Strategic Design of Novel Zinc and Cadmium Metal-Organic Frameworks for Enhanced, Reversible, and Multi-Phase Iodine Sequestration

Abstract

Radioactive iodineisotopes (¹²⁹I and ¹³¹I), generated duringnuclear fission, persist in gaseous and aqueous phases due to their volatilityand bioaccumulation, posing severe health risks. Multiphase iodine removalremains challenging due to the low efficiency of conventional materials, especially in aqueous media where high polarity hinders effective adsorption. Herein, a novel bidentate precursor, 4, 4′-(((2, 3, 5, 6-tetramethyl-1, 4-phenylene)bis(methylene))bis(azanediyl))dibenzoicacid (PMBADH₂), was strategically designed having two -NH linkages to enhance interactions withiodine in the phases. Using PMBADH₂, Two new isostructural metal-organic frameworks(MOFs), {[Zn₂(PMBADH₂)₄(DMF)₂]·4DMF}_n (SVNIT-1) and {[Cd₂(PMBADH₂)₄(DMF)₂]·4DMF}_n (SVNIT-2), were synthesized. The MOFs werealso prepared on a gram scale to enhance practical applicability. Comprehensive characterization of both MOFs was performed using SCXRD, PXRD, FTIR, XPS, BET, and TGA. Both MOFs exhibited outstanding iodine uptake across vapor, organic, and aqueous phases. SVNIT-1 achieved capacities of 6.5 g g⁻¹ (vapor), 2.8 g g⁻¹ (organic), and 2.5 g g⁻¹ (aqueous, including seawater), while SVNIT-2 showed comparable values of 6.1, 2.6, and 2.4 g g⁻¹, respectively. Extensive studies on desorption, recyclability, and stability confirmed the robustness and reusability of thesematerials. Mechanistic studies using FTIR, PXRD, Raman, UV-DRS, XPS, and ESR highlighted the pivotal role of NH linkages in promoting iodine adsorption via strong hostguest interactions.