Hierarchical Ternary MoO2 /MoS2 /Heteroatom-Doped Carbon Hybrid Materials for High-Performance Lithium-Ion Storage

Manipulation of the MoO2/MoSe2 Heterointerface Boosting High Rate and Durability for Sodium/Potassium Storage

The main challenge for sodium/potassium ion storage is to find the suitable host materials to accommodate the larger-sized Na⁺/K⁺ and conquer the sluggish chemical kinetics. Herein, by selenation of polyoxometalate in electrospinning fiber, a novel MoO₂/MoSe₂ heterostructure embedded in one-dimensional (1D) N,P-doped carbon nanofiber (MoO₂/MoSe₂@NPC) is rationally constructed to show distinct enhancement of rate performance and cycle life for sodium ion batteries (SIBs) and potassium ion batteries (PIBs). The 1D skeleton of MoO₂/MoSe₂@NPC decreases the diffusion pathway of Na⁺/K⁺, and the doping of N/P heteroatoms in carbon fiber creates abundant active sites and provides good reachability for Na⁺/K⁺ transportation. MoSe₂ nanosheets grow in the bulk phase of MoO₂ via in situ local phase transformation to achieve effective and firm heterointerfaces. Especially, the exposure extent of heterointerfaces can be controlled by treatment temperature during the preparation process, and the optimized heterointerfaces result in an ideal synergic effect between MoO₂ and MoSe₂. DFT calculations confirm that the internal electric field in the heterogeneous interface guides the electron transfer from MoO₂ to MoSe₂, combined with strong adsorption capacity toward sodium/potassium, facilitating ion/electron transfer kinetics. It is confirmed that the MoO₂/MoSe₂@NPC anode for SIBs delivers 382 mA h g^-1 under 0.1 A g^-1 upon 200 cycles; meanwhile, a reversible capacity of 266 mA h g^-1 is maintained even under 2 A g^-1 after 2000 cycles. For PIBs, it can reach up to 216 mA h g^-1 in the 200th cycle and still retain 125 mA h g^-1 after 2000 cycles under 1 A g^-1. This study opens up a new interface manipulation strategy for the design of anode materials to boost fast Na⁺/K⁺ storage kinetics.

Ultrafast photoresponse of vertically oriented TMD films probed in a vertical electrode configuration on Si chips

Integrated photodetectors based on transition metal dichalcogenides (TMDs) face the challenge of growing their high-quality crystals directly on chips or transferring them to the desired locations of components by applying multi-step processes. Herein, we show that vertically oriented polycrystalline thin films of MoS₂ and WS₂ grown by sulfurization of Mo and W sputtered on highly doped Si are robust solutions to achieve on-chip photodetectors with a sensitivity of up to 1 mA W^-1 and an ultrafast response time in the sub-μs regime by simply probing the device in a vertical arrangement, i.e., parallel to the basal planes of TMDs. These results are two orders of magnitude better than those measured earlier in lateral probing setups having both electrodes on top of vertically aligned polycrystalline TMD films. Accordingly, our study suggests that easy-to-grow vertically oriented polycrystalline thin film structures may be viable components in fast photodetectors as well as in imaging, sensing and telecommunication devices.

Exploring the Effects of the Interaction of Carbon and MoS2 Catalyst on CO2 Hydrogenation to Methanol

Hydrogenation of CO2 to form methanol utilizing green hydrogen is a promising route to realizing carbon neutrality. However, the development of catalyst with high activity and selectivity to methanol from the CO2 hydrogenation is still a challenge due to the chemical inertness of CO2 and its characteristics of multi-path conversion. Herein, a series of highly active carbon-confining molybdenum sulfide (MoS2@C) catalysts were prepared by the in-situ pyrolysis method. In comparison with the bulk MoS2 and MoS2/C, the stronger interaction between MoS2 and the carbon layer was clearly generated. Under the optimized reaction conditions, MoS2@C showed better catalytic performance and long-term stability. The MoS2@C catalyst could sustain around 32.4% conversion of CO2 with 94.8% selectivity of MeOH for at least 150 h.

