Photodegradation performance and mechanism of sulfadiazine in Fe(III)-EDDS-activated persulfate system

Abstract

In order to overcome the shortcomings in the traditional Fenton process, Fe(III)-EDDS-activated persulfate advanced oxidation process under irradiation is carried out as a promising technology. The photodegradation of sulfadiazine (SD) in Fe(III)-EDDS-activated persulfate system was investigated in this paper. The results showed that SD could be effectively degraded in Fe(III)-EDDS/$S_2{O}_8^{2-}$/hv system. The effects of Fe(III):EDDS molar ratio, the concentration of Fe(III)-EDDS, and the concentration of $S_2{O}_8^{2-}$ on SD degradation were explored. At neutral pH, when Fe(III):EDDS = 1:1, Fe(III)-EDDS = 0.1 mM, $S_2{O}_8^{2-}$ = 1.5 mM, the best SD degradation was achieved. The experiment of external influence factors showed that the degradation of SD could be obviously inhibited by the presence of ${CO}_3^{2-}$, ${SO}_4^{2-}$, whereas the degradation of SD was almost unaffected by the addition ofCl^-. The degradation of SD could be slightly inhibited by the presence of humic acid and NO₃^-. The effect of pH on SD degradation was investigated, and SD could be degraded effectively in the pH range of 3-9. ESR proved that ¹O₂, ·OH, $S{O}_4^{-}$, and O₂^- were produced in the process. $S{O}_4^{-}$ and ·OH were identified as the main radicals while O₂^·- also played non-ignorable role. Eleven intermediate products of SD were analysed. The C = N, S-N, and S-C bonds of SD were attacked by radicals firstly, leading to a series of reactions that eventually resulted in the destruction of SD molecules and the formation of small organic molecules.

Keywords: Fe(III)-EDDS/${\mathrm{S}}_2{\mathrm{O}}_8^{2-}$/hv system; internal and external influence factors; mechanism analysis; radicals; sulfadiazine.