Mechanism of Li+/Na+ separation by crown ether and butyrate acid root

Lithium is critical for economic growth since it is the primary component of batteries. Na+ is one of the main impurity ions in solution during the separation and enrichment of Li+. According to the size-matching effect between the cavities of crown ethers and Li+, crown ethers can selectively adsorb Li+. Herein, 1,8-dihydroxyl-4,4,5,5-tetramethylbenzo-14-crown-4 was synthesized and used to extract lithium from a Li+/Na+ mixed solution. Density functional theory (DFT) was used to explore the properties of complexes with M062X. The results show that the interactions between crown ethers and metal ions are due to electrostatic attraction. Hydroxyl functional groups can synergistically extract Li+/Na+ from solutions with the oxygen atom in the crown ether ring. The stability of the complex is also enhanced by van der Waals interactions between the butyrate acid root and crown ether. 1,8-dihydroxyl-4,4,5,5-tetramethylbenzo-14-crown-4 has a stronger interaction with lithium butyrate than with sodium butyrate for most conformations. The adsorption selectivity for Li+ is proportional to the number of ether oxygen atoms that interact with Li+. The Li+ extraction efficiency increases from 3.93% to 20.93% in lithium hydroxide solution with the presence of butyrate acid root. When the butyrate acid root is added to the mixed Li+/Na+ solution, the Li+ extraction efficiency increases from 6.54% to 31.20%, while the Li+/Na+ separation coefficient decreases from 33.25 to 1.32.

Automated summary

Lithium, as a primary component of batteries, plays a critical role in economic growth. The presence of sodium ions in Li+ separation and enrichment can be addressed using crown ethers that selectively adsorb Li+ due to the size-matching effect. 1,8-dihydroxyl-4,4,5,5-tetramethylbenzo-14-crown-4 was synthesized and employed to extract lithium from a Li+/Na+ mixed solution, with interactions primarily driven by electrostatic attraction and enhanced by van der Waals interactions. The adsorption selectivity for Li+ is influenced by the number of ether oxygen atoms interacting with Li+. The addition of butyrate acid root promotes Li+ extraction efficiency but decreases Li+/Na+ separation coefficient.