Alkylamine-Modified Dialdehyde Cellulose Nanofibers for PFAS Adsorption

Functionalized cellulose is attracting considerable interest for its potential use in adsorptive removal of perfluoroalkyl and polyfluoroalkyl substances (PFASs). In this study, we demonstrate a novel alkylamine-modified dialdehyde cellulose (DAC) nanofiber adsorbent system derived from bleached wood pulp for PFAS removal. The DAC modification scheme involved the grafting of alkylamines with varying carbon chain lengths (C4, C8, and C12) to adjust the suspensibility and hydrophobicity of the adsorbent, which are found to be crucial for effective removal of PFAS. All three modified DAC adsorbents exhibit high adsorption capacity toward the adsorption of two long-chain PFAS compounds: 576–697 mg/g for perfluorooctanesulfonic acid (PFOS) and 235–346 mg/g for perfluorooctanoic acid (PFOA). However, C8-DAC exhibited superior removal efficiency for short-chain perfluorobutanoic acid (PFBA, 132 ± 6 mg/g) compared to C4-DAC (72 ± 10 mg/g) and C12-DAC (75 ± 5 mg/g), which could be attributed to its optimized surface charge and available surface area. Specifically, C8-DAC showed over 2 times higher PFOA adsorption capacity and 4 times higher PFBA adsorption capacity when compared with those of granular activated carbon (GAC). The results suggest the synergistic relationship between hydrophobic and electrostatic interactions in alkylamine-modified DAC during the adsorption of PFAS, especially for short-chain PFAS.