Carbon nanotube-MoS2 composites as solid lubricants

Electrodeposited MoxSyOz/Ni Tribological Coatings

Deposition of molybdenum disulfide (MoS2) coatings using physical vapor deposition (PVD) and mechanical burnishing has been widely assessed for solid lubricants in space applications but still suffers from line-of-sight constraints on complex geometries. Here, we highlight one of the first demonstrations of electrodeposited MoxSyOz and MoxSyOz/Ni thin-film coatings from aqueous solutions of ammonium tetrathiomolybdate for solid lubricant applications and their remarkable ability to provide low coefficients of friction and high wear resistance. Characterization of the coating morphology shows amorphous microstructures with a high oxygen content and cracking upon drying. Even so, electrodeposited MoxSyOz can achieve low steady-state coefficients of friction (μ ∼ 0.05-0.06) and wear rates (2.6 × 10-7 mm3/(N m)) approaching those of physical vapor deposited coatings (2.3 × 10-7 mm3/(N m)). Additionally, we show that adding dopants such as nickel increased the wear rate (7.5 × 10-7 mm3/(N m)) and initial coefficient of friction (μi = 0.23) due to compositional modifications such as dramatic sub-stoichiometry (S/Mo ∼ 1) and expression of a NiOx surface layer, although doping did reduce the degree of cracking upon drying.

Unveiling the tribological potential of MXenes-current understanding and future perspectives

Reducing energy consumption and CO2 emissions by improving the tribological performance of mechanical systems relies on the development of new lubrication concepts. Two-dimensional (2D) materials have been the subject of extensive tribological research due to their unique physical and chemical properties. 2D transition metal carbides, nitrides, and carbonitrides (MXenes), with their tuneable chemistry and structure, are a relatively new addition to the family of 2D materials. MXenes' good strength and stiffness, easy-to-shear ability, capability to form wear-resistant tribofilms, and the possibility to control their surface chemistry make them appealing candidates to be explored for tribological purposes. This review provides a comprehensive overview of MXenes' tribology, covering their structure-property relationship, synthesis approaches, deposition methods to generate MXene coatings for tribological purposes, and their fundamental tribological mechanisms. Furthermore, detailed insights into studies exploring MXenes' tribological performance from the nano- to the macro-scale are presented with special emphasis on their use as self-lubricating solid lubricants, lubricant additives, and reinforcement phases in composites.

Contact and Tribological Study of Micro/Nano Groove Texture on the Surface of Gas Bearing Materials Based on Nanoscale

As a kind of sliding bearing, the gas bearing is widely used in high-speed rotating machinery. It realizes energy cleaning in the field of high-speed rotating machinery. In order to solve the problem of reducing the service life of gas bearings due to friction during startup and shutdown, we use micromachining technology to process groove textures with different groove widths on the surface of 0Cr17Ni7Al, a common material for gas bearings. A ball-disc friction contrast test is conducted under dry friction conditions with and without texture. The experiment shows that the lowest average friction coefficient of 0.8 mm texture is σ = 0.745. When the friction radius is 22.5 mm, the wear rate of 1.0 mm texture is the lowest at ω = 3.118 × 10-4mm3/N·mm. However, the maximum friction coefficient reached is σ = 0.898. Under the nanometer scale, the contact between friction pairs is fully analyzed. The influence mechanism of different groove widths, friction impacts and climbing heights on the friction and wear properties of the micromechanical groove texture on the surface of 0Cr17Ni7Al stainless steel is studied at the nano-fractal scale. The effects of different width grooves on the surface texture and tribological properties of the micromachine are studied.

