Photoluminescent and photocatalytic properties of layered caesium titanates, Cs2TinO2n+1 (n=2, 5, 6)

Photoluminescence and photocatalytic H-2 evolution reactions of layered caesium titanates, Cs2TinO2n + 1 (n = 2,5,6), have been studied to evaluate the photoactivity of these materials. Cs2Ti2O5 showed abroad emission around 420 nm upon excitation at 270 Mn at 77 K, while both Cs2Ti5O11 and Cs2Ti6O13 showed an emission around 490 nm upon excitation at 290 nm. Cs2Ti2O5 showed a blue emission even at 300 K. The Raman spectrum of Cs2Ti2O5 was similar to that of the well characterized K2Ti2O5 The results of the luminescence and the Raman spectrum suggested that Cs2Ti2O5 consists of a layered structure with TiO5 units, as observed in K2Ti2O5. Cs2Ti2O5 with the five-coordinate structure showed higher photocatalytic activity for H-2 evolution from aqueous methanol solutions than Cs2Ti5O11 and Cs2Ti6O13 with ordinary six-coordinate structures.