MoO3 Nanowires Research Articles

Exploring the reactivity of distinct electron transfer sites at CVD grown monolayer graphene through the selective electrodeposition of MoO2 nanowires

The origin of electron transfer at Chemical Vapour Deposition (CVD) grown monolayer graphene using a polymer-free transfer methodology is explored through the selective electrodeposition of Molybdenum (di)oxide (MoO2). The electrochemical decoration of CVD monolayer graphene with MoO2 is shown to originate from the edge plane like- sites/defects. Edge plane decoration of MoO2 nanowires upon monolayer graphene is observed via electrochemical deposition over short time periods only (ca. −0.6 V for 1 second (vs. Ag/AgCl)). At more electrochemically negative potentials (ca. −1.0 V) or longer deposition times, a large MoO2 film is created/deposited on the graphene sheet, originating and expanding from the original nucleation points at edge plane like- sites/defects/wrinkles. Nanowire fabrication along the edge plane like- sites/defects of graphene is confirmed with Cyclic Voltammetry, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Raman Spectroscopy. Monitoring the electrochemical response towards [Ru(NH3)6]3+/2+ and comparing the heterogeneous electron transfer (HET) kinetics at CVD grown monolayer graphene prior and post nanowire fabrication reveals key understandings into the fundamental electrochemical properties of carbon materials. The HET kinetics ({{boldsymbol{k}}}_{{boldsymbol{obs}}}^{{bf{0}}}) at MoO2 nanowire decorated monolayer graphene sheets, when edge plane like- sites/defects have been coated/blocked with MoO2, are significantly reduced in comparison to the unmodified graphene alternative. Interestingly, MoO2 nucleation originates on the edge plane like- sites/defects of the graphene sheets, where the basal plane sites remain unaltered until the available edge plane like- sites/defects have been fully utilised; after which MoO2 deposition propagates towards and onto the basal planes, eventually covering the entire surface of the monolayer graphene surface. In such instances, there is no longer an observable electrochemical response. This work demonstrates the distinct electron transfer properties of edge and basal plane sites on CVD grown monolayer graphene, inferring favourable electrochemical reactivity at edge plane like- sites/defects and clarifying the origin of graphene electro-activity.

Improvement of thermal stability and flame retardancy of polypolypropylene composite modified by ZnO and MoO3 nanowires

ABSTRACTHerein, zinc oxide (ZnO) and molybdenum trioxide (MoO3) nanowires were prepared via the hydrothermal method. Then as‐prepared ZnO and MoO3 nanowires were fabricated to form ZnO/MoO3 compound nanostructure. ZnO/MoO3 compounds were incorporated into polypropylene (PP) with various loadings by melt blending. The D‐Optimal mixing design in Design‐Expert software was employed to study the effects of ZnO/MoO3 compound content on flame retardancy and mechanical properties of nanocomposites. Information on performance of thermal stability and flame retardancy of PP/ZnO/MoO3 nanocomposites was obtained through thermogravimetric analysis, cone calorimeter tests, and limiting oxygen index (LOI). The results reflected that the synthesized ZnO/MoO3 compound possessed high thermal stability and flame retardancy. The addition of 15 wt % ZnO nanowires and 13 wt % MoO3 nanowires increased LOI from 18.2 to 23.0%. Meanwhile, the tensile strength of the PP/ZnO/MoO3 nanocomposite decreased by 13.8% and the elongation at break of the PP nanocomposite increased by 20.4% compared with pure PP. Response surface analysis results also indicated that the loading of ZnO/MoO3 compound had an influence on the mechanical properties and flame retardancy of PP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48312.

Stabilized Molybdenum Trioxide Nanowires as Novel Ultrahigh-Capacity Cathode for Rechargeable Zinc Ion Battery.

Exploration of high‐performance cathode materials for rechargeable aqueous Zn ion batteries (ZIBs) is highly desirable. The potential of molybdenum trioxide (MoO3) in other electrochemical energy storage devices has been revealed but held understudied in ZIBs. Herein, a demonstration of orthorhombic MoO3 as an ultrahigh‐capacity cathode material in ZIBs is presented. The energy storage mechanism of the MoO3 nanowires based on Zn2+ intercalation/deintercalation and its electrochemical instability mechanism are particularly investigated and elucidated. The severe capacity decay of the MoO3 nanowires during charging/discharging cycles arises from the dissolution and the structural collapse of MoO3 in aqueous electrolyte. To this end, an effective strategy to stabilize MoO3 nanowires by using a quasi‐solid‐state poly(vinyl alcohol)(PVA)/ZnCl2 gel electrolyte to replace the aqueous electrolyte is developed. The capacity retention of the assembled ZIBs after 400 charge/discharge cycles at 6.0 A g−1 is significantly boosted, from 27.1% (in aqueous electrolyte) to 70.4% (in gel electrolyte). More remarkably, the stabilized quasi‐solid‐state ZIBs achieve an attracting areal capacity of 2.65 mAh cm−2 and a gravimetric capacity of 241.3 mAh g−1 at 0.4 A g−1, outperforming most of recently reported ZIBs.

