Photoelectrochemical study of lanthanide titanium oxides, Ln2Ti2O7 (Ln = La, Sm, and Gd)

Photocatalytic activities for hydrogen evolution of lanthanide titanium oxides, Ln2Ti2O7 (Ln = La, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb) prepared by a solid-state reaction were studied. Hydrogen gas was clearly evolved in distilled water suspension of La2Ti2O7 and Sm2Ti2O7. From the photoelectrochemical measurements, the values of the flat band potential were estimated to be −0.04, −0.02, +0.27 eV for La2Ti2O7, Sm2Ti2O7, Gd2Ti2O7, respectively, versus the normal hydrogen electrode (NHE). The values of the band gap energy were calculated to be about 3.29, 2.79, 2.82 eV for La2Ti2O7, Sm2Ti2O7, Gd2Ti2O7, respectively. The photocatalytic activities of Ln2Ti2O7 (La, Sm, and Gd) were discussed along with detailed band structures estimated in this study. From the band structures, Sm2Ti2O7 is a possible candidate of photocatalyst responding to visible light.