Engineering an amine-functionalized Zn(ii) interpenetrated metal–organic framework for comprehensive iodine uptake across diverse phases and selective azo dye adsorption

Abstract

In this study, a two-fold interpenetrated 3D Zn-based metal–organic framework, {[Zn₂(btc)(Hata)(H₂O)₂]}_n (AR-2), was successfully synthesized via a hydrothermal approach using 1,2,4,5-benzene tetracarboxylic acid and 3-amino-1,2,4-triazole as oxygen and nitrogen donor ligands, respectively. Single-crystal X-ray diffraction (SCXRD) analysis reveals the presence of two distinct Zn nodes (Zn1 and Zn2) adopting tetrahedral and square-pyramidal geometries, confirmed by the τ geometric index. The topological analysis identifies a 3D bbf-3,4-Cccm net. Thorough analysis using elemental analysis, FT-IR, PXRD, TGA, SEM, EDS, and TEM demonstrates the robust structural integrity of AR-2. The framework of AR-2 possesses numerous π-electron-rich rings and accessible nitrogen donor sites, which significantly enhance its adsorption efficiency for iodine and azo dyes. It demonstrates remarkable iodine uptake across vapor, aqueous, and organic phases, with an uptake capacity of 828 mg g⁻¹ (dry, 75 °C) and 415 mg g⁻¹ (dry, 25 °C). At the same time, under humid conditions, it captures 523 mg g⁻¹ (75 °C) and 131 mg g⁻¹ (25 °C). AR-2 also achieves 89–91% iodine adsorption in aqueous and organic solvents. Remarkably, iodine-loaded AR-2 retains up to 96–97% of its captured iodine at 25 °C, demonstrating its potential for long-term storage and safe transportation of radioiodine. Furthermore, AR-2 selectively adsorbs hazardous azo dyes, such as Bismarck Brown and Methyl Orange, from aqueous solutions, showcasing rapid kinetics, high stability, and reusability. These findings position AR-2 MOF as a promising candidate for environmental remediation, including off-gas filtration and wastewater treatment in nuclear and chemical industries.