CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly...CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons.Iron-molybdenum catalysts have found numerous applications in catalysis,but have been never evaluated in the CO_(2)hydrogenation.In this work,the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal(Li,Na,K,Rb,or Cs)were characterized using X-ray diffraction,hydrogen temperatureprogrammed reduction,CO_(2)temperature-programmed desorption,in-situ^(57)Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy.Their catalytic performance was evaluated in the CO_(2)hydrogenation.During the reaction conditions,the catalysts undergo the formation of an iron(Ⅱ)molybdate structure,accompanied by a partial reduction of molybdenum and carbidization of iron.The rate of CO_(2)conversion and product selectivity strongly depend on the promoting alkali metals,and electronegativity was identified as an important factor affecting the catalytic performance.Higher CO_(2)conversion rates were observed with the promoters having higher electronegativity,while low electronegativity of alkali metals favors higher light olefin selectivity.展开更多
In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. We investigated the influences of two inorganic corrosion inhibitors(ammoniu...In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. We investigated the influences of two inorganic corrosion inhibitors(ammonium dihydrogen phosphate and sodium molybdate) on the corrosion resistance of anodic oxidation films on 2024 aluminum alloy, and studied the synergistic effect of two corrosion inhibitors. The corrosion resistance of anodic oxidation film in 3.5 wt% NaCl solution was evaluated by electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization curves. Results show that, after adding the single ammonium dihydrogen phosphate or sodium molybdate of 0.01 M to oxalic acid electrolyte, inhibition efficiencies of the anodized samples are 10% and 47%, respectively. However, in the presence of two inhibitors with the same concentration of 0.01 M, inhibition efficiency can be as high as 92%. Therefore, we observed the significantly synergistic corrosion inhibition effect of molybdate and phosphate ions for anodic oxidation film formed on 2024 aluminum alloy.展开更多
The purpose of this work was to enhance the corrosion resistance of the passive fi lm on 304 stainless steel(SS)by chemical modifi cation in alkaline phosphate–molybdate solutions.The 304 SS was passivated in both ph...The purpose of this work was to enhance the corrosion resistance of the passive fi lm on 304 stainless steel(SS)by chemical modifi cation in alkaline phosphate–molybdate solutions.The 304 SS was passivated in both phosphate and phosphate–molybdate mixed solutions to investigate the eff ect of molybdate on its corrosion resistance.The experimental results indicated that the passive fi lm showed better corrosion resistance in Cl?-containing solutions after modifi cation in phosphate–molybdate solutions than in phosphate-only solutions.Energy-dispersive spectroscopy analyses revealed that the passive fi lm formed in phosphate–molybdate solutions contained Mo and P after modifi cation,which is the reason for the enhanced corrosion resistance.展开更多
This study was conducted to comprehensively evaluate the effects of salicylic acid and sodium molybdate on cold tolerance of an ornamental plant Bougainvillea glabra and to provide a theoretical guidance for landscape...This study was conducted to comprehensively evaluate the effects of salicylic acid and sodium molybdate on cold tolerance of an ornamental plant Bougainvillea glabra and to provide a theoretical guidance for landscape maintenance.B.glabra plants were treated with 0.5 mmol/L salicylic acid and 2.0 μmol/L alone or in combination,and then exposed to low temperature stress before physiological indices were measured.The results showed that all salicylic acid and sodium molybdate treatments reduced the relative conductivity and malondialdehyde( MDA) content of B.glabra to varying extents under the stress of low temperature,and more significant effect was achieved by using the two agents in combination.Oxygen free radicals production rate increased with decreasing temperature from 20 to 6 ℃,but declined with temperature decreasing from 3 