Commonly encountered molybdenum compounds
Molybdenum is widely distributed in nature. It is found in the minerals molybdenite,MoS2 which is the major ore of molybdenum, wulfenite, ferrimolybdate, jordisite, and powellite. Most molybdenum compounds are derived from molybdenum trioxide which is prepared by roasting molybdenum disulfide ores in air. Commonly used molybdenum-oxygen compounds are molybdenum trioxide, MoO3, sodium molybdate, Na2MoO4.2H2O, ammonium dimolybdate, (NH4)2 Mo2O7, and ammonium heptamolybdate, (NH4)6Mo7O24.4H2O.
Molybdenum is used mainly as an alloying element in steel, cast iron, and superalloys and in the electronics industries.
Leichtfried, G., in Ullmann's Encyclopedia of Industrial Chemistry ,5th ed. 1990, A16 , 668.
Molybdenum trioxide and molybdenum-oxygen compounds are added to steel and corrosion-resistant alloys. They are used in industrial catalysts, corrosion inhibitors, pigments, glass, ceramics, and enamels, flame retardant for polyester and polyvinyl chloride resins, as crop nutrients in agriculture, and as reagents in chemical analyses.
Vukasovich, M. S., in Ullmann's Encyclopedia of Industrial Chemistry ,5th ed., 1990, A16 , 682.
Molybdenum-sulfur compounds are used in lubrication to reduce friction and wear: molybdenum disulfide as a dry or suspended lubricant and molybdenum-sulfur complexes as soluble oil additives.
Mitchell, P. C. H., Wear , 1984, 100 , 281.
Other molybdenum compounds which find some application, for example, in the electronics industries and in chemical vapour deposition, are molybdenum pentachloride and molybdenum hexacarbonyl.
Environmental release of molybdenum compounds from industrial activities can occur in air (stack emissions), water (liquid effluents), or solid wastes (sludge): see Industrial and Environmental Exposure of Humans to Molybdenum.
MOLYBDENUM METAL ALLOY BIOACCESSIBILITY
The European chemical framework REACH requires that hazards and risks posed by chemicals, including alloys and metals, that are manufactured, imported or used in different products (substances or articles) are identified and proven safe for humans and the environment. Metals and alloys need hence to be investigated on their extent of released metals (bioaccessibility) in biologically relevant environments. Read-across from available studies may be used for similar materials. This study investigates the release of molybdenum and iron from powder particles of molybdenum metal (Mo), a ferromolybdenum alloy (FeMo), an iron metal powder (Fe), MoO2, and MoO3 in different synthetic body fluids of pH ranging from 1.5 to 7.4 and of different composition. Spectroscopic tools and cyclic voltammetry have been employed to characterize surface oxides, microscopy, light scattering and nitrogen absorption for particle characterization, and atomic absorption spectroscopy to quantify released amounts of metals. The release of molybdenum from the Mo powder generally increased with pH and was influenced by the fluid composition. The mixed iron and molybdenum surface oxide of the FeMo powder acted as a barrier both at acidic and weakly alkaline conditions. These findings underline the importance of the surface oxide characteristics for the bioaccessibility of metal alloys.
Morsdorf, A.,Wallinder, I. O.,and Hedberg, Y.,Bioaccessibility of micron-sized powder particles of molybdenum metal, iron metal, molybdenum oxides and ferromolybdenum - Importance of surface oxides, Regul Toxicol Pharmacol, 2015.
