Bulk hydrolysis and solid–liquid sorption of heavy metals in multi-component aqueous suspensions containing porous inorganic solids: Are these mechanisms competitive or cooperative?

Fundamental aspects of the removal of heavy metals from aqueous streams under conditions of competition among the various species have been studied between pH 3 and 9 on Spherosil XO75LS, ordered mesoporous MCM-41 and MCF silicas, as well as a MCF sample grafted with (3-aminopropyl)methoxydimethylsilane (AMPS-MCF). Cd(II), Co(II), Pb(II), or Sr(II) nitrate solutions were used to determine the percentage of metal uptake by each solid at 298K as a function of the pH of the equilibrium solution, at an initial metal concentration of 0.0001molL(-1) and the ionic strength being fixed with 0.01molL(-1) NaNO(3). Almost complete retention of the heavy metals on the four solid samples was observed, with the process beginning at pH values smaller than those marking the onset of "bulk" precipitation of a given metal in "free" solution. The heavy metal-uptake mechanism was regarded as hydrolysis-like phenomenon in metal-containing solid suspensions. Weak adsorption of metal species from slightly acidic and neutral solutions was a kind of nucleation step. Adding cadmium to an equimolar solution containing cobalt, lead, or strontium showed no significant effect on the retention of the main metal component. This indicated the great independence of the retention mechanisms.     

Synthesis of the trans-hydrindane core of dictyoxetane

A concise, stereoselective synthesis of the trans-hydrindane core of the marine natural product dictyoxetane is reported, starting from a Robinson annelation derived bicyclic enone. A phosphorane-mediated, pinacol-like rearrangement of a cis-diol, via a formal 1,2-hydride shift, is used to establish the requisite trans ring junction. (31)P NMR supports the formation of the intermediate phosphorane, generated in situ from the reaction of a diol with Ph(3)PCl(2).     

New alkaline earth-zirconium oxalates M2Zr(C2O4)4·nH2O (M=Ba, Sr, Ca) synthesis, crystal structure and thermal behavior

Three new alkaline earth-zirconium oxalates M₂Zr(C₂O₄)₄·nH₂O have been synthesized by precipitation methods for M=Ba, Sr, Ca. For each compound the crystal structure was determined from single crystals obtained by controlled diffusion of M²⁺ and Zr⁴⁺ ions through silica gel containing oxalic acid. Ba₂Zr(C₂O₄)₄·7H₂O, monoclinic, space group C2/c, a=9.830(2), b=29.019(6), , , , Z=4, R=0.0427; Sr₂Zr(C₂O₄)₄·11H₂O, tetragonal, space group I4₁/acd, a=16.139(4), , ,Z=8, R=0.0403; Ca₂Zr(C₂O₄)₄·5H₂O, orthorhombic, space group Pna2₁, a=8.4181(5), b=15.8885(8), , , Z=4, R=0.0622. The structures of the three compounds consist of chains of edge-shared MO₆(H₂O)_x (x=2 or 3) polyhedra connected to ZrO₈ polyhedra through oxalate groups. Depending on the arrangement of chains, the ZrO₈ polyhedron geometry (dodecahedron or square antiprism) and the connectivity, two types of three-dimensional frameworks are obtained. For the smallest M²⁺ cations (Sr²⁺, Ca²⁺), large tunnels are obtained, running down the c direction of the unit cell, which can accommodate zeolitic water molecules. For the largest Ba²⁺ cation, the second framework is formed and is closely related to that of Pb₂Zr(C₂O₄)₄·nH₂O. The decomposition at 800°C into strontium carbonate, barium carbonate or calcium oxide and MZrO₃ (M=Sr, Ba, Ca) perovskite is reported from thermal analyses studies and high temperature X-ray powder diffraction.     

Structural and electrochemical characterization of mesoporous thin films of Nb2xV2 − 2xO5 upon lithium intercalation

Nb_2xV_2 ? 2xO₅ (0 ≤ x ≤ 1) powders were prepared by a synthetic route based on the inorganic polymerization of alkoxy-choride precursors and characterized by a combination of X-ray diffraction, ⁵¹V and ⁹³Nb NMR and Raman spectroscopy. Amorphous mesoporous thin films of similar compositions were successfully prepared by a modified Evaporation Induced Self Assembly method using polystyrene-b-polyethyleneoxide diblock copolymer as structuring agent. The electrochemical properties of the mesoporous films upon lithium insertion–deinsertion are investigated by cyclic voltammetry. This study highlights the advantages of such nanoarchitecture in terms of increased capacity to insert lithium.     

Ultrafast breathinglike oscillation in the exciton density of ZnSe quantum wells

The spatial density profile of a low-density exciton ensemble in ZnSe quantum wells shows a breathinglike oscillation on a 30-ps time scale. This breathing results from the emission of the first acoustic phonon at the end of the quasiballistic transport phase of the excitons which reverses their direction of propagation. Since the scattering destroys the phase of the excitonic wave function, one can deduce simultaneously the coherence length and the coherence time of excitonic transport by evaluation of the oscillation measured from a single experiment. The breathing, which can be modeled by Monte Carlo simulations, is quenched for rising lattice temperature, i.e., increasing phonon absorption, and in samples with significant disorder. These results were obtained by time-resolved nanophotoluminescence with 5 ps and 250 nm temporal and spatial resolution, respectively.     

