Sorption of organic compounds to two diesel soot black carbons in water evaluated by liquid chromatography and polyparameter linear solvation energy relationship

Substantial variability in sorption capacity of black carbon (BC) has been a major challenge for accurate fate and risk assessment of organic pollutants in soils and sediments. 16 model organic sorbates (logKOW = 0.38-4.21) encompassing diverse chemical functionalities were used to probe the sorption capacity of two diesel soot samples representative of graphitic BC (BC1, specific surface area (SSA) = 87 m2/g) and amorphous, oxygenated BC (BC2; SSA = 3.6 m2/g). The BC-water sorption coefficients (logKBC) of the model sorbates were determined using reversed-phase liquid chromatography (RP-LC) on soot-filled columns. It was found that mass-based logKBC's of BC1 (1.64-3.66 L/kgBC) exceeded those of BC2 (0.68-3.48 L/kgBC) consistently for all model sorbates. However, area-normalized logKBC's of BC2 were larger than those of BC1, suggesting that the overall sorption was more favored on the oxygenated sorbent per area basis. Linear solvation energy relationships (LSERs) for sorption onto BC1 and BC2 were found to be logKBC = (2.49 ± 0.65)E + (−2.71 ± 0.88)S + (1.17 ± 0.46)A + (2.52 ± 0.34)V and logKBC = (1.12 ± 0.39)E + (−1.68 ± 0.32)S + (−3.70 ± 0.57)B + (4.37 ± 0.38)V + (−1.51 ± 0.22), respectively. The LSERs indicated that sorption onto soot was generally enhanced with increasing non-specific van der Waals and decreasing cavitation cost (i.e., eE, sS, and vV terms). The logKBC difference between BC1 and BC2, ΔlogKBC, appeared to be correlated with the H-bonding capacity of the sorbates but not logKOW. Analysis of literature and experimental logKBC's revealed that logKBC and logSSA across different types of BC (i.e., soot, char, charcoal, activated carbon) were linearly correlated for benzene and toluene (r2 = 0.88-0.91). This work illustrates the utility of RP-LC in determining the sorption coefficients of high-capacity sorbents and suggests the possibility of a unified sorption model for the continuum of black carbon.