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

Bruno Azambre,Mouheb Chebbi,Nagham Ibrahim

doi:10.3390/nano11051300

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).

Highlights

Accidental releases of radiotoxic species from nuclear plants to the environment are known to cause serious damages
The most studied silver-based adsorbents for the capture of volatile iodine are silver zeolites and silver supported on various forms of silica
Additional information about the location, electronic state, and morphology of silver species and silver nanoparticles will be discussed from XRD, DRS-UV-Vis, and Transmission Electron Microscopy (TEM)

Summary

Introduction

Accidental releases of radiotoxic species from nuclear plants to the environment are known to cause serious damages. Among the most hazardous radionuclides, iodine is of specific interest due to its high radiological impact associated with its ability to exist both as aerosols and volatile species, namely I2 and CH3 I [1,2,3]. One efficient technological approach to overcome such releases is to trap the released iodine forms onto a sorbent. Owing to the possibility of forming thermally stable and insoluble AgI precipitates, silver-loaded materials were identified as efficient candidates for the trapping of methyl iodide, molecular iodine, and iodide ions at an industrial scale [5,6,7,8]. The most studied silver-based adsorbents for the capture of volatile iodine are silver zeolites and silver supported on various forms of silica.

Methods

Results

Conclusion