Heterogeneity-Guided Interlayer Tuning in Vermiculite-MOF Membranes for Efficient Li⁺/Mg²⁺ Separation

Precise separation of Li⁺/Mg²⁺ with similar ionic size remains a critical challenge for two-dimensional (2D) membranes, largely due to the inherently tortuous and poorly regulated transport channels in the 2D interlayer. Herein, we propose a heterogeneity-guided interlayer engineering strategy to reprogram the lamellar ion transport pathways of vermiculite (Vm) membranes through the incorporation of ultrathin ZrBTB (Zr) metal organic framework nanosheets. Owing to the intrinsic electrostatic environment and sub-nanometer apertures, the resulting vermiculite/ZrBTB heterolamina membranes exhibit reorganized interlayer nanochannels without changing the average interlayer spacing. Systematic structural analysis reveals that ZrBTB incorporation suppresses long-range lamellar ordering while enriching sub-nanoconfinement domains and partially reversing the channel-wall charge. These synergistic modifications generate enhanced Li⁺ transport pathways and a strengthened electrostatic/steric exclusion environment for Mg²⁺. As a result, the optimum membrane achieves a Li⁺ permeation rate of 0.379 mol m^-2 h^-1 and an outstanding Li⁺/Mg²⁺ selectivity of ∼46.2, surpassing most diffusion-based separation membranes. Comparative studies using CuTCPP nanosheets further confirm that channel size, charge, and energy barriers can be effectively tuned through rational selection of 2D MOF building blocks. This work establishes interlayer heterogeneity as a powerful and generalizable design parameter for constructing next-generation 2D membranes for efficient ion sieving under mild conditions.