New insights into physicochemical properties of different particulate size-fractions and dissolved organic matter derived from biochars and their sorption capacity for phenanthrene

Abstract

To improve the knowledge of the heterogeneity and sorption behavior of biochars on hydrophobic organic contaminants (HOCs), pristine biochars (PBCs, 400 and 700 °C) were fractionated into four particulate fractions (SfBCs) and dissolved organic matter derived from biochars (DBC), then the sorption capacities of them towards phenanthrene were examined. Results showed that the OC-normalized sorption distribution coefficients (Koc) of PBCs were generally at intermediate levels among that of SfBCs and DBCs. The logKoc values of SfBCs increased as particle sizes decreased. By virtue of the higher micropore volume, specific surface area, aromaticity and hydrophobicity, the lowest SfBCs (0.45–10 µm, BC0.45–10) exhibited remarkably higher logKoc. Besides, although SfBCs from 700 °C generally showed larger logKoc than counterparts from 400 °C, almost no difference was observed for logKoc values of BC0.45–10 fractions from 400 and 700 °C. We thus speculated that particle size might have stronger effect on their sorption capacity than pyrolysis temperature. Although DBCs exhibited dramatically lower logKoc values than nano-scale SfBCs, they were interestingly comparable to large-sized SfBCs. Our findings thus suggested the importance of small particulate biochar species and DBCs on HOCs transport should be both highlighted since these fractions were highly dynamic in the environment.