Mannitol-assisted architecture of BiOBr with two kinds of anion vacancies and high specific surface area for excellent photocatalytic applications

Abstract

The key to photocatalytic efficiency lies in the use of catalytic materials. In this paper, BiOBr5HyMLA nanorod-assembled blocks with a high specific surface area (66.73 m² g⁻¹) containing oxygen vacancies (V_Os) and bromine vacancies (V_Brs) were prepared by the room temperature precipitation method with the assistance of mannitol, which shows significantly enhanced photocatalytic performance. Without adding any sacrificial agent, the molar conversion frequency of BiOBr5HyMLA transforming CO₂ to CO reached 39.51 μmol g⁻¹ h⁻¹, which is 5.3 times that of BiOBr5Hy synthesized in aqueous solution. In addition, under visible light irradiation, the mass conversion frequency of BiOBr5HyMLA for a 20 mg L⁻¹ high-concentration methyl orange (MO) aqueous solution reached 0.0482 g g⁻¹ min⁻¹, which is 2.2 times that of BiOBr5Hy. The results are attributed to the synergistic effects of more V_Os, V_Brs, surface –OH functional groups and high specific surface area in BiOBr5HyMLA, which increase the absorption range and intensity of light, improve the separation efficiency of photogenerated carriers, provide more active sites, and reduce the adsorption activation energy of reactants. The photocatalytic mechanisms of BiOBr5HyMLA were further analyzed and explored by in situ infrared test and active species capture experiment. This study offers new insights for designing efficient photocatalytic materials and analyzing the photocatalytic mechanism.