Time-of-flight neutron powder diffraction data have been collected from Na2MoO4 and Na2WO4 to a resolution of sin (theta)/lambda = 1.25 A(-1), which is substanti-ally better than the previous analyses using Mo Kalpha X-rays, providing roughly triple the number of measured reflections with respect to the previous studies [Okada et al. (1974 ). Acta Cryst. B30, 1872-1873; Bramnik & Ehrenberg (2004 ). Z. Anorg. Allg. Chem. 630, 1336-1341]. The unit-cell parameters are in excellent agreement with literature data [Swanson et al. (1962 ). NBS Monograph No. 25, sect. 1, pp. 46-47] and the structural parameters for the molybdate agree very well with those of Bramnik & Ehrenberg (2004 ). However, the tungstate structure refinement of Okada et al. (1974 ) stands apart as being conspicuously inaccurate, giving significantly longer W-O distances, 1.819 (8) A, and shorter Na-O distances, 2.378 (8) A, than are reported here or in other simple tungstates. As such, this work represents an order-of-magnitude improvement in precision for sodium molybdate and an equally substantial improvement in both accuracy and precision for sodium tungstate. Both compounds adopt the spinel structure type. The Na(+) ions have site symmetry .-3m and are in octa-hedral coordination while the transition metal atoms have site symmetry -43m and are in tetra-hedral coordination.
Fortes, A. D.,Crystal structures of spinel-type Na2MoO4 and Na2WO4 revisited using neutron powder diffraction, Acta Crystallogr E Crystallogr Commun, 2015, 71, 592.
Sodium molybdate - solubility
Determination and modelling for the solubility of Na2MoO4.2H2O in the (Na+ + MoO42- + SO42-) system
The solubility of Na2MoO4.2H2O in ( Na+ + MoO42- + SO42-) system was carried out using a dynamic method within the temperature range from 293.15 K to 343.15 K. The new model was established via regression of the published and the determined values to predict the solubility.
From the results, the solubility of sodium molybdate increases with the temperature increase, however, it decreases with the increasing concentration of sodium sulfate. The Pitzer parameters and the solubility product constant of sodium sulfate and sodium molybdate in aqueous solution were obtained using the literature data. The solubilities of the sodium molybdate in the sodium sulfate solution as well as the thermodynamic parameters were calculated based on the experimental values obtained. The new model was also applied to estimate the solubility of the sodium molybdate under various conditions. The calculated values agree well with the experiment results. (C) 2015 Published by Elsevier Ltd.
Ning, P. G., Xu, W. F., Cao, H. B., Lin, X., and Xu, H. B.,Determination and modeling for the solubility of Na2MoO4.2H2O in the (Na+ + MoO42- + SO42-) system, Journal of Chemical Thermodynamics, 2016, 94, 67-73.
The crystallographic structure and morphology of redox active transition metal oxides have a pronounced effect on their electrochemical properties. In this work, h-MoO3 nanostructures with three distinct morphologies, i.e., pyramidal nanorod, prismatic nanorod and hexagonal nanoplate, were synthesized by a facile solvothermal method. The morphologies of h-MoO3 nanostructures were tailored by a controlled amount of hexamethylenetetramine. An enhanced specific capacitance about 230 F g(-1) at an applied current density of 0.25 A g(-1) was achieved in h-MoO3 pyramidal nanorods. Electrochemical studies confirmed that the h-MoO3 pyramidal nanorods exhibit superior charge-storage ability. This improved performance can be ascribed to the coexistence of its well exposed crystallographic planes with abundant active sites, i.e., hexagonal window (HW), trigonal cavity (TC) and four-coordinated square window (SW). The mechanism of charge-storage is likely facilitated by the vehicle mechanism of proton transportation due to the availability of the vehicles, i.e., NH4(+) and H2O. The promising, distinct and unexploited features of h-MoO3 nanostructures reveal a strong candidate for pseudocapacitive electrode materials.
Kumar, V., Wang, X., and Lee, P. S.,Formation of hexagonal-molybdenum trioxide (h-MoO3) nanostructures and their pseudocapacitive behavior, Nanoscale, 2015, 7, 11777.
Molybdenum trioxide MoO3 – structure, surface, vacant sites, hydration,
Influence of calcination temperature on the structural and photochromic properties of nanocrystalline MoO3
Nanocrystalline metastable hexagonal and thermodynamically stable orthorhombic MoO3were successfully synthesized by precipitation, and calcined at various temperatures in the range 200-500 degrees C.