Highly Durable Antimicrobial Tantalum Nitride/Copper Coatings on Stainless Steel Deposited by Pulsed Magnetron Sputtering

Highly durable and antimicrobial tantalum nitride/copper (TaN/Cu) nanocomposite coatings were deposited on D-9 stainless steel substrates by pulsed magnetron sputtering. The Cu content in the coating was varied in the range of 1.42-35.42 atomic % (at.%). The coatings were characterized by electron probe microanalyzer, X-ray diffraction, scanning electron microscope and atomic force microscope. The antibacterial properties of the TaN/Cu coatings against gram-negative Pseudomonas aeruginosa were evaluated using a cell culture test. The peak hardness and Young's modulus of TaN/Cu with 10.46 at.% Cu were 24 and 295 GPa, respectively, which amounted to 15 and 41.67% higher than Cu-free TaN. Among all, TaN/Cu with 10.46 at.% exhibited the lowest friction coefficient. The TaN/Cu coatings exhibited significantly higher antibacterial activity than Cu-free TaN against Pseudomonas aeruginosa. On TaN, the bacterial count was about 4 × 10⁶ CFU, whereas it was dropped to 1.2 × 10² CFU in case of TaN/Cu with 10.46 at.% Cu. The bacterial count was decreased from 9 to 6 when the Cu content increased from 25.54 to 30.04 at.%. Live bacterial cells were observed in the SEM images of TaN, and dead cells were found on TaN/Cu. Overall, TaN/Cu with 10.46 at.% Cu was found to be a potential coating composition in terms of higher antimicrobial activity and mechanical durability.

Enhancement of Thermal Stability, Conductivity and Smoke Suppression of Polyethylene Composites with Exfoliated MoS2 Functionalized with Magnetite

This work reports a facile fabrication method to modify exfoliated molybdenum disulfide (e-MoS2) nanosheets with magnetite nanoparticles with various size distribution. The obtained materials have been utilized as nanofillers of polyethylene to enhance its thermal properties and flame retardance. The incorporation of magnetite modified MoS2 nanosheets leads to the reduction of the peak heat release rate. The best thermal conductivity has been noticed for composites with e-MoS2/Fe3O4 with 2 wt. % of nanofillers. The lowest CO emission was observed for the PE/e-MoS2 composite containing also 2 wt. % of Fe3O4. All composites with exfoliated MoS2 exhibited greater thermal properties in respect to the pristine polyethylene.

Tungsten Disulfide Inorganic Nanotubes Functionalized by PTFE for Friction Application

Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfoliate at the contact interface and facilitate tribofilm formation. While the tribological properties are greatly improved by exfoliated NPs that shed easily, they may be diminished by agglomeration in oil. Therefore, surface functionalization is employed to improve dispersion in oil-based suspensions. Here, WS2 INTs were functionalized by polytetrafluoroethylene (PTFE) in a simple and cost-effective bath sonication method. WS2-INTs with two concentrations of added PTFE were characterized by scanning and transmission electron microscopy, micro-Raman spectroscopy, and thermogravimetric analysis. Superior distribution of WS2 was observed before and during friction experiments. Chemical analysis showed a significantly greater amount of PTFE-coated INTs on rubbed surfaces, in accordance with the improved friction and wear properties.

Temperature-Adaptive Ultralubricity of a WS2/a-C Nanocomposite Coating: Performance from Room Temperature up to 500 °C

This study reports on the ultralubricity of a high-temperature resilient nanocomposite WS₂/a-C tribocoating. The coefficient of friction of this coating remains at around 0.02 independently of a thermal treatment up to ∼500 °C, as confirmed by high-temperature tribotests. Moreover, the coating annealed at 450 °C keeps exhibiting a similar ultralubricity when cooled back down to room temperature and tested there, implying a tribological self-adaptation over a broad temperature range. High-resolution TEM observations of the tribofilms on the wear track unveil that WS₂ nanoplatelets form dynamically via atomic rearrangement and extend via unfaulting geometrical defects (bound by partial climb dislocations). The (002) basal planes of the WS₂ nanoplatelets, reoriented parallel to the tribo-sliding direction, contribute to a sustainable ultralubricity. The declining triboperformance beyond 500 °C is associated with sulfur loss rather than the transformation of WS₂ into inferior WO₃ via oxidation as suggested earlier. This self-adaptive WS₂/a-C tribocoating holds promise for a constant ultralubrication with excellent thermal performance.

