During the reprocessing of spent nuclear fuel rods, a highly moist off-gas mixture containing various volatile radioactive species, such as iodine (I-2), organic iodides and nitric acid, is produced. Efforts have been made to devise materials, which can effectively capture radioactive iodine (I-2) and organic iodides from the off-gas mixture without being damaged by moisture, nitric acid, and I-2. In the investigation described herein, we observed that all-silica zeolites, such as silicalite-1 and Si-BEA, are stable in 5 M nitric acid and adsorb I-2, CH3I, and CH3CH2I from highly acidic off-gas mixture to much greater extents than activated carbon does. In particular, the hydrophobicity-intensified silicalite-1 performs best. We further found that I-2 forms a unique semiconducting three-dimensional supramolecular network within the silicalite-1 channels. The conductivity of the fully I-2 loaded silicalite-1 is observed to be ca. 10(4) S m(-1), which is ca. 10(8)-fold higher than that of solid I-2.
2016. Vol. 9, no 3, 1050-1062 p.