Optical and photocatalytic properties of two-dimensional MoS<Subscript>2</Subscript>

The electronic structure and optical spectrum of monolayer MoS<Subscript>2</Subscript> are calculated using both the modified Becke-Johnson (mBJ) approximation and Bethe-Salpeter equation. Bulk MoS<Subscript>2</Subscript> is an indirect band gap semiconductor, but thinned to a monolayer it converts to a direct band gap semiconductor with increased gap. The calculated mBJ band gaps of MoS<Subscript>2</Subscript> amount to 1.15 eV for the bulk and 1.90 eV for the monolayer, in excellent agreement with experiment. The experimental excitonic peaks of monolayer MoS<Subscript>2</Subscript> at 1.88 eV and 2.06 eV are reproduced by the calculations. The high photoluminescence yield can be attributed to a high binding energy of the excitons and is not due to a splitting of the valence bands, as is commonly assumed. We also show that monolayer MoS<Subscript>2</Subscript> has the ability to oxidize H<Subscript>2</Subscript>O and produce O<Subscript>2</Subscript> as well as to reduce H<Superscript>+</Superscript> to H<Subscript>2</Subscript>. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2012