Polyoxometalate@MOF derived porous carbon-supported MoO2/MoS2 octahedra boosting high-rate lithium storage

Structural stability and rapid charge-discharge capability of electrode materials are required for high performance lithium-ion batteries (LIBs). The materials derived from polyoxometalates (POMs) show special advantages in inhibiting capacity attenuation, and good dispersion or combination of POMs with metal-organic frameworks (MOFs) is an important method to obtain high activity anode composites for LIBs. In this study, a uniform MoO₂/MoS₂ heterostructure with surface supported carbon (C-MoO₂/MoS₂) was successfully fabricated from a [Cu₂(BTC)_4/3(H₂O)₂]₆[H₃PMo₁₂O₄₀] precursor, which showed not only the designed octahedral morphology but also fast charge transfer, long working life, and high rate performance. Superior reversible lithium storage capacity of 1047 mA h g^-1 after 300 cycles was obtained at 1 A g^-1. Even after 700 cycles at 5 A g^-1, the discharge specific capacity of 646 mA h g^-1 was maintained, and rate capability of 610 mA h g^-1 could be achieved at 10 A g^-1. The high capacitive contribution could be explained by the relatively large specific surface area of porous C-MoO₂/MoS₂, which was mainly caused by the supported carbon network and MoS₂ nanosheets, resulting in fast lithiation/delithiation processes.

MoS2 nanoparticle/activated carbon composite as a dual-band material for absorbing microwaves

In the search for novel high-performance microwave (MW) absorbers, MoS2 has shown promise as a MW-absorbing material, but its poor impedance matching limits its applications. Herein, a facile hydrothermal method was used to produce a composite consisting of activated carbon (AC) derived from waste biomass and in situ-grown MoS2 nanoparticles. Its microwave absorption properties were examined in the 2-18 GHz frequency range, and FESEM and HRTEM images confirmed the formation of MoS2 nanoparticles on the AC. The maximum reflection loss (RLmax) for the MoS2/AC composite was -31.8 dB (@16.72 GHz) at 20 wt% filler loading. At 50 wt% filler loading, the MoS2/AC (MAC50) composite exhibited unique dual-band absorption characteristics in the C and Ku bands. An effective absorption bandwidth (RL < -10 dB) of 10.4 GHz (3-5.2 GHz, 9.8-18 GHz) was achieved at various thicknesses that covered the entire Ku band. Therefore, a sole dielectric absorber can easily be tuned to absorb MWs at multiple frequency ranges. The large surface area and conduction losses of AC combined with the superior dielectric loss properties of MoS2 resulted in improved impedance matching and attenuation ability of the MoS2/AC composite. Thus, MoS2/AC is a promising low-cost dielectric absorber for MW absorption applications.

Confining Ultrafine MoO2 in a Carbon Matrix Enables Hybrid Li Ion and Li Metal Storage

Poor cycle and rate performance caused by volume effects and sluggish kinetics is the main bottleneck for most lithium-ion battery (LIB) anode materials run on the conversion reaction. Although nanostructure engineering has shown to be an effective method to reduce the undesirable volume effects, cycling instability usually remains in nanostructured electrodes owning to particle aggregation in discharge and loss of active materials in charge. Here, to make these kinds of materials practical, we have developed a structure of ultrafine MoO₂ nanoparticles (<3 nm) confined by a conductive carbon nanosheet matrix (MoO₂/C). Instead of running on the conversion mechanism, the Li storage in the MoO₂/C composite is through a two-step mechanism in discharge: intercalation followed by the formation of metallic Li, acting as a hybrid host for both Li ion intercalation and metallic Li plating. The Li-storage mechanism has been revealed by in situ X-ray diffraction analysis and in situ scanning transmission electron microscopy with corresponding electron energy loss spectrum analysis, which explains the natural origin of such high capacity along with good cyclability. This unique MoO₂/C structure exhibits an excellent discharge capacity (810 mAh g^-1 at 200 mA g^-1) and cyclability (75% capacity retention over 1000 cycles). The carbon sheet plays a vital role in both a conductive network and a structure supporter with a robust confining effect that keeps the size of MoO₂ uniformly under 3 nm even after high-temperature calcination. Our finding provides insights for the design of next-generation LIB anode materials with high capacity and longevity.

