Effects of environmental factors on sulfamethoxazole photodegradation under simulated sunlight irradiation: Kinetics and mechanism

To advance the knowledge of the environmental fate of sulfamethoxazole (SMX), we systematically investigated the effects of natural water constituents and synthetic substances (i.e., TiO₂ nanoparticles (nTiO₂) and Ti-doped β-Bi₂O₃ (NTB)) on the photodegradation kinetics of SMX under xenon lamp irradiation. The photolysis of SMX in aqueous solution followed first-order kinetics. Our results showed that higher concentrations of SMX, fulvic acid, suspended sediments, NTB and higher pH value decreased the photodegradation rates of SMX, whereas H₂O₂ improved the SMX photodegradation. TiO₂ nanoparticles had a dual effect on photodegradation due to their photocatalytic activity and photoabsorption of photons. No intermediates more toxic toward Vibrio fischeri than SMX were produced after direct photolysis and photocatalytic degradation for 3 hr. The photolysis of SMX involved three pathways: hydroxylation, cleavage of the sulfonamide bond, and fragmentation of the isoxazole ring. This study lays the groundwork for a better understanding of the environmental fate of SMX.