Covalent dispersion of surfactant-encapsulated polyoxometalates and in situ incorporation of metal nanoparticles in silica spheres.

In this paper, we have exhibited a novel strategy for the construction of polyoxometalate (POM) and metal nanoparticle (MNP) integrated silica spheres. To introduce MNPs into the POM embedded silica spheres, we employed the controllable in situ synthesis of MNPs through the photoreduction property of POMs that were pre-incorporated into silica spheres. Through electrostatic encapsulation with hydroxyl-terminated cationic surfactants, the POM polyanions with photoinduced redox property formed surfactant encapsulated clusters first. The complex was then grafted into a silica matrix by means of a co-condensation with hydrolyzed tetraethoxylsilicane covalently, and stable silica spheres containing surfactant-encapsulated POMs were obtained. The dispersion and the concentration of POM complex in the silica spheres can be tuned in a quite large extent, where the structure and property of POMs were maintained. In addition, the POMs can be photochromically changed to the reduced state through the irradiation with UV light. The well-dispersed POMs in a hydrophobic microenvironment within the hybrid spheres can be used as reductants for the in situ synthesis of MNPs. More significantly, the size and content of MNPs were tuned by controlling the experiment condition and the possible locations of both POMs and MNPs were characterized by IR, XPS, TEM and Raman spectra. The hybrid silica spheres combining both POMs and MNPs may provide potential applications in catalysis and antibacterial materials.