Bi vacancy simultaneous manipulation of bulk adsorption and carrier utilization to replenish the mechanism of Cr(VI) photoreduction at universal pH

Constructing atomic-level cation vacancies is an effective strategy to modulate the electronic properties of host materials, thus promoting charge transfer and redox reaction kinetics. Herein, ultrathin Bi₂₄O₃₁Br₁₀ nanosheets with cationic vacancy was synthesized via an inventive precipitation strategy by adding appropriate arginine. The difunctional arginine can changes the pH of the synthetic system and selectively deprive Bi atoms on the surface to form Bi vacancies through strong affinity between functional groups and cations. The abundant Bi vacancy decrease the Gibbs free energy change and provide channels to promote bulk adsorption of Cr(VI), thus effectively reduces the carrier migration distance during in situ bulk photocatalytic reduction of Cr(VI) and induces the formation of new impurity states to improve the utilization of visible light. Bi vacancy mitigates strong excitonic effects confined by significantly reducing exciton binding energies, thus effectively promote the separation of photo-generated charges and suppress reorganization of photon-generated carrier. Benefiting from these merits, these exclusive V_Bi-Bi₂₄O₃₁Br₁₀ ultra-thin nanosheets exhibit superior reduction performance for Cr(VI), and the removal rate was more than 90% at universal pH (2–10). This work provides a new idea for the construction of cation vacancies and a feasible method for the removal of Cr(VI) under alkaline conditions.