Ultrathin WS2 Nanosheets Research Articles

Liquid Nitrogen Exfoliation and Nanodispersion of WS2 for Thermocatalysts.

The efficient and clean exfoliation of single and/or few-layer nanosheets of WS2, a two-dimensional transition metal dichalcogenides, remains a significant challenge. In this study, a simple exfoliation method was proposed to produce ultrathin WS2 nanosheets by combining the liquid nitrogen exfoliation and nanodispersion techniques. This approach efficiently exfoliated WS2 into several layers of nanosheets via rapid temperature changes and mechanical stress without inducing defects or contamination. After five cycles of heating/liquid nitrogen and nanodispersion, the resulting WS2 nanosheets (WS2-5N ND) were confirmed to have been successfully exfoliated into 1-4 layers. When applied as a promoter in a thermocatalyst for the selective catalytic reduction of NOX using NH3, 2V3WS2/Ti (WS2-5N ND) exhibited excellent NOX conversion and N2 selectivity, along with excellent durability even in the presence of SO2. This result was greater than 2V3WS2/Ti (WS2-5N) subjected to only liquid nitrogen exfoliation, proving the importance of the simultaneous action of both methods. This method is expected to be an important contribution to ongoing research on high-performance WS2-based catalysts, thereby opening up potential opportunities for a wide range of applications.

Ultra-thin WS2 decorated Co-based Metal‒organic framework derived materials for synergistic electrocatalysis towards pH-Universal hydrogen evolution reaction

Rational designing of a WS2-based hybrid material is extremely important to resolve low-edge sites and poor conductivity of bare WS2, but it is still challenging to construct applicable structures. In this study, an electrocatalyst with ultra-thin WS2 nanosheets homogeneously decorated on Co–N-co-doped carbon hollow nanocages (WS2-3/Co–N–CN-750) is developed, which has favorable hydrogen evolution reaction (HER) activity and stability. The performance of WS2-3/Co–N–CN-750 is significantly improved due to the collective synergy of the specific micro-morphology, interfacial structure, and electronic property. The hybridization of WS2 and Co9S8 can optimize the electronic structure, reduce hydrogen adsorption energy, slash the decomposition barrier of H2O, and accelerate the electron transfer to WS2. Furthermore, the marginal sites of WS2 are significantly increased by optimizing the aggregation growth of WS2. Besides, the precipitation of appropriate Co particles and the Co-based metal-organic framework (Co-MOF) lay a solid foundation for the favorable conductivity of the hybrid material. However, samples after stability tests reveal that cobalt sulfide is corroded and transformed in a locally strong alkali condition. This study highlights the synergies of multicomponent hybridization and provides insights into the stability of congeneric materials.

Hydrothermal synthesis of ultrathin WS2 nanosheets as anodes for sodium-ion batteries

In this study, ultrathin WS2 nanosheets with an average thickness of about 10 nm were successfully synthesized via a facile hydrothermal method. Their electrochemical properties were systematically investigated by various electrochemical testing techniques, and the morphology and structure were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). When applied as anode for sodium ion batteries, ultrathin WS2 nanosheets exhibit an impressive high-rate capability and good cyclic stability, a reversible capacity of 250 mAh g-1 after the following cycling test of 100 cycles is still achieved at 100 mA g-1 . The excellent rate performance and cycling stability are attributed to better electronic conductivity and well-developed layered structure.

Self‐Assembled 2D WS2 Interconnected Nanosheets: An Anode Material with Outstanding Lithium‐Storage Performance

The unique lithium‐ion battery anodes consisting of interconnected nano‐architectures with high specific surface areas, adequate buffer space to tolerate the volume change, excellent conductivities, and admirable mechanical stabilities demand for next‐generation lithium‐ion battery (LIB). Herein this report, highly interconnected and self‐assembled tungsten disulfide nanosheets (WS2 NS) array is constructed through simple hydrothermal process. The ultrathin nature of nanosheet array can not only efficiently buffer the huge volumetric change but also abbreviate the Li‐ion and electron diffusion path. As expected, the ultrathin WS2 nanosheets array is endowed with excellent structural stability and also very fast electrochemical kinetics, and hence extraordinary lithium‐storage performance, such as delivering high capacities of 813.33 mAh g−1 at a C rate of C/8, admirable rate capability and good cycling stability, that is, 242 and 226 mAh g−1 at a C rate of 1 and 2 C, respectively, up to 600 cycles.

