Molybdate Ions Research Articles

The influence of microwave irradiation on stereospecific Mo(VI)-catalyzed transformation of deoxysugars

The stereospecific mutual isomerization of 5-, 6-, and 7-deoxysugars in a microwave field with Mo(VI) as a catalyst is reported. The reaction cycle allows the use of catalytic amounts of molybdate ions to form highly reactive catalytically active dimolybdate complexes that create conditions for stereospecific intramolecular rearrangement. The microwave-enhanced Mo(VI)-catalyzed transformation of deoxyaldoses occurred with full stereospecificity resulting in the formation of the corresponding epi-deoxyaldoses in very good yields. The microwave field has a substantial effect on the transformation studied.

Investigation of the effect of CrO 42− and MoO 42− on carbon steel corrosion using AFM and electrochemical techniques

The effect of chromate () and molybdate () ions on the corrosion of carbon steel in 0.5 M NaCl solution has been studied using electrochemical measurements and atomic force microscopy (AFM) technique. Potentiodynamic polarization data suggest that both and have inhibition effect on carbon steel corrosion, and the inhibition efficiency increases with increase in concentrations of and ; at the same concentration, the inhibition efficiency of is higher than that of . The increase in concentrations of and anions causes a shift of the breakdown potential (Eb) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. At the same concentrations, the breakdown potential of is higher than that of . Electrochemical impedance spectroscopy (EIS) tests reveal that the charge transfer resistance and passive film resistance increase with increase in concentrations of or ; at the same concentrations, as for the charge transfer resistance and passive film resistance were bigger than those of . AFM imaging technique shows that local corrosion was inhibited obviously after the addtion of or , and passive film of was much more compact than that of . AFM force–distance curves indicate that the passive film of is much stiffer than that of .

Laser-Heating Thermal Modulation Voltammetric Determination of Phosphate Ion Using a Graphite-Reinforced Carbon Electrode

Thermal modulation (TM) voltammetry was successfully applied to the determination of phosphate ion in natural water, by using a He-Cd dual laser as a heating source and a graphite-reinforced carbon (GRC) electrode. A heteropoly ion, i.e., 12-molybdophosphate ion ([PMo(VI)(12)O(40)](3-)), was formed through a reaction between a phosphate ion and molybdate ions in an acidic solution, and its electroreduction was examined in a flow electrolytic cell by TM voltammetry. Measured TM voltammograms showed two peaks corresponding to two successive two-electron reductions of the 12-molybdophosphate ion, and the peak intensities were proportional to the concentration of the phosphate ion. Because of the strong adsorption of 12-molybdophosphate ion onto the GRC electrode, a detection limit as low as 0.8 nmol dm(-3) (S/N = 3) was achieved. The determination of phosphate ion in real samples (river water) was carried out by spectrophotometry (the molybdenum-blue method) and TM voltammetry, and the determination values obtained by both methods were in a good agreement with each other. These results prove the possibility of TM voltammetry as an electroanalytical method.

Effect of Molybdate, Nitrite and Zinc Ions on the Corrosion Inhibition of Mild Steel in Aqueous Chloride Media Containing Cupric Ions

An investigation has been conducted on the corrosion inhibition of mild steel by molybdate, nitrite and zinc ions in aqueous chloride media containing cupric ions. Molybdate inhibits mild steel corrosion in near neutral and alkaline (pH 6 and above) chloride media and accelerates corrosion in acidic media (below pH 6) both in the presence and absence of cupric ions. Nitrite inhibits mild steel corrosion in chloride media at pH 4.5 and above, but accelerates corrosion below pH 4.5 both in the presence and absence of cupric ions. Molybdate and nitrite act as a synergistic corrosion inhibitor in chloride media with or without cupric ions at pH 4.5 and above. In the acidic region between pH 3 and 4.5, the combination can decrease corrosion with a low concentration of molybdate and high concentration of nitrite. These concentrations depend on the relative amounts of molybdate and nitrite present in the system. Zinc ions inhibit mild steel corrosion only in acidic chloride media. Based on the experimental results, mechanisms of action of molybdate, nitrite and zinc ions on mild steel corrosion in aqueous chloride media with or without cupric ions have been proposed.Keywords: Molybdate; Nitrite; Mild steel; Corrosion rate; Synergistic corrosion inhibitor.© 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.DOI: 10.3329/jsr.v1i1.1053

