Polystyrene Sulfonate Threaded through a Metal–Organic Framework Membrane for Fast and Selective Lithium‐Ion Separation

Abstract

Extraction of lithium ions from salt-lake brines is very important to produce lithium compounds. Herein, we report a new approach to construct polystyrene sulfonate (PSS) threaded HKUST-1 metal-organic framework (MOF) membranes through an in situ confinement conversion process. The resulting membrane PSS@HKUST-1-6.7, with unique anchored three-dimensional sulfonate networks, shows a very high Li conductivity of 5.53×10 S cm at 25 °C, 1.89×10 S cm at 70 °C, and Li flux of 6.75 mol m h , which are five orders higher than that of the pristine HKUST-1 membrane. Attributed to the different size sieving effects and the affinity differences of the Li , Na , K , and Mg ions to the sulfonate groups, the PSS@HKUST-1-6.7 membrane exhibits ideal selectivities of 78, 99, and 10296 for Li /Na , Li /K , Li /Mg and real binary ion selectivities of 35, 67, and 1815, respectively, the highest ever reported among ionic conductors and Li extraction membranes.

Mass transport through metal organic framework membranes

“…Thanks to the high degree of designability and adjustability of MOF, the pore structure and interaction can be tuned by decorating function groups onto the ligand or introducing various components into its cavities. Apart from molecules, ions and protons can also transport through the channels of MOF after constructing hydrogen-bond networks inside the MOF membranes [79,116]. The ions transport follows the Grutthuss mechanism and the pore size of MOF and the affinity of function groups suggest a selective ion transport process of hybrid MOF membranes.…”

“…5 [79,115,116]. As mentioned above, the CHNs, CuO NSs and ZHNs are highly positively charged, which means the negatively charged components would assemble on them via electrostatic attraction.…”

“…Thus, the guest components were well encapsulated into the MOF crystals, and nice guest-component@MOF membranes were obtained. In the last few years, we have introduced ions, proteins, linear polymers, DNA, carbon nanotubes, nanoparticles, polymer spheres into MOF membranes [79,115,116] to obtain multifunctionlized MOFs membranes. This solid conversion method would pave a new way to fabricate hybrid MOF membranes with determined multifunctions.…”

“…As mentioned above, the self-confined solid conversion method exhibits great advantage especially in the formation of hybrid MOF membranes [79,115,116]. Au nanoparticles (NPs) were successfully encapsulated into the HKUST-1 membrane via the solid conversion method in spite of the larger size of Au NPs than the HKUST-1 cavities [115].…”

“…And there is still great hindrance on the fabrication of MOF membranes with high ion conductivity Very recently, well-intergrown polystyrenesulfonate (PSS) threaded HKUST-1 (PSS@HKUST-1) membranes and DNA threaded ZIF-8 (DNA@ZIF-8) membranes were successfully fabricated by our group via a solid conversion process [79,116]. The ample sulfonate groups of PSS were favorable to coordinate to H 2 O and aid to build a 3D hydrogen-network along PSS inside the channels of HKUST-1 membranes [116]. Notably, not only the size sieve effect but also the binding affinity of sulfonate groups to ions had influence on the ions transport.…”