Effects of NO aging on bismuth nanoparticles and bismuth-loaded silica xerogels for iodine capture.

The capture of long-lived radioactive iodine (I) from oxidizing off-gasses produced from reprocessing used nuclear fuel is paramount to human health and environmental safety. Bismuth has been investigated as a viable iodine getter but the phase stability of bismuth-based sorbents in an oxidizing environment have not yet been researched. In the current work, bismuth nanoparticle-based sorbents, as free particles (Bi-NPs) and embedded within silica xerogel monoliths made with a porogen (TEO-5), were exposed to I before and after aging in 1 v/v% NO at 150 °C. For unaged sorbents, BiI was the dominant phase after iodine capture with 8-30 mass% BiOI present due to native BiO on the surface of the unaged nanoparticles. After 3 h of aging, 82 mass% of the Bi-NPs was converted to BiO with only a small amount of iodine captured as BiOI (18 mass%). After aging TEO-5 for 3 h, iodine was captured as both BiI (26 %) and BiOI (74 %) and no BiO was detected.". Additionally, bismuth lining the micrometer-scale pores in the TEO-5 led to enhanced iodine capture. In a subsequent exposure of the sorbents to NO (secondary aging), all BiI converted to BiOI. Thus, direct capture of iodine as BiOI is desired (over BiI) to minimize loss of iodine after capture.