Photodegradation of benzophenones sensitized by nitrite

Benzophenone UV filters (BPs) are a group of contaminants of emerging concern due to their widespread occurrence and adverse effects on aquatic ecosystems. In this study, the transformation of BPs by nitrite sensitized photodegradation was comprehensively investigated. OH and NO₂ generated by nitrite photolysis reacted with BPs, forming hydroxylated and nitrated products, respectively. Kinetic modeling revealed that the steady-state concentrations of NO₂ were approximately six orders of magnitude higher than those of OH in the UV/nitrite process, although the second-order rate constants of NO₂ reactions with BPs were six orders of magnitude lower. With the increase in nitrite concentration, BPs degradation was accelerated, and the contribution of NO₂ increased as well. At initial nitrite concentration of 10 μM, the contributions of OH and NO₂ to the degradation of 2,4-dihydroxybenzophenone (BP1) were 66.1% and 21.5%, respectively. However, NO₂ only contributed a tiny fraction to the degradation of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (BP4), due to the presence of an electron-withdrawing sulfonate group in the molecule. Natural organic matter (NOM) inhibited the nitrite sensitized degradation of BPs, due to light screening and radical scavenging effects. This study suggests that BPs can be effectively transformed in sunlit waters in the presence of nitrite, leading to nitrated products.