Hydroxyl radical involvement in the decomposition of hydrogen peroxide by ferrous and ferric-nitrilotriacetate complexes at neutral pH

Abstract

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by Fe III/H 2O 2 (pH = 2.85), Fe IIINTA/H 2O 2 (neutral pH), Fe II/O 2, Fe IINTA/O 2, Fe II/H 2O 2 and Fe IINTA/H 2O 2 (neutral pH) have been investigated using the competitive kinetic method. Experiments were carried out in batch and in semi-batch reactors, in the dark, at 25 °C. The data showed that the three probe compounds could be degraded by all the systems studied, and in particular by Fe IINTA/H 2O 2 and Fe IIINTA/H 2O 2 at neutral pH. The relative rate constants of degradation of the three probe compounds obtained for all the systems tested were identical and equal to 1.45 ± 0.03 and 0.47 ± 0.02 for k Atrazine/ k pCBA and k Fenuron/ k pCBA, respectively. These values as well as the decrease of the rates of degradation of the probe compounds upon the addition of hydroxyl radical scavengers ( tert-butanol, bicarbonate ions) suggest that the degradation of atrazine, fenuron and pCBA by Fe IINTA/O 2, Fe IINTA/H 2O 2 and Fe IIINTA/H 2O 2 is initiated by hydroxyl radicals.