Bandgap Engineering and Near-Infrared-II Optical Properties of Monolayer MoS2: A First-Principle Study

The fluorescence-based optical imaging in the second near-infrared region (NIR-II, 1,000-1,700 nm) has broad applications in the biomedical field, but it is still difficult to find new NIR-II fluorescence materials in the two dimension. As a crucial characteristic of the electronic structure, the band structure determines the fundamental properties of two-dimensional materials, such as their optical excitations and electronic transportation. Therefore, we calculated the electronic structures and optical properties of different crystalline phases (1T phase and 2H phase) of pure monolayer MoS2 films and found that the 1T phase has better absorption and thus better fluorescence in the NIR-II window. However, its poor stability makes the 1T-phase MoS2 less useful in vivo bioimaging. By introducing vacancy defects and doping with foreign atoms, we successfully tuned the bandgap of the monolayer 2H-MoS2 and activated it in the NIR-II. Our results show that by engineering the vacancy defects, the bandgap of the 2H phase can be tailored to around 1 eV, and there are three candidates of vacancy structures that exhibit strong absorption in the NIR-II.

Mechanical Properties and Vacuum Tribological Performance of Mo-S-N Sputtered Coatings

MoS₂ is the most widely used dry lubricant for low friction applications in vacuum environments. However, due to its lamellar nature it exfoliates during sliding, leading to high wear, high coefficient of friction (COF), and low stability. Here, we report the mechanical properties and the vacuum (10^-4 Pa) tribological performance of nitrogen-alloyed transition-metal-dichalcogenide (TMD-N) coatings. The coatings were deposited using a hybrid deposition method, that is, reactive direct current (DC) sputtering of MoS₂ target assisted by an additional plasma source. The tribological tests were performed at relatively low contact stresses to replicate real industrial needs. The interaction between different mating surfaces (coating versus steel, coating versus coating) has been reported. Additionally, the effects of loads on the sliding properties were also studied for coating versus coating interactions. A maximum hardness of 8.9 GPa was measured for the 37 atom % N-alloyed coating. In all mating conditions, the pure MoS₂ coating had COF in the range of 0.1-0.25 and the least specific wear rates were found to be 3.0 × 10^-6 mm³/N·m for flat and 2.5 × 10^-6 mm³/N·m for cylinder. As compared to MoS₂ coating, the COF and specific wear rates decreased with N additions. The COF was in the range of 0.05-0.1 for Mo-S-N coatings, while coating versus coating displayed the lowest specific wear rates (8.6 × 10^-8 mm³/N·m for flat and 4.4 × 10^-8 mm³/N·m for cylinder). Finally, the increase in load resulted in a decrease of COF, but an increase in the wear rate was observed. The detailed mechanism behind the behavior of the COF for the different mating conditions was presented and discussed. This work brings some important issues when testing transition metal dichalcogenide-based coatings under low contact stress conditions more appropriate for simulating real service applications.

Enhanced Mechanical Toughness of Isotactic Polypropylene Using Bulk Molybdenum Disulfide

Herein, we report the use of bulk molybdenum disulfide (MoS2) as the reinforcing agent to enhance the toughness of isotactic polypropylene (iPP). The iPP-MoS2 nanocomposites with varying amounts of MoS2 (0.1 to 5 wt %) were prepared by a one-step melt extrusion method, and the effects of MoS2 on the morphology, thermal, and mechanical properties were evaluated by different instrumental techniques such as Raman, ATR-FTIR, UTM, TEM, TGA, and DSC. TEM images showed the uniform dispersion of multilayer MoS2 in the polymer matrix, and XRD results suggested the formation of the β phase when a low amount of MoS2 is loaded in the composites. Mechanical tests revealed a significant increase in the toughness and elongation at break (300-400%) in the composites containing low amounts of MoS2 (0.25 to 0.5 wt %). Enhanced toughness and elongation in iPP could be related to the combined effect of the β phase and the exfoliation of bulk MoS2 under applied stress. The thermal stability of the composites was also improved with the increase in MoS2 loading. Direct utilization of bulk MoS2 and one-step melt extrusion process could be a cost-effective method to induce high elasticity and toughness in iPP.

