Iodine sequestration from solution and vapor phase systems using Zr-based inorganic and hybrid polymeric granules†

Abstract

The growing global energy demand, fuelled by urbanization and globalization, has highlighted nuclear energy as a key sustainable solution. However, managing radioactive waste, particularly iodine, remains a critical challenge for its long-term viability. Recent studies indicate that nitrogen-rich adsorbents exhibit a strong affinity for iodine due to forming charge-transfer complexes with I₂, enhancing interaction forces. In this context, an N-heteroatom engineering strategy was employed to synthesize a hybrid zirconium triethylenetetramine (ZrT) exchanger of the class of tetravalent metal acid (TMA) salts. To further improve its potential for large-scale industrial applications, ZrT was subsequently fabricated into a spherical ZrT@PVDF composite granule for iodine adsorption. Adsorption experiments revealed that ZrT and ZrT@PVDF exhibit outstanding iodine capture performance in vapor (1262.5 and 945.2 mg g⁻¹), including saturated I₂ (886 and 706 mg g⁻¹) and I₃⁻ (NaI/I₂) (920 and 746 mg g⁻¹) aqueous solution and organic phase (772 and 598 mg g⁻¹). However, the presence of single, double, and triple interfering ions had only a marginal impact on the iodine removal efficiency of both adsorbents. Spectroscopic, kinetic, and several isothermal studies demonstrate that iodine adsorption occurs through both physisorption and chemisorption mechanisms. The interaction between iodine and the nitrogen atoms of ZrT, leading to the formation of a stable charge-transfer complex, contributes to the high performance of the material in adsorption applications. Notably, ZrT@PVDF exhibited outstanding regeneration and reusability, retaining 87% of its initial adsorption capacity over five adsorption–desorption cycles, highlighting its potential for practical applications. This research presents an effective strategy for developing efficient iodine sorbents with tuneable morphologies, offering a promising solution to environmental challenges.