Impact of the Simulated Diagenesis on Sorption of Naphthalene and 1-Naphthol by Soil Organic Matter and its Precursors

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Abstract

Soil organic matter (SOM) in a peat soil, humic acid, and humin and their precursors (i.e., cellulose and lignin) were treated at high temperature (250 and 400 °C) with high pressure in a sealed platinum reaction kittle to simulate the influence of diagenesis on their composition and structure, and impact of the simulated diagenesis on sorption behaviors of hydrophobic organic compounds (HOCs) (i.e., naphthalene and 1-naphthol) by these samples was investigated. High temperature and pressure treatment greatly influenced chemical composition and physical properties of the original samples and their sorption for both naphthalene and 1-naphthol. Sorption of naphthalene by all samples was jointly regulated by hydrophobic and π-π interactions with their alkyl and aromatic carbon moieties, which was derived from the positive correlation between total hydrophobic carbon content of all sorbents and their organic carbon content-normalized sorption coefficients (Koc) for this compound (p = 0.075). However, sorption of 1-naphthol by the tested sorbents was governed by hydrogen bonding with their O-containing polar functionalities, as derived from the positive correlation between Koc values of 1-Naph and their polarity index ((O+N)/C). Difference in sorption mechanisms of naphthalene and 1-naphthol by the original and treated samples noted the great influence of chemical composition of sorbates on their interaction and essential roles of specific interactions (e.g., hydrogen bonding) in sorption of polar compound (i.e., 1-naphthol) to these sorbents. Surface area (SA) and porosity data of sorbents obtained from N2 sorption-desorption isotherms at 77 K showed that new SA and pores were created during the diagenetic process of all original samples, which provided substantial sorption sites and thus enhanced sorption of naphthalene and 1-naphthol. Among all tested samples, physicochemical properties of cellulose were most strongly affected by the simulated diagenetic process, and impact of such a process on its sorption intensity for the tested compounds was the most significant. The characterization data of the treated sorbents showed that the high temperature and pressure treatment similarly simulated the naturally occurring diagenesis of SOMs and their precursors, which is a first attempt. These findings are valuable for better understanding of the sorption behaviors of HOCs to SOM and its precursors as affected by diagenesis, which in turn is critical for elucidating the transport and fate of HOCs in the environment.

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