Photocatalytic activity of RBi₂O₄NO₃ (R: Tb, Dy, Er, Gd, and Ho) for phenol degradation under visible light irradiation

Abstract

Rare-earth metal bismuth oxynitrates, RBi₂O₄(NO₃) (R: Tb, Dy, Er, Gd, and Ho), were prepared by hydrothermal reactions using hydrated sodium bismuthate (NaBiO₃·nH₂O) and rare earth nitrates. The optical band gap of the Tb compound was 2.10 eV, and those for the Dy, Er, Gd, and Ho compounds ranged between 2.92 and 2.94 eV. All the compounds were yellowish white in color, except the Tb compound, which was yellowish brown. Surface area of all the compounds varied from 2.46 to 8.17 m²/g. The Tb compound showed the highest photocatalytic activity for phenol degradation under visible light irradiation than other compounds (Dy, Er, Gd, and Ho). At elevated temperatures, TbBi₂O₄(NO₃) was changed to (Tb_0.333Bi_0.667)O_1.50 having a fluorite-type structure, which exhibited poor photocatalytic activity for phenol degradation under visible light irradiation.