Kinetics of induced electrodeposition of alloys containing Mo from citrate solutions

AbstractThe kinetics of Ni‐Mo alloy electrodeposition from complex citrate‐sulphate baths has been investigated by means of steady‐state polarization measurements in a system with a rotating disk electrode (RDE). The partial current densities for deposition of Ni and Mo as a function of the solution composition, the cathode potentials and the rate of mass transport were determined. Strong interaction between the discharging metal ions occur: nickel induces molybdenum deposition, but its discharge is markedly inhibited by molybdenum. This effect, related to the formation of intermediate molybdenum oxides, becomes less pronounced when the rotation speed was increased. Hydrogen evolution is associated with molybdenum deposition. An increase of the molybdate ions concentration in the bath, as well as an increase in the rate of mass transport lead to an increase in Mo content in deposits and to the reduction of current efficiency. The surface morphology as a function of the content of molybdenum in the alloy were also investigated. Crack‐free, compact, semi‐bright Ni‐Mo coatings, containing up to about 40 wt% of Mo, characterized by good adhesion to steel substrate were obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A decontamination system for chemical weapons agents using a liquid solution on a solid sorbent

A decontamination system for chemical warfare agents was developed and tested that combines a liquid decontamination reagent solution with solid sorbent particles. The components have fewer safety and environmental concerns than traditional chlorine bleach-based products or highly caustic solutions. The liquid solution, based on Decon Green™, has hydrogen peroxide and a carbonate buffer as active ingredients. The best solid sorbents were found to be a copolymer of ethylene glycol dimethacrylate and n-lauryl methacrylate (Polytrap 6603 Adsorber); or an allyl methacrylate cross-linked polymer (Poly-Pore E200 Adsorber). These solids are human and environmentally friendly and are commonly used in cosmetics. The decontaminant system was tested for reactivity with pinacolyl methylphosphonofluoridate (Soman, GD), bis(2-chloroethyl)sulfide (Mustard, HD), and S-(2-diisopropylaminoethyl) O-ethyl methylphosphonothioate (VX) by using NMR Spectroscopy. Molybdate ion (MoO 4 −2) was added to the decontaminant to catalyze the oxidation of HD. The molybdate ion provided a color change from pink to white when the oxidizing capacity of the system was exhausted. The decontaminant was effective for ratios of agent to decontaminant of up to 1:50 for VX ( t 1/2 ≤ 4 min), 1:10 for HD ( t 1/2 < 2 min with molybdate), and 1:10 for GD ( t 1/2 < 2 min). The vapor concentrations of GD above the dry sorbent and the sorbent with decontamination solution were measured to show that the sorbent decreased the vapor concentration of GD. The E200 sorbent had the additional advantage of absorbing aqueous decontamination solution without the addition of an organic co-solvent such as isopropanol, but the rate depended strongly on mixing for HD.

Removal of nuisance aqueous anions with Ferrilig

The present study describes an improved synthesis of Ferrilig, an iron(III) salt of a commercially available immobilized ligand, IMLIG, called Octolig®. The resulting composite, called “Ferrilig” was used to remove arsenate, chromate, molybdate, and selenite ions from aqueous solutions by means of column chromatography. The synthesis of Ferrilig was accomplished by treating an aqueous suspension of Octolig®-21 with an equal weight of ferrous sulfate heptahydrate under nitrogen. The ferrous salt was then collected by sieving and allowed to oxidize to the iron (III) salt by exposure to air; treatment with dilute sodium hydroxide converted the composite to the hydroxide. Using 300 ppb As (as Na2HAsO4·7H2O) and column chromatography, the arsenic concentration in the effluent was less than the detection limit (< 2 ppb). Chromium as sodium chromate, molybdenum as (NH4)6 Mo7O24·4H2O, and selenium as Na2Se03, were removed with fair success. The elements, their initial concentrations and their percentage removal (parenthetically) were: As (280 ppb, 99%), Cr (50.6 ppm, 95.5%), Mo (50.7 ppm, 94.6%), Se (258 ppm, 99.9%).

