive number of pores in the material. Through the experimental research, the effects of contact time, solution pH, and the initial concentration of Na＋on the cation exchange properties were investigated. The batch sorption kinetics and equilibria can be described by Pseudo-second-order kinetic equations and Langmuir isotherm equations respectively. Furthermore, the experiments with an industrial solution show that the removal rate of sodium from industrial （NH4）2WO4 is higher than 97%. Cycle experiment also shows that the NATP has a good cyclic performance.展开更多
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 ...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.展开更多
Nd^3＋ ：NaLa（WO4）2 crystals with a dimension up to 7 mm were grown from a high temperature solution using a double-crucible method. Scanning electron microscopy observations of the crystals showed that there were n...Nd^3＋ ：NaLa（WO4）2 crystals with a dimension up to 7 mm were grown from a high temperature solution using a double-crucible method. Scanning electron microscopy observations of the crystals showed that there were no small cracks on the surface of the crystals although they underwent two phase transitions when cooling down from high temperatures. X-ray diffraction studies indicated that the as-obtained product is pure low- temperature tetragonal Nd^3＋ ：NaLa（WO4）2. The absorption and fluorescence spectra for Nd^3＋ ：NaLa（WO4）2 were measured at room temperature. The absorption band at 804 nm has a wide full-width half maximum of 23 nm whose origin is discussed. The absorption and emission cross sections were calculated to be 7.24×10^-20 cm^2 at 804 nm and 6.54×10 ^-20 cm^2 at 1057 nm, respectively.展开更多
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. Th...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.展开更多
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-V...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.展开更多
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-temperat...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.展开更多
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 crysta...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.展开更多
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.T...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.展开更多
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 calcu...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.展开更多
The photocatalytic ability of ZnO is improved through the addition of flower‐like Bi2WO6 to prepare a Bi2WO6/ZnO composite with visible light activity.The composite is characterized by X‐ray diffraction,transmission...The photocatalytic ability of ZnO is improved through the addition of flower‐like Bi2WO6 to prepare a Bi2WO6/ZnO composite with visible light activity.The composite is characterized by X‐ray diffraction,transmission electron microscopy,scanning electron microscopy with UV–vis diffuse reflectance spectroscopy,X‐ray photoelectron spectroscopy and N2 adsorption‐desorption isotherms.After modification,the band gap energy of Bi2WO6/ZnO is reduced from 3.2 eV for ZnO to 2.6 eV.Under visible light irradiation,the Bi2WO6/ZnO composite shows an excellent photocatalytic activity for degrading methylene blue(MB)and tetracycline.The photo‐degradation efficiencies of(0.3:1)Bi2WO6/ZnO for MB and tetracycline are approximately 246 and 4500 times higher than those of bare ZnO,respectively,and correspondingly,the photo‐degradation rates for the two pollutants are approximately 120 and 200 times higher than those with bare ZnO,respectively.Moreover,the photocatalyst of(0.3:1)Bi2WO6/ZnO exhibits a higher transient photocurrent density of approximately 4.5μA compared with those of bare Bi2WO6 and ZnO nanoparticles.The successful recombination of Bi2WO6 and ZnO enhances the photocatalytic activity and reduces the band gap energy of ZnO,which can be attributed to the effective separation of electron–hole pairs.Active species trapping experiments display that[O2]-is the major species involved during photocatalysis rather than·OH and h+.This study provides insight into designing a meaningful visible‐light‐driven photocatalyst for environmental remediation.展开更多
The photocatalytic degradation of norfloxacin by bismuth tungstate(Bi2WO6)with different hierarchical architectures wasinvestigated under visible light irradiation.Bi2WO6was prepared by hydrothermal method with the re...The photocatalytic degradation of norfloxacin by bismuth tungstate(Bi2WO6)with different hierarchical architectures wasinvestigated under visible light irradiation.Bi2WO6was prepared by hydrothermal method with the reaction solution pH rangingfrom4to11.The relatively ultrathin Bi2WO6nanoflakes prepared at pH4showed excellent adsorption and photodegradationefficiency towards norfloxacin.The characterization results showed that Bi2WO6prepared at pH4had a larger specific area andfaster photo-generated carrier separation rate.The decay rate reached the maximum in weak alkaline reaction solution,which couldbe attributed to the presence of moderate OH-anions.The present study demonstrated that the smaller size of Bi2WO6could be anefficient photocatalyst on the degradation of norfloxacin in the aquatic environment.展开更多
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.% ZrW2O...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/℃.展开更多
文摘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.
文摘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.
