Kinetics and mechanism of the sensitized photodegradation of uracil--modeling the fate of related herbicides in aqueous environments.

摘要: The dye-sensitized photodegradation of uracil (UR), the parent compound several profusely employed herbicides, has been studied as a model their environmental fate. In order to mimic conditions frequently found in nature, aqueous solutions UR have irradiated with visible light presence natural sensitizer riboflavin (Rf). results indicate that is photostable acid media, but quickly degraded pH 7 or 9 solutions, where singlet molecular oxygen [O 2 ( 1 Δ g )] and, lesser extent, superoxide radical anion (O ·- )-both species photogenerated from triplet excited Rf, 3 Rf*-participate photodegradation. At 7, slowly through an O -mediated mechanism, whereas Rf disappears its reaction ) form Rf*, UR. On contrary, at photoprotected two processes: regeneration formed species-a back electron transfer also produces - and elimination medium Δg) by overall result preservation ground state continuity photosensitized process hence, degradation. Media higher values could not be due fast Rf. With rose bengal (RB) photosensitizer, rate constants for interaction between were range 5 × 10 M -1 s (at 7) 1.3 8 (in NaOH solution, mainly physical quenching). maximum )-mediated photooxidation efficiencies RB reached 11, only )-reactive quenching was observed.