Capturing ammonium nitrate in a synthetic uranium oxide hydrate phase: revealing the role of ammonium ions and anion inclusions.

Although uranium oxide hydrate (UOH) minerals and synthetic phases have been extensively studied, the role of ammonium ions in the formation of UOH materials is not well understood. In this work, the stabilization of a synthetic UOH phase with ammonium ions and the inclusion of ammonium nitrate were investigated using a range of structural and spectroscopic techniques. Compound (NH4)2(NO3)[(UO2)3O2(OH)3] (U-N1) crystallises in the orthorhombic Pmn21 space group, having a layered structure with typical α-U3O8 type layers and interlayer (NH4)+ cations as well as (NO3)- anions. The presence of uranyl, (NH4)+ cations and (NO3)- anions were further confirmed with a combination of FTIR and Raman spectroscopies through characteristic vibrational modes. The roles of the (NH4)+ cations for charge compensation and facilitating the inclusion of (NO3)- anions via hydrogen bonding were revealed and discussed. The findings have implications for uranium geochemistry, reprocessing of spent nuclear fuel and possible spent nuclear fuel alteration pathways under geological disposal.

Synthesis of hierarchical mesoporous cerium titanate brannerite and uranyl adsorption properties at pH 3.8.

Cerium titanates possessing brannerite structure are produced by employing soft and hard templates via sol-gel processing. Powders synthesized with various hard template sizes and template to brannerite weight ratios are composed of nanoscale 'building blocks' with size ∼20-30 nm and characterized on macro-, nano- and atomic scales. These polycrystalline oxide powders exhibit specific surface area up to ∼100 m2 g-1, pore volume ∼0.4 cm3 g-1, and uranyl adsorption capacity ∼0.221 mmol (53 mg) U per gram powder. Remarkably, the materials possess significant proportion of mesopores with 5-50 nm pores representing 84-98% of total pore volume, which facilitate fast accessibility of the adsorbate to the internal surfaces of the adsorbent with adsorbed uranyl reaching over 70% of the full capacity within 15 min of contact. These mesoporous cerium titanate brannerites synthesized by the soft chemistry route are highly homogenous, stable at least in 2 mol L-1 acidic or basic solution, and may attract attention for other applications like catalysis at high temperature.

Thorium(iv) and uranium(vi) compounds of cucurbit[10]uril: from a one-dimensional nanotube to a supramolecular framework.

Cucurbit[10]uril {Q[10]} has the largest portal size and cavity in the series of Q[n] (n = 5-10) molecules. In contrast to its rich host-guest chemistry, its coordination chemistry is underdeveloped with only limited metal ions being investigated so far. In this work, we initiated the study of Q[10] complexes with Th(iv) and U(vi) ions in HCl solutions via a self-assembly approach. The coordination of Th(iv) ions with Q[10] led to the formation of a compound, {Th4(Cl)16(H2O)20(Q[10])}·nH2O (Q[10]-Th), with a unique nano-tubular structure, while U(vi) ions facilitated the formation of a compound, [(UO2)2(Cl)4(H2O)6]·(Q[10])2·HCl·nH2O (Q[10]-U), with a Q[10]-based supramolecular framework structure via intermolecular outer-surface and second-shell interactions. The structural and spectroscopic aspects of the two compounds together with their optical and thermal properties have been investigated. The successful preparation and characterization of the first two Q[10] compounds with Th(iv)/U(vi) ions highlighted the potential for further exploration of Q[10] coordination chemistry with actinide ions.

Syntheses, Crystal Structures, and Spectroscopic Studies of Uranyl Oxide Hydrate Phases with La(III)/Nd(III) Ions.