文摘The leaching of sulfuric acid converted product of scheelite in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammonium paratungstate production.The results showed that the WO_(3)leaching efficiency was about 99%under optimal conditions of 350 r/min,liquid-to-solid ratio of 3 mL/g,1 mol/L NH_(4)HCO_(3),4 mol/L NH_(3)·H_(2)O,25℃,and 15 min.During the leaching,CaSO_(4)almost had no change and was still in a banding or rod-like shape in short leaching time,while conglobate CaCO_(3)was gradually formed on the CaSO_(4)surface.A secondary reaction might occur between CaSO_(4)and WO_(4)^(2−),which could be restrained by a certain amount of CO_(3)^(2−)in the solution.There was no CaCO_(3)phase determined by XRD in leaching residue of converted product for scheelite concentrate under optimal conditions,which was different from that for synthetic scheelite.The leaching process could be explained by neutralization reaction of H_(2)WO_(4)and solid transformation of CaSO_(4)in NH_(3)·H_(2)O−NH_(4)HCO_(3)solution.
基金financially supported by the Outstanding Youth Foundation of Jiangsu Province of China(No.BK20211548)Yangzhou Science and Technology Plan Project(No.YZ2023246)+1 种基金China Scholarship Council(No.202308320445)the Postgraduate Research and Practice Innovation Program of Jiangsu Province of China(No.KYCX23_3551)
文摘Bismuth-doped antimony tungstate(Bi-doped Sb_(2)WO_(6))microspheres were synthesized via a novel hydrothermal synthesis approach.These microspheres were then used as active layers in gas sensors for the detection of carbon dioxide(CO_(2)),a significant greenhouse gas and a critical parameter for evaluating air quality.The incorporation of bismuth significantly enhances the gas-sensing performance of the Sb_(2)WO_(6)microspheres,with the 4%Bidoped sensing active layer achieving a remarkable response value of 15 when exposed to 200 ppm of CO_(2),outperforming the undoped Sb_(2)WO_(6).Furthermore,the selectivity of the 4%Bi-Sb_(2)WO_(6)sensor toward CO_(2)gas was enhanced relative to the Sb_(2)WO_(6)sensor.The fundamental mechanisms of gas sensing and the factors contributing to the improved CO_(2)response of 4%Bi-Sb_(2)WO_(6)micro spheres were investigated using density functional theory.Bi-doped Sb_(2)WO_(6)materials exhibit significant advantages in gas-sensing applications,including improved conductivity,enhanced gas adsorption capacity,increased reaction rates,good chemical stability,excellent selectivity,and the ability to adjust electron density.These characteristics enable Bi-doped Sb_(2)WO_(6)to demonstrate higher sensitivity and rapid response capabilities in gas sensors,making it suitable for practical applications.
基金Project(2012BAB10B04)supported by the National Key Technologies R&D Program of China
文摘The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from the tungstate solution by magnesium salt precipitation were obtained. The results show that when the concentration of total magnesium increases from 0.01 mol/L to 1.0 mol/L, the optimal pH for the phosphorus removal by magnesium phosphate decreases from 9.8 to 8.8. The residual concentration of total phosphorus almost keeps the level of 4.0×10-6 mol/L in the system. MgHPO4, Mg3（PO4）2 and the mixture of Mg3（PO4）2 and Mg（OH）2 are stabilized in these system, respectively. However, increasing the total concentration of magnesium has little effect on phosphorus removal by magnesium ammonium phosphate, while it is helpful for phosphorus removal by increasing the total ammonia concentration. The calculated results demonstrate that the residual concentration of total phosphorus can decrease to 5.0×10-7 mol/L as the total concentration of ammonia reaches 5.0 mol/L and the optimal pH value is 9-10. Finally, verification experiments were conducted with home-made ammonium tungstate solution containing 50 g/L WO3 and 13 g/L P. The results show that when the dosage of MgCl2 is 1.1 times of the theoretical amount, the optimum pH for removing phosphorus is 9.5, which matches with the results of the theoretical calculation exactly.
