Synthesis and Properties of the Keggin Structure (NH4)4 SiW12 O40 Nanoparticles by Solid State Reaction at Room Temperature

(NH4)4SiW12O40nanoparticles were prepared firstly by the solid state reaction of H4SiW12O40·22H2O with (NH4)2C2O4·H2O at the room temperature. The nanoparticles were characterized by elemental analysis, FTIR, XRD,TEM, TG-DTA and BETtechniques. The experimental result indicates that the nanoparticles were found still to exhibit Keggin structure and had the mean grain size 60 nm and BETspecific surface areas 108.7 m2/g. The nanometermaterials had a higher thermal stability at a temperature below 430℃. The forming mechanism of nanoparticles has also been discussed. In this solid state reaction, grind and reaction thermal energy could accelerate the speed ofH4SiW12O40·22H2O with (NH4)2C2O4·H2O diffusion and its product (NH4)4SiW12O40nucleationwhile decreasing particles size. The water of crystallization of reactants forms easily small water cells in the reaction and restricts (NH4)4SiW12O40particle size, and the productH2C2O4·2H2O crystal play a key role in prohibiting (NH4)4SiW12O40crystal growth and formingthe small size of nanoparticles.