Enhanced degradation and deiodination of diatrizoate in a sulfite mediated photolytic system: performance, products and possible pathways

This study systematically investigated the performance of a sulfite mediated photolytic system on diatrizoate (DTZ) degradation and deiodization under different UV intensity, sulfite dosage, initial solution pH, initial DTZ concentration and co-present constituents. As compared with sole UV photolysis and sole sulfite reduction system, the UV/sulfite system performed a higher efficiency of DTZ degradation and deiodization. At the same time, the scavenging experiments were conducted by respectively adding KNO3, KNO2, MeOH and TBA, which indicated eaq− was the dominant active species responsible for the enhanced degradation and deiodination of DTZ. Effects of reaction factors showed that the UV/sulfite system was a promising technique for DTZ degradation. A complete removal of DTZ (40 µM) could be obtained under the UV intensity of I0 (6.67 × 10−7 einstein/cm2∙s), sulfite dosage of 0.50 mM and pH ranging from 8∼10. In addition, the intermediate products of DTZ degradation were identified and possible degradation mechanism was proposed. Four possible products including TP504, TP488, TP486 and TP236 were obtained in this study. The main degradation pathways might include protonation, deiodination, substitution and heterocyclic formation.