Cation-Doped\nNanocarbons for Enhanced Perfluoroalkyl\nSubstance Removal: Exotic Bottom-Up Solution Plasma Synthesis and\nCharacterization

Perfluorinated\nalkyl substances (PFAS), such as perfluorooctanesulfonic\nacid (PFOS) and perfluorooctanoic acid (PFOA), are pervasive organic\ncontaminants that are widespread in aquatic environments, posing significant\nhealth risks to humans and wildlife. Due to their persistent nature,\nurgent removal is necessary. Conventional adsorbents are inefficient\nat removing PFOS and PFOA, highlighting the need for alternative materials.\nHerein, we present a synthetic method for quaternary ammonium cation-doped\ncarbon nanoparticles (QACNs) using a solution plasma process for the\nefficient removal of PFOS and PFOA. QACN is formed simultaneously\nthrough a one-step discharge of nonequilibrium plasma at the interface\nof benzene and pyridinium chloride. The resulting material exhibited\na high surface electrical charge and enhanced hydrophilicity as well\nas an amorphous structure of a nonporous nature, involving nanoparticles\nwith an undefined shape. The obtained adsorbent demonstrated high\nadsorption efficiency and stability, adsorbing 998.45 and 889.37 mg\ng<sup>–1</sup> of PFOS and PFOA, respectively, exceeding the\nefficiencies of conventional carbon-based adsorbents (80.89–313.15\nmg g<sup>–1</sup>). The adsorption performance was dependent\non the adsorbent dosage, pH of the solution, and the coexisting ionic\nspecies. Adsorption studies, including adsorption kinetics, isotherms,\nand thermodynamics, revealed that PFOS and PFOA were chemisorbed to\nthe QACN surface, forming multilayers endothermically and spontaneously.\nExperimental and computational analyses revealed that adsorption primarily\noccurs via electronic interactions between the PFAS active sites and\nthe quaternary ammonium group in the carbon framework. The slightly\nlower adsorption potential of the PFOS and PFOA fluorocarbon chains\non the adsorbent was elucidated. Furthermore, the dispersibility of\nthe adsorbent in solution significantly affected the adsorption performance.\nThese findings highlight the potential of the novel synthetic method\nproposed in this study, offering a pathway for the development of\nhighly effective carbon adsorbents for environmental remediation.