Excitonic-engineered bismuth oxyhalide nanosheets with superior performance for environmental photocatalysis

The escalating severity of global environmental pollution and energy crises demands innovative and sustainable remediation technologies. Solar-driven photocatalysis offers a green solution, and bismuth oxyhalide (BiOX, X = Cl, Br, I) nanosheets have emerged as promising candidates because of their layered structure, tunable band gaps, and internal electric fields. This review summarizes recent progress in excitonic engineering of BiOX nanosheets, including synthesis, characterization, pollutant removal performance, and structure-property relationships. We show that surface asymmetry weakens excitonic effects and switches O₂ activation from ¹O₂ to ˙O₂^-, enabling efficient organic synthesis. Surface boronizing induces staggered band alignment and oxygen vacancies for selective NO oxidation to nitrate. Homogeneous B doping manipulates bulk excitons and surface defects for selective, ultrastable CO₂ photoreduction, while van der Waals gap engineering reduces exciton binding energy and creates active defect sites for pure-water CO₂-to-CO conversion. Nitrogen doping enables spatial charge separation for simultaneous CO and HClO production from seawater. Moiré superlattice construction destabilizes surface Bi-Cl bonds and reinforces interlayer coupling for methane chlorination. Ag single-atom modification creates Cl-Ag₁-Cl sites for superior O₂ activation and NO oxidation. Finally, we discuss challenges and opportunities for practical pollution control and environmental remediation.