2.3. Iodine Adsorption Tests

Adsorption tests with molecular iodine were performed using the different silver-impregnated sorbents in liquid medium. Cyclohexane was selected as a solvent owing to its ability to solubilize large amounts of iodine crystals (2.719 g I₂ for 100 g of C₆H₁₂ at 25 °C). In addition, Cyclohexane–I₂ solutions display in UV-visible range two absorption maxima at 223 and 523 nm, the latter being responsible of the pink-violet color. Adsorption tests were carried out at (20 ± 5 °C) using 75 mg of sorbent (m_ads) contacted in dark with 50 mL of a 400 mg·L⁻¹ solution prepared from I₂ pellets (ALFA AESAR, Ward Hill, MA, USA, purity 99.5%). The slurry was stirred for a sufficiently long time (about 24–48 h) to ensure reaching the adsorption equilibrium. Then, the adsorbent particles loaded with iodine were separated by filtration, and the solid was recovered for further characterization. Initial and final I₂ concentrations were measured both on the initial solution and after 24–48 h exposure to iodine using a double-beam Cary 4000 UV-Vis spectrophotometer (AGILENT TECHNOLOGIES, Santa Clara, CA, USA) with 1 cm quartz cuvettes thanks to the Beer’s law applied at 523 nm:

Hence, the adsorption capacity at equilibrium was deduced from the following mass balance:

CH₃I adsorption tests in liquid medium (cyclohexane) were also carried out according to a protocol rather similar to the one used for I₂ tests. However, some precautions were undertaken in order to take into account the volatile character of CH₃I (boiling point of about 43 °C): (i) the adsorption temperature was maintained to 10 ± 1 °C using a refrigerated bath; (ii) a blank experiment was performed systematically for each adsorption test in order to account for any loss of iodomethane by evaporation (Δ_blank). Adsorption tests were conducted using an initial CH₃I concentration of 450 mg·L⁻¹. Colorless Cyclohexane-CH₃I solutions were characterized by a unique absorption band at 258 nm. Here also, the solutions were carefully filtrated to recover the spent adsorbents for further characterization. Absorbance measurements allowed us to determine the initial CH₃I concentrations and at equilibrium (48 h). The adsorption capacity at equilibrium was then deduced using the following formula: