A Novel Green MIP-202/TOCNF composite aerogel for rapid PFAS adsorption: Performance, kinetics, and mechanistic insights

Per- and polyfluoroalkyl substances (PFAS) are often termed "forever chemicals" due to their persistence in the environment. PFAS are commonly used in everyday consumer products and ends up in the air, soil, and, particularly, water. They can cause various types of cancer and disrupt aquatic life. This study focused primarily on developing a sustainable, green adsorbent with ultra-fast adsorption of PFAS from water. A one-pot hydrothermal technique was used to synthesize the MIP-202/TOCNF composite aerogel by replacing 50% of the aspartic acid linker in the MIP-202 metal-organic framework (MOF) with TEMPO-oxidized cellulose nanofiber (TOCNF). Structural characterization of the in-situ MIP-202/TOCNF composite aerogel revealed it has a surface area of 129.6 m 2 /g, a 26.7% increase over MIP-202. The aerogel exhibited ultra-fast adsorption of perfluorooctane sulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) in less than 10 and 30 seconds, respectively, under environmentally relevant conditions. The adsorption results fit second-order kinetics and the Freundlich isotherm model, with maximum adsorption capacities of 157.1 and 38.5 mg/g for PFOS and PFHxA, respectively. Density functional theory (DFT) calculations were performed to elucidate the adsorption mechanism, revealing that the adsorption process was governed by the synergistic contribution of electrostatic and hydrophobic interactions. The sustainable MIP-202/TOCNF composite aerogel retained excellent performance over four adsorption cycles. However, the surface area was reduced to zero after four cycles due to mesoporous structural collapse upon freeze-drying.