Programming Migration Energy Landscapes in Isoreticular Hydrogen-Bonded Organic Framework Nanochannels for Kinetic Cs+/Sr2+ Separation.

Precise separation of Cs+ and Sr2+ remains a critical challenge in nuclear waste remediation, where subtle variations in migration energetics under sub-nanometer confinement limit separation fidelity. Here, we demonstrate migration energy-landscape programming in an isoreticular series of hydrogen-bonded organic framework (HOF) nanochannels to achieve kinetic Cs+/Sr2+ separation. To overcome the intrinsic processability limitations of hydrogen-bonded assemblies, we develop an interfacial chemical reaction-mediated confined assembly strategy that suppresses stochastic nucleation and yields continuous, defect-minimized crystalline HOF membranes. This isoreticular platform preserves identical channel geometry while enabling systematic modulation of pore-wall nitrogen density as an independent chemical variable, effectively decoupling structural confinement from chemical regulation. Multiscale simulations and temperature-dependent transport measurements reveal that nitrogen enrichment selectively amplifies the translocation energy barrier for Sr2+ while maintaining low-barrier hopping pathways for Cs+. The resulting migration-barrier asymmetry transforms structurally equivalent nanochannels into precise kinetic discriminators. Under competitive and electrically assisted conditions, the optimized membrane achieves a record-high Cs+/Sr2+ selectivity of 155.5. This work establishes programmable migration energy landscapes in crystalline nanochannels as a general strategy for engineering kinetic ion separations beyond conventional size- or valence-governed limits.