What question did this study set out to answer?

This research aims to improve the adsorption of perfluoroalkyl substances (PFAS) using modified activated carbon.

July 16, 2026Open Access

Perfluoroalkyl Substance Adsorption Using Activated Carbon Modified Sequentially with Polyethyleneimine and Poly(chlorotrifluoroethylene–co-vinylidene fluoride) (Kel-F)

OAOmobolaji AyeseniMiami University CACatherine B. AlmquistMiami University JBJason A. BerberichMiami University

Key Points

This research aims to improve the adsorption of perfluoroalkyl substances (PFAS) using modified activated carbon.
Activated carbon was modified with polyethyleneimine and poly(chlorotrifluoroethylene–co-vinylidene fluoride).
Fixed-bed column adsorption performance was tested for perfluorooctanoic acid (PFOA).
Kinetic analysis assessed the adsorption behavior and stability during multiple cycles.
The AC–PEI–KelF–PEI formulation achieved a maximum breakthrough time of 1500 min for PFOA.
Adsorption capacities were 65 mg/g for AC, 490 mg/g for AC–PEI–KelF, and 1130 mg/g for AC–PEI–KelF–PEI.
After six cycles, regeneration stability retained 79% adsorption performance.

Abstract

Per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) persist in aquatic environments due to their extremely strong C–F bonds and high environmental stability/poor biodegradability, creating an urgent demand for high-performance and scalable adsorption treatment technologies. This study reports the synthesis, characterization, and fixed-bed column adsorption performance of a dual-polymer-modified activated carbon adsorbent engineered for enhanced PFAS capture. Activated carbon (AC) was sequentially functionalized with polyethyleneimine (PEI) and poly(chlorotrifluoroethylene–co-vinylidene fluoride) (Kel–F) to form the fluorine-rich, amine-grafted composites AC–PEI–KelF and AC–PEI–KelF–PEI. Surface-area studies of the modified AC adsorbents showed a reduction in surface area of about a factor of two, possibly due to pore blockage by the polymers. Continuous-flow column breakthrough studies demonstrated dramatic improvements in perfluorooctanoic acid (PFOA) removal efficiency, with 50% maximum breakthrough time increasing from 80 min for AC to 540 min for AC–PEI–KelF and 1500 min for the AC–PEI–KelF–PEI formulation. Thomas model adsorption capacities for AC, AC–PEI–KelF and AC–PEI–KelF–PEI were, respectively, 65, 490, and 1130 mg/g. The adsorption mechanism, using selective mobile phases, was shown to be due to a combination of electrostatic and hydrophobic/fluorophilic interactions. Kinetic analysis showed that adsorption exhibited pseudo-second-order behavior, with multi-stage intraparticle diffusion. The optimized composite also exhibited strong regeneration stability, retaining 79% performance after six adsorption–desorption cycles, and displayed high selectivity for PFOA, even in the presence of structurally related competitors such as octanoic acid. The adsorption of perfluoropentanoic acid and undecafluoro-2-methyl-3-oxahexanoic acid (GenX) was also significant, and some interaction with trifluoroacetic acid was noted.

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