Enhanced PFAS adsorption with N-doped porous carbon beads from oil-sand asphaltene

Abstract

Highly porous carbon beads with radially aligned macrochannels were synthesized from asphaltene for wastewater treatment and water filtration purposes. The unique porous structure of these beads facilitates efficient solute diffusion and maximizes liquid accommodation capacity, thanks to the well-ordered inwardly aligned macrovoids. Additionally, N-doping was employed to enhance the beads' adsorption properties, particularly for organic and inorganic solvents. Surface characterization data revealed that N2 modification introduced new surface functionalities, likely pyridine, and amine moieties, which actively participate in the adsorption process of polyfluoroalkyl and perfluoroalkyl substances (PFAS). Although the highest adsorbed amount of up to 74 μmol g−1 was observed for the unmodified materials, it is noteworthy that achieving equilibrium required an extensive period, exceeding 300 h. Interestingly, adsorption onto N2-modified asphaltene carbon beads exhibited higher efficiency for shorter-chain PFAS, with perfluorobutanoic acid adsorbing at 66.41 μmol g−1 and perfluorooctanoic acid reaching up to 7.67 μmol g−1. Overall, the maximum adsorption capacity of all asphaltene carbon beads followed the order PFHxA < PFOA < PFBA, indicating that the length of the carbon chain in PFAS is not the sole determining factor for adsorption. This observation suggests that the modification of asphaltene carbon beads and the introduction of N2 in the form of amino groups provide additional sites for hydrogen bond formation, influencing the adsorption process. The presented results highlight the enhanced efficiency of PFAS removal achieved by utilizing sustainable materials and methods in wastewater treatment.