Water-dispersible Ti3C2Tz MXene nanosheets by molten salt etching.

Molten-salt etching of TiAlC MAX phase offers a promising route to produce 2D TiCT (MXene) nanosheets without hazardous HF. However, molten-salt etching results in MXene clays that are not water dispersible, thus preventing further processing. This occurs because molten-salt etching results in a lack of -OH terminal groups rendering the MXene clay hydrophobic. Here, we demonstrate a method that produces water-dispersible TiCT nanosheets using molten salt (SnF) to etch. In molten salt etching, SnF diffuses between the layers to form AlF and Sn as byproducts, separating the layers. The stable, aqueous TiCT dispersion yields a ζ potential of -31.7 mV, because of -OH terminal groups introduced by KOH washing. X-ray diffraction and electron microscopy confirm the formation of TiCT etched clay with substantial d-spacing as compared with clay etched with HF. This work is the first to use molten salt etching to successfully prepare colloidally stable aqueous dispersions of TiCT nanosheets.