Maghemite nanoparticles and maghemite/silica nanocomposite microspheres as magnetic Fenton catalysts for the removal of water pollutants

Maghemite nanoparticles (γ-Fe2O3 NP) and maghemite/silica nanocomposite microspheres (γ-Fe2O3/SiO2 MS) have been evaluated as magnetic heterogeneous Fenton catalysts. The catalysts were fully characterized by electronic microscopies, magnetometry, XRD, UV–vis–NIR spectroscopy, and sorption volumetry. It was found that the two materials differ in size, morphology, porosity and microstructure, although the maghemite nanoparticles are not modified by their encapsulation into the silica. Both catalysts have a strong magnetic susceptibility, but only the MS catalyst can be easily recovered by magnetic settlement. The mineralization and decolorization of aqueous solutions containing a model pollutant in presence of the catalysts were comparatively studied. Three model pollutants differing in their structure and their electrostatic charge were tested. The obtained reaction rates depend on the nature of the pollutant and catalyst. The results indicate the existence of a correlation between the amount of adsorbed pollutant and the decolorization rate. The free NP are usually more active than the MS catalyst, but larger velocity can also be obtained with the MS catalyst when the pollutant is strongly adsorbed on this material. Moderate mineralization rates were observed for both catalysts illustrating the larger stability towards oxidation of the uncoloured organic intermediates resulting from the primary degradation of the model pollutants. Moreover the efficiency and stability of the MS catalyst were established since this material showed an activity for a pollutant during five consecutive tests. This was also confirmed by characterization of the catalyst after these tests.

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► Maghemite nanoparticles and maghemite–silica nanocomposite microspheres were designed.
► These materials were fully characterized and tested as magnetic Fenton catalysts.
► Both were active on three aqueous pollutants, which were quickly decomposed.
► The activity depends on the adsorption capacity and the accessibility to the catalyst.
► The microspheres can be easily removed with a magnet and were reused five times.