基金supported by the National Natural Science Foundation of China(21567008,21263005)the Yangfan Project of Guangdong Province+2 种基金the Natural Science Foundation of Jiangxi Province(20133BAB21003,20161BAB203090)the Landing Project of Science and Technology of Colleges and Universities in Jiangxi Province(KJLD14046)the Graduate Innovation Project of Jiangxi Province(YC2015-S293)~~
文摘Ag2S/Ag2WO4 composite microrods,with lengths of 0.2-1μm and diameters of 20-30 nm,were fabricated by a facile sonochemical route.The as-synthesized products were intensively investigated by a series of physicochemical characterizations,such as N2 physical adsorption,X-ray diffraction,scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectroscopy,diffuser reflectance spectroscopy,X-ray photoelectron spectroscopy,photoluminescence spectroscopy and photocurrent response measurements.Ultrasonic irradiation yields an obvious improvement in the photocatalyst texture,for example,an increase in crystallinity and surface area.Moreover,sonochemically fabricated Ag2S/Ag2WO4 microrods display strong visible light absorption and a high transient photocurrent response.The produced intimate Ag2S/Ag2WO4interface between Ag2S and Ag2WO4 crystal phases largely promotes the separation of photogenerated holes and electrons.High photocatalytic activity and stability were obtained over Ag2S/Ag2WO4composite microrods.The dye degradation rate constant of Ag2S/Ag2WO4 was 4.7 times and 29.8times higher than that of bare Ag2WO4 and Ag2S,respectively.
基金supported by the National Natural Science Foundation of China(2106700421567008+5 种基金21263005)Project of Jiangxi Province Natural Science Foundation China(20133BAB21003)Training Programs of Innovation and Entrepreneurship for Undergraduates of Jiangxi Province(201310407046)The Landing Project of Science and Technology of Colleges and Universities in Jiangxi Province(KJLD14046)Young Scientist Training Project of Jiangxi Province(20122BCB23015)Yuanhang Engineering of Jiangxi Province~~
文摘Rod-shaped PbW O4 microcrystals of length 1 μm were fabricated by a hydrothermal route and subsequent calcination. Pt nanoparticles（NPs） of different contents（0.5 wt%,1 wt% and 2 wt%） were subsequently deposited on the PbW O4 microcrystals,producing robust Pt/PbW O4 composite microcrystals. The PbW O4 microcrystals and Pt/PbW O4 photocatalysts were characterized by X-ray diffraction,N2 sorption measurements,scanning electron microscopy,transmission electron microscopy,and X-ray photoelectron,photoluminescence,Fourier-transform infrared,and ultraviolet-visible diffuse reflectance spectroscopies. The photocatalytic performances of the catalysts were evaluated by the consecutive photocatalytic degradation of acid orange II dye. The Pt/PbW O4 composite microcrystals exhibited high photocatalytic activity and stability. The deposition of Pt NPs produced surface plasmon resonance（SPR）,which induced a large visible light absorption. A Pt NP content of 1-2 wt% resulted in an ~2 times increase in photocatalytic activity,compared with the activity of Pt/PbW O4. The crystal structure and high crystallinity of PbW O4 resulted in its favorable photocatalytic property,and the SPR effect of the Pt NPs promoted visible light harvesting. The Pt NPs also enhanced the separation of photo-generated electrons and holes,which further promoted the photocatalytic reaction.
基金Project(51174232)supported by the National Natural Science Foundation of China
文摘Based on the difference in tendency to polymerize between tungsten and molybdenum, a new method using D309 resin was propounded. The batch tests indicate that the optimum pH value and contact time for the separation are 7.0 and 4 h respectively, the maxium separation factor of W and Mo is 9.29. And the experimental resules show that isothermal absorbing tungsten and molybdenum belongs to Langmuir model and Freundlich model respectively, and the absorbing kinetics for tungsten is controlled by intra-particle diffusion. With a solution containing 70 g/L WO3 and 28.97 g/L Mo, the effluent with a mass ratio of Mo to WO3 of 76 and the eluate with a mass ratio of WO3 to Mo of 53.33 are obtained after column test.
基金Project(2012AA063205)supported by the High-tech Research and Development Program of China
文摘An adsorbent, Na1.6Al0.6Ti1.4（PO4）3 （or NATP）, was prepared by controlled crystallization of glasses in the Na2O-Al2O3-CaO-TiO2-P2O5 system. The crystalline phases characterized by X-ray diffraction （XRD） show that the sample glasses crystallizes into two phases, i.e. NATP and Ca9Al（PO4）7, while the Ca9Al（PO4）7 phase can be leached selectively with HCl, leaving a massive number of pores in the material. Through the experimental research, the effects of contact time, solution pH, and the initial concentration of Na＋on the cation exchange properties were investigated. The batch sorption kinetics and equilibria can be described by Pseudo-second-order kinetic equations and Langmuir isotherm equations respectively. Furthermore, the experiments with an industrial solution show that the removal rate of sodium from industrial （NH4）2WO4 is higher than 97%. Cycle experiment also shows that the NATP has a good cyclic performance.
