Carbon-dot-modified polyacrylonitrile fiber as recyclable adsorbent for removing anionic, cationic, and zwitterionic perfluorooctane sulfonates from water

Abstract

There are few adsorbents that can efficiently adsorb perfluorooctane sulfonate (PFOS) with differently polarized head-groups. In the present study, carbon dot (CD)-modified polyacrylonitrile fiber (PAN-g-CD) was found to be a good adsorbent for removing PFOS and its derivatives with zwitterionic or cationic head-groups from neutral water. The maximum adsorption capacities at 25 °C were found to be 1.28, 1.75, 1.87, and 2.11 mmol/g for PFOS, cationic PFOS, betaine-type PFOS, and PFOS with an amine oxide head-group, respectively. Adsorption kinetic models indicated that the surface of PAN-g-CD is energetically heterogeneous and that chemisorption occurs during the adsorption of PFOS and its derivatives. The Sips and Hill isotherm adsorption models were found to be most appropriate, and they indicated that PFOS derivatives were more preferentially adsorbed than PFOS by PAN-g-CD. The high-efficiency and wide substrate range of PAN-g-CD adsorption may be ascribed to its zwitterionic nature and its hydrophobic CDs. Moreover, PAN-g-CD can be regenerated and reused up to four times without pronounced loss of adsorption capacity.