Effect of iron precursor on the Fenton-like activity of Fe2O3 /mesoporous silica catalysts prepared under mild conditions

Fe2O3/mesoporous silica catalysts were prepared by adding Fe2+ or Fe3+ ions, as an iron precursor, during the synthesis of silica gel. Low angle XRD data showed that both iron precursors affected the hexagonal ordered arrays of silica, which were more perturbed by Fe2+ than by Fe3+ ions, as confirmed by TEM images. Based on the Mössbauer spectroscopy, XPS, EPR and NH3-TPD data was possible to identify the iron species supported on the silica matrix are constituted of hematite and maghemite. The iron precursor strongly changed the specific area of the materials from 1406 m^2 g^−1, in pure silica sample, to 1165 and 799 m^2 g^−1 for the Fe3-MS and Fe2-MS samples, respectively, but the pore size distribution was maintained in the range of 15–40 Å in both samples. These Fe-containing silica nanoparticles showed good catalytic activity to degrade methylene blue in aqueous medium. However, the Fe3-MS sample was more active than the Fe2-MS sample because the iron in the first is more exposed, which facilitated the accessibility to the active Fenton-like sites. These synthesized samples showed to be more stable against the Fe leaching than samples prepared by simple impregnation of hematite on the silica surface. This was because the strong interaction of iron and silica matrix was achieved by adding iron in the course of the synthesis of silica gel