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. center dot OH and NO2 center dot generated by nitrite photolysis reacted with BPs, forming hydroxylated and nitrated products, respectively. Kinetic modeling revealed that the steadystate concentrations of NO2 center dot were approximately six orders of magnitude higher than those of center dot OH in the UV/nitrite process, although the second-order rate constants of NO2 center dot reactions with BPs were six orders of magnitude lower. With the increase in nitrite concentration, BPs degradation was accelerated, and the contribution of NO2 center dot increased as well. At initial nitrite concentration of 10 mu M, the contributions of center dot OH and NO2 center dot to the degradation of 2,4-dihydroxybenzophenone (BP1) were 66.1% and 21.5%, respectively. However, NO2 center dot 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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study found that nitrite can sensitize the photodegradation of BPs, forming hydroxylated and nitrated products. The increase in nitrite concentration accelerated the degradation of BPs, with different contributions of NO2 center dot and center dot OH in various circumstances.