Fe containing MoO3 nanowires grown along the [110] direction and their fast selective adsorption of quasi-phenothiazine dyes

Herein, MoO3 nanowires (Fe–MoO3 NWs) along the [110] direction were successfully synthesized in the presence of Fe3+ cations.

Transforming layered MoS2 into functional MoO2 nanowires.

A new in situ synthesis method for the growth of MoO2 nanowires via controlled thermal oxidation of MoS2 flakes is presented, going from a 2D transition metal chalcogenide to a transition metal oxide nanostructure. The wire growth is performed under an optical microscope using a heating stage with adjustable atmospheric conditions. In contrast to prevalent syntheses, this templated growth leads to highly directional wires along defined MoS2 crystallographic directions. We examine the growth kinetics of the wires in dependence of the process temperature. In the temperature regime from 650 °C to 710 °C high quality MoO2 nanowires are formed in a reaction-limited growth process with an activation energy of 596 kJ mol-1. The functional properties of the nanowires are studied by a combination of in situ electron microscopy techniques. Four point measurements in an SEM reveal outstanding metal-like behavior of the nanowires with resistivity values as low as 3.5 × 10-6 Ω m. Surprisingly, junctions between intergrown nanowires show hardly any increase in resistivity which can be attributed to the well-defined orientational relationship of the nanowires resulting from their templated growth on MoS2. Elastic properties of the nanowires are studied by complementary in situ bending and resonance measurements in SEM yielding consistent values of 383 GPa for the Young's modulus. Finally, field emission of single MoO2 nanowires is studied in situ inside the TEM, and an emission current of 500 nA is achieved. The combination of simple synthesis route with outstanding functional properties make the MoO2 nanowires promising candidates for functional devices in the field of novel 1D-oxide/2D-chalcogenide hybrids. The presented synthesis can be generalized and applied to other metal chalcogenides such as WS2, as well.

Facile construction of MoO3@ZIF-8 core-shell nanorods for efficient photoreduction of aqueous Cr (VI)

Recently, hexavalent chromium (Cr(VI)) in wastewater has become a threat to the ecosystem and human health. The synthesis of high-performance and recyclable photocatalysts still remains a challenge. The photoreduction efficiency of Cr(VI) is inhibited by the high rate of recombination of electron-hole pairs and the low adsorption capacity of Cr(VI). In this study, three-dimensional (3D) MoO3/ZIF-8 core-shell nanorod composite photocatalysts were prepared via a facile two-step method and applied to the reduction of Cr(VI). The chemical state of the elements, microstructure, surface elements, and optical properties of the MoO3/ZIF-8 core-shell nanorods were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy. The as-prepared MoO3@ZIF-8 catalysts displayed superior photocatalytic activity for Cr(VI) reduction under visible light, compared to the pure ZIF-8 and MoO3 nanowires. Further, MoO3@ZIF-8 (with 15% of ZIF-8) exhibited the best photocatalytic activity, and promoted 100% reduction of Cr(VI) (15 mg L−1) within 45 min. The 3-D core-shell structure not only provided a large surface area, but also separated the electron-hole pairs effectively. The photocatalytic activity of the composite remained almost unchanged after four cycles. The mechanism of Cr(VI) reduction is also discussed in detail.

Co-N-doped MoO2 modified carbon felt cathode for removal of EDTA-Ni in electro-Fenton process.