to-3 ℃.The SOD activity of the control( CK) was significantly lower than that of other treatments at 0 and-3 ℃.The treatments with salicylic acid and sodium molybdate alone and in combination increased POD activity of B.glabra plants,especially at 0 ℃,as the POD activity of treatments T1,T2 and T3 was significantly higher than that of CK at 0 ℃.In addition,under low temperature stress,the contents of soluble sugar,starch and proline increased initially and decreased subsequently with temperature decreasing.The soluble sugar content at 3 ℃,starch and proline contents at 0 and-3 ℃ in treatments with salicylic acid and sodium molybdate alone and in combination were significantly higher than those of CK.All above results proved that salicylic acid and sodium molybdate are able to improve cold tolerance of B.glabra,and better effect can be achieved by using them together.展开更多
Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on st...Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe2(SO4)3 as iron precursor. In addition, as for Fe2(SO4)3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO3)3·9H2O due to the reduction in Fe2(MoO4)3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO3 and Fe2(MoO4) for FeCl3·6H2O and Fe2(SO4)3 as precursors. Iron molybdate catalyst prepared with Fe(NO3)3·9H2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.展开更多
Titanium alloys are extensively used in power, chemical and petroleum industries as constructional materials for vessels and heat transfer tubes. Moreover they are candidate materials for nuclear waste disposal. These...Titanium alloys are extensively used in power, chemical and petroleum industries as constructional materials for vessels and heat transfer tubes. Moreover they are candidate materials for nuclear waste disposal. These alloys have superior resistance to localized forms of corrosion compared to stainless steels and Ni-base alloys. However, this resistance is not as remarkable in crevice corrosion conditions in some aggressive media. Electrochemical corrosion tests were conducted on two ASTM Ti grades namely, Ti-2 and Ti-12 in extremely low pH acidic environment. Results indicated that Ti-2 has less resistance to both general and crevice corrosion attack than Ti-12. Both alloys possess better resistance to general corrosion than to crevice corrosion. Also, results showed that the molybdate addition improves remarkably the resistance of Ti-2 to both types of attack. The increase of molybdate ions concentration from 0.03 mol/L to 0.15 mol/L made Ti-2 to be as resistant as, or somewhat higher than, Ti-12. The elecrochemical findings were further supplemented by optical examination of the corroded surface.展开更多
Anabaena variabilis ATCC 29413 has two distinct nitrogenases that function in heterocysts, a conventional Mo-nitrogenase and an alternative V-nitrogenase. Synthesis of these two enzymes was repressed in cells growing ...Anabaena variabilis ATCC 29413 has two distinct nitrogenases that function in heterocysts, a conventional Mo-nitrogenase and an alternative V-nitrogenase. Synthesis of these two enzymes was repressed in cells growing with a source of fixed nitrogen, such as ammonium;however, the V-nitrogenase was also repressed by Mo. Expression of the V-nitrogenase which was not affected by V and expression of the Mo-nitrogenase was not affected by the presence or absence of either Mo or V. In the absence of both Mo and V in an environment lacking fixed nitrogen, cells became starved for both metals;however, low levels of nitrogen fixation and slow growth persisted. A mutant lacking the V-nitrogenase was still able to grow very slowly in Mo-and V-free medium;however, loss of the Mo-nitrogenase in a nifDK1 mutant abolished the residual growth, suggesting that only the Mo-nitrogenase functioned under these conditions to support slow growth. The addition of vanadate, molybdate, or tungstate, which is transported by the molybdate transporter, to cells starved for these metals resulted in an increase in nitrogenase activity within two hours after the addition of the metal and this increase required new protein synthesis. While tungstate functioned about as well as vanadate in supporting acetylene reduction, the cells were not able to grow any better with tungstate than with no added metal. A mutant lacking the V-nitrogenase showed no increase in nitrogenase activity upon addition of tungstate, suggesting that the V-nitrogenase was able to incorporate tungstate. Tungstate was able to substitute for molybdate in repressing transcription of a Mo-transport gene, but it did not repress transcription of the vnfH gene, which was repressed by Mo. The availability of Mo and V plays an important role in controlling whether the Mo-or the V-nitrogenase is used for nitrogen fixation.展开更多