The influence of calcination temperature on crystal structure, crystallite size, thermal properties, morphology, optical properties, and photochromic properties was determined.
The 432 degrees C phase transformation temperature of hexagonal flower-like MoO3to an orthorhombic platelet structure was determined.
The band gap energy of MoO3 varied from 3.13 to 3.20 eV, depending on calcination temperature.
The photochromic properties were determined with UV irradiation and CIE Lab colour system. The hexagonal MoO3 from low temperature calcination had an about seven-fold photochromic efficiency relative to orthorhombic MoO3.
Jittiarporn, P., Sikong, L., Kooptarnond, K., and Taweepreda, W.,INFLUENCE OF CALCINATION TEMPERATURE ON THE STRUCTURAL AND PHOTOCHROMIC PROPERTIES OF NANOCRYSTALLINE MoO3, Digest Journal of Nanomaterials and Biostructures, 2015, 10, 1237-1248.
Molybdenum trioxide, MoO3 - structure, surface hydration, vacant sites, catalysis, nano, antimicrobial
Band energy control of molybdenum oxide by surface hydration
The application of oxide buffer layers for improved carrier extraction is ubiquitous in organic electronics. However, the performance is highly susceptible to processing conditions. Notably, the interface stability and electronic structure is extremely sensitive to the uptake of ambient water.
In this study we use density functional theory calculations to asses the effects of adsorbed water on the electronic structure of MoOx, in the context of polymer-fullerene solar cells based on PCDTBT. We obtain excellent agreement with experimental values of the ionization potential for pristine MoO3 (010). We find that IP and EA values can vary by as much as 2.5 eV depending on the oxidation state of the surface and that adsorbed water can either increase or decrease the IP and EA depending on the concentration of surface water. (C) 2015 AIP Publishing LLC.
Butler, K. T., Crespo-Otero, R., Buckeridge, J., Scanlon, D. O., Bovill, E., Lidzey, D., and Walsh, A.,Band energy control of molybdenum oxide by surface hydration, Applied Physics Letters, 2015, 107.
Oxygen deficiency in MoO3 polycrystalline nanowires and nanotubes
We report on the synthesis of polycrystalline molybdenum oxide (MoO3) nanowires via oxidation of molybdenum-sulfur-iodine (Mo6S2I8) nanowires. This unique synthesis route results in an interesting morphology comprising porous nanowires and nanotubes.
We found the nanowires to have the orthorhombic MoO3 structure. The structure is slightly oxygen deficient which results in the appearance of a new resonant Raman band (1004 cm-1) and paramagnetic defects (Mo5+) of both the point and crystallographic shear plane nature. (C) 2015 Elsevier B.V. All rights reserved.
Varlec, A., Arcon, D., Skapin, S. D., and Remskar, M.,Oxygen deficiency in MoO3 polycrystalline nanowires and nanotubes, Materials Chemistry and Physics, 2016, 170, 154-161.
Probing edge-activated resonant Raman scattering from mechanically exfoliated 2D MoO3 nanolayers
We report spatially resolved vibrational analysis of mechanically exfoliated single-crystalline alpha-MoO3 nanolayers.
Raman scattering from alpha-MoO3 was enhanced predominantly at the outside edges of the nanolayers. The enhanced Raman scattering at the edges was attributed primarily to the enhanced resonant Raman effect caused by a high density of oxygen vacancies localized at the edges.
The localized vacancy sites corresponded to a non-stoichiometric phase of MoO3, which would provide reactive sites with high catalytic activity.
Yano, T. A., Yoshida, K., Hayamizu, Y., Hayashi, T., Ohuchi, F., and Hara, M.,Probing edge-activated resonant Raman scattering from mechanically exfoliated 2D MoO3 nanolayers, 2d Materials, 2015, 2.
Nanoscale Insights into the Hydrogenation Process of Layered alpha-MoO3
The hydrogenation process of the layered alpha-MoO3 crystal was investigated on a nanoscale.
