Water content modulation enables selective ion transport in 2D MXene membranes

YG Zhu and QS Xiong and WC Jeon and M Blum and F Camino and GC Schatz and KB Hatzell, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 122, e2501017122 (2025).

DOI: 10.1073/pnas.2501017122

Separation membranes are critical for a range of processes, including but not limited to water desalination, chemical and fuel production, and recycling and recovery applications. Fundamentally, there are intrinsic trade-offs between permeability and selectivity. Local water organization and content can impact membrane structure and impact selective ion permeation. Intercalation of chaotropic cesium (Cs+) ions within the layers reduces the water content in the membrane and at the surface which cannot be found in the intercalation of other ions. Additionally, 3D imaging using focused ion beam scanning electron microscopy showed fewer defects in the Cs-MXene membrane, due to reduced local water content, leading to more efficient ion sieving. Xray diffraction and density functional theory calculations on the nanochannel structure demonstrated that the chaotropic ion results in the smallest nanochannel size and induces a stronger resistance to water-induced nanochannel swelling. With a narrower more selective transport of lithium over other metal cations, as evidenced in both experiment and molecular dynamics simulations. Our findings highlight the potential demand transport of ions for diverse applications.

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