Synthesis of 2D anatase TiO 2 with highly reactive facets by fluorine-free topochemical conversion of 1T-TiS 2 nanosheets.

Two-dimensional (2D) anatase titanium dioxide (TiO 2 ) is expected to exhibit different properties as compared to anatase nanocrystallites, due to its highly reactive exposed facets. However, access to 2D anatase TiO 2 is limited by the non-layered nature of the bulk crystal, which does not allow use of top-down chemical exfoliation. Large efforts have been dedicated to the growth of 2D anatase TiO 2 with high reactive facets by bottom-up approaches, which relies on the use of harmful chemical reagents. Here, we demonstrate a novel fluorine-free strategy based on topochemical conversion of 2D 1T-TiS 2 for the production of single crystalline 2D anatase TiO 2 , exposing the {001} facet on the top and bottom and {100} at the sides of the nanosheet. The exposure of these faces, with no additional defects or doping, gives rise to a significant activity enhancement in the hydrogen evolution reaction, as compared to commercially available Degussa P25 TiO 2 nanoparticles. Because of the strong potential of TiO 2 in many energy-based applications, our topochemical approach offers a low cost, green and mass scalable route for production of highly crystalline anatase TiO 2 with well controlled and highly reactive exposed facets.