Triplet Photochemistry of Dissolved Black Carbon and Its Effects on the Photochemical Formation of Reactive Oxygen Species

Dissolved black carbon (DBC) is an important component of dissolved organic matter pool; however, its photochemical properties are not fully understood. In this study, we determined the excited triplet-state quantum yields of DBC ( 3 DBC*) and 1 O 2 quantum yields (Φ 1 O 2 ) of six diverse DBCs using sorbic alcohol, 2,4,6-trimethylphenol (TMP), and furfuryl alcohol and compared the results with quantum yields of reference natural organic matters (NOMs). The average Φ 1 O 2 of six DBCs (4.2 ± 1.5%) was greater than that of terrestrial NOM (2.4 ± 0.3%) and comparable to autochthonous NOM (5.3 ± 0.2%). Using TMP as a probe for oxidizing triplets, DBC presented significantly higher apparent quantum yield coefficients for degrading TMP ( f TMP ) than the reference NOM, reflecting that the f TMP values of low-energy 3 DBC* were approximately 12-fold greater than those of low-energy 3 NOM*. The differences in the f TMP and Φ 1 O 2 trends among the DBCs indicated that the 3 DBC* responsible for these reactions may be from different sources. In addition, DBC was much more effective than NOM, on a carbon-normalized basis, during photodegradation of pharmaceutically active compounds. This result confirms that the presence of DBC can accelerate the photodegradation of contaminants that are susceptible to one-electron oxidation by triplets.