The Application of Nano-MoS2 Quantum Dots as Liquid Lubricant Additive for Tribological Behavior Improvement

Molybdenum disulfide quantum dots (MoS₂ QDs) are a promising lubricant additive for enhanced engine efficiency. In this study, MoS₂ QDs were used as lubricating oil additives for ball-on-disc contact and had adequate dispersity in paroline oil, due to their super small particle size (~3 nm). Tribological results indicate that the friction coefficient of paroline oil with 0.3 wt.% MoS₂ QDs reached 0.061, much lower than that of pure paroline oil (0.169), which is due to the formation of a stable tribo-film formed by the MoS₂, MoO₃, FeS, and FeSO₄ composite within the wear track. Synergistic lubrication effects of the tribo-film and ball-bearing effect cooperatively resulted in the lowest friction and wear.

Rolling Contact Performance of a Ti-Containing MoS2 Coating Operating Under Ambient, Vacuum, and Oil-Lubricated Conditions

Solid lubricant molybdenum disulfide (MoS2) coatings have been frequently used to lubricate mechanisms operating in environments where oil and grease lubrication are ineffective. This work evaluated the rolling contact performance of a Titanium-containing MoS2 coating under humid ambient, vacuum, and oil-lubricated conditions. Weibull analyses of L50 lifetimes of AISI 52100 steel balls coated with a Ti-MoS2 coating paired with uncoated M50 steel rods were determined to be 3.7, 14.5, and 158.6 million cycles in ambient, vacuum, and oil-lubricated environments, respectively. In the ambient and vacuum tests, failures were determined to be associated with the onset of abrasive wear rather than fatigue or spalling. The L50 lifetimes of tests performed in those environments were found to depend upon the wear rate of the coatings on the balls. That is, the Ti-MoS2 functioned as a barrier to the onset of abrasive wear between the steel alloys until the coating was sufficiently worn away. Under oil-lubricated (boundary lubrication) conditions, L50 was found to depend on the durability and composition of tribofilms formed in-situ on the surfaces of the uncoated M50 rods. The tribofilms were comprised of mixtures of MoS2 crystallites and amorphous hydrocarbon (a-C:H). The crystalline MoS2 in the tribofilm originated from the amorphous Ti-MoS2 coating and likely underwent a thermodynamic phase transition as a result of the applied Hertz stress and frictional heating in the contact. The a-C:H in the tribofilm probably originated from a catalytic scission of the polyalphaolefin (PAO) molecules caused by the d-band character of the Mo or Ti in the coating. Overall, the Ti-MoS2-coated balls were effective at extending the operational lifetimes of M50 rods under ambient, vacuum, and oil-lubricated conditions by an order of magnitude.

Efficient Removal of Pb(II) and Cd(II) from Industrial Mine Water by a Hierarchical MoS2/SH-MWCNT Nanocomposite

In this study, we investigate the adsorption capability of molybdenum sulfide (MoS₂)/thiol-functionalized multiwalled carbon nanotube (SH-MWCNT) nanocomposite for rapid and efficient removal of heavy metals [Pb(II) and Cd(II)] from industrial mine water. The MoS₂/SH-MWCNT nanocomposite was synthesized by acid treatment and sulfurization of MWCNTs followed by a facile hydrothermal reaction technique using sodium molybdate and diethyldithiocarbamate as MoS₂ precursors. Morphological and chemical features of the nanocomposite material were studied using various characterization techniques. Furthermore, the effects of adsorbent (MoS₂/SH-MWCNT nanocomposite) concentration, contact time, initial concentration of heavy-metal ions, and reaction temperature were examined to determine the efficiency of the adsorption process in batch adsorption experiments. Kinetics and isotherm studies showed that the adsorption process followed pseudo-second-order and Freundlich adsorption isotherm models, respectively. Thermodynamic parameters calculated using van't Hoff plots show the spontaneity and endothermic nature of adsorption. MoS₂/SH-MWCNT nanocomposite demonstrates a high adsorption capacity for Pb(II) (90.0 mg g^-1) and Cd(II) (66.6 mg g^-1) following ion-exchange and electrostatic interactions. Metal-sulfur complex formation was identified as the key contributor for adsorption of heavy-metal ions followed by electrostatic interactions for multilayer adsorption. Transformation of adsorbent into PbMoO_4-x S _x and CdMoO_4-x S _x complex because of the adsorption process was confirmed by X-ray diffraction and scanning electron microscopy-energy-dispersive spectrometry. The spent adsorbent can further be used for photocatalytic and electrochemical applications; therefore, the generated secondary byproducts can also be employed for other purposes.

