Toward Sustainable Li-Ion Batteries Recycling: Green MOF as a Molecular Sieve for the Selective Separation of Cobalt and Nickel

The growing demand for Li-ions batteries (LIBs) has made their postconsumer recycling an imperative need towards the recovery of valuable metals, such as cobalt and nickel. Nevertheless, their recovery and separation from active cathode materials in LIBs, via an efficient and environmentally friendly process, have remained a challenge. In this work, we approach a simple and green method for the selective separation of nickel ions from mixed cobalt-nickel aqueous solutions under mild conditions. We discovered that the bioinspired microporous metal–organic framework (MOF), Bi₂O(H₂O)₂(C₁₄H₂O₈)∙nH₂O is a selective sorbent towards Ni(II) ions at pH 5-7, but does not adsorb Co(II) ions. According to the Freundlich isotherm, the adsorption capacity towards Ni(II) reached 100.9 mg∙g⁻¹, while a near-zero adsorption capacity was found for Co(II) ions. Ni(II) removal from aqueous solutions was performed at mild conditions (22 °C and pH 5), with a high yield up to 96%. Presence on Ni(II) ions adsorbed on the surface of the material has been proven by solid state ¹H nuclear magnetic resonance (NMR) spectroscopy. Finally, separation of Ni(II) from Co(II) from binary solutions was obtained with approximately 30% yield for Ni(II), with a near-zero adsorption of Co(II), which has been demonstrated by UV-Vis spectroscopy. These results offer a green pathway toward the recycling and separation of valuable metals from cobalt-containing LIBs, while providing a sustainable route for waste valorization in a circular economy.