Long-term aging of multiwall nanotubes and fullerene-like nanoparticles of WS2

Tungsten disulfide is an important compound with layered structure (2D-material). Chemically it is less stable than tungsten trioxide and hence undergoes oxidation upon exposure to the ambient atmosphere. Although nanoparticles of tungsten disulfide are metastable, hollow-closed nanostructures , i.e. fullerene-like WS 2 (IF-WS 2 ) and nanotubes thereof are kinetically stabilized because they present their basal ( 001 ) surface to the outer world. In this work, the oxidation of IF-WS 2 and nanotubes stored under different conditions for 17–26 years have been studied. It was found that the degree of oxidation depends on the storage conditions. In fact, nanoparticles which were stored for long time and protected from the ambient atmosphere oxidized only marginally, while others kept under less favorable conditions suffered severe oxidation. Furthermore, the degradation of the IF nanoparticles is autocatalytic with clear acceleration over time. This work has also practical significance, since the shelf-life of IF-WS 2 nanoparticles , which are used as solid-state lubricants commercially have not been studied before. The oxidation of powders of fullerene-nanoparticles and nanotubes of WS 2 stored for up to 27 years has been studied. Properly stored materials were oxidized very little. The oxidation mechanism is found to be autocatalytic and relevance to applications is discussed, as well. • The oxidation process of fullerene-like nanoparticles of WS 2 (IF-WS 2 ) and multiwall nanotubes thereof which were stored for 17–27 years in our lab under different conditions were studied. • The oxidation process of properly stored nanoparticles is slowed down substantially, notwithstanding the fact that the nanoparticles are only ∼100 nm in diameter and possess large surface area (10–20 m 2 /g). • The oxidation process is autocatalytic, i.e. after initial oxidation it is largely accelerated. • These results have practical importance since the IF-WS 2 nanoparticles are used as commercial solid-lubricants and metal working fluids, and their shelf-life was not known before.