Solid Lubrication with MoS2: A Review

Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.

Fabrication of Novel CeO2/GO/CNTs Ternary Nanocomposites with Enhanced Tribological Performance

Increasing demands of multi-functional lubricant materials with well distributed nanoparticles has been generated in the field of oil lubrication. In this study, one-dimensional (1-D) acidified multi-walled carbon nanotubes (CNTs) and two-dimensional (2-D) graphene oxide (GO) sheets were dispersed together under an ultra-sonication condition to form CNTs/GO hybrids and the corresponding CNTs/GO hybrids decorated with uniform zero-dimensional (0-D) cerium oxide (CeO2) nanoparticles were prepared via a facile hydrothermal method. The tribological performance of CeO2/CNTs/GO ternary nanocomposite was systematically investigated using a MS-T3000 ball-on-disk tester. The results demonstrated that CeO2/GO/CNTs nanocomposites can effectively reduce the friction of sliding pairs in paraffin oil. Moreover, the oil with 1 wt% of CeO2/GO/CNTs exhibited the best lubrication properties with the lowest friction coefficient and wear scar diameters (WSD) compared with adding only GO nanosheet, CeO2, and CeO2/CNTs hybrid nanocomposite as lubricant additives. It is concluded that due to the synergistic effect of 0D CeO2, 1D CNTs, and 2D GO during sliding process, a dimensionally mixed CeO2/GO/CNTs nanocomposite exhibits excellent lubricating properties, providing innovative and effective additives for application in the field of lubrication.

In situ tribochemical sulfurization of molybdenum oxide nanotubes

MoS₂ nanoparticles are typically obtained by high temperature sulfurization of organic and inorganic precursors under a S rich atmosphere and have excellent friction reduction properties. We present a novel approach for making the sulfurization unnecessary for MoO₃ nanotubes during the synthesis process for friction and wear reduction applications while simultaneously achieving a superb tribological performance. To this end, we report the first in situ sulfurization of MoO₃ nanotubes during sliding contact in the presence of sulfur-containing lubricant additives. The sulfurization leads to the tribo-chemical formation of a MoS₂-rich low-friction tribofilm as verified using Raman spectroscopy and can be achieved both during sliding contact and under extreme pressure conditions. Under sliding contact conditions, MoO₃ nanotubes in synergy with sulfurized olefin polysulfide and pre-formed zinc dialkyl dithiophosphate tribofilms achieve an excellent friction performance. Under these conditions, the tribochemical sulfurization of MoO₃ nanotubes leads to a similar coefficient of friction to the one obtained using a model nanolubricant containing MoS₂ nanotubes. Under extreme pressure conditions, the in situ sulfurization of MoO₃ nanotubes using sulfurized olefin polysulfide results in a superb load carrying capacity capable of outperforming MoS₂ nanotubes. The reason is that while MoO₃ nanotubes are able to continuously sulfurize during sliding contact conditions, MoS₂ nanotubes progressively degrade by oxidation thus losing lubricity.

