High-efficiency preparation of oil-dispersible MoS<Subscript>2</Subscript> nanosheets with superior anti-wear property in ultralow concentration

Molybdenum disulfide (MoS₂) nanosheets are a promising lubricant additive for enhanced engine efficiency in cars. However, high-cost production methods and poor dispersion have limited their application in industry. In this study, the ball milling process is demonstrated as a low-cost and high-efficient method for fabrication of oil-dispersible MoS₂ nanosheet, and the ball milling parameters are optimized. Moreover, the lubrication effectiveness of ball-milled MoS₂ nanosheet was also evaluated. Results indicated that well-dispersed MoS₂ nanosheets with a size of 250 nm can be manufactured with optimized surfactants of zinc dialkyldithiphosphates (ZDDP) and polyisobutylene succinimide (PIBS) after being ball milled for 36 h. Tribological results revealed that a friction coefficient of white oil with 0.25% MoS₂ nanosheets reached 0.075, much lower than that of lubricant without nanosheets (0.16). The wear scar radius of 0.015% MoS₂ nanosheets was similar with that of Hertz contact, and the wear scar radius reduction reached 20% compared with that of 1% ZDDP. In addition, EDS and XPS results indicated the formation of a MoS₂ and FeS tribofilm on the wear surface.     

Facile growth of monolayer MoS<Subscript>2</Subscript> film areas on SiO<Subscript>2</Subscript>

Areas of single-layer MoS₂ film can be prepared in a tube furnace without the need for temperature control. The films were characterized by means of Raman spectroscopy, photoluminescence, low-energy electron diffraction and microscopy, and X-ray photoelectron spectroscopy and mapping. Transport measurements show n-doped material with a mobility of 0.26 cm² V^-1 s^-1.     

Enhanced lithium-ion storage and hydrogen evolution reaction catalysis of MoS<Subscript>2</Subscript>/graphene nanoribbons hybrids with loose interlaced three-dimension structure

Molybdenum disulfide hybridized with graphene nanoribbon (MoS₂/GNR) was prepared by mild method. MoS₂/GNR hybrids interlace loosely into a three-dimension structure. GNR hybridization can improve the dispersity of MoS₂, reduce the grain size of MoS₂ to 3–6 nm, increase the specific surface area, and broaden the interlamellar spacing of MoS₂ (002) plane to 0.67–0.73 nm, which facilitates the transportation of Li⁺ ions for lithium-ion battery. MoS₂/GNR hybrids have better cyclic durability, higher specific discharge capacity, and superior rate performance than MoS₂. The electrocatalytic activity in hydrogen evolution reaction shows that MoS₂/GNR hybrids have the lower overpotential and the larger current density with a negligible current loss after 2000 cycles. Hybridizing with GNRs enhances both the lithium-ion electrochemical storage and the electrocatalytic activity of MoS₂.

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Graphical abstract MoS₂/GNR hybrid prepared by a mild method is interlaced loosely into a three-dimension structure. Superior electrochemical performances of MoS₂/GNR hybrids than MoS₂ have been highlighted for the potential application for long- term durability energy-storage devices and HER electrocatalytic materials.

     

Photodeposition of ultrathin MoS<Subscript>2</Subscript> nanosheets onto cubic CdS for efficient photocatalytic H<Subscript>2</Subscript> evolution

In this work, the photocatalyst composed of ultrathin MoS₂ nanosheets onto the surface of cubic CdS nanoparticles with an average diameter of 7~10 nm has been successfully fabricated through a facile and mild photodeposition route. The ultrathin MoS₂ nanosheets as a cocatalyst were demonstrated to greatly boost photocatalytic H₂ evolution over cubic CdS upon visible light irradiation. It was clearly revealed that both the cubic CdS substrate and structure of ultrathin MoS₂ nanosheets play critical roles in the observed efficient H₂ evolution. The cubic CdS offers a strong adherence for ultrathin MoS₂ nanosheets to form a well contact interface, across which the photogenerated charge transfer and charge separation are achieved. The ultrathin MoS₂ nanosheets introduce a high density of unsaturated active S atoms for H₂ evolution.     

The interfacial properties of SrRuO<Subscript>3</Subscript>/MoS<Subscript>2</Subscript> heterojunction: a first-principles study

First-principles calculation was used to study the interfacial properties of theSrRuO₃ (1 1 1)/MoS₂(√3 × √3) heterojunction. It is found that the huge magneticmoments in of monolayer MoS₂ largely originate from the Ru-S hybridization for theRu-terminated interface. Moreover, for the SrO-terminated interface, we studied mainly themetal and semiconductor contact characteristic. The calculated results show that theSchottky barrier height can be significantly reduced to zero for the SrO-terminatedinterface. Schottky barrier heights dominate the transport behavior of theSrRuO₃/MoS₂ interface. Our results not only have potentialapplications in spintronics devices, but also are in favour of the scaling of field effecttransistors.     