A highly sensitive fourth derivative spectrophotometric method is presented for the residue analysis of ethylenebis dithiocarbamate fungicide Maneb. The fungicide maneb forms a blue complex with sodium molybdate on he...A highly sensitive fourth derivative spectrophotometric method is presented for the residue analysis of ethylenebis dithiocarbamate fungicide Maneb. The fungicide maneb forms a blue complex with sodium molybdate on heating which is studied spectrophotometrically. The method has been successfully applied to maneb determination in wheat grains and soft drinks with high recoveries. The analytical sensitivity of the present method has been found to be 0.0011 μg/mL.展开更多
Polyaniline stannic molybdate—an organic-inorganic composite material, was prepared via sol-gel mixing of organic polymer polyaniline into matrices of inorganic precipitate of stannicmolybdate. The composite material...Polyaniline stannic molybdate—an organic-inorganic composite material, was prepared via sol-gel mixing of organic polymer polyaniline into matrices of inorganic precipitate of stannicmolybdate. The composite material synthesized at pH 1.2 showed an ion exchange capacity 1.8 meq/g for Na+?ions. Ion exchange capacity, pH titration and distribution studies were carried out to determine the preliminary ion exchange properties of the material. The distribution studies showed the selectivity of Hg(II) ions by this material. The effect of temperature on the ion exchange capacity of the material at different temperatures had been studied. The sorption behavior of metal ions was also explored in different surfactant media.展开更多
Transition metal molybdate(RMoO4)has been extensively studied in optics,electricity and catalysis due to its low cost and multivalent Mo atoms,while its poor electrical conductivity limits its application in electroma...Transition metal molybdate(RMoO4)has been extensively studied in optics,electricity and catalysis due to its low cost and multivalent Mo atoms,while its poor electrical conductivity limits its application in electromagnetic wave absorption(EMA).Compounding molybdate with conductive materials is an effective way to improve its electrical conductivity.In this work,a homogeneous coating on the molybdate surface was achieved by utilizing a pyrrole oxidation polymerization mechanism,and then stabilized composites of Molybdate@Carbon(RMoO4@C)were obtained by high-temperature pyrolysis.The EMA properties of the nanocomposites were tuned by substituting the species of transition metal elements(RMoO_(4)@C,R=Fe,Co,Cu).Among them,Fe_(2)(MoO_(4))_(3)@C has a minimum reflection loss of−60.62 dB at an ultra-low thickness of 1.7 mm,and the effective absorption bandwidth(EAB)can reach 4.75 GHz at 3.00 mm.This work expands the range of applications for molybdate and provides a new material basis for building high-performance EMA materials.展开更多
Eu^(2+),Dy^(3+)and Zr_(4+)ions co-doped strontium aluminate(i.e.,SrAl_(2)O_(4):Eu^(2+),Dy^(3+),Zr_(4+))/molybdate(i.e.,Ho2MoO6or Nd2MoO6)with photo-/mechano-luminescence and allochroic effect as multi-optical function...Eu^(2+),Dy^(3+)and Zr_(4+)ions co-doped strontium aluminate(i.e.,SrAl_(2)O_(4):Eu^(2+),Dy^(3+),Zr_(4+))/molybdate(i.e.,Ho2MoO6or Nd2MoO6)with photo-/mechano-luminescence and allochroic effect as multi-optical functional hybrid pigments were prepared via solid state reactions and subsequent mixing.The phosphor and hybrid pigments were characterized by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray spectroscopy,ultraviolet-visible spectroscopy,L*a*b*color scale analysis,spectrophotometry and mechanoluminescent measurement.The results show that the optimum luminescent emission intensity of SrAl_(2)O_(4):Eu^(2+),Dy^(3+),Zr_(4+)phosphor can be obtained when 5 mol%Zr_(4+)ions is doped into the lattice.Under the excitation of 365 nm wavelength,the hybrid pigments prepared with the phosphor and molybdate at a mass ratio of 1:1 present a green broad band emission located at 460-650 nm due to 4f65d1→4f7transitions of Eu^(2+)ions.The hybrid pigments have the superior mechanoluminescent property and emit light after being exerted by mechanical stresses.Besides,the hybrid pigments also exhibit an allochroic effect under different illuminants.In addition,the anti-counterfeiting of the hybrid pigments as a promising application was also presented.展开更多
