Photodegradation of three benzotriazoles induced by four FeIII-carboxylate complexes in water under ultraviolet irradiation

The effects of Fe-III-carboxylate complexes on the photodegradation of three benzotriazoles (BTs), i.e. benzotriazole (BT), 5-methylbenzotriazole (5-TTri) and 5-chlorobenzotriazole (CBT) in aqueous solutions were investigated under exposure to UV irradiation at 254 nm in the presence of Fe-III and four carboxylate ions (oxalate, tartrate, succinate and citrate). The results showed that the presence of Fe-III-carboxylate complexes significantly enhanced the photodegradation rates of all three selected BTs. The photodegradation of BT, 5-TTri and CBT followed first-order reaction kinetics with half-lives ranging from 0.57 to 3.98 h for BT, 6.08 to 8.25 h for 5-TTri and 2.63 to 5.50 h for CBT in the four systems of the Fe-III-carboxylate complexes. In comparison, the half-lives ranged between 3.40 and 4.81 h for BT, 6.42 and 11.55 h for 5-TTri and 4.13 and 6.79 h for CBT in pure aqueous solution and in the presence of Fe-III or carboxylate. The degradation rates of these BTs were dependent on the pH values, type of carboxylate and Fe-III/carboxylate ratios. Both BT and CBT showed the highest photodegradation rates with the shortest respective half-lives of 0.57 and 2.63 h at the initial Fe-III/oxalate ratio of 10/200 mu mol L-1 in aqueous solutions at pH 3, whereas 5-TTri had the highest photodegradation rate with the shortest half life of 6.08 h at the initial Fe-III/succinate ratio of 10/10 mu mol L-1.