Trimetal-organic framework composite-modified sponge for efficient removal of F− and PFAS from wastewater

Fluoride ions (F − ) and per- and polyfluoroalkyl substances (PFAS) in industrial wastewater pose a serious threat to the global environment. Adsorption is the most widely used treatment technology for F − and PFAS in the field of water pollution control. However, existing zirconium-based MOFs face challenges such as the inability to synergistically and efficiently adsorb PFAS, high preparation costs, limited adsorption capacity, and an insufficiently understood adsorption mechanism in multi-component pollution systems. Here, we prepared a novel cerium/zirconium/lanthanum tri-metallic MOF (denoted as Ce/Zr/La-M) by doping low-cost metals and loaded it onto a sponge modified with dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DTSACL), ultimately obtaining Ce/Zr/La-MSD. The practical adsorption capacity of Ce/Zr/La-MSD for F − is 255 mg/g, which is the highest reported value at similar initial concentrations, while the removal rates for PFAS (C 6 -C 8 ) and PFAS (C 4 ) exceed 96% and 84%, respectively.DFT calculations revealed that doping with La shifted the d-band center of the metals in the MOF closer to the Fermi level, enhancing the material's electron-donating capability. A series of characterization and kinetic simulation results demonstrated that the adsorption mechanism of F − by Ce/Zr/La-MSD involves electrostatic interactions, complexation effects, ion exchange and hydrogen bonding. The primary adsorption sites for PFBA, PFBS, PFOS, and PFHxS were the quaternary ammonium groups containing three carbon atoms, whereas the primary adsorption sites for PFOA and PFHxA were the C 18 chains on DTSACL. In summary, this study provides new insights for the rational design of multifunctional adsorbents and the interpretation of their mechanisms.