Kinetic and mechanism investigation on the photochemical degradation of atrazine with activated H₂O₂, S₂O₈^2- and HSO₅^-

Degradation of atrazine was investigated under UV-254nm irradiation, alone or in combination with peroxides, i.e., hydrogen peroxide, persulfate (PS) or peroxymonosulfate (PMS). UV/PS was found to be the most efficient process in this study, which was probably due to its higher radical quantum yield under UV irradiation, considering atrazine's comparable second order rate constant of 2.59×10⁹M^-1s^-1 and 2.25×10⁹M^-1s^-1 with sulfate radical and hydroxyl radical, respectively. The pH values showed no significant effect on direct photolysis of atrazine, with observed UV fluence based pseudo-first-order rate constant (k_obs) of 7.59×10^-4, 7.73×10^-4 and 6.72×10^-4cm²mJ^-1 at pH 3.0, 5.7 and 11.0, respectively. Performance of UV/H₂O₂ and UV/PMS were more independent of initial pH values while that of UV/PS appeared to be more efficient at neutral pH condition. UV/PS was observed as a less energy consumption process. Eight new degradation by-products were identified in this study, namely, 2-chloro-4-acetamido-6-(2-hydroxy-isopropylamino)-s-triazine (CDHT), 2-hydroxy-4-(2-hydroxy-ethylamino)-6-isopropylamino-s-triazine (ONIT), 2-chloro-4-vinylamino-6-isopropylamino-s-triazine (CVIT), 2-hydroxy-4-vinylamino-6-(2-hydroxy-isopropylamino)-s-triazine (OVHT), 2-hydroxy-4-acetamido-6-isopropenylamino-s-triazine (ODPT), 2-hydroxy-4-(2-hydroxy-ethylamino)-6-vinylamino-s-triazine (ONVT), 2-hydroxy-4-(2-hydroxy-ethylamino)-6-methylamino-s-triazine (ONMT) and 2-chloro-4-vinylamino-6-amino-s-triazine (CVAT). Potential degradation pathways were further proposed.