Light-Switchable Oxygen Vacancies Enhanced Nitrogen Fixation Performance on BiOBr: Mechanism of Formation, Reconversion and Function

Abstract

Although BiOBr has been demonstrated to be a promising photocatalyst for the synthesis of ammonia, it still remains challenging to the recombination of photoproduction carriers and how to cleave the strong N≡N bond effectively. Herein, we report light-switchable oxygen vacancies (OVs) on BiOBr by a facile one-step alcoholysis method with excellent photocatalytic nitrogen fixation activity. The BiOBr with light-switchable OVs uplift the conduction band position, afford more active sites to activate N≡N, and promote the charges separation, thus the NH4+ yield rate reaches 246 µmol‧g−1‧h−1 under mild conditions. Meanwhile, in order to explore the formation and reconversion mechanism of light-switchable OVs, DFT calculation and Raman spectroscopy were used to reveal the essential phenomenon of BiOBr sample, and the photoelectrochemical characterizations were also employed to analyze the samples. Results prove that light-switchable OVs are created by dislodging the O atoms to form H2O molecules under light irradiation due to the high-density O atoms exposure and weak Bi-O bond in BiOBr. Furthermore, the light-induced OVs will be refilled by seizing the O atoms from O2 after turning off the light, leading to a fine recovery of the origin stable OV-free composition. This work provides a practical new strategy of light-switchable OVs formation for the development of catalysts with enhanced nitrogen fixation rate under mild conditions.