基金support of NSFC 51702284Fundamental Research Funds for the Central Universities (112109*172210171)+2 种基金the Startup Foundation for Hundred-Talent Program of Zhejiang University (112100-193820101/001/022)support of the NSFC 21501138the Science Research Foundation of Wuhan Institute of Technology (K201513)
文摘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.
文摘Nd^3＋ ：NaLa（WO4）2 crystals with a dimension up to 7 mm were grown from a high temperature solution using a double-crucible method. Scanning electron microscopy observations of the crystals showed that there were no small cracks on the surface of the crystals although they underwent two phase transitions when cooling down from high temperatures. X-ray diffraction studies indicated that the as-obtained product is pure low- temperature tetragonal Nd^3＋ ：NaLa（WO4）2. The absorption and fluorescence spectra for Nd^3＋ ：NaLa（WO4）2 were measured at room temperature. The absorption band at 804 nm has a wide full-width half maximum of 23 nm whose origin is discussed. The absorption and emission cross sections were calculated to be 7.24×10^-20 cm^2 at 804 nm and 6.54×10 ^-20 cm^2 at 1057 nm, respectively.
文摘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.
文摘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.
基金supported by the China Postdoctoral Science Foundation (No.20080430556)the Major State Basic Research and Development Program of China (No.2006CB705600)
文摘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.
基金supported by the National Natural Science Foundation of China (0041814161)
文摘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.
文摘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.
基金supported by the National Natural Science Foundation of China (No 60778035)the Special Project of Jiangsu University for Young Scientist (No 1283000287)
文摘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.
基金supported by the National Natural Science Foundation of China(51578354)Six Talent Peaks Program(2016-JNHB-067)+1 种基金Suzhou Science and Technology Bureau(SS201667)Qing Lan Project and Research Innovation Project for College Graduates of Jiangsu Province(KYCX17_2067)~~
文摘The photocatalytic ability of ZnO is improved through the addition of flower‐like Bi2WO6 to prepare a Bi2WO6/ZnO composite with visible light activity.The composite is characterized by X‐ray diffraction,transmission electron microscopy,scanning electron microscopy with UV–vis diffuse reflectance spectroscopy,X‐ray photoelectron spectroscopy and N2 adsorption‐desorption isotherms.After modification,the band gap energy of Bi2WO6/ZnO is reduced from 3.2 eV for ZnO to 2.6 eV.Under visible light irradiation,the Bi2WO6/ZnO composite shows an excellent photocatalytic activity for degrading methylene blue(MB)and tetracycline.The photo‐degradation efficiencies of(0.3:1)Bi2WO6/ZnO for MB and tetracycline are approximately 246 and 4500 times higher than those of bare ZnO,respectively,and correspondingly,the photo‐degradation rates for the two pollutants are approximately 120 and 200 times higher than those with bare ZnO,respectively.Moreover,the photocatalyst of(0.3:1)Bi2WO6/ZnO exhibits a higher transient photocurrent density of approximately 4.5μA compared with those of bare Bi2WO6 and ZnO nanoparticles.The successful recombination of Bi2WO6 and ZnO enhances the photocatalytic activity and reduces the band gap energy of ZnO,which can be attributed to the effective separation of electron–hole pairs.Active species trapping experiments display that[O2]-is the major species involved during photocatalysis rather than·OH and h+.This study provides insight into designing a meaningful visible‐light‐driven photocatalyst for environmental remediation.
基金Projects(51579096,51222805,51521006,51508175) supported by the National Natural Science Foundation of ChinaProject supported by the National Program for Support of Top-Notch Young Professionals of China+1 种基金Project(NCET–11–0129) supported by the Program for New Century Excellent Talents in University from the Ministry of Education of ChinaProject(CX2015B095) supported by the Hunan Province Innovation Foundation for Postgraduate,China
文摘The photocatalytic degradation of norfloxacin by bismuth tungstate(Bi2WO6)with different hierarchical architectures wasinvestigated under visible light irradiation.Bi2WO6was prepared by hydrothermal method with the reaction solution pH rangingfrom4to11.The relatively ultrathin Bi2WO6nanoflakes prepared at pH4showed excellent adsorption and photodegradationefficiency towards norfloxacin.The characterization results showed that Bi2WO6prepared at pH4had a larger specific area andfaster photo-generated carrier separation rate.The decay rate reached the maximum in weak alkaline reaction solution,which couldbe attributed to the presence of moderate OH-anions.The present study demonstrated that the smaller size of Bi2WO6could be anefficient photocatalyst on the degradation of norfloxacin in the aquatic environment.
基金supported by the Research Academies and Institutes Funds of the Ministry of Science and Technology of China (Ke-05021050)
文摘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/℃.
