@article{37,
  author = {Luzhu Xu and Adam Tetreault and Michael Pope},
  title = {Chemical Insights into the Rapid, Light-Induced Auto-Oxidation of Molybdenum Disulfide Aqueous Dispersions},
  abstract = {<p>The production of exfoliated MoS<sub>2</sub>&nbsp;via lithium intercalation has been widely used to prepare 1T polytype dominated MoS<sub>2</sub>&nbsp;(1T-MoS<sub>2</sub>) monolayers. These metallic single layers hold promise as high-performance electrodes for various electrochemical applications as well as for direct conversion to the semiconducting 2H polytype (2H-MoS<sub>2</sub>), a material of significant interest for next-generation electronics and optoelectronics. The performance in these applications is largely determined by defects introduced during processing. In this work, we systematically investigate the degradation rate and products resulting from the aging of aqueous MoS<sub>2</sub>&nbsp;dispersions, obtained by chemical exfoliation under a variety of common processing conditions. Depending on the size and number of defects initially present in the material, the resulting MoS<sub>2</sub>&nbsp;is found to have a surprisingly short half-life of only 2 to 6 days under alkaline conditions and exposure to both light and air. By aging samples under various environments and analyzing by UV–vis, Raman, Fourier-transform infrared, and X-ray photoelectron spectroscopies, we demonstrate that light-induced generation of superoxide by MoS<sub>2</sub>&nbsp;is largely responsible for its oxidation (both 1T and 2H polytypes are affected equally). This process is accelerated under alkaline conditions because of the solubility of MoO<sub>3</sub>, which we suggest would otherwise passivate defects and edge sites. The soluble molybdates are found to be a strong indicator of oxidation, which can easily be followed by measuring the absorption at 209 nm using UV–vis spectroscopy. We hope that this work will help guide researchers in minimizing or controlling degradation, which will accelerate the successful use of MoS<sub>2</sub>&nbsp;in applications.</p>
},
  year = {2019},
  journal = {Chemistry of Materials},
  volume = {32},
  pages = {148-156},
  publisher = {American Chemical Society},
  url = {https://doi.org/10.1021/acs.chemmater.9b02987},
}