Few-layer WS2 Nanosheets Research Articles

WS2 nanosheets-based electrochemical biosensor for highly sensitive detection of tumor marker miRNA-4484

In this paper, a few-layer WS2 nanosheets-based electrochemical biosensor was fabricated for the highly sensitive detection of breast cancer tumor marker miRNA-4484. Firstly, few-layer WS2 nanosheets were prepared by shear stripping and characterized by SEM, TEM, AFM and UV spectrophotometer. After modification of few-layer WS2 nanosheets on the electrode surface, the miRNA probe was fixed on the few-layer WS2 nanosheets by polycytosine (PolyC). Then short-chain miRNA containing PolyC was used as the blocking agent to close the excess active sites on the surface of WS2 nanosheets to complete the fabrication of the sensor biosensing interface. Finally, the current changes caused by the specific binding of miRNA-4484 to the probe were analyzed by differential pulse voltammetry (DPV). The results showed that the sensor had a good linear relationship for the detection of miRNA-4484 in the concentration range of 1 aM–100 fM, and the detection limit was as low as 1.61 aM. In addition, the electrochemical sensor had excellent selectivity, stability and reproducibility. The artificial sample tests indicated that the developed biosensors have the potential for clinical application in the future.

Au–WS2 Nanohybrids with Enhanced Optical Nonlinearity for Optical Limiting Applications

Utilizing plasmonic effects of metal nanostructures on tailoring the properties of semiconducting materials has gained substantial research attention in the past 10 years. Here, we report the plasmon resonance-induced enhanced optical nonlinearity of Au–WS2 nanohybrids prepared via the blending of liquid phase exfoliated few-layer WS2 nanosheets with chemically synthesized spherical gold nanoparticles (NPs). Nonlinear optical properties were studied using the open aperture Z-scan technique with nanosecond laser pulses of wavelength 532 nm, which lie in the plasmonic band of Au NPs (480–550 nm) and B-excitonic transition range of WS2 nanosheets (520–535 nm). Au–WS2 nanohybrids exhibited an enhanced nonlinear absorption and optical limiting activity with an effective nonlinear absorption coefficient of 182 cm/GW at an on-axis input intensity of 0.14 GW/cm2, which is 3.87 times higher than that of bare WS2 nanosheets. The improved NLO response of nanohybrids is due to the plasmon resonance-induced local field effects, which significantly enhance B-excitonic transitions in WS2 nanosheets. The simulated field intensity enhancement profile also confirmed the effect of formation, where a strong interaction of plasmonic fields with WS2 nanosheets is clearly visible. The enhancement observed in simulated absorption density profiles indicated improved B-excitonic transitions in WS2 nanosheets due to the resonant plasmonic field. Au–WS2 nanohybrids exhibited a low limiting threshold of 0.55 J/cm2, which is better than that of many eminent nanohybrids reported so far. The strategy followed in this work for attaining superior nonlinear optical responses in Au–WS2 nanohybrids will be useful to develop novel nonlinear optical materials for photonic device applications.

Feather-like few-layer WSe2 nanosheets grown on W substrates: an excellent electrocatalyst for the hydrogen evolution reaction.

Thin films of few-layer WS2 nanosheets and WSe2 nanosheets were directly grown on W substrates via a scalable infrared-heating CVD method. The WSe2 nanosheets are in a unique feather-like assembly, and mainly composed of the 2H phase, while the presence of a metallic 1T phase was confirmed through atomic resolution TEM observation. Feather-like WSe2 nanosheets delivered excellent electrocatalytic performances for the HER in acid, including a low overpotential of 141 mV to yield a current at 10 mA cm−2, and superb long-term stability at high currents. The highly efficient electrocatalysis is mainly attributed to the unique feather-like morphology of the WSe2 nanosheets with numerous sharp barbules to help maximize the exposed edge sites, along with other beneficial factors including the presence of a 1T phase and slight O-doping.

