Theoretical and extraction studies on the selectivity of lithium with 14C4 derivatives

Abstract

Lithium is a critical strategic metal for world economy development and is used in various fields, such as daily life, aviation, medicine, chemical industry, etc. Crown ethers can adsorb Li⁺ from a mixed ionic solution based on the size matching effect and synergistic effects of functional groups. The selective adsorption properties with Li⁺, Na⁺, Mg²⁺ and the interaction between crown ethers and metal ions were analyzed to guide the design of crown ethers with high selectivity for Li⁺. The geometric structural characteristics of 1,8-dihydroxyl-4,4,5,5-tetramethylbenzo-14-crown-4 (CE) and complexes with Li⁺, Na⁺, and Mg²⁺ metal ions were investigated using density functional theory modeling (DFT) at the M062X/def2SVP, def2TZVP level. The nature and strength of the interactions were analyzed by atoms in molecules (AIM) topological analysis and symmetry-adapted perturbation theory (SAPT) energy decomposition analysis. The results showed that the interaction strength of CE with metal ions followed the order: CE-Mg²⁺ > CE-Li⁺ > CE-Na⁺. The interaction energies can be separated into four kinds: electrostatics, exchange, induction, and dispersion. The stability of these complexes was mainly driven by electrostatics and induction. According to the analysis results of reduced density gradient (RDG), the metal ions mainly interacted with the oxygen atoms on the ring and did not interact with the hydroxyl groups directly. CE was synthesized and the extraction rates of Mg²⁺ and Li⁺ were better than that of Na⁺.