Probing the Synthetic Landscape of Thorium 2-Aminoterephthalic Acid MOFs: Implications for MOF Characteristics and Iodine Adsorption

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A systematic multiparametric investigation was performed to elucidate the synthesis−structure−property relationship of a UiO-66-type thorium-based 2-aminoterephthalate metal−organic framework (Th-ABDC) for iodine capture. The effects of synthesis temperature (100, 125, 150, and 175 °C), reaction duration (16 h, 24 h, and 48 h), metal-to-linker (M/L) ratio (1:1, 1:1.5, and 1:2), and modulator type (acetic acid, 2-fluorobenzoic acid, 4-aminobenzoic acid, and trifluoroacetic acid) were systematically investigated. Notably, 4-aminobenzoic acid (ABA) was employed as a modulator to mitigate the loss of amino functionality resulting from modulator incorporation into the framework during synthesis. Preserving the amino groups is expected to enhance iodine uptake through favorable host−guest interactions. The synthesized MOFs were comprehensively characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), 1H nuclear magnetic resonance (1H NMR) spectroscopy, field-emission scanning electron microscopy (FESEM), and N2 adsorption−desorption isotherms to establish correlations between synthesis parameters, framework composition, morphology, porosity, structural defects, and iodine adsorption performance. The optimized MOF synthesized at lower temperatures, shorter reaction durations, an M/L ratio of 1:1, and using ABA as the modulator exhibited smaller particles with a bimodal size distribution, fewer linker defects, and a higher specific surface area, resulting in superior gas-phase iodine adsorption capacity. Furthermore, MOF−polyethersulfone (MOF−PES) composite beads were fabricated and evaluated for iodine removal from cyclohexane solution. Dynamic iodine adsorption studies demonstrated a maximum iodine uptake of approximately 1.5 g g−1 for the optimized MOF−PES beads synthesized at 150 °C using ABA as the modulator. The MOF−PES composite also exhibited excellent acid resistance, retaining its UiO-66 crystal structure after prolonged exposure (100 h) to nitric acid while maintaining its iodine adsorption capability. The findings provide valuable design principles for the rational development of robust, high-performance thorium MOFs for radioactive iodine capture and related environmental remediation applications.