Strong Adsorption of Anionic Pfas by Iron-Amended Graphitized Bonechar: Electrostatic Bonding to Iron Oxide

Abstract

Biochar emerges as a promising carbonaceous material for replacing activated carbon in the remediation of PFAS-contaminated groundwater, but its limited adsorption efficiency and incompletely understood adsorption mechanisms hinder practical application. Herein, 16 types of biochar were screened for their efficacy in removing PFAS, ultimately selecting a Fe-amended graphitized bonechar (BM-Fe) synthesized through one-step pyrolysis (850 °C) for its superior performance in simultaneous adsorbing 7 types of PFAS. SEM, TEM, and XRD demonstrated that α-Fe2O3 is the primary Fe mineral coating the surface of BM-Fe. The distribution coefficients (log Kd) for various PFAS ranged from 4.2 to 5.4, higher than those of pure bonechar (3.4-5.0) and lower-temperature-formed biochar (3.3-4.0). The improved adsorption affinities are mainly attributed to the enhanced electrostatic interaction, demonstrated by the more positively charged surface and pH-sensitive responsiveness. Theoretical calculations confirmed the higher adsorption energies of α-Fe2O3 for all 7 PFAS compared to graphite carbon. Dissolved organic matter and alkaline conditions were two main environmental factors adversely affecting PFAS adsorption. The adsorption affinity also decreased in real groundwater, typically with log Kd 3.4-5.4 for alkaline and hard groundwater. This study shows the great potential of the iron oxide and graphitized bonechar composite for the remediation of PFAS-contaminated groundwater.

Keywords: Adsorption affinity, Electrostatic interaction, DFT calculation, Groundwater remediation