Metal ions removal is inhibited in aqueous solution containing ethylenediaminetetraacetic acid (EDTA). In this study, the non-noble metals-based Co-N-doped MoO2 nanowires (Co-N-MoO2) were successfully synthesized using cyanamide and Co(Ac)2 as precursors by pyrolysis, then immobilized on carbon felt (CF), and firstly used as cathode to remove EDTA-Ni complex through oxygen reduction reaction (ORR) in electro-Fenton (EF) process. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that a synergetic coupling effect of doping of N and Co induced structural modifications of MoO2 lattice, and produced more lattice defects. The electrochemical analysis results showed that the superior ORR electrochemical catalysis activities were obtained at pH = 3 with the lowest cathodic peak potentials (- 0.157V vs. Ag/AgCl), the highest electrochemical active surface area (EASA: 3.971mCcm-2), the extraordinarily high of the ring current (35.5μA) and high H2O2 yield (> 20%). Under the optimum conditions, about 68% of EDTA-Ni was removed with the Co-N-MoO2/CF as cathode after 120min with lower specific energy consumption (0.0226kWhmg-1 (DOC)) in EF system. Mechanism analysis indicated that the production of strong oxidizing property of hydroxyl radical (•OH) on the cathode played an important role in the removal of EDTA-Ni in the EF process, synergetic effect of cobalt and nitrogen co-doped could facilitate the high generation of H2O2, which greatly promote the formation of •OH. The EF system with Co-N-MoO2/CF cathode has a potential for breaking metal-complex with good stability, showing that this cathode is a candidate for application for applications in EAPOs.

Bimetallic AuPd alloy nanoparticles deposited on MoO3 nanowires for enhanced visible-light driven trichloroethylene degradation

Photocatalytic oxidation reactions are regarded as promising green methods for the photodegradation of volatile organic compounds such as trichloroethylene. However, the low efficiency and selectivity of the existing photocatalysts limit practical applications of this technique. In this work, MoO3 nanowires were easily decorated with well-dispersed bimetallic Au–Pd alloyed nanoparticles (AuPd NPs) by a two-step wet-chemical strategy (hydrothermal and chemical reduction). The morphology, size, crystal structures, and mechanism of operation of the photocatalysts were investigated by a series of techniques (X-ray diffraction, scanning and transmission electron microscopy, and photoluminescence spectroscopy, etc.). Deposition of the AuPd NPs on the surface of the MoO3 nanowires led to a dramatic enhancement (11.5 times higher than that of the pure MoO3 nanowires) of the photocatalytic activity of the synthesized photocatalysts. This remarkable improvement of the activity can be attributed to the synergistic effect between Au and Pd NPs, which results in effective separation of the electron and holes and promotes the charge-separation efficiency. The enlarged specific surface area and enhanced stability of the catalysts also resulted in excellent photocatalytic performance. The developed photocatalysts are promising for the removal of volatile organic compounds.

Catalyst free single-step processes to grow crystalline MoO3 nanowires by reactive sputtering method

In this paper for the first time, we report a single-step catalyst free method to grow crystalline molybdenum oxide nanowires over a large area using a reactive DC sputtering technique. We demonstrate that the shape and size of the nanostructures can be tuned by choosing the appropriate temperature and sputtering power as controlled parameters. A pin-like nanowire structure was observed at 400 °C, which subsequently was converted to nanowires (NWs) at 500 °C. An increase in the temperature to 600 °C converted the NWs to a rough film. In addition, the length of the nanowires was increased by performing the deposition for a longer time. Furthermore, the effect of the sputtering power on the transformation of the shape and size of the nanostructures was shown. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the high crystalline nature of the well grown NWs. The present study will be useful to grow various shaped and sized MoO3 nanostructures over a large area for future optoelectronic applications including solar cells and photodetectors.

Oxygen-deficient and nitrogen-doped MnO2 nanowire-reduced graphene oxide–cellulose nanofibril aerogel electrodes for high-performance asymmetric supercapacitors

Oxygen vacancies and nitrogen doping dramatically enhance the conductivity and capacitive performance of the MnO2 and MoO3 nanowires, leading to superb energy density and cycling stability of the asymmetric supercapacitors.

Structure Confined Porous Mo2C for Efficient Hydrogen Evolution

AbstractMolybdenum carbide (Mo2C) has been widely applied in energy conversion, electrocatalysis, and other electronic devices, but its nanostructure with certain morphology and porous structure is tough to control. In this work, 1D or 2D porous Mo2C nanostructures can be synthesized by carburizing cobalt‐based zeolitic imidazolate framework (ZIF‐67) cladding MoO3 nanowires or nanosheets hybrid structure under high temperature. The obtained 2D porous Mo2C shows a low onset overpotential (η = 25 and 36 mV) and a small Tafel slope (40 and 47 mV dec−1) in 0.1 m HClO4 and 0.1 m KOH as well as great stability. This work highlights a new strategy for the design and synthesis of porous nanostructure Mo2C electrocatalysts.

