Photoreductive BiOCl Ultrathin Nanosheets for Highly Efficient Photocatalytic Color Switching.

The reversible photocatalytic color switching systems (PCSSs) driven by semiconductor nanoparticles have attracted considerable attention because of their wide applications. However, the developed semiconductor nanoparticles with photoreductive activity are mainly limited to TiO2-based photocatalysts, which greatly hinder their broad applications. Here we report a cocapping ligand-assisted strategy for the development of photoreductive BiOCl ultrathin nanosheets with abundant oxygen vacancies. Both the cocapping ligands and oxygen vacancies in BiOCl ultrathin nanosheets act as sacrificial electron donors to efficiently scavenge the photogenerated holes, endowing the BiOCl ultrathin nanosheets high photoreductive activity and thus enabling the photocatalytic color switching of redox dyes, such as methylene blue (MB) and neutral red. By successfully integrating the BiOCl ultrathin nanosheet/MB/H2O color switching system with poly(vinyl alcohol) hydrogel to fabricate a twistable gel film and simultaneously solving the dye-leaching issue of the gel film in a water environment, we further demonstrate its application in a colorimetric oxygen indicator for food packaging, exhibiting high sensitivity to monitor oxygen leakage by the naked eye. We believe the work opens a new avenue for designing photoreductive semiconductor nanomaterials to enrich the PCSSs and their applications.