Evidence for immobilized photo-Fenton degradation of organic compounds on structured silica surfaces involving Fe recycling

Abstract

The present study reports on the use of novel structured inorganic silica fabrics loaded with Fe ions by exchange-impregnation as a heterogeneous photocatalyst. These Fe–silica fabrics are denoted EGF/Fe(0.4%). Experimental evidence shows that Fe ions are released from the silica fabrics and react with H₂O₂ to form oxidative radicals in solution; the Fe ions are reduced to Fe(II) during oxalic acid and oxalate oxidation. The Fe³⁺ is extracted from the support to the aqueous medium where it is re-oxidized by being re-adsorbed onto the silica fabric. The contributions of the homogeneous and heterogeneous photocatalysis processes during the degradation of oxalic acid and oxalates were quantified as a function of the solution pH and the results presented agree with the modeling of the iron oxide surface in the presence of oxalates at different pH values. By attenuated total reflection infrared spectroscopy (ATRIR), the asymmetric stretching vibration doublet band at 1740 cm⁻¹ and the satellite peaks corresponding to surface carboxylates were followed during the photocatalytic destruction of the oxalates. The results obtained indicate that the oxalate decomposition channel involves a fast light-activated decarboxylation of the Fe complex: [RCO₂Fe]²⁺ → [R˙] + CO₂ + Fe²⁺. The structural features of the EGF/Fe(0.4%) surfaces were investigated before and after the oxalate photocatalysis by high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and gas adsorption studies (BET).