Reduction Of Molybdate Research Articles

Bioreduction potential of Providencia sp. and microbial consortium for hexavalent molybdenum: Isolation, identification, characterization, and optimization by response surface methodology

Molybdenum, a heavy metal with industrial applications, poses global toxicity concerns at concentrations exceeding 0.07 mg/L. This study aimed to isolate, characterize and optimize the molybdenum (Mo) reduction potential of bacterial strain and a mixed consortia. We used low phosphate media (LPM) for the isolation and optimization, employing one-factor-at-a-time (OFAT) and Response Surface Methodology (RSM) approaches. Molecular identification based on 16S ribosomal RNA sequencing of the Mo-reducing bacterial isolate revealed Providencia sp. Optimization via OFAT showed that this isolate effectively reduced 60 mM molybdate with optimal conditions of 2 mM phosphate and 10 mM fructose. The mixed consortium achieved remarkable reduction of molybdate at concentration up to 100 mM, the highest reported concentration to date. The RSM optimization of Providencia sp. revealed that the best reduction was supported by a pH of 6.50 and 60 mM molybdate. However, RSM was not successful with the consortium using the Plackett-Burman Design, suggesting that alternative designs should be explored for future optimization. This study advances understanding of Mo-reduction and highlights significant achievements in handling high molybdate concentrations.

Formation of one-dimensional hierarchical MoO2@C–Ni/CoNi hybrids as highly efficient catalysts and protein adsorbents

We have developed a facile approach to produce a hierarchical carbon tubular structure with Ni/NiCo NPs intercalated with MoO2 NPs, which manifested excellent performance in protein adsorption and the reduction of 4-nitrophenol.

Isolation and Characterization of a Molybdenum-reducing and the Congo Red Dye-decolorizing Pseudomonas putida strain Neni-3 in soils from West Sumatera, Indonesia

The elimination of heavy metals and organic contaminants, such as phenols, hydrocarbons, and amides, by bioremediation, is the most effective choice for the foreseeable future. This is especially true at low levels, where other methods, such as physical or chemical methods, may not be successful. Each year, a few million tons of these contaminants are emitted. In this study, we examined the ability of a molybdenum-reducing bacteria that were isolated from polluted soil to decolorize azo dyes independently of its ability to reduce molybdenum. The ideal conditions for the bacterium to convert molybdate to molybdate blue are a pH range of 6.0 to 6.5 and a temperature range of 25 to 37 degrees Celsius. After glucose, fructose and galactose were the most effective donors of electrons to enable the reduction of molybdate. Galactose was the least effective supplier of electrons. There are a few other prerequisites that need to be met as well, such as a phosphate concentration of between 2.5 and 7.5 mM and a molybdate concentration of between 10 and 15 mM. Its absorption spectra were identical to that of the phosphomolybdate reduction process and to that of the earlier Mo-reducing bacterium. At a concentration of 2 ppm, the heavy metals Ag (I), Hg (II), and Cu (II) each inhibited the reduction of molybdenum by a per centage of 62.8, 61.1, and 36.8 per cent, respectively. We put the bacterium through a test to see if it can remove the color from a variety of dyes. The Congo Red dye was able to lose its color when exposed to the bacterium. Based on the results of the biochemical study, the bacterium has been provisionally identified as Pseudomonas putida strain Neni-3. This bacteria's ability to detoxify various toxicants is a desirable quality, as it makes the bacterium an efficient bioremediation approach. As a result, this bacterium is in high demand. Purification of the molybdenum-reducing enzyme that was produced by this bacterium is presently being studied in order to characterize decolorization research in a more accurate manner.

Synthesis and Characterization of Molybdenum Oxide Nanoparticles by Green Method Useful in Antifungal Applications Against Colletotrichum Gloeosporioides

In the present study, the synthesis of molybdenum oxide nanoparticles is done by the reduction of Ammonium molybdate with the extract from the leaves of Citrus sinensis. The optical studies like Fourier Transform Infrared studies and UV-vis-NIR gives insight on the details of presence of functional groups and absorption of light. The X ray diffraction studies reveal its crystallinity and its particle size have been calculated. The zeta potential, which is used to characterize the metal nanoparticles, has been studied. The antifungal property of the nanoparticles has been studied and a plot for disease index has been discussed. This natural method of synthesizing the molybdenum oxide nanoparticles can find numerous applications in biophysics.

