Adjacent Rare-Earth Separation via a Protein Atomic Ruler

The separation of rare-earth elements (REEs) poses a formidable challenge due to their nearly identical ionic radii and chemical properties. Here, we present a transformative strategy for REE separation using a multimetal ion-stacking metalloprotein framework (MIF) that functions as an atomic ruler, effectively amplifying subtle differences in REE ionic radii. This approach achieves exceptional selectivity, enabling the separation of all 13 adjacent REE pairs with ultrahigh purity (up to 99.999%). Remarkably, the MIF retains its lanthanide-binding capacity over 410 consecutive absorption-desorption cycles, demonstrating outstanding stability. Structural insights reveal that the MIFs densely packed REE coordination environment magnifies minute radius variations--a key mechanism underlying its unparalleled separation efficiency. Our MIF-based strategy offers a sustainable, scalable solution to rare-earth separation in industrial applications.