Impact of humic acid coating on sorption of naphthalene by biochars

Impact of humic acid (HA) coating on biochar properties and the associated influence on naphthalene (Naph) sorption were studied. Coating with HA evidently decreased the sorption capacity and isotherm nonlinearity of Naph by the biochars, resulting from their chemical composition and surface property changes. At low solute concentrations, the suppression of HA coating on Naph sorption was primarily due to pore blockage. At high solute concentrations, sorption suppression of Naph gradually shifted to be a result of surface coverage by the coated HA molecules. The aromatic carbon components in the original and HA-coated biochars served as more effective domains for Naph sorption over the alkyl carbon ones. HA coating reduced aromatic carbon content of the biochars, thereby weakening the pi-pi and hydrophobic interactions between biochars and Naph. Such a process also introduced O-containing polar moieties, especially the O-alkyl and C = O polar components, to the surfaces of biochars, which reduced accessibility of Naph to their hydrophobic carbon domains. Hence, Naph sorption was suppressed. Results of this work are critical for better understanding of the mechanisms controlling influence of dissolved organic matter loading on sorption of aromatics to biochars, which in turn is helpful for elucidating the environmental behaviors of HOCs. (C) 2015 Elsevier Ltd. All rights reserved.