Promoting the photocatalytic H2 evolution activity of CdLa2S4 nanocrystalline using few-layered WS2 nanosheet as a co-catalyst

In this work, a series of few-layered WS2 nanosheets were fabricated through an ultrasonic stripping method assisted by a hydrothermal process, then the WS2/CdLa2S4 composites were prepared by growing CdLa2S4 nanocrystallines in situ on the surface of few-layered WS2 nanosheets through an ultrasonic stripping method followed by a hydrothermal process. Investigation shows that the prepared WS2/CdLa2S4 composite shows an excellent photocatalytic activity toward hydrogen evolution from water with visible light response. The optimized content of few-layer of WS2 nanosheet was estimated to be around 5 wt% of CdLa2S4 nanocrystalline and the corresponding hydrogen evolution rate is about 6 times higher than that of single phase of CdLa2S4 nanocrystalline. Furthermore, the WS2/CdLa2S4 composites still keep high photocatalytic activity after 4 times circles. Combining few-layered WS2 nanosheets as a co-catalyst with CdLa2S4 nanocrystallines not only facilitate the efficient separation of photogenerated carriers, but also promote more active sites for hydrogen evolution. Considering its excellent photocatalytic activity toward H2 evolution with visible light response and photochemistry stability, the obtained WS2/CaLa2S4 composite photocatalyst has promising application for practical photocatalytic H2 production from H2O drived by solar energy.

Role of Nanodiamond Grains in the Exfoliation of WS2 Nanosheets and Their Enhanced Hydrogen-Sensing Properties.

Herein, for the first time, a combination of detonation nanodiamond (DND)-tungsten disulfide (WS2) was devised and studied for its selective H2-sensing properties at room temperature. DND-WS2 samples were prepared by a sonication-assisted (van der Waals interaction) liquid-phase exfoliation process in low-boiling solvents with DND as a surfactant. The samples were further hydrothermally treated in an autoclave under high pressure and temperature. The as-prepared samples were separated as two parts named DND-WS2 BH (before hydrothermal) and DND-WS2 AH (after hydrothermal). The exfoliated bilayer to few-layer DND-doped WS2 nanosheets were confirmed by ultraviolet-visible spectra, atomic force microscopy, and transmission electron microscopy studies. It was observed that the DND powder not only acted as a surfactant but also doped and expanded on WS2 nanosheets. The difference between samples BH and AH treatment was further investigated using Raman spectroscopy. The WS2 and DND-WS2 samples on SiO2/Si were fabricated using a sputtered Pd/Ag interdigitated electrode and utilized for H2 gas-sensing measurements. Surprisingly, the DND-WS2 exhibits an ultrahigh sensor response of 72.8% to H2 at 500 ppm when compared to only 9.9% for WS2 alone. Also, the DND-WS2 shows a fast response/recovery time, high selectivity, and stability toward H2 gas. It can be attributed to the correlation of the intergrain phase of DND nanoparticles and WS2 nanosheets, which contributes to the easy transportation of charge carriers when exposed to the air and H2 gas atmosphere. Moreover, it is believed that DND-induced WS2 exfoliation might inspire future synthesis of transition metal dichalcogenides induced by DND in green solvents.

Enhanced electrocatalytic hydrogen evolution performance of 2D few-layer WS2 nanosheets via piezoelectric effects

Two-dimensional transition metal disulfides are considered a great candidate for non-noble metal catalyst because of their abundant reserves and excellent electrochemical activity in hydrogen evolution reaction (HER). Herein, two-dimensional (2D) few-layer WS2 nanosheets were synthesized via a facile liquid phase stripping technique. The piezoelectricity of the synthesized WS2 nanosheets was verified by piezoelectric force microscope (PFM) and used to promote the piezo-catalytic hydrogen generation, where the piezoelectric charges generated under ultrasound vibration are utilized for hydrogen evolution. Moreover, the effect of various mechanical vibration conditions on the piezo-catalytic HER of WS2 was also discussed. The results show that under the same overpotential, the hydrogen production rate with ultrasound vibration (40 kHz, 40 W) is 6 times higher and the impedance is 4 times lower than that without ultrasound. The catalytic efficiency of WS2 can be significantly increased through this method, which paves the way towards non-noble metal HER catalysts to produce hydrogen with aid of piezoelectricity.

