Silver-functionalized silica aerogel for iodine capture: Adsorbent aging by NO2 in spent nuclear fuel reprocessing off-gas

Ziheng Shen, Alexander I. Wiechert, Seungrag Choi, Austin P. Ladshaw, Lawrence L. Tavlarides, Costas Tsouris, Sotira Yiacoumi

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11 Scopus citations

Abstract

Silver-functionalized silica aerogel (Ag0-Aerogel) is considered a promising porous adsorbent for the capture of iodine from nuclear fuel reprocessing off-gas. The Ag0-Aerogel, nevertheless, experiences a steady loss of capacity when exposed to NO2 in the off-gas. This phenomenon is known as aging and its governing processes remain unclear. We exposed Ag0-Aerogel samples to 2% NO2 in dry air at 150 °C for up to 1 month, followed by I2 loading. Samples were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Our results elucidated the precise Ag species in Ag0-Aerogel that adsorb I2: (i) Ag0 nanoparticles, (ii) Ag thiolates (Ag–S-r) covering the nanoparticles and the aerogel backbone, and (iii) Ag–S complexes including amorphous Ag2S. We unraveled the two predominant underlying processes of aging in NO2: (i) Ag–S-r is oxidized by NO2 forming silver sulfonate (Ag–SO3-r) which is oxidized further to silver sulfate (Ag2SO4) molecules, (ii) Ag2SO4 molecules then migrate from the pores to the aerogel surface and aggregate yielding Ag2SO4 particles that do not adsorb I2. Plausible reaction pathways and aggregation mechanisms are explored. These findings may be used to guide the discovery of more advanced materials for iodine capture and the development of accurate predictive models.

Original languageEnglish
Article number111898
JournalMicroporous and Mesoporous Materials
Volume336
DOIs
StatePublished - May 2022

Funding

The authors are thankful to Dr. Yong Ding (Georgia Institute of Technology) for TEM imaging. This research was supported by the Nuclear Energy University Program, Office of Nuclear Energy, U.S. Department of Energy [grant number 18-15596]. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The beamline used in this study (10-ID-B) is supported by the Materials Research Collaborative Access Team (MRCAT). MRCAT operations are supported by the Department of Energy and the MRCAT member institutions.

FundersFunder number
U.S. Department of Energy18-15596
Office of Science
Office of Nuclear Energy
Argonne National LaboratoryDE-AC02-06CH11357
Nuclear Energy University Program

    Keywords

    • Adsorbent aging
    • Adsorption
    • Nuclear fuel reprocessing
    • Off-gas radioactive iodine
    • Silver functionalized silica aerogel

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