Synthesis and characterization of platinum nano sized particles by laser ablation in C<Subscript>2</Subscript>H<Subscript>6</Subscript>O<Subscript>2</Subscript> solution

Platinum nano sized particles (Pt NPs) are superior catalysts for many intentions, such as glucose sensors, cancer therapy, gas sensors, etc. Here, Pt NPs were produced by pulsed laser ablation in C₂H₆O₂ solution using Q-switched Nd:YAG laser, for the first time. Then, the influence of the laser fluence during synthesis of them was investigated; and they were characterized by UV–vis spectroscopy, TEM, FE-SEM, XRD, FT-IR, and Raman spectroscopy. The results showed that with increasing laser fluence, the mean particle size of the spherical NPs enhanced. Meanwhile, they had a polycrystalline cubic structure. Correspondingly, the plasmon peak position of generated NPs in the absorption spectra shifted from 257 to 266 nm, with a rise of laser fluence. The IR and Raman spectroscopy was used to achieve the information about the surface state of Pt NPs. We propose that the optimum adjusted laser fluence is an important factor to increase the ablation efficiency.     

Flower-like MoS<Subscript>2</Subscript> supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS₂ supported on three-dimensional graphene aerogel (MoS₂/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS₂ microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS₂/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g^?1 at a current density of 0.1 A g^?1 and good cycling performance (348.6 mAh g^?1 after 30 cycles at 0.1 A g^?1). The good Na⁺ storage properties of the MoS₂/GA composite could be attributed to the unique structure which flower-like MoS₂ are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS₂/GA composite has a great potential prospect as anodes for SIBs.     

Templated synthesis of plate-like MoS<Subscript>2</Subscript> nanosheets assisted with HNTs and their tribological performance in oil

Two-dimensional MoS₂ nanosheets were synthesized by using halloysite nanotubes (HNTs) as template under the hydrothermal synthesis. The structure and morphology of the as-synthesized MoS₂ nanosheets were determined by a series of characterizations. The results showed that the as-synthesized MoS₂ nanosheets were of the plate-like structure with about five layers, and the basal spacing was about 0.63 nm. It was demonstrated that HNTs played a crucial template role in the formation of the plate-like MoS₂ nanosheets. The formation mechanism was proposed. Furthermore, the tribological performance of the as-prepared MoS₂ nanosheets in oil was intensively examined on the ball-on-ball wear tester. The testing results verified that the as-prepared MoS₂ nanosheets as additive could significantly improve the friction performance of oil, which exhibited the good antifriction, antiwear, and load-carrying properties.     

High-peak-power,high-repetition-rate LD end-pumped Nd:YVO<Subscript>4</Subscript> burst mode laser

A compact high-peak-power, high-repetition-rate burst mode laser is achieved by an acousto-optical Q-switched Nd:YVO₄ 1064 nm laser directly pumped at 878.6 nm. Pulse trains with 10–100 pulses are obtained using acousto-optical Q-switch at repetition rates of 10–100 kHz under a pulsed pumping with a 1 ms duration. At the maximum pump energy of 108.5 mJ, the pulse energy of 10 kHz burst mode laser reaches 44 mJ corresponding to a single pulse energy of 4.4 mJ and an optical-to-optical efficiency of 40.5 %.The maximum peak power of ~468.1 kW at 10 kHz is obtained with a pulse width of 9.4 ns. The beam quality factor is measured to be M ² ~1.5 and the pulse jitter is estimated to be less than 1 % in both amplitude and time region.     

Perfect valley polarization in MoS<Subscript>2</Subscript>

We study perfect valley polarization in a molybdenum disulfide (MoS₂) nanoribbon monolayer using two bands Hamiltonian model and non-equilibrium Green’s function method. The device consists of a one-dimensional quantum wire of MoS₂ monolayer sandwiched between two zigzag MoS₂ nanoribbons such that the sites A and B of the honeycomb lattice are constructed by the molecular orbital of Mo atoms, only. Spin-valley coupling is seen in energy dispersion curve due to the inversion asymmetry and time-reversal symmetry. Although, the time reversal symmetry is broken by applying an external magnetic field, the valley polarization is very small. A valley polarization equal to 46% can be achieved using an exchange field of 0.13 eV. It is shown that a particular spin-valley combination with perfect valley polarization can be selected based on a given set of exchange field and gate voltage as input parameters. Therefore, the valley polarization can be detected by detecting the spin degree of freedom.     

