Gaseous Iodine Sorbents: A Comparison between Ag-Loaded Aerogel and Xerogel Scaffolds

Silver-exchanged aluminosilicate aerogels and xerogels were investigated as gaseous iodine [I_2(g)] sorbents. The structures, morphologies, compositions, and porosities of aerogels (as-made and heat-treated at 350 °C) and xerogels are compared by using powder X-ray diffraction (PXRD), scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and specific surface area (SSA) as well as pore size analyses. The as-made aerogels, xerogels, and heat-treated aerogels were ion exchanged with Ag in AgNO₃ solutions of deionized water and methanol (5:1 by volume), and PXRD patterns showed the presence of nanocrystalline Ag⁰ after the Ag exchange. Gravimetric iodine loadings of Ag-aerogels and Ag-xerogels were 0.33-0.41 g g^-1. The Ag-aerogels without heat treatment showed an ∼8 mass % higher iodine loading than Ag-impregnated xerogels and ∼3 mass % higher than heat-treated Ag-impregnated aerogels. All gels after iodine uptake showed the presence of AgI, indicating chemisorption of iodine to silver. The SSA values of the as-made gels were 420-600 m² g^-1 but decreased significantly to 34-120 m² g^-1 after Ag impregnation and iodine uptake. Overall, changes in physical and chemical properties of aerogels and xerogels after iodine uptake were similar and the differences in iodine loading capacities of the aerogels and xerogels were minimal, providing a driver for using xerogels due to their less complex synthesis process as compared to aerogels.