MoO3 Nanowires Research Articles

Self-supporting Co-MoOx@N-doped carbon/expanded graphite paper for efficient water splitting catalyst

Molybdenum oxides are widely used as electrocatalysts due to their polymetallic oxidation state, abundant reactive sites and low production cost. However, the low electrical conductivity and easy agglomeration has limited their practical application. Here, MoO3 nanowires encapsulated with ZIF-67 polyhedra were grown in situ on expanded graphite paper (EGP) by a simple hydrothermal synthesis method, and then the precursors were pyrolyzed to obtain self-supported Co-MoOx@N-doped carbon/EGP composites. Thanks to the three-dimensional porous structure and the synergistic effect of Co and multi-valance MoOx, the as-prepared Co-MoOx@N-doped carbon/EGP exhibits the excellent performances of OER (η10 = 256 mV) and HER (η10 = 138 mV), and a small Tafel slope and good durability. Furthermore, the assembled water splitting device achieved a current density of 10 mA cm−2 at a low voltage of 1.62 V and the excellent stability after 24 h continuous water splitting.

Application and characterization of a novel PVDF-HFP/PVP polymer composite with MoO3 nanowires as a protective coating for wood

The coatings on wood must sometimes give aesthetic and basic protection to wooden elements and prevent the development and transmission of microorganisms. Several polymers containing different nanoparticles have already been offered to day for this purpose. The research presents a novel poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/polyvinylpyrrolidone (PVP) polymer composite with MoO3 nanowires with the ability to form coating films on wood. The films of the developed coating exhibit elastic behaviour, which depends on the coating film thickness [tested wet film thicknesses (90, 180 and 360) µm]. The coating showed the ability to interact well with the surface of common beech (Fagus sylvatica L.) wood, in terms of wetting (contact angles of 15.6°), fast spilling on the surface, good penetration of the coating in wood structure and formation of up to 40 µm-thick films with excellent pull-off adhesion strength (6 MPa). An increased roughness of wood coated with C + MoO3 was a consequence of wood etching by the dimethylformamide solvent present in the coating. Moreover, the presence of C + MoO3 on wood made it considerably more hydrophobic, with contact angle of water raising to 123° from initially 46° measured on uncoated wood. The irradiation of wood surfaces with ultra-violet light resulted in visible colour changes on both uncoated and coated wood. The wood coated with C + MoO3 has a good resistance to water, alcohol and dry heat (grade 3 to 4). The antimicrobial testing showed that the presence of MoO3 in the coating plays an important role in the resistance of the coated wood to blue-stain fungi and mould development. The developed PVDF-HFP/PVP/MoO3 coating has an excellent ability to interact with the wood surface and has the potential to be used as a protection for wood in sensitive environments.

Synthesis of Epitaxial MoS2/MoO2 Core-Shell Nanowires by Two-Step Chemical Vapor Deposition with Turbulent Flow and Their Physical Properties.

MoO2 nanowires (NWs), MoO2/MoS2 core-shell NWs, and MoS2 nanotubes (NTs) were synthesized by the turbulent flow chemical vapor deposition of MoO2 using MoO3, followed by sulfurization in the sulfur gas flow. The involvement of MoO x suboxide is suggested by density functional theory (DFT) calculations of the surface energies of MoO2. The thickness of the MoS2 layers can be controlled by precise tuning of sulfur vapor flow and temperatures. MoS2 had an armchair-type winding topology due to the epitaxial relation with the MoO2 NW surface. A single ∼ few-layer MoO2/MoS2 core-shell structure showed photoluminescence after the treatment with a superacid. The resistivities of an individual MoO2 NW and a MoS2 NT were measured, and they showed metallic and semiconducting resistivity-temperature relationships, respectively.

