Engineering surface functional groups of 2D organic metal chalcogenides to regulate lubrication performance across scales

Abstract

Two-dimensional (2D) layered materials are widely used to enhance lubrication performance in various conditions due to their low friction and sliding interfaces. However, the uncontrolled modification and dispersion of functional groups on 2D materials limit their lubrication performance and ultra-low friction capabilities at different scales. Herein, we developed three Pb-based organic metal chalcogenides nanosheets, Pb(SPh-NH₂/-COOH/-OH), with long-range ordered functional groups on the [PbS₂] layer, to reduce friction and wear across scales. We organically modified these nanosheets prior to exfoliation, achieving micro-lateral and nano-vertical size. As ethanol additives, these nanosheets reduced the coefficient of friction (COF) and wear volume by over 44.8 % and 78.9 %, respectively. Dry tests demonstrated the Pb(SPh-OH) coating on SiO₂/Si substrate reduced the COF from 0.65 to 0.07. Compared to SiO₂/Si substrate, lateral force microscopy revealed friction reducing up to 57.5 %, 85.5 %, and 90.9 % for Pb(SPh-NH₂/-COOH/-OH), respectively. These novel 2D materials provide a heuristic strategy for lubrication, suitable for anti-friction applications under different conditions across scales.