Photocatalytic Activity Enhancement for Bi₂WO₆ by Fluorine Substitution

F⁻ substituted Bi₂WO₆ (Bi₂WO_6−<i>X</i>F_2<i>X</i>) photocatalysts with high activity have been successfully synthesized by a two-step process. The effects of F⁻ substitution on the crystal structure and photocatalytic activity of Bi₂WO₆ were investigated. F⁻ substitution could change the original coordination around the W and Bi atoms. Comparing with Bi₂WO₆, the photocatalytic activity of Bi₂WO_6−<i>X</i>F_2<i>X</i> increased about 2 times for degradation of MB under visible-light (λ > 420 nm) irradiation. Density functional calculations revealed that Bi₂WO_6−<i>X</i>F_2<i>X</i> has a wider valence bandwidth and lower valence band position. The high activities of Bi₂WO_6−<i>X</i>F_2<i>X</i> photocatalysts come from its valence band which increase the mobility of photoexcited charge carriers and possess a stronger oxidation power.