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

Abstract

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.

Aqueous synthesis of mesostructured BiVO4 quantum tubes with excellent dual response to visible light and temperature

“…3(d)), mainly due to the associated reduction in surface energy [16], with a concomitant rearrangement of oleate ions on the surface of the BiVO 4 pearl-necklace-shaped quantum wires. Previous studies of the rearrangement of surfactant ions on the surface of polyoxometalates [17,18] support our suggestion of oleate ion rearrangement on the surface of the BiVO 4 pearl-necklace-shaped quantum wires. As the BiVO 4 has three surface oleate ligands, it may be expected that the forces generated when BiVO 4 pearl-necklace-shaped quantum wires come into contact with each other result in the rearrangement of the oleate ions on the BiVO 4 surface leading to a Y-shaped arrangement-one oleate ion moves in one direction while the other two move in the opposite direction along the planes perpendicular to the pearlnecklace-shaped quantum wires (Scheme 1(d)).…”

“…As the BiVO 4 has three surface oleate ligands, it may be expected that the forces generated when BiVO 4 pearl-necklace-shaped quantum wires come into contact with each other result in the rearrangement of the oleate ions on the BiVO 4 surface leading to a Y-shaped arrangement-one oleate ion moves in one direction while the other two move in the opposite direction along the planes perpendicular to the pearlnecklace-shaped quantum wires (Scheme 1(d)). When the Y-shaped arrangements of oleate ions are aligned in the same direction, their mutual repulsion-coming from the direction of the pair of oleate ions-will inevitably force the side-to-side assembly of the pearl-necklace-shaped quantum wires to tilt a certain angle [17,19], thus, making them gradually assemble into tubular nanostructures (Scheme 1(d) and 1(e)). Published reports of the formation of tubular or spherical shapes by polyoxometalates with three or four surfactant ions further support our assumption that the BiVO 4 quantum tubes are formed because of the specific number of oleate ions attached and their peculiar rearrangement [17,18].…”

“…When the Y-shaped arrangements of oleate ions are aligned in the same direction, their mutual repulsion-coming from the direction of the pair of oleate ions-will inevitably force the side-to-side assembly of the pearl-necklace-shaped quantum wires to tilt a certain angle [17,19], thus, making them gradually assemble into tubular nanostructures (Scheme 1(d) and 1(e)). Published reports of the formation of tubular or spherical shapes by polyoxometalates with three or four surfactant ions further support our assumption that the BiVO 4 quantum tubes are formed because of the specific number of oleate ions attached and their peculiar rearrangement [17,18]. As shown in Fig.…”

Polyoxometalate Nanocone Nanoreactors: Magnetic Manipulation and Enhanced Catalytic Performance

“…[2] The recent progresses in the synthesis of POM-based amphiphilic units have revolutionized POM chemistry, and consequently a variety of robust and well-defined assembly architectures with tunable properties have been developed, including one-dimensional wires [3] and fibers, [4] two-dimensional thin-films [5] and disks, [6] and threedimensional vesicles, [7] spheres, [8] tubes, [6,9] and flowers. [10] Although, these assembly structures hold great promise for the design of new functional materials, in reality they have been less explored for their potential use in various scientific fields.…”

“…Recently, we reported well-defined, robust Keggin ion based nanocones, obtained by a simple and fast synthesis technique at room temperature. [6] Herein, we report the functionalization of nanocones with magnetite nanocrystals and their controlled manipulation in the reaction system. For example, we applied these nanocones for the catalytic oxidation of sulfides in which they act as nanoreactors to provide enhanced efficiency, selectivity, and easier recovery under an external magnetic field.…”