Isolated and Linear Arrays of Surfactant-Encapsulated Polyoxometalate Clusters on Graphite

Abstract

We report on the self-assembly of several surfactant-encapsulated clusters (SECs) on the basal plane of graphite consisting of the doughnut-shaped tungstophosphate anion [Na(H2O)P5W30O110] covered by a hydrophobic shell of surfactants. Well-ordered rodlike structures are observed using scanning force microscopy. No such ordering is observed if the surfactant methyltrioctadecylammonium is used for encapsulation, suggesting that the density of alkyl chains around the polyoxometalate cluster is an important factor in determining the order of SEC assemblies on graphite. Coadsorption of tetratetracontane (n-C44H90) and (DODA)14[Na(H2O)P5W30O110] results in single, isolated SECs on a buffer layer of tetratetracontane, as determined by scanning tunneling microscopy.

Controlling the dispersion of supported polyoxometalate heterogeneous catalysts: impact of hybridization and the role of hydrophilicity–hydrophobicity balance and supramolecularity

“…The heights of the hybrid assemblies were smaller when compared to the theoretical height of POM and DODA combined. A similar reduction in the vertical height of surfactant encapsulated clusters (SECs) of POM on HOPG, was also observed by Wu et al [17] for their hybrid made of DODA and a larger (1.7 nm diameter) doughnut-shaped Preyssler anion [Na(H 2 O)P 5 W 30 O 110 ] 14− . The reduction in the vertical height of the nanorods was attributed to a flattening effect due to the interactions between flexible alkyl chains and the graphite surface.…”

“…1 nm [31], and the length of a fully extended DODA molecule is ca. 2.25 nm [17]. Because the POM structures used in this study do not possess a ring structure that can hold water molecules [19], and because we have used a dehydrated solvent (ethanol), the theoretical size of a DODA encapsulated single Keggin anion unit can be estimated to be roughly 5.5 nm.…”

“…The organization of the hybrid material on surfaces is dependent on the interaction between various factors such as the type of hybridization (i.e., through electrostatic interaction or covalent bonding), the nature of the POM building block (formula, charge density), and the chemical nature and hydrophilic or hydrophobic character of the surface on which the hybrids are deposited. For instance, surfactant-encapsulated clusters of POM anions, formed through electrostatic interactions, were reported to form well-ordered straight nanorods on graphite [17], whereas hybrid materials formed through covalent functionalization of POM formed planar layer-by-layer assemblies on a hydrophobic surface [16]. Recently Musumeci et al [18] have shown the formation of nano-hexagons in a hybrid made from an alkyl-functionalised Mn-Anderson POM and dimethyldioctadecylammonium bromide (DODA) as counter cation.…”

“…Often cationic surfactants such as DODA were used as host organic matrix to synthesize organic–inorganic hybrid materials, with their organization having mostly been investigated on hydrophobic surfaces [17] or in bulk [19]. However, a clear understanding of their structure and molecular assembly as a function of the hydrophobic or hydrophilic nature of the substrate is absolutely necessary for further progress towards a wider application.…”

Controllable synthesis of polyoxometalates nanocubes and their specific interactions with prion proteins

“…The liquid-assisted method has been understood much more. The liquid-assisted way like synthesis in the organic solvents [9] and the surfactant-aqueous synthesis method [5][6][7][8]13] used widely have been reported. In our work, we chose the Keggin-type POM as an investigative object which is investigated most concerning the five-type POM structures [14] .…”