Interaction of arsenite ions with molybdate in aqueous solution

Interaction of arsenite ions with molybdate ions in aqueous HClO4 at pH of 3–5 were studied using spectrophotometry. A heteropoly anion (HPA) with the AsMo4 stoichiometry was revealed. Elemental analysis, X-ray photoelectron spectroscopy, and IR spectroscopy were used to characterize the composition and structure of the cesium salt of As(III)-Mo(VI) HPA precipitated from solution. The comparison of the IR spectra of cesium salts of the synthesized HPA and dimethylarsenite HPA (CH3)2AsMo4O15H2−, whose structure is known, implies that AsMo4O153− has a similar structure, where the AsO2− group is linked by four connected molybdenum octahedra (Mo4O12)O2−.

Composition and structure of cobalt-molybdenum-boron alloys produced by chemical catalytic reduction with dimethylamine borane

The co-reduction of cobalt and molybdate ions with dimethylamine borane in pyrophosphate solutions is shown to produce Co-Mo-B alloy coatings. Molybdate is reduced concurrently with cobalt to metal forming a solid solution in cobalt matrix with a hexagonal lattice. The alloy deposits have a pronounced [001] texture with the easy magnetization direction normal to the coating surface. The composition of alloys is heterogeneous in their thickness. The alloys contain cobalt and molybdenum hydroxide admixtures, as well as intermediate products of molybdenum reduction, in the superficial layers.

A possible capture of molybdenum during early diagenesis of dysoxic sediments

Abstract Molybdenum is a trace metal commonly used as a marker of paleoredox conditions of ancient depositional settings. Pyrite is an important molybdenum (Mo) host for enriched sedimentary rocks. In this paper we study the relationship between Mo and pyrite in the Bancs Jumeaux Formation, a Jurassic succession in northern France consisting of limestone and pyrite-rich marls. This formation is relatively enriched in Mo compared to other redox-sensitive trace metals. Our approach is grounded on bulk rock chemical analysis and delineation of two contrasting types of pyrite that can be extracted from the rocks: polyframboids and nonframboidal concretionary masses. The morphological characteristics of both morphotypes were studied using scanning electronic microscopy. The polyframboids are richer in Mo than the concretions but are not markedly enriched in other trace metals. This discrepancy in geochemical composition could result from pyrite precipitation at different times during early diagenesis. Our results tend to indicate that the polyframboids would have formed very early in reducing “microniches”, within dominantly dysoxic sediment. This early pyrite precipitation occurred at shallow depth below the sediment-water interface close to the abundant Mo source in overlying oxic seawater (molybdate ions), and would have fostered Mo-capture by the polyframboids in relatively large amounts. The concretions would have formed later during early diagenesis (within the sulfidic zone) under conditions of more limited Mo availability.

Structural characteristics and catalytic activities of nanocrystalline Ni-Mo-B coatings obtained by catalytic electroless reduction

The structures, chemical states of elements, and catalytic activities of Ni-Mo-B alloys with different molybdenum contents, which were obtained by catalytic electroless reduction of metal ions, were studied. The rates of the partial reactions (heterogeneous hydrolysis of dimethylamine borane, reduction of nickel ions, and evolution of molecular hydrogen) were found to make a bell-shaped curve when plotted versus the concentration of molybdate ions in solution.

Evolution of corrosion protection for sol–gel coatings doped with inorganic inhibitors

One the way to improve the self-repair properties of sol–gel films on aluminium alloy is the addition of corrosion inhibitors which could be released from the coating, minimising the corrosion of the unprotected area. Environmentally friendly corrosion inhibitors are studied (chromium III, molybdate, permanganate and cerium III) and compared to the standard corrosion inhibitor, i.e. hexavalent chromium. Corrosion performances are studied by polarisation resistance (Rp) in chloride medium. Evolution of composition of sol–gel coatings, during the corrosion test, is examined by GDOES (glow discharge optical emission spectroscopy). The results show that the morphology of sol–gel and the solubility of the additive play a role in the effectiveness of corrosion protection for a long term. Additives such as molybdate and permanganate ions decrease the sol–gel network stability and are too soluble (they are rapidly lost from the sol–gel films, in an aggressive medium), decreasing the power to prevent corrosion. Incorporation of Ce III is not efficient for a long time due to its high solubility. Sol–gel films containing Cr VI and Cr III provide adequate corrosion protection, due to the sol–gel stability and their low solubility.