Free‐Standing Pearl‐Chains‐like MoO2 Hierarchical Nanowires with Enhanced Pseudocapacitive Energy Storage

AbstractNanostructure construction is an efficient strategy to achieve high pseudocapacitive behavior with excellent charge storing ability and good cyclability. In this work, we constructed a novel pearl‐chains‐like MoO2 nanowires (MoO2 PNWs) on nickel foam via a facile solvothermal method. The formation mechanism can be inferred from the oriented growth and self‐assembly process under the contribution of benzyl alcohol and sodium dodecyl sulfate (SDS). The MoO2 PNWs deliver a high specific capacitance of 1254 F g−1 at 1 A g−1, outstanding rate performance with 73 % retention from 1 to 20 A g−1, and 91.5 % retention of capacitance after 2000 cycles at 10 A g−1. The outstanding performance is attributed to the continuous electron conductive path, short ion diffusion length and enlarged electrode‐electrolyte interface provided by the pearl chains like hierarchical nanowire, and good electrical conductivity owing to the free‐standing structures.

Fabrication of MoO3 Nanowires/MXene@CC hybrid as highly conductive and flexible electrode for next-generation supercapacitors applications

A facile hydrothermal and ultrasonication method used to synthesize the MoO3 nanowires (NWs) intercalated MXene composite. MoO3/MXene nanocomposite was fabricated on carbon cloth (CC) to prepare the MoO3/MXene@CC electrode. Intercalation of MoO3 NWs in MXene layers prevented the collapse of Al etched MXene sheets and enhanced the conductive channels in ultimate nanostructures. When applied for electrochemical measurements, MoO3/MXene@CC significantly improved specific capacity. For pristine MoO3@CC, the specific capacitance was calculated as 466.7 F/g (at 5 mV/s) and 442 F/g (at 1 A/g) from cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) data, respectively. Meanwhile, MoO3/MXene@CC showed a high specific capacitance of 783.4 F/g at 5 mV/s and 775 F/g at 1 A/g under the CV and GCD measurements. Electrochemical impedance spectroscopy (EIS) data evaluated the resistivity performance of MoO3/MXene@CC. The calculated equivalent series resistance (RES) and charge transfer resistance (RCT) values for MoO3/MXene@CC were 5.4 Ω and 31.3 Ω, respectively. Moreover, MoO3/MXene@CC showed excellent cyclic stability with 96.4% retention of its initial specific capacitance even after 6000 cycles. Results suggest that the prepared MoO3/MXene@CC hybrid can be used as an efficient electrode material for electrochemical energy storage applications.

Hierarchical ternary composites using coaxial polyphosphazene-coated MoO3 nanowires as substrate for advanced supercapacitors

Supercapacitors with outstanding merits including extraordinary cycle stability, safety and high power density are complementary energy storage devices to batteries. The construction of one-dimensional hierarchical ternary composites is conducive to the synergy between different materials, and can be used to assemble high-performance asymmetric supercapacitors. To this end, coaxial polyphosphazene (PZS)-coated MoO3 nanowires are used as the substrate, and CoFe layered double hydroxide (CoFe-LDH) or Ni(OH)2 is grown in-situ on the nanowires followed by high-heat treatment to form MoO3 NWs @ PZSC / CoFe2O4 and MoO3 NWs @ PZSC / NiO as the negative and positive electrodes, respectively, as confirmed by a series of spectroscopic measurements. Electrochemical characterizations confirm the excellent electrochemical performance of both electrode materials. The supercapacitors exhibit a potential window of 1.7 V in KOH aqueous electrolyte, with the maximum specific capacity of 48.55 mAh g−1 at 2 A g−1 and the energy density of 41.27 Wh kg−1 at 1707.72 W kg−1. This work provides an applicable approach to utilize the synergistic effect between PZSC and transition metal oxides in order to enhance the performance of supercapacitors.

