FORMATION OF HYDROXYL RADICALS AND CO3+ IN THE REACTION OF CO2+-EDTA WITH HYDROGEN-PEROXIDE - CATALYTIC EFFECT OF FE3+

Co2+ ions (Co(NO3)2.6H2O) react with H2O2 only in presence of EDTA to yield OH radicals and Co3+. This reaction was carried out in unbuffered aqueous solutions (pH = 2.6). The formation of Co3+ was confirmed by spectroscopy. The Co3+-EDTA complex shows two typical absorptions at 382 nm and 532 nm. The Co3+-EDTA complex can be prepared by a number of oxidixing agents, like Fe3+, Fe3+-EDTA, Ag+, Ag2+, Ce4+, and hydroxyl radicals. Since Fe3+ oxidizes Co2+-EDTA to Co3+-EDTA and Fe2+ we initiate a chain reaction for .OH formation. Our results show that there are two modes for H2O2 decomposition: (1) One electron transfer to give OH radicals and (2) Decomposition of H2O2 to H2O and O2 without intermediate .OH formation. This reaction depends strongly on the pH of the buffer. The H2O2 decomposition increases with increasing pH and increasing Co2+ concentration.