Nanostructured MoO3 Research Articles

Carbon-Coated Nano-Structured MoO3 as Cathode Materials for Lithium Batteries, Synthesis, Structure and Electrochemical Performance

We report the synthesis of carbon-coated a-MoO3 nano-materials and their structural and electrochemical properties. The carbon deposit performed by the lactose method allows enhancement of the electronic conductivity of the composite. The structure of the carbon film is investigated by Raman spectroscopy. The electrochemical tests were carried out in Li/LiPF6-EC–DEC/MoO3 cells. The charge–discharge reaction is investigated as a function of C-rate and the influence of electrode preparation on the electrochemical performance was examined.

Reusable α-MoO3 nanobelts catalyzes the green and heterogeneous condensation of 1,2-diamines with carbonyl compounds

Crystalline nanobelts of α-MoO3 have been obtained successfully using novel and safe agents through a simple and safe sol–gel method (polymerizing–complexing) and characterized by XRD, FT-IR, Raman spectroscopies, high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and the temperature programmed desorption (TPD) of ammonia. An orthorhombic lattice system for nano-MoO3 was established. The HRTEM images showed that the nanobelt morphology of α-MoO3 mostly ranged from 20–70 nm in width and 200–400 nm in length. The ammonia TPD profile demonstrated strong acidic sites. The spectral and analysis data confirmed the effectiveness of the method for the preparation of α-MoO3 nanobelts by prevention of grain growth or agglomeration of the particles. The nanostructured MoO3 exhibited a high efficiency in catalyzing the condensation reaction of various 1,2-diamine and carbonyl compounds for synthesis of heterocyclic compounds. The recovery of the title heterogenous nanocatalyst was easy and efficient and its catalytic activity was strikingly different from the bulk material.

Enhancing the stability of polymer solar cells by improving the conductivity of the nanostructured MoO3 hole-transport layer

This article demonstrates improvements in the operational stability of organic solar cells (OSCs) by taking advantage of the relationship between oxygen stoichiometry and conductivity in nanostructured metal oxide semiconductors (n-MOS). OSCs in the inverted device configuration of ITO/Ca/P3HT:PCBM/MoO3/Ag were employed in the present study. A high degree of oxygen defects were introduced in the hole-conducting MoO3 layer by annealing the devices under vacuum (≥10(-5) mbar) for nominal temperature (120 °C) and time (10 min). The above devices had much higher operational stability, when tested following the ISOS-D-1 (shelf) protocol, than control devices annealed conventionally, i.e., in nitrogen atmosphere. Employing current-voltage measurement as functions of temperature and photon flux, we show that the devices annealed under vacuum have a lesser density of traps than those annealed in nitrogen. The lesser trap density is shown to be beneficial in reducing the rate of electron recombination thereby increasing the operational stability of the corresponding device. A number of experiments were undertaken to show that the difference in the operation stability of the device results from the difference in conductivity of the nanostructured MoO3 hole transporting layer. The charge extraction by linear increasing voltage spectroscopy shows that charges are relaxed at the trap states in the device annealed in nitrogen whereas they are efficiently transported in the other device. We identify that building up of an interfacial potential barrier as a result of the charge relaxation at the trap states and the corresponding chemical changes in the devices annealed conventionally is the source of degradation of the device performance over time. To our knowledge, this is the first report that successfully overcomes hole-conductivity induced degradation in organic solar cells.

Carbon-Coated Nano-Structured MoO3 as Cathode Materials for Lithium Batteries, Synthesis, Structure and Electrochemical Performance

Carbon-Coated Nano-Structured MoO3 as Cathode Materials for Lithium Batteries, Synthesis, Structure and Electrochemical Performance

Facile synthesis of α-MoO3 nanobelts and their pseudocapacitive behavior in an aqueous Li2SO4 solution

α-MoO3 nanobelts were successfully prepared by a facile hydrothermal method with sodium molybdate (Na2MoO4) as the Mo source and NaCl as the capping agent. The as-prepared products were characterized using Fourier transformation infrared spectrophotometry (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected area electronic diffraction (SAED) and their pseudocapacitive properties were investigated in a 0.5 M aqueous Li2SO4 solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence. The results show that the dimensions of the as-prepared α-MoO3 nanobelts are 200–400 nm in width, ca. 60 nm in thickness and 3–8 µm in length. The redox potential for the α-MoO3 nanobelts is found in the range of −0.3 to −1.0 V vs. SCE, which indicates that the α-MoO3 nanobelts can be used as anode electrode materials for hybrid supercapacitors. The specific capacitances of the α-MoO3 nanobelts at 0.1, 0.25, 0.5 and 1 A g−1 are 369, 326, 256 and 207 F g−1, respectively. The maximum specific capacitance of the α-MoO3 nanobelts is much higher than those of MoO3 nanoplates with 280 F g−1, MoO3 nanowires with 110 F g−1 and MoO3 nanorods with 30 F g−1 recently reported in literature. Furthermore, the α-MoO3 nanobelt electrode exhibits a good cycle stability with more than 95% of the initial specific capacitance maintained after 500 cycles. Additionally, the present route to prepare nanostructured MoO3 is much less expensive than those with Mo powders as the Mo source. Overall, the obtained high performance α-MoO3 nanobelts could be a promising electrode material for supercapacitors.

