Comparative kinetic study of atrazine photodegradation in aqueous Fe(ClO4)3 solutions and TiO2 suspensions

Abstract

Kinetics of oxidative photodegradation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) in both homogeneous solutions of Fe(ClO4)3 and heterogeneous suspensions of TiO2 were investigated and compared. Besides laboratory experiments in a batch-mode photoreactor with monochromatic irradiation at 365nm, solar radiation was applied. Hydrolysis and oligomerization processes occurring in aqueous solutions of Fe(ClO4)3 strongly affected the degradation kinetics. Initial reaction rates decreased with age of the solutions reflecting decreased concentration of the most photoactive complex [Fe(OH)(H2O)5]2+. Comparing freshly prepared solutions of Fe(ClO4)3 with aqueous slurry of TiO2 P25 (Degussa), the photodegradation rates were similar. Colloidal suspensions of quantum-sized particles Q-TiO2 were less photoactive than the P25 slurry. Doping of the quantum-sized particles by Fe3+ caused a red shift of the semiconductor absorption but influenced the photocatalytic activity negatively. Comparing to Q-TiO2, the degradation rate for Q-TiO2 (1% Fe3+) decreased, while for the corresponding mixture of Q-TiO2 and 1% Fe(ClO4)3 it increased.Besides atrazine, photodegradation of its intermediates 2-chloro-4-ethylamino-6-amino-1,3,5-triazine (CEAT), 2-chloro-4-isopropylamino-6-amino-1,3,5-triazine (CIAT) and 2-chloro-4,6-diamino-1,3,5-triazine (CAAT) was also investigated separately. While the degradation rates for CEAT and CIAT were found similar as for atrazine in all investigated systems, the degradation of CAAT proceeded comparably fast only in the Q-TiO2 colloidal suspension but was markedly slower in the other systems.