Mechanistic Insights into Environmental Aging and Reactive Nitrogen Species Generation on Dissolved Black Nitrogen and Their Contribution to Bisphenol A Photodegradation

Abstract

Beyond dissolved black carbon (DBC), wildfires also produce substantial amounts of dissolved black nitrogen (DBN) in aquatic and soil systems; however, the activity and reactivity of DBN remain poorly understood. This study simulated environmental microbial oxidation and UV exposure using H₂O₂ oxidation and UV irradiation, respectively, and investigated their effects on the structural evolution of DBN and its subsequent photocatalytic degradation of bisphenol A (BPA). DBN was derived from nitrogen-rich biomass pyrolyzed at 350, 550, and 750 °C, respectively. The results showed that H₂O₂ oxidation increased the content of oxygen-containing groups and nitrogen oxides, as well as structural defects on DBN surfaces, more substantially than UV irradiation. H₂O₂ oxidation markedly enhanced the photodegradation of BPA by DBN, especially for DBN prepared at 350 °C. In contrast, UV-aged DBN exhibited only a modest effect on BPA photodegradation. Correlation analysis revealed that BPA removal correlated strongly with the electron-accepting capacity (EAC) of DBN (R² = 0.9143). The increased oxygen and nitrogen contents and the elevated EAC played dominant roles in the photodegradation of BPA by aged DBN. Nitrogen oxides promoted the generation of reactive nitrogen species (RNS), while the enhanced EAC facilitated the photoexcitation of aged DBN to form charge-separated intermediates (DBN^•+/•–), leading to hydroxyl-radical production. Both RNS and hydroxyl radicals served as the dominant free radicals, collectively oxidizing BPA and accelerating its photodegradation. This study provides novel insights into the structural transformation of DBN during environmental aging and its impact on the fate of organic pollutants.