Direct Insight into the Confinement Effect of WS₂ Nanostructures in an Ordered Carbon Matrix

A new growth mechanism of WS2 nanostructures with well-defined shapes (nanocages or nanotubes), induced by a confinement effect in a mesoporous structure, is reported. As evidenced by high resolution electron microscopy, the growth of these peculiar structures is governed by a restructuration mechanism that occurs in an ordered mesoporous carbon matrix with a nanometric pore size via a one-pot synthesis method (soft-template process) in which W-based clusters are initially dispersed in the carbon walls. During a thermal treatment carried in an Ar/H2S gas mixture and a carbonaceous reductive atmosphere, small WS2 nanolayers stacked and shaped as nanoribbons are produced in a first step within the mesopores at 350 °C. In the second step, at higher sulfidation temperature, a solid/gas growth mechanism occurs in which H2S and W gaseous species (originating from the W clusters) decompose and react on initially formed WS2 nanoribbon seeds. That leads to a spatially restricted growth with the progressive formation of curved WS2 nanolayers characterized by ellipsoidal–based shapes characteristic of the inorganic fullerenes (at 550 °C) and finally to cylindrical shapes similar to the typical structures observed for most of inorganic nanotubes (at 750 °C).