High iodine adsorption by polyethyleneimine impregnated nanosilica sorbents

In this study, several nanoporous silica of SBA-15 and Aerosil types were impregnated with branched polyethyleneimine (PEI) with the aim to evaluate their iodine adsorption performance. First, the influence of the PEI content of the sorbents on their textural, structural, thermal and chemical characteristics, was studied by different techniques including N2 porosimetry at 77 K, SAXS, FTIR/ATR, elemental analysis, and TGA. Then, I2 adsorption capacities were determined in liquid phase (cyclohexane) at 20 °C, or during static or dynamic gas-phase tests, performed at 60 and 100 °C, respectively. An exceptionally high adsorption capacity superior to 2 g/g in the 20–100 °C range was determined for the SBA-15 sorbent with 38 wt% PEI (corresponding to N content of 12.3 wt%). The adsorption capacities of the sorbents increase almost linearly with the N content below this threshold, whereas the presence of excess PEI in the pores or at the pore mouth reduces the accessibility of I2 molecules to the most buried nitrogen sites. The interaction mechanisms of iodine with amine-containing molecules were investigated both from experiments carried out in solution and from the after-test characterization of the spent solids by DR-UV-Vis, FTIR/ATR, Raman spectroscopies and iodine desorption monitored by TGA. This allowed shedding light on the nature of charge-transfer complexes and the formation of ionic and neutral iodine ad-species during iodine adsorption.