Influence of natural organic matter fractions on PAH sorption by stream sediments and a synthetic graphene wool adsorbent

The sorption of selected PAHs onto sediment components and graphene wool were studied. Different natural organic matter (NOM)- mineral-deficient (MDF), mineral-rich (MRF), and black carbon (BCF) fractions were recovered from natural sediment (NAS) using sequential separation methods. Detailed characterization of sediment components using BET, ICP-OES, SEM-EDS, XRD, and FTIR were carried out and significant changes in the physicochemical properties of sorbents due to the treatment procedure were revealed. Experimental data showed that a pseudo-second-order and Freundlich adsorption model best fit kinetic and isotherm studies, validated by the least values of Error Sum of Squares (SSE). Isotherm data revealed that complementary processes involving both multilayer adsorption and partitioning of PAHs occurred. NAS, BCF, and MDF with higher % OC had higher Freundlich and maximum adsorption capacities (K-f and q(max)) than MRF for PAHs and an S-type sorption curve (N > 1) dominated the PAH-NOM interaction, with few exceptions for LMW PAHs. MRF significantly diminished the efficiency of graphene wool in the removal of selected PAHs from aqueous solution, as both adsorption capacity (K-d) and efficiency reduced from 16.9 g L-1 and 95.4% to 0.3 g L-1 and 18.5% respectively. Sorption of the selected PAHs was slightly favored under acidic pH and higher temperatures. The sorption reaction was endothermic for NAPH & PHEN, and exothermic for PYR & PERY. Furthermore, aromaticity and hydrophobic moieties of the different PAHs and NOM significantly influenced the pi-pi and hydrophobic-organophilic interactions that may have occurred, which led to some degree of irreversible sorption as shown by H-indices. Therefore, the probable impact of each NOM fraction on the mobility and environmental risk management/remediation of PAHs is herewith evaluated. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the sorption of selected PAHs onto sediment components and graphene wool. Different natural organic matter (NOM) fractions were recovered from natural sediment using sequential separation methods. Experimental data showed that the Freundlich adsorption model best fit kinetic and isotherm studies, with higher temperatures slightly favoring the sorption of the selected PAHs under acidic pH conditions.