Ionic-Liquid-Controlled Two-Dimensional Monolayer Bi₂MoO₆ and Its Adsorption of Azo Molecules

Two-dimensional (2D) nanosheets with a single-layer thickness are currently an emerging field in synthetic chemistry. The preparation of these sheets is a challenge due to their predicted thermodynamic instability. Here, we determined that Bi2MoO6 nanosheets can be controlled by ionic liquids (ILs) with ammonium cation alkyl chain lengths and polar anions, and their adsorption capacities for azo molecules are in good agreement with the σ-profiles obtained from conductor-like screening models for realistic solvents. Particularly, monolayer Bi2MoO6 exhibits a superhigh adsorption capacity of 468 mg/g for Congo red (CR), and a molecular dynamics simulation reveals that the adsorption process has diffusion, association, and equilibrium steps. The interactions between the positively charged [BiO]+ groups on the surface of the monolayer Bi2MoO6 and the negatively charged center of CR molecules in aqueous solution are strong, leading to a large negative adsorption free energy of −81.8 kcal/mol. This work establishes a method to control the 2D monolayer and provides insight into the adsorption behavior.