Highly Crystalline TiO2-MoO3 Composite Materials Synthesized via a Template-Assisted Microwave Method for Electrochemical Application

TiO2-MoO3 composite systems were successfully prepared using a template-assisted microwave method at molar ratios TiO2:MoO3 = 8:2, 5:5 and 2:8. The synthesized material systems were comprehensively characterized, in terms of their crystalline structure (XRD and Raman spectroscopy), morphology (SEM, TEM and HRTEM analysis) and parameters of the porous structure (low-temperature N2 sorption). The materials exhibited highly crystalline phases: anatase and hexagonal molybdenum trioxide. Moreover, TEM analysis revealed hexagonal prism particles of MoO3 and nanocrystalline particles of TiO2. The proposed template-assisted microwave synthesis enabled the incorporation of TiO2 particles on the surface of hexagonal particles of MoO3, which resulted in a stable junction between titania and molybdenum trioxide. The values of BET surface area were 57, 29 and 11 m2/g for samples obtained at molar ratios TiO2:MoO3 = 8:2, 5:5 and 2:8 respectively. In electrochemical applications, titanium dioxide plays a crucial role as an intercalation intensifier, in which MoO3 is responsible for current conduction. Taking account of the potential electrochemical applications, the best system was obtained at the molar ratio TiO2:MoO3 = 5:5. The anode could maintain a capacity of 400 mAh/g at current densities in the range 100–1000 mA/g at potential values ranging from 1.00 to 3.30 V vs. Li/Li+. X-ray photoelectron spectroscopy (XPS) confirmed the effective intercalation of lithium ions into the TiO2-MoO3 composite materials.

One-Step Hydrothermal Synthesis of P25 @ Few Layered MoS2 Nanosheets toward Enhanced Bi-catalytic Activities: Photocatalysis and Electrocatalysis

P25 loaded few layered molybdenum disulfide (MoS₂) nanosheets (P25@MoS₂) are successfully synthesized through a facile one-step hydrothermal process. The bi-catalytic activities, i.e., photocatalytic and electrocatalytic activities, of the as-prepared nanomaterials have been investigated. For the as-prepared products, the photocatalytic performances were investigated by degrading simulated pollutant under sunlight irradiation, and the hydrogen evolution reaction evaluated the electrocatalytic performances. The results indicate that P25@MoS₂ possesses excellent activities in both photocatalysis and electrocatalysis. The presence of MoS₂ broadens the light absorption range of P25 and improves the separation and transformation efficiency of photogenerated carriers, thus improving its photocatalytic performance. The existence of P25 inhibits the aggregation of MoS₂ to form more dispersed MoS₂ nanosheets with only few layers increasing its active sites. Thereby, the electrocatalytic performance is heightened. The excellent multifunction makes the as-prepared P25@MoS₂ a promising material in the fields of environment and energy.

One-Step Low Temperature Hydrothermal Synthesis of Flexible TiO₂/PVDF@MoS₂ Core-Shell Heterostructured Fibers for Visible-Light-Driven Photocatalysis and Self-Cleaning