In-Situ growing tungsten Sulfide/Carbon nanosheets on sodium titanate nanorods to stabilize Surface-Structure for enhanced Sodium-ion storage

Sodium-ions hybrid capacitors (SIHCs) have been recognized as one of the most potential energy storage devices, which can deliver high power and energy densities simultaneously. However, the sluggish kinetics of electrode materials severely restricts the performance of SIHCs. Herein, N, P-codoped carbon and WS2 nanosheets coating on sodium titanate nanorods (NTO@WS2/N, PC) were first designed by in-situ growing process and sulfuration treatment for boosting sodium-ion storage. Specifically, NTO@WS2/N, PC electrodes displayed a satisfactory specific capacity of 274.7 mAh g−1 at 3.0 A g−1 after 1200 cycles. Furthermore, as-assembled SIHCs delivered high-energy density of 112.1 Wh kg−1 and high-power density of 4334.4 W kg−1. Besides, long-term cycling test revealed that a remarkable capacity retention rate of 89.7% was obtained at 8.0 A g−1 after 2000 cycles. The excellent cycling stability and rate property could be ascribed to following aspects. On the one hand, N, P-codoped carbon could enhance the electrical conductivity and strengthen the structural integrality of the composites. On the other hand, ultrathin WS2 nanosheets and one-dimensional (1D) NTO nanorods structure were conducive to the rapid diffusion of Na+. This work provides a convenient technique to stabilize the structure of electrode materials, which can promote the practical application of SIHCs.

Long-term catalytic durability in Z-scheme CdS@ 1T-WS2 heterojunction materials

This study aimed to improve the long-term durability of CdS catalysts by reducing the deterioration of catalytic activity caused by photocorrosion. An ultrathin 1T-WS2 2D nanosheet was introduced to enclose the CdS nanorods. The crystal defects in the wrapped CdS particles were reduced, and the WS2 sheet became thinner in the junction particle. The 2CdS@1WS2 junction particle exhibited the slowest decay time of the photoluminescence curve, and the photocurrent density increased by more than 3.5-fold in the junction particle than the single CdS particle. Eventually, the optimized 2CdS@1WS2 catalyst exhibited a high rate of H2 production of ≈3935 μmol g−1h−1 under simulated solar light irradiation with a quantum efficiency of 50%. Although the recycling experiment was repeated over 10 times using the 2CdS@1WS2 junction particle, the produced hydrogen amount did not decrease. This result is because CdS nanorods wrapped stably by the ultrathin WS2 nanosheets, which suppressed the photocorrosion of CdS, and furthermore, the 1T phase WS2 rapidly attracted photogenerated electrons from CdS, facilitating charge separation and inhibiting their recombination, thereby improving the catalyst activity. Finally, it was revealed that an effective Z-scheme charge transfer mechanism in the CdS@1T-WS2 junction particle follows during water splitting.

Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets

Wet-chemical syntheses for quasi two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising methods for straightforward solution-processing of these materials. However, photoluminescence properties of colloidal TMDs are virtually unexplored due to the typically non-emitting synthesis products. In this work, we demonstrate room temperature micro-photoluminescence of delicate ultrathin colloidal WS2 nanosheets synthesized from WCl6 and elemental sulfur in oleic acid and oleylamine at 320 {\deg}C for the first time. Both, mono- and multilayer photoluminescence are observed, revealing comparable characteristics to exfoliated TMD monolayers and underpinning the high quality of colloidal WS2 nanosheets. In addition, a promising long-term air-stability of colloidal WS2 nanosheets is found and the control of photodegradation of the structures under laser excitation is identified as a challenge for further advancing nanosheet monolayers. Our results render colloidal TMDs as easily synthesized and highly promising 2D semiconductors with optical properties fully competitive with conventionally fabricated ultrathin TMDs.