Ultrahigh sensitive and selective triethylamine sensor based on h-BN modified MoO3 nanowires

In this work, a novel structure of 1D MoO3 nanowires wrapped by 2D hexagonal boron nitride (h-BN) was synthesized via a simple solvothermal method with subsequent annealing process for triethylamine (TEA) detection. The samples were characterized by XPS, SEM, HRTEM and N2 adsorption-desorption. Gas sensing performance test results illuminate that the typical 2 wt% h-BN/MoO3 sensor possesses an ultrahigh response (8616) toward 500 ppm TEA. The promoted sensing performance of TEA may be caused by the forming of heterojunction between h-BN and MoO3, the increased specific surface area of h-BN modification, providing a highly active sites for the adsorption of TEA gas, which greatly enhance the response of the sensor. The adsorption energy of a single oxygen molecule on MoO3 (010) surface was calculated by DFT, indicating the most stable site is the terminal oxygen position (Top O-1), with an adsorption energy of −2.075 eV. This work provides an inspiration to design highly efficient TEA gas sensor on basis of h-BN/MoO3 nanocomposites.

Calcination effects of 2D molybdenum disulfides

Designing earth abundant, cost effective 2D-layered materials capable replace graphene and precious metal nanoparticulated arrays in optoelectronic and catalytically working devices are among global challenges. The key factor for these applications is thermostability of MoS2 layered nanostructures. Herein, calcination effects of hydrothermally synthesized MoS2 and commercial MoS2 crystal as well as 1.7 and 6.0 μm-sized MoS2 powders were studied in the synthetic air and argon gas environments by thermogravimetric and differential thermal analysis, mass spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. Markedly lower thermal stability of hydrothermally synthesized 2D MoS2 species both in the synthetic air and Ar environments compared to MoS2 crystal and commercial powders have been established and transformations up to 1000 °C estimated. It was determined that oxidation of hydrothermally synthesized MoS2 films in the synthetic air starts below 200 °C and results in a transformation of nanoplatelet-shaped films to MoO3 sheets and nanowires at higher temperatures. The annealing in argon atmosphere, however, resulted in the MoS2 crystallinity increase, S/Mo ratio reduction, and temperature-dependent transition of 3R-MoS2 phase to 2H-MoS2 no influencing markedly the morphology of nanoplatelets up to 520 °C.

MoO2 Nanowire Electrochemically Decorated Graphene Additively Manufactured Supercapacitor Platforms

AbstractAdditively manufactured (AM) supercapacitor platforms are fabricated from bespoke filaments, which are comprised of electro‐conductive graphene (20 wt%) incorporated polylactic acid (80 wt%), via fused deposition modeling and denoted as G/AMEs. The G/AMEs are shown to be capable of acting as a template for the electrodeposition of metals/metal oxides, in particular MoO2 nanowires (MoO2‐G/AMEs), which are subsequently explored as a capacitor within 1 m H2SO4, 1‐butyl‐3‐methylimidazolium hexafluorophosphate, and 1‐butyl‐3‐methylimidazolium tetrafluoroborate. Optimization of the MoO2‐G/AMEs demonstrates capacitance up to 1212 F g–1 when used in a symmetric arrangement. The material science described herein represents a significant enhancement in unlocking AMs potential as a valid manufacturing route for device level capacitance architectures.

Thermal diffusivity of molybdenum oxide nanowire film: A photothermal beam deflection study

The paper reports the preparation of thin film with MoO3 nanowires (NWs) by the doctor blade method and the study of its thermal diffusivity (α) by the sensitive photothermal beam deflection (PTD) method. When the Field Emission Scanning Electron Microscopic and Atomic Force Microscopic analysis unveil its morphology as NW bundles, the X-ray diffraction analysis reveals the structure to be orthorhombic. The NWs formed are of diameter ~ 20 nm and length up to 5 μm. The standardization of the transverse PTD setup is done by determining the value of α of iron, which agrees well with literature reports. The thermal diffusivity of MoO3 NW film is obtained as 0.0036 cm2/s, which is 9.48% of its bulk counterpart. The reduction in the thermal diffusivity of NW makes it a suitable candidate for thermoelectric applications.

