Jocelyne Brendlé

U(VI) sorption and reduction by Fe(II) sorbed on montmorillonite.

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.

Functionalization of synthetic talc-like phyllosilicates by alkoxyorganosilane grafting

A range of talc-like phyllosilicates were prepared via a hydrothermal synthesis performed at five different temperatures from 160 to 350 °C. The organization of the lattice and the degree of crystallinity of the new materials were evaluated by different techniques such as XRD, FTIR, solid-state 29Si NMR, TEM, FEG-SEM and TG-DTA. When synthesized at low temperature the material presents high degree of hydration, low crystallinity and flawed structure. This was attributed to stevensite-talc interstratified product present in the samples. The stevensite/talc ratio and the hydration decrease in the talc-like phyllosilicate samples when the hydrothermal synthesis temperature increases and so the crystallinity becomes higher. A thermal treatment at 500 °C allowed a significant flaw reduction in talc-like phyllosilicate structure; the synthesized sample at 350 °C and heat treated presents a structure close to that of talc. The different talc-like phyllosilicates were grafted covalently by two organoalkoxysilane reagents, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (IM2H) and 2-hydroxy-4-(3-triethoxysilylpropoxy)-diphenylketone (HTDK). The grafted amounts of the hybrids, determined by elemental analysis and confirmed by thermogravimetric data, are dependent on the hydrothermal synthesis temperature and organoalkoxysilanes; they become smaller when the synthesis temperature increases and when HTDK is used. FTIR and solid-state 13C CP MAS NMR were applied to characterize the grafted organic groups. So, in this work it is shown that by choosing the hydrothermal synthesis temperature or by performing an additional annealing it is possible to adjust the amount of defects in the structure of talc-like phyllosilicates which seems to be strongly correlated to the grafting performance.

Bridged polysilsesquioxane films via photoinduced sol–gel chemistry

The synthesis and characterization of bridged polysilsesquioxane films was performed via a photoacid-catalyzed sol–gel method using a series of three precursors with different organic moiety structures.

Self-Organized Poly(n-octadecylsilsesquioxane) Films via Sol–Gel Photopolymerization

We describe a novel solvent- and water-free sol-gel process for n-octadecyltriclorosilane (C(18)H(37)SiCl(3)) film catalyzed by photogenerated Brönsted acids. Driven by hydrophobic van der Waals interactions, a photoinduced self-assembly process occurs to afford a long-range ordered lamellar mesostructure, characterized by X-ray diffraction and transmission electron microscopy. Real-time Fourier transform IR spectroscopy was instrumental to probe the fast hydrolysis kinetics and assess the change of conformational behavior of the alkyl chains during UV irradiation. A unique combination of different solid-state NMR techniques ((29)Si, (13)C, (1)H) provided an insight into the supramolecular organization of this hybrid film.

Photoinduced synthesis and ordering of lamellar n-alkylsiloxane films†

Self-assembled organosilica films exhibiting various lamellar structures were prepared without solvent and watervia the fast photoacid-catalyzed sol–gel process of n-alkyltrimethoxysilanes (CnTMS, n = 8, 10, 12, 16 and 18). This facile photochemical route towards nanostructured hybrid films relies on superacid photocatalyst generated by the UV photolysis of a soluble lipophilic iodonium salt: (C12H25)2Φ2I+ SbF6−. A main emphasis has been on discussing the effect of the alkyl chain length on the level of ordering of the layered mesostructure (short- or long-range order), the alkyl chain packing arrangement (bilayered or interdigitated) and its conformational order (gauche and trans). X-Ray diffraction and electron microscopy (TEM and SEM) proved the high periodicity achieved with the long chain alkylsilanes (n = 16 and 18). Real-time Fourier transform infrared spectroscopy (RT-FTIR) was also instrumental in giving a unique insight into the sol–gel reaction kinetics and the progressive conformational ordering of the alkyl chains during the photoinduced self-assembly. Further, the combination of different solid-state NMR techniques (29Si and 13C) shed light on the siloxy layer microstructure and the conformational structure of the alkyl chain respectively.

