WS2 Platelets Research Articles

Amplifying Flutamide Sensing through the Synergetic Combination of Actinidia-Derived Carbon Particles and WS2 Platelets.

The development of electrochemical sensors for flutamide detection is a crucial step in biomedical research and environmental monitoring. In this study, a composite of Actinidia-derived carbon particles (CPs) and tungsten disulfide (WS2) was formed and used as an electrocatalyst for the electrochemical detection of flutamide. The CPs had an average diameter of 500 nm and contained surface hydroxyl and carbonyl groups. These groups may help anchor the CPs onto the WS2 platelets, resulting in the formation of a CPs-WS2 nanocomposite with a high surface area and a conducting network, enabling electron transfer. Using the CPs-WS2 composite supported at a glassy carbon electrode, a linear concentration range extending from 1 nM to 104 μM, a limit of detection of 0.74 nM, and a sensitivity of 26.9 ± 0.7 μA μM-1 cm-2 were obtained in the detection of flutamide in a phosphate buffer. The sensor showed good recovery, ranging from 88.47 to 95.02%, in river water samples, and exhibited very good selectivity in the presence of inorganic ions, including Al3+, Co2+, Cu2+, Fe3+, Zn2+, NO3 -, SO4 2-, CO3 2-, and Cl-.

Spark plasma sintering behavior and structural stability of 2D- WS2 nanosheets

The sintering behavior and structural stability of two-dimensional (2D) WS2 nanosheet powder under high-temperature pressure-assisted spark plasma sintering (SPS) were investigated. Transformation of the 2D particle morphology to coarse WS2 platelets was observed during sintering at a higher temperature of and above 1000 oC. Particle coarsening was caused by diffusion bonding of multiple 2D-WS2 nanosheet particles on the basal plane surface. Consolidation of the 2D-WS2 nanosheet particles at lower sintering temperatures primarily involved particle-particle interlocking and limited particle-particle diffusion bonding. About 94% of the theoretical density was achieved without any sintering additives on SPS at 1200 oC. The WS2 stoichiometry was retained even at 1200 °C with no indication of any thermal degradation. A fraction of the hexagonal 2H-type structure of the 2D-WS2 transformed to rhombohedral 3R phase during SPS at and above 800 °C. The as-sintered 2D-WS2 showed a low coefficient of friction in the range of 0.06–0.1. The observed tribological behavior was correlated with its thermo-mechanical properties and sintering characteristics at different temperatures.

The Tribological Behavior of As-Sprayed Graphene Oxide–Tungsten Disulfide Hybrid Coatings

The application of solid lubricants in the metal forming of aluminum alloys is imperative due to their potential for the reduction of both friction and aluminum adhesion. This study focuses on examining the potential application of hybrid graphene oxide–tungsten disulfide (GO/WS2) coatings in the forming of aluminum alloys. A series of experiments with different GO/WS2 concentrations (between 1:1 and 12:1) was conducted to investigate the effects of increasing GO concentration on the tribological performance of the coatings. The coefficient of friction (COF) was evaluated using pin-on-disc experiments. The durability of the coatings (the sliding distance prior to the initiation of coating failure) was also recorded. Subsequent surface characterization was performed from within the sliding tracks induced on the coated Al-Mg discs and the mechanisms responsible for friction and wear are discussed. The GO/WS2 hybrid coatings provided low COF values (within the range of 0.18−0.27) and mitigated against aluminum adhesion before failure. An optimum GO/WS2 ratio (6:1) was noted as providing the optimum combination of low friction and improved durability. The concentration of GO in the hybrid coatings influenced the friction performance and durability of coatings, which was related to the formation of tribolayers on the aluminum surface and wear-induced transfer layers on the counterface surface. The formation of the tribolayers was attributed to the mixture of fragmented WS2 platelets, GO flakes, and carbon binder comprising the tribolayer.

