[supramolecular chemistry] the latest exploration of lithium recovery: extraction of lithium from solid and liquid by supramolecular interaction

In the past 20 years, the world's demand for lithium has grown explosively, mainly because lithium plays an indispensable role in modern materials such as lithium-ion batteries However, the amount of lithium on earth is limited Some scholars predict that with the current trend of consumption, the supply balance of lithium will be broken in 2023, and then there will be a global lithium shortage Compared with the trend of lithium consumption, the recovery of lithium resources is insignificant According to statistics, less than 1% of lithium is recovered every year In the face of the increasingly urgent shortage of lithium resources, how to effectively recover lithium has become a research topic of great practical significance Figure 1 The structural formula of the ion receptor (image source: angel Chem Int ed.) recently, Professor J L sesster of the University of Texas at Austin, Dr B A Moyer of Oak Ridge National Laboratory, and Professor S K Kim of the national gyeongshan University of South Korea jointly synthesized two kinds of Calix [4] pyrrole based ion receptors 2 and 3 (Figure 1) 。 These two compounds can be selectively identified with lithium ions, and can effectively recover lithium resources under the action of solid-liquid extraction (SLE) and liquid-liquid extraction (LLE) This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201805127) under the title of "selective solid – liquid extraction and liquid – liquid extraction of lithium chloride using strapped calix [4] mirrors" The idea of recycling lithium resources with cupyrrole compounds is not groundless As early as the 1980s, Professor cram, the Nobel Prize winner in chemistry, synthesized the lithium-ion receptor, and then the ion receptor appeared like a mushroom However, most of them are limited to cation receptor, and the development of ion pair receptor is relatively slow In 2016, the J.L sesster team reported an ion receptor (Fig 1.1) that can capture lino2 from the aqueous phase, but this receptor can not effectively transfer LiCl from the aqueous phase to the organic phase, so they modified the receptor and obtained two new ionomer receptors (Fig 1.2 and 3) ）Its structure was characterized in detail by NMR and single crystal X-ray diffraction Fig 2 Crystal structure (left) of compound 2 and LiCl and crystal structure (right) of compound 3 and LiCl (photo source: angelw Chem Int ed.) in order to test whether 2 and 3 have the ability to bind LiCl, the author first characterized them by NMR: the obvious chemical shift before and after proved that both receptors can form stable complexes with LiCl In addition, the crystal structure of these two compounds with alkali metal chloride was also obtained (Fig 2), which further confirmed the binding ability of ion receptor and ion pair In addition, the author found the difference between compound 2 and compound 3 through the crystal structure: compound 2 can accommodate LiCl, NaCl, KCl and CSCL molecules, while compound 3 can only accommodate LiCl molecules Fig 3 Flame test (left) and selective extraction of alkali metal chloride by ion receptor (right) (picture source: angelw Chem Int ed.) from crystal structure, it can be seen that compound 2 can adsorb almost all alkali metal chloride Through the solid-liquid extraction experiment, the author found that the adsorption of LiCl is much better than other alkali metal chloride salts, even when the content of LiCl is relatively small, it can be effectively transferred from the solid phase to the liquid phase However, for LiCl in the aqueous phase, due to the presence of water molecules, although compound 2 can also effectively transfer LiCl to the organic phase, the selectivity is not good enough Compared with compound 2, the cavity size of compound 3 is slightly smaller, and only one molecule of LiCl can be found in the crystal structure of compound 3, so the author speculates that its selectivity to LiCl will be better The fact also proves this conjecture: the solid-liquid extraction test and the realization of liquid-liquid extraction prove that compound 3 can effectively extract LiCl from solid, but has no trapping effect on other alkali metal chloride salts Full text author: Qing He, Neil J Williams, Ju Hyun Oh, Vincent M Lynch, sung kukkim, * Bruce A Moyer, * and Jonathan L Sessler