Rapid Synthesis of Various Electrocatalysts on Ni Foam Using a Universal and Facile Induction Heating Method for Efficient Water Splitting

AbstractElectrocatalytic water splitting for the production of hydrogen proves to be effective and available. In general, the thermal radiation synthesis usually involves a slow heating and cooling process. Here, a high‐frequency induction heating (IH) is employed to rapidly prepare various self‐supported electrocatalysts grown on Ni foam (NF) in liquid‐ and gas‐phase within 1–3 min. The NF not only serves as an in situ heating medium, but also as a growth substrate. The as‐synthesized Ni nanoparticles anchored on MoO2 nanowires supported on NF (Ni‐MoO2/NF‐IH) enable catalysis of hydrogen evolution reaction (HER), showing a low overpotential of −39 mV (10 mA cm−2) and maintaining the stability of 12 h in alkaline condition. Moreover, the NiFe layered double hydroxide (NiFe LDH/NF‐IH) is also synthesized via IH and affords outstanding oxygen evolution reaction (OER) activity with an overpotential of 246 mV (10 mA cm−2). The Ni‐MoO2/NF‐IH and NiFe LDH/NF‐IH are assembled to construct a two‐electrode system, where a small cell voltage of ≈1.50 V enables a current density of 10 mA cm−2. More importantly, this IH method is also available to rapidly synthesize other freestanding electrocatalysts on NF, such as transition metal hydroxides and metal nitrides.

PEDOT:PSS-glued MoO3nanowire network for all-solid-state flexible transparent supercapacitors

Flexible transparent supercapacitors (FTSCs) are essential for the development of next-generation transparent electronics, however, a significant challenge is to achieve high-areal-capacitance FTSCs without sacrificing optical transparency. Herein, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-glued MoO3 nanowires anchored on the Ag nanofiber (AgNF) network are employed as FTSC film electrodes, in which the AgNF network provides primary conducting pathways and guarantees rapid electron transport, while wide-bandgap semiconductor MoO3 nanowires glued by the ultrathin PEDOT:PSS layer provide abundant redox-active sites to store energy. Benefiting from the PEDOT:PSS as the conducting glue to promote the connection at the junctions between AgNFs and MoO3 nanowires, the as-prepared AgNFs/MoO3/PEDOT:PSS (AMP) film electrode demonstrates a high transmittance (82.8%) and large areal capacitance (15.7 mF cm−2), and has outperformed all the transparent conductive films known to date. Even after 11 000 charge/discharge cycles, the capacitance still remains at 92.4% of the initial value. The assembled all-solid-state FTSC device delivers an energy density of 0.623 μW h cm−2, a power density of 40 μW cm−2, and excellent mechanical robustness, implying a great potential in high performance FTSCs.

In-vitro toxicity of molybdenum trioxide nanoparticles on human keratinocytes

Molybdenum trioxide (MoO3) nanoparticles (NPs) embedded in polymer films have been proposed as a cheap way of producing antibacterial coatings on external surfaces. Recently, we synthesized MoO3 nanowires in a unique shape and degree of anisotropy, which enables their fast water dissolution and quick antimicrobial reaction. Potential human health risks following the exposure to MoO3 NPs however need to be assessed prior their wide use. We therefore, investigated the biological effect of these newly synthesized MoO3 NPs on the human keratinocyte cell line HaCaT, used here as a model for the human skin. Exposure of HaCaT cells to 1 mg/mL MoO3 NPs concentration for 1 h showed no effect on cell survival, had no influence on reactive oxygen species production, expression of proteins involved in antioxidant defense, secretion of pro-inflammatory cytokines, nor induced DNA damage. Interestingly however, ERK and p38 MAP kinases were activated, and upon longer time exposure, induced a moderate release of the pro-inflammatory cytokine interleukin 6, increased DNA damage and increased the level of caspase independent cell death. Our study indicates that exposing HaCaT cells to antibacterial MoO3 NPs water-based solution in durations less than 1 h exhibits no cytotoxicity, but rather triggers cell signalling involved in cell survival and inflammation; which should be taken into consideration when evaluating MoO3 NPs for medical applications.

