Fast Perfluorooctanoic Acid (PFOA) Removal with Honeycomb-like Nitrogen-Doped Carbon Nanosheets: Mechanisms for the Selective Adsorption of PFOA over Competing Contaminants/Water Matrix

Carbon-based adsorbents have been recently identified as advanced materials for the efficient removal of perfluorooctanoic acid (PFOA); however, the fundamental understanding of the selective adsorption of PFOA over competing contaminants/water matrix is still lacking. Herein, a novel honeycomb-like nitrogen-doped carbon nanosheet (HL-NC@Ni-800) material was reported for the rapid adsorption of PFOA. The PFOA selective adsorption was attributed to (i) favorable steric hindrance that allowed rapid and stable PFOA adsorption, (ii) abundant adsorption sites provided by the honeycomb-like mesoporous structure, (iii) electrostatic attraction between the PFOA anion and nickel cation, (iv) hydrophobic effect between the PFOA tail and nitrogen functional groups, and (v) Lewis acid-base effect. Consequently, PFOA was efficiently removed from the competing contaminants such as 1,4-dioxane and sulfamethoxazole by 94.6 and 89.6%, respectively, as well as the water matrix such as inorganic anions by ∼84-94% and real high-salinity seawater by 75.6-78.4%. The calculated maximum adsorption capacities (q_m) of HL-NC@Ni-800 for PFOA soared to 184.89 mg·g^-1. In addition, the thermodynamically favorable adsorption of PFOA with different steric conformations on HL-NC@Ni-800 provided theoretical explanations for its high-efficiency adsorption performance toward PFOA. This study provides a novel strategy for the synthesis method of efficient adsorbents for PFOA and also elucidates the mechanistic understandings of PFOA selective adsorption over competing contaminants/water matrix, for guiding the design of more efficient adsorbents to treat PFOA-contaminated water.