Photopatterning of Multilayer n-Alkylsilane Films

Surface photopatterning of organosilane self-assembled monolayers (SAM) has received increasing attention since its introduction 20 years ago. Herein we report for the first time a cost-efficient soft photopatterning technique affording amplified 3D multilayer structures. The essential chemistry relies on a spatially controlled photoacid-catalyzed hydrolysis and polycondensation of n-alkyltrimethoxysilane precursors (n-C(12)H(25)Si(OCH(3))(3),). Amphiphilic siloxane species are photogenerated locally and are able to self-assemble spontaneously into a long-range-ordered lamellar mesostructure.

A Novel Fluoride Route for the Synthesis of Aluminosilicate Nanotubes

In this work we present a novel method for synthesis of aluminosilicate nanotubes: the fluoride route. F-containing imogolite (F-IMO) exhibits an improved crystallization rate and improved yield. The structure of F-IMO was investigated and compared with F-free imogolite (IMO) by means of X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR) confirming imogolite structure. Solid state nuclear magnetic resonance (NMR) analyses show an increased crystallization rate for F-IMO and confirm the incorporation of fluorine ion in the structure.

Hydrophilic/Hydrophobic Film Patterning by Photodegradation of Self-Assembled Alkylsilane Multilayers and Its Applications

While the photopatterning of self-assembled monolayers (SAMs) has been extensively investigated, much less attention has been given to highly ordered multilayer systems. By being both thicker (0.5-2 μm) and more stable (cross-linked) than SAMs, patterned hybrid multilayers lend themselves more easily to the development of technology-relevant materials and characterization. This paper describes a facile two-step UV approach to patterning an alkylsilane multilayer by combining photoinduced self-assembly for multilayer synthesis and photodegradation through a mask for creating patterns within the film. In this second stage, a spatially resolved removal of the alkyl tail via a photooxidation mechanism took place, yielding regular and uniform silica microdomains. The result was a regular array of features (alkylsiloxane/silica) differing in chemical composition (hybrid/inorganic), ordering (crystal-like/disordered), and wettability (hydrophobic/hydrophilic). Such a photopatterned film was of utility for a range of applications in which water droplets, inorganic crystals, or aqueous polymer dispersions were selectively deposited in the hydrophilic silica microwells.

Hydration and hydrolysis of samarium (III) in montmorillonite clay: a neutron diffraction study

Neutron diffraction with isotopic substitution was carried out at room temperature on hydrated samples of Sm montmorillonite, prepared at pH = 4 and 8, in order to find out whether Sm is present as aqueous Sm(OH)3o, Sm3+, or intermediate hydrolyzed species, and how it is linked to the clay surface. It was found that the number of hydrogen atoms (5.5 ± 2.0) nearest to Sm3+ at pH = 4 is equal to or even slightly smaller than that of oxygen atoms (7.5 ± 1.0). This means that Sm3+ is bound to the clay surface and it is probably partially hydrolyzed. This result is very close to those obtained earlier for Yb3+ and Nd3+, despite the different methods of sample preparation and the different mineralogy of the samples.

Interaction of titanium with smectite within the scope of a spent fuel repository: A spectroscopic approach

Abstract The Swedish and Finnish nuclear waste repository design, KBS-3H, foresees horizontal emplacement of copper canisters-bentonite modules surrounded by a titanium shell. The interaction of titanium with bentonite was studied here using a combination of wet chemistry and a spectroscopic approach to evaluate the potential impact of Ti corrosion on the clay. For natural analogue clays with high Ti contents, spectroscopic investigations showed that titanium occurs as crystalline TiO2. In contrast, the Ti in the MX-80 bentonite occurs in the clay structure, presumably in the octahedral sheet. Hydrothermal tests conducted at 200°C using synthetic montmorillonite showed little if any change in the montmorillonite structure at near-neutral and acidic conditions. Under alkaline conditions, limited alteration was observed, including the formation of trioctahedral clay minerals and zeolite. These changes, however, occurred independently of the addition of Ti. In the batch tests conducted at 80°C, Ti did not occur as separate TiO2 particles. The comparison of experimental data with spectroscopic simulations provides sound evidence that Ti was incorporated in a neoformed phyllosilicate structure.