Synthesis of Negative-Charged Metal-Containing Cyclomatrix Polyphosphazene Microspheres Based on Polyoxometalates and Application in Charge-Selective Dye Adsorption

A negative-charged, metal-containing cyclomatrix polyphosphazene microsphere (MCPM) is synthesized using the strategy of precipitation polymerization of di-functionalized polyoxometalates (POMs) and hexachlorocyclotriphosphazene. The chemical structure of these MCPMs is well characterized by ¹³C MAS NMR and ³¹P MAS NMR, as well as FT-IR, electron microscopy, and X-ray photoelectron spectroscopy. The covalent grafting of the rigid POMs clusters into the framework of these microspheres prevents the collapsing of the pores, making these MCPMs porous materials. Taking advantage of the porous structure and the negative charges in the frameworks, these materials show interesting charge-selective adsorption properties, as demonstrated by the selective adsorption of positive-charged dyes in comparison with negative-charged dyes.