Solving the "MoS2 Nanotubes" Synthetic Enigma and Elucidating the Route for Their Catalyst-Free and Scalable Production.

This study solves more than two decades-long "MoS2 Nanotubes" synthetic enigma - the futile attempts to synthesize inorganic nanotubes (INT) of MoS2 via vapor-gas-solid (VGS) reaction. Among them was replication of the recently reported pure-phase synthesis of the analogous INT-WS2. During these years, successful syntheses of spherical nanoparticles of WS2 and MoS2 were demonstrated, as well. All these nanostructures were obtained by VGS reaction of corresponding oxides with H2/H2S gases, at elevated temperatures (>800 °C) and one-pot process in fluidized bed reactor (FBR). This success and apparent similarity between the two compounds hid from us the option of looking for the INT-MoS2 reaction parameters in entirely different regime. The main challenge in the synthesis of INT-MoS2 via VGS was the instability of the in situ prepared suboxide nanowhiskers against over-reduction and recrystallization at high temperatures. The elucidated growth mechanism dictates separation of the reaction into five steps, as properties of the intermediate products are not consistent with single process and require individual conditions to each step. A horizontal reactor with a porous-quartz reaction cell, which creates proper quasi-static (contrary to FBR) conditions for the reaction involving sublimation, was imperative for the INT-MoS2 effective nanofabrication. These findings render the reproducible synthetic route for production of highly crystalline pure phase MoS2 nanotubes via multi-step VGS process, without the assistance of a catalyst and in scalable fashion. Being semiconductor, flexible and strong, INT-MoS2 offer a platform for much research and numerous potential applications in the field of optoelectronics, reinforcement of polymer composites and more.