Since graphene-based materials have shown great potential in many fields,it is important to explore ultrafast and high-efficient methods to synthesize reduced graphene oxide(rGO) using inexpensive reducing agents unde...Since graphene-based materials have shown great potential in many fields,it is important to explore ultrafast and high-efficient methods to synthesize reduced graphene oxide(rGO) using inexpensive reducing agents under mild conditions.Here,we reported a novel method for the ultrafast chemical reduction of graphene oxide(GO) at room temperature using sodium borohydride(NaBH_(4)),sodium molybdate(Na_(2)MoO_(4)) and hydrochloric acid(HCl).The reduction was carried out within 2 min.A series of characterization results revealed that the obtained reduced graphene oxide has higher reduction degree than that synthesized by NaBH_(4) alone at high temperature.Moreover,rGO electrode based on the present reducing method exhibited a superior specific capacitance of 139.8 F/g at a current density of1 A/g,indicating that it can be used as electrode materials for supercapacitors.展开更多
The existence of many anions in wastewater reduces the removal efficiency of phosphate by adsorbents under realistic conditions.Facing this challenge,the study reports on an insistent and stable composite adsorbent of...The existence of many anions in wastewater reduces the removal efficiency of phosphate by adsorbents under realistic conditions.Facing this challenge,the study reports on an insistent and stable composite adsorbent of molybdate complexes Fe-(MoO_(x))embedded in a macroporous anion exchange resin(D-201).[Fe(MoO_(x))]-D-201 shows 93.7%adsorption capacity(28.3 mg/g)for phosphate even when the molar concentration of coexisting ions is 5 times higher than phosphate.The capacity of adsorbent is maintained more than 84.2%after five regeneration cycles to remove phosphate in the wastewater containing coexisting ions.The ability of highly selective removal of phosphate is maintained during the regeneration cycles explained by the change of the binding of molybdate clusters with phosphate,which is due to the different structures of molybdate clusters depending on various pH.In general,this work puts forward a new idea for the development of phosphorus removal adsorbents for the treatment of wastewater containing coexisting ions.展开更多
A mechanochemical method was employed to prepare modified iron molybdate catalysts with various metal salts as precursors.The physicochemical properties of the iron molybdate catalysts were characterized,and their per...A mechanochemical method was employed to prepare modified iron molybdate catalysts with various metal salts as precursors.The physicochemical properties of the iron molybdate catalysts were characterized,and their performances in catalyzing the reaction from methanol to formaldehyde(HCHO)were evaluated.Iron molybdate catalysts doped with Co(NO_(3))_(2)·6H_(2)Oand Al(NO_(3))_(3)·9H_(2)O resulted in high HCHO yields.Compared with a commercial catalyst,the HCHO yields in the reaction with the modified catalyst at an optimal Co/Mo molar ratio reached 97.37%.According to chemical state analysis,the formation of CoO and the efficient decrease in the MoO_(3)sublimation rate could be important factors enhancing the HCHO yield in reactions catalyzed with iron molybdate doped with different Co/Mo mole ratios.展开更多
