Coordination‑dominated selectivity for divalent transition‑metal ions in thiol/carboxyl‑functionalized MXene nanochannels

Biological ion channels realize exceptional selectivity for transition metal ions through the synergistic effects of angstrom-scale confinement and highly specific ligand-ion coordination. Inspired by this molecular recognition principle, we develop mercaptosuccinic acid (MSA) functionalized Ti 3 C 2 Tx MXene biomimetic nanochannel membranes that operate under a coordination-dominated ion transport pattern. The introduction of MSA induces chemically regulated angstrom-scale nanochannels with stabilized hydrated spacing, thereby effectively suppressing structural swelling in aqueous environments. In this system, highly selective separation of Cd 2+ or Ni 2+ is achieved mainly through specific coordination between thiol-carboxyl functional groups and transition metal ions, with K + /Cd 2+ and K + /Ni 2+ selectivity reaching ∼10 3 . By contrast, the K + /Mg 2+ selectivity is much lower. Theoretical calculations reveal that strong coordination interactions between transition metal ions and MSA functional groups impose significantly elevated translocation energy barriers, effectively immobilizing Cd 2+ and Ni 2+ within the confined channels, while K + and Mg 2+ experience weaker interactions and retain facile transport pathways. The selective accumulation of divalent ions at channel entrances reflects the combined effects of strong ligand-ion interactions and high dehydration barriers. This work establishes a thiol-carboxyl coordination-dominated transition metal ion recognition pattern in angstrom-confined two-dimensional nanochannels and provides a theoretical basis for the rational design of artificial ion channels with programmable selectivity.