Phase-dependent ion-to-electron transducing efficiency of WS2 nanosheets for anall-solid-state potentiometric calcium sensor.

Ultrathin metallic WS2 (M-WS2) nanosheets and semiconductive WS2 (S-WS2) nanosheets were exfoliated and for the first time employed as ion-to-electron transducing layer to construct anall-solid-state ion-selective electrode. Importantly, we found that the transducing efficiency of WS2 nanosheet-based solid-contact layer is phase-dependent. The M-WS2 nanosheets with larger content of 1T-phase structure exhibit higher transducing efficiency than S-WS2 nanosheets, which can be ascribed to the remarkable conductivity of M-WS2 nanosheets. In order to demonstrate the excellent properties of theM-WS2 nanosheet-based tranducing layer, an all-solid-state calcium ion potentiometric sensor was constructed as the model. As expected, a Nernstian response (27.41mV per decade, R2 = 0.9998) with a wide linear range of 1.0 × 10-5.0 to 1.0 × 10-2.0 M and a limit of detection of 2.0μM was obtained. The developed all-solid-state potentiometric sensor using M-WS2 nanosheets as ion-to-electron transducing layer is expected to bring new progress for routine detection in various fields. Graphical Abstract Schematic illustration of the introduction of WS2 nanosheets with different phase structures as a new-generation solid-contact ion-to-electron transducing layer for all-solid-state potentiometric sensors.

Modulation of oligonucleotide-binding dynamics on WS2 nanosheet interfaces for detection of Alzheimer's disease biomarkers

Non-covalent adsorption and desorption of oligonucleotides on two-dimensional nanosheets are widely employed to design nanobiosensors for the rapid optical detection of targets. A precise control over the weak interactions between nanosheet interfaces and oligonucleotides is crucial for a high-sensing performance. Herein, the interface of ultrathin WS2 nanosheets used as a fluorescence quencher was engineered by four different dextran polymers in an aqueous solution to control the adsorption kinetics and thermodynamics of the DNA probe. The WS2 nanosheets, functionalized by the carboxyl group-bearing dextran (CM-dex-WS2) or the trimethylammonium-modified dextran (TMA-dex-WS2), exhibited 3.6-fold faster adsorption rates of the fluorescein-labeled DNA probe (FAM-DNA), which led to the effective fluorescence quenching of FAM, compared to the nanosheets functionalized with pristine dextran (dex-WS2) or the hydrophobic phenoxy groups-bearing dextran (PhO-dex-WS2). Isothermal titration calorimetry measurements showed that the adsorption strength of FAM-DNA for CM-dex-WS2 was one order of magnitude greater than its hybridization energy for a target microRNA (miR-29a) that is well-known as an Alzheimer's disease (AD) biomarker, leading to the unfavorable desorption of the DNA probe from the surface. In contrast, TMA-dex-WS2 exhibited the proper adsorption strength of FAM-DNA, which was lower than its hybridization energy for miR-29a, leading to its favorable desorption from the nanosheet surface along with the noticeable restoration of the quenched fluorescence after its hybridization with miR-29a. Finally, the interface modulation of WS2 nanosheets allowed the selective and sensitive recognition of miR-29a against non-complementary RNA and single base-mismatched RNA in human serum via increases in target-specific fluorescence.

Ultrathin exfoliated WS2 nanosheets in low-boiling-point solvents for high-efficiency hydrogen evolution reaction

Two-dimensional mono-or few-layer WS2, as a typical transition metal dichalcogenide, usually exhibits excellent electrocatalytic hydrogen evolution reaction (HER) activity. In this work, low-boiling-point solvents are adopted for the controllable preparation of ultra-thin WS2 nanosheets by an improved liquid phase exfoliation process directly from the raw WS2 powder. The thickness of as-obtained WS2 nanosheets is about ∼1.5 nm with lateral size of ∼1.2 μm. Their HER performance was investigated by loading them onto a glass carbon electrode in 0.5M H2SO4 solution. The resulting polarization and Tafel curves indicate that the as-obtained WS2 nanosheets are effective electrocatalysts for HER with a low onset potential of 65mV and a Tafel slope of 55mV/dec. The proposed liquid phase exfoliation technique is lucrative for exfoliating transition metal disulfide materials in various applications.

