Evidence of non-photo-Fenton degradation of ibuprofen upon UVA irradiation in the presence of Fe(III)/malonate

The degradation of ibuprofen (IBP) in the presence of the complex Fe(III)-malonate in aqueous solution under 365 nm radiation has been investigated. Photolysis of Fe-malonate mainly generates the (CH2COOH)-C-center dot radical, instead of HO center dot radicals. This is contrary to the generally observed behaviour with other iron-carboxylate complexes, where H2O2 is produced and HO center dot radicals are generated. The photodegradadon of the IBP/Fe(III)-malonate/UVA system is slower than expected because the photo-Fenton reaction takes place only to a limited extent. Reaction rate profiles show an induction period, and IBP/Fe-malonate system runs inversely to Fe(II) formation. Almost complete IBP disappearance takes place after five hours with [IBP](0) = 0.05 mM, [Fe (III)] = 0.3 mM, [malonate](0) = 1.2 mM, pH = 2.8, lambda(irr) = 365 nm, T ca. 293 K. Kinetic profiles resemble first order decays as [H2O2] increases, and both the efficiency of the process and the reaction rate increase with acidity. Addition of Ca(II), Mg(II) and Mn(II) to the system IBP/Fe(III)-malonate/UVA has no effect on the degradation, whereas Cu(II) slightly inhibits it. Transformation photoproducts are more difficult to photo degrade than the mixture itself, only ca. 40% TOC disappears after 360 min and 64% COD is removed after 24 h of irradiation (IBP/Fe(III)-malonate/LIVA system). Seven transformation photoproducts were identified by HPLC-MS and the corresponding reaction mechanism has been proposed. Sunlight irradiation improves the reaction, showing the feasibility of IBP photodegradation in natural environments under carefully controlled conditions.