Molybdenum Dioxide Nanosheets Research Articles

Anchoring cobalt molybdenum nickel alloy nanoparticles on molybdenum dioxide nanosheets as efficient and stable self-supported catalyst for overall water splitting at high current density

Developing bifunctional electrocatalysts with efficient and stable catalytic performance at high current density to improve the productivity of water splitting is important for relieving the environmental pollution and energy crisis. Herein, the Ni4Mo and Co3Mo alloy nanoparticles were anchored on MoO2 nanosheets (H-NMO/CMO/CF-450) by annealing the NiMoO4/CoMoO4/CF (CF: self-made cobalt foam) under Ar/H2 atmosphere. Benefitting from the nanosheets structure, synergistic effect of the alloys, existence of oxygen vacancy and the cobalt foam with smaller pore sizes as conductive substrate, the self-supported H-NMO/CMO/CF-450 catalyst demonstrates outstanding electrocatalytic performance, which delivers small overpotential of 87 (270) mV at 100 (1000) mA·cm−2 for HER and 281 (336) mV at 100 (500) mA·cm−2 for OER in 1 M KOH. Meanwhile, the H-NMO/CMO/CF-450 catalyst is used as working electrodes for overall water splitting, which just require 1.46 V @ 10 mA·cm−2 and 1.71 V @ 100 mA·cm−2, respectively. More importantly, the H-NMO/CMO/CF-450 catalyst can stabilize for 300 h at 100 mA·cm−2 in both HER and OER. This research provides an idea for the preparation of stable and efficient catalysts at high current density.

Comprehensive study on the nonlinear optical response of MoO2 nanosheets in pulsed lasers

Molybdenum dioxide nanosheets (MoO2-NSs), as two-dimensional (2D) materials, have attracted broad attention owing to their high damage threshold, good stability, strong localized surface plasmon resonance (LSPR), affordability, and excellent physicochemical properties. In this work, we successfully synthesized high-quality MoO2-NSs through chemical vapor deposition synthesis method and characterized the morphology and structure of the prepared materials in detail. The saturable absorption characteristics of the MoO2-NSs were measured using Z-scan experiments for the first time. Additionally, the compact Q-switched laser and stable mode-locked laser were successfully realized based on a MoO2-NSs saturable absorber (SA). To the best of our knowledge, this is the first presentation of the application of MoO2-NSs SA in the field of ultrafast photonics. These findings indicate that high-quality MoO2-NSs can be an effective optical modulator for generating high-repetition-rate pulsed lasers, and exhibit promising potential applications in mode-locked ultrafast lasers.

Transparent, photothermal and stretchable alginate-based hydrogels for remote actuation and human motion sensing

Multifunctional hydrogels show potential applications in actuators and wearable sensors. However, it is still a challenge to develop a photothermal responsive conductive hydrogel with high transparency, mechanical properties, broad sensing range, and low-temperature resistance. In this work, a transparent, photothermal responsive, and highly stretchable alginate-based hydrogels was feasibly constructed by adding two-dimensional non-layered molybdenum dioxide nanosheets (2D-MoO2) to sodium alginate/polyacrylamide mixture and then soaking into the calcium chloride solution. The introduction of 2D-MoO2 renders the hydrogels excellent photothermal properties and controllable photomechanical deformation under near-infrared irradiation, while maintaining high transparency (~60 %).The calcium ions give the hydrogel excellent mechanics, conductivity, and freezing tolerance concurrently. The transparent hydrogel-based sensor shows wide sensing range (0–1800 %) and cycling stability in detecting deformations and real-time human motions even in harsh environments. Therefore, this work provides a new route for generating transparent multifunctional hydrogels towards the applications of remote actuation and strain sensing.

Physical Vapor Deposition Growth of Ultrathin Molybdenum Dioxide Nanosheets with Excellent Conductivity

A single crystal of 2D layered α‐MoO2 using a simple technique of physical vapor deposition (PVD) method is generated. By adjusting the growth temperature, the thickness of α‐MoO2 single crystals can be tuned to sub ten nanometers. High‐resolution transmission electron microscopy (HRTEM) images verified the atomic structural details of PVD grown orthorhombic MoO2 (α‐MoO2) nanosheet with high quality. Additionally, the unsaturated linear magnetic range (LMR) in the grown nanosheets is up to 5 T. Also, α‐MoO2 nanosheet with low defect displays excellent conductivity that is comparable to the metal silver. Thus, this new nanomaterial can show a promising application as a potential 2D conductor.

