Perfluorooctane sulfonate removal by metal-organic frameworks (MOFs): Insights into the effect and mechanism of metal nodes and organic ligands

The metal-organic frameworks (MOFs) with different metal nodes and organic ligands have been prepared and used to remove perfluorooctane sulfonate (PFOS) from water. The results show that among three metal nodes of the MIL-53(A1), MIL-53(Fe) and MIL-101(Cr), MIl-53(Al) exhibit the best PFOS adsorption performance owing to the combined action of the highest unsaturated metal active sites and the smallest pore size. MIL-53(Al)-terephthalic acid (BDC), MIL-53(Al)-dimethyl 2,6-naphthalene dicarboxylate (NDC) and MIL-53(Al)-biphenyl-4,4'-dicarboxylic acid (BPDC) differs from the length of the organic ligand and MIL-53(Al)-BPDC achieves superior PFOS adsorption performance. We propose that longer organic ligand will contribute to larger 1D channel window and provide more PFOS entry. Adsorption kinetics shows that the experimental values can be well fitted to pseudo-second-order model, indicating that chemical adsorption demonstrate in the adsorption process. Besides, the existence of Fe3+ ions in MOFs/PFOS system could improve PFOS removal because of the bridging and interaction between Fe3+ ions and the PFOS molecule, which is confirmed by the density functional theory (DFT) calculation. These optimized MOFs are hopeful adsorbents to remove PFOS from water in a sustainability perspective.