Structure–Activity Relationships between the State of Silver on Different Supports and Their I2 and CH3I Adsorption Properties

Abstract

In this study, the performances of silver-impregnated adsorbents prepared from different host supports (SBA-15, alumina, ceria, and faujasite Y zeolite) and calcined or not at 500 °C (1 h) were compared for the capture of I2 and CH3I. By keeping the silver content rather similar (about 15–17 wt %) among the sorbents, it was possible to assess the effect of silver dispersion and speciation on the adsorption capacities measured for both adsorbates. In a first part, several characterization techniques (XRD, DRS-UV-Vis, TEM, etc.) were used to probe the state of silver in the calcined and non-calcined materials. It was found that the characteristics of silver species are strongly influenced by the thermal treatment, the presence or absence of exchange sites, and the stability of the supports. Silver agglomeration was enhanced after calcination at 500 °C especially for supports bearing no exchange sites (SBA-15) or no ordered pores (alumina and ceria). Then, the adsorption performances of the studied silver sorbents were discussed in relation with their physicochemical characteristics. After-test characterizations were useful to assess the proportion of silver species that have reacted with CH3I and I2 to yield AgI precipitates. Depending on the adsorbate, different trends were obtained. I2 adsorption/reaction with silver sites was found to be quantitative (I/Ag ≈1), whatever the silver speciation and dispersion on the support. By contrast, a high proportion of cationic silver species was found essential to increase CH3I adsorption (I/Ag about 0.6–0.7 against 0.2–0.3 for Ag agglomerated species).

Role of Zeolite Structural Properties toward Iodine Capture: A Head-to-head Evaluation of Framework Type and Chemical Composition

“…Generally, on-site implemented sorbent-based approaches have the potential to prevent the release of radioiodine from these sources. Examples of sorbents that can be used to mitigate radioiodine release are metal–organic frameworks (MOFs), , covalent organic frameworks (COFs), zeolites and mesoporous silica, − metal-functionalized aerogels or xerogels, − and other metal-functionalized porous substrates. , These nanoporous materials have been shown to capture and separate various types of gases. − For example, zeolites exhibit stability under various conditions such as elevated temperatures, humidity, radiation fluxes, and exposures to different oxidizers [e.g., NO x (g) ]. Therefore, they are suitable materials to withstand severe conditions that are highly likely to occur during nuclear accidents.…”

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

“…3,4 Solid adsorbent systems are usually favored since they are simpler to design and are less costly to operate and maintain. 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.…”

“…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.…”

SuFEx‐Enabled Elastic Polysulfates for Efficient Removal of Radioactive Iodomethane and Polar Aprotic Organics through Weak Intermolecular Forces

“…However, the high cost of silver and the limited loading of silver atoms in zeolite hinder their large-scale application. [7][8][9][10][11] Although many organic materials, including metal-organic frameworks (MOFs), [3,12] porous organic polymers (POPs), [13] and covalent-organic frameworks (COFs), [14,15] provide large surface areas and abundant active sites for efficient iodomethane deposition, their complicated manufacturing processes and still limited deposition capacity prohibit their further application. In addition, polymeric adsorbents for iodomethane adsorption are mainly based on the chemical reaction between the iodomethane and their functional groups, resulting in poor recyclability.…”

“…Among them, inorganic adsorbents, such as silver‐modified zeolites, have been used. However, the high cost of silver and the limited loading of silver atoms in zeolite hinder their large‐scale application [7–11] . Although many organic materials, including metal–organic frameworks (MOFs), [3, 12] porous organic polymers (POPs), [13] and covalent‐organic frameworks (COFs), [14, 15] provide large surface areas and abundant active sites for efficient iodomethane deposition, their complicated manufacturing processes and still limited deposition capacity prohibit their further application.…”