Enhanced photocarrier separation in Br substitution-induced [W_(VI)O_6−x] units for highly efficient photocatalytic nitrate reduction under alkaline conditions

Photocatalytic nitrate (NO₃^-) reduction is considered a promising green and non-polluting technology to solve the nitrate pollution of groundwater and surface water. Herein, a novel Br-substituted Bi₂WO_6−x ultrathin nanosheets were prepared by a simple hydrothermal method in a strong acid environment containing sixteen alkyl three methyl bromide (CTAB). The catalytic system solves the problems of low carrier separation efficiency, poor performance under alkaline conditions, and a hard-to-activate N = O bond, achieving efficient NO₃^- removal under alkaline conditions along with high N₂ selectivity. It was confirmed that Br-substituted Bi₂WO_6−x produced the [W_(VI)O_6−x] units with a strong electron-withdrawing property by changing the polarity of the O-W-O bond. As a result, the effective space charge separation caused by the change of the W valence state and the spontaneous fracture behavior of the N = O bond improved the carriers utilization efficiency and distinctly reduced the reaction energy consumption, synergistically achieving excellent performance.