Creation of robust oxygen vacancies in 2D ultrathin BiOBr nanosheets by irradiation through photocatalytic memory effect for enhanced CO2 reduction

An interesting photocatalytic memory effect was found in 2D ultrathin BiOBr nanosheets, which endowed them the capability to trap photogenerated electrons on Bi3+ and Br- in this material system for an extended period of time and resulted in the creation of stable oxygen vacancies (Ov) by just visible light irradiation due to the charge balance requirement. Thus, a broader visible light absorption, more negative conduction band minimum, stronger piezoelectric response, better charge carrier separation and transfer, and enhanced CO2 adsorption and activation were occurred in these BiOBr nanosheets with prior visible light irradiation, all of which were beneficial for their enhanced CO2 reduction performances in photocatalysis, piezocatalysis, and photopiezocatalysis, respectively, than their counterparts without it. This work demonstrated a novel approach to create oxygen vacancies by light irradiation through the photocatalytic memory effect, which could be readily applied to similar photocatalyst systems to boost their performances and generate novel functionalities.