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.
The micron grade multi-metal oxide bismuth silicate (Bi 12 SiO 20,BSO) was prepared by the chemical solution decomposition technique.Photocatalytic degradation of pentachlorophenol (PCP) was investigated in the presence of BSO under xenon lamp irradiation.The reaction kinetics followed pseudo first-order and the degradation ratio achieved 99.1% after 120 min at an initial PCP concentration of 2.0 mg/L.The pH decreased from 6.2 to 4.6 and the dechlorination ratio was 68.4% after 120 min at an initial PCP concentration of 8.0 mg/L.The results of electron spin resonance showed that superoxide radical (O 2 · ) was largely responsible for the photocatalytic degradation of PCP.Interestingly,this result was different from that of previous photocatalytic reactions where valence band holes or hydroxyl radicals played the role of major oxidants.Some aromatic compounds and aliphatic carboxylic acids were determined by GC/MS as the reaction intermediates,which indicated that O 2 · can attack the bond between the carbon and chlorine atoms to form less chlorinated aromatic compounds.The aromatic compounds were further oxidized by O 2 · to generate aliphatic carboxylic acids which can be finally mineralized to CO 2 and H 2 O.
Yang Li Junfeng Niu Lifeng Yin Wenlong Wang Yueping Bao Jing Chen Yanpei Duan
