Studies in structural characterization of silica–heteropolyacids composites prepared by sol–gel method

Abstract

Heteropolyacids (HPAs) which are included in mesoporous silica, H 3PMo 12O 40/SiO 2 and H 4PMo 11VO 40/SiO 2 have been synthesized by a sol–gel technique that involves hydrolysis of ethyl orthosilicate. The effect of incorporation of heteropolyacids species on silica matrix was studied by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA), N 2 adsorption–desorption, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray powder patterns prove that heteropolyacids are uniformly dispersed in the silica network. IR and Raman spectra have show that the HPAs anions preserved their Keggin structure on the surface of silica–HPA composites. SEM images and BET adsorption–desorption isotherms confirm the presence of nanometer particles and mesoporous structures. SEM micrographs of silica–HPAs composites show that silica–HPAs composites are composed of spherical particles with an average diameter of approximately 20–30 μm. The silica-included heteropolyacids were thermally more stable than the parent ones.