Role of
Structure and Microporosity in Phenanthrene
Sorption by Natural and Engineered Organic Matter
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Abstract
Natural sorbents
including one humic acid (HA), humins (HMs), nonhydrolyzable
carbons (NHCs), and engineered sorbents (biochars) were subject to
bleaching to selectively remove a fraction of aromatic C. The structural
properties and sorption isotherm data of phenanthrene (Phen) by original
and bleached sorbents were obtained. Significant correlations between
Phen <i>K</i><sub>oc</sub> values by all sorbents and their
organic carbon (OC)-normalized CO<sub>2</sub> cumulative surface area
(CO<sub>2</sub>–SA/OC) suggested that nanopore-filling mechanism
could dominate Phen sorption. After bleaching, natural sorbents still
contained large amounts of aromatic C, which are resistant to bleaching,
suggesting that they are derived from condensed or nonbiodegradable
organic matter (OM). After eliminating the effect of aromatic C remaining
in the bleached samples, a general trend of increasing CO<sub>2</sub>–SA/OC of natural sorbents with increasing aliphaticity was
observed, suggesting that nanopores of natural sorbents are partially
derived from their aliphatic moieties. Conversely, positive relationships
between CO<sub>2</sub>–SA/OC or Phen log<i>K</i><sub>oc</sub> of engineered sorbents and their aromaticity indicated the
aromatic structures of engineered sorbents primarily contribute to
their nanopores and dominate their sorption of HOCs. Therefore, this
study clearly demonstrated that the role of structure and microporosity
in Phen sorption is dependent on the sources of sorbents