Analysis of Acidic Drugs in Swiss Wastewaters

Five acidic drugs (clofibric acid, ibuprofen, ketoprofen, mefenamic acid and diclofenac) were chosen in order to determine their behavior in a sewage treatment plant (STP). An analytical method using solid phase extraction (SPE) and a gas chromatograph coupled with a mass spectrometer (GC-MS) was used. The results show that four pharmaceuticals (clofibric acid, ketoprofen, mefenamic acid and diclofenac) are not well removed by treatment in Swiss STPs. Maximum concentration in the effluent was determined for mefenamic acid up to 1.0 µg/L. This component seems to be relevant in Swiss STPs effluents and we can expect its presence in surface waters.     

Hydrogen-bonded polycatenar mesogens

The tricatenar, hydrogen-bonded complexes formed between alkoxystilbazoles and an imine were found to be mesomorphic. Subsequently, related tetracatenar complexes were also investigated and found to be non-mesomorphic. We report the transition temperatures of these complexes and discuss structural modifications.     

U(IV)/Ln(III) unexpected mixed site in polymetallic oxalato complexes. Part I. Substitution of Ln(III) for U(IV) from the new oxalate (NH4)2U2(C2O4)5·0.7H2O

A new ammonium uranium (IV) oxalate (NH₄)₂U₂(C₂O₄)₅·0.7H₂O (1) and three mixed uranium (IV)-lanthanide (III) oxalates, (N₂H₅)_2.6U_1.4M_0.6(C₂O₄)₅·xH₂O (M=Nd (2) and M=Sm (3)), Na_2.56U_1.44Nd_0.56(C₂O₄)₅·7.6H₂O (4) and Na₃UCe(C₂O₄)₅·10.4H₂O (5), have been prepared. The crystal structures of compounds 1, 4 and 5 have been determined by single-crystal X-ray diffraction. The crystal structures were solved by the direct methods and Fourier difference techniques, and refined by a least square method on the basis of F² for all unique reflections. Compounds 2 and 3 are isotypic with 1. Crystallographic data: 1, hexagonal, space group P6₃/mmc, a=19.177(3), c=12.728(4) Å, Z=6, R₁=0.0575 for 52 parameters with 1360 reflections with I?2σ(I); 2, hexagonal, space group P6₃/mmc, a=19.243(4), c=12.760(5) Å, Z=6; 3, hexagonal, space group P6₃/mmc, a=19.211(3), c=12.274(4) Å, Z=6; 4, orthorhombic, space group Pbcn, a=18.79(3), b=11.46(1), c=12.77(2) Å, Z=4, R₁=0.0511 for 183 parameters with 3026 reflections with I?2σ(I); 5, monoclinic, space group C2/c, a=18.878(6), b=11.684(4), c=12.932(4) Å, β=95.97(1)°, Z=4, R₁=0.0416 for 213 parameters with 4060 reflections with I?2σ(I). The honeycomb-like structure of the five compounds is built from the same three-dimensional arrangement of metallic and oxalate ions. Similar hexagonal rings of alternating metallic and oxalate ions form layers parallel to the (001) plane that are pillared by another oxalate ion. Indeed, some torsions or rotations of the bridging oxalate ligands led to modifications of the network symmetry. The monovalent cations and the water molecules occupy the hexagonal tunnels running down the [001] direction. Starting from the uranium (IV) compound A₂U₂(C₂O₄)₅·0.7H₂O with A=NH₄⁺ (1), the mixed U(IV)/Ln(III) oxalates are obtained by partial substitution of U(IV) by Ln(III) in a ten-coordinated site, the charge deficit being compensated by intercalation of supplementary monovalent ions within the tunnels. The distortion of the arrangement in the [001] direction for the Na-containing compounds allows the accommodation of a greater number of water molecules that insure an octahedral coordination of the Na atoms.     

Kinetic and product study of the gas‐phase reaction of sabinaketone with OH radical

Sabinaketone is one major photooxidation product of sabinene, an important biogenic volatile organic compound. This article provides the first product study and the second rate constant determination of its reaction with OH radicals. Experiments were investigated under controlled conditions for pressure and temperature in the LISA indoor simulation chamber using FTIR spectrometry. Kinetic study was carried out at 295 ± 2 K and atmospheric pressure using the relative rate technique with isoprene as the reference compound. The rate constant was found to be k_{sabinaketone + OH} = (7.1 ± 1.0) × 10^?12 molecule^?1 cm³ s^?1. Acetone and formaldehyde were detected as products of the reaction with the respective yields of R_acetone = 0.9 ± 0.2 and R_HCHO = 1.2 ± 0.3. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 415–421, 2007