Cluster-Based Self-Assembly: Reversible Formation of Polyoxometalate Nanocones and Nanotubes

Reversible self-assembly of Keggin structure polyoxometalate (POM) nanoclusters into nanodisks, nanocones, and nanotubes is described. The surface of POM clusters was modified by organic surfactant through single-phase approach. By carefully controlling and varying clusters surrounding environment, all assemblies were found to reverse into each other. The different assemblies and their evolutions from each other were studied by scanning electron microscopy and optical microscopy while the inner structure was investigated by transmission electron microscopy. The formation and transformation of different assembly shapes into each other is interpreted by considering electrostatic binding of surfactant molecules with the POM cluster, number of surfactant molecules attached, and particular surrounding environment arising from the optimized mixed solvent.