Surface Functionalization of WS₂ Nanosheets with Alkyl Chains for Enhancement of Dispersion Stability and Tribological Properties

Abstract

Tungsten disulfide (WS 2 ) exhibits intriguing tribological properties and has been explored as an excellent lubricious material in thin-film and solid lubricants. However, the poor dispersibility of WS 2 has been a major challenge for its utilization in liquid lubricant applications. Herein, a top-down integrated approach is presented to synthesize oxygenated WS 2 (WS 2 −O) nanosheets via strong acid-mediated oxidation and ultrasound-assisted exfoliation. The ultrathin sheets of WS 2 −O, comprising 4−7 molecular lamellae, exhibit oxygen/hydroxyl functionalities. The organosilanes having variable surface-active leaving groups (chloro and ethoxy) are covalently grafted, targeting the hydroxyl/oxygen functionalities on the surface of WS 2 −O nanosheets. The grafting of organosilanes is governed by the reactivity of chloro and ethoxy leaving groups. The DFT calculations further support the covalent interaction between the WS 2 −O nanosheets and organosilanes. The alkyl chain-functionalized WS 2 −O nanosheets displayed excellent dispersibility in mineral lube base oil. A minute dose of chemically functionalized-WS 2 (0.2 mg.mL −1 ) notably enhanced the tribological properties of mineral lube oil by reducing the friction coefficient (52%) and wear volume (79%) for a steel tribopair. Raman analysis of worn surfaces revealed WS 2 -derived lubricious thin film formation. The improved tribological properties are attributed to ultralow thickness, stable dispersion, and low shear strength of chemically functionalized WS 2 nanosheets, along with protective thin film formation over the contact interfaces of a steel tribopair. The present work opens a new avenue toward exploiting low-dimensional nanosheets for minimizing energy losses due to high friction.

MoS2 Nanostructures for Solar Hydrogen Generation via Membraneless Electrochemical Water Splitting

“…Therefore, the effective non-noble metal-based electrocatalysts, composed of earth-abundant elements, are quite attractive with the aim of providing cost-competitive hydrogen. − These earth-abundant catalysts in nanostructures demonstrate excellent catalytic performance. Furthermore, among nanomaterials, two-dimensional nanomaterials like graphene, MoS 2 , and WS 2 are particularly of greater significance because of their predominant quantum effect and unique physicochemical properties. , The MoS 2 domain’s catalytic activity is primarily derived from its edge sites, while its basal plane is catalytically inert; however, aggregate formation or the folding of 2D layers makes it difficult for the edge active site to act . Several approaches have been planned, mainly aiming at increasing the number of catalytically active edge sites or activating the inert basal planes, and so forth, to optimize the catalytic activity of MoS 2 in HER .…”

Macroscale Superlubricity Induced by MXene/MoS2 Nanocomposites on Rough Steel Surfaces under High Contact Stresses

“…The observed lubricity results were significantly lower compared to those of previously reported coatings deposited using similar technologies such as burnished or (magnetron, rf) sputtered MoS 2 under dry, ambient, and humid sliding conditions. The results also outperform composite and chameleon coatings, MoS 2 doped or blended with other materials such as gold, silica, nickel, graphene, and graphene oxide, MXenes, and MXene blends and even in comparison to oil- or liquid-based lubrication with MXene or MoS 2 additives as illustrated in the Ashby plot shown in Figure . ,,− ,,,,− …”

“…Slip and/or shear between the atomic planes in layered structures such as in graphite, graphene, , graphene oxide, MoS 2 , ,− and WS 2 , − among others, are primarily responsible for lubricity in solid-state sliding. The tribomechanical or chemical phenomena such as crumbling of the layered structure under high contact pressure, reactions between the substrate and coating material changing its chemical/crystal structure, − or materials degradation by intercalation with impurities, oxygen, or water molecules (also referred to as structural water) are generally attributed to the loss of lubricity over prolonged sliding and are barriers to realizing superior performance.…”

Surface-Functionalized Ti3C2Tx MXene as a Kind of Efficient Lubricating Additive for Supramolecular Gel

“…Friction-reducing and antiwear performances were evaluated with a SRV-V reciprocating sliding tribometer and 3D optical surface profilometer. According to some studies, neither low nor excessive additives can improve the tribological properties of base oils. ,, Therefore, the supramolecular gels with various concentrations were prepared to explore the optimal addition amount (Figure a,b). When the addition of Ti 3 C 2 T x -ODPA was 0.10 wt %, it ran smoothly during the whole friction test.…”