Possible role of lattice dynamics in the photocatalytic activity of BaM1/3N2/3O3 (M = Ni, Zn; N=Nb, Ta)

New photocatalysts BaNi1/3M2/3O3 (M = Nb, Ta) and BaZn1/3M2/3O3 (M = Nb, Ta) with the ABO(3) perovskite structure were synthesized by the solid-state reaction method. They were characterized by X-ray diffraction, UV-vis reflectance spectroscopy, Raman spectroscopy, and photocatalytic activity measurement under UV light irradiation. Because of the same ionic radius of Nb5+ and Ta5+ in each pair, both compounds show the same lattice parameters. The Nb-containing photocatalyst with a narrower band gap and a smaller surface area shows a higher photocatalytic activity in evolving H-2 from the CH3OH/H2O solution under UV light irradiation than the Ta-containing photocatalyst. Some phonon modes in the bending branch of the Raman spectrum for the Ta-containing photocatalyst show an obvious red shift in their frequency, compared with those for the corresponding Nb-containing photocatalyst. It is suggested that these phonon modes play an important role in the migration of the charge carriers inside the photocatalysts, thus dominating their photocatalytic activities.