WS2 Nanoparticles Research Articles

Liquid Crystal Systems with WS2 Nanoparticles in the Optical Limiting Effect

Liquid Crystal Systems with WS2 Nanoparticles in the Optical Limiting Effect

Band gap tailoring of hydrothermally synthesized WS2 nanoparticles by the sulfurization time duration

In current study, WS2 nanoparticles were systematically synthesized by hydrothermal method. After successful growth, the effect of sulfurization time duration on various optical parameters such as band gap, absorbance, admittance and refractive index was investigated by sulfurization the grown samples for different time durations (0–1 h). XRD patterns have confirmed the pure phase formation of WS2 nanoparticles having crystallite size in the range of 24.4–29.26 nm. SEM images showed the flakes like structures which becomes more visible in combination with rectangular shapes when sulfurization time duration was increased. Synthesized WS2 nanoparticles have been further studied to see their optical properties as a function of sulfurization time duration. All the synthesized samples showed high absorption and low transmission in UV/near visible region at wavelength of 550 nm. By increasing the sulfurization time duration, crystallinity of sulfurized nanoparticles increased which resulted in the decreases of transmission. Optical parameters such as refractive index and the extinction coefficient were also found to be greatly affected by sulfurization. Optical band gap of synthesized nanomaterials have been found to decreases from 2.98 to 2.19eV with increasing sulfurization time duration.

Highly sensitive acetone sensor based on WO3 nanosheets derived from WS2 nanoparticles with inorganic fullerene-like structures

Metal oxide semiconductor (MOS) gas sensors are promising for applications in environmental monitoring, dangerous gas detection, and disease diagnosis. Seeking for advanced MOS sensing materials that possess high sensitivity and low limit of detection (LOD) at sub-ppm level is a great challenge. Here, we report the first creation of two-dimensional (2D) WO3 nanosheets by annealing of the inorganic fullerene (IF)-like WS2 nanoparticles that were prepared via sulfurization of WO3 nanoparticles. Transformation of WS2 to WO3 was realised during the annealing process, simultaneously accompanied by the collapse of the hollow IF-WS2 structures and the formation of tiny 2D WO3 nanosheets with a lateral size of 40−80 nm. The resulting 2D WO3 nanosheets exhibited highly enhanced acetone-sensing performance in terms of sensitivity, selectivity, and response/recovery rates compared with the WO3 nanoparticles used as precursor for the synthesis of the IF-WS2 nanoparticles. The nanosheets also demonstrated great repeatability, reliable long-term stability, and very low LOD, making them a promising candidate as gas sensor to detect breath acetone.

Enhancing the Capacity and Stability of a Tungsten Disulfide Anode in a Lithium-Ion Battery Using Excess Sulfur.

Tungsten disulfide (WS2) is a transition metal disulfide and a promising anode material due to its layered structure, making it favorable for attaining lithium-ion batteries with rate capability and thermal/mechanical stability. Although WS2 has a rich redox chemistry and a large density, which can increase the specific capacity and volumetric energy density, it still has an inferior specific capacity and poor long-term stability for practical use due to its insufficient space for the accommodation of lithium ions and large volume change during cycling. Herein, to overcome the chronic limitations of WS2-based anodes, we propose a micron-sized tungsten disulfide/reduced graphene oxide composite by employing excess sulfur (Sx-WS2/r-GO). In particular, the excess sulfur modifies the polarity of r-GO by chemically binding on the r-GO sheet during WS2 formation, leading to an increase in the adsorption strength due to WS2. Moreover, the excess sulfur increases the lattice parameter of WS2 and decreases the crystallinity degree, securing additional sites for the accommodation of lithium ions. Therefore, the excess sulfur can increase the specific capacity and impede the separation of the pulverized WS2 nanoparticles, hence mitigating structural decay during cycling. As a result, the Sx-WS2/r-GO anode exhibits an enhanced specific capacity of 1426 mAh g-1 at 0.4 A g-1 and a high cyclic performance, with 87.9% capacity retention after 4000 cycles at a high current density (2.0 A g-1).

