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

Abstract

Environmental context Benzotriazoles are chemicals widely used to inhibit corrosion in various industrial processes and in household products. They persist in aquatic environments, even under UV irradiation, and thus there is a need to improve their photolytic degradation to minimise the environmental exposure risks. We investigated the effects of four iron–carboxylate complexes on the UV photodegradation of three benzotriazoles in aqueous solutions and show that they significantly increase the degradation rates of benzotriazoles. Abstract The effects of FeIII–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 254nm in the presence of FeIII and four carboxylate ions (oxalate, tartrate, succinate and citrate). The results showed that the presence of FeIII–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 3.98h for BT, 6.08 to 8.25h for 5-TTri and 2.63 to 5.50h for CBT in the four systems of the FeIII–carboxylate complexes. In comparison, the half-lives ranged between 3.40 and 4.81h for BT, 6.42 and 11.55h for 5-TTri and 4.13 and 6.79h for CBT in pure aqueous solution and in the presence of FeIII or carboxylate. The degradation rates of these BTs were dependent on the pH values, type of carboxylate and FeIII/carboxylate ratios. Both BT and CBT showed the highest photodegradation rates with the shortest respective half-lives of 0.57 and 2.63h at the initial FeIII/oxalate ratio of 10/200µmolL–1 in aqueous solutions at pH 3, whereas 5-TTri had the highest photodegradation rate with the shortest half life of 6.08h at the initial FeIII/succinate ratio of 10/10µmolL–1.