N₂ photofixation promoted by in situ photoinduced dynamic iodine vacancies at step edge in Bi₅O₇I nanotubes

Heterogeneous photosynthesis is a promising route for sustainable ammonia production, which can utilize renewable energy and water as the hydrogen source under ambient condition. In this study, a series of Bi₅O₇I (BOI) nanosheets and nanotubes are synthesized, and the surface tensile strain is formed by curling the nanosheets into nanotubes to tune the concentration and location of dynamic vacancies. Scanning transmission electron microscopy (STEM) with spherical aberration correction confirms the presence of intrinsic areal defects on the surface of the BOI nanotube resulted from surface tensile strain. The presence of areal defects lowers the formation energy of I vacancies (IV) at step edge site, thus the IV with higher concentration would be favorably generated under visible light. Rapid scan in situ Fourier transform infrared (FT-IR) analysis in the aqueous media reveals that the IV promotes photocatalytic N₂ activation and reduction, and proceeds through an associative alternating mechanism. Specially, after turning off the light, the surface vacancy sites can be reoccupied by I⁻ ions, which enables the protection and regeneration of photocatalyst surface in an aerobic and dark environment. This work provides an innovative strategy to tune concentration and location of dynamic surface vacancies on photocatalysts by building surface tensile strain for advancing sustainable ammonia production.