Edge-enriched WS2 nanosheets on carbon nanofibers boosts NO2 detection at room temperature

Two-dimensional (2D) transition metal dichalcogenides (TMDs) hold great promise for room temperature (RT) NO2 sensors. However, the exposure of the edges of TMDs with high adsorption capability and electronic activity remains a great obstacle to achieve high sensor sensitivity. Herein, we demonstrate a high-performance RT NO2 gas sensor based on WS2 nanosheets/carbon nanofibers (CNFs) composite with abundant intentionally exposed WS2 edges. Few-layer WS2 nanosheets are anchored on CNFs through a hydrothermal process. The approach permits to achieve a coating presenting an optimized active surface area and accessibility of the sensing layers. The exposure of WS2 edges remarkably improves the sensing properties. Consequently, the WS2@CNFs composite exhibits excellent selectivity to NO2 at RT with improved response and much lower detection limit in comparison to the WS2 and CNFs counterparts. Density functional theory (DFT) calculations verify a surprisingly strong NO2 adsorption on WS2 edge sites (adsorption energy 3.40 eV) with a partial charge transfer of 0.394e, while a week adsorption on the basal surface of WS2 (adsorption energy 0.25 eV) with a partial charge transfer of 0.171e. The strategy proposed herein will be instructive to the design of efficient material structures for low-power NO2 sensors with optimized performances.

Phonon scattering mechanism in van der Waals heterostructures comprising of MoS2 and WS2 nanosheets

In this work, the effect of temperature on the phononic modes (E12g and A1g) of few-layered MoS2 and WS2 nanosheets and their van der Waals heterostructure has been investigated in the temperature regime: 80–600 K. The E12g and A1g modes showed a red-shift with an increase in temperature and exhibited non-linear temperature dependency above 300 K for the constituent nanosheets and their co-stacked heterostructure. A physical model comprising of both thermal and volume effects, is used to quantitatively understand the origin of non-linear temperature dependency of E12g and A1g modes. The observed non-linearities in the phononic modes is well described by the higher-order phonon scattering as a consequence of greater amount of sulphur vacancies in the nanosheets as compared to the bulk counterparts. However, the MoS2-WS2 heterostructure exhibited higher structural stability (lesser sulphur vacancies) as compared to its constituent counterparts owing to the enhanced van der Waals coupling at the hetero-interface and subsequently it decreases with rise in temperature.

Unique ternary Cd0.85Zn0.15S@WO3/WS2 core-shell nanorods for highly-efficient photocatalytic H2 evolution under visible-light irradiation

Development of noble-metal-free photocatalysts for efficient solar-powered water-splitting is of great interest yet still challenging to date. In this work, unique ternary Cd0.85Zn0.15S@WO3/WS2 (CZ0.15S@WO3/WS2) core-shell nanorods consisting of amorphous WO3 and few-layered WS2 nanosheets were synthesized through a two-step solvothermal method for the first time. The composition of WO3/WS2 shell is found to vary with the change of W content, which has a significant impact on the photocatalytic property of CZ0.15S@WO3/WS2 toward H2 evolution reaction (HER). Under visible-light irradiation (λ > 420 nm), the optimized CZ0.15S@WO3/WS2 composite (n (WO3): n (WS2) = 3:1) demonstrates a superior HER activity of 76.33 mmol h−1 g−1 (corresponding to an AQY of 23.9% at 420 nm), which can be further remarkably increased to 157.29 mmol h−1 g−1 when the reaction is driven by full Xe-lamp spectrum. The HER capability of CZ0.15S@WO3/WS2 is much better than that of Pt-decorated CZ0.15S and most CdS-based photocatalysts ever reported, due to the notably enhanced charge transfer and separation via the synergistic cooperation of Z-scheme and type-I charge transfer processes. The findings displayed here could inspire new strategies to optimize the charge separation of multi-component photocatalysts for highly-effective solar conversion and utilization.