We have synthesized two uranyl oxide hydrate (UOH) phases incorporating La(III) or Nd(III) ions under hydrothermal conditions. Investigations with scanning electron microscopy and transmission electron microscopy (TEM) revealed thin-plate morphologies with a U-to-Ln atomic ratio of 2:1 (Ln = La or Nd), while single-crystal X-ray diffraction and TEM electron diffraction studies confirmed that both UOH phases crystallized in the trigonal P31m space group with uranyl oxide layered structures incorporating La(III)/Nd(III) ions as interlayer species. Vibrational spectroscopic studies revealed typical vibrational modes for U ions, with the derived U═O bond lengths being comparable to the values reported on other UOH phases. Bond-valence-sum calculations suggest hexavalent uranium in the uranyl form, which was confirmed by the results of diffuse-reflectance and X-ray absorption near-edge structure spectroscopies. This work reports the first single-crystal structural investigation of UOH phases with Ln ions, which has significant implications in the weathering products of uraninite mineral in nature as well as the alteration products of spent nuclear fuels during interim storage and safe disposal over geological timespans.

Lanthanoid Heteroleptic Complexes with Cucurbit[5]uril and Dicarboxylate Ligands: From Discrete Structures to One-Dimensional and Two-Dimensional Polymers.

Lanthanoid heteroleptic complexes with cucurbit[5]uril {Q[5]} and two dicarboxylate ligands, e.g., diglycolic acid (H2DGC) and glutaric acid (H2GT), have been investigated with six new compounds featuring a tetrametallic and dimetallic discrete structures, a one-dimensional (1D) polymer, and three two-dimensional (2D) polymers with a unique honeycomb-type topology being synthesized and structurally characterized. [La4(Q[5])3(DGC)2(NO3)2(H2O)12][La(DGC)(H2O)6]·7NO3· nH2O (1) has a tetrametallic structure constructed with three bis-bidentate Q[5] ligands linking two [La(DGC)(H2O)2]+ species in the middle and two [La(H2O)4(NO3)]2+ species at both ends. [Ce2(Q[5])(DGC)(NO3)(H2O)10]·3NO3·4H2O (2) has a dimetallic structure built up with a bis-bidentate Q[5] ligand linking [Ce(DGC)(H2O)3(NO3)] and [Ce(H2O)7]3+ on each side of the Q[5] portals. [Ce3(Q[5])3(DGC)2(H2O)9][Ce(DGC)(H2O)6]2·7NO3· nH2O (3) has a 1D polymeric structure built up with bis-bidentate Q[5] ligands in-turn linking one [Ce(H2O)6]3+ and two [Ce(DGC)(H2O)6]1+ cationic species. [Ln2(Q[5])2(GT)(H2O)6]·4NO3· nH2O [Ln = La (4), Ce (5) and Nd (6)] have similar 2D polymeric structures built up with two types of 9-fold coordinated Ln polyhedra linked by Q[5] via bis-bidentate carbonyl groups on both sides forming 1D chains which are further connected by bridging GT2- ligands to form 2D polymers with a unique honeycomb-type topology. Their vibrational modes and electronic structures have also been investigated.

Thorium(IV) and Uranium(IV) Complexes with Cucurbit[5]uril.

Tetravalent thorium and uranium complexes with cucurbit[5]uril (Q[5]) were investigated with eight new complexes being synthesized and structurally characterized. [Th(Q[5])(OH)(H2O)2]6·18NO3· nH2O (1) has a hexagonal nanowheel structure with each of the six Th4+ ions being cap-coordinated by a Q[5] and monodentate-coordinated to the nearby Q[5]. [Th(Q[5])(HCOO)(H2O)4][Th(NO3)5(H2O)2]2[Th(NO3)3(HCOO)(H2O)2]0.5·NO3· nH2O (2) has a heteroleptic mononuclear structure with a Th4+ ion cap-coordinated on one side of the Q[5] portal and monodentate-coordinated to a formate anion inside the Q[5] cavity. [KTh1.5(Q[5])Cl(NO3)3][Th(NO3)5(H2O)2]·2NO3·2.5H2O (3) has a heterometallic structure with both Th4+ and K+ ions each occupying one side of the two Q[5] portals forming a capsule. [CsTh(Q[5])Cl(NO3)2(H2O)3]·2NO3· nH2O (4) has a heterometallic 1D polymeric structure with both Th4+ and Cs+ ions each occupying one side of the two Q[5] portals, forming monomers which are linked together by sharing two water molecules and one carbonyl oxygen atom between Th4+ and Cs+ ions. [Th(Q[5])Cl(H2O)][CdCl3][CdCl4]·0.5HCl·4H2O (5), [Th(Q[5])Cl(H2O)][Ru2OCl9(H2O)]·0.5HCl·9.5H2O (6), [Th(Q[5])Cl(H2O)][IrCl6]1.5·3H2O (7), and [U(Q[5])Cl(H2O)][ZnCl3(H2O)][(ZnCl4)]·8H2O (8) have similar 1D polymeric structures with Th4+/U4+ ions cap-coordinated on one side of a Q[5] and bidentate coordinated to the nearby Q[5]. The transition metal chlorides act as anions for charge compensation as well as structure inducers via cation-anion interactions forming various anion patterns around the 1D polymers. Actinide contraction has been observed in the early actinide series.

