Search Results (24)

Molybdenum disulfide (MoS₂) is a promising catalyst for hydrogen evolution through water electrolysis with low cost and high efficiency, but its hydrogen evolution performance can be further improved. Using sodium molybdate (Na₂MoO₄·2H₂O) and thiourea (NH₂CSNH₂) as raw materials, MoS₂ was prepared by the hydrothermal method. Ni-doped MoS₂(Ni-MoS₂) was prepared by using nickel dichloride dihydrate (NiCl₂·2H₂O) as a Ni source and doping Ni into MoS₂ by the hydrothermal method. Under the conditions of different temperatures (190 °C, 200 °C, and 210 °C) and different Ni doping molar ratios (2%, 3%, and 4%), the optimum temperature and doping ratio of the prepared materials were explored by conducting a hydrogen evolution reaction (HER) by the electrolysis of water. The results showed that the optimum preparation temperature was 200 °C and the optimum molar ratio of Ni doping was 3%. Graphene oxide (GO) was obtained by oxidation of graphite (G), and then Ni-MoS₂/GO was prepared by the hydrothermal method with Ni-MoS₂ and GO. The performance of HER was tested. The materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), and X-ray photoelectron spectroscopy (XPS). The results show that the composite Ni-MoS₂/GO has good HER performance, which is better than that of MoS₂ or Ni-MoS₂. In 0.5 M H₂SO₄ solution, the η₁₀ is as low as 196 mV, the Tafel slope is 122 mV/dec, the C_dl is 13.98 mF/cm², and it has good stability. The enhancement of electrocatalytic activity is mainly due to the doping of a small amount of Ni, which increases the defects of the catalyst and forms more active sites. GO improves the conductivity of the material. Ni doping and GO compounding promote the HER performance of MoS₂. Full article

Nickel disulfide (NiS₂) nanoparticles are encapsulated within nitrogen and sulfur co-doped carbon nanosheets, which are grown onto carbon nanofibers to form an array structure (NiS₂/C@CNF), resulting in a self-supporting film. This encapsulated structure not only prevents the agglomeration of NiS₂ nanoparticles, but also memorably buffers its volume changes during charge/discharge cycles, thereby maintaining structural integrity. The nitrogen and sulfur co-doping enhances electronic conductivity and facilitates the faster ion transport of the carbon backbone, improving the low conductivity of the NiS₂/C@CNF anodes. Consequently, the NiS₂/C@CNF electrode exhibits a remarkable rate ability, reaching 55.4% of its capacity at 5 A g⁻¹ compared to that at 0.1 A g⁻¹, alongside an impressive cycling stability, with 89.9% capacity retention over 1500 cycles at 2 A g⁻¹. This work underscores the efficacy of the 3D carbon backbone encapsulation strategy for enhancing the sodium storage property of transition metal-based anodes. Full article

In recent years, there has been significant interest in transition-metal sulfides (TMSs) due to their economic affordability and excellent catalytic activity. Nevertheless, it is difficult for TMSs to achieve satisfactory performance due to problems such as low conductivity, limited catalytic activity, and inadequate stability. Therefore, a catalyst with a heterostructure constituted of a nickel–iron-layered double hydroxide, nickel sulfide, molybdenum disulfide, and cerium dioxide was designed. At the current density of 10 mA cm⁻² in an alkaline solution, the catalyst exhibits a HER overpotential of 116 mV. In addition, an overpotential of 235 mV@150 mA cm⁻² was displayed for OER. The catalyst showed a good retention rate (94.7% for HER, 98.6% for OER) after 160 h stability tests. The excellent electrochemical performance is attributed to the following points: 1. The self-supporting three-dimensional hierarchical structure provides abundant sites, fast ion diffusion channels, and electron transfer paths, and ensures structural stability. 2. The strong interfacial electron interaction between Ni₃S₂/MoS₂ heterojunction and NiFe-LDH improves the OER reaction kinetics. 3. The Ce³⁺ and oxygen vacancies in CeO₂ promote the dissociation of H₂O and promote the HER reaction kinetics. This approach paves the way for developing highly efficient electrocatalysts for various electrochemical applications. Full article

