Photocatalytic degradation pathway of sulfadiazine over Ag–TiO2 under visible light irradiation

Abstract

In the past decades, TiO2-based photocatalysis has received much research attention as an effective strategy for decomposing the antibiotics in a water system. However, the degradation pathway of antibiotics over TiO2-based photocatalysts has seldom been studied. In this work, Ag–TiO2 was prepared via photo-reduction method and the photocatalytic degradation pathway of sulfadiazine over Ag–P25 under visible light irradiation was explored with the assistance of high performance liquid chromatography-mass spectrometry (HPLC–MS). Based on the HPLC–MS results, the chemical formulas of five degradation intermediates were proposed: one is the product of desulfonating reaction; the second is the product of sulfanilamide bond-breaking reaction; the others are the oxidation and substitution products initiated by ·OH. The contributions of ·O2−, ·OH and h+ during the photocatalytic degrading process of sulfadiazine were investigated by reactive species trapping experiments. On the basis of the above results, it can be deduced that there exist three possible photocatalytic degrading pathways of sulfadiazine, i.e., desulfonation, sulfanilamide bond-breakage and the oxidation of amino groups. Moreover, the photocatalytic mechanism of Ag–P25 was also proposed.