Ultrathin WS2 nanosheets vertically aligned on TiO2 nanobelts as efficient alkaline hydrogen evolution electrocatalyst

Highly efficient and durable non-noble metal-based hydrogen evolution electrocatalysts are critical to advance the production of hydrogen energy via alkaline water electrolysis. Herein, we prepared a novel TiO2@WS2 hybrid via a facile and scalable two-step hydrothermal strategy combined with selective etching. Benefited from acid-etched TiO2 nanobelts with rough surface as substrate, ultrathin WS2 nanosheets nucleated and vertically grew into few layers in the confined configuration with more exposed active edges. Furthermore, the partial incorporation of oxygen in WS2 inherited from the remaining O–W bonds of tungsten precursor enhanced the electrical conductivity of the hybrid. Therefore, TiO2@WS2 hybrid was proved to be efficient and durable electrocatalyst for hydrogen evolution in alkaline medium. Upon optimal conditions, the hybrid only required a small onset overpotential of 95 mV and a low overpotential of 142 mV at 10 mA cm−2, superior to pristine WS2 and TiO2. In addition, better cycling stability during the alkaline HER process was also obtained, indicating its capability in future practical application. The synthesis strategy presents a cost-effective approach to produce efficient WS2-based HER electrocatalyst for electrochemical water splitting.

Crystal phase control synthesis of metallic 1T-WS2 nanosheets incorporating single walled carbon nanotubes to construct superior microwave absorber

Two-dimensional transition metal dichalcogenides (TMDs) have attracted tremendous attentions due to their unique properties, and the development of phase control technique brings out new opportunities in emerging application fields. In this work, tungsten disulfide (WS2) nanosheets containing 1T phase predominately were incorporated with single walled carbon nanotubes (SWCNTs) through a facial hydrothermal method. Two-dimensional flexible and ultrathin WS2 nanosheets were in-situ grown on one-dimensional SWCNTs bundles, further forming typical urchin-like microsphere with diameters distributing in the range of 2–3 μm uniformly. Accordingly, dielectric loss could be significantly enhanced due to the strong interface coupling effect between WS2 nanosheets and SWCNTs bundles, which induced considerable electrical conductivity and abundant capacitor-like structures. Consequently, the minimum reflection loss (RL) could reach up to −66 dB at 8.3 GHz with a matching thickness of 2.2 mm. Furthermore, RL values lower than −10 dB could be attained in the range of 3.0–18.0 GHz with integrated thicknesses from 5.0 to 1.0 mm. Prospectively, our present work may provide new opportunity to design TMDs based composites by means of crystal phase control technique as lightweight and high-performance microwave absorbers.

WS2 Nanosheets with Highly‐Enhanced Electrochemical Activity by Facile Control of Sulfur Vacancies

AbstractTungsten disulfide (WS2) is a promising and low‐cost material for electrochemical hydrogen evolution reaction (HER) and has been extensively studied due to its excellent performance. However, the development of a facile and controllable defect‐engineering to activate its basal planes is still crucial to improve its HER activity. Here, we put forward an annealing strategy to create controllable sulfur vacancies (S‐vacancies) in ultrathin WS2 nanosheets, which can result in the increase of active sites and enhanced electrocatalytic activity accordingly. Our density‐functional‐theory (DFT) calculations reveal that the Gibbs free energy of hydrogen adsorption (ΔGH*) can be tuned to near zero by controlling the density of S‐vacancies, leading to thermal‐neutral HER performance. We find that optimal HER performance can be achieved by tuning the density of S‐vacancies in WS2 through annealing in the mixture of Ar and H2 (5 %). The WS2 nanosheets with the optimal density of S‐vacancies show lower overpotential by 116 mV at 10 mA/cm2 and smaller Tafel slope by 37.9 mV/dec than as‐prepared counterpart, and super‐excellent stability in acid. Additionally, the WS2 with optimal S‐vacancies also shows the best HER activity in alkaline solution. Our findings present a facile and general strategy to design electrocatalysts with more active sites, which is applicable to other materials for the improvement of their catalytic activities.

