A photoactive titanate with a stereochemically active Sn lone pair: Electronic and crystal structure of Sn ₂TiO ₄ from computational chemistry

TiO ₂ remains the most widely studied metal oxide for photocatalytic reactions. The standard approach to reduce the band gap of titania, for increasing the absorption of visible light, is anion modification. For example the formation of an oxynitride compound, where the nitrogen 2p states decrease the binding energy of the valence band. We demonstrate that cation modification can produce a similar effect through the formation of a ternary oxide combining Ti and an ns ² cation, Sn(II). In Sn ₂TiO ₄, the underlying Ti 3d conduction states remain largely unmodified and an electronic band gap of 2.1 eV (590 nm) is predicted by hybrid density functional theory. Our analysis indicates a strong potential for Sn ₂TiO ₄ in visible-light driven photocatalysis, which should prove superior to the alternative (SnO ₂) _1-x(TiO ₂) _x solid-solution.