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(H2O)(6)}(12){Mo2O4(SO4)}(30)](72-) (Mo-132 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 Mo-132 nanocapsules self-organize into a cubic phase stacking state in the assemblies. The ion-trapping properties of Mo-132 are active in the assemblies, which enables the Mo-132 to uptake and release Li+ ions. Furthermore, the speed of Mo-132 uptaking and releasing Li+ ions in the assemblies is remarkably decreased compared with that of the naked Mo-132, 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 Mo-132 nanocapsules but also demonstrates a new concept of using the microenvironment of supramolecular assemblies to adjust the ion-trapping properties of Mo-132.