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

Abstract

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 (3DBC*) and 1O2 quantum yields (Φ 1O2 ) 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 1O2 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 3DBC* were approximately 12-fold greater than those of low-energy 3NOM*. The differences in the f TMP and Φ 1O2 trends among the DBCs indicated that the 3DBC* 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.

Microbial labilization and diversification of pyrogenic dissolved organic matter

“…4. ROS have been previously shown to be very important in pyDOM photochemistry (Ward et al, 2014;Fu et al, 2016;Wang et al, 2020), and we speculate that they play an important role in the microbial degradation of pyDOM as well.…”

“…In sunlit aquatic environments, photodegradation is the most significant sink for the fraction of ConAC of pyDOM (Stubbins et al, 2012). The photochemistry of ConAC and pyDOM has been studied utilizing either laboratory-prepared pyDOM (Ward et al, 2014;Fu et al, 2016;Li et al, 2019;Bostick et al, 2020;Goranov et al, 2020;Wang et al, 2020) or natural organic matter rich in ConAC (Stubbins et al, 2010(Stubbins et al, , 2012Wagner and Jaffé, 2015). These studies have reported that ConAC are exceptionally photolabile and they degrade through a series of oxygenation, ring opening, and decarboxylation reactions leading to a pool of smaller aliphatic by-products.…”

“…These studies have reported that ConAC are exceptionally photolabile and they degrade through a series of oxygenation, ring opening, and decarboxylation reactions leading to a pool of smaller aliphatic by-products. Additionally, pyDOM photochemistry has been associated with the production of high fluxes of reactive oxygen species (ROS), important transients involved in the photo-transformation and photodegradation of pyDOM (Fu et al, 2016;Li et al, 2019;Goranov et al, 2020;Wang et al, 2020). These studies have contributed to a better understanding of the biogeochemical cycling of pyDOM in the presence of sunlight in the environment.…”

Photogeneration of Reactive Species from Biochar-Derived Dissolved Black Carbon for the Degradation of Amine and Phenolic Pollutants

“…7 In comparison to some well-studied natural organic matter (NOM), DBC exhibits higher aromatic structure contents and smaller molecular sizes. 13,15 As a result, DBC has a significantly higher yield of 3 DBC* for one-electrontransfer reactions than 3 NOM*. 13 The quantum yield of 1 O 2 from DBC was also determined to be 2−3 times higher than that of humic substance (HS).…”

Labilization and diversification of pyrogenic dissolved organic matter by microbes

“…4. ROS have been previously shown to be very important in pyDOM photochemistry (Ward et al, 2014;Fu et al, 2016;Goranov et al, 2020;Wang et al, 2020), and it is likely that they play an important role in the microbial degradation of pyDOM as well.…”