Ar<sup>+</sup> ion bombardment induced reduction effect on Bi<sub>2</sub>O<sub>3</sub>, MoO<sub>3</sub> and Bi-Mo complex oxides, α-Bi<sub>2</sub>Mo<sub&...Ar<sup>+</sup> ion bombardment induced reduction effect on Bi<sub>2</sub>O<sub>3</sub>, MoO<sub>3</sub> and Bi-Mo complex oxides, α-Bi<sub>2</sub>Mo<sub>3</sub>O<sub>13</sub>, β-Bi<sub>2</sub>Mo<sub>2</sub>O<sub>9</sub>, and γ-Bi<sub>2</sub>MoO<sub>6</sub>, has been studied with XPS. The results show that, owing to the presence of the oxygen anion bridge in Bi（Ⅲ）-O（Ⅱ）-Mo（Ⅵ）, the reduction behavior of Bi（Ⅲ） and Mo（Ⅵ） metal ions in all the three complex oxides is contrary to that in the single oxides. While Mo（Ⅵ） in MoO<sub>3</sub> is reduced to Mo（Ⅵ） in UHV under Ar<sup>+</sup> ion bombardment, the valence state of Bi（Ⅲ） in Bi<sub>2</sub>O<sub>3</sub> is unchanged. However, Bi（Ⅲ） in the three complex oxides is reduced to Bi（0） without noticeable reduction of Mo（Ⅵ）. Nevertheless, the rates of Bi（Ⅲ） reduction are in correspondence with the difference in Bi/Mo atomic ratio and the crystallographic features of the three phases of bismuth molybdate are decreasing in the order of α-Bi<sub>2</sub>Mo<sub>3</sub>O<sub>12</sub>≥β-Bi<sub>2</sub>Mo<sub>2</sub>O<sub>9</sub>】γ-Bi<sub>2</sub>MoO<sub>6</sub>. A new O -species is observed on the bismuth molybdate surface reduced by Ar<sup>+</sup> ion bombardment.Wc discuss the above phenomena展开更多
基金financial support from European Union(Interreg FWVL V project PSYCHE)from the French National Research Agency(Multiprobe project,ANR-20-CE42-0007)。
文摘CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons.Iron-molybdenum catalysts have found numerous applications in catalysis,but have been never evaluated in the CO_(2)hydrogenation.In this work,the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal(Li,Na,K,Rb,or Cs)were characterized using X-ray diffraction,hydrogen temperatureprogrammed reduction,CO_(2)temperature-programmed desorption,in-situ^(57)Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy.Their catalytic performance was evaluated in the CO_(2)hydrogenation.During the reaction conditions,the catalysts undergo the formation of an iron(Ⅱ)molybdate structure,accompanied by a partial reduction of molybdenum and carbidization of iron.The rate of CO_(2)conversion and product selectivity strongly depend on the promoting alkali metals,and electronegativity was identified as an important factor affecting the catalytic performance.Higher CO_(2)conversion rates were observed with the promoters having higher electronegativity,while low electronegativity of alkali metals favors higher light olefin selectivity.
基金Funded by the General Program of Natural Science Foundation of Jiangsu Province of China(No.BK20171440)the Natural Science Foundation of Nanjing University of Posts and Telecommunications(NY218039)
文摘In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. We investigated the influences of two inorganic corrosion inhibitors(ammonium dihydrogen phosphate and sodium molybdate) on the corrosion resistance of anodic oxidation films on 2024 aluminum alloy, and studied the synergistic effect of two corrosion inhibitors. The corrosion resistance of anodic oxidation film in 3.5 wt% NaCl solution was evaluated by electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization curves. Results show that, after adding the single ammonium dihydrogen phosphate or sodium molybdate of 0.01 M to oxalic acid electrolyte, inhibition efficiencies of the anodized samples are 10% and 47%, respectively. However, in the presence of two inhibitors with the same concentration of 0.01 M, inhibition efficiency can be as high as 92%. Therefore, we observed the significantly synergistic corrosion inhibition effect of molybdate and phosphate ions for anodic oxidation film formed on 2024 aluminum alloy.
基金supported by the National Natural Science Foundation of China(No.51701140).
文摘The purpose of this work was to enhance the corrosion resistance of the passive fi lm on 304 stainless steel(SS)by chemical modifi cation in alkaline phosphate–molybdate solutions.The 304 SS was passivated in both phosphate and phosphate–molybdate mixed solutions to investigate the eff ect of molybdate on its corrosion resistance.The experimental results indicated that the passive fi lm showed better corrosion resistance in Cl?-containing solutions after modifi cation in phosphate–molybdate solutions than in phosphate-only solutions.Energy-dispersive spectroscopy analyses revealed that the passive fi lm formed in phosphate–molybdate solutions contained Mo and P after modifi cation,which is the reason for the enhanced corrosion resistance.
