ABSTRACT
Silver-exchanged aluminosilicate aerogels and xerogels were investigated as gaseous iodine [I2(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 â¼8 mass % higher iodine loading than Ag-impregnated xerogels and â¼3 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.
ABSTRACT
In this paper, sodium aluminosilicate aerogels and xerogels were evaluated as scaffolds for a variety of different getters including Ag+, Cs+, Cu2+, Fe3+, K+, Li+, Rb+, Sb3+, Sn2+, and Sn4+ for the capture of gaseous iodine coming from nuclear facilities. The exchange capacities varied widely from a near complete exchange in the case of Ag+ to much lower exchange levels for some of the Sn compounds [i.e., colloidal SnO2, Sn(II) acetate, and Sn(IV) acetate]. Several of the additives showed great promise at allowing for high iodine loadings in the base materials including the following: AgNO3, colloidal SnO2, Sn(II) acetate, Sn(IV) acetate, Cu(NO3)2, and CuSO4. From the standpoint of iodine uptake as a function of getter loading, Sn4+ was the most promising with a getter utilization (mass of iodine divided by mass of Sn, in atomic %) of 8.4, a chemical uptake of 60.7 mass % (oxygen excluded), and an mI ms-1 (mass of iodine per mass of sorbent) value of 0.881; these are some of the highest values reported to date for inorganic iodine sorbents.
ABSTRACT
Six different rare-earth oxyapatites, including Ca2 RE 8(SiO4)6O2 (RE = La, Nd, Sm, Eu, or Yb) and NaLa9(SiO4)6O2, were synthesized using solution-based processes followed by cold pressing and sinter-ing. The crystal structures of the synthesized oxyapatites were determined from powder X-ray diffraction (P-XRD) and their chemistries verified with electron probe microanalysis (EPMA). All the oxyapatites were isostructural within the hexa-gonal space group P63/m and showed similar unit-cell parameters. The isolated [SiO4]4- tetra-hedra in each crystal are linked by the cations at the 4f and 6h sites occupied by RE 3+ and Ca2+ in Ca2 RE 8(SiO4)6O2 or La3+ and Na+ in NaLa9(SiO4)6O2. The lattice parameters, cell volumes, and densities of the synthesized oxyapatites fit well to the trendlines calculated from literature values.
ABSTRACT
In this paper, aluminosilicate aerogels were used as scaffolds for silver nanoparticles to capture I2(g). The starting materials for these scaffolds included Na-Al-Si-O and Al-Si-O aerogels, both synthesized from metal alkoxides. The Ag0 particles were added by soaking the aerogels in aqueous AgNO3 solutions followed by drying and Ag+ reduction under H2/Ar to form Ag0 crystallites within the aerogel matrix. In some cases, aerogels were thiolated with 3-(mercaptopropyl)trimethoxysilane as an alternative method for binding Ag+. During the Ag+-impregnation steps, for the Na-Al-Si-O aerogels, Na was replaced with Ag, and for the Al-Si-O aerogels, Si was replaced with Ag. The Ag-loading of thiolated versus nonthiolated Na-Al-Si-O aerogels was comparable at â¼35 atomic %, whereas the Ag-loading in unthiolated Al-Si-O aerogels was significantly lower at â¼7 atomic % after identical treatment. Iodine loadings in both thiolated and unthiolated Ag0-functionalized Na-Al-Si-O aerogels were >0.5 mI ms-1 (denoting the mass of iodine captured per starting mass of the sorbent) showing almost complete utilization of the Ag through chemisorption to form AgI. Iodine loading in the thiolated and Ag0-functionalized Al-Si-O aerogel was 0.31 mI ms-1. The control of Ag uptake over solution residence time and [Ag] demonstrates the ability to customize the Ag-loading in the base sorbent to regulate the loading capacity of iodine.
