Silver-Loaded Xerogel Nanostructures for Iodine Capture: A Comparison of Thiolated versus Unthiolated Sorbents

Abstract

This paper describes the development and provides comparisons of thiolated (−SH) and unthiolated Ag–Al–Si–O xerogels for iodine gas capture. These xerogels were produced from alkoxides and then heat-treated at 350 °C to provide mechanical strength for subsequent processing steps. Then, a portion of the xerogels was thiolated using (3-mercaptopropyl)­trimethoxysilane. Next, thiolated and unthiolated batches were ion-exchanged in AgNO3 solutions where Ag+ replaced Na+ in the gel network on a near 1:1 molar basis. Subsamples of the Ag-exchanged xerogels were subjected to a reduction step in H2/Ar to convert Ag+ to Ag0 where the rest of the Ag-exchanged (Ag+) were not reduced. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy revealed nanoscale Ag0 in the Ag+ samples despite no active reduction where actively reduced samples had bimodal Ag0 distribution of ∼2–3 nm hexagonal and ∼6–7 nm cubic crystallites. Synchrotron X-ray absorption spectroscopy was used to assess the oxidization states of Ag, S, and I within the different xerogel samples. The specific surface areas of the base xerogels decreased as subsequent treatments were performed on the as-made samples, albeit the decreases were smaller than aerogel equivalents of these samples from a previous study. All iodine-loaded Ag-based samples showed a mixture of β-AgI and γ-AgI. Comparisons of iodine-loading results with other Ag-based iodine sorbents show that the thiolated Ag0-xerogels in this work have one of the highest iodine-loading capacities (q e) reported to date in saturated conditions with the thiolated Ag0-xerogel showing 522 mg iodine per g of the sorbent.

Iodine Capture with Metal-Functionalized Polyacrylonitrile Composite Beads Containing Ag0, Bi0, Cu0, or Sn0 Particles

“…The iodine loading capacities of PAN composites and metal particles from this study are compared to other chemisorption-based sorbents from previous studies ,,,− ,,− in Table S11 (Supporting Information) where the Cu-PAN+I and Sn-PAN+I composites showed notably higher iodine loading capacities compared zeolites. This move from wires to utilizing metals with higher specific surface areas, such as small particles, should help increase the interactions with the available metal surfaces in flow-through systems but will likely never be as effective as using microporous and mesoporous substrates with embedded nanosized getters such as the metal-exchanged zeolites, aerogels, or xerogels.…”

Iodine Capture by Ag-Loaded Solid Sorbents Followed by Ag Recycling and Iodine Immobilization: An End-to-End Process

“…The iodine loading capacities of AgX granules were consistent and higher than AgZ (i.e., 11 m % I or Q e ≈ 0.12–0.13 g/g; see Table S3, SI) . A comparison of iodine loading capacities between AgX, AgZ, and Ag-based and other metal-based aerogels and xerogels are provided in Figures S7 and S8 and Table S4 (SI). ,,,− …”

Radioiodine sorbent selection criteria

“…Transition metals and post-transition metals have been extensively evaluated, most commonly in the form of metalexchanged sorbents (Maeck et al, 1968;Maeck and Pence 1970;Pence et al, 1970;Pence et al, 1972;Riley et al, 2017;Riley et al, 2020) or metal-impregnated sorbents (Matyáš et al, 2011; (Riley et al, 2014) for sulfide-based chalcogels and CH 3 I for Ag 0 -aerogels (Tang et al, 2021) [in parts per billion by volume (ppbv) CH 3 I concentration streams] (criterion-2), (C) performance under relevant conditions based off data for I/Cl coadsorption (Matyáš et al, 2021b) and other studies in this area (Riley et al, 2021;Riley et al, 2022a) (criterion-3), (D) inherent properties of sorbent substrate (Riley et al, 2021) (criterion-4), and (E) iodide stability and disposition pathways (Riley et al, 2021;Reiser et al, 2022) (criterion-5). Matyáš et al 2018;Matyáš et al 2021b).…”

“… Summary of various parameters for consideration when selecting sorbents for radioiodine: (A) optimal capture performance including different types of Ag-zeolites that have different Ag loadings ( Riley et al, 2022b ) (criterion-1), (B) sorbent kinetics including examples based off actual data for I 2 ( Riley et al, 2014 ) for sulfide-based chalcogels and CH 3 I for Ag 0 -aerogels ( Tang et al, 2021 ) [in parts per billion by volume (ppbv) CH 3 I concentration streams] (criterion-2), (C) performance under relevant conditions based off data for I/Cl coadsorption ( Matyáš et al, 2021b ) and other studies in this area ( Riley et al, 2021 ; Riley et al, 2022a ) (criterion-3), (D) inherent properties of sorbent substrate ( Riley et al, 2021 ) (criterion-4), and (E) iodide stability and disposition pathways ( Riley et al, 2021 ; Reiser et al, 2022 ) (criterion-5). …”