Polymer Blend Containing MoO3 Nanowires with Antibacterial Activity against Staphylococcus epidermidis ATCC 12228

Antibacterial activity of a polymer nanocomposite containing water-soluble poly(ethylene oxide) (PEO), water insoluble poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and MoO3 nanowires or MoO3 microparticles as antibacterial active substances is reported. The UV-vis absorption method was used for the illumination of dissolving of the MoO3 particles of different size and morphology in water. Dissolving of MoO3 nanowires (1 mg ml-1) decreases pH bellow 3.6 in only 3 min and below 3 in 15 min, while dissolving of the PEO/PVDF-HFP/MoO3 nanowires coating (5 mg ml-1) decreases pH bellow 3.6 in 90 min. These coatings completely destroy the Staphylococcus epidermidis ATCC 12228 bacterial strain within 3 h. The proposed applications are antibacterial protective coatings of contact surfaces.

Synergistic enhancement effect of MoO3@Ag hybrid nanostructures for boosting selective detection sensitivity.

An ex situ method was used to synthesize noble metals and metal oxide composite materials, due to the selective adsorption properties of metal oxides, the adsorption of different probe molecules by this composite structure had been studied. In the ex situ approach, we use (3-aminopropyl) diethoxy methylsilane (ATES) as a coupling agent which is easy for noble metal nanoparticles deposited on metallic oxide nanomaterials. The Raman scattering (SERS) substrate of 1D MoO3 nanowires (MoO3-NWs) @Ag nanoparticles (Ag-NPs) hybrid surface had been fabricated. Several parameters are presented in the following which influences the morphology of self-assembly and SERS activity: (i) coupling agent of ATES, (ii) ATES content (iii) Ag-NPs content. The finite difference time domain (FDTD) method is to explain the enhancement mechanism distribution of the hybrid substrate. Different probe molecules (R6G, Methylene Blue, Crystal Violet, and 4-ATP) have been adsorbed for SERS tests. Improved principle component analysis (PCA) is adopted to obtain the minimum detection limit of probe molecules. Through the DFT calculation, different absorption strengths between the target molecules and the MoO3(010) surface have been illustrated, which is also the main reason for the selective enhancement effect of MoO3@Ag hybrid nanostructures. This paper might propose a method to prepare such enhancement substrate based on the selective absorption properties of oxide semiconductors.

Electrochemical Decoration of Additively Manufactured Graphene Macroelectrodes with MoO2 Nanowires: An Approach to Demonstrate the Surface Morphology

Additive manufacturing (AM) provides a unique platform for the rapid design and fabrication of complex structures. Printed structures can be used as is or as templates to be decorated with electrochemical deposited nanomaterials, which may be utilised as electrocatalytic sensing platforms. Novel methods are required to determine the electrochemical deposited morphology present on the electrode surfaces. Additively manufactured graphene macroelectrodes (AM-GMs) were fabricated using a commercially available feedstock and molybdenum (di)oxide (MoO2) was successfully electrochemically deposited onto the electrode surface. The electrochemically deposited MoO2 was analysed using scanning electron microscopy (SEM), optical interferometry, Raman spectroscopy and multifractal analysis (MFA). Although the electrochemical deposition of MoO2 nanowires were clearly visible using SEM, MFA enabled quantification of the MoO2 nanowires, deposited at a variety of time points (20 – 300 s). MFA was utilised to generate quantitative data, derived from ƒ(α) curves, to determine the area of the electrochemical deposited MoO2 nanowires, including coverage, density, dispersion and clustering. The AM-GMs which were subjected to 300 s (maximum time period) of MoO2 electrodeposition demonstrated the greatest percentage area coverage (20.14 %). The use of such mathematical systems offers an inexpensive method to characterise the parameters of electrochemically-deposited materials.

