Ionic liquid-grafted activated carbon for selective removal of PFAS by adsorption in drinking water

Hydrophobic interaction and anion exchange are major adsorption mechanisms of per- and poly-fluoroalkyl substances (PFAS) for most adsorbents. Activated carbon (AC) primarily adsorbs PFAS through hydrophobic interactions, but its removal efficiency decreases in drinking water treatment plants (DWTP) due to competition from other water constituents. To address this challenge, we grafted hydrophobic ionic liquids (ILs) onto AC, producing hydrophobic adsorbents with PFAS-selective anion exchange sites. Comprehensive material characterization confirmed the successful grafting of ILs to AC. One of the twelve synthesized IL-grafted ACs exhibited 2.26-fold increase in removal efficiency compared to pristine AC for six PFAS in a DWTP influent, showcasing its potential in real-world applications. The adsorption of 1 mol of perfluorooctane sulfonate to IL-grafted AC was accompanied by the release of 0.39 mol of exchangeable anions, verifying that both anion exchange and hydrophobic interaction were key PFAS adsorption mechanisms. This study is the first to demonstrate the effectiveness of IL-grafted ACs for PFAS removal in environmental water samples and suggests the possibility of further optimizing the synthesis process for enhanced selectivity and capacity of PFAS adsorption.