Parameters affecting sulfonamide photo-Fenton degradation – Iron complexation and substituent group

The photo-Fenton degradation of the sulfonamide antibiotics sulfadiazine (SDZ) and sulfathiazole (STZ) mediated by Fe(III)-oxalate was studied in this work. The influence of iron complexation, H2O2 concentration and pH on the initial SDZ and STZ degradation rate was evaluated. Degradation of both antibiotics is drastically improved in the presence of Fe(III)-oxalate in comparison to free iron, achieving complete degradation after 8 min irradiation at pH 2.5 in the presence of 5 mM H2O2 (equivalent to H2O2/antibiotic = 50). It was also possible to extend pH range of the photo-Fenton reaction by the use of Fe(III)-oxalate reaching more the 70% degradation at pH 6, however without significant mineralization. Comparison of the degradation kinetics of both sulfonamides indicated higher recalcitrance of STZ due to the lower electron density of its thiazol ring in relation to pyrimidine ring in SDZ.

► Fe(III)-oxalate complex improves drastically the photo-Fenton degradation of sulfonamide antibiotics.
► Sulfonamide antibiotics complex free iron hindering the photo-Fenton efficiency.
► The lower electron density of thiazol ring in relation to pyrimidine ring is responsible for the higher recalcitrance of sulfathiazole in relation sulfadiazine.