Currently, the role of amorphous carbon structure (ACS) in sorption of chlorinated hydrocarbons (CHs) to biochars remains little known. Therefore, three CHs (1,1,2,2-tetrachloroethane, 1,3,5-trichlorobenzene and γ-hexachlorocyclohexane) with different molecular properties were selected as model adsorbates to investigate the effect of ACS on sorption of CHs to biochars produced at seven different pyrolysis temperatures (300-900 °C). There were two main mechanisms for ACS controlling the sorption of CHs. First, the polar sites on ACS are hydrophilic, CHs with greater polarity could strongly compete with the water molecule for the hydrophilic sites. Second, ACS of low temperature (300-400 °C) produced biochars possessing the natural organic matter (NOM)-like structure occupied some hydrophobic sites on condensed graphitic structure (CGS) of biochars. CHs with great hydrophobicity possibly seized the hydrophobic sorption sites on CGS from the NOM-like structure. Therefore, ACS of biochar was more benefit for sorption of strong polar CHs (1,1,2,2-tetrachloroethane: π∗ = 0.95; LogKow = 2.39) or strong hydrophobic CHs (1,3,5-trichlorobenzene: π∗ = 0.70; LogKow = 4.19) than CHs (γ-hexachlorocyclohexane: π∗ = 0.68; LogKow = 3.72) with relatively low polarity and hydrophobicity. The result reflects that the interaction between NOM and natural black carbon/biochars in soil and water environment possibly plays the similar role in controlling the environmental behavior of various polar or hydrophobic organic pollutants. Moreover, with increasing concentration of adsorbate (Ce), the first mechanism enhanced, while the second mechanism weakened. This study gives a deep insight into the roles of ACS of biochars in controlling the fate and availability of CHs with different molecular properties in environment.
Keywords: Amorphous carbon structure (ACS); Biochars; Chlorinated hydrocarbons (CHs); Molecular properties; Sorption.
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