Novel chemical synthesis and characterization of CeTi(2)O(6) brannerite.

Cerium titanate CeTi2O6 was prepared by a new soft chemistry route in aqueous solution. A suite of characterization techniques, including X-ray diffraction, thermal analysis, vibrational spectroscopy, and scanning and transmission electron spectroscopy, were employed to investigate the brannerite structure formation and its bulk properties. The synthesized powder formed the brannerite crystal structure upon calcination at temperatures as low as 800 °C. Samples sintered at 1350 °C possess a high level of crystallinity. X-ray absorption near-edge structure results indicate the presence of six-coordinated Ce(4+) in the brannerite samples.

Synthesis and characterization of functionalized silica-based nanohybrid materials for oxyanions adsorption.

This study investigates the structural evolution of a series of nanohybrid powders and coatings synthesized by direct co-condensation of amino-functionalized alkyltrialkoxysilanes and tetraalkoxysilanes with an aromatic carboxylic acid (trimesic acid, TMA) as a structure directing agent. Fourier transform infrared spectroscopy (FTIR) and (13)C CP-MAS NMR results have suggested the formation of secondary (-CO-NH-) amide linkages upon interaction of TMA with the amino functionalized silane thus creating a "scaffold" around which the silica network is formed and also assisting in more homogeneous distribution of nitrogen sites within the nanohybrid structure. Functionalized silica powders were investigated for their potential to remove toxic oxyanions from mildly acidic or basic solutions. The uptake of Mo(VI), Se(VI), and Cr(VI) oxyanions was investigated as a function of the nanohybrid composition, oxyanion concentration, and solution pH using laser diffraction particle sizing, gas adsorption, and various spectroscopic techniques. The adsorption data obtained for Mo and Se could be adequately described by Langmuir adsorption isotherms, while the Freundlich isotherm is employed to fit the adsorption data for Cr. An easily accessible processing window (of pH, aging time, etc.) has been identified allowing production of continuous and uniform thin nanohybrid coatings on silicon and glass substrates. These coatings were tested as chemical barriers against Mo leaching from specially prepared Mo-doped glass. Leaching studies were conducted over 200 days in water at 90 degrees C and the Mo leaching from coated and uncoated samples compared.

Structure of organic-inorganic nanohybrids incorporating titanium(IV) oxoalkoxyacylate nanoclusters: a SANS study.

The small angle neutron scattering (SANS) technique was used to investigate the structure of nanohybrids consisting of a poly(methylmethacrylate) (PMMA) and one of two types of titanium(IV) nanoclusters. Cluster 1, [Ti6O4](OC2H5)8(CH2=CCH3COO)8, with polymerizable MMA ligands, formed covalent bonds with the polymer chains during the copolymerization, whereas cluster 2, [Ti6O4](OC2H5)8(CH3COO)8, had no polymerizable linkers and was blended into the polymeric matrix purely as a filler. In this study, SANS with contrast variation was used to investigate the size, shape and aggregation of the clusters in the hybrid materials, and their effect on the structure of the matrix. A polydispersed core-diffusion zone model was employed to explain the scattering contribution from the titanium clusters in both nanohybrid materials. No significant differences between the structures of the two nanohybrids were found. The fitted models suggest that the interface region between the cluster and matrix (the diffusion zone) is heavily occupied by the PMMA chains; however, they do not penetrate into the core region (titanium cluster).