Novel flexible and recyclable core-shell heterostructured fibers based on cauliflower-like MoS₂ and TiO₂/PVDF fibers have been designed through one-step hydrothermal treatment based on electrospun tetrabutyl orthotitanate (TBOT)/PVDF fibers. The low hydrothermal temperature avoids the high temperature process and keeps the flexibility of the as-synthesized materials. The formation mechanism of the resultant product is discussed in detail. The composite of MoS₂ not only expands the light harvesting window to include visible light, but also increases the separation efficiency of photo-generated electrons and holes. The as-prepared product has proven to possess excellent and stable photocatalytic activity in the degradation of Rhodamine B and levofloxacin hydrochloride under visible light irradiation. In addition, the TiO₂/PVDF@MoS₂ core-shell heterostructured fibers exhibit self-cleaning property to dye droplets under visible light irradiation. Meanwhile, due to its hydrophobicity, the resultant product can automatically remove dust on its surface under the rolling condition of droplets. Hence, the as-prepared product cannot only degrade the contaminated compounds on the surface of the material, but also reduce the maintenance cost of the material due to its self-cleaning performance. Therefore, the as-prepared product possesses potential applications in degradation of organic pollutants and water treatment, which makes it a prospective material in the field of environmental treatment.

Vertically Oxygen-Incorporated MoS2 Nanosheets Coated on Carbon Fibers for Sodium-Ion Batteries

Developing a high-performance anode with high reversible capacity, rate performance, and great cycling stability is highly important for sodium-ion batteries (SIBs). MoS₂ has attracted extensive interest as the anode for SIBs. Herein, the vertically oxygen-incorporated MoS₂ nanosheets/carbon fibers are constructed via a facile hydrothermal method and then by simple calcination in air. Oxygen incorporation into MoS₂ can increase the defect degree and expand the interlayer spacing. Vertical MoS₂ nanosheet array coated on carbon fibers not only can expose rich active sites and reduce the diffusion distance of Na⁺, but also improve the electronic conductivity and enhance structural stability. Meanwhile, interlayer-expanded MoS₂ can decrease Na⁺ diffusion resistance and increase accessible active sites for Na⁺. In this work, the electrode combining the oxygen-incorporated strategy with vertical MoS₂ nanosheet-integrated carbon fibers displays high specific capacities of 330 mAh g^-1 over 100 cycles at a current density of 0.1 A g^-1 together with excellent rate behavior as the anode for SIBs. This strategy offers a helpful way for improving the electrochemical performance.

Anisotropic Polymer Adsorption on Molybdenite Basal and Edge Surfaces and Interaction Mechanism With Air Bubbles

The anisotropic surface characteristics and interaction mechanisms of molybdenite (MoS₂) basal and edge planes have attracted much research interest in many interfacial processes such as froth flotation. In this work, the adsorption of a polymer depressant [i.e., carboxymethyl cellulose (CMC)] on both MoS₂ basal and edge surfaces as well as their interaction mechanisms with air bubbles have been characterized by atomic force microscope (AFM) imaging and quantitative force measurements. AFM imaging showed that the polymer coverage on the basal plane increased with elevating polymer concentration, with the formation of a compact polymer layer at 100 ppm CMC; however, the polymer adsorption was much weaker on the edge plane. The anisotropy in polymer adsorption on MoS₂ basal and edge surfaces coincided with water contact angle results. Direct force measurements using CMC functionalized AFM tips revealed that the adhesion on the basal plane was about an order of magnitude higher than that on the edge plane, supporting the anisotropic CMC adsorption behaviors. Such adhesion difference could be attributed to their difference in surface hydrophobicity and surface charge, with weakened hydrophobic attraction and strengthened electrostatic repulsion between the polymers and edge plane. Force measurements using a bubble probe AFM showed that air bubble could attach to the basal plane during approach, which could be effectively inhibited after polymer adsorption. The edge surface, due to the negligible polymer adsorption, showed similar interaction behaviors with air bubbles before and after polymer treatment. This work provides useful information on the adsorption of polymers on MoS₂ basal/edge surfaces as well as their interaction mechanism with air bubbles at the nanoscale, with implications for the design and development of effective polymer additives to mediate the bubble attachment on solid particles with anisotropic surface properties in mineral flotation and other engineering processes.