Atrazine photodegradation in aqueous solution induced by interaction of humic acids and iron: Photoformation of Iron(II) and hydrogen peroxide

The photochemical formation of Fe(II) and hydrogen peroxide (H2O2) coupled with humic acids (HA) was studied to understand the significance of iron cycling in the photodeg radation of atrazine under simulated sunlight. The presence of HA significantly enhanced the formation of Fe(II) and H2O2, and their subsequent product, hydroxyl radical ((OH)-O-center dot), was the main oxidant responsible for the atrazine photodegradation. During 60 h of irradiation, the fraction of iron presented as Fe(II) (Fe(II)/Fe(t)) decreased from 20-32% in the presence of the Fe(III)-HA complex to 10-22% after adding atrazine. The rate of atrazine photodegradation in solutions containing Fe(III) increased with increasing HA concentration, suggesting that the complexation of Fe(III) with HA accelerated the Fe(III)/Fe(II) cycling. Using fluorescence spectrometry, the quenching constant and the percentage of fluorophores participating in the complexation of HA with Fe(III) were estimated by the modified Stern-Volmer equation. Fourier transform infrared spectroscopy (FTIR) offered the direct evidence that Fe(III)-carboxylate complex could be formed by ligand exchange of HA with Fe(III). Based on all the information, a possible reaction mechanism was proposed.