At low hydrogen concentration, the hydrogenation can lead to formation of HxMoO3 without breaking the MoO3 atomic flat surface. For hydrogenation with high hydrogen concentration, hydrogen atoms accumulated along the < 101 > direction on the MoO3, which induced the formation of oxygen vacancy line defects. The injected hydrogen atoms acted as electron donors to increase electrical conductivity of the MoO3.
Near-field optical measurements indicated that both of the HxMoO3 and oxygen vacancies were responsible for the coloration of the hydrogenated MoO3, with the latter contributing dominantly.
On the other hand, diffusion of hydrogen atoms from the surface into the body of the MoO3 will encounter a surface diffusion energy barrier, which was for the first time measured to be around 80 meV. The energy barrier also sets an upper limit for the amount of hydrogen atoms that can be bound locally inside the MoO3 via hydrogenation.
We believe that our findings has provided a clear picture of the hydrogenation mechanisms in layered transition-metal oxides, which will be helpful for control of their optoelectronic properties via hydrogenation.
Xie, W. G., Su, M. Z., Zheng, Z. B., Wang, Y., Gong, L., Xie, F. Y., Zhang, W. H., Luo, Z., Luo, J. Y., Liu, P. Y., Xu, N. S., Deng, S. Z., Chen, H. J., and Chen, J.,Nanoscale Insights into the Hydrogenation Process of Layered alpha-MoO3, Acs Nano, 2016, 10, 1662-1670.
A theoretical study of stability and vacancy replenishing of MoO3(010) surfaces in oxygen atmosphere
Oxygen vacancies on transition metal oxide surfaces are catalytically very important. The stability, shape and replenishing process of the vacancies are critical to understanding reactions happening on the surfaces.
In this paper we investigate the stability of various defective MoO3 (0 1 0) surfaces and examine the influence of environmental oxygen on the stability as well as the active sites for the replenishing process.
Our calculations reveal that the line oxygen defect along a (asymmetric oxygen) direction is thermodynamically most favorable at higher defect concentration whereas point defect surfaces are unfavorable. Under normal experimental conditions the perfect surface dominates the MoO3 (0 1 0).
We show that for stoichiometric surfaces of any oxides (A(x)O(y)) the formation energy per vacancy controls the favorable defect shape (line or point defects). Calculations indicate that O-2 can dissociate readily on the surfaces that double vacancies share one Mo atom. The replenishing process of the oxygen vacancies through O-2 dissociation most likely occurs on the double-vacancy containing one terminal and one asymmetrical oxygen vacancies. (C) 2015 Elsevier B.V. All rights reserved.
Lei, Y. H., and Chen, Z. X.,A theoretical study of stability and vacancy replenishing of MoO3(010) surfaces in oxygen atmosphere, Applied Surface Science, 2016, 361, 107-113.
Facile synthesis of a green metastable MoO3 for the selective oxidation of methanol to formaldehyde
Metastable MoO3 was successfully synthesized by a chemical transformation of alpha-MoO3 and characterized by TG-DSC, BET, XRD and Raman spectroscopy. The prepared material was highly active and selective to formaldehyde formation from methanol over a wide range of reaction temperatures. The formaldehyde selectivity can reach up to 99 % at about 98 % methanol conversion. The stability of the prepared catalysts was also investigated.
Phuong, P. T. T., Duy, N. P. H., Tai, V. T., Huan, N. M., Phuc, N. H. H., and Loc, L. C.,Facile synthesis of a green metastable MoO3 for the selective oxidation of methanol to formaldehyde, Reaction Kinetics Mechanisms and Catalysis, 2016, 117, 161-171.
Isoprenoid Alcohols are Susceptible to Oxidation with Singlet Oxygen and Hydroxyl Radicals
Isoprenoids, as common constituents of all living cells, are exposed to oxidative agents-reactive oxygen species, for example, singlet oxygen or hydroxyl radicals. Despite this fact, products of oxidation of polyisoprenoids have never been characterized.