Synthesis and microstructure of Co/Ni: MgGa<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

This report discusses the preparation and microstructure of Co/Ni co-doped MgGa₂O₄ nanoparticles. The nanoparticles with the size of 20–55 nm were synthesized by sol-gel method. The phase and crystallinity were confirmed by X-ray powder diffraction (XRD) pattern. The particle size was estimated according to XRD data and transmission electron microscopy. The electronic structure was studied using X-ray photoelectron spectroscopy (XPS). The XPS studies showed that Ga³⁺ ions possess tetrahedral and octahedral sites of spinel structure and the inverse degree (two times of the fraction of tetrahedral Ga³⁺ ions) has increased with the increase of the doping concentration of Co²⁺ and Ni²⁺ ions. For Co/Ni co-doped MgGa₂O₄, two broad absorption bands of 350~500 and 550~700 nm were observed in the absorption spectra. The broad band at 350~500 nm was assigned to the combination of the absorption of octahedral Co²⁺ and Ni²⁺ ions, whereas the absorption band at 550~700 nm is mainly due to tetrahedrally coordinated Co²⁺ ions and octahedrally coordinated Ni²⁺ ions.     

Regular hexagonal MoS<Subscript>2</Subscript> microflakes grown from MoO<Subscript>3</Subscript> precursor

Regular hexagonal MoS₂ microflakes with high yield were grown from MoO₃ precursor by a sulfurization process using S powders as sulfuration reducer. The precursors, long and smooth MoO₃ microbelts, were synthesized through a direct oxidation reaction of Mo plates in air. X-ray powder diffraction and scanning electron microscopy revealed that the sulfurized products were hexagonal MoS₂ with regular hexagonal flake-like morphology. The results of transmission electron microscopy examinations demonstrated that the microflakes were single crystalline MoS₂. Elemental analysis by EDAX and XPS showed that the microflakes consist of Mo and S with the atomic ratio near to 0.5. Factors influencing the formation of the product were systematically studied. PACS 81.15.Gh; 81.15.Kk; 81.05.Hd; 78.67.Pt; 82.40.Ck     

Grain size effects on dynamics of Li-ions in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites

Li₃V₂(PO₄)₃ glass-ceramic nanocomposites, based on 37.5Li₂O-25V₂O₅-37.5P₂O₅ mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li⁺ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li⁺ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li⁺ ions/electrons and higher surface area of contact between cathode and electrolyte.     

Controlled synthesis of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by chemical reducing method in ethylene glycol

Antimony trioxide (Sb₂O₃) nanoparticles with particle size range from 2 to 12 nm were successfully synthesized by chemical reducing method. Antimony trichloride was reduced by hydrazine with the presence of sodium hydroxide (NaOH) as catalyst in ethylene glycol at 120 °C for 1 h. Effects of hydrazine concentration ([N₂H₅OH]/[Sb³⁺] = 0.75, 5, 10, 20, and 30, when concentration of NaOH was fixed [NaOH]/[Sb³⁺] = 3) and NaOH concentration ([NaOH]/[Sb³⁺] = 0, 1, 3, and 5, when concentration of hydrazine was fixed [N₂H₅OH]/[Sb³⁺] = 10) on the particle size and shape of the Sb₂O₃ nanoparticles were investigated. Transmission electron microscope, selected area electron diffraction pattern, and high resolution electron microscope were employed to study the morphology and crystallinity of the nanoparticles. It was observed that the particle size decreased and remained constant when [N₂H₅OH]/[Sb³⁺]) ≥ 10 and [NaOH]/[Sb³⁺] = 3. Further study on the crystallinity and phase of the nanoparticles was assisted by X-ray diffractometer (XRD). XRD revealed a cubic phase of Sb₂O₃ (ICDD file no. 00-043-1071) with preferred plane of (622) and lattice spacing of 1.68 Å. Correlation between UV–visible absorption wavelengths of the nanoparticles and their sizes was established.     

Surface Plasmon Polaritons in MoS<Subscript>2</Subscript> Nanostructures

The surface plasmon polaritons (SPPs) in monolayer MoS₂ nanostructures are theoretically investigated in detail. Our study shows that the strong SPPs are induced in gigahertz (GHz) frequency range. The frequencies of SPPs are very sensitive on the substrates in the nanostructures. Moreover, the frequency of such SPPs can be controlled by varying the electron densities. Our study can be applied to understand the recent experimental results and is relevant to the applications of plasmonic nano-devices based on MoS₂.     