Long-lasting solid lubrication by CNT-coated patterned surfaces

The use of lubricants (solid or liquid) is a well-known and suitable approach to reduce friction and wear of moving machine components. Another possibility to influence the tribological behaviour is the formation of well-defined surface topographies such as dimples, bumps or lattice-like pattern geometries by laser surface texturing. However, both methods are limited in their effect: surface textures may be gradually destroyed by plastic deformation and lubricants may be removed from the contact area, therefore no longer properly protecting the contacting surfaces. The present study focuses on the combination of both methods as an integral solution, overcoming individual limitations of each method. Multiwall carbon nanotubes (MWCNT), a known solid lubricant, are deposited onto laser surface textured samples by electrophoretic deposition. The frictional behaviour is recorded by a tribometer and resulting wear tracks are analysed by scanning electron microscopy and Raman spectroscopy in order to reveal the acting tribological mechanisms. The combined approach shows an extended, minimum fivefold longevity of the lubrication and a significantly reduced degradation of the laser textures. Raman spectroscopy proves decelerated MWCNT degradation and oxide formation in the contact. Finally, a lubricant entrapping model based on surface texturing is proposed and demonstrated.

Preparation and tribological properties of graphene oxide/nano-MoS2 hybrid as multidimensional assembly used in the polyimide nanocomposites

A three-step strategy was employed to prepare a self-lubricating and anti-wear graphene oxide/nano-MoS₂ (GO/nano-MoS₂, abbreviated GMS) hybrid by chemical compounding as a novel multidimensional assembly.

Tribological Properties of Water-lubricated Rubber Materials after Modification by MoS2 Nanoparticles

Frictional vibration and noise caused by water-lubricated rubber stern tube bearings, which are generated under extreme conditions, severely threaten underwater vehicles’ survivability and concealment performance. This study investigates the effect of flaky and spherical MoS₂ nanoparticles on tribological properties and damping capacity of water-lubricated rubber materials, with the aim of decreasing frictional noise. A CBZ-1 tribo-tester was used to conduct the sliding tests between rubber ring-discs and ZCuSn₁₀Zn₂ ring-discs with water lubrication. These materials’ typical mechanical properties were analysed and compared. Coefficients of friction (COFs), wear rates, and surface morphologies were evaluated. Frictional noise and critical velocities of generating friction vibration were examined to corroborate above analysis. Results showed that spherical MoS₂ nanoparticles enhanced rubber material’s mechanical and tribological properties and, in turn, reduced the friction noise and critical velocity. Flaky MoS₂ nanoparticles reduced COF but did not enhance their mechanical properties, i.e., the damping capacity, wear resistance property; thus, these nanoparticles did not reduce the critical velocity obviously, even though increased the frictional noise at high load. The knowledge gained in the present work will be useful for optimizing friction pairs under extreme conditions to decrease frictional noise of water-lubricated rubber stern tube bearings.

High temperature friction and wear properties of graphene oxide/polytetrafluoroethylene composite coatings deposited on stainless steel

Polytetrafluoroethylene (PTFE) coating is known as a low friction material that is often used as a solid lubricant coating.

Molybdenum disulfide nanoflakes through Li-AHA assisted exfoliation in an aqueous medium

A novel route to synthesize MoS₂ nanoflakes though Li-AHA assisted liquid phase exfoliation.

A feasible multilayer structure design for solid lubricant coatings in a lunar environment

Solid lubricant coatings have received considerable research attention in space applications owing to their remarkably improved tribological characteristics.

MoS2 Nanosheets Hosted in Polydopamine-Derived Mesoporous Carbon Nanofibers as Lithium-Ion Battery Anodes: Enhanced MoS2 Capacity Utilization and Underlying Mechanism

In this work, solid, hollow, and porous carbon nanofibers (SNFs, HNFs, and PNFs) were used as hosts to grow MoS2 nanosheets hydrothermally. The results show that the nanosheets on the surface of SNFs and HNFs are comprised of a few grains stacked together, giving direct carbon-MoS2 contact for the first grain and indirect contact for the rest. In contrast, the nanosheets inside of PNFs are of single-grain size and are distributed evenly in the mesopores of PNFs, providing efficient MoS2-carbon contact. Furthermore, the nanosheets grown on the polydopamine-derived carbon surface of HNFs and PNFs have larger interlayer spacing than those grown on polyacrylonitrile-derived carbon surface. As a result, the MoS2 nanosheets in PNFs possess the lowest charge-transfer resistance, the most accessible active sites for lithiation/delithiation, and can effectively buffer the volume variation of MoS2, leading to its best electrochemical performance as a lithium-ion battery anode among the three. The normalized reversible capacity of the MoS2 nanosheets in PNFs is about 1210 mAh g(-1) at 100 mA g(-1), showing the effective utilization of the electrochemical activity of MoS2.