Nitrogen anion-decorated cobalt tungsten disulfides solid solutions on the carbon nanofibers for water splitting

A facile method to prepare nitrogen anion-decorated cobalt tungsten disulfides solid solutions, retaining ultra-thin WS2-like nanosheet structures (The N–CoxW1−xS2) anchored on carbon nanofibers (CNFs), is developed. The synergistic effect of the WS2 nanosheets provides a secure framework for stabilizing the amorphous Co–S clusters, CNFs substrate and nitrogen anion-decoration significantly enhances the inherent conductivity of the catalyst, resulting in a significantly promoted hydrogen evolution reaction activity and stable performance compared to pure Co9S8 nanoparticles or ultra-thin WS2 nanosheets. The N–CoxW1−xS2 electrode demonstrates the excellent electrocatalytic performance, with current density of 10 mA cm−2 at a low overpotential of 93 mV and Tafel slope of 85 mV dec−1, as well as the long-term stability in acid electrolyte. The present investigation may provide a feasible strategy for incorporating other heteroatoms into transitional metal disulfides materials to design catalysts with highly active and stable performance for water splitting.

Vertically Aligned Ultrathin 1T-WS2 Nanosheets Enhanced the Electrocatalytic Hydrogen Evolution

Efficient evolution of hydrogen through electrocatalysis holds tremendous promise for clean energy. The catalytic efficiency for hydrogen evolution reaction (HER) strongly depends on the number and activity of active sites. To this end, making vertically aligned, ultrathin, and along with rich metallic phase WS2 nanosheets is effective to maximally unearth the catalytic performance of WS2 nanosheets. Metallic 1T polymorph combined with vertically aligned ultrathin WS2 nanosheets on flat substrate is successfully prepared via one-step simple hydrothermal reaction. The nearly vertical orientation of WS2 nanosheets enables the active sites of surface edge and basal planes to be maximally exposed. Here, we report vertical 1T-WS2 nanosheets as efficient catalysts for hydrogen evolution with low overpotential of 118 mV at 10 mA cm−2 and a Tafel slope of 43 mV dec−1. In addition, the prepared WS2 nanosheets exhibit extremely high stability in acidic solution as the HER catalytic activity and show no degradation after 5000 continuous potential cycles. Our results indicate that vertical 1T-WS2 nanosheets are attractive alternative to the precious platinum benchmark catalyst and rival MoS2 materials that have recently been heavily scrutinized for hydrogen evolution.Graphical Vertical 1T-WS2 for hydrogen evolution.

Ultrathin WS2 nanosheets vertically embedded in a hollow mesoporous carbon framework – a triple-shell structure with enhanced lithium storage and electrocatalytic properties

HTSHNs WS2/C with ultrathin WS2 nanosheets vertically embedded in HMCSs provide abundant active sites, high conductivity and superior structural stability.

The ultra-high NO2 response of ultra-thin WS2 nanosheets synthesized by hydrothermal and calcination processes

Ultra-thin WS2 nanosheets with a thickness of about 5 nm were synthesized by an economical hydrothermal method and the following calcination process. A three dimensional wall-like structure was formed by the interconnecting WS2 nanosheets. The growth mechanism of as-prepared WS2 nanosheets was discussed, and it was deduced that mesolamellar tungsten sulfide (WS-L) with intercalated CTA+ cations was formed by co-condensation reaction of WS42− and CTAB in the hydrothermal process. The resistive gas sensors based on as-prepared WS2 nanosheets showed a p-type character, achieved a superior response of 9.3% to 0.1 ppm NO2 gas at room temperature (25 °C) and a good stability in low and moderate humidity. The excellent NO2 sensing properties can be attributed to the ultra-thin nanostructure of the WS2 nanosheets.

