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

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by FeIII/H2O2 (pH = 2.85), FeIIINTA/H2O2 (neutral pH), FeII/O2, FeIINTA/O2, FeII/H2O2 and FeIINTA/H2O2 (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 FeIINTA/H2O2 and FeIIINTA/H2O2 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 kAtrazine/kpCBA and kFenuron/kpCBA, 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 FeIINTA/O2, FeIINTA/H2O2 and FeIIINTA/H2O2 is initiated by hydroxyl radicals.

► The Fe(II)/NTA/H2O2 and Fe(III)NTA/H2O2 systems have been studied at neutral pH.
► Atrazine, fenuron and parachlorobenzoic acid were used as hydroxyl radical probes.
► Competitive kinetic method was used to demonstrate the formation of OH radicals.
► The reaction of H2O2 with iron-NTA complexes generates OH radicals at neutral pH.
► The reaction of O2 with Fe(II) and Fe(II)NTA also generates OH radicals at neutral pH.