Self-assembly of amphiphilic polyoxometalates for the preparation of mesoporous polyoxometalate-titania catalysts

Abstract

Amphiphilic polyoxometalate (POM) surfactants were prepared by covalently grafting double hydrophobic tails with chain lengths C₁₂H₂₅, C₁₄H₂₉, C₁₆H₃₃ or C₁₈H₃₇ onto the lacunary Wells–Dawson {P₂W₁₇O₆₁} headgroup. The critical micelle concentrations (CMCs) of these novel surfactants in aqueous solutions were determined by conductivity, and micelle formation was studied by small angle neutron scattering (SANS). Surprisingly, the amphiphiles with longer hydrophobic tails tend to form less elongated and more globular micelles in water. The self-assembled amphiphilic polyoxometalates were used as templates in the hydrothermal synthesis of mesoporous TiO₂ containing dispersed, immobilised {P₂W₁₇O₆₁} units, which showed enhanced activity for the photodegradation of rhodamine B (RhB). The catalyst was recycled eight times with no loss of efficiency, demonstrating the stability of the hybrid structure. The amphiphilic polyoxometalates, therefore have excellent potential for the synthesis of various types of catalytically active porous materials.