Environmental Remediation with Functional Aerogels and Xerogels

Abstract

Zn 2+). These sorbents have unique properties, which include high specific surface areas, high pore volumes, a range of pore sizes, and functionalities that provide methods for binding radionuclides and other contaminants, generally through physisorption, chemisorption, or a combination thereof. This combination of properties and functionalities makes these types of materials ideal for use as sorbents for capturing radionuclides. The primary base materials that will be discussed in this paper include Ag 0-functionalized silica aerogels, Ag +-impregnated aluminosilicate aerogels, Ag 0-functionalized aluminosilicate aerogels, metal-impregnated (non-Ag) aluminosilicate aerogels and xerogels, sulfide-based aerogels, and carbon-based aerogel composites. For the capture of I 2(g) , the materials reported herein show some of the highest iodine loadings ever reported for inorganic sorbents. For the capture of ionic species, these materials also show promise as next-generation materials for active radionuclide remediation. This progress report describes materials fabrication, general properties, and environmental remediation applications.

Silver Sulfide and Silver Sulfate as Aging Byproducts and Adsorbents for Gaseous Iodine Capture in Spent Nuclear Fuel Reprocessing

“…1 Compared to the "once-through" approach (i.e., permanently storing SNF in a geological repository without any treatment), SNF reprocessing allows for the reuse of recyclable materials ( 235 U and 239 Pu) for power generation while also dramatically reducing the amount of high-level wastes that must be disposed of geologically. 2 Various volatile radionuclides ( 3 H, 85 Kr, 129 I, 131 I, 14 C, etc.) are, nonetheless, released during reprocessing and need to be properly captured due to their mobility in aqueous environments and the atmosphere.…”

“…3,4 Over the past few decades, a variety of iodine adsorbents have been developed, including various zeolites, 4,5,10 metal organic frameworks, 11 covalent organic frameworks, 12 and some aerogel/chalcogel-based materials. 13,14 examined in the 1960s, are still considered the most promising choice for iodine capture due to Ag's high selectivity and affinity for organic and inorganic iodine. 5 In several countries, Ag adsorbents are considered to be baseline technologies for the capture of radioiodine.…”

“…Aqueous scrubbing and adsorption using solid adsorbents are, generally speaking, the two most promising methods for iodine capture. , Solid adsorbent systems are usually favored since they are simpler to design and are less costly to operate and maintain. , Over the past few decades, a variety of iodine adsorbents have been developed, including various zeolites, ,, metal organic frameworks, covalent organic frameworks, and some aerogel/chalcogel-based materials. , Silver (Ag)-based adsorbents, which were first examined in the 1960s, are still considered the most promising choice for iodine capture due to Ag’s high selectivity and affinity for organic and inorganic iodine . In several countries, Ag adsorbents are considered to be baseline technologies for the capture of radioiodine.…”

Iodine Capture with Mechanically Robust Heat-Treated Ag–Al–Si–O Xerogel Sorbents

“… 9 , 10 , 13 , 14 Both aerogels and xerogels are typically brought to the same alcogel stage (i.e., a solidified gel in an alcohol matrix) under identical preparation processes, but their drying processes vary. 1 , 4 , 5 Xerogels are generally synthesized through slow evaporation of the matrix solvent in the gel at a relatively low temperature (<40 °C) or at room temperature under vacuum, resulting in volume shrinkage and pore collapse by capillary forces on the pore walls. Collapse of the gel pore structure during drying can also be minimized by exchanging the solvent matrix to a nonpolar solvent (e.g., hexane) prior to the drying step.…”

“…Aerogels and xerogels of various compositions have been demonstrated as effective sorbents for the capture of iodine gas [i.e., I 2(g) ]. − Aerogels and xerogels are porous solids characterized by large specific surface areas (SSAs), high porosities, various pore sizes ( s p ), small apparent densities, small indices of refraction, and low thermal conductivities. − Compared to aerogels, xerogels generally have smaller SSA, smaller porosities, smaller s p , and larger apparent densities due to differences in the synthesis routes. ,,, Both aerogels and xerogels are typically brought to the same alcogel stage (i.e., a solidified gel in an alcohol matrix) under identical preparation processes, but their drying processes vary. ,, Xerogels are generally synthesized through slow evaporation of the matrix solvent in the gel at a relatively low temperature (<40 °C) or at room temperature under vacuum, resulting in volume shrinkage and pore collapse by capillary forces on the pore walls. Collapse of the gel pore structure during drying can also be minimized by exchanging the solvent matrix to a nonpolar solvent (e.g., hexane) prior to the drying step .…”