The synthesis and characterization of a metal–organic framework based on N,N'-dioxide for the selective adsorption of iodine anions

Introduction:

This study presents the synthesis and characterization of a new metal–organic framework (MOF) incorporating cobalt(II) and 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide (odabco), namely [Co₂(H₂O)(NO₃)(odabco)₅](NO₃)₃. The anion substitution reaction in the framework has been studied, and the adsorption selectivity and reversibility of the iodide ions with this compound have been investigated.

Methods:

Synthesis: A mixture of Co(NO₃)₂·6H₂O (0.10 mmol) and odabco·3H₂O₂ (0.30 mmol) was prepared in a glass vial. The mixture was dispersed in a solution of DMF (5.0 ml), water (0.4 ml), and nitric acid (25 μl, 62%). The mixture was kept at 70°C for 72 hours. The crystal structure of the compound was confirmed using powder X-ray diffraction (PXRD) analysis. The chemical purity of the sample was verified using CHN analysis, infrared (IR) spectroscopy, and thermogravimetric analysis (TGA).

Ion exchange was studied using capillary zone electrophoresis (CZE). The iodide positions within the porous adsorbent were determined by single-crystal XRD. The structural integrity of the samples was verified using XRD and other methods.

Results:

The cationic coordination network was found to exhibit a high affinity for iodide, and the degree of substitution of the guest nitrates by iodides was 75%. The iodide positions were directly determined by a single-crystal XRD method within an anion-exchanged adduct, [Co₂(H₂O)(NO₃)(odabco)₅]I₂(NO₃)·1.85H₂O. The adsorption of iodide is selective and reversible. The iodide anions occupied specific positions within the network, stabilized by the aliphatic core of the odabco ligands. The incorporation of iodide into the pore structure stabilizes it and has the potential to effectively remove iodide from solutions.

Conclusions:

This study emphasizes the significance of MOFs for addressing challenges related to selective ion sorption and has potential applications in environmental management and health protection. Further research into similar systems and modifications may lead to the development of improved adsorbent materials for removing ions from solutions.