Facile and Reproducible Electrochemical Synthesis of the Giant Polyoxomolybdates.

Giant polyoxomolybdates are traditionally synthesized by chemical reduction of molybdate in aqueous solutions, generating complex nanostructures such as the highly symmetrical spherical {Mo102} and {Mo132}, ring-shaped {Mo154} and {Mo176}, and the gigantic protein sized {Mo368}, which combines both positive and negative curvature. These complex polyoxometalates are known to be highly sensitive to reaction conditions and are often difficult to reproduce, especially {Mo368}, which is often produced in yields far below 1%, meaning further investigation has always been limited. While the electrochemical properties of these materials have been studied, their electrochemical synthesis has not been explored. Herein, we demonstrate an alternative reliable synthetic method by means of electrochemistry. By using electrochemical synthesis, we have shown the synthesis of various reported polyoxomolybdates, along with some unreported structures with unique features that have yet to be reported by traditional synthetic methods. The six different giant polyoxomolybdates that were obtained via electrochemical synthesis range from the spherical {Mo102-xFex} and {Mo132} to the ring-shaped {Mo148} and {Mo154-x}, as well as the largest known polyoxometalate {Mo368}, with improved yield (up to 26.1% for {Mo368}), increased reproducibility, and shorter crystallization time compared to chemical reduction methods.

Molybdenum-Tungsten Blue Nanoparticles as a Precursor for Ultrafine Binary Carbides.

Herein, we demonstrate a promising method for the synthesis of ultrafine carbide particles using dispersions of molybdenum–tungsten nanoparticles. Dispersions of molybdenum–tungsten blue nanoparticles with different initial molar ratios of molybdenum/tungsten were synthesized through the reduction of molybdate and tungstate ions by ascorbic acid in an acidic medium (pH = 1.0–2.5). Molybdenum–tungsten blue nanoparticles were characterized by ultraviolet–visual (UV–VIS), infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies; transmission electronic microscopy (TEM); and dynamic light scattering (DLS). We demonstrated that molybdenum–tungsten blue nanoparticles belong to toroidal polyoxometalate clusters (λmax = 680–750 nm) with a predominant particle size of 4.0 nm. Molybdenum–tungsten blue dispersions were shown to be monodispersed systems with a small particle size and long-term stability (>30 days) and are suitable for further catalytic applications.

Optimizing the Reduction of Molybdate by Two Novel Thermophilic Bacilli Isolated from Sinai, Egypt.

The aim of this study was to isolate thermophilic bacteria to be used in in situ bioremediation of molybdate at elevated temperatures. Two molybdate reducing bacteria (Pharon2 and Pharon3) were isolated from the hot Spring at Pharaoh's Bath, Sinai, Egypt. The isolates were identified by 16S rRNA genes sequencing and were submitted to GenBank as Bacillus tequilensis strain Pharon2 (MK078034) and Bacillus sonorensis strain Pharon3 (MK078035). The molybdenum blue production was optimized using multifactorial statistical approaches, Plackett-Burman and central composite designs. According to the results obtained by response optimizer, the maximum molybdenum blue production achieved was 1.04 and 1.12 represented as absorbance at 865nm, with the optimum salt concentration of 1.1 and 2.5%; at pH 7.02 and 7.07; incubation temperature of 46.1 and 52.2 °C; sucrose and glucose as an electron donor for Bacillus tequilensis strain Pharon2 and Bacillus sonorensis strain Pharon3, respectively. In conclusion, the thermophilic bacterial isolates belonging to the genus Bacillus could be used in in situ bioremediation under elevated temperatures. To the best of our knowledge, this is the first record of molybdenum blue production by thermophilic Bacillus tequilensis and Bacillus sonorensis.

Production of molybdenum blue by two novel molybdate-reducing bacteria belonging to the genus Raoultella isolated from Egypt and Iraq.

