Ultrathin BiOBr nanosheets have been prepared via an ionic liquid induced mechanochemical synthesis method at ambient temperature for the first time using 1-hexadecyl-3-methy-limidazolium bromine ([C(16)mim]Br). Transmission electron microscope and atomic force microscope images show that the ultrathin BiOBr nanosheets possessed an average diameter of approximately 200-300 nm with a thickness of 3-4 nm. For comparison, KBr was selected as Br source for the preparation of BiOBr nanosheets and the experimental results demonstrate that the ionic liquid and mechanical ball milling method had a significant impact on the fabrication of nanosheet structures. Compared with the as-prepared control samples, the ultrathin BiOBr nanosheet photocatalyst exhibited significantly increased photocatalytic performance for the removal of organic pollutants. A possible mechanism for this enhanced activity was proposed based on the shorter diffusion distance for charge transfer provided by the ultrathin nanosheet structure, which inhibits the recombination of photogenerated charge carriers. This work not only opens up a possible pathway for the large-scale industrial preparation of BiOX (X = Cl, Br, I) with superior photocatalytic activity, but also provides new insight into environmental restoration and energy conversion. (C) 2020 Elsevier Inc. All rights reserved.