基金Supported by Applied Basic Research Project of Yunnan Province(2017FD087)National Natural Science Foundation of China(31660559)
文摘This study was conducted to comprehensively evaluate the effects of salicylic acid and sodium molybdate on cold tolerance of an ornamental plant Bougainvillea glabra and to provide a theoretical guidance for landscape maintenance.B.glabra plants were treated with 0.5 mmol/L salicylic acid and 2.0 μmol/L alone or in combination,and then exposed to low temperature stress before physiological indices were measured.The results showed that all salicylic acid and sodium molybdate treatments reduced the relative conductivity and malondialdehyde( MDA) content of B.glabra to varying extents under the stress of low temperature,and more significant effect was achieved by using the two agents in combination.Oxygen free radicals production rate increased with decreasing temperature from 20 to 6 ℃,but declined with temperature decreasing from 3 to-3 ℃.The SOD activity of the control( CK) was significantly lower than that of other treatments at 0 and-3 ℃.The treatments with salicylic acid and sodium molybdate alone and in combination increased POD activity of B.glabra plants,especially at 0 ℃,as the POD activity of treatments T1,T2 and T3 was significantly higher than that of CK at 0 ℃.In addition,under low temperature stress,the contents of soluble sugar,starch and proline increased initially and decreased subsequently with temperature decreasing.The soluble sugar content at 3 ℃,starch and proline contents at 0 and-3 ℃ in treatments with salicylic acid and sodium molybdate alone and in combination were significantly higher than those of CK.All above results proved that salicylic acid and sodium molybdate are able to improve cold tolerance of B.glabra,and better effect can be achieved by using them together.
基金supported by the Chang Jiang Scholars Programme of China, the Key research and development project of Xinjiang Uygur Autonomous Region (2017B02012)the Natural Science Foundation of Xinjiang University (BS62331)the Xinjiang Uygur Autonomous Region 100 Young Doctors Introduction Program。
文摘Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe2(SO4)3 as iron precursor. In addition, as for Fe2(SO4)3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO3)3·9H2O due to the reduction in Fe2(MoO4)3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO3 and Fe2(MoO4) for FeCl3·6H2O and Fe2(SO4)3 as precursors. Iron molybdate catalyst prepared with Fe(NO3)3·9H2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.
文摘Titanium alloys are extensively used in power, chemical and petroleum industries as constructional materials for vessels and heat transfer tubes. Moreover they are candidate materials for nuclear waste disposal. These alloys have superior resistance to localized forms of corrosion compared to stainless steels and Ni-base alloys. However, this resistance is not as remarkable in crevice corrosion conditions in some aggressive media. Electrochemical corrosion tests were conducted on two ASTM Ti grades namely, Ti-2 and Ti-12 in extremely low pH acidic environment. Results indicated that Ti-2 has less resistance to both general and crevice corrosion attack than Ti-12. Both alloys possess better resistance to general corrosion than to crevice corrosion. Also, results showed that the molybdate addition improves remarkably the resistance of Ti-2 to both types of attack. The increase of molybdate ions concentration from 0.03 mol/L to 0.15 mol/L made Ti-2 to be as resistant as, or somewhat higher than, Ti-12. The elecrochemical findings were further supplemented by optical examination of the corroded surface.
文摘Anabaena variabilis ATCC 29413 has two distinct nitrogenases that function in heterocysts, a conventional Mo-nitrogenase and an alternative V-nitrogenase. Synthesis of these two enzymes was repressed in cells growing with a source of fixed nitrogen, such as ammonium;however, the V-nitrogenase was also repressed by Mo. Expression of the V-nitrogenase which was not affected by V and expression of the Mo-nitrogenase was not affected by the presence or absence of either Mo or V. In the absence of both Mo and V in an environment lacking fixed nitrogen, cells became starved for both metals;however, low levels of nitrogen fixation and slow growth persisted. A mutant lacking the V-nitrogenase was still able to grow very slowly in Mo-and V-free medium;however, loss of the Mo-nitrogenase in a nifDK1 mutant abolished the residual growth, suggesting that only the Mo-nitrogenase functioned under these conditions to support slow growth. The addition of vanadate, molybdate, or tungstate, which is transported by the molybdate transporter, to cells starved for these metals resulted in an increase in nitrogenase activity within two hours after the addition of the metal and this increase required new protein synthesis. While tungstate functioned about as well as vanadate in supporting acetylene reduction, the cells were not able to grow any better with tungstate than with no added metal. A mutant lacking the V-nitrogenase showed no increase in nitrogenase activity upon addition of tungstate, suggesting that the V-nitrogenase was able to incorporate tungstate. Tungstate was able to substitute for molybdate in repressing transcription of a Mo-transport gene, but it did not repress transcription of the vnfH gene, which was repressed by Mo. The availability of Mo and V plays an important role in controlling whether the Mo-or the V-nitrogenase is used for nitrogen fixation.
