Charging Metal‐Organic Framework Membranes by Incorporating Crown Ethers to Capture Cations for Ion Sieving

Abstract

Protein channels on the biofilm conditionally manipulate ion transport via regulating the distribution of charge residues, making analogous processes on artificial membranes a hot spot and challenge. Here, we employ metal‐organic frameworks (MOFs) membrane with charge‐adjustable subnano‐channel to selectively govern ion transport. Various valent ions are binded with crown ethers embedded in the MOF cavity, which act as charged guest to regulate the channels’ charge state from the negativity to positivity. Compared with the negatively charged channel, the positive counterpart obviously enhances Li+/Mg2+ selectivity, which benefit from the reinforcement of the electrostatic repulsion between ions and the channel. Meanwhile, theoretical calculations reveal that Mg2+ transport through the more positively charged channel needed to overcome higher entrance energy barrier than that of Li+. This work provides a subtle strategy for ion‐selective transport upon regulating the charge state of insulating membrane, which paves the way for the application like seawater desalination and lithium extraction from salt lakes.

Built-In Positive Valence Space Shifting the Chemical Equilibrium Forward for Nitrate Reduction to Ammonia

“…Therefore, the shear layer of FeCu NC /CS around the FeCu nanocrystals should also be positive in the solution, creating a positive valence space at the interface to trigger a built-in electric field, which is capable of accelerating the anion attraction and cation repulsion at the active surface. To validate the function of a positive valence space on NO 3 – /NH 4 + transfer, FESs were first conducted based on the results of zeta potentials . The initial configuration for Fe SA /CS was set up by placing four conterminous semicircles representing the negatively charged carbon spheres (Figure S7), whereas the model of FeCu NC /CS was established by further immobilizing positively charged particles on the surface. ,, Specifically, the NO 3 – reactant underwent free diffusion to the active surface from the top of the computational domain, and the NH 4 + product was continuously produced from the surface of the models.…”

“…In great contrast, FeCu NC /CS possesses an overall positive charge with a zeta potential of 2.3 + transfer, FESs were first conducted based on the results of zeta potentials. 48 The initial configuration for Fe SA /CS was set up by placing four conterminous semicircles representing the negatively charged carbon spheres (Figure S7), whereas the model of FeCu NC /CS was established by further immobilizing positively charged particles on the surface. 12,49,50 Specifically, the NO 3 − reactant underwent free diffusion to the active surface from the top of the computational domain, and the NH 4 + product was continuously produced from the surface of the models.…”