Ultrathin BiOCl nanosheets (NST) with the thickness about 1.5 nm was prepared as a photocatalyst for the oxidation of benzylamine (BA) to N-benzyleneamine under visible light. The photocatalytic activity of NST is over 2.5 times higher than that of its bulk counterpart. More oxygen vacancies (OVs) in NST were revealed by EPR and XPS. UV-DRS result indicates that light adsorption of NST can be extended to visible light due to the presence of OVs. In addition, rich OVs result in Bi atoms in sublayer to be exposed as Lewis acid sites. In situ FTIR spectrum shows that BA is chemosorbed on the Lewis acid sites forming surface -N center dot center dot center dot Bi- coordination species, resulting in the activation of BA. The surface coordination species would also result in the red shift of the photo-absorption spectrum. Finally, a synergistic mechanism based on surface coordination activation and photocatalysis was proposed to explain the enhanced photocatalytic activity over NST. (C) 2019 Elsevier Inc. All rights reserved.