Sorption Selectivity in Natural Organic Matter Probed with Fully Deuterium-Exchanged and Carbonyl-¹³C-Labeled Benzophenone and ¹H–¹³C NMR Spectroscopy

Abstract

Specific functional-group or domain interactions of fully deuterium-exchanged, carbonyl-(13)C-labeled benzophenone and different types of natural organic matter (NOM) were investigated through two-dimensional (1)H-(13)C heteronuclear correlation NMR spectroscopy. The sorbents included Beulah-Zap lignite, type II kerogen (IL-6), Pahokee peat, Amherst humic acid, and a polystyrene-poly(vinylmethyl ether) (PS-PVME) blend. PS-PVME consists of PS and PVME chains that are mixed on a scale of <5 nm. The NOM sorbents all consist predominantly of a mixed aromatic-alkyl or aromatic-O-alkyl matrix that is homogeneous on the 3 nm scale, as evidenced by fast equilibration of aromatic and alkyl (1)H magnetization. In addition, Beulah lignite and IL-6 kerogen exhibit small fractions of distinct polymethylene (CH2)n domains, and Pahokee peat contains significant fractions of polar and nonpolar alkyl domains. Benzophenone-((13)C═O)-d10 shows proximity to both aromatic rings and alkyl segments in all samples but preferentially interacts with aromatic rings in PS-PVME and Beulah lignite, possibly due to π-π electron donor-acceptor interactions. The data for IL-6 kerogen are also compatible with preferential location of benzophenone near the alkyl-substituted edges of aromatic rings, while in Pahokee peat, clear signatures of benzophenone affinity to both aromatic-rich and nonpolar alkyl domains have been detected. Amherst humic acid shows evidence of some affinity to polar alkyl segments but which is weaker than that to aromatic rings. Our results indicate that specific interactions of the sorbate and the presence of domains in the sorbent influence the magnitude and selectivity of sorption.

Humic Acids Isolated from Selected Soils from the Russian Arctic and Antarctic: Characterization by Two-Dimensional 1H-13C HETCOR and 13C CP/Mas NMR Spectroscopy

“…Solid-state 2D dipolar HETCOR experiments were performed to correlate 13 C and 1 H chemical shifts. This experiment is analogous to the wideline separation (WISE) experiment previously described by Schmidt-Rohr et al, with the exception that it is performed at a higher MAS speed [29][30][31]. Two-dimensional C-H correlation spectra were obtained using the standard HETCOR technique [34] with frequency switched Lee-Goldburg (FSLG) homonuclear dipolar decoupling at 13 kHz.…”

“…However, the use of 1 H-13 C (HETCOR) NMR spectroscopy can complement the 13 C (CP/MAS) NMR spectroscopy method, thereby increasing the accuracy of detection of individual HAs fragments in soils. At present, the use of 1 H-13 C (HETCOR) NMR has been performed mostly for kerogen and polymers [29,30,32]. However, we were unable to find any works devoted to the study of two-dimensional NMR spectroscopy of HAs of polar soils, so further studies using this method are necessary to expand the database on the structure of HAs of polar soils.…”

Interactions between natural organic matter and organic pollutants as revealed by NMR spectroscopy

“…[126] The advanced multiCP pulse technique was applied to characterize different NOM types, which were then investigated by twodimensional 1 H- 13 C HETCOR correlation NMR spectroscopy after their interactions with a fully deuterium-exchanged, carbonyl-13 C-labeled benzophenone. [127] The full deuteration for benzophenone had the objective to eliminate intramolecular 1 H- 13 C correlations, thus allowing the benzophenone 13 C-carbonyl to interact exclusively with the nearby protons in NOM. The spin diffusion from benzophenone carbons to NOM protons was followed by HETCOR experiments, which employed three different mixing times (0.01, 0.3, and 10.25 ms).…”

“…7d), in order to detect the spatial proximity of NOM domains and predict their availability for interactions. [127] The 19 F spectroscopy was also employed in the solid state to investigate the role of lipid composition in geosorbents, such as coastal sediments, humin, and HAs, on the adsorption of phenanthrene. [70] The authors used the 2,2,2-trifluoroethyl laurate as a probe to show the relevant contribution of the lipid components of the selected geosorbents.…”

“…[128] In particular, the 19 F nuclei of organofluorine compounds were used to induce observable [127] Copyright 2014 by American Chemical Society). transverse magnetization to the 1 H nuclei in the peat molecular components, which were in direct interaction with the sorbed xenobiotics.…”