Formation of Tungsten Oxide Nanowires by Electron-Beam-Enhanced Oxidation of WS2 Nanotubes and Platelets

Formation of Tungsten Oxide Nanowires by Electron-Beam-Enhanced Oxidation of WS2 Nanotubes and Platelets

Vacuum Tribological Performance of WS2–MoS2 Composite Film Against Oil-Impregnated Porous Polyimide: Influence of Oil Viscosity

To achieve the desired levels of performance and durability for bearings applied in space, a novel solid–liquid dual lubricating system was established via the WS2–MoS2 composite films sliding against oil-impregnated porous polyimide (PPI), in which polyalphaolefin (PAO) oils with different viscosities were used, respectively. The contact angle measurement indicated that the PAO oil had good wettability on the surfaces of the composite film and the PPI. The vacuum tribological behaviors of single WS2–MoS2 composite film and the dual lubricating system were mainly evaluated under different loads and speeds. In comparison with single WS2–MoS2 composite film, the dual lubricating system exhibited the low friction coefficient and synergistic lubricating effect for the low-viscosity PAO oil under severe sliding conditions. It was concluded that the cleavages of the WS2 and MoS2 crystals along the basal plane were more sufficient and formed small and thin WS2 and MoS2 platelets in the dual lubricating system. Meanwhile, it was found that oil-impregnated PPI readily released PAO lubricating oil with low viscosity, which further decreased friction on the contact interface. The lubricating mechanism of the dual lubricating system was also revealed after correlating the tribological behaviors of the different lubricating systems.

The tribological evaluation of graphene oxide and tungsten disulfide spray coatings during elevated temperature sliding contact of aluminum-on-steel

The high tendency of aluminum to adhere to steel has led to extensive research into the application of lubricants to reduce adhesion and friction during forming processes. The behavior of lubricants like tungsten disulfide (WS2) and graphene oxide (GO) are sensitive to their deposition method. WS2 applied through aerosol spray has been observed to increase its working temperature range. This research aims to evaluate the tribological and durability properties of WS2 and GO (deposited as an aerosol spray coating) at temperatures between 25 °C and 450 °C, using ball-on-disc sliding tests. The spray coatings displayed low COF during sliding contact which has been attributed to the formation of transfer layers on the steel counter-faces and tribolayers on the coated Al-Mg surfaces, while their durability was observed to be related to the stability of the tribolayers. The WS2 spray coating was noted to possess more durable tribolayers, which could be a result of the superior adhesion properties of the carbon-bonded WS2 platelets to each other and the AlMg substrate.

Enhanced solar light-driven photocatalytic degradation of pollutants and hydrogen evolution over exfoliated hexagonal WS2 platelets

Two-dimensional (2D) layered structure transition metal dichalcogenides (TMDs) has been attracted huge attention and importance for photocatalytic energy conversion due to their unique properties. In this paper, exfoliated hexagonal WS2 (e-h-WS2) platelets were successfully synthesized by liquid-phase exfoliation (LPE) process from hexagonal WS2 (h-WS2) platelets in DMF solvent. The photocatalytic activity of e-h-WS2 and h-WS2 catalysts were compared systematically for degradation of various organic dye such as Congo red (CR), Methyl orange (MO), Phenol red (PR) and Rhodamine B (RhB)) pollutants and hydrogen production under simulated solar light irradiation. UV-vis and N2 absorption-desorption studies revealed that e-h-WS2 have shown narrow band gap and higher specific surface area than that of h-WS2. Enhanced photocatalytic activity was obtained for e-h-WS2 than h-WS2 i.e. 1.71 fold enhancement for hydrogen production rate. More importantly, this synthetic exfoliated procedure may open up an opportunity to synthesize other transition metal sulfides.