Few-layered WS2 nanosheets onto 1D CdS@ZnCdS as efficient visible-light photocatalyst for hydrogen evolution

Exploiting highly efficient and non-expensive visible-light photocatalysts is a huge challenge for H2 photocatalytic production. Here we synthesized an efficient non-precious metal photocatalyst WS2/CdS@ZnCdS (WS2/CdS@ZCS) consisting of few-layered WS2 attached on the core/shell structure of CdS@ZnCdS (CdS@ZCS) via three-step hydrothermal and electrostatic adsorption methods, in which the morphology and structure of the components were regulated independently. The optimum photocatalytic H2 evolution rate of 8 wt% WS2/CdS@ZCS is 34860 μmol h−1 g−1, which is almost 5.2 times as high as that of pure CdS nanorods (6730 μmol h−1 g−1) and superior to most previously reported CdS-based photocatalysts. Moreover, it can maintain 91% of its initial hydrogen evolution rate after 20 hours photocatalytic experiment, indicating WS2/CdS@ZCS is very stable. A possible mechanism of H2 generation on WS2/CdS@ZCS photocatalyst is also proposed. It is thought that this work may provide a promising way to design nanosheets/1D core@shell heterostructured photocatalysts for high-performance and steady H2 production.

Few-layer WS2 nanosheets with oxygen-incorporated defect-sulphur entrapped by a hierarchical N, S co-doped graphene network towards advanced long-term lithium storage performances.

Tungsten sulfide (WS2) with two-dimensional layered graphene-like structure as an anode for lithium-ion batteries (LIBs) has attracted large attention owing to its high theoretical capacity and unique S–W–S layer structure. However, it also always suffers from poor electrical conductivity and volume expansion during lithiation/delithiation process in the practical application. Herein, we demonstrate the successful synergistic regulation of both structural and electronic modulation by simultaneous oxygen incorporation in defect-sulphur WS2 nanosheets embedded into a conductive nitrogen and sulfur co-doped graphene framework (denoted as O-DS-WS2/NSG), leading to dramatically enhanced lithium storage. Such a unique structure not only increases the accessible active sites for Li+ and enhances the kinetics of ion/electron transport, but also relieves the volume effect of WS2. Furthermore, the surface defects and heteroatom incorporation can effectively regulate the electronic structure, improve the intrinsic conductivity and offer more active sites. Consequently, electrochemical performance results demonstrate that the obtained O-DS-WS2/NSG nanocomposites possess great application prospects in LIBs with high specific capacity, superior rate performance as well as excellent cycle stability.

Preparation of Few-Layered WS2 and Its Thermal Catalysis for Dihydroxylammonium-5,5′-Bistetrazole-1,1′-Diolate

In this study, few-layered tungsten disulfide (WS2) was prepared using a liquid phase exfoliation (LPE) method, and its thermal catalytic effects on an important kind of energetic salts, dihydroxylammonium-5,5′-bistetrazole-1,1′-diolate (TKX-50), were investigated. Few-layered WS2 nanosheets were obtained successfully from LPE process. And the effects of the catalytic activity of the bulk and few-layered WS2 on the thermal decomposition behavior of TKX-50 were studied by using synchronous thermal analysis (STA). Moreover, the thermal analysis data was analyzed furtherly by using the thermokinetic software AKTS. The results showed the WS2 materials had an intrinsic thermal catalysis performance for TKX-50 thermal decomposition. With the few-layered WS2 added, the initial decomposition temperature and activation energy (Ea) of TKX-50 had been decreased more efficiently. A possible thermal catalysis decomposition mechanism was proposed based on WS2. Two dimensional-layered semiconductor WS2 materials under thermal excitation can promote the primary decomposition of TKX-50 by enhancing the H-transfer progress.