文摘A highly sensitive fourth derivative spectrophotometric method is presented for the residue analysis of ethylenebis dithiocarbamate fungicide Maneb. The fungicide maneb forms a blue complex with sodium molybdate on heating which is studied spectrophotometrically. The method has been successfully applied to maneb determination in wheat grains and soft drinks with high recoveries. The analytical sensitivity of the present method has been found to be 0.0011 μg/mL.
文摘Polyaniline stannic molybdate—an organic-inorganic composite material, was prepared via sol-gel mixing of organic polymer polyaniline into matrices of inorganic precipitate of stannicmolybdate. The composite material synthesized at pH 1.2 showed an ion exchange capacity 1.8 meq/g for Na+?ions. Ion exchange capacity, pH titration and distribution studies were carried out to determine the preliminary ion exchange properties of the material. The distribution studies showed the selectivity of Hg(II) ions by this material. The effect of temperature on the ion exchange capacity of the material at different temperatures had been studied. The sorption behavior of metal ions was also explored in different surfactant media.
基金the National Natural Science Foundation of China(No.52273267)the Fundamental Research Funds for the Central Universities(No.30920041102)。
文摘Transition metal molybdate(RMoO4)has been extensively studied in optics,electricity and catalysis due to its low cost and multivalent Mo atoms,while its poor electrical conductivity limits its application in electromagnetic wave absorption(EMA).Compounding molybdate with conductive materials is an effective way to improve its electrical conductivity.In this work,a homogeneous coating on the molybdate surface was achieved by utilizing a pyrrole oxidation polymerization mechanism,and then stabilized composites of Molybdate@Carbon(RMoO4@C)were obtained by high-temperature pyrolysis.The EMA properties of the nanocomposites were tuned by substituting the species of transition metal elements(RMoO_(4)@C,R=Fe,Co,Cu).Among them,Fe_(2)(MoO_(4))_(3)@C has a minimum reflection loss of−60.62 dB at an ultra-low thickness of 1.7 mm,and the effective absorption bandwidth(EAB)can reach 4.75 GHz at 3.00 mm.This work expands the range of applications for molybdate and provides a new material basis for building high-performance EMA materials.
基金supported by the National Natural Science Foundation of China(52072125)the Foshan Science and Technology Innovation Project,China(FSOAA-KJ419-4401-009)the Major Scientific and Technological Projects of Foshan,China(2016AG101415)。
文摘Eu^(2+),Dy^(3+)and Zr_(4+)ions co-doped strontium aluminate(i.e.,SrAl_(2)O_(4):Eu^(2+),Dy^(3+),Zr_(4+))/molybdate(i.e.,Ho2MoO6or Nd2MoO6)with photo-/mechano-luminescence and allochroic effect as multi-optical functional hybrid pigments were prepared via solid state reactions and subsequent mixing.The phosphor and hybrid pigments were characterized by X-ray diffraction,scanning electron microscopy with energy dispersive X-ray spectroscopy,ultraviolet-visible spectroscopy,L*a*b*color scale analysis,spectrophotometry and mechanoluminescent measurement.The results show that the optimum luminescent emission intensity of SrAl_(2)O_(4):Eu^(2+),Dy^(3+),Zr_(4+)phosphor can be obtained when 5 mol%Zr_(4+)ions is doped into the lattice.Under the excitation of 365 nm wavelength,the hybrid pigments prepared with the phosphor and molybdate at a mass ratio of 1:1 present a green broad band emission located at 460-650 nm due to 4f65d1→4f7transitions of Eu^(2+)ions.The hybrid pigments have the superior mechanoluminescent property and emit light after being exerted by mechanical stresses.Besides,the hybrid pigments also exhibit an allochroic effect under different illuminants.In addition,the anti-counterfeiting of the hybrid pigments as a promising application was also presented.
文摘Since graphene-based materials have shown great potential in many fields,it is important to explore ultrafast and high-efficient methods to synthesize reduced graphene oxide(rGO) using inexpensive reducing agents under mild conditions.Here,we reported a novel method for the ultrafast chemical reduction of graphene oxide(GO) at room temperature using sodium borohydride(NaBH_(4)),sodium molybdate(Na_(2)MoO_(4)) and hydrochloric acid(HCl).The reduction was carried out within 2 min.A series of characterization results revealed that the obtained reduced graphene oxide has higher reduction degree than that synthesized by NaBH_(4) alone at high temperature.Moreover,rGO electrode based on the present reducing method exhibited a superior specific capacitance of 139.8 F/g at a current density of1 A/g,indicating that it can be used as electrode materials for supercapacitors.