Structural, Mechanical, and Tribological Properties of WS2-Al Nanocomposite Film for Space Application

In this paper, WS2-Al nanocomposite films were deposited by closed-field unbalanced magnetron sputtering to improve the microstructure and wear resistance of pure WS2 film. Results revealed that pure WS2 film presented a columnar microstructure, but the growth of WS2 platelets could be significantly suppressed by doping Al. Correspondingly, the WS2-Al composite film showed a dense fiber-like microstructure at low Al content (~ 3 at.%) and a featureless one at higher Al content (~ 6–12 at.%). The film densification resulted in a significantly improved hardness from ~ 0.3 GPa for pure WS2 film to 2.9 GPa for WS2-3 at.% Al film and to 4.7–5.7 GPa for WS2 composite films with higher Al contents of ~ 6–12 at.%, but the composite films with higher Al contents were brittle. As a result, only the composite film with Al content of ~ 3 at.% exhibited a much better wear resistance than pure WS2 film. In vacuum environment, the wear life of WS2-3 at.% Al composite film about 1.5 × 106 cycles was much higher than that of pure WS2 film ~ 6.5 × 105 cycles, exhibiting a potential application in space technology.

Instant WS2 platelets reorientation of self-adaptive WS2/a-C tribocoating

WS2/a-C nanocomposite coatings were deposited by magnetron co-sputtering using WS2 and graphite targets. The microstructure and triboperformance of the coatings were scrutinized via microscopy (AFM, SEM, FIB, HRTEM), spectroscopy (XRD, XPS) and tribometry. Atomic WS2 platelets are randomly embedded in an amorphous carbon matrix of the as-deposited nanocomposite coating. HRTEM observations of tribofilm/transfer layer reveal that the sliding contact immediately reorients WS2 platelets parallel to the sliding interface and thereby leads to self-adaptive “frictionless” response. The coefficient of friction falls to 0.02 in dry air and reaches 0.10 in humid air, and is reversible as testing atmosphere cycles between dry air and humid air.

On the S/W stoichiometry and triboperformance of WSxC(H) coatings deposited by magnetron sputtering

WSxC(H) coatings were deposited on single crystal silicon(100) wafers by magnetron co-sputtering and reactive sputtering at various target-substrate distances. Upon increasing the distance, the stoichiometric S/W ratio increases from 0.51 to 1.89. Also, the porosity of coatings gradually augments and a columnar microstructure tends to form. Preferential sulfur resputtering rather than contaminations primarily accounts for the low S/W ratio. TEM reveals randomly oriented WS2(002) platelets in the WSxC coatings when deposited at a large distance, which is supported by XRD. The composite coatings exhibit a decreasing hardness and elastic modulus with increasing target-substrate distance. The triboperformance is strongly affected by the coating composition, the target-substrate distance and the testing environment. Cross-sectional TEM of formed tribofilms reveals an obvious reorientation of WS2(002) basal planes parallel to the plane of sliding, leading to an ultralow friction.

Microstructure evolution and enhanced vacuum tribological performance of Ni-doped WS2 composite coating

Ni-doped WS2 composite coatings with various Ni contents were co-deposited using a radio frequency sputtering system on silicon wafer and AISI 440C stainless steel substrates. The microstructural characteristics of the WS2-Ni composite coatings and their tribological properties in vacuum were assessed. During introduction of Ni dopant in the WS2-Ni composite coating the sulfur/tungsten (S/W) ratio in the coating increased due to reduced preferential resputtering of sulfur atoms in the growing coating. The microstructure of the WS2-Ni composite coating varied from a fine columnar structure for Ni content equal to or less than 7.7at.% to a featureless structure as the Ni content increased further. The Ni dopant inhibited the growth of the coarse columnar WS2 platelets which was accompanied by nanocrystallization and amorphization of the composite coating structure. WS2-Ni composite coatings with fine columnar structure exhibited relatively low hardness but showed a high tendency to form a lubricating transfer layer. It also demonstrated low brittleness and prolonged wear life in vacuum condition compared to coatings with dense featureless structure. The variation in tribological performance between the composite coatings resulted from the different wear mechanisms associated with their distinct microstructures.

