Nanoscale hierarchically porous metal-organic frameworks: Reverse microemulsion synthesis and enhanced iodine capture

Radioactive iodine constitutes a critical and persistent contaminant in nuclear waste management and environmental remediation. Nanoscale hierarchically porous metal-organic frameworks (NH-MOFs) exhibit considerable potential for iodine removal. However, the synthesis of NH-MOFs with tunable porosity and high stability remains an immense challenge. In this study, bimetallic nanoscale hierarchically porous Zn/Co-MOFs were synthesized via a reverse microemulsion method. The resulting nanoscale hierarchically porous Zn/Co-MOFs were characterized using a complementary combination of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, and thermogravimetric analysis (TGA). These characterization results confirmed that the crystal size, pore size, and number of unsaturated metal sites in the nanoscale hierarchically porous Zn/Co-MOFs (Zn/Co-MOF_An) could be easily tuned by controlling the microemulsion parameters (e.g., the aqueous-to-oil ratio and surfactant concentration). The as-synthesized Zn/Co-MOF_An exhibited excellent iodine adsorption capacities (iodine vapor: 6.55 g/g; liquid-phase iodine: 585 mg/g) owing to the combined effects of shortened diffusion distances and hierarchical porosity. This work highlights the potential of Zn/Co-MOFs as high-performance and scalable adsorbents for radioactive iodine remediation.