Mechanism of WS2 Nanotube Formation Revealed by in Situ/ex Situ Imaging

Vojtěch Kundrát, Libor Novák, Kristýna Bukvišová, Jakub Zálešák, Eva Kolíbalová, Rita Rosentsveig, M. Sreedhara, Hila Shalom, Lena Yadgarov, Alla Zak, Miroslav Kolíbal, Reshef Tenne

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Multiwall WS2 nanotubes have been synthesized from W18O49 nanowhiskers in substantial amounts for more than a decade. The established growth model is based on the “surface-inward” mechanism, whereby the high-temperature reaction with H2S starts on the nanowhisker surface, and the oxide-to-sulfide conversion progresses inward until hollow-core multiwall WS2 nanotubes are obtained. In the present work, an upgraded in situ SEM μReactor with H2 and H2S sources has been conceived to study the growth mechanism in detail. A hitherto undescribed growth mechanism, named “receding oxide core”, which complements the “surface-inward” model, is observed and kinetically evaluated. Initially, the nanowhisker is passivated by several WS2 layers via the surface-inward reaction. At this point, the diffusion of H2S through the already existing outer layers becomes exceedingly sluggish, and the surface-inward reaction is slowed down appreciably. Subsequently, the tungsten suboxide core is anisotropically volatilized within the core close to its tips. The oxide vapors within the core lead to its partial out-diffusion, partially forming a cavity that expands with reaction time. Additionally, the oxide vapors react with the internalized H2S gas, forming fresh WS2 layers in the cavity of the nascent nanotube. The rate of the receding oxide core mode increases with temperatures above 900 °C. The growth of nanotubes in the atmospheric pressure flow reactor is carried out as well, showing that the proposed growth model (receding oxide core) is also relevant under regular reaction parameters. The current study comprehensively explains the WS2 nanotube growth mechanism, combining the known model with contemporary insight.

Original languageEnglish
Pages (from-to)12284-12294
Number of pages11
JournalACS Nano
Volume18
Issue number19
DOIs
StatePublished - 14 May 2024
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2024 The Authors. Published by American Chemical Society

Keywords

  • WS nanotube
  • electron microscopy
  • ex situ
  • in situ
  • reaction mechanism
  • sulfidation

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