Strategies for high-temperature methyl iodide capture in azolate-based metal-organic frameworks

Efficiently capturing radioactive methyl iodide (CH₃I), present at low concentrations in the high-temperature off-gas of nuclear facilities, poses a significant challenge. Here we present two strategies for CH₃I adsorption at elevated temperatures using a unified azolate-based metal-organic framework, MFU-4l. The primary strategy leverages counter anions in MFU-4l as nucleophiles, engaging in metathesis reactions with CH₃I. The results uncover a direct positive correlation between CH₃I breakthrough uptakes and the nucleophilicity of the counter anions. Notably, the optimal variant featuring SCN^- as the counter anion achieves a CH₃I capacity of 0.41 g g⁻¹ at 150 °C under 0.01 bar, surpassing all previously reported adsorbents evaluated under identical conditions. Moreover, this capacity can be easily restored through ion exchange. The secondary strategy incorporates coordinatively unsaturated Cu(I) sites into MFU-4l, enabling non-dissociative chemisorption for CH₃I at 150 °C. This modified adsorbent outperforms traditional materials and can be regenerated with polar organic solvents. Beyond achieving a high CH₃I adsorption capacity, our study offers profound insights into CH₃I capture strategies viable for practically relevant high-temperature scenarios.