Research into layered transition metal dichalcogenides (TMDCs), most notably those of molybdenum and tungsten disulfides, has become extensive, involving fields as diverse as optoelectronics, spintronics, energy storage, lubrication, and catalysis. The modification of TMDCs by transition metal doping can improve their performance in such applications and hence extend their potential for technological applications. This review concerns the synthetic strategies that have been used to incorporate transition metals into TMDCs and the applications of the resultant materials and relevant computational studies on the predicted properties of the doped materials.

http://pubsdc3.acs.org/doi/pdfplus/10.1021/acs.chemmater.6b00430

Synthesis, Properties, and Applications of Transition Metal-Doped Layered Transition Metal Dichalcogenides

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.

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Solid Lubrication with MoS2: A Review

Transition-metal dichalcogenides (TMDs) are at the forefront of research for their promising catalytic abilities and unique materials properties. With great interest in the study of mono- or few-layered TMDs, we seek to fundamentally explore the effects of doping on bulk TMDs, particularly MoS2 and WS2 for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) with p-dopants Nb and Ta. Despite promises reported in the computational studies of doped TMDs on the HER, our results show otherwise. Doped bulk TMDs display less catalytic activity in comparison to their undoped counterparts for the HER. A similar effect is observed for ORR catalysis. Characterization was done to shed light on its surface elemental composition, properties, and morphologies. It was found that doped WS2 has a high percentage of 1T phase but this does not correlate with a lower overpotential for the HER at −10 mA cm–2, which contradicts the general consensus. We therefore show that p-dopants have a negative electro...

Negative Electrocatalytic Effects of p-Doping Niobium and Tantalum on MoS2 and WS2 for the Hydrogen Evolution Reaction and Oxygen Reduction Reaction

The metalcutting process, which includes turning, milling, drilling, and other methods for shaping metals, generates large mechanical forces and high temperatures at the point of contact between the cutting tool and workpiece material. The cutting tool is damaged substantially in these severe service conditions and has to be replaced when the tool cannot produce the desired product at the specified tolerances. To improve the lifetime for which it functions properly, the cutting tool has to be protected, often by coatings that are specifically designed to prevent certain damage modes that occur in particular applications. In fact, over 90% of all cemented carbide inserts are currently coated using chemical vapor deposition, CVD, physical vapor deposition, PVD, or their combination. This paper will present PVD coatings that are specially designed to protect the cutting tool and extend its functionality (lifetime). The paper is organized in two parts. First, it will briefly describe the metalcutting process, the resulting challenges to the cutting edge and the components of a functional tool. The second and the main part will present and discuss the key PVD architectures employed to protect the tool: monolithic, multilayer and nanostructured coatings. The paper will conclude with a summary and outlook on the development of new PVD coatings for cutting tools.

Architecture of PVD coatings for metalcutting applications: A review

With the rapid development of industry, heavy metal pollution has become a potential hazard to public health and the ecological system. Herein, molybdenum disulfide coated Mg/Al layered double hydroxide composites (LDHs@MoS2) were prepared via a simple hydrothermal method and applied for the adsorption of Cr(VI) from a water solution. The removal capacity of Cr(VI) on LDHs@MoS2 reached 76.3 mg/g at pH = 5.0, and the removal process relied on ionic strength and pH. The results confirmed that the uptake of Cr(VI) on LDHs@MoS2 followed a spontaneous endothermic process. In contrast to the LDHs, LDHs@MoS2 showed excellent chemical stability, which was beneficial for practical applications. Specifically, the coexisting ions had little influence on the uptake of Cr(VI). The interaction of Cr(VI) with the LDHs@MoS2 composites was mainly controlled by electrostatic attraction and outer-sphere surface complexation. The findings can provide new insights into the uptake of heavy metal ions in a natural aquatic envir...

Preparation of Molybdenum Disulfide Coated Mg/Al Layered Double Hydroxide Composites for Efficient Removal of Chromium(VI)

Solid-lubricant MoS 2 coatings have been successfully applied in high vacuum and aerospace environments. However, these coatings are very sensitive to water vapor and not suitable for applications in moist environments. In this work, Cr- and T-doped MoS 2 composite coatings were developed. The results demonstrated that these composite coatings are promising for applications in high humidity environments. MoS 2 –Cr and MoS 2 –Ti composite coatings with different Cr or Ti content were deposited on high speed steel substrate by unbalanced magnetron sputtering. The composition, microstructure, and mechanical properties of the as-deposited MoS 2 -metal composite coatings were analyzed by energy dispersive analysis of X-ray (EDX), X-ray diffraction (XRD), and nanoindentation experiments. The tribological properties of the coatings were evaluated against an alumina ball under different relative humidity atmosphere using a ball-on-disc tribometer. The MoS 2 –Cr and MoS 2 –Ti coatings showed a maximum hardness of 7.5 GPa and 8.4 GPa at a dopant content of 16.6 at.% Cr or 20.2 at.% Ti, respectively. The tribological test results showed that, with a small amount of Cr and/or Ti doping, the tribological properties of MoS 2 coatings under humid atmosphere could be significantly improved. The optimum doping level was found to be around 10 at.% for both MoS 2 –Cr coatings and MoS 2 –Ti coatings to show the best tribological properties, with both the lowest friction coefficient and wear rate. The excellent tribological properties of the MoS 2 –Cr and MoS 2 –Ti coatings with an appropriate metal doping level in moist atmosphere are found due to their ability to form stable transfer layer on the surface of the counterbody, which supplies lubrication for the contact surface.

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X.Y. He

Papers

Tribological properties of Cr- and Ti-doped MoS2 composite coatings under different humidity atmosphere