Properties of iron-based mesoporous silica for the CWPO of phenol: A comparison between impregnation and co-condensation routes

Iron-based mesoporous silica materials were prepared according to different impregnation and co-condensation procedures. Several complementary techniques, including XRD, TEM/EDX and nitrogen sorption isotherms were used to evaluate the final structural and textural properties of the calcined Fe/SBA-15 materials. While Fe2O3 isolated particles of which the size is close to the silica pore diameter (∼7-8 nm) were obtained using classical wet impregnation procedure, smaller iron oxide particles (∼2-4 nm) homogeneously dispersed within the hexagonal pore structure of the SBA15 host support were generated by self-combustion of an impregnated iron-glycinic complex. By contrast, the various co-condensation routes used in this work were less efficient to generate iron oxide nanoparticles inside the silica mesopores. Catalytic performances of the materials were evaluated in the case of total phenol oxidation by H2O2 in aqueous solution at ambient conditions. Large differences in terms of catalytic activity and iron species stability were observed. While the impregnated solids proved to be the most active catalysts (highest Fe2O3 nanoparticles dispersion), iron leaching was observed in aqueous solution, accounting for a homogeneous catalytic contribution. In contrast, the co-condensed samples exhibiting larger iron oxide clusters stabilized over the silica surface proved more efficient as active sites in Fenton catalysis.