Bimetallic Fe/K γ-cyclodextrin metal–organic frameworks with enhanced loading capacity and tunable release behavior

Cyclodextrin-based metal-organic frameworks (CD-MOFs) are bio-derived porous coordination materials that combine hierarchical porosity with intrinsic host-guest recognition. Here, we report the synthesis of a bimetallic γ-cyclodextrin metal-organic framework incorporating potassium and iron ions (Fe/K-CD-MOF) via a controlled vapor diffusion method and examine the influence of dual-metal coordination on structural organization and guest transport behavior. Structural characterization by Fourier-transform infrared spectroscopy, powder X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller analysis confirmed preservation of the γ-cyclodextrin framework together with improved crystallographic ordering and increased accessible surface area following iron incorporation. Curcumin was used as a model hydrophobic guest molecule to evaluate encapsulation efficiency and host-guest interactions. The Fe/K-CD-MOF exhibited higher loading capacity than the monometallic analogue, which is attributed to modified coordination environments and enhanced pore accessibility arising from heterometallic crosslinking. Release studies conducted under acidic and neutral conditions demonstrated pH-responsive behavior, indicating diffusion-controlled transport influenced by framework-guest interactions. Kinetic modeling using Freundlich, Ritger-Peppas, and Elovich equations suggested a combined adsorption-diffusion mechanism with anomalous transport characteristics. These findings establish a direct relationship between bimetallic coordination and functional performance in γ-cyclodextrin MOFs, providing a rational strategy for tuning carbohydrate-based porous materials for controlled molecular delivery.