Synthesis of Novel 1T/2H-MoS2 from MoO3 Nanowires with Enhanced Photocatalytic Performance.

Metallic 1T-phase MoS2 is a newly emerging and attractive catalyst since it has more available active sites and high carrier mobility in comparison with its widely used counterpart of semiconducting 2H-MoS2. Herein, 1T/2H-MoS2(N) (N: MoO3 nanowires were used to prepare 1T/2H-MoS2) was synthesized by using molybdenum trioxide (MoO3) nanowires as the starting material and applied in the photodegradation of antibiotic residue in water. Enhanced photocatalytic performance was observed on the obtained 1T/2H-MoS2(N), which was 2.8 and 1.3 times higher than those on 1T/2H-MoS2(P) (P: commercial MoO3 powder was used to prepare 1T/2H-MoS2) and 2H-MoS2, respectively. The active component responsible for the photodegradation was detected and a reaction mechanism is proposed.

Synthesis and resistivity of topological metal MoP nanostructures

Due to the increased surface to volume ratios, topological nanomaterials can enhance contributions from the topological surface states in transport measurements, which is critical for device applications that exploit the topological properties. It is particularly important for topological semimetals in which bulk carriers are unavoidable to make them into nanostructures to reveal the nature of the topological surface states, such as the Fermi arcs or nodal lines. Here, we report the nanostructure synthesis of the recently discovered triple-point topological metal MoP by direct conversion of MoO3 nanostructures and study their transport properties. We observe that the initial size of the MoO3 templates critically determines the crystalline quality of the resulting MoP nanostructures: large MoO3 flakes lead to porous MoP flakes, while narrow MoO3 nanowires lead to MoP nanowires without pores. The size-dependent porosity observed in MoP nanostructures is attributed to the volume change during the conversion reaction and nanoscale confinement effects. For MoO3 nanowires with diameters less than 10 nm, the resulting MoP nanowires are single crystalline. The resistivity values of MoP nanostructures are higher than the reported values of MoP bulk crystals owing to the porous nature. However, despite the high porosity present in MoP flakes, the residual resistance ratio is ∼2 and the temperature-dependent resistivity curves do not show any strong surface or grain-boundary scattering. Demonstration of the facile synthesis of MoP nanostructures provides opportunities for careful investigations of the surface states in transport measurements and exploration of future electronic devices, including nanoscale interconnects.

Hexagonal Molybdenum Trioxide (h‐MoO3) as an Electrode Material for Rechargeable Aqueous Aluminum‐Ion Batteries

AbstractAqueous aluminum‐ion batteries are at an early development stage and there is a need to discover new electrode materials for the fabrication of high energy density devices. To address this issue, we investigate MoO3 nanowires as a possible electrode material for use in rechargeable Al‐ion batteries that can operate in aqueous conditions. We present a hexagonal structure of MoO3 microrods as an Al‐ion intercalation host material and show its first‐time use as a potential electrode for an aqueous Al‐ion battery system. This yields a discharge capacity of approximately 300 mAh g−1 for 150 cycles and around 90 % retention after 400 cycles at a current density of 3 A g−1. The utilization of this type of material and aqueous electrolytes guarantees both safety during operation and simple recycling of spent batteries.

Formation of two-dimensional MoS2 and one-dimensional MoO2 nanowire hybrids

Oxidation of two-dimensional (2D) transition metal dichalcogenides have received great interests because it significantly influences their electrical, optical, and catalytic properties. Monoclinic MoO2 nanowires grow along the zigzag direction of 2D MoS2 via thermal annealing at a high temperature with a low oxygen partial pressure. The hybrids of semiconducting 2D MoS2 and metallic 1D MoO2 nanowires have potential to be applied to various devices such as electrical devices, gas sensors, photodetectors, and catalysts.