Laser-diode-pumped Nd:YVO<Subscript>4</Subscript>/Nd:YAG MOPA burst-mode laser

We report a high-repetition-rate, high-peak-power laser diode (LD) pumped burst-mode 1064 nm laser from a Nd:YVO₄/Nd:YAG master oscillator power amplifier. 10–100 kHz pulse burst in a duration up to 2 ms is achieved in LD end-pumped Nd:YVO₄ acousto-optically Q-switched laser. After amplification with LD side-pumped Nd:YAG rod amplifiers, the single pulse energy reaches 73 mJ in 10 kHz pulse burst laser with a peak power of 7.8 MW.     

A study of oleic acid-based hydrothermal preparation of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Nearly monodisperse, well crystalline, superparamagnetic CoFe₂O₄ nanoparticles with diameter of 6 nm were synthesized in oleic acid–water–pentanol system at 180 °C. Hydrothermal procedure, as an efficient and environment friendly alternative to organic decomposition methods, was investigated by variation of reaction conditions, and the particle formation mechanism was finally proposed (i.e., hydrolysis of metal oleates in organic phase, with size of the particles (5–8 nm) controlled by polarity-driven precipitation into water phase). As-prepared particles were hydrophobic due to coating by oleic acid. Further modification with dimercaptosuccinic acid led to water-dispersible particles with hydrodynamic diameter of 20 nm. Prepared particles were investigated by TEM, XRD, ICP-AES, light scattering, SQUID magnetometry, and Mössbauer spectroscopy.     

Synthesis of hierarchical MoS<Subscript>2</Subscript> microspheres composed of nanosheets assembled via facile hydrothermal method as anode material for lithium-ion batteries

A hierarchical MoS₂ architecture composed of nanosheet-assembled microspheres with an expanded interplanar spacing of the (002) planes was successfully prepared via a simple hydrothermal reaction. Electron microscopy studies revealed formation of the MoS₂ microspheres with an average diameter of 230 nm. It was shown that the hierarchical structure of MoS₂ microspheres possesses both the merits of nanometer-sized building blocks and micrometer-sized assemblies, which offer high surface area for fast kinetics and buffers the volume expansion during lithium insertion/deinsertion, respectively. The micrometer-sized assemblies were found to contribute to the enhanced electrochemical stabilities of the electrode materials. The mentioned advantages of the MoS₂ electrode prepared in this work allowed enhanced cyclability and high rate capability of the material. Along with this, the material delivered a high initial discharge capacity of 1206 mAh g^?1 and a reversible discharge capacity of 653 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1. Furthermore, the material delivered a high reversible capacity of 480 mAh g^?1 at a high current density of 1000 mA g^?1.     

Synthesis and structural determination of twisted MoS<Subscript>2</Subscript> nanotubes

In the present work we report the synthesis of MoS₂ nanotubes with diameters greater than 10 nm using a template method. The length and properties of these nanotubes are a direct result of the preparation method. High-resolution transmission electron microscopy is used to study the structure of these highly curved entities. Molecular dynamics simulations of MoS₂ nanotubes reveal that one of the stable forms of the nanotubes is a twisted one. The twisting of the nanotubes produces a characteristic contrast in the images, which is also studied using simulation methods. The analysis of the local contrast close to the perpendicular orientation shows geometrical arrays of dots in domain-like structures, which are demonstrated to be a product of the atomic overlapping of irregular curvatures in the nanotubes. The configuration of some of the experimentally obtained nanotubes is demonstrated to be twisted with a behavior suggesting partial plasticity. PACS 61.16.Bg; 79.60.Jv; 61.46.+w; 61.50.Ah     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> quantum dots on 3D-framed graphene aerogel as an advanced anode material in lithium-ion batteries

Three-dimensional fabricated Fe₃O₄ quantum dots/graphene aerogel materials (Fe₃O₄ QDs/GA) were obtained from a facile hydrothermal strategy, followed by a subsequently heat treatment process. The Fe₃O₄ QDs (2–5 nm) are anchored tightly and dispersed uniformly on the surface of three-dimensional GA. The as-prepared anode materials exhibit a high reversible capacity of 1078 mAh g^?1 at a current density of 100 mA g^?1 after 70 cycles in lithium-ion batteries (LIBs) system. Moreover, the rate capacity still remains 536 mAh g^?1 at 1000 mA g^?1. The enhanced electrochemical performance is attributed to that the GA not only acts as a three-dimensional electronic conductive matrix for the fast transportation of Li⁺ and electrons, but also provides with double protection against the aggregation and pulverization of Fe₃O₄ QDs during cycling. Apparently, the synergistic effects of the three-dimensional GA and the quantum dots are fully utilized. Therefore, the Fe₃O₄ QDs/GA composites are promising materials as advanced anode materials for LIBs.