Formation of hydroxyl radicals and Co 3+ in the reaction of Co 2+-EDTA with hydrogen peroxide. catalytic effect of Fe 3+

Abstract

Co 2+ ions (Co(NO 3) 2 · 6H 2O) react with H 2O 2 only in presence of EDTA to yield OH radicals and Co 3+. This reaction was carried out in unbuffered aqueous solutions (pH = 2.6). The formation of Co 3+ was confirmed by spectroscopy. The Co 3+-EDTA complex shows two typical absorptions at 382 nm and 532 nm. The Co 3+-EDTA complex can be prepared by a number of oxidizing agents, like Fe 3+, Fe 3+-EDTA, Ag +, Ag 2+, Ce 4+, and hydroxyl radicals. Since Fe 3+ oxidizes Co 2+-EDTA to Co 3+-EDTA and Fe 2+ we initiate a chain reaction for ·OH formation. Our results show that there are two modes for H 2O 2 decomposition: (1) One electron transfer to give OH radicals and (2) Decomposition of H 2O 2 to H 2O 2 and O 2 without intermediate ·OH formation. This reaction depends strongly on the pH of the buffer. The H 2O 2 decomposition increase with increasing pH and increasing Co 2+ concentration.