In this study, chemical oxidation of isoprenoid alcohols (Prenol-2 and -10) was performed using singlet oxygen (generated in the presence of hydrogen peroxide/molybdate or upon photochemical reaction in the presence of porphyrin), oxygen (formed upon hydrogen peroxide dismutation) or hydroxyl radical (generated by the hydrogen peroxide/sonication, UV/titanium dioxide or UV/hydrogen peroxide) systems.
The structure of the obtained products, hydroxy-, peroxy- and heterocyclic derivatives, was studied with the aid of mass spectrometry (MS) and nuclear magnetic resonance (NMR) methods. Furthermore, mass spectrometry with electrospray ionization appeared to be a useful analytical tool to detect the products of oxidation of isoprenoids (ESI-MS analysis), as well as to establish their structure on the basis of the fragmentation spectra of selected ions (ESI-MS/MS analysis). Taken together, susceptibility of polyisoprenoid alcohols to various oxidizing agents was shown for the first time.
Komaszylo Nee Siedlecka, J., Kania, M., Masnyk, M., Cmoch, P., Lozinska, I., Czarnocki, Z., Skorupinska-Tudek, K., Danikiewicz, W., and Swiezewska, E.,Isoprenoid Alcohols are Susceptible to Oxidation with Singlet Oxygen and Hydroxyl Radicals, Lipids, 2016, 51, 229-44.
Degradable Molybdenum Oxide Nanosheets with Rapid Clearance and Efficient Tumor Homing Capabilities as a Therapeutic Nanoplatform
Molybdenum oxide (MoOx) nanosheets with high near-infrared (NIR) absorbance and pH-dependent oxidative degradation properties were synthesized, functionalized with polyethylene glycol (PEG), and then used as a degradable photothermal agent and drug carrier.
The nanosheets, which are relatively stable under acidic pH, could be degraded at physiological pH. Therefore, MoOx-PEG distributed in organs upon intravenous injection would be rapidly degraded and excreted without apparent in vivo toxicity. MoOx-PEG shows efficient accumulation in tumors, the acidic pH of which then leads to longer tumor retention of those nanosheets.
Along with the capability of acting as a photothermal agent for effective tumor ablation, MoOx-PEG can load therapeutic molecules with high efficiencies.
This concept of inorganic theranostic nanoagent should be relatively stable in tumors to allow imaging and treatment, while being readily degradable in normal organs to enable rapid excretion and avoid long-term retention/toxicity.
Song, G., Hao, J., Liang, C., Liu, T., Gao, M., Cheng, L., Hu, J., and Liu, Z.,Degradable Molybdenum Oxide Nanosheets with Rapid Clearance and Efficient Tumor Homing Capabilities as a Therapeutic Nanoplatform, Angewandte Chemie (International ed. in English), 2016, 55, 2122-6.
A perspective on molybdenum biocompatibility and antimicrobial activity for applications in implants
The use of biomaterials has become routine in dentistry, reconstructive surgery of the locomotor system, treatment of congenital, traumatic and tumor situations, and knee or hip arthroplasty. The main issue related to metal biomaterials is the systemic release of metal ions and the related biological risks. When placed in contact with a living organism, they must meet a set of criteria: they must be biocompatible and biofunctional, as well as have the ability to produce a specific biological response at the surface, leading to the formation of a bond between the material and the receiving tissue and a surface texture which allows cell adhesion and bone growth; they must also provide adequate structure and mechanical strength, without causing adverse reactions in the surrounding physiological environment; they must not cause oncogenic effects; they must be easy to manipulate during surgery; and they must be amenable to visible imaging and sterilization.
The ability to use biomaterials is linked to the degree of biocompatibility and biofunctionality which in turn, are dependent on their physicochemical and mechanical properties, macroscopic and microscopic configuration, and the biological environment where they are deployed.
