Raw montmorillonite modified with iron for photo-Fenton processes: influence of iron content on textural, structural and catalytic properties

A raw montmorillonite was exchanged with the trinuclear Fe(III) acetate complex and calcined at 400 °C. Ratios of 0.5, 1.0 and 3.5 mmol of complex per gram of clay were employed. The pillared solids (Fe-PILCs) were analyzed by X-ray fluorescence spectroscopy, thermogravimetry analysis, scanning electron microscopy, Mössbauer spectroscopy, X-ray diffraction and nitrogen adsorption isotherms. Total iron amount incorporated by the clay increases with the complex/clay ratio used from 6.1% to 17.6%. Iron is incorporated mainly in the interlayer space when the clay is pillared with the smallest complex/clay ratio and a microporous network is generated. Adsorption of iron on the outer surface is favored for higher iron loads and results in the creation of a mesoporous structure. Mössbauer analysis shows the presence of iron as maghemite (γ-Fe2O3) particles with a wide particle size distribution. All the Fe-PILCs were active as catalysts for phenol degradation under photo-Fenton like conditions using UVA radiation and a maximum in their activity is achieved for an intermediate iron content (13.4%).