The aim of this study was to isolate potential molybdate-reducing bacteria to be used for bioremediation. Two molybdate-reducing bacteria (Mo1 and MoI) were isolated from polluted soil samples from Ismailia Canal, Egypt and Sallah Elddin Governorate, Iraq respectively. The isolates exhibited dark blue colonies when grown on solid medium containing sodium molybdate which indicated the reduction of molybdate to molybdenum (Mo) blue. The absorbance values at 865nm were 0·743±0·007 and 0·453±0·005 for Mo1 and MoI respectively. The Mo blue produced showed characteristic absorption spectrum peak at 865nm and a shoulder at 700nm. The isolates were identified by 16S rRNA genes sequencing and were submitted to GenBank as Raoultella ornithinolytica strain Mo1 and Raoultella planticola strain MoI. The optimum conditions were glucose as electron donor, initial pH of 6 and incubation temperature of 30°C. Scanning electron micrographs were taken for both isolates in the presence and absence of molybdate source. To the best of our knowledge, this is the first recordation of molybdate reduction by Raoultella sp. isolated from Egypt and Iraq. The isolated bacteria belonging to the Raoultella could be used in insitu bioremediation.

ANTIOXIDANT ACTIVITIES AND TOTAL PHENOLIC AND FLAVONOID CONTENT VARIATIONS OF LEAF EXTRACTS OF LAURUS NOBILIS L. FROM MOROCCO

Objective: The present study was undertaken to determine antioxidant activity and total phenolic and flavonoid content of ethanol, methanol, ethyl acetate, and aqueous extracts of the leaves of Laurus nobilis L.Methods: Antioxidant properties were measured using three tests: Free radical scavenging activity against 2,2-diphenyl picrylhydrazyl (DPPH), reduction of molybdate, and reducing (Fe3+/Fe2+) power. Total phenolic and flavonoid content was measured by Folin–Ciocalteu and rutin reagent, respectively.Results: The results showed that both the ethanol and water extracts had greater antioxidant activity than ethyl acetate. Aqueous extract exhibited a higher DPPH radical scavenging and reducing molybdate 545.83±5.89 mg equivalent to ascorbic acid/g dry extract. The strong antioxidant activity of water extract was probably due to its high content of phenols. Furthermore, ethanol and water extracts showed higher total flavonoid content with the values: 153.33±3.59 and 127.25±2.60 mg equivalent rutin/g dry extract, respectively.Conclusion: Our results suggested a potent and excellent antioxidant activity of L. nobilis L. extracts of Morocco. Further research has to be done to isolate the pure bioactive compound and could be considered as a potential source of biomolecules for pharmaceutical and food industry.

Formation of Molybdenum Blue Particles via the Reduction of a Molybdate Solution with Glucose

Molybdenum blue dispersions are synthesized via the reduction of molybdate with glucose in an acidic medium. Spectrophotometry and photon correlation spectroscopy show that, depending on the reducing agent/molybdate ratio and the pH value, both colored complex Mo compounds and dispersed phase particles (large molybdenum oxide clusters) can form. It is shown that particles form in the 1.4–2.2 range of the dispersion medium’s pH and ceases 21 days after synthesis (at room temperature).

Isolation and characterization of molybdenum-reducing and PEG-degrading Enterobacter cloacae strain KIK-14 in agricultural soil from Nigeria

Today, numerous researches have demonstrated the cost-effectiveness of bioremediation to waste removal from agricultural and industrial sectors particularly at lower levels of the toxicants, where other physicochemical techniques are ineffective. Multiple toxicant remediation by a single microorganism is important for remediation of sites contaminated with numerous toxicants. In this work, a molybdenum-reducing bacterium was screened for its ability to use the xenobiotic polyethylene glycol (PEG) as the sole source of carbon for growth and as electron donor source for molybdate reduction. Biochemical analysis results in the tentative identification of the isolate as Enterobacter cloacae strain KIK-14. The use of PEGs as an electron donor in this bacterium did not support molybdenum-blue production, even though the bacterium grew well on PEGs 200, 300, 600 and 1000 independent of molybdate reduction. Reduction of molybdate to Mo-blue was optimal at pH between 6.0 and 6.3, the temperature between 25 and 37 oC, molybdate and phosphate concentrations between 15 and 20 mM and between 5.0 and 7.5 mM respectively. The best electron donor source supporting the reduction process was glucose. The Mo-blue absorption spectrum resembles reduced phosphomolybdate and is similar to that of the previous Mo-reducing bacterium. At 2 ppm of silver, mercury and copper, molybdenum reduction was inhibited by 41.5, 57.1 and 40.5%, respectively. The ability of this bacterium to detoxify mixed toxicants makes it an important tool for bioremediation.

