Incorporation of iron(III) into nanoporous silica spheres

Iron(III) containing silica spheres with the average diameter of 800 nm were prepared by the hydrolysis and the condensation of tetraethoxysilane in the presence of hexadecyltrimethylammonium chloride and subsequent reaction with aqueous or ethanol solution of iron(III) nitrate. The iron(III)-containing silica spheres were calcined in air at 400 degree celsius to obtain nanoporous silica spheres containing iron(III). The location and the states of the iron in the nanoporous silica spheres were examined using scanning electron microscopy, transmission electron microscopy, elemental mapping, diffuse reflectance ultraviolet -visible absorption as well as Fe K -edge X-ray absorption spectroscopy. Iron(III) was located at the surface of the spheres as octahedrally coordinated species when iron(III) was adsorbed from ethanol solution of iron(III) nitrate. When the incorporation of iron(III) was done from the aqueous solution of iron(III) nitrate, tetrahedrally coordinated iron(III) was dispersed homogeneously through the spherical silica particles. Both of the silica spheres were microporous with the large BET surface area (ca. 1000 m(2)/g). The iron(III) containing silica spheres absorbed UV and were inactive for the photocatalytic degradation of methylene blue.