Synthesis of NiGa layered double hydroxides. A combined EXAFS, SAXS, and TEM study. 3. Synthesis at constant pH

The present paper focuses on the direct synthesis of NiGa layered double hydroxides (LDHs) by concomitant addition of Ni and Ga chloride in solution with NaOH solution, at a constant pH value of 6.5. Various Ni/Ga ratios (Ni/Ga = 2, Ni/Ga = 4, or Ni/Ga = 6) were investigated, and samples were collected after successive additions. Each sample was then analyzed by small-angle X-ray scattering (SAXS) to derive information about the shape of the objects formed upon synthesis. In parallel Ni K-edge and Ga K-edge extended X-ray absorption fine structure (EXAFS) analysis were carried out on relevant samples to obtain information on the local structure of the species in suspension. SAXS curves reveal significant changes. At the beginning of the synthesis, for low added volumes (V(s)), the suspension appears to contain both monodimensional and bidimensional objects. For higher V(s), the monodimensional objects disappear and only platelike particles are detected in the suspension. EXAFS results show that all the added gallium atoms are involved in a solid Ni-Ga LDH phase throughout the whole synthesis. In contrast, some nickel cations do not precipitate in the Ni-Ga LDH. At the beginning of the synthesis, for low added volumes they are also involved in the formation of fibrous polycations. For higher added volumes, the fibers are not observed anymore and monomeric nickel species are then present in the suspension.     

Precipitation of Zn2Al LDH by urease enzyme

A biomineralization process based on the promotion of precipitating agent by the urea-urease enzymatic system is developed to prepare ZnAl layered double hydroxide materials and the effects of the enzymatic reaction parameters on the structural and textural properties of the materials are investigated on the basis of XRD and EM analysis.     

Use of analytical microscopy to analyze the speciation of copper and chromium ions onto a low-cost biomaterial

In this paper, we present our study of the speciation of copper and hexavalent chromium sorbed onto a lignocellulosic substrate, using analytical microscopy. The lignocellulosic substrate constitutes a low-cost biomaterial that can be used in wastewater treatment. Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) was used to determine the speciation of the two metal ions on the constitutive moieties of the lignocellulosic substrate. The use of a staining agent sensitive to carbon unsaturation allowed us to differentiate between the microstructures rich in lignin entities and those rich in cellulose entities. The EDX analysis showed that metal ions are preferentially sorbed onto microstructures rich in lignin moieties. The energy electron loss spectroscopy (EELS) was used to determine the oxidation states of chromium in association with lignocellulosic moieties. We showed that the sorption process of hexavalent chromium requires the reduction of Cr(VI) into Cr(III) and the probable oxidation of lignin moieties.     

Alumina‐supported nickel catalyst for liquid‐phase reactions: an expedient and efficient heterogeneous catalyst for hydrogenation reactions

The preparation of a new nickel(0)/Al₂O₃ catalyst for hydrogenation reactions is described. The nickel(0)/Al₂O₃ catalysts were prepared by impregnation of alumina with a solution of a nickel(II) salt. After drying, the nickel(II) salt was reduced under mild conditions into nickel(0) using t‐BuONa‐activated sodium hydride in tetrahydrofuran at 65 °C. The nickel(0)/Al₂O₃ catalysts obtained were characterized by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The supported catalysts were successfully used in solution‐phase hydrogenation of double and triple bonds. Although the activity of the nickel(0)/Al₂O₃ is comparable to non‐supported nickel(0) reagents, it has the advantage of being reusable more than ten times with only a slight decrease of reactivity. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis and characterization of new highly selective polyaryloxyphosphazene-polysiloxane crosslinked copolymer films. Application to the extraction of organic compounds from water by pervaporation

A series of polyaryloxyphosphazene/polydimethylsiloxane (PABMP/PDMS) crosslinked copolymer films containing various PDMS contents were prepared by platinum-catalyzed hydrosilylation reaction. The physical morphology of these membranes was characterized by IR, DSC and transmission electron microscopy. Their transport properties were studied by pervaporation of saturated ethyl acetate aqueous solutions at 30°C. Each copolymer film led to preferential permeation of ethyl acetate. Moreover, selectivity and flux proved to be higher than a PABMP membrane, increasing with the PDMS content up to a 70 wt% value. At the maximum point, an aqueous solution of 7 wt% ethyl acetate was concentrated to 97 wt% with a normalized permeation flux of 25 kg/m².h.