Strain-Mediated Anisotropic Growth of Metal-Organic Framework Belts

Metal-organic frameworks (MOFs), such as zeolitic imidazolate framework-L (ZIF-L), are organized porous materials that are sensitive to synthesis and processing conditions. Here, we report a one-pot, purely aqueous route that couples pH-controlled anisotropic growth of ZIF-L platelets to unique belt morphologies and surface functionalization with citric-acid-capped Fe₃O₄ magnetic nanoparticles. This interfacial stabilization control of originally metastable layered MOF phases yields magnetically responsive nanomaterials without organic solvents, surfactants, or post-synthetic processing. By adjusting the basicity of the 2-methylimidazole environment, conventional ZIF-L leaf platelets reproducibly evolve into high-aspect-ratio, elongated, belt-like platelets with an aspect ratio of ∼10, while retaining the layered organization of the original ZIF-L phase. Plane-resolved x-ray peak shifts (Δd/d ratio) show distinct, anisotropic lattice distortions, suggesting a stabilization mechanism in which interfacial coordination of carboxylate groups to under-coordinated surface Zn²⁺ sites moderates layer relaxation and reconstruction pathways during synthesis and nanoparticle addition. This approach provides unique MOF belt morphology with enhanced phase stability and may be suggested as a scalable strategy for producing stable, anisotropic, magnetically responsive MOF-based nanocomposites with non-traditional shapes.