Blocking defects of zeolite membranes with WS2 nanosheets for vapor permeation dehydration of low water content isopropanol

It is difficult for zeolite membrane to behave good separation selectivity in dehydration of low water content isopropanol (IPA) by vapor permeation (VP) because capillary condensation in small intercrystalline defects is usually insufficient for excluding IPA molecules and adsorbate-induced contraction of zeolite crystals open new defects at low water content. To address this issue, a facile and high-efficiency modification strategy was proposed to block defects of NaA zeolite membranes on hollow fibers by using WS2 nanosheets. Effect of nanosheets thickness on VP separation performance of modified membranes was investigated. It showed that the separation factor of membrane was improved by more than two orders of magnitude (from 60 to >10000) after modified with the few-layer WS2 nanosheets while the loss in water flux was only 18.6% in VP dehydration of 10 wt% water/IPA mixture at 373 K. Moreover, the modified membrane still maintained a high separation factor of ~5000 rather than that of pristine membrane (336) even when the feed water content lowered to 0.5 wt%, indicating that not only intrinsic defects but also the crystal contraction-induced defects were blocked simultaneously by the thin WS2 nanosheets.

Ultrafast carrier dynamics in colloidal WS2 nanosheets obtained through a hot injection synthesis.

In recent years, hot injection synthesis has emerged as a promising route for the production of nanostructured transition metal dichalcogenides, in large due to its better control over the crystallinity and monodispersity compared to other solution based methods. Understanding the photophysics of excitons in the thus obtained colloidal nanosheets is of great importance to explore their potential for applications in optoelectronics. Here, we study the carrier dynamics in these few-layer colloidal WS2 nanosheets by use of broadband transient absorption spectroscopy. The dynamics of both the bleach, linewidth broadening and energy shift across the entire visible and near-infrared spectrum, allows us to identify subpicosecond electron trapping as the main carrier loss channel. A more quantitative analysis shows that the intrinsic properties of colloidally synthesized nanosheets are on par with other synthesis methods, paving the way for this method to produce high quality nanosheets.

Synergetic dielectric loss and magnetic loss towards superior microwave absorption through hybridization of few-layer WS2 nanosheets with NiO nanoparticles

WS2 nanomaterials have attracted great attention in the field of electromagnetic wave absorption due to their high specific surface area, layered structure, and peculiar electronic properties. However, further improvements on their limited electromagnetic absorbing (EMA) capacity and bandwidth are urgently required for their practical application as EMA absorbents. In this work, WS2/NiO hybrids with heterostructures are prepared by a hydrothermal method and developed into EMA absorbents. The maximum reflection loss of the hybrids with 20% NiO loading could reach −53.31 dB at a thickness of 4.30 mm; the bandwidth with a reflection loss value of less than −10 dB is determined to be 13.46 GHz (4.54–18 GHz) when the thickness of the absorbent is between 3.5 and 5.5 mm. It is found that the enhanced EMA performance of WS2/NiO hybrids is caused by the addition of magnetic NiO, which could result in the interfaces between WS2 and NiO being responsible for the synergetic magnetic loss and dielectric loss in the hybrids. This work provides a new approach for the design of excellent EMA materials for practical applications.

Scalable exfoliation and friction performance of few-layered WS2 nanosheets by microwave-assisted liquid-phase sonication

The convenient and high efficient exfoliation for few-layer nanosheets was indispensable for their potential applications. In fact, many reported approaches have been used to successfully exfoliate bulk layered materials into few layers, which fundamentally confronted a few challenges in practice, such as high cost, complicate process, low efficiency and environmental problem. Hence, developing the novel exfoliation process without the above issues was imperative to the prospective application of nanosheets. In this work, we presented a facile and high-quality exfoliation process for few-layer WS2 nanosheets via microwave-assisted sonication method. Detailedly, the crucial highlight in this process was employed the microwave heating expansion via the decomposition of ammonium carbonate pre-impregnated in the interlayers of bulk layered WS2, which was conductive to the second-step liquid phase sonication. The structure characterizations of the as-exfoliated WS2 nanosheets revealed that the high-quality nanosheets had the average lateral size of ca.400 nm and thickness of ca.2.33 nm. Additionally, the tribological performance of the as-exfoliated WS2 nanosheets in oil was investigated, showing that the average friction coefficient of the WS2-based oil was reduced by 28.47% and the wear scar diameter was decreased by 51.67% compared to pristine oil.