PEG-mediated hydrothermal synthesis of hierarchical microspheres of MoS2 nanosheets and their potential for lubrication application

Lamellar-structured nanomaterials are gaining large interest for tribological applications owing to their remarkable mechanical and low shearing properties. Herein, polyethylene glycol (PEG)-mediated hierarchical microspheres of MoS2 nanosheets are synthesized by a facile and single-step hydrothermal reduction of ammonium molybdate in the presence of thiourea. The PEG functions as a soft templating material and provides hierarchical microspheres of MoS2 nanosheets. Detailed chemical and microstructural features of hierarchical microspheres of MoS2 nanosheets are probed by FTIR, XPS, Raman, XRD, TGA, FESEM, and HRTEM analyses. Each nanosheet of MoS2 microspheres is composed of limited number (10–20) of atomic-thick lamellae as deduced from HRTEM images. The MoS2 microspheres, as additive provide significantly improved lubrication properties for steel tribo-pair by reducing the friction (∼21%) and the wear (42%) compared to that of fully formulated 10W40 lubricant. The elemental mapping of worn surfaces revealed the deposition of MoS2 nanosheets on the contact-interfaces. The improved lubrication properties are attributed to collective effect of deposition of delaminated MoS2 lamellae on the contact interfaces, low shearing and high mechanical strength of MoS2 nanosheets.

Graphene Porous Foam Loaded with Molybdenum Carbide Nanoparticulate Electrocatalyst for Effective Hydrogen Generation.

A facile method is developed for the synthesis of graphene porous foam (Gr PF) loaded with dispersed molybdenum carbide (Mo2 C) nanoparticles; the material exhibits effective catalytic activity in the hydrogen evolution reaction (HER). Mo2 C/Gr PF is synthesized by the carbonization of glucose and the carbothermal reduction of hexaammonium molybdate in a confined space defined by the intervals between sodium chloride nanoparticles. The synthesis in the confined space results in thin Gr PF (≈8 nm) loaded with aggregation-free small Mo2 C nanoparticles [(13±2) nm]. The overpotential required for a current density of 20 mA cm(-2) in the electrochemical hydrogen generation is as small as 199 mV in acidic solution and 380 mV in basic solution. The performance is superior to that of a Mo2 C/C composite and compares favorably to those reported for Mo2 C nanostructures. The Mo2 C/Gr PF affords stable water electrolysis in both acidic and basic solution and exhibits nearly 100 % faradaic efficiency. The prominent performance, long-term stability, and high faradic efficiency make Mo2 C/Gr PF a promising HER catalyst for practical hydrogen generation from water electrolysis.

Dialysis Tubing Experiment Showed that Molybdenum Reduction in S. marcescens strain DrY6 is Mediated by Enzymatic Action

Reduction of metal ions by microbes has long been afflicted by the contribution of abiotic and nonabiotic metal-reducing chemicals. The discrimination between enzymatic and chemical action upon metal must be solved to present a clear reduction mechanism. In this work, a previously developed method using dialysis tubing was employed to study the contribution of these agents upon molybdenum reduction to molybdenum blue in S. marcescens strain Dr.Y6. We discovered that approximately 95 % of molybdenum blue formed was found in the inside of the dialysis tubing. This suggests that the reduction of molybdate by this bacterium requires the presence of cells or mediated enzymatically.

Electrochemical Reduction of Molybdate on Glassy Carbon Electrode in Acidic Media

The reduction of molybdate on glassy carbon electrodes was studied in a solution of 0.5 M H2SO4 + 3.8 x 10-3 M MoO4 2- using potentiostatic polarization, cyclic voltammetry and chronoamperometry. The results indicate that molybdate reduction processes depends on potential and polarization time. Initial states correspond to reversible adsorption of reduced molybdate species. At -700 mV, molybdate reduction is influenced by the hydrogen evolution reaction. Under these conditions, polarization promotes the formation of hydrogen molybdenum bronzes.

An EPR and NMR study on Mo/HZSM-5 catalysts for the aromatization of methane: Investigation of the location of the pentavalent molybdenum

EPR and 27Al NMR were used to probe the nature of the phases that formed during the conversion of methane at high temperature on the Mo/HZSM-5 catalyst. It was shown that ammonium 6-molybdoaluminate III supported over silica gave rise, when reduced, to an EPR signal due to Mo5+ ions with the odd electron interacting with the nonzero nuclear spin of aluminum in much the same way as in HZSM-5. Therefore, the occurrence of this particular spin interaction should not be taken as evidence of the location of the Mo5+ ions at the exchange sites of the zeolites. Rather, combined 27Al NMR and EPR investigation of the reduction of a pure polycrystalline aluminum molybdate suggested that the observed signal in the case of the zeolite composite catalyst was due to Mo5+ ions formed within the Al2(MoO4)3 extra phase that formed upon dealumination of the zeolite in the presence of molybdenum.

