Hierarchical mesoporous TiO2 microspheres for the enhanced photocatalytic oxidation of sulfonamides and their mechanism

Sulfonamides, a group of antibacterial agents, are not readily biodegradable and as a result have often been detected in wastewater effluents, rivers and lakes. This work investigated the photocatalytic degradation of sulfadimethoxine (SDM) and related sulfonamides in H2O2 containing aqueous suspensions of mesoporous TiO2 microspheres exposed to simulated solar light irradiation. The three-dimensional mesoporous TiO2 microsphere catalyst was fabricated by a facile method via a one-step solvothermal process without templates. The performance of mesoporous TiO2 microspheres exceeded the commercially available P25 TiO2 catalyst in the photocatalytic degradation of sulfonamides. Sulfadimethoxine degradation increased and reached the optimal H2O2 concentration of 5.9 mM. Particularly, the disappearance of SDM as well as the formation and decomposition of some degradation intermediates were determined by high-performance liquid chromatography-mass spectroscopy (HPLC-MS) and high-performance liquid chromatography-selective ion recording (HPLC-SIR) data modules, and possible photocatalytic degradation mechanisms were proposed. The hydroxylation and cleavage of the S-N or C-N bonds through (OH)-O-center dot attacks on the aromatic rings and aminopyrimidine rings under simulated solar light irradiation with the assistance of H2O2 played important roles during SDM photocatalytic degradation.