Self-assembly and ion-trapping properties of inorganic nanocapsule- surfactant hybrid spheres

Spherical hybrid assemblies based on cationic surfactants and anionic porous polyoxometalate nanocapsules [{(Mo)Mo₅O₂₁(H ₂O)₆}₁₂{Mo₂O₄(SO ₄)}₃₀]^72- (Mo₁₃₂ for short) are fabricated by the method combining an electrostatic encapsulation process and a polarity induced self-assembly process. The spherical assemblies possess a size of several hundred nanometres and the incorporated Mo₁₃₂ nanocapsules self-organize into a cubic phase stacking state in the assemblies. The ion-trapping properties of Mo₁₃₂ are active in the assemblies, which enables the Mo₁₃₂ to uptake and release Li⁺ ions. Furthermore, the speed of Mo₁₃₂ uptaking and releasing Li⁺ ions in the assemblies is remarkably decreased compared with that of the naked Mo₁₃₂, which shows that the microenvironment of the assemblies has an efficient blockage effect on the interaction and recognition between Mo ₁₃₂ and Li⁺ ions, consequently delaying the ion-trapping process. This work not only presents a new route to assemble Mo₁₃₂ nanocapsules but also demonstrates a new concept of using the microenvironment of supramolecular assemblies to adjust the ion-trapping properties of Mo ₁₃₂.