Influence of Surfactants on the Tribological Behavior of Nanoparticle Additives Under Boundary Lubrication Conditions

Lubricants can significantly improve the anti-wear performance and prolong the service life of machines. It has been found that the introduction of additives can further enhance the performance of lubricating oil and meet harsh working conditions, such as high temperature, high speed, and high load. In this study, 1% by weight of CuO, WC, and WS2 nanoparticles were added to Polyalphaolefins (PAO) base oil to evaluate tribological response. The study focused on using different surfactants including Oleic acid (OA) and Polyisobutylene succinimides (PIBS), to determine their impact of agglomeration and the observed tribological response in the boundary lubrication regime. The results showed that adding 10% OA while sonicating the particles for 30 min reduced the agglomeration the most, and adding 1% OA while sonicating for 120 min produced a more uniform dispersion of the nanoparticles used in this study. Friction studies showed that the nanoparticles additives do not appreciably impact the friction compared to base oil. Wear resistance was improved by about 60% for CuO and WC with 1% OA and sonicated for 120 min. The study suggests that conditions that minimize agglomeration and promote high dispersion lead to favorable wear resistance under boundary lubricant conditions.

Experimental evaluations on tribological performance of oil-based WS2 nanofluid applied on steel/brass friction pairs

The present research evaluated the tribological performance of oil-based WS2 nanofluids applied on steel-brass friction pairs. It was found that the coefficient of friction could be reduced by up to 39%, and the wear width and depth could be reduced by up to 28.7% and 66.4% using 1 wt% WS2 nanofluid. While using the WS2 nanofluids, almost no adhesive wear was detected on the worn surfaces. By analyzing the chemical compositions, carbon percentage increased after engaging the oleic acid which suggested tribo-films with low shear resistance were formed. In addition, elements of sulfur and tungsten were found within the wear track lubricated by WS2 nanofluids. It was believed that the WS2 nanoparticles were involved in the formation of the tribo-layers and mixed with the oleic acid tribo-films to improve the tribological behavior. Moreover, the tribo-layers produced by the WS2 nanoparticles could provide solid lubricating and mending effects on the mating surfaces.

The effect of 2D tungsten disulfide nanoparticles on Lewis lung carcinoma cells in vitro.

The unique physicochemical properties of modern two-dimensional (2D) nanomaterials with graphene-like structures make them promising candidates for biology and medicine purposes. In this article, we investigate the influence of the two-dimensional tungsten disulfide (2D WS2) water suspension nanoparticles obtained by an improved mechanochemical method from powdered WS2 on morphological and structural characteristics of Lewis lung carcinoma cells using FT-IR, Raman spectroscopy, and confocal microscopy. The characterization of the 2D WS2 nanoparticles by different physical methods is given also. We have highlighted that 2D WS2 does not exert cytotoxic activity in the case of 1 day incubation with tumor cells. Prolongation of the incubation period up to 2 days has caused a statistically significant (p < 0.05) concentration-dependent decrease of the number of viable cells by more than 30% with the maximum cytotoxic effect at concentrations of 2D WS2 close to 2 μg ml−1. In the Raman spectra of 2D WS2 treated cells the bands centered at 354 cm−1 and 419 cm−1, which are assigned to characteristics and modes of WS2 nanoparticles were observed. The obtained data indicate, that the cytotoxic effect of 2D WS2 on tumor cells in the case of long-term incubation is realized particularly through the ability of 2D WS2 to enter tumor cells and/or accumulate on their surface, which gives a rationale to conduct further studies of their antitumor efficacy in vitro and in vivo when combined with chemotherapeutic drugs.

Effect of WS2 particles in cutting fluid on tribological behaviour of Ti–6Al–4V and on its machining performance

ABSTRACT Tribological behaviour of Ti–6Al–4V alloy sliding against WC-Co was evaluated by employing WS2 nanoparticles blended in a cutting fluid used for machining of this alloy. Pin-on disk tests were carried out under boundary-lubricated condition using a cutting fluid (70% water and 30% oil) blended with WS2 nanoparticles (CF + WS2). When a cutting fluid with ≥ 0.5 wt.% WS2 was used, the COF of the tribosystem was reduced compared to CF + 0%WS2. The lowest COF of 0.05 was obtained when 1.0 wt.% WS2 was used. Low and stable COF values were accompanied by the formation of a tribolayer incorporating WS2 and WO3 on the WC-Co surfaces. During orthogonal machining of Ti–6Al–4V using CF + 1.0%WS2, a tribolayer with the similar composition was formed on the cutting edge of the WC-Co tool and the average cutting force was reduced by 35% compared to cutting with CF + 0%WS2. Machining with CF + 1.0%WS2 produced thinner chips. Other improvements in machining performance attained using CF + 1.0%WS2 included reduction of adhesive wear on the tool and a lower roughness of the machined surface.

