Sulfonated Sub-1-nm Metal-Organic Framework Channels with Ultrahigh Proton Selectivity

Abstract

Biological proton channels are sub-1-nm protein pores with ultrahigh proton (H⁺) selectivity over other ions. Inspired by biological proton channels, developing artificial proton channels with biological-level selectivity is of fundamental significance for separation science. Herein we report synthetic proton channels fabrication based on sulfonated metal-organic frameworks (MOFs), UiO-66-X, X = SAG, NH-SAG, (NH-SAG)₂ (SAG: sulfonic acid groups), which have sub-1-nm windows and a high density of sulfonic acid groups mimicking natural proton channels. The ion conductance of UiO-66-X channels follows the sequence: H⁺ ≫ K⁺ > Na⁺> Li⁺, and the sulfonated UiO-66 derivative channels show proton selectivity much higher than that of the pristine UiO-66 channels. Particularly, the UiO-66-(NH-SAG)₂ channels exhibit ultrahigh proton selectivities, H⁺/Li⁺ up to ∼100, H⁺/Na⁺ of ∼80, and H⁺/K⁺ of ∼70, which are ∼3 times of that of UiO-66-NH-SAG channels, and ∼15 times of that of UiO-66@SAG channels. The ultrahigh proton selectivity in the sulfonated sub-1-nm MOF channels is mainly attributed to the narrow window-cavity pore structure functionalized with nanoconfined high-density sulfonic acid groups that facilitate fast proton transport and simultaneously exclude other cations. Our work opens an avenue to develop functional MOF channels for selective ion conduction and efficient ion separation.