Thermal/Near-Infrared Light Dual-Responsive Reversible Two-Way Shape Memory cEVA/2D-MoO2 Composite for Multifunctional Applications.

Light-responsive reversible two-way shape memory polymers (2W-SMPs) are highly promising for many fields due to indirect heating, clean, and remote control. In this work, a composite with both thermal- and near-infrared (NIR) light-induced reversible two-way shape memory effect (2W-SME) is prepared by doping extremely little quantities of 2D non-layered molybdenum dioxide nanosheets (2D-MoO2 ) into semicrystalline poly(ethylene-co-vinyl acetate) (EVA) networks. This is the first report on light-induced reversible two-way shape memory composites employing 2D-MoO2 as photothermal fillers. Upon switching the NIR light on and off, due to the excellent photothermal feature and stability of 2D-MoO2 , the composite exhibits remarkable light-induced reversible 2W-SME. A light-driven actuator for sensing applications is designed based on the composite and the circuit, where the lamp acting as an alarm can raise and fade upon responding to NIR light. A completely flexible, fuel-free self-walking soft robot is designed based on the advantages of the light-responsive reversible 2W-SMPs. Additionally, the composite acting as a light-fueled crane is able to lift and lower a load that is 3846 times its own weight. The results demonstrate that the prepared composite has a promising prospect for applications as actuators, self-walking soft robot and crane.

A sandwich-type electrochemical immunosensor based on Au@Pd nanodendrite functionalized MoO2 nanosheet for highly sensitive detection of HBsAg

In this work, a sandwich-type electrochemical immunosensor was fabricated to the effective detection of hepatitis B surface antigen (HBsAg). The designed electrochemical immunosensor was based on Au core and Pd shell nanodendrites loaded on amino functionalized molybdenum dioxide nanosheets (Au@Pd NDS/NH2–MoO2 NSs) as the secondary antibody (Ab2) label and silver nanoparticles were loaded by electrodeposited (D-Ag NPs) on the surface of electrode as the platform. Because of the synergistic effect and abundant catalytic activity sites provided by surface dendrite structure, Au@Pd NDs were more effective than single gold and palladium nanoparticles in catalytic reduction of hydrogen peroxide (H2O2). MoO2 had the good catalytic capacity for reduction of H2O2 and favourable electrical conductivity. Hence, the obtained Au@Pd NDS/NH2–MoO2 NSs were more effective than Au@Pd NDs and NH2–MoO2 NSs in catalytic reduction of hydrogen peroxide attribute to a synergistic effect. Also, Ag NPs with admirable electrical conductivity and biocompatibility were used as sensing platforms and primary antibodies (Ab1) carriers, which can accelerate the electron transfer and improve the sensitivity of the immunosensor. Here, the proposed electrochemical immunosensor offered a wide linear interval from 10 fg mL−1 to 100 ng mL−1 and the lower limit of detection of 3.3 fg mL−1 (S/N = 3) for detection of HBsAg under optimal experimental conditions. Furthermore, the accuracy of the actual serum sample analysis was satisfactory, which showed that the electrochemical immunosensor possessed a good application prospect in clinical detection.

The intrinsic hydrogen evolution performance of 2D molybdenum carbide

A new approach for the synthesis of 2D molybdenum carbide single crystals through low-temperature carbonization of 2D molybdenum dioxide nanosheets.

Liquid phase exfoliation of MoO2 nanosheets for lithium ion battery applications.

