New Insights Into The Degradation Of Atrazine By Ultraviolet-Based Techniques

The combination of ultraviolet (UV) light and H2O2 is generally considered a promising technology for removing atrazine from the aqueous environment due to its high degradation efficiency, but the generation of toxic chloro-dealkylated intermediates is usually neglected. In addition, the dechlorination mechanism of the UV/H2O2 system has seldom been investigated. In this study, atrazine degradation is comparatively investigated in the UV and UV/H2O2 systems to clarify the dechlorination mechanism. The results show that direct UV photolysis can induce dechlorination of atrazine to form nontoxic hydroxyatrazine via a nucleophilic substitution reaction of (3)atrazine* with nucleophile H2O. For comparison, the degradation rate of atrazine can be enhanced in the UV/H2O2 system but the dechlorination efficiency is dramatically inhibited because in situgenerated center dot OH preferentially attacks the side chains of atrazine to form chlorodealkylated intermediates. Meanwhile, further dechlorination of chloro-dealkylated intermediates by H2O via nucleophilic substitution under UV irradiation is substantially slower than that of atrazine. In addition, laser flash photolysis combined with theoretical calculation also confirms that (3)chloro-dealkylation intermediates* are more resistant to dechlorination than (3)atrazine*. Overall, this study suggests that it is not beneficial to upgrade direct UV photolysis to the UV/H2O2 system for degrading atrazine in light of the dechlorination efficiency.