Systematic investigation of PFOS adsorption from water by Metal Organic Frameworks, Activated Carbon, Metal Organic Framework@Activated Carbon, and functionalized Metal Organic Frameworks

The presence of Per- and Polyfluoroalkyl Substances (PFAS) in water causes health effects on humans and animals over time. Among all techniques, the adsorption methodology has shown effective performance in removing PFAS from water. Different adsorbents, including classical powder activated carbon (AC) and Metal Organic Frameworks (MOFs) as a new generation of adsorbents have been used for the removal of short-chain (C < 6) and long-chain (C > 7) PFAS. However, due to the complexity of the adsorption process, the diversity of adsorbents and PFAS compounds, and the lack of standard experimental protocol, the effectiveness and undergoing sorption mechanisms for each of these adsorbents have not been investigated and compared systematically yet. In this work, we synthesized and characterized the adsorbents and then performed a systematic isotherm adsorption protocol to study the adsorption mechanisms and performance of adsorbents, including nanosized activated carbon AC, MIL-101 (Cr), MIL-101 (Cr)–NH2 and novel hybrid adsorbent MIL-101 (Cr)@AC for the removal of perfluorooctane sulfonic acid (PFOS) from water. Based on the comparative analysis to investigate the effective parameters governing the PFOS adsorption with respect to each adsorbent, AC with around 93 % PFOS removal showed supreme performance over other MOFs; however, MOF-based adsorbents showed faster adsorption compared to AC. The MIL-101(Cr)@AC (with 80 % removal performance and 2 h adsorption time) possessed the advantages of both AC and MIL-101 (Cr). The hydrophobic-hydrophobic and electrostatic interactions were the main dominant adsorption interactions for AC and MOFs, respectively, while both interactions were influential in the MIL-101 (Cr)@AC adsorption. All adsorbents were regenerated, and AC showed the best regeneration efficiency (>70 %) after 4 cycles.