Electrochemical mediatorless detection of norepinephrine based on MoO3 nanowires

Achieving direct electron transfer between a biomolecule and modified electrodes is paramount for fabricating advanced biosensor devices. In this report, 1-dimensional (1D) MoO3 nanowires (NWs) were synthesized in a systematic growth evolution study. These MoO3 NWs, with the glassy carbon electrodes (GCEs), were further used as a mediatorless biosensor electrode for the detection of norepinephrine (NE) by cyclic voltammetry and chronoamperometry techniques. The MoO3 NWs/GCE had a magnificent response time of 2s in the electrochemical detection of NE, with a detection limit of 0.11μM. This excellent bio-electrochemical performance is attributed to its high catalytic activity and 1D microstructure, providing a path for electron transport and increasing their sensitivity. The MoO3 NWs/GCE also had a promising diffusion constant (D) value of 3.34×10−5cm2/s and a heterogeneous rate constant (k) of 8.03×10−4cm/s. The modified electrode possessed high stability, reproducibility, and selectivity.

Co-N-doped MoO2 nanowires as efficient electrocatalysts for the oxygen reduction reaction and hydrogen evolution reaction

Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are traditionally carried out with noble metals (such as Pt) as catalysts, respectively. Herein, Co-N-doped MoO2 nanowires catalysts were synthesized by employing MoO2 nanowires as templates and conductive substrates. The effect of nanowire structure and non-metal/metal doping on ORR and HER performance were scientific discussed. The most active Co-N-MoO2 (Co-N-doped MoO2) exhibited high ORR catalytic activity (an onset potential of +0.87V vs. RHE, n values of 3.56 and 3.68, excellent electrochemical stability) and outstanding HER performance with a low overpotential (69mV vs. RHE), high electrochemical area and robust stability in 0.1M KOH, which are associated with the defined nanowires structure, and homogeneous doping of Co/N into MoO2 with numerous active sites.

Revelation of the Excellent Intrinsic Activity of MoS2|NiS|MoO3 Nanowires for Hydrogen Evolution Reaction in Alkaline Medium.

Loading an electrocatalyst on poorly conducting substrate can easily lead to undervaluation of its intrinsic property. In this study, the excellent activity of MoS2|NiS|MoO3 nanowires for hydrogen evolution is revealed. The precursor NiMoO4 synthesized on chemically polished Ti foil can be successfully converted to MoS2|NiS|MoO3 catalyst via gas-phase sulfurization. Without deep polish in sulfuric acid for 2 h, the as-synthesized materials do not show competitive results. After sulfurization, the surface morphology of the precursor is transformed into rough features, and the peripheries of these electrocatalysts are coated by multilayered and misaligned MoS2 with a high density of active sites and conductive component NiS. Further analysis shows that defect MoO3 is embedded inside each nanowire, which may facilitate fast electron transfer. Such nanostructured architecture shows promising results for hydrogen evolution reaction in alkaline medium with only 91 mV overpotential for the current density of 10 mA cm-2 and robust long-term stability during more than 20 h of tests.

Rapid hydrogen sensing response and aging of α-MoO3 nanowires paper sensor

In order to improve the hydrogen sensing of transition metal oxide nanomaterials at room temperature, MoO3 nanowire paper was prepared and used as a hydrogen sensing materials on substrate. In this paper, orthorhombic phase, ultra-long (∼1 mm) MoO3 nanowires were synthesized through conventional hydrothermal method at 260 °C for 96 h. A flexible nanowires paper with size of 200 mm × 300 mm was obtained by further self-assembly formation process of pure α-MoO3 nanowires in aqueous solution on hydrophobic substrate, and the thickness of paper can be controlled depend on the concentration of disperse nanowires. A novel hydrogen sensor with sensing area of 10 mm × 10 mm was obtained after Pt interdigital electrodes (IDE) deposited on the surface of α-MoO3 nanowires paper and transferred into ceramic circuit board (CCB) without any surface modification. The response and recovery time are about 3.0 and 2.7 s toward 1.5% H2, respectively. The sensors also show good selectivity toward H2 against other reduce gas, such as C2H5OH, CO and CH4. Large amounts of the porous structures and high specific surface of nanowires paper is beneficial to the absorption of oxygen molecules, which would lead to the high sensitivity, fast response and recovery speed of sensor at room temperature. MoO3 nanowires paper sensors have excellent stability and reliability, which could work for 5.56 years at room temperature.