Dual effect of 2D WS2 nanoparticles on the lysozyme conformation

In the present work we studied the effect of 2D WS2 nanoparticles on the conformational changes in lysozyme protein at different pH values (2.0–11.5). The contributions of various structural conformations (α-helix, β-sheets parallel and antiparallel, unordered structure and side groups) were determined by decomposition of Amid I absorbance bands. The 2D WS2 were shown to have different impact on secondary structure depending on pH of the solution and protein concentration.The amyloid fibril presence was confirmed with confocal microscopy enhanced by gold support, and fluorescent spectroscopy with amyloid-sensitive dye Thioflavin T. Our data show that WS2 can both inhibit and stimulate amyloid formation. Additionally, we have also reported an unusual spectroscopic behavior displayed by lysozyme, indicated by narrowing of Amide I and Amide II bands at pH 2.5 and 3.5 when incubated with 2D WS2 nanoparticles.

Chemical control of the surface of WS2 nanoparticles

Tungsten disulfide is an inorganic compound with layer structure. Nanoparticles of WS2 were found to be excellent candidates for reinforcing various polymer materials. However, long storage times in ambient conditions lead to sorption of water molecules and slow oxidation of defect sites. In the present study, the influence of various treatments on the surface composition and reactivity of several kinds of WS2 nanoparticles, were investigated. This study reveals some complex interplay between water and organic moieties desorption and the subsequent oxidation of “nascant” surfaces. Remarkably, simple immersion in HF solution seems to produce the ultimately cleanest surface of these particles.

Insights into the tribological behavior of IF-WS2 nanoparticle reinforced mild extreme pressure lubrication for coated chromium/bulk grey cast iron interface

This study reports a novel synergetic approach combining nano-lubrication and conventional extreme pressure additivation, to explore the tribological performance of piston ring/cylinder liner conformal contact. Three typical lubricating formulations, viz, (i) PAO (poly-alpha-olefin) base oil (ii) base oil with mild extreme pressure (MEP) additive, and (iii) base oil with composite blend of mild extreme pressure (MEP) additive and WS2 nano-particles, were investigated using an ASTM G-99 Standard customized universal tribometer for evaluating friction and wear behavior of coated chromium/bulk grey cast iron (CI) tribopair. The lubricant formulations were tested at engine working temperature of 200 °C, reciprocated under a normal load of 30 N, stroke length of 10 mm and a constant sliding velocity of 0.2 ms−1. Wear attributes were evaluated by employing non-contact based 3 D optical profilometry. For assessment of tribo-surface morphology and associated surface characterization, Elemental Dispersion Spectral (EDS) incorporated Scanning Electron Microscope (SEM) was utilised. Green Laser Raman spectroscopy investigated tribo-chemistry, synergetic interactions and tribo-film formations. A state approaching super-lubricity and ultralow friction was achieved by sliding grey CI (Plateau Honed) cylinder liner against electroplated chrome stainless steel top compression ring with PAO10 base oil ultrasonically dispersed with 1 vol% of Isopropyl phenyl Phosphate (IPP), a mild extreme pressure (MEP) triaryl phosphate additive &amp; 1 wt.% of WS2. Results obtained therein demonstrated four dominating forms of wear on the cast iron surface, i.e. plowing wear, abrasive wear, adhesive wear and oxidative wear. Counterpart chromium surface exhibited plowing and abrasive wear only. This substantial friction and wear reduction are attributed to the coalesced intrinsic characteristics of MEP and IF-WS2 additives, thus improving the overall lubrication characteristics of base oil.

Correlations Between Spectral, Time and Orientation Parameters of Liquid Crystal Cells with WS2 Nanoparticles

Correlations Between Spectral, Time and Orientation Parameters of Liquid Crystal Cells with WS2 Nanoparticles

Sensor based on diamond nanoparticles and WS2 for ponceau 4R and tartrazine determination: Influence of green solvents employed for WS2 exfoliation

We report on the development of an electrochemical sensor for the simultaneous determination of ponceau 4R (P4R) and tartrazine (TR) dyes in non-alcoholic beverages. The sensor is based on the sequential modification of a glassy carbon (GC) electrode with WS2 and diamond nanoparticles (DNP). First, we have performed a computational study to select, among several eco-friendly solvents, the most adequate for exfoliating the 2D nanomaterial from bulk WS2. From this study, four solvents (triacetin, triethyl citrate, dimethylisosorbide and ethanol/water) were preselected for obtaining WS2 dispersions that were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The sensors obtained with these WS2 dispersions and DNP were tested for the determination of both dyes, finding the best results for ethanol/water. We have verified that the presence of both nanomaterials gives rise to an enhancement in the response with respect to both the bare GC and the sensor containing only one of them. The response consists of a pair of peaks corresponding to P4R (+0.69 V) and TR (+0.96 V) and a peak at around +0.2 V, coming from both dyes. After optimizing the initial potential in differential pulse voltammetric (DPV) measurements, we found that when −0.30 V is applied, the peak at +0.2 V is only due to P4R. This lower potential value is more adequate than that at +0.69 V to perform the determination of P4R. As a result of the capability to determine P4R at a low potential together with the synergistic effect between both nanomaterials, which leads to improved sensitivities, our methodology allows the simultaneous determination of both dyes with good analytical properties.

