Mechanism of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide degradation in UV light-emitting diodes lamp driven sodium sulfite activation process

DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is emerging organic phosphorus flame retardant, which has gained greatly attention because of its adverse health effects on aquatic organisms. In this study, UV light-emitting diodes lamp driven sodium sulfite activation (UV254/Sulfite) process was employed as an advanced reduction process to remove DOPO, and its mechanisms were revealed. The pseudo first order rate constant of DOPO (kobs-DOPO) in UV254/Sulfite process initially decreased from 6.95 x 10(-5) s(-1) to 5.11 x 10(-5) s(-1), and subsequently increased to 1.61 x 10(-4) s(-1) as the sulfite concentration increased from 0 to 10 mM, indicating that the negative effect of HSO3- on DOPO degradation was the dominate factor in UV254/Sulfite process at low sulfite concentration (< 2 mM), while the yields of hydrated electron (e-aq) increased as the sulfite concentration gradually reaching to a high value (10 mM), resulting in enhancing DOPO degradation significantly. In addition, the coexisted water matrix in deionized water and natural surface water weakened DOPO degradation in UV254/Sulfite process, and this inhibition strengthened as the concentrations of water matrix raised. The DOPO degradation pathway indicated that e-aq attacked phosphaphenanthrene structure of DOPO and contributed to its detoxification which was confirmed by Quantitative Structure-Activity Relationship (QSAR) assessment.