Iron oxide nanoparticles dispersed in SBA-15 silica as efficient catalysts for methanol oxidation: interplay between photocatalysis and Fenton chemistry

The development of efficient catalysts for advanced oxidation processes is of major importance for the removal of organic contaminants from water and industrial effluents. In this context, this work investigates the preparation, structural characterization, and catalytic performance of Fe-loaded SBA-15 mesostructured silica materials. This work investigates the preparation, structural characterization, and catalytic performance of Fe-loaded SBA-15 mesostructured silica materials. SBA-15 silicas were first synthesized under different preparation conditions and calcination treatments and subsequently used as supports for the deposition of iron species, followed by controlled calcination to obtain Fe-containing catalysts. The physicochemical properties of the Fe-loaded materials were characterized using complementary techniques. X-ray diffraction and nitrogen adsorption-desorption measurements were used to determine the crystalline phases and textural properties of the materials. Microscopic analyses by scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy provided information on the size, morphology, and spatial distribution of iron oxide nanoparticles located either inside the mesopores or on the external surface of silica grains. Additional structural analysis combining X-ray diffraction and modelling methods allowed identification of crystalline iron oxide phases, mainly hematite and maghemite. Optical and semiconducting properties were investigated by UV-visible spectroscopy and Tauc plot analysis to determine the band-gap energies of the iron oxide nanoparticles. The Fe-loaded samples calcined in air at 700 degrees C were found to contain hematite nanoparticles together with dispersed iron species and iron-containing colloidal phases. Their catalytic reactivity was investigated through methanol oxidation in aqueous solution under air in the presence of hydrogen peroxide. The main reaction product was formaldehyde, followed by methyl formate and ultimately carbon dioxide. Formaldehyde formation was monitored using a colorimetric trapping method based on the formation of a strongly absorbing yellow diacetyldihydrolutidine (DDL) complex. The catalytic activity was found to depend strongly on the structural and electronic properties of the iron oxide nanoparticles, particularly their size, dispersion, and semiconducting behavior, providing insight into the structure-reactivity relationships governing iron-oxide-based photocatalysts for advanced oxidation processes.