Molybdenum dioxide (MoO2) is a layered material which shows promise for a number of applications in the electrochemical energy storage arena. Mostly studied as a bulk layered material, MoO2 has not previously been exfoliated in large quantities. Here we demonstrate the liquid phase exfoliation of MoO2 in the solvent isopropanol, yielding reasonable amounts of good quality nanosheets. However, we found that, when dispersed in isopropanol under ambient conditions, MoO2 nanosheets are gradually oxidized to higher oxides such as MoO3 over a period of days. Conversely, if the nanosheets are processed into dried films immediately after exfoliation, and before oxidation has had a chance to progress, the nanosheets are relatively stable under ambient conditions, remaining unoxidised unless the films are heated. We also found that MoO2 nanosheets can be size selected by controlled centrifugation and show size-dependent optical properties. This allows us to propose spectroscopic metrics which allow concentration- and size-estimation from extinction spectra. Finally, we found that liquid-exfoliated MoO2 nanosheets could be used to produce lithium ion battery anodes with capacities of up to 1140 mA h g−1.

Ultrathin Molybdenum Dioxide Nanosheets as Uniform and Reusable Surface-Enhanced Raman Spectroscopy Substrates with High Sensitivity.

Metal oxides have advantages over the traditional noble metals to be used as substrate materials for surface-enhanced Raman spectroscopy (SERS) with low cost, versatility, and biocompatibility, but their enhancement factors are generally quite low with a poor limit of detection. Here, ultrathin molybdenum dioxide (MoO2 ) nanosheets synthesized by chemical vapor deposition demonstrated in large area are used as SERS substrates with superior signal uniformity in the whole area with a limit of detectable concentration down to 4 × 10-8 m and enhancement factor up to 2.1 × 105 , exceeding that of 2D materials and comparable to that of noble metal films. More practically important, the planar MoO2 substrate is more robust than noble metals and shows excellent reusability and uniformity, which is usually prohibited for nanostructured or nanoparticle-based metal oxide substrates. The enhancement is mainly attributed to the surface plasmon resonance effect as evidenced by the first principle calculations and UV-vis absorption spectroscopy characterization, which can be further increased by decreasing the thickness of the MoO2 nanosheets. The overall superior performance makes the MoO2 nanosheets an ideal substrate for practical SERS applications.

Nitrogen-promoted molybdenum dioxide nanosheets for electrochemical hydrogen generation

A simple and repeatable strategy has been developed for synthesizing an N–MoO2 nanosheet with excellent stable Pt-like HER performance.

Construction of molybdenum dioxide nanosheets coated on the surface of nickel ferrite nanocrystals with ultrahigh specific capacity for hybrid supercapacitor

Recently, nickel ferrite with high theoretical capacity over the other metal oxide has been applied as electrode material for batteries and supercapacitors. However, owing to the serious aggregation and low specific surface area, the electrochemical performance of nickel ferrite (NiFe2O4) should be in urgent need of improvement. Here, we report the synthesis of unique molybdenum dioxide (MoO2) and nickel ferrite composite (MoO2/NiFe2O4) material via a facile strategy for the first time. The composite material presents a nanosheets-nanocrystals heterostructure. When evaluated as an electrode for hybrid supercapacitor in an alkaline solution, the MoO2/NiFe2O4 composite material presents a greatly enhanced specific capacity (2105 mA h/g at 4 A/g), which is better than those of individual component and exceeds some of the reported MoO2 and NiFe2O4 based electrodes. The capacity retention of MoO2/NiFe2O4 composite is about 81.1% after 1900 cycles. Such composite material also has great potential in other energy storage and conversion system.

Chemical vapor deposition of ultra-thin molybdenum dioxide nanosheets

We report the growth of ultra-thin molybdenum dioxide nanosheets on SiO2/Si substrate via chemical vapor deposition using molybdenum trioxide and sublimated sulfur as precursors. The thicknesses of the obtained MoO2 nanosheets show notable dependence on the baking temperature of the sulfur precursor. At sulfur temperature of 90°C, the obtained nanosheets can be 5.5nm thin, more than one order of magnitude thinner than that previously reported, in a narrow scatter ranging from 5.5 to 11.5nm. Two-probe electrical measurements show that the as-prepared ultrathin MoO2 nanosheets preserve a high electrical conductivity of 3600S/cm with thermal stability up to 200°C. Above 250°C, metallic MoO2 nanosheets are oxidized into insulating MoO3 flakes in air.