Mechanism for lithium extraction with ether and ester oxygens in armed crown ethers

Lithium plays a vital role in the development of batteries. The synergistic effect of the functional groups in crown ethers was analyzed to determine the mechanism for the selective adsorption of Li+ in solution. The results show that the ester oxygen atoms are more reactive than the ether oxygens. The Hirshfeld charges are suitable for evaluating the reactivities of individual atoms. The electrostatic potential illustrates the synergistic interactions of functional groups and predicts the initial complexation sites. The binding energies demonstrate that the most stable complexes are formed on the ether ring. Moreover, for all of these complexes, the C–O bond lengths of the C–O---Li+ system are increased by the Li+-O interaction. The Li+ separation efficiency of the armed crown ether is only 8.07 % and increases to 56.72 % with the addition of phenol. The increased extraction efficiency is reflected by the binding energies of the complexes.