基金supported by the National Natural Science Foundation of China(Nos.52070100,51978341)the Natural Science Foundation of Jiangsu Province of China(No.BK20190087).
文摘The existence of many anions in wastewater reduces the removal efficiency of phosphate by adsorbents under realistic conditions.Facing this challenge,the study reports on an insistent and stable composite adsorbent of molybdate complexes Fe-(MoO_(x))embedded in a macroporous anion exchange resin(D-201).[Fe(MoO_(x))]-D-201 shows 93.7%adsorption capacity(28.3 mg/g)for phosphate even when the molar concentration of coexisting ions is 5 times higher than phosphate.The capacity of adsorbent is maintained more than 84.2%after five regeneration cycles to remove phosphate in the wastewater containing coexisting ions.The ability of highly selective removal of phosphate is maintained during the regeneration cycles explained by the change of the binding of molybdate clusters with phosphate,which is due to the different structures of molybdate clusters depending on various pH.In general,this work puts forward a new idea for the development of phosphorus removal adsorbents for the treatment of wastewater containing coexisting ions.
基金the Natural Science Foundation Project of Xinjiang Uygur Autonomous(Grant No.2019D01C084)for financial support.
文摘A mechanochemical method was employed to prepare modified iron molybdate catalysts with various metal salts as precursors.The physicochemical properties of the iron molybdate catalysts were characterized,and their performances in catalyzing the reaction from methanol to formaldehyde(HCHO)were evaluated.Iron molybdate catalysts doped with Co(NO_(3))_(2)·6H_(2)Oand Al(NO_(3))_(3)·9H_(2)O resulted in high HCHO yields.Compared with a commercial catalyst,the HCHO yields in the reaction with the modified catalyst at an optimal Co/Mo molar ratio reached 97.37%.According to chemical state analysis,the formation of CoO and the efficient decrease in the MoO_(3)sublimation rate could be important factors enhancing the HCHO yield in reactions catalyzed with iron molybdate doped with different Co/Mo mole ratios.
基金Project supported by the National Natural Science Foundation of China
文摘Ar<sup>+</sup> ion bombardment induced reduction effect on Bi<sub>2</sub>O<sub>3</sub>, MoO<sub>3</sub> and Bi-Mo complex oxides, α-Bi<sub>2</sub>Mo<sub>3</sub>O<sub>13</sub>, β-Bi<sub>2</sub>Mo<sub>2</sub>O<sub>9</sub>, and γ-Bi<sub>2</sub>MoO<sub>6</sub>, has been studied with XPS. The results show that, owing to the presence of the oxygen anion bridge in Bi（Ⅲ）-O（Ⅱ）-Mo（Ⅵ）, the reduction behavior of Bi（Ⅲ） and Mo（Ⅵ） metal ions in all the three complex oxides is contrary to that in the single oxides. While Mo（Ⅵ） in MoO<sub>3</sub> is reduced to Mo（Ⅵ） in UHV under Ar<sup>+</sup> ion bombardment, the valence state of Bi（Ⅲ） in Bi<sub>2</sub>O<sub>3</sub> is unchanged. However, Bi（Ⅲ） in the three complex oxides is reduced to Bi（0） without noticeable reduction of Mo（Ⅵ）. Nevertheless, the rates of Bi（Ⅲ） reduction are in correspondence with the difference in Bi/Mo atomic ratio and the crystallographic features of the three phases of bismuth molybdate are decreasing in the order of α-Bi<sub>2</sub>Mo<sub>3</sub>O<sub>12</sub>≥β-Bi<sub>2</sub>Mo<sub>2</sub>O<sub>9</sub>】γ-Bi<sub>2</sub>MoO<sub>6</sub>. A new O -species is observed on the bismuth molybdate surface reduced by Ar<sup>+</sup> ion bombardment.Wc discuss the above phenomena
