Graphite-Controlled Fabrication of Ultrathin WSe2 Nanosheets with Tower-Like Structure and Their Tribological Properties

Abstract

Uniform hexagonal tungsten diselenide (WSe2) nanosheets, with thicknesses as small as 10 nm and diameters as small as 100 nm, self-assembled into tower-like arrays, were successfully synthesized by the solid-state reaction of the elements W and Se in the presence of graphite in a sealed stainless steel reactor at 800°C. However, scattered submicrometer WSe2 sheets, 250 nm thick and 1–3 μm in diameter, were obtained in the absence of graphite. Subsequently, the formation mechanism of this assembled structure was proposed. Furthermore, the lubricity of as-fabricated arrays added into paraffin in steel–steel interaction was investigated by a ball-on-disc tribometer, as compared to that of commercial graphite and as-obtained submicrometer WSe2 sheets, respectively. The results showed that the addition of small amounts (0.5 wt%) of as-fabricated arrays greatly improved the friction reduction and antiwear properties of paraffin and did well then the same amount of commercial graphite and submicrometer WSe2 sheets, suggesting that as-fabricated arrays are an excellent lubricating material. Therefore, this process provides a strategy for the large-scale, cost-effective, and environmental friendly preparation and tribological application of small-sized laminar transition-metal dichalcogenide with good lubricity.