Kinetics of molybdenum reduction to molybdenum blue by Bacillus sp. strain A.rzi.

Molybdenum is very toxic to agricultural animals. Mo-reducing bacterium can be used to immobilize soluble molybdenum to insoluble forms, reducing its toxicity in the process. In this work the isolation of a novel molybdate-reducing Gram positive bacterium tentatively identified as Bacillus sp. strain A.rzi from a metal-contaminated soil is reported. The cellular reduction of molybdate to molybdenum blue occurred optimally at 4 mM phosphate, using 1% (w/v) glucose, 50 mM molybdate, between 28 and 30°C and at pH 7.3. The spectrum of the Mo-blue product showed a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of bacterial electron transport system (ETS) such as rotenone, sodium azide, antimycin A, and potassium cyanide could not inhibit the molybdenum-reducing activity. At 0.1 mM, mercury, copper, cadmium, arsenic, lead, chromium, cobalt, and zinc showed strong inhibition on molybdate reduction by crude enzyme. The best model that fitted the experimental data well was Luong followed by Haldane and Monod. The calculated value for Luong's constants p max, K s, S m, and n was 5.88 μmole Mo-blue hr−1, 70.36 mM, 108.22 mM, and 0.74, respectively. The characteristics of this bacterium make it an ideal tool for bioremediation of molybdenum pollution.

Voltammetric Study of the Molybdate Reduction and Subsequent Oxidation on Glassy Carbon Electrode in Acid Media

The electroreduction of molybdate and subsequent electro-oxidation on glassy carbon electrodes was studied by cyclic voltammetry in acid medium. The results show that the reduction of molybdate depends on applied potential and molybdate concentration in solution. The molybdate reduction process is characterized by cathodic peaks Ic (-0.143 mV), IIc (-0.270 mV) and the cathodic band (Bc) around -400 mV. Cathodic peaks Ic and IIc correspond to the early stages of reduction of molybdate. Both peaks show some degree of reversibility with respect to the anodic peaks Ia and IIa. As the cathode switching potential is more negative than -400 mV and the concentration of molybdate increases, the band Bc is the dominant factor in the reduction process, resulting in the formation of the anodic peaks IIIa (-217 mV) and IVa (477 mV) on voltammogram. This behaviour can be justified through the formation and oxidation of hydrogen molybdenum bronzes on the surface of glassy carbon.

Reduction of molybdate to molybdenum blue by Klebsiella sp. strain hkeem

A novel molybdate-reducing bacterium, tentatively identified as Klebsiella sp. strain hkeem and based on partial 16s rDNA gene sequencing and phylogenetic analysis, has been isolated. Strain hkeem produced 3 times more molybdenum blue than Serratia sp. strain Dr.Y8; the most potent Mo-reducing bacterium isolated to date. Molybdate was optimally reduced to molybdenum blue using 4.5 mM phosphate, 80 mM molybdate and using 1% (w/v) fructose as a carbon source. Molybdate reduction was optimum at 30 °C and at pH 7.3. The molybdenum blue produced from cellular reduction exhibited absorption spectrum with a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide, and potassium cyanide did not inhibit the molybdenum-reducing enzyme. Mercury, silver, and copper at 1 ppm inhibited molybdenum blue formation in whole cells of strain hkeem.

Direct reduction of ammonium molybdate to elemental molybdenum by combustion reaction

Self-sustaining reduction of ammonium molybdate tetrahydrate (AMT) by mixture of zinc and magnesium is investigated. It is shown that utilizing mixtures of metallic reducers is an attractive methodology to control the reduction conditions and product characteristics. Optimal intervals of key parameters, e.g. composition of reducing mixtures and pressure of inert gas are determined. Analysis of combustion temperature profiles, XRD, SEM/FESEM, DTA, microanalysis, and quenching techniques are applied to investigate the reduction mechanism. Based on the obtained fundamental knowledge, for the first time, highly crystalline molybdenum powder with particle sizes in the range 0.1–1 μm is produced by direct reduction of AMT in a single-stage and energy saving process. Proposed combustion-based approach of Mo production has high potential to become an alternative to the conventional hydrogen reduction processes.