Novel Fluorine-Pillared Metal–Organic Framework for Highly Effective Lithium Enrichment from Brine

The continuously developing lithium
battery market makes seeking
a reliable lithium supply a top priority for technology companies.
Although metal–organic frameworks have been extensively researched
as adsorbents owing to their exceptional properties, lithium adsorption
has been scarcely investigated. Herein, we prepared a novel cuboid
rod-shaped three-dimensional framework termed TJU-21 composed
of fluorine-pillared coordination layers of Fe–O inorganic
chains and benzene-1,3,5-tricarboxylate (BTC) linkages. Besides thermal
and chemical robustness, a remarkably high lithium uptake of about
41 mg·g–1 was observed on TJU-21 as a fast-spontaneous endothermic process. Single-crystal X-ray
diffraction demonstrated that the adsorbed lithium was located in
the cavity symmetrically assembled by iron sites and organic ligands
between adjacent layers, while another kind of cavity in the framework
circled by Fe–O–Fe–O–Fe–O–Fe
chains and shared BTC linkages was occupied by hydrogen-bonded water
molecules. Lithium adsorption resulted in decreased curviness of the
coordination layers, and the binding energy change at O 1s as well
as the increased Fe 2p peak, suggested potential interaction with
iron sites. The practicability of TJU-21 as a lithium
adsorbent was further proved by the considerable capacity and selectivity
in simulated salt brines with excellent reusability.