Nanometer-Size Polyoxometalate Anions Adsorb Strongly on Neutral Soft Surfaces

Polyoxometalates (POMs) are nanometric metal-oxide anions with unique chemical and physical properties. During the past decade, significant efforts have been made to give POMs surface activity and self-assembly properties that are essential for catalysis applications and for producing organic-inorganic hybrid materials. In this work, POMs-based surfactants are produced spontaneously through noncovalent interactions in water by mixing nonionic surfactants with POM. The most common POMs of tungstosilicate and tungstophosphate have indeed an unexpected strong tendency to adsorb on polar and neutral interfaces. Micelles in water and water/air interfaces were investigated by SAXS and ion flotation showing the POM anions adsorbed at the micelle surface and on monolayers of nonionic surfactants. This general property of POM provides a unique opportunity for deeper understanding of many medicinal effects of POMs, i.e., their antiviral and antitumor activities that involve their specific adsorption on biological surfaces.