Enhanced positive humidity sensitive behavior of p-reduced graphene oxide decorated with n-WS2 nanoparticles

Most resistance-type humidity sensors exhibit negative humidity sensitivity, i.e., their resistance decreases with a corresponding increase in humidity. This is primarily attributed to the dominant role of ionic conduction in adsorbed water. In this work, a humidity sensor based on a p-type reduced graphene oxide (p-rGO) with positive humidity sensitivity is proposed. Moreover, its positive humidity sensing response is further enhanced by n-type WS2 nanoparticles modification. The results show that both rGO and rGO/WS2 humidity sensors have good linear response in the relative humidity (RH) range of 0% − 91.5%. The sensitivity of the rGO/WS2 humidity sensor is 1.87 times that of rGO humidity sensor, which is mainly attributed to p–n heterojunction between rGO and WS2. Besides, the rGO/WS2 humidity sensor has small humidity hysteresis (~ 3% RH) and good repeatability. This work demonstrates a humidity sensor based on rGO/WS2 composite film and provides a facile route for fabricating humidity sensor with positive humidity sensing properties.

Two-Dimensional Tungsten Disulfide-Based Ethylene Glycol Nanofluids: Stability, Thermal Conductivity, and Rheological Properties.

Developing stable nanofluids and improving their thermo-physical properties are highly important in heat transfer applications. In the present work, the stability, thermal conductivity, and rheological properties of tungsten disulphide (WS2) nanoparticles (NPs) with ethylene glycol (EG) were profoundly examined using a particle size analyzer, zeta-sizer, thermal property analyzer, rheometer, and pH measuring system. WS2 NPs were characterized by various techniques, such as XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), FESEM (Field emission scanning electron microscopy), and high-resolution transmission electron microscopy (HRTEM). The nanofluids were obtained with the two-step method by employing three volume concentrations (0.005%, 0.01%, and 0.02%) of WS2. The influence of different surfactants (Sodium dodecyl sulphate (SDS), Sodium dodecylbenzenesulfonate (SDBS), Cetyltrimethylammonium bromide (CTAB)) with various volume concentrations (0.05–2%) on the measured properties has also been evaluated. Pristine WS2/EG nanofluids exhibit low zeta potential values, i.e., −7.9 mV, −9.3 mV, and −5 mV, corresponding to 0.005%, 0.01%, and 0.02% nanofluid, respectively. However, the zeta potential surpassed the threshold (±30 mV) and the maximum values reached of −52 mV, −45 mV, and 42 mV for SDS, SDBS, and CTAB-containing nanofluids. This showed the successful adsorption of surfactants onto WS2, which was also observed through the increased agglomerate size of up to 1720 nm. Concurrently, particularly for 0.05% SDS with 0.005% WS2, thermal conductivity was enhanced by up to 4.5%, with a corresponding decrease in viscosity of up to 10.5% in a temperature range of 25–70 °C, as compared to EG. Conversely, the viscoelastic analysis has indicated considerable yield stress due to the presence of surfactants, while the pristine nanofluids exhibited enhanced fluidity over the entire tested deformation range. The shear flow behavior showed a transition from a non-Newtonian to a Newtonian fluid at a low shear rate of 10 s−1. Besides this, the temperature sweep analysis has shown a viscosity reduction in a range of temperatures (25–70 °C), with an indication of a critical temperature limit. However, owing to an anomalous reduction in the dynamic viscosity of up to 10.5% and an enhancement in the thermal conductivity of up to 6.9%, WS2/EG nanofluids could be considered as a potential candidate for heat transfer applications.