Inhibitory effect of tungstate, molybdate and nitrite ions on the carbon steel pitting corrosion in alkaline formation water containing Cl − ion

The pitting corrosion of carbon steel in carbonate-formation water solution in the presence of chloride ions and the effect of addition WO 4 2−, MoO 4 2− and NO 2 − anions on the pitting corrosion were studied using cyclic voltammetry and potentiostatic current–time measurements and complemented by scan electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) investigations. Cyclic voltammograms of carbon steel in the presence of chloride ions in carbonate-formation water solution show one anodic peak, corresponding to the formation green rust carbonate and the two cathodic peaks. As the addition of Cl − ions concentration increases, the anodic peak current density increases and pitting potential E pit shifts to more negative potential. It is shown that the rate of pit initiation ( t i − 1 ) decreases and the pitting potential E pit moves to more positive direction upon the addition of inorganic anions. It was found that pitting inhibition of carbon steel increases in the sequence: (WO 4) 2− > (MoO 4) 2− > (NO 2) −.

Microwave assisted stereospecific synthesis of d- erythro- l- gluco-nonulose

A convenient, highly efficient synthesis of d- erythro- l- gluco-nonulose from a new 2- C-(hydroxymethyl) branched-chain aldose is presented. The nucleophilic addition of the appropriately protected aldose to formaldehyde afforded 2- C-(hydroxymethyl)- d- erythro- l- manno-octose. The branched sugar bearing a CH 2OH group at C-2 provides access to a nine-carbon sugar in a single step through a stereospecific isomerization. The isomerization exploited the catalytic effect of molybdate ions and microwave irradiation. The structure of the product was analyzed by NMR spectra and quantum-chemical DFT calculations. DFT-computed proton–proton coupling constants were found to be comparable with the experimentally obtained coupling constants and agreed with the pyranose form of this branched-chain aldose.

Ni–Mo alloying of nickel surface by alternating pulsed electrolysis using molybdenum(VI) baths

Electrochemical Ni–Mo alloying of the surface of a nickel substrate was investigated using alternating pulsed electrolysis in an aqueous solution containing only molybdate ions (MoO 4 2−) as a metal ion component. In this electrochemical process, the nickel substrate was slightly dissolved during the anodic pulses, providing nickel ions into the solution in the vicinity of the substrate, while Ni and Mo were both electrodeposited on the substrate surface during the subsequent cathodic pulses. Through the optimization of anodic and cathodic conditions independently based on a set of direct-current electrolysis data, amorphous Ni–Mo alloy layers were found to be formed at the surface of the nickel substrate by the alternating pulsed electrolysis using the MoO 4 2− solution of pH 3.0–5.0. The conditions for Ni–Mo alloy formation were discussed in terms of the dissolving regime of ionic species in the electrolytes determined by an equilibrium calculation.

Micellar effect on the sensitivity of spectrophotometric Mo(VI) determination based on the formation of gallic acid complex providing evidence for the polyoxoanion structure of molybdate ions

In this study effects of anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and nonionic (Triton X-100, TX100) micelles on the sensitivity of spectrophotometric molybdenum(VI) (Mo) determination based on the formation of a binary complex with gallic acid (GA) were investigated. Micellar CTAB was found to enhance the formation of Mo–GA complex. SDS micelles exerted an inhibitory effect while TX100 micelles had no effect on the complex formation. By the optimization of experimental conditions, the determination limit of the method suggested in the literature was lowered from 5.2 × 10 −5 to 4.6 × 10 −6 and to 5.7 × 10 −7 M, in the absence and presence of CTAB, respectively. The mechanism of the effect of CTAB was investigated by spectrophotometric titrations and it was concluded that CTAB did not form a ternary complex with Mo and GA. The stoichiometry of the complex, deduced from the results of spectrophotometric titrations, provided evidence for the formation of para-Mo 7O 4 6− polyanions at pH 4.5, indicating to the formation of a charge transfer complex between these ions and GA in micellar medium.