Few-layer WS2 modified BiOBr nanosheets with enhanced broad-spectrum photocatalytic activity towards various pollutants removal

Herein, an efficient broad-spectrum WS2/BiOBr heterostructure with ultrathin nanosheet was successfully prepared by one-pot hydrothermal route. The self-assembled flower-like WS2/BiOBr nanostructure was formed by few-layer WS2 and BiOBr nanosheets. The optimized heterojunction presented broad-spectrum high-efficiency photocatalytic activity towards the removal of various pollutants under visible-light irradiation, including organic dyes, antibiotics and phenols. This efficiency was linked to high light harvesting combined with effective charge separation/transfer. Meanwhile, the degradation efficiencies varied with nature of the pollutant decreased in the following order: LR5B (99%) > MNZ (97%) > TC (92%) > OTC (92%) > RhB (90%) > CIP (83%) > MB (78%) > MO (62%) > bisphenol (42%) > phenol (40%). The photocatalytic process of ciprofloxacin was explored, and the results indicated that high ciprofloxacin concentrations, low pH values and elevated concentrations of ions (PO43−, HPO42‐, H2PO4−, and Cu2+) restrained the photocatalytic performances. Trapping experiments and ESR revealed the significant contribution of holes (h+) in the mechanism, where both superoxide radicals (O2−) and hydroxyl radicals (OH) acted as assistants. Overall, this work could offer a new protocol for the design of highly efficient heterostructure photocatalysts for environmental remediation.

Temperature dependent Raman investigations of few-layered WS2 nanosheets

We studied the temperature dependent phononic response of few-layered liquid phase exfoliated WS2 nanosheets using Raman spectroscopy over a wide temperature range from 80 to 600 K. We find that the E12g (in-plane) and A1g (out-of plane) modes follow a systematic red shift with increase in temperature and exhibits weak non-linear temperature dependence in the temperature range of 350–600 K. The first-order temperature coefficients are found to be −0.0111 cm−1 K−1 and -0.0103 cm−1 K−1 for E12g and A1g modes, respectively. From our analysis which is based on a semi-quantitative model, we find that at higher temperatures the non-linear temperature dependence of E12g and A1g modes primarily originates from the an-harmonic effects of three-phonon process as a consequence of creation of S vacancies in the WS2 nanosheets. The thermal expansion contribution is mainly dominant in low temperature region.

Poly(diallydimethylammonium chloride)-Induced Dispersion and Exfoliation of Tungsten Disulfide for the Sensing of Glutathione and Catalytic Hydrogenation of p-Nitrophenol

Poly(diallydimethylammonium chloride) (PDDA) has been demonstrated to be valuable in diverse fields, such as layer-by-layer assembly and material surface modification. Herein, we report a novel application of PDDA for exfoliating bulk tungsten disulfide (WS2) into few-layer WS2 nanosheets (FL-WS2-NSs) under ultrasonication treatment. Cationic PDDA molecules were capable of firmly binding to the WS2 surface to expose quaternary ammonium moieties in water, thereby creating electrostatic repulsion between each FL-WS2-NS. The formation of FL-WS2-NSs was proven by absorption spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. Additionally, PDDA molecules enable FL-WS2-NSs to be stable in 200 mM NaCl for more than six months without thermal-triggered nanosheet aggregation. Given that PDDA-stabilized FL-WS2-NSs (PDDA-FL-WS2-NSs) exhibit sulfur vacancy sites, thiolated boron–dipyrromethene (BODIPY) molecules were self-assembled onto the surface of PDDA-FL-WS2-NSs. As a res...

Two-dimensional (2D) few-layers WS2 nanosheets: An ideal nanomaterials with tunable electromagnetic absorption performance

In this study, few-layer (FL) WS2 nanosheets were fabricated through liquid phase exfoliation, and the dielectric and electromagnetic absorption (EA) properties were first reported. The results show that a composite consisting of 30 wt. % FL-WS2 exhibited an effective EA bandwidth of 4.6 GHz at a thickness of 2.5 mm. Meanwhile, the strongest absorption point (RLstr) can reach −63.0 dB. The most noteworthy is that the FL-WS2 based composite can completely absorb the electromagnetic energy from X (8–12 GHz) and Ku (12–18 GHz) bands. These results indicate that FL-WS2 has practical applications against electromagnetic pollution in the future.