Transition metal dichalcogenide (TMD) monolayers exhibit unique valleytronics properties due to the dependency of the coupled valley and spin state at the hexagonal corner of the first Brillouin zone. Precisely controlling valley spin-polarization via manipulating the electron population enables its application in valley-based memory or quantum technologies. This study uncovered the uncompensated spins of the antiferromagnetic nickel oxide (NiO) serving as the ferromagnetic (FM) order to induce valley spin-polarization in molybdenum disulfide (MoS₂) monolayers via the magnetic proximity effect (MPE). Spin-resolved photoluminescence spectroscopy (SR-PL) was employed to observe MoS₂, where the spin-polarized trions appear to be responsible for the MPE, leading to a valley magnetism. Results indicate that local FM order from the uncompensated surface of NiO could successfully induce significant valley spin-polarization in MoS₂ with the depolarization temperature approximately at 100 K, which is relatively high compared to the related literature. This study reveals new perspectives in that the precise control over the surface orientation of AFMs serves as a crystallographic switch to activate the MPE and the magnetic sustainability of the trion state is responsible for the observed valley spin-polarization with the increasing temperature, which promotes the potential of AFM materials in the field of exchange-coupled Van der Waals heterostructures. Full article

Battery-type hybrid supercapacitors (HSCs) (otherwise known as supercapatteries) are novel electrochemical energy storage devices bridge the gap between rechargeable batteries and traditional SCs. Herein, we report the synthesis of layered two-dimensional (2D) nickel disulfide (NiS₂) nanosheets (NSNs) modified with poly(3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) and their successful implementation in battery-type SCs. Initially, a layered 2D NSN is synthesized via a microwave-assisted hydrothermal method and further used as a template to coat PEDOT:PSS in order to prepare NiS₂@PEDOT:PSS nanocomposite electrodes by a facile drop-casting method. This is the first-time report on the synthesis of a hierarchical NiS₂@PEDOT:PSS nanocomposite electrode for battery-type HSC applications. An asymmetric battery-type HSC fabricated with NSN@PEDOT:PSS nanocomposite as positrode and activated carbon as negatrode delivers a maximum energy density of 52.1 Wh/kg at a current density of 1.6 A/g with a corresponding power density of 2500 W/kg. Full article

This article reports a simple hydrothermal method for synthesizing nickel disulfide (NiS₂) on the surface of fluorine-doped tin oxide (FTO) glass, followed by the deposition of 5 nm Au nanoparticles on the electrode surface by physical vapor deposition. This process ensures the uniform distribution of Au nanoparticles on the NiS₂ surface to enhance its conductivity. Finally, an Au@NiS₂-FTO electrochemical biosensor is obtained for the detection of dopamine (DA). The composite material is characterized using transmission electron microscopy (TEM), UV-Vis spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrochemical properties of the sensor are investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and time current curves in a 0.1 M PBS solution (pH = 7.3). In the detection of DA, Au@NiS₂-FTO exhibits a wide linear detection range (0.1~1000 μM), low detection limit (1 nM), and fast response time (0.1 s). After the addition of interfering substances, such as glucose, L-ascorbic acid, uric acid, CaCl₂, NaCl, and KCl, the electrode potential remains relatively unchanged, demonstrating its strong anti-interference capability. It also demonstrates strong sensitivity and reproducibility. The obtained Au@NiS₂-FTO provides a simple and easy-to-operate example for constructing nanometer catalysts with enzyme-like properties. These results provide a promising method utilizing Au coating to enhance the conductivity of transition metal sulfides. Full article

Refolding multi-disulfide bonded proteins expressed in E. coli into their native structure is challenging. Nevertheless, because of its cost-effectiveness, handiness, and versatility, the E. coli expression of viral envelope proteins, such as the RBD (Receptor-Binding Domain) of the influenza Hemagglutinin protein, could significantly advance research on viral infections. Here, we show that H1N1-PR8-RBD (27 kDa, containing four cysteines forming two disulfide bonds) expressed in E. coli and was purified with nickel affinity chromatography, and reversed-phase HPLC was successfully refolded into its native structure, as assessed with several biophysical and biochemical techniques. Analytical ultracentrifugation indicated that H1N1-PR8-RBD was monomeric with a hydrodynamic radius of 2.5 nm. Thermal denaturation, monitored with DSC and CD at a wavelength of 222 nm, was cooperative with a midpoint temperature around 55 °C, strongly indicating a natively folded protein. In addition, the ¹⁵N-HSQC NMR spectrum exhibited several ¹H-¹⁵N resonances indicative of a beta-sheeted protein. Our results indicate that a significant amount (40 mg/L) of pure and native H1N1-PR8-RBD can be produced using an E. coli expression system with our refolding procedure, offering potential insights into the molecular characterization of influenza virus infection. Full article

