Manipulating Excitonic Effects in Layered Bismuth Oxyhalides for Photocatalysis

Two-dimensional semiconductors have attracted considerable attention in recent years because of their ability to utilize solar energy to mitigate environmental pollution through reactive oxygen species (ROSs) and synthesize solar fuels using superfluous CO2 as a raw material. However, low-dimensional materials usually display robust Coulomb interaction between electron and hole pairs because of their strong structure confinement ability, thus leading to the formation of electroneutral excitons. In light of this, excitonic effects overwhelmingly influence the photocatalytic properties of two-dimensional semiconductors, which should be comprehensively explored. Bismuth oxyhalides (BiOX, X = Cl, Br, I) of giant exciton binding energies are usually recognized as an excellent platform for excitonic effect investigation because their flexible geometric and electronic structures allow us to rationally manipulate the excitonic effects. This review first summarizes the recent progress in accelerating exciton dissociation for enhancing charge-carrier-dominated photocatalytic reactions and then demonstrates that harnessing the excitonic effects allows for the generation of singlet oxygen (1O2) for green chemical synthesis through a unique energy-transfer-dominated O2 activation route. We believe that a critical understanding of the excitonic effects in two-dimensional semiconductors can offer new perspectives and guidelines for the rational fabrication of advanced materials for photocatalytic applications.