Electronic Band Structure and Photocatalytic Activity of Ln2Ti2O7 (Ln = La, Pr, Nd)

Photocatalytic activity in the water splitting of Ln 2 Ti 2 O 7 (Ln = La, Pr, Nd) with a layered structure was highly dependent on their electronic band structure. The conduction band of La 2 Ti 2 O 7 consisted mainly of Ti 3d and La 5d, whereas the valence band consisted mainly of O 2p and Ti 3d. The empty La 4f level was found to be located ca. 3.6 eV above the bottom of the conduction band from both the electronic band-structure calculation and the XPS measurement. The occupied and unoccupied Ln 4f level in Ln 2 Ti 2 O 7 was shifted to lower energy as the number of 4f electrons increased. This shift of the Ln 4f band made it possible for the band-gap energy of both Pr 2 Ti 2 O 7 and Nd 2 Ti 2 O 7 to be decreased. For Nd 2 Ti 2 O 7, the unoccupied Nd 4f level located between the conduction band and the valence band was found to be detrimental to photocatalytic activity in water splitting because it could act as an electron-trapping site.