A bifunctional electrocatalyst with high efficiency and low costs for overall water splitting is critical to achieving a green hydrogen economy and coping with the energy crisis. However, developing robust electrocatalysts still faces huge challenges, owing to unsatisfactory electron transfer and inherent activity. Herein, NiFe LDH/NiS₂/VS₂ heterojunctions have been designed as freestanding bifunctional electrocatalysts to split water, exhibiting enhanced electron transfer and abundant catalytic sites. The optimum NiFe LDH/NiS₂/VS₂ electrocatalyst exhibits a small overpotential of 380 mV at 10 mA cm⁻² for overall water splitting and superior electrocatalytic performance in both hydrogen and oxygen evolution reactions (HER/OER). Specifically, the electrocatalyst requires overpotentials of 76 and 286 mV at 10 mA cm⁻² for HER and OER, respectively, in alkaline electrolytes, which originate from the synergistic interaction among the facilitated electron transfer and increasingly exposed active sites due to the modulation of interfaces and construction of heterojunctions. Full article

Transition metal sulfides have excellent electrochemical performance and show great potential for improving the energy density of asymmetric supercapacitors. This study demonstrates a two-step synthesis technique and highlights the enhanced energy storage efficiency of ZnS-NiS₂ composite materials for asymmetric supercapacitors. The composite materials of ZnS nanosheets and NiS₂ nanocrystals are characterized by a rough surface and spherical shape. The sample with the optimal ratio (ZnS-NiS₂-1:7) exhibits a maximum specific capacitance of 1467.9 F g⁻¹ (550.5 C g⁻¹) at 1 A g⁻¹. The specific capacitance of the ZnS-NiS₂-1:7 sample is 26.1% higher compared to the pure NiS₂ sample. Furthermore, the assembled ZnS-NiS₂-1:7//AC device shows a high specific capacitance of 127.8 F g⁻¹ (217.3 C g⁻¹) at 1 A g⁻¹ and an energy density of 51.3 Wh kg⁻¹ at a power density of 820.8 W kg⁻¹. The ZnS-NiS₂-1:7 sample has exceptional energy storage capability on its own, but it can also be composited with graphene to further increase the specific capacitance (1681.0 F g⁻¹ at 1 A g⁻¹), suggesting promising prospects for the ZnS-NiS₂-based composite material in the future. Full article

This paper investigated the fretting failure of axial thrust steel bearings as per ASTM 4170 in the presence of anti-fretting pastes used in process industries. The pastes were differentiated based on the content of additives in them. The results indicated that the paste containing the additive package of copper, molybdenum disulfide, and graphite exhibited excellent anti-fretting properties (75–80% less bearing race mass loss) as compared with other lubricating pastes that contained only graphite/molybdenum disulfide and nickel as primary additives. There was less surface damage to the bearing races in the lubricating paste containing copper, graphite, and molybdenum disulfide. The machine vision images of the false brinelling indicated that the average area of false brinelling on the bearing races with the paste containing copper, molybdenum disulfide, and graphite was 2.537 ± 0.623 mm², while that of the other pastes containing graphite/molybdenum disulfide and nickel as primary additives were 4.504 ± 0.566 mm² and 4.914 ± 0.621 mm², respectively, indicating 50% less false brinelling area in the paste containing copper, molybdenum disulfide, and graphite as compared with the paste containing graphite/molybdenum disulfide and nickel. An asymmetric wear pattern was also observed in the thrust bearings used during the tribo test. Surface characterizations indicated the formation of wear debris, plastic deformations, and surface cracks during the tribo tests. The physico-chemical properties of the lubricating pastes such as the viscosity and work penetration properties played an important role in controlling the failure of the bearings due to fretting. Full article

The chemical transformation of carbon dioxide (CO₂) not only reduces the amount of carbon dioxide emitted into the Earth’s atmosphere by humans, but also produces carbon compounds that can be used as precursors for chemical and fuel production. Herein, a selective catalytic conversion of carbon dioxide to methanol is achieved by a bifunctional molybdenum disulfide catalyst (MoS₂) with magnesium oxide and nickel and potassium promoters. Molybdenum disulfide prepared by the supercritical ethanol method has a large specific surface area and presents good catalytic performance with high methanol selectivity when loaded with potassium (K) and nickel (Ni) promoters. In addition, the catalysts were evaluated and it was founded that the addition of the K-promoter improved methanol selectivity. This research provides a new strategy for improved product selectivity and space–time yield (STY) of methanol in CO₂ hydrogenation. Full article