Kinetics of isotopic exchange between calcium molybdate and molybdate ions in aqueous solution

The heterogeneous isotopic anion exchange kinetics and equilibria between calcium molybdate and sodium molybdate solutions have been studied by using 99Mo as tracer in batch experiments. The values of exchange ratio lower than unity suggest that rate-limiting step is particle diffusion process and the effect of re-crystallization can be neglected. The self-diffusion coefficients calculated using both Paterson´s and Nernst–Plank approximations are increased by the temperature. The observed values for isotope exchange characteristics such as exchange fractions, exchanging amounts and fractional attainment of equilibrium are consistent with those of their calculated values. Activation energy and thermodynamic parameters calculated based on transition state theory indicate the existence of both energy and entropy barrier in the system.

PVC membrane electrode based on triheptyl dodecyl ammonium iodide for the selective determination of molybdate(VI)

Novel polyvinyl chloride (PVC) membrane electrodes based on triheptyl dodecyl ammonium iodide have been developed. In the presence of 12.5 m M H 2O 2, these electrodes are capable of determining molybdate(VI) ion. The electrodes exhibit near-Nernstian responses over a wide concentration range (2.0 × 10 −6 to 5.0 × 10 −3 M). The proposed electrodes demonstrate satisfying selectivity for molybdate(VI) ion in the presence of a wide variety of anions other than iodide, and can be used in the pH range 5.0–7.0. Moreover, the electrodes show an average response time of 2–3 min and can be used over a period of 2 months without any significant deviation being observed. In the light of our results, the response mechanism of the electrode is discussed and HMoO 2(O 2) 2 − is suggested as the response ion. The proposed electrode has been used to measure molybdenum in ore samples, and the results were in agreement with those obtained by means of ICP analysis.

Sodium molybdate—a possible alternate additive for sodium dichromate in the electrolytic production of sodium chlorate

Sodium dichromate is commonly used in sodium chlorate production to maintain high current efficiency; however, it is also a well documented carcinogen. To reduce the environmental impact, identification of a suitable alternative with similar buffering characteristics to dichromate and without adverse effect on the electrolytic performance of sodium chlorate production is important; sodium molybdate is a good candidate. Molybdate ion and its conjugated acid work as a buffer pair at pH 5–6, a lower and slightly narrower pH window than the typical buffer region of dichromate. Nonetheless, the molybdate buffer works effectively during the electrolytic process by maintaining pH at 5.9. Although the use of molybdate buffer will lower the overpotential of hydrogen evolution reaction (HER) by 100 mV, the average off-gas oxygen content is noticeably compromised at 3.6–4.6%, measured using a pilot cell operated at 3 kA m−2and 80 °C during a 3-day trial. The resulting current efficiency of 91 92% is significantly lower than when dichromate is employed as the process additive (> 96%). Mixtures of different dichromate and molybdate ratio were also investigated in terms of the resulting cathode surface potential.

Polypyrrole Coating on Zinc for Corrosion Prevention of Zinc-coated Steels

The polypyrrole (PPy) coating was prepared by constant current oxidation on zinc from aqueous solution of sodium tartrate containing sodium molybdate and pyrrole monomer to make new coating for corrosion prevention of zinc-coated steels.The coating is started with an initial formation of salt layer of zinc tartrate and/nor zinc molybdate during the oxidation. Nucleation and growth of PPy take place on the salt layer in the second stage. The PPy layer thus formed is doped by tartrate ions and/nor molybdate ions, which was confirmed by a depth profile measurement of glow discharge optical emission spectroscopy (GD-OES). The conductance of the coatings was as small as 1×10−3 S cm−2 for the 5 μm-thick layer probably due to the formation of the salt layer underneath the PPy layer. Corrosion test of the PPy-coated zinc electrode in 3.5 wt% NaCl solution showed that the zinc electrode was passivated and protected over 48 h by action of the oxidative PPy coating doped by tartrate and molybdate ions.