Interaction mechanism of benzene and phenanthrene in condensed organic matter: Importance of adsorption (nanopore-filling)

- The CO2 adsorption estimates the nanoporosity of natural organic matter (NOM).
- The adsorption of gaseous benzene can measure the nanooporosity of NOM.
- The adsorption for benzene and Phen is related to aliphatic carbon of NOM.
- The nanopore filling for Phen and benzene is the dominating mechanism.
- The nanopore filling mechanism is not be affected by water molecules.

Although microporosity and surface area of natural organic matter (NOM) are crucial to mechanistic evaluation of the sorption process for nonpolar organic contaminants (NOCs), they have wrongly been estimated by the N2 adsorption technique. Nuclear magnetic resonance spectroscopy (13C NMR), and benzene, carbon dioxide, and nitrogen adsorption techniques were used to characterize structural and surface properties for different condensed NOM samples, which were related to the sorption behavior of phenanthrene (Phen). It was found that the revised Freundlich model by taking the chemical activity into account can well describe the isotherms for benzene and Phen. The benzene and Phen adsorption volumes for the coal samples are similar to or lower than the CO2-nanopore volumes. Adsorption volumes of both benzene and Phen are significantly related to the aliphatic carbon structure, and their correlation lines are nearly overlapped, suggesting that the nanopore filling for Phen and benzene on the investigated samples is the dominating mechanism, and also is not affected by water molecules. The entrapment of benzene and/or the pore deformation in the NOM nanopore are likely responsible for the observed hysteresis of benzene. The above results demonstrate that Phen and benzene adsorption on the condensed NOM is closely associated with the aliphatic carbon structure of the investigated samples.