The toxicity of commonly used drugs, such as acetaminophen (ACAP) and its degradation-derived metabolite of 4-aminophenol (4-AP), underscores the need to achieve an effective approach in their simultaneous electrochemical determination. Hence, the present study attempts to introduce an ultra-sensitive disposable electrochemical 4-AP and ACAP sensor based on surface modification of a screen-printed graphite electrode (SPGE) with a combination of MoS₂ nanosheets and a nickel-based metal organic framework (MoS₂/Ni-MOF/SPGE sensor). A simple hydrothermal protocol was implemented to fabricate MoS₂/Ni-MOF hybrid nanosheets, which was subsequently tested for properties using valid techniques including X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transformed infrared spectroscopy (FTIR), and N₂ adsorption-desorption isotherm. The 4-AP detection behavior on MoS₂/Ni-MOF/SPGE sensor was followed by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). Our experimental findings on the generated sensor confirmed a broad linear dynamic range (LDR) for 4-AP from 0.1 to 600 μM with a high sensitivity of 0.0666 μA/μM and a low limit of detection (LOD) of 0.04 μM. In addition, an analysis of real specimens such as tap water sample as well as a commercial sample (acetaminophen tablets) illuminated the successful applicability of as-developed sensor in determining ACAP and 4-AP, with an impressive recovery rate. Full article

The transition metal dichalcogenides have instigated a lot of interest as harmonic generators due to their exceptional nonlinear optical properties. Here, the molybdenum disulfide (MoS₂) molecular structures with dopants being in a plasma state are used to demonstrate the generation of intense high-order harmonics. The MoS₂ nanoflakes and nickel-doped MoS₂ nanoflakes produced stronger harmonics with higher cut-offs compared with Mo bulk and MoS₂ bulk. Conversely, the MoS₂ with nickel nanoparticles and carbon nanotubes (MoS₂-NiCNT) produced weaker coherent XUV emissions than other materials, which is attributed to the influence of phase mismatch. The influence of heating and driving pulse intensities on the harmonic yield and cut-off energies are investigated in MoS₂ molecular structures. The enhanced coherent extreme ultraviolet emission at ~32 nm (38 eV) due to the 4p-4d resonant transitions is obtained from all aforementioned molecular structures, except for MoS₂-NiCNT. Full article

The paper provides results of a detailed mineralogical study of some chromitite ores from two deposits in the Southern Urals of Kazakhstan: Almaz-Zhemchuzhina and Geofizicheskoe-VII. It is revealed that the main ore minerals are Cr-spinel with high Cr# (Cr/(Cr + Al) = 0.8–0.83), as well as serpentine and chlorite, replacing primary olivine. Chromium spinel grains contain mineral inclusions, which are distributed rather unevenly. The most common mineral inclusions are olivine (serpentine) and amphibole; phlogopite, pyroxenes, and base metal sulfides are rare. Olivine from inclusions in chromite is the highest in magnesium (Fo_97–98), and is anomalously high in nickel (up to 1.8 wt.% NiO). The closure of exchange reactions between olivine and chromite occurred in the temperature range of 700–850 °C and in the oxygen fugacity range of −1.04 … +2.8 ΔFMQ, which most likely corresponds to the upper mantle settings of the fore-arc basin. A few tens of monomineral grains and polymineral intergrowths of platinum group minerals (PGMs) were found in chromite aggregates. Notably, monomineral grains are mainly represented by Ru, Os, and Ir disulfides, while in polymineral inclusions, iridium prevails (with widespread native phases, sulfides, and sulfoarsenides). PGM grains included in chromite are often associated with hydrous silicates: amphibole, and less often with phlogopite or chlorite. Discussed in the paper is the possible genesis of ores and inclusions. As a preliminary conclusion, we suggest that the solid-phase processes played the most significant role in the crystallization of Cr-spinel in the investigated chromitite ores. Full article

In the current world of coatings and nanomaterials, specifically bearings, zinc, chromium, nickel, diamond-like coatings, and molybdenum disulfide are being used, to name but a few. Boron nitride in various forms has been used to enhance the surface properties, such as hardness, wear resistance, and corrosion resistance of dies, tools, etc. In this paper, a significant focus is being given to the improvement of the surface properties of bearing-steel materials by the impregnation of cubic and hexagonal boron nitride nanoparticles. The vacuum heat treatment method is used for treating the sample pins of material equivalents to EN31. In the design of the experiments, the Taguchi method with L₂₇ orthogonal array is used for the optimization of various parameters, such as the weight % of c-BN and h-BN nanoparticles and the temperature of the vacuum treatment. With the help of preliminary experimentation, the three levels of three parameters are decided. The microhardness analysis shows an improvement from 321 HV0.1 to 766 HV0.1 for a 50 µm case depth of nanoparticle impregnation. The evaluation of the influence of selected factors is also performed using ANOVA and the S/N ratio, and it was revealed that hex boron nitride (h-BN) affects the microhardness value more than the other two factors. The friction and wear testing reveal that the wear properties are improved by approximately 1.6 times, and the frictional force also decreases by approx. 1.4 times. Scanning electron microscope (SEM) analysis shows that the nanoparticles are penetrated by 21.09% and 46.99% atomic weight. In addition, a reduction in the friction coefficient and better wear response were achieved as a result of the heat treatment with nanoparticle impregnation. Full article