Degradation mechanism of sulfa drugs based on theoretical prediction and experimental examination in TiO2 suspension

Photodegradations of Sulfamethazine (SMT) and Sulfametoxydiazine (SMD) in TiO₂ suspension were investigated experimentally and theoretically under UV irradiation. The degradations of SMT and SMD by TiO₂ photocatalysis increased with prolonging the reaction time, and three main intermediates for SMT and four main intermediates for SMD were indentified by LC/MS. The N–S bond, the C–C bond (benzene ring) in the SMT, and the N–C bond, the S–N bond and the C–O bond in the SMD, had higher frontier electron densities. Initial photodegradation of SMT proceeded mainly via the break of the N–S bond and the hydroxylation of SMT, and initial photodegradation of SMD was similar to SMT. There existed a plausible consistency between the experimental results and the theoretical calculations on the basis of results obtained.