A sensitive electrochemical aptasensor based on palladium nanoparticles decorated graphene-molybdenum disulfide flower-like nanocomposites and enzymatic signal amplification

In the present study, with the aggregated advantages of graphene and molybdenum disulfide (MoS2), we prepared poly(diallyldimethylammonium chloride)-graphene/molybdenum disulfide (PDDA-G-MoS2) nanocomposites with flower-like structure, large surface area and excellent conductivity. Furthermore, an advanced sandwich-type electrochemical assay for sensitive detection of thrombin (TB) was fabricated using palladium nanoparticles decorated PDDA-G-MoS2 (PdNPs/PDDA-G-MoS2) as nanocarriers, which were functionalized by hemin/G-quadruplex, glucose oxidase (GOD), and toluidine blue (Tb) as redox probes. The signal amplification strategy was achieved as follows: Firstly, the immobilized GOD could effectively catalyze the oxidation of glucose to gluconolactone, coupling with the reduction of the dissolved oxygen to H2O2. Then, both PdNPs and hemin/G-quadruplex acting as hydrogen peroxide (HRP)-mimicking enzyme could further catalyze the reduction of H2O2, resulting in significant electrochemical signal amplification. So the proposed aptasensor showed high sensitivity with a wide dynamic linear range of 0.0001 to 40 nM and a relatively low detection limit of 0.062 pM for TB determination. The strategy showed huge potential of application in protein detection and disease diagnosis.

A novel label-free electrochemiluminescence aptasensor based on layered flowerlike molybdenum sulfide-graphene nanocomposites as matrix

A label-free and ultrasensitive electrochemiluminescence (ECL) aptasensor was constructed for the detection of thrombin. Molybdenum sulfide-graphene nanocomposites with good conductivity and large surface area were immobilized on glassy carbon electrode (GCE), and then Nafion was fixed to chemosorb the Ru(bpy)3(2+) used as luminescence agent. Subsequently, gold nanoparticles (AuNPs) were modified on the electrode to immobilize the thiol-modified thrombin aptamer for fabrication of the thrombin aptasensor. The proposed ECL aptasensor produced the ultrasensitive detection of thrombin with a low detection limit of 3.6×10(-15)M (S/N=3) and over a wide target concentration range from 1.0×10(-14) to 5.0×10(-9)M. The aptasensor has been successfully applied in the determination of thrombin in human plasma samples of both traumatic and non-traumatic injury patients, indicating its promise in biochemical analysis. The recoveries of thrombin in human plasma samples are between 88.6% and 105.0%, and the RSD values are no more than 3.7%. The results demonstrate that this aptasensor has excellent sensitivity, selectivity and stability.

Three-dimensional assembly of single-layered MoS(2)

Assembly of single layers: Three-dimensional assembly of single-layered MoS2 is achieved on a large scale via a solution method. The as-prepared tubular architectures have tunable size and mesopores in the shell, which are desirable for applications. As a example, they exhibit excellent lithium storage properties and are highly active for hydrodesulfurization of thiophene resulting from their structural advantages.

Preparation and utility of a self-lubricating & anti-wear graphene oxide/nano-polytetrafluoroethylene hybrid

Graphene oxide/nano-PTFE (GNF), combining intrinsic functions from graphene oxide and nano-PTFE, as a self-lubricating and anti-wear additive, reduces friction coefficient and further increases wear resistance.

