or metal co-catalyst deposition . Among those strategies, introduction of defects is a simple and efficient way to improve the photocatalytic performance of BiOCl. . According to the differences in atomic structure, defects can be categorized as point defect, line defects, planar defects and volume defects. The relation between these defects and photocatalytic activity may be complex and elusive. For instance, oxygen vacancies (OVs) in metal oxide semiconductors, considered point defects, can sensitively influence photoelectrochemical properties. Recently, the study of surface OVs has emerged as a hot research topic, because most catalytic reactions occur on the surface of catalytic materials and a deep understanding of the nature of surface OVs is needed to design and prepare highly efficient photocatalysts. For example, that surface OVs in BiOCl can improve water adsorption and reduce activation energy barriers for photocatalytic water oxidation . discovered that different pathways of molecular oxygen activation are prevailing on (001) and (010) crystal planes of BiOCl nanosheets in the presence of surface OVs .