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

Abstract

Abstract 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 radical, instead of HO radicals. This is contrary to the generally observed behaviour with other iron-carboxylate complexes, where H2O2 is produced and HO radicals are generated. The photodegradation 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\u2009=\u20090.05 mM, [Fe(III)]\u2009=\u20090.3 mM, [malonate]0\u2009=\u20091.2 mM, pH\u2009=\u20092.8, λirr\u2009=\u2009365 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 photodegrade than the mixture itself, only ca. 40% TOC disappears after 360 min and 64% COD is removed after 24\u2009h of irradiation (IBP/Fe(III)-malonate/UVA 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.