A MoO2 sheet as a promising electrode material: ultrafast Li-diffusion and astonishing Li-storage capacity

The potential of MoO2 crystal as an electrode material is reported, and nanostructural MoO2 systems, including nanoparticles, nanospheres, nanobelts and nanowires, were synthesized and proved to be advanced electrode materials. A two-dimensional (2D) geometric structure represents an extreme of surface-to-volume ratio, and thus is more suitable as an electrode material in general. Stimulated by the recent fabrication of 2D MoO2, we adopted an ab initio molecular dynamics simulation and density functional theory calculation to study the stability and electrochemical properties of a MoO2 sheet. Identified by a phonon dispersion curve and potential energy curve calculations, the MoO2 sheet proved to be dynamically and thermally stable. After lithiation, similar to most promising 2D structures, we found that a Li atom can strongly adsorb on a MoO2 sheet, and the lithiated MoO2 sheet presented excellent metallic properties. Note that, compared with most promising 2D structures, we unexpectedly revealed that the diffusion barrier of the Li atom on the MoO2 sheet was much lower and the storage capacity of the MoO2 sheet was much larger. The calculated energy barrier for the diffusion of Li on the MoO2 sheet was only 75 meV, and, due to multilayer adsorption, the theoretical capacity of the MoO2 sheet can reach up to 2513 mA h g−1. Benefiting from general properties, such as strong Li-binding and excellent conductivity, and unique phenomena, such as ultrafast diffusion capacity and astonishing storage capacity, we highlight a new promising electrode material for the Li-ion battery.

Porous MoO2 nanowires as stable and high-rate negative electrodes for electrochemical capacitors.

Free-standing porous MoO2 nanowires with extraordinary capacitive performance are developed as high-performance electrodes for electrochemical capacitors. The as-obtained MoO2 electrode exhibits a remarkable capacitance of 424.4 mF cm-2 with excellent electrochemical durability (no capacitance decay after 10 000 cycles at various scan rates).

Integrated 3D self-supported Ni decorated MoO2 nanowires as highly efficient electrocatalysts for ultra-highly stable and large-current-density hydrogen evolution

Ni decorated MoO2 nanowires gives platinum-like HER activity and unprecedented stability over 320 hours even in the order of 1000 mA cm−2 in alkaline solution.

In situ TEM observation of dissolution and regrowth dynamics of MoO2 nanowires under oxygen

Direct observation of the dissolution behavior of nanomaterials could provide fundamental insight to understanding their anisotropic properties and stability. The dissolution mechanism in solution and vacuum has been well documented. However, the gas-involved dissolution and regrowth have seldom been explored and the mechanisms remain elusive. We report herein, an in situ TEM study of the dissolution and regrowth dynamics of MoO2 nanowires under oxygen using environmental transmission electron microscopy (ETEM). For the first time, oscillatory dissolution on the nanowire tip is revealed, and, intriguingly, simultaneous layer-by-layer regrowth on the sidewall facets is observed, leading to a shorter and wider nanowire. Combined with first-principles calculations, we found that electron beam irradiation caused oxygen loss in the tip facets, which resulted in changing the preferential growth facets and drove the morphology reshaping.

Carbon Coated MoO3 Nanowires/Graphene oxide Ternary Nanocomposite for High-Performance Supercapacitors

A ternary nanocomposite of molybdenum trioxide (α-MoO3) nanowires coated with a thin layer of carbon, which is intertwined with graphene oxide is synthesized by hydrothermal and ultrasonication route. It is found that high conductivity of carbon coated MoO3 nanowires is further increased by introducing the graphene sheets. The ternary nanocomposite (rGO/MoO3@C) exhibits high specific capacitance, excellent cyclic stability compared to the carbon coated MoO3 (MoO3@C) and virginal MoO3 nanowires due to the synergistic effect of carbon layer and graphene. The electrochemical impedance measurements show that rGO/MoO3@C nanocomposite have lower charge transfer resistance as compared to MoO3@C and MoO3 nanowires electrodes. Two probe electrical conductivity (I–V) measurements confirm the enhanced conductivity of rGO/MoO3@C nanocomposite relative to MoO3@C and bare MoO3 nanowires. The electrical and electrochemical measurements indicate that the rGO/MoO3@C nanocomposite is promising candidate for energy storage applications.