Metal alloys, particularly stainless steel, cobalt, molybdenum, chromium alloys, and titanium-based alloys find wide application in orthopedics for making joint replacement prostheses, systems for external or internal fixation of bone fractures, surgical correction of degenerative conditions, or in the composition of staples, screws, and wires. Any synthetic biomaterial can replace or restore the function of body tissues while maintaining a continuous or intermittent contact with the fluid. When in contact with the fluid, it is essential that materials be biocompatible, so they do not produce adverse biological responses or induce systemic effects. Thus, they must not be toxic, carcinogenic, mutagenic, or antigenic. Bioactive materials with antibacterial properties are also of significant medical interest. Materials exhibiting good antimicrobial activity that minimize the formation of biofilm without the risk of promoting the development of resistant microorganisms are desirable. In this respect, this review briefly summarizes the recent successes of this metal as a biocompatible material with antibacterial activity for biomedical applications.
Ribeiro, A. M., Flores-Sahagun, T. H. S., and Paredes, R. C.,A perspective on molybdenum biocompatibility and antimicrobial activity for applications in implants, Journal of Materials Science, 2016, 51, 2806-2816.
Redox and ligand binding reactivity in iron and chromium -substituted polyoxometalates
Using UV-vis and EPR (electron paramagnetic resonance) spectroscopy, iron- and chromium- substituted polyoxometalates were shown to undergo controlled reduction, involving the iron and chromium as well as the molybdenum/tungsten framework; furthermore, reoxidation was also shown to be possible with molecular oxygen or hydrogen peroxide in a cycle reminiscent of iron-containing enzymes. The influence of pH, ligands and/or potential redox agents such as imidazole, thiocyanate, thiosulfate, mercaptoethanol and ascorbate were examined.
Kakes, M., Cioloboc, D., Tomsa, A. R., Silaghi-Dumitrescu, R., and Damian, G.,REDOX AND LIGAND BINDING REACTIVITY IN IRON AND CHROMIUM -SUBSTITUTED POLYOXOMETALATES, Revue Roumaine De Chimie, 2015, 60, 707-720.
Quantitative measurement of Bronsted acidity by TPD of ammonia on H3 PMo12O40 and its Cs1 salt, in bulk and supported on SBA-15
The method for acidity measurement through temperature programmed desorption (TPD) of ammonia was adapted for simultaneous TG/DTG-DTA analysis of the H-3[PMo12O40] and its Cs acid salts, in bulk and supported on SBA-15 support. The desorption of NH3 consists of the NH3 and H2O release in steps as a result of temperature increase. The last step corresponds to expelling of NH3 by decomposition of species strong bonded like the ammonium cation, simultaneously with constitutive water, within the 300-600 A degrees C range. The MS analysis showed that the oxidation of ammonia to N2O and NO during desorption had occurred simultaneously with reduction of Mo6+. The reoxidation of samples with air in all cases was done finally. In order to separate the water release (water formed by condensation of hydroxyl groups belonging to SBA-15) from the ammonia desorption for supported samples, a TPD of H2O was done for every sample. In the case of pure compounds, the mass loss corresponding to the last stage of desorption (after correction with the mass loss as a result of reduction, equal with the mass increase owing to the reoxidation) gives the amounts of NH3 and constitutive water, which correspond stoichiometrically with the Bronsted acidity. The subtraction of mass loss for TPD of water from the corrected mass loss for TPD of ammonia and water (because of the mass loss as a result of the reduction) gives the amount of NH3 corresponding stoichiometrically with the Bronsted acidity. The acidic strength was estimated on the basis of the temperatures for the DTG peaks.
Sasca, V. Z., Popa, A., and Verdes, O.,Quantitative measurement of Bronsted acidity by TPD of ammonia on H-3 PMo12O40 and its Cs1 salt, in bulk and supported on SBA-15, Journal of Thermal Analysis and Calorimetry, 2016, 123, 557-569.