Guanidinium-based covalent organic framework membrane for single-acid recovery.

Acids are extensively used in contemporary industries. However, time-consuming and environmentally unfriendly processes hinder single-acid recovery from wastes containing various ionic species. Although membrane technology can overcome these challenges by efficiently extracting analytes of interest, the associated processes typically exhibit inadequate ion-specific selectivity. In this regard, we rationally designed a membrane with uniform angstrom-sized pore channels and built-in charge-assisted hydrogen bond donors that preferentially conducted HCl while exhibiting negligible conductance for other compounds. The selectivity originates from the size-screening ability of angstrom-sized channels between protons and other hydrated cations. The built-in charge-assisted hydrogen bond donor enables the screening of acids by exerting host-guest interactions to varying extents, thus acting as an anion filter. The resulting membrane exhibited exceptional permeation for protons over other cations and for Cl over SO and HPO with selectivities up to 4334 and 183, respectively, demonstrating prospects for HCl extraction from waste streams. These findings will aid in designing advanced multifunctional membranes for sophisticated separation.