Structural-Defect-Mediated Grafting of Alkylamine on Few-Layer MoS2 and Its Potential for Enhancement of Tribological Properties

2D graphene/FeOCl heterojunctions with enhanced tribology performance as a lubricant additive for liquid paraffin

The purpose of this study is to prepare graphene/FeOCl (G/FeOCl) heterojunctions via a microwave-pyrolysis approach and probe into the synergistic lubrication of G with FeOCl in liquid paraffin (LP). The morphology and chemical composition of specimens were analysed by utilizing scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The tribological property of G/FeOCl was determined, and the interaction between the G/FeOCl heterojunction and friction pair was carried out through simulation calculations. The results indicated that neither G nor FeOCl significantly improved the lubrication performance of LP. However, together with FeOCl, G as lubrication additives greatly improved the lubrication performance of LP. Under the load of 1.648 GPa, the mean friction coefficient and wear scar diameter of LP containing 0.20 wt% G/FeOCl were 66.1% and 44.7% inferior to those of pure LP, respectively. Scanning electron microscopy (SEM) and elemental mapping analyses of worn scars revealed the formation of G/FeOCl layer tribofilms that prevent direct contact between metals. In addition, the high interfacial energy between graphene and FeOCl calculated based on first-principles density functional theory (DFT) further confirmed that graphene and FeOCl simultaneously form friction films with wear resistance and wear reduction effect at the friction interface, which is consistent with the experimental results. This study, therefore, provides a pathway for low-friction lubricants by deploying G/FeOCl two-dimensional material systems.

Graphene/FeOCl (G/FeOCl) heterojunctions were prepared by microwave-pyrolysis, thoroughly characterised and used to probe the synergistic lubrication of G with FeOCl in liquid paraffin. We provide a pathway for low-friction lubricants by deploying G/FeOCl 2D materials.

Covalent photofunctionalization and electronic repair of 2H-MoS2via nitrogen incorporation

A route towards covalent functionalization of chemically inert 2H-MoS₂ exploiting sulfur vacancies is explored by means of (TD)DFT and GW/BSE calculations. Functionalization via nitrogen incorporation at sulfur vacancies is shown to result in more stable covalent binding than via thiol incorporation. In this way, defective monolayer MoS₂ is repaired and the quasiparticle band structure as well as the remarkable optical properties of pristine MoS₂ are restored. Hence, defect-free functionalization with various molecules is possible. Our results for covalently attached azobenzene, as a prominent photo-switch, pave the way to create photoresponsive two-dimensional (2D) materials.

Cu-Doped Co3O4 microstructure as an efficient non-noble metal electrocatalyst for methanol oxidation in a basic solution

Co₃O₄ doped with copper at different concentrations was used to catalyze methanol oxidation reactions.

Dependence of Friction and Wear on the Microstructures of WS2 Films under a Simulated Space Environment

Atomic oxygen (AO) has an important influence on the performance of solid lubricating materials applied in space. The tribological behaviors of both sputtered WS₂ films without and with a dense layer were mainly investigated under the ex situ AO irradiation condition. AO irradiation results in the worse tribological property for the WS₂ film without a dense layer. On the contrary, it is surprising that the WS₂ film with the dense layer exhibits a lower friction coefficient after irradiation, which is different from the reported results that the solid lubricating films always increased the friction and wear because the surfaces of the films were oxidized by AO. Meanwhile, it is found that the generated W oxides contributes to the partial surface of the wear track becoming smooth because of the shear and slip of crystal planes for WS₂ crystals on the surface of the dense layer. Eventually, the lubricating mechanisms of the irradiated WS₂ films are also revealed via correlating the friction and wear characteristics of the films.

Surface chemistry of graphene and graphene oxide: A versatile route for their dispersion and tribological applications

Graphene, the most promising material of the decade, has attracted immense interest in a diversified range of applications. The weak van der Waals interaction between adjacent atomic-thick lamellae, excellent mechanical strength, remarkable thermal conductivity, and high surface area, make graphene a potential candidate for tribological applications. However, the use of graphene as an additive to liquid lubricants has been a major challenge because of poor dispersibility. Herein, a thorough review is presented on preparation, structural models, chemical functionalization, and dispersibility of graphene, graphene oxide, chemically-functionalized graphene, and graphene-derived nanocomposites. The graphene-based materials as additives to water and lubricating oils improved the lubrication properties by reducing the friction, protecting the contact interfaces against the wear, dissipating the heat from tribo-interfaces, and mitigating the corrosion by forming the protecting thin film. The dispersion stability, structural features, and dosage of graphene-based dispersoids, along with contact geometry, play important roles and govern the tribological properties. The chemistry of lubricated surfaces is critically reviewed by emphasizing the graphene-based thin film formation under the tribo-stress, which minimizes the wear. The comprehensive review provides variable approaches for the development of high-performance lubricant systems and accentuates the lubrication mechanisms by highlighting the role of graphene-based materials for enhancement of tribological properties.