Which affect the photoreactivity of BiOBr single-crystalline nanosheets with different hydrothermal pH value: Size or facet?

The different photocatalytic activity of BiOBr is mainly attributed to the size rather than the facet effect. •Hydrothermal pH value cannot change the dominant exposed facet of BiOBr nanosheets.•The UV and visible light (λ>500nm) photocatalytic activity of BiOBr increased with are hydrothermal pH value increasing.•The photocatalytic activity order of BiOBr is mainly attributed to the size rather than the facet effect. In this paper, three BiOBr samples with different hydrothermal pH have been prepared and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and the corresponding selected-area electron diffraction (SAED) pattern. It can be found that hydrothermal pH value cannot change the dominant exposed facet of BiOBr single-crystalline nanosheets. But, hydrothermal pH value can affect the size, surface area and band structure, which all result in the UV and visible light (λ>500nm) photocatalytic activity orders of BiOBr single-crystalline nanosheets: BOB-10>BOB-6>BOB-0.4. This finding indicates that the size, surface area and band structure affect the photoreactivity of BiOBr with different hydrothermal pH value rather than exposed facet.