Polyoxometalate-based frameworks as chemical nanoreactors: in situ synthesis of active silver nanoparticles in confined spaces

Abstract

The synthesis of metal catalysts confined in porous materials is still a great challenge. Here, a framework sustained by bulky rigid polyoxometalate (POM) blocks [Mo₃₆O₁₁₂(H₂O)₁₆]⁸⁻ ({Mo₃₆}) is used to restrict the size of Ag particles to obtain a novel composite of well-sized silver nanoparticles encapsulated in a POM framework. This composite is formed by in situ reduction of the POM framework containing silver ions ({Ag^I–Mo^VI₃₆}) by dimethylformamide (DMF), and it is characterized by PXRD, UV-vis spectroscopy and TEM. The formation of silver nanoparticles is very sensitive to ultraviolet light, and only POM reduction species rather than silver reduction species can be obtained under light irradiation. Furthermore, the active silver nanoparticles are confirmed by a model experiment involving the reduction of 4-nitrophenol.