A zirconium-incorporated Ia3d cubic three-dimensional (3-D) mesoporous silicate, KIT-6, with different zirconium loadings, was synthesized via a one-step direct hydrothermal synthesis procedure employing Pluronic P123 triblock copolymer as the structure-directing agent under acidic conditions. Various characterization techniques, such as two-dimensional (2-D) small-angle X-ray scattering (SAXS), nitrogen sorption, temperature-programmed desorption of ammonia (NH3-TPD), and ultraviolet–visible-light (UV-Vis) spectra, showed that zirconium was incorporated as Zr4+ ions in the KIT-6 framework, which retained the structural integrity with a highly ordered pore structure. The Zr-KIT-6 materials exhibit very high surface areas (810–980 m2/g) and large pore volumes (1.07–1.65 cm3/g) that decrease with an increase in zirconium content. In contrast, the pore size distribution remains relatively unaffected by zirconium loading with an average pore diameter of ∼9.3 nm. The Zr-KIT-6 materials possess Lewis acidity that increases with zirconium loading. In the 180–300 °C range, the Zr-KIT-6 materials are shown to be highly active for the test reaction of isopropanol (IPA) dehydration to propylene (selectivity >98%). The activation energy for IPA dehydration, estimated from intrinsic rate constants normalized with respect to the Lewis acid sites, was ∼49 ± 1 kJ/mol and found to be lower than most other Brønsted or Lewis acidic heterogeneous catalysts reported in the literature for IPA dehydration. Furthermore, these catalysts showed nearly stable activity with very little deactivation during extended runs at 260 and 300 °C.

To model the structures of dissolved uranium contaminants adsorbed on mineral surfaces and further understand their interaction with geological surfaces in nature, we have performed periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO(2) rutile (110) surface. Two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered in this study. The uranyl dication was simulated as penta- or hexa-coordinated in the equatorial plane. Two bonds are contributed by surface bridging oxygen atoms and the remaining equatorial coordination is satisfied by H(2)O, OH(-), and CO(3)(2-) ligands; this is known to be the most stable sorption structure. Experimental structural parameters of the surface-[UO(2)(H(2)O)(3)](2+) system were well reproduced by our calculations. With respect to adsorbates, [UO(2)(L1)(x)(L2)(y)(L3)(z)](n) (L1=H(2)O, L2=OH(-), L3=CO(3)(2-), x≤3, y≤3, z≤2, x+y+2z≤4), on the ideal surface, the variation of ligands from H(2)O to OH(-) and CO(3)(2-) lengthens the U-O(surf) and U-Ti distances. As a result, the uranyl-surface interaction decreases, as is evident from the calculated sorption energies. Our calculations support the experimental observation that the sorptive capacity of TiO(2) decreases in the presence of carbonate ions. The stronger equatorial hydroxide and carbonate ligands around uranyl also result in U=O distances that are longer than those of aquouranyl species by 0.1-0.3 Å. Compared with the ideal surface, the hydrated surface introduces greater hydrogen bonding. This results in longer U=O bond lengths, shorter uranyl-surface separations in most cases, and stronger sorption interactions.

A polypyrrolic macrocycle with naphthalenyl linkers between the N(4)-donor compartments (L(2)) was designed theoretically according to its experimentally-known analogues with phenylenyl (L(1)) and anthracenyl (L(3)) linkers. The uranyl and bis(uranyl) complexes formed by this L(2) ligand have been examined using scalar-relativistic density functional theory. The calculated structural properties of the mononuclear uranyl-L(2) complexes are similar to those of their L(1) counterparts. The binuclear L(2) complexes exhibit a butterfly-like bis(uranyl) core in which a linear uranyl is coordinated in a side-by-side fashion to a cis-uranyl unit. The calculated U[double bond, length as m-dash]O bond orders in the uranyl-L(2) complexes indicate partial triple bonding character with the only exceptions being the U-O(endo) bonds in the U(2)O(4) core of the butterfly-shaped binuclear complexes. Overall, the bond orders agree with the trends in the calculated U[double bond, length as m-dash]O stretching vibrational frequencies. Regarding the bis(uranyl) L(1), L(2) and L(3) complexes, the phenylenyl-hinge L(1) complexes adopt a butterfly-like and a T-shaped isomer in the oxidation state of U(vi), but only a butterfly-like one in the U(v), which differs from that of the naphthalenyl-hinge L(2) complexes as well as the lateral twisted structure of the anthracenyl-hinge L(3) complexes. The intramolecular cation-cation interactions are found in the L(1) and L(2) complexes, but are absent in the L(3) complexes. Finally, using model uranyl transfer reactions from the L(1) complexes, the formation of the mononuclear L(2) complexes is calculated to be a slightly endothermic process. This suggests that it should be possible to synthesize the L(2) complexes using similar protocols as employed for the L(1) complexes.