UiO-66-(COONa)₂ membrane with programmable ionic channels for lithium ion-selective transport

Membrane technology with low carbon emissions and environmental footprint is widely used in environmental and energy applications. Developing membranes with adaptive filtering and chemical/molecular species selective transport functionalities are essential for widening their practical use. This research explores a Zr-based metal-organic framework (MOF) membrane via post-synthetic modification, forming a network of ionic channels with large carboxylic functional groups that exhibit smart ion permeability and selectivity. Ion-selective performance of the new MOF-based membrane can be affected by the ionic environments they are exposed to and is modulated by the activation of specific ions. The experimental results assess the effects of different ionic activators, including Mg²⁺ and K⁺ ions, respectively, on ion-selective transport in artificial subnanometer channels of UiO-66-(COONa)₂ membranes in single-component or multi-component systems. Pre-activated membranes exhibit excellent Li⁺/Mg²⁺ selectivity, including Li⁺/Mg²⁺ of 468.8 ± 36.3 with Mg²⁺-activated membrane and Li⁺/Mg²⁺ of 331.31 ± 14.04 with K⁺-activated membrane at a high salinity of 0.5 M Mg²⁺ and 0.01 M K⁺, Na⁺, Li⁺. Molecular dynamics simulations further assess ion-selective transport behaviors in different ionic activated channels. This work opens a new way for programmable materials designs and energy-efficient and sustainable separation technology developments for lithium recovery in the mineral and energy industries.