Simultaneous oxidation of EDTA and reduction of metal ions in mixed Cu(II)/Fe(III)-EDTA system by TiO₂ photocatalysis

Both the photooxidation of EDTA and the photoreduction of metal ions in metal-EDTA systems were investigated. EDTA oxidation by TiO₂ photocatalysis occurred sequentially as Cu(II)-EDTA > Cu(II)/Fe(III)-EDTA > Fe(III)-EDTA. For Cu(II)-EDTA, EDTA was completely decomposed after only 60 min of irradiation. The rate of EDTA decomposition was directly correlated with the initial Cu(II) concentration in the case of a mixed Cu(II)/Fe(III)-EDTA system. The metal ions in a single metal-EDTA complex were removed following significant decomposition of EDTA. For a mixed Cu(II)/Fe(III)-EDTA system, however, no copper was removed whereas almost all of the iron was removed. The iron and copper species deposited on the TiO₂ surface were identified via EPR and XPS as mixed FeO/Fe₃O₄ and Cu⁰/Cu₂O, respectively.