Tribological characteristics and micromilling performance of nanoparticle enhanced water based cutting fluids in minimum quantity lubrication

Friction and wear characteristics of water-based nanofluids were studied. Deionized water-based nanofluids were prepared with alumina (Al2O3), hBN, MoS2, and WS2 nanoparticles. Tribological study of the prepared nanofluids was undertaken on a ball-on-disk tribometer in minimum quantity lubrication (MQL) mode on Ti-6Al-4 V workpiece. The effect of flow rate on the coefficient of friction (μ) and wear of the workpiece was reported for different nanofluids. 3D profiles of the wear tracks were obtained to study the wear depth and wear profile. Alumina-based nanofluids have shown excellent performance in terms of friction and wear as compared to the other nanofluids. The coefficient of friction, wear track depth and specific wear were reduced by 53.89 %, 23.4 %, and 37.03 % respectively for alumina nanofluid in MQL mode as compared to the dry environment. A commercial cutting fluid (UNILUB 2032) was used for comparative studies. The commercial cutting fluid performed slightly better than the alumina nanofluid, both used in MQL mode. Even though hBN, MoS2, and WS2 are solid lubricants, their performance as nanofluids in MQL mode was not better than alumina nanofluids. Alumina particles, being spherical shaped, were able to provide better lubrication owing to the ball-bearing effect. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of the wear tracks were conducted to understand the mechanism of friction and wear reduction. Micromilling experiments were done on Ti-6Al-4 V using the prepared cutting fluids in MQL mode to evaluate their effect on machining forces and burr formation. Alumina nanofluids and the commercial lubricant have shown significant reduction in machining forces and burr formation as compared to the other nanofluids. This is in correlation to the tribological performance of these cutting fluids.

Convenient synthesis of inorganic fullerene-like WS2 self-lubricating films and their tribological behaviors

Abstract

Temporal Characteristics of Liquid Crystal Cell with WS2 Nanoparticles: Mesophase Sensitization and Relief Features

Temporal Characteristics of Liquid Crystal Cell with WS2 Nanoparticles: Mesophase Sensitization and Relief Features

Solving the “MoS2 Nanotubes” Synthetic Enigma and Elucidating the Route for Their Catalyst-Free and Scalable Production

This study solves a more than two-decades-long "MoS2 Nanotubes" synthetic enigma: the futile attempts to synthesize inorganic nanotubes (INTs) of MoS2 via vapor-gas-solid (VGS) reaction. Among them was replication of the recently reported pure-phase synthesis of the analogous INT-WS2. During these years, successful syntheses of spherical nanoparticles of WS2 and MoS2 were demonstrated as well. All these nanostructures were obtained by VGS reaction of corresponding oxides with H2/H2S gases, at elevated temperatures (>800 °C), in a fluidized bed reactor (FBR) and a one-pot process. This success and apparent similarity between the two compounds "hid" from us the option of looking for the INT-MoS2 reaction parameters in entirely different regimes. The main challenge in the synthesis of INT-MoS2 via VGS was the instability of the in situ prepared suboxide nanowhiskers against over-reduction and recrystallization at high temperatures. The elucidated growth mechanism dictates separation of the reaction into five steps, as properties of the intermediate products are not consistent with a single process and require individual conditions for each step. A horizontal reactor with a porous-quartz reaction cell, which creates proper quasi-static (contrary to the FBR) conditions for the reaction involving sublimation, was imperative for the effective nanofabrication of INT-MoS2. These findings render a reproducible synthetic route for the production of highly crystalline pure-phase MoS2 nanotubes via a multistep VGS process, without the assistance of a catalyst and in a scalable fashion. Being a semiconductor, flexible, and strong, INT-MoS2 offers a platform for much research and numerous potential applications, particularly in the field of optoelectronics and reinforcement of polymer composites.

Synthesis of WS2/CNT hybrid nanoparticles for fabrication of hybrid aluminum matrix nanocomposite

In this study, a simple, safe and cost-effective method was developed for fabricating the tungsten disulfide/carbon nanotube (WS2/CNT) hybrid nanoparticles via chemical vapor deposition (CVD) process. Hybrid nanoparticles used for reinforcing the aluminum matrix. The hybrid nanocomposites were prepared by powder metallurgy processing and consolidated by the Hot-Pressing process. The chemical composition and morphology of the WS2/CNT hybrid particles were studied by x-ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), Raman spectra, Fourier-transform infrared spectroscopy (FTIR) and thermo gravimetric analysis (TGA). The results proved that the uniform, pure and tubular WS2/ CNT hybrid nanoparticles were produced and WS2 nanoparticles were decorated the CNT surface successfully. Optical microscopy (OM) and FESEM used for characterization of the microstructure of hybrid nanocomposite, indicate a good distribution of hybrid nanoparticles in the aluminum matrix. Maximum values of relative density, hardness and compressive strength were measured for sample with WS2/CNT ratio of 1:1. A relative density of more than 99.5% was obtained for this sample. Hardness and compressive strength were improved by 43% and 60% compared with pure aluminum respectively.