Correlation of Poly(methylene)-Rich Amorphous Aliphatic Domains in Humic Substances with Sorption of a Nonpolar Organic Contaminant, Phenanthrene

Abstract

The structural makeup of natural organic matter plays a major role in regulating its capacity to retain nonionic hydrophobic organic compounds (HOCs). We used a model HOC--phenanthrene--to investigate the correlations between sorption capacity, specifically the modified Freundlich coefficient (K'f), and compositional data of humic acids, humins, and a peat obtained from quantitative 13C solid-state NMR spectroscopy. A positive correlation between K'f and the weight fraction of amorphous poly(methylene) in the sorbents was observed. In contrast, the correlation between phenanthrene sorption capacity and aromaticity or polarity indices of the sorbents was insignificant. The nonpolar aliphatic carbon fraction, excluding poly(methylene), was only partially correlated with K'f. Detailed NMR analyses of the sorbents using 1H inversion-recovery experiments showed that 10-nm diameter domains of branched nonpolar aliphatic groups, which account for 20-50% of all nonpolar aliphatic segments and may be associated with the poly(methylene), were responsible for the partial correlation. The correlation between K'f and the amorphous nonpolar aliphatic domains including amorphous poly(methylene) was strong. The rubbery, relatively low-density, and amorphous nonpolar aliphatic domains can be expected to offer an excellent environment for the sorption of phenanthrene by partitioning. These observations suggest that the domains of amorphous poly(methylene) and branched nonpolar aliphatics, which make up 2-9 wt % of the organic fraction in our samples, may serve as good descriptors for the potential of natural organic matter to retain HOCs in the natural environments.

Biosorption of phenanthrene by pure algae and field-collected planktons and their fractions

“…Previous study reported negative relationship between paraffinic carbon contents and (O + N)/C, which suggests that high paraffinic carbon contents would often be associated with low polarity in a sorbent (Chen et al, 2005). Significant positive correlation was also reported between K OC values of Phen and paraffinic carbon content (Chefetz et al, 2000;Mao et al, 2002;Salloum et al, 2002). Moreover, as the NHC fraction isolated in this study for the Porphyra samples contains higher polymethylene carbon than that for the Seaweed or Spirulina, it exhibits higher biosorption capacity.…”

Biochar: Pyrogenic Carbon for Agricultural Use - A Critical Review

“…Similar to humic substances, that have a different sorption (by partition) capacity, correlated with the content of amorphous poly-(methylene) structures, but poorly correlated with polarity and aromaticity indices (Mao et al, 2002), the sorption of polar and nonpolar aromatic contaminants by biochar occurs by different mechanisms (partition and adsorption), each with specific transitions (Chen et al, 2008).…”

Effects of humic acid and lipid on the sorption of phenanthrene on char

“…2), a peak at 1720 cm − 1 (-COOH) was observed, but the -COOH peak in the 13 C NMR spectra of 165-190 ppm was very weak. Mao et al (2002) reported that the sp 2 carbons (110-220 ppm) or -COOH tend to be underrepresented by CP MAS 13 C NMR due to their longer relaxation times (T 1 , spin-lattice relaxation time). According to this observation, -COOH of the lipid may be in rigid domains, corresponding to longer T 1 Mao et al, 2000).…”