Unprecedented ultrahigh photocatalytic activity of δ-Bi₂O₃ for cylindrospermopsin decomposition

The delta phase of bismuth oxide (δ-Bi₂O₃) is an important metal oxide due to its highest conductivity of any oxide material. However, it is only stable over a narrow high temperature range, and thus, incorporation of small, high-valence cation is a prerequisite for stabilizing its cubic structure to room temperature. The δ-Bi₂O₃ is also known to have low photocatalytic activity because of its low conduction band edge. As a consequence, the conduction band electrons cannot be consumed by the dissolved oxygen to produce superoxide radicals. Herein, for the first time, the δ-Bi₂O₃ has been successfully synthesized through a facile hydrothermal route without addition of any dopant. The as-synthesized δ-Bi₂O₃ shows ultrahigh photocatalytic activity for cylindrospermopsin decomposition. Within only 20 min of UV irradiation, the degradation efficiency for cylindrospermopsin by 0.5 g/L of the δ-Bi₂O₃ with a cylindrospermopsin concentration of 5 mg/L reaches 98%. Restricted charge carrier recombination and effective consumption of the conduction band electrons are behind such an unprecedented high photocatalytic activity of the δ-Bi₂O₃.