Long-range order and preferred orientation in WS2 scaffold created by freeze casting

WS2 scaffolds with long-range order lamellar structures and preferred orientation particles were fabricated by freeze casting. The nucleation and growth processes of ice crystals were controlled via the double-side temperature fields and polydimethylsioxane (PDMS) wedge, which resulted in the formation of lamellar structure ranging at the centimeter scale. Additionally, the WS2 platelets particles in each layer of WS2 scaffolds are arranged in preferred orientation along (001) plane. This novel WS2 scaffold is expected to be a potential novel porous material for numerous applications, especially in sliding process.

Selective hydrothermally synthesis of hexagonal WS2 platelets and their photocatalytic performance under visible light irradiation

Hexagonal WS2 platelets have been synthesized via simple hydrothermal synthesis method. The hexagonal WS2 is formed by the oriented attachment (OA)-self-assembly (SA). The thickness of the WS2 platelets was between ∼20 and 100 nm. The specific surface area of these platelets is 94.63 m2 g−1. The hexagonal WS2 platelets exhibited excellent photocatalytic activity compared to irregular WS2 platelets for the degradation of rhodamine B (RhB) under visible light irradiation. This work paves the method for designing hexagonal shaped WS2 platelets with great potential for a wide spectrum of applications in photocatalysis. Moreover, this synthetic procedure may open up an opportunity to tailor the morphologies of the other nanomaterials especially transition metal sulfides.

Pulsed cathodoluminescence and Raman spectra of MoS2 and WS2 nanocrystals and their combination MoS2/WS2 produced by self-propagating high-temperature synthesis

Molybdenum and tungsten disulfide nanoplates were produced by self-propagating high-temperature synthesis in argon atmosphere. This method provides an easy way to produce MoS2 and WS2 from nanoplates up to single- and several layers. The Raman peak intensities corresponding to in-plane E12g and out-of-plane A1g vibration modes and their shifts strongly depend on the thicknesses of the MoS2 and WS2 platelets indicating size-dependent scaling laws and properties. An electron beam irradiation of MoS2 and WS2 powders leads to an occurrence of pulsed cathodoluminescence (PCL) spectra at 575 nm (2.15 eV) and 550 nm (2.25 eV) characteristic to their intrinsic band gaps. For the combination of MoS2 and WS2 nanopowders, a PCL shoulder at 430 nm (2.88 eV) was observed, which is explained by the radiative electron-hole recombination at the MoS2/WS2 grain boundaries. The luminescence decay kinetics of the MoS2/WS2 nanoplates appears to be slower than for individual MoS2 and WS2 platelets due to a spatial separation of electrons and holes at MoS2/WS2 junction resulting in extension of recombination time.

Microtribology and Friction-Induced Material Transfer in WS2 Nanoparticle Additives

The tribological behavior of platelet and nested colloidal particles of tungsten disulfide was studied using the surface forces apparatus, atomic force microscopy, lateral force microscopy, and Auger spectroscopy. Shear-induced material transfer from the colloidal particles to the surfaces was shown to be a dominant factor in the tribological behavior observed for both structures. An ultrathin, ordered layer was observed when nested particles were sheared, while WS2 platelets produced a rough and disordered transfer layer, with substantially inferior lubricating properties.

Microtribology and Friction-Induced Material Transfer in WS2 Nanoparticle Additives

The tribological behavior of platelet and nested colloidal particles of tungsten disulfide was studied using the surface forces apparatus, atomic force microscopy, lateral force microscopy, and Auger spectroscopy. Shear-induced material transfer from the colloidal particles to the surfaces was shown to be a dominant factor in the tribological behavior observed for both structures. An ultrathin, ordered layer was observed when nested particles were sheared, while WS2 platelets produced a rough and disordered transfer layer, with substantially inferior lubricating properties.