Impacts of properties of dissolved organic matters on indirect photodegradation of genistein

Excited triplet states of dissolved organic matters (3DOM*) are one of the most important photochemically-produced reactive intermediates leading to transformation of organic contaminants. However, relationships of photodegradation kinetics of different dissociation states of phenolic organic contaminants with chemical components or properties of 3DOM* are largely unknown. In this study, roles of 3DOM* in photodegradation of polyhydroxy phe-nolic genistein (Gs) at pH 5, 8 and 12 were investigated taking five kinds of DOM from different sources as examples. Relationships between photodegradation kinetics constants and DOM properties were built. Results showed that the contributions of direct 3DOM*-induced reactions to the total indirect photodegradation of Gs and second-order reac-tion rate constants (kDOM,Gs) of Gs with 3DOM* increased with pH increases. This was mainly attributed to decreases in vertical ionization energy of Gs at higher pH, endowing Gs with stronger electron donating capacities. kDOM,Gs was found to positively correlate with the specific ultraviolet absorbance at 254 nm, reflecting aromaticity of DOM, and negatively correlate with the absorbance ratio at 254 and 365 nm and contents of dissociated acidic functional groups of DOM, representing molecular weights of DOM, antioxidants and the repulsive forces between 3DOM* and Gs. This study provided a new insight into relationship between DOM properties and indirect photodegradation kinetics of phenolic contaminants in aquatic environments.

Automated summary

This study investigates the effect of excited triplet states of dissolved organic matters (3DOM*) on the photodegradation of polyhydroxy phenolic genistein (Gs), and establishes the relationship between the properties of 3DOM* and the degradation kinetics constants. The results show that the contributions of 3DOM*-induced reactions to the photodegradation of Gs and the reaction rate constants (kDOM,Gs) increase with pH, which is mainly attributed to the decrease in ionization energy of Gs. The study also reveals that kDOM,Gs positively correlates with the specific ultraviolet absorbance at 254 nm, representing DOM aromaticity, and negatively correlates with the absorbance ratio at 254 and 365 nm and the content of dissociated acidic functional groups of DOM, representing DOM molecular weights and the repulsive forces between 3DOM* and Gs. This study provides insights into the relationship between DOM properties and the indirect photodegradation kinetics of phenolic contaminants in aquatic environments.