Carbonization-derived Al@Carbon composite for efficient fluoride elimination: Structural modification, selective adsorption, and dual ligand exchange mechanism.

Currently, the availability of defluoridativel materials to simultaneously achieve the high adsorption capacity and selectivity in complex aquatic environments remains limited. To this end, we constructed an aluminum-carbon composite (Al@C) with a near-network/highly interconnected microporous structure via carbonizating Al-based metal-organic frameworks (Al-MOF), for the selective and efficient elimination of F in water environment. Results indicated that Al@C composite exhibited higher F adsorption capacity (985.1 mg·g), outperforming the most reported adsorbents. Notably, Al@C maintained high selectivity for F adsorption (97.8 %) even in the presence of high concentration of competing ions (SO, CO, HCO, Cl, PO, and NO) and wide pH range (3-10). The superior adsorption capacity and selectivity were primarily attributed to the dual-ligand exchange mechanism, involving ligand exchange between F and lattice oxygen to form Al-F bonds, and interaction between F and carbon-based functional groups generating F-C-F/C-F bonds. Additionally, the heterogeneous diffusion process driven by surface adsorption and transition from carbon bond energies to higher binding energies induced by carbonization strategy, collectively strengthen the immobilization of F. Overall, the work further provides an innovation, green, and low-energy solution for F removal in environmental water treatment.