Degradation of sulfamethoxazole by the heterogeneous Fenton-like reaction between gallic acid and ferrihydrite
Yu Huang, Jiewen Yang
Abstract
In soils, the Fenton-like reaction can be initiated when phenolic acids (PCs) existed simultaneously with iron oxides and dissolved O 2 , which would have great impact on transformation of organic pollutants . This study probed the mechanism of the Fenton-like reaction that occurs in a heterogeneous system containing ferrihydrite (Fh) and gallic acid (GA), and evaluated its performance in sulfamethoxazole (SMX) degradation. In the absence of dissolved O 2 , only reductive dissolution of Fh by GA occurred. It was further showed that Fh is capable of catalyzing the oxidation of GA by O 2 , in which the Fenton-like reaction was involved with the formation of reactive oxygen species (ROS) (semiquinone free radicals , superoxide, singlet oxygen , hydroxyl radical and H 2 O 2 ) together with the adsorbed and aqueous Fe(II). At pH 4.0, this Fenton-like reaction could lead to SMX degradation at a rate of 38.2% and 65.6% when GA concentration were set at 0.1 and 0.2 mM, respectively. Elevating pH inhibited SMX degradation process. Citric acid had no effect on SMX degradation, while ascorbic acid showed a promotive effect. Moreover, HPLC-MS showed the presence of 12 intermediate products, and the proposed pathways for SMX degradation included cleavage, demethylation , oxidation and electrophilic substitution . This work could enhance our understanding on how the abiotic soil Fenton-like reaction controls the fate of SMX in soil environments.