In situ preparation of few-layered WS2 nanosheets and exfoliation into bilayers on CdS nanorods for ultrafast charge carrier migrations toward enhanced photocatalytic hydrogen production

Transition-metal dichalcogenides (TMD) have emerged as a fascinating new class of noble-metal-free materials for photocatalytic hydrogen evolution from the water. Recently, numerous approaches have been established to develop single- or few-layered TMDs to improve their physical properties. Although WS2 has a higher intrinsic electric conductivity than the MoS2 analogue, most photocatalytic studies using TMD have focused on the nanocomposite using MoS2 as a co-catalyst. In the present study, we synthesized in situ and highly efficient few-layered WS2 nanosheets and exfoliated them to bilayers (i.e., ultrathin) on CdS nanorods (UWC) by a simple ultrasonication process. The optimized UWC-6 photocatalyst exhibits a tremendous rate of H2 production of ∼185.79mmolh−1g−1 using simulated solar light irradiation, with a quantum efficiency of 40.5%. The performance of this photocatalyst is 33 times greater than that of pristine CdS and 3.5-fold greater than that of few-layered WS2–CdS nanocomposite (BWC) photocatalysts. The ultrathin WS2 nanosheets are long and discontinuously stacked along the CdS nanorods, with high coverage of mixed-phase layers. This combination leads to the efficient photogeneration of charge carriers and enhances the surface shuttling properties of the photocatalyst for greater effective H2 production via active edge sites and superior intrinsic electrical conductivity. The H2 evolution rate reported here is much higher than for bulk or few-layered WS2-assisted CdS photocatalysts. To the best of our knowledge, this is the highest H2 production rate achieved by a WS2-based CdS photocatalyst by splitting water using simulated solar light irradiation.

Improved Lithium-Ion and Sodium-Ion Storage Properties from Few-Layered WS2 Nanosheets Embedded in a Mesoporous CMK-3 Matrix.

An integrated WS2 @CMK-3 nanocomposite has been prepared by a one-step hydrothermal method and then used as the anode material for lithium-ion and sodium-ion batteries. Ultrathin WS2 nanosheets have been successfully embedded into the ordered mesoporous carbon (CMK-3) framework. Owing to the few-layered nanostructure of WS2 , as well as the high electronic conductivity and the volume confinement effect of CMK-3, the material shows larger discharge capacity, better rate capability, and improved cycle stability than pristine WS2 . When tested in lithium-ion batteries, the material delivers a reversible capacity of 720 mA h g-1 after 100 cycles at a current density of 100 mA g-1 . A large discharge capacity of 307 mA h g-1 is obtained at a current density of 2 A g-1 . When used in sodium-ion batteries, the material exhibits a capacity of 333 mA h g-1 at 100 mA g-1 without capacity fading after 70 cycles. A discharge capacity of 230 mA h g-1 is obtained at 2 A g-1 . This excellent performance demonstrates that the WS2 @CMK-3 nanocomposite has great potential as a high-performance anode material for next-generation rechargeable batteries.

Synthesis of Ultrathin WS2 Nanosheets and Their Tribological Properties as Lubricant Additives.

In this paper, ultrathin WS2 nanosheets with thickness of about 5 nm were successfully prepared by a facile solid phase reaction method. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). On the basis of experimental results obtained under different reaction durations, a possible formation mechanism of WS2 nanosheets is proposed. The tribological performance of ultrathin WS2 nanosheets as additives in the 500SN base oil was tested by an UMT-2 ball-on-disc tribotester, and the worn surface of the steel disc was investigated by a non-contact optical profile testing instrument and SEM. The results showed that the friction coefficient and anti-wear property of base oil can be improved strikingly by adding ultrathin WS2 nanosheets. Especially, when the concentration of WS2 nanosheets was 1.0 wt.%, the corresponding lubricating oil exhibited the best tribological properties. Moreover, according to the investigation of the wear scar, an anti-friction and anti-wear mechanism is proposed. It is believed that the reduction of friction and wear must come from the addition of ultrathin WS2 nanosheets which can penetrate and enter the friction interface and form a continuous tribofilm on the rubbing face.