Multi-walled carbon/IF-WS2 nanoparticles with improved thermal properties

A unique new class of core-shell structured composite nanoparticles, C-coated inorganic fullerene-like WS2 (IF-WS2) hollow nanoparticles, has been created for the first time in large quantities, by a continuous chemical vapour deposition method using a rotary furnace. Transmission electron microscopy and Raman characterisations of the resulting samples reveal that the composite nanoparticles exhibited a uniform shell of carbon coating, ranging from 2-5 nm on the IF-WS2 core, with little or no agglomeration. Importantly, thermogravimetric analysis and differential scanning calorimetry analysis confirm that their thermal stability against oxidation in air has been improved by about 70 °C, compared to the pristine IF-WS2, making these new C-coated IF-WS2 nanoparticles more attractive for critical engineering applications.

Atomic structure and edge magnetism in MoS(2+x) parallelogram shaped platelets

The structural, electronic, and magnetic properties of MoS(2+x) parallelogram shaped platelets having m and n Mo atoms on the adjoining edges have been studied using first principles calculations and by varying m and n from 1 to 6. These platelets have 100% S coverage on two adjoining edges while 50% S coverage on the other two edges. The structural stability of the platelets increases with size but the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap in general decreases. There is a triangular metallic corner at the intersection of 100% S covered edges of the platelets when m = n. On the other hand magnetism is observed on the 50% S covered edges of the platelets for the sizes greater than that of the (3,4) platelet. The magnetic moments mainly arise from the undercoordinated S(2c) atoms at the 50% S covered edges rather than from Mo atoms. The criteria for the existence of the magnetic moments on S(2c) atoms are suggested and the electronic structure of the platelets on the edges as well as inside is discussed.

New 'chimie douce' approach to the synthesis of hybrid nanosheets of MoS2 on CNT and their anti-friction and anti-wear properties

Hybrid organic-inorganic oleylamine@MoS2-CNT nanocomposites with different compositions were obtained by thermal decomposition of tetrathiomolybdate in the presence of oleylamine and high quality multiwalled carbon nanotubes (CNTs) previously prepared by the CCVD technique. The nanocomposite samples were characterized by the TEM, SEM TG-MS, Raman and XRD techniques and successfully tested as anti-friction and anti-wear additives for grease lubricants.

Facile synthesis of MoS2@CMK-3 nanocomposite as an improved anode material for lithium-ion batteries

MoS(2)@CMK-3 nanocomposite consisting of confined nanosized MoS(2) in CMK-3 carbon matrix exhibits much improved cycling performance and rate capability due to the enlarged interlayer distance and favorable conductivity.

Facile synthesis of hierarchical MoS₂ microspheres composed of few-layered nanosheets and their lithium storage properties

In this work, we demonstrate an interesting polystyrene microsphere-assisted synthesis of hierarchical MoS(2) spheres composed of ultrathin nanosheets. The as-prepared sample exhibits promising lithium storage properties with improved cyclic capacity retention and rate capability.

The role of water in modifying friction within MoS2 sliding interfaces

To explore the environmental dependence of friction for solid lubricants containing molybdenum disulfide (MoS(2)), we have investigated friction on the basal plane of single-crystal MoS(2) with atomic force microscopy (AFM) as a function of relative humidity (RH) and tip composition. For both a bare Si(3)N(4) tip and a MoS(2)-coated tip, changes in interfacial friction are observed with increasing relative humidity, however, with markedly different behaviors. For sliding contacts involving bare Si(3)N(4) tips, the friction coefficient is observed to increase with increasing RH, from 0% to the point of water saturation. For Si(3)N(4) tips precoated with MoS(2) particles, friction appears to be relatively insensitive to increasing RH in the range of 0-40%. However, above 40% RH, a drastic increase in friction is observed and is accompanied by evidence for interfacial wear provided in images of the basal plane following the friction measurements. A comparison to the tribological properties of the basal plane of highly oriented pyrolytic graphite (HOPG) using identical probe tips highlights the unique character of self-mated MoS(2) interfaces.