Fabrication and regulation of vacancy-mediated bismuth oxyhalide towards photocatalytic application: Development status and tendency

• This review focuses on the vacancy engineering of BiOX. • Popular vacancies creating approaches for BiOX are introduced. • Advanced characterization techniques for determining vacancies are summarized. • Inherent functionality of BiOX vacancies in photocatalysis is clarified. • Photocatalytic applications and behavior of vacancy-mediated BiOX are discussed. Recently, layered bismuth oxyhalides (BiOX) have been a well-deserved hotspot in the field of photocatalysis owning to their fascinating physicochemical properties derived from unique layered structures. Nevertheless, insufficient sunlight absorption, rapid recombination of electron-hole (e - -h + ) pairs, finite carrier concentration, and weak interaction between BiOX surface and reactant molecules inevitably limit the photocatalytic performance of BiOX. Given this, vacancy engineering, which can unleash the great potential to manipulate crystal and electronic structures and surface chemistry of BiOX, is widely applied to improve BiOX to meet the increasingly diverse theoretical and applicable needs. In this review, we focus on recent development in the design of appropriate vacancies on the BiOX for photocatalytic application. The introduction and analysis of popular vacancies creating approaches for BiOX and techniques to distinguish various vacancies are provided. The inherent functionality of BiOX vacancies in photocatalysis at the molecular level is clarified. Then we present representative photocatalytic applications, performance, and corresponding vacancy behavior of vacancy-mediated BiOX. Finally, based on an unambiguous understanding of the vacancy–property relationships and a complete view of the state of the art of vacancy-mediated BiOX, the future directions and possibilities for the rational design of vacancies to acquire ideal properties are explored.