The influence of surface-bound Fe(II) on uranium oxidation state and speciation was studied as a function of time (6 min-72 h) and pH (6.1-8.5) in a U(VI)-Fe(II)-montmorillonite (Ca-montmorillonite, MONT) system under CO(2)-free, anoxic (O(2) <1 ppmv) conditions. The results show a rapid removal of U(VI) from the aqueous solution within 1 h under all pH conditions. U L(III)-edge X-ray absorption near-edge structure spectroscopy shows that 96% of the total sorbed U(VI) is reduced at pH 8.5. However, the extent of reduction significantly decreases at lower pH values as specifically sorbed Fe(II) concentration decreases. The reduction kinetics followed by X-ray photoelectron spectroscopy during 24 h at pH 7.5 demonstrates the presence of partially reduced surface species containing U(VI) and U(IV). Thermodynamically predicted mixed valence solids like U(3)O(8)/beta-U(3)O(7)/U(4)O(9) do not precipitate as verified by transmission electron microscopy and extended X-ray absorption fine-structure spectroscopy. This is also supported by the bicarbonate extraction results. The measured redox potentials of Fe(II)/Fe(III)-MONT suspensions are controlled by the Fe(II)/hydrous ferric oxide [HFO(s)] couple at pH 6.2 and by the Fe(II)/lepidocrocite [gamma-FeOOH(s)] couple at pH 7.5. The key finding of our study is the formation of a sorbed molecular form of U(IV) in abiotic reduction of U(VI) by sorbed Fe(II) at the surface of montmorillonite.

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A second generation of boron nitride-based porous materials has been synthesized by a double nanocasting process via a carbonaceous template as a medium starting from a zeolite. In the multistep process, we coupled several synthetic strategies such as chemical vapor deposition (CVD) and polymer-derived ceramic (PDCs) routes to prepare carbonaceous templates through infiltration of zeolite Y (FAU structure type) by propylene in the gaseous phase then infiltration of the carbonaceous replica having a high micropore volume (0.67 cm3/g) with polyborazylene in the liquid phase followed by pyrolysis and mold destruction. These porous BN-based architectures present a bimodal pore size distribution with a high portion of micropores (∼0.20 cm3/g) that are unambiguously evidenced by nitrogen physisorption based on a nonporous BN reference isotherm. They exhibited a high specific area (570 m2/g), a high pore volume (0.78 cm3/g), and a lack of long-range ordering as evidenced by BET, XRD and TEM experiments. The two first properties allow to open catalyst applications of these materials.

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The present study highlights the reactivity of carbon nanofibers (CNFs) with fluorine gas. Highly purified and graphitized CNFs were treated under a stream of fluorine gas for 16 h at temperatures ranging from 380 to 480 °C. Different fluorination temperature zones have been revealed by direct physicochemical analysis such as XRD, Raman spectroscopy, EPR, and solid-state NMR (13C and 19F). The comparison between various parameters such as covalence of C−F bond, T 1 spin−lattice nuclear relaxation time, density, and environment of the dangling bonds, among others, allows the fluorination mechanism to be determined, i.e., the formation of (C2F) n type graphite fluoride as the precursor of richer (CF) n compound. This is supported by TEM characterization as the fluorination proceeds from the external parts of the carbon nanofibers and then propagates through the core without a major structural change of the fluorinated parts. A low exfoliation of the sheets is necessary for extended fluorination and conversion into (CF) n ; this occurs for fluorination temperatures higher than 472 °C, with concomitant disappearance of the graphitic structure.

-Fluoroallenoate Synthesis via N-Heterocyclic Carbene-Catalyzed Fluorination Reaction of Alkynals. -The first catalytic synthesis of fluoroallenoates, versatile synthetic intermediates toward useful fluorine-containing building blocks, is described.-(WANG, X.; WU, Z.; WANG*, J.; Org. Lett. 18 (2016) 3, 576-579,

Single crystals of thiophene−phenelyne co-oligomers (TPCOs) have previously shown their potential for organic optoelectronics. Here we report on solution growth of large-area thin single-crystalline films of TPCOs at the gas−liquid interface by using solvent−antisolvent crystallization, isothermal slow solvent evaporation, and isochoric cooling. The studied co-oligomers contain identical conjugated core (5,5′diphyenyl-2,2′-bithiophene) and different terminal substituents, fluorine, trimethylsilyl, or trifluoromethyl. The fabricated films are molecularly smooth over areas larger than 10 × 10 μm 2 , which is of high importance for organic field-effect devices. The low-defect structure of the TPCO crystals is suggested from the monoexponential kinetics of the PL decay measured in a wide dynamic range (up to four decades) and from low crystal mosaicity assessed by microfocus X-ray diffraction. The TPCO crystal structure is solved using a combination of X-ray and electron diffraction. The terminal substituents affect the crystal structure of TPCOs, bringing about the formation of a noncentrosymmetric crystal lattice with a crystal symmetry Cc for the bulkiest trimethylsilyl terminal groups, which is unusual for linear conjugated oligomers. Comparing the different crystal growth techniques, it is concluded that the solvent−antisolvent crystallization is the most robust for fabrication of single-crystalline TPCOs films. The possible nucleation and crystallization mechanisms operating at the gas−solution interface are discussed.