No abstract

Raman spectra of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [C 2 mIm + ][FSA − ] ionic liquid solutions dissolving LiFSA salt of various concentrations were measured at 298 K. FSA − ((FSO 2 ) 2 N − ) is an analogue anion of bis(trifluoromethanesulfonyl)amide ((CF 3 SO 2 ) 2 N − ; TFSA − ). We found that a solvation number of the Li + ion in [C 2 mIm + ][FSA − ] is 3, though it has been well established that Li + ion is solvated by two TFSA − anions in the corresponding ionic liquids below the Li + ion mole fraction of x Li + < 0.2. To yield further insight into larger solvation numbers, Raman spectra were measured at higher temperatures up to 364 K. The Li + ion solvation number in [C 2 mIm + ][FSA − ] evidently decreased when the temperature was elevated. Temperature dependence of the Li + ion solvation number was analyzed assuming an equilibrium between [Li(FSA) 2 ] − and [Li(FSA) 3 ] 2− , and the enthalpy ΔH°and the temperature multiplied entropy TΔS°for one FSA − liberation toward a bulk ionic liquid were successfully evaluated to be 35(2) kJ mol −1 and 29(2) kJ mol −1 , respectively. The ΔH°and ΔS°suggest that the Li + ion is coordinated by one of bidentate and two of monodentate FSA − at 298 K, and that the more weakly solvated monodentate FSA − is liberated at higher temperatures. The high-energy X-ray diffraction (HEXRD) experiments of these systems were carried out and were analyzed with the aid of molecular dynamics (MD) simulations. In radial distribution functions evaluated with HEXRD, a peak at about 1.94 Å appeared and was attributable to the Li + −O(FSA − ) correlations. The longer Li + −O(FSA − ) distance than that for the Li + −O(TFSA − ) of 1.86 Å strongly supports the larger solvation number of the Li + ions in the FSA − based ionic liquids. MD simulations at least qualitatively reproduced the Raman and HEXRD experiments.

Using porous materials to cope with environmental issues is promising but remains a challenge especially for removing the radioactive vapor wastes in fission because of harsh adsorption conditions. Here we report a new, stable covalent organic framework (COF) as a porous platform for removing iodine vapor-a major radioactive fission waste. The three-dimensional COF consists of a diamond topology knotted by adamantane units, creates ordered one-dimensional pores and are highly porous. The COF enables the removal of iodine vapor via charge transfer complex formation with the pore walls to achieve exceptional capacity. Moreover, the 3D COF is "soft" to trigger structural fitting to iodine while retaining connectivity and enables cycle use for many times while retaining high uptake capacity. These results set a new benchmark for fission waste removal and suggest the great potential of COFs as a designable porous material for challenging world-threatening pollution issues.

Liquid structure and the closest ion-ion interactions in a series of primary alkylammonium nitrate ionic liquids [C(n)Am(+)][NO(3)(-)] (n = 2, 3, and 4) were studied by means of high-energy X-ray diffraction (HEXRD) experiments with the aid of molecular dynamics (MD) simulations. Experimental density and X-ray structure factors are in good accordance with those evaluated with MD simulations. With regard to liquid structure, characteristic peaks appeared in the low Q (Q: a scattering vector) region of X-ray structure factors S(Q)'s for all ionic liquids studied here, and they increased in intensity with a peak position shift toward the lower Q side by increasing the alkyl chain length. Experimentally evaluated S(Q(peak))(r(max)) functions, which represent the S(Q) intensity at a peak position of maximum intensity Q(peak) as a function of distance (actually a integration range r(max)), revealed that characteristic peaks in the low Q region are related to the intermolecular anion-anion correlation decrease in the r range of 10-12 Å. Appearance of the peak in the low Q region is probably related to the exclusion of the correlations among ions of the same sign in this r range by the alkyl chain aggregation. From MD simulations, we found unique and rather distorted NH···O hydrogen bonding between C(n)Am(+) (n = 2, 3, and 4) and NO(3)(-) in these ionic liquids regardless of the alkyl chain length. Subsequent ab initio calculations for both a molecular complex C(2)H(5)NH(2)···HONO(2) and an ion pair C(2)H(5)NH(3)(+)···ONO(2)(-) revealed that such distorted hydrogen bonding is specific in a liquid state of this family of ionic liquids, though the linear orientation is preferred for both the N···HO hydrogen bonding in a molecular complex and the NH···O one in an ion pair. Finally, we propose our interpretation of structural heterogeneity in PILs and also in APILs.