Carbon-Coated Nano-Structured MoO3 as Cathode Materials for Lithium Batteries: Synthesis, Structure and Electrochemical Performance

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Gas sensing properties of nanostructured MoO3 thin films prepared by spray pyrolysis

Thin films of molybdenum trioxide (MoO3) were deposited on common glass using the chemical spray pyrolysis technique. A (NH4)6Mo7O244H20 solution 0.1M was used as the precursor one. The influence of substrate temperature on the crystallographic structure, surface morphology and electrical behavior of MoO3 thin films was studied. MoO3 can exist in two crystalline forms, the thermodynamically stable orthorhombic α-MoO3 and the metastable monoclinic β-MoO3 phase. XRD-spectra showed a growth of α-MoO3 phase percentage as substrate temperature increases from 420K up to 670K. Films deposited in the 500–600K range have a clearly porous surface structure of nanometer order as can be seen in SEM images. Changes up to six magnitude orders were observed in MoO3 thin films electrical resistance when films temperature varied from 100K up to 500K. The sensing property of these MoO3 films was also studied. The sensitivity was investigated in the temperature range 160 and 360K for H2O and CO gases, respectively. Both of them are of reducing nature. In all studied cases sensitivity decreases slowly as film temperature is raised. At room temperature the sensitivity changes from 12 up to 75% depending on substrate temperature. The sensitivity for CO gas was found to be lower than that of H2O.

Single-material multilayer with enhanced photoactivity

Molybdenum trioxide (MoO3) patterned at the nanometer scale is combined with the same material in its bulk form to produce Bragg mirrors with enhanced photoactive properties. MoO3 undergoes coloration with exposure to UV light but a multilayer structure which alternates between nanostructured and bulk MoO3 is 2.5 times more effective. Measurements with various multilayer arrangements suggest the proximity of bulk and nanostructured MoO3 favors the photoreaction with structural water. A possible minor contribution from electronic band shifting is also discussed.

High Catalytic Efficiency of Nanostructured Molybdenum Trioxide in the Benzylation of Arenes and an Investigation of the Reaction Mechanism

The synthesis and characterization of nanostructured MoO(3) with a thickness of about 30 nm and a width of about 450 nm are reported. The composition formula of the MP (precipitation method) precursor was estimated to be [(NH(4))(2)O](0.169) x MoO(3) x (H(2)O)(0.239). The calcination of the precursor in air afforded nanostructured pellets of the alpha-MoO(3) phase. The nanostructured MoO(3) catalyst exhibited high efficiency in catalyzing the benzylation of various arenes with substituted benzyl alcohols, which were strikingly different to common bulk MoO(3). Most reactions offered >99% conversion and >99% selectivity to monoalkylated compounds. MoO(3) is a typical acid catalyst. However, the benzylation reaction over nanostructured MoO(3) does not belong to the acid-catalyzed type or defect site-catalyzed type, since the catalyst has no acidity and defect site on surface. Characterization with thermal, spectroscopic, and electronic techniques reveal that the catalyst contains fully oxygen-coordinated MoO(6) octahedrons on the surface but partially reduced species (Mo(5+)) within the bulk phase. The terminal oxygen atoms of Mo=O bonds on the (010) basal plane resemble oxygen anion radicals and act as active sites for the adsorption and activation of benzyl alcohols by electrophilic attack. Such sites are indispensable for catalytic reactions since the blocking of these sites by electron acceptors, such as tetracyanoethylene (TCNE), can greatly decrease catalytic activity. This work represents a successful example of combining a heterogeneous catalysis study with nanomaterial synthesis.

Synthesis of Ni-Mo-W Sulfide Nanorods as Catalyst for Hydrodesulfurization of Dibenzothiophene

Two trimetallic sulfurs, MoWNiS and MoWSNi, were synthesized to be used as a catalyst in hydrodesulfurization reactions. The mixed oxide mesoporous nanostructured MoO3 -WO3 with an Mo:W atomic ratio of 1:1 was used as the precursor. The first catalyst was prepared by impregnating nickel in the oxide precursor and then subsequent sulfiding with an H2S/H2 mix at 400 degrees C for 2 hours. The second catalyst was prepared by sulfiding the precursor and then impregnating the nickel, and finally reducing the material with a H2/N2 at 350 degrees C. In both catalysts the Mo:W:Ni atomic ratio was maintained at 1:1:0.5. The materials obtained were characterized by physical adsorption of nitrogen, X-ray diffraction, scanning electron microscopy, transmission electron microscopy. Furthermore, the materials obtained were evaluated by a dibenzothiophene hydrodesulfuration reaction. The diffraction patterns show that both materials are polycrystalline and mainly of MoS2 and WS2 phases.

Proton coupled electron transfer tunneling reactions in WO3 and MoO3 nanostructured films

WO3 and MoO3 are famous hydrogenphilics, hydrogen loving materials, capable of performing various functions concerning atomic hydrogen. They are active catalysts in photochemical reactions connected with detachment of hydrogen atoms, being, at the same time, capable of accomodating great quantities of the detached hydrogen atoms, and transporting them to other functional materials via employment of various heterostructures. It was shown that tunneling proton-coupled electron transfer is the mechanism of the photochemical hydrogen abstraction reaction on the surface of highly disordered nanostructured WO3 and MoO3 thin films. Specially selected hydrogen donor molecules were adsorbed on the oxide surface bonding via donor-acceptor and hydrogen bonds which yield a decrease in the energy barrier for the hydrogen transfer from the adsorbed hydrogen donor molecule to the oxide surface. The very rough and heterogeneous film surface yields space fluctuations of the energy barrier parameters whereas intermolecular vibrations yield time fluctuations; the fluctuative barrier preparation being responsible for the tunneling photo-stimulated proton-coupled electron transfer.