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1.
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Michelle Delayette-Mills Lya Karm Gilbert E. Janauer Ping-Kwan Chan William E. Bernier 《Analytica chimica acta》1981,124(2):365-372
The in situ precipitation of traces of cadmium(II) and zinc(II) ions as hexacyanoferrates from aqueous matrices was studied on conventional polystyrene gel and macroporous cation- and anion-exchange resins. Coprecipitation with each other or with copper(II) ions present in binary cation resins or in solution, and the influence of added nonprecipitating ions of the same charge type such as magnesium(II) were investigated. Microporous (gel) cation exchangers gave reasonable recoveries and macroporous cation exchangers gave very good recoveries; but macroporous anion exchangers performed best, suggesting macroporous hexacyanoferrate(II) resin as an ideal phase for collection/preconcentration of traces of Cu2+, Cd2+, Zn2+, and possibly Co2+, Ni2+, and Pb2+ from waters. As expected, very low yields were obtained with conventional anion exchange resin in the hexacyanoferrate form. Uniform distribution of Cu2+, Zn2+, and Cd2+ over macroporous anion-exchange resin phases were established by means of electron probe scans and taken as evidence for the formation of a uniform, well-developed precipitate layer covering the entire resin particle surface. 相似文献
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Sanford TW Allshouse GO Marder BM Nash TJ Mock RC Spielman RB Seamen JF McGurn JS Jobe D Gilliland TL Vargas M Struve KW Stygar WA Douglas MR Matzen MK Hammer JH De Groot JS Eddleman JL Peterson DL Mosher D Whitney KG Thornhill JW Pulsifer PE Apruzese JP Maron Y 《Physical review letters》1996,77(25):5063-5066
5.
Jourdain V Paillet M Almairac R Loiseau A Bernier P 《The journal of physical chemistry. B》2005,109(4):1380-1386
Sequential catalytic growth provides an efficient tool for the synthesis of carbon nanotubes periodically inserted with catalyst nanoparticles. Several synthesis parameters were found crucial in order to induce this particular growth mechanism. The presence of phosphorus is required to form metal phosphide particles active for the formation of carbon nanotubes with a matchstick morphology. The metal composition (Ni/Fe ratio) and the carbon supply have no influence on the nanofilament type but strongly affect the nanotube yield. The synthesis temperature induces important changes on both the nanofilament type and yield, which are correlated with important transformations of the catalyst layer in terms of composition, particle size, and physical state. 相似文献
6.
An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations. 相似文献
7.
H. P. Lang V. Thommen-Geiser C. Bolm M. Felder J. Frommer R. Wiesendanger H. Werner R. Schlögl A. Zahab P. Bernier G. Gerth D. Anselmetti H. -J. Güntherodt 《Applied Physics A: Materials Science & Processing》1993,56(3):197-205
Fullerene powder mixtures with different C60/C70 ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C60/C70 ratios show that C70 molecules display a larger apparent diameter (0.8 nm) and corrugation than C60 molecules (0.7 nm). The C60/C70 ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C60/C70 ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C70 molecules and vacancies). In films prepared to have a C60 coverage of less than one monolayer, stable structural units of the C60(111) surface consisting of three or seven C60 molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed. 相似文献
8.
M.R. BabaaI. Stepanek K. Masenelli-VarlotN. Dupont-Pavlovsky E. McRaeP. Bernier 《Surface science》2003,531(1):86-92
Adsorption isotherms of krypton between 77 and 93 K and xenon between 110 and 120 K on mechanically-opened single-walled carbon nanotubes (SWNTs) have been measured. The comparison of the results with those obtained under the same conditions on closed nanotubes is discussed. Evidence of adsorption inside the tubes is given through the appearance of an additional adsorbed amount at very low relative pressure on the isotherms. Different orderings are predicted for xenon and krypton, based on their respective adsorbed amounts inside the nanotubes, and on geometrical considerations. Finally, the fraction of opened nanotubes accessible to xenon and krypton was estimated, as well as the impurity content originating from the cutting process. 相似文献
9.
Classically, the condensation of cyanoacetic acid and monoalkylurea gives 1-alkyl-6-amino-1,2,3,4-tetrahydropyrimidine-2,4-dione. However, this was verified only in two instances involving a long and delicate synthesis. The structure of the N′-cyanoacetyl-N-isobutylurea, an intermediate in the preparation of this type of pyrimidine, was confirmed by nmr. This method is capable of extension. 相似文献
10.
Trans polyacetylene (CH)x has been doped with FeCl3 solutions in Nitromethane. In the “in-situ” EPR experiment we have observed the evolution of the EPR spectra with time during the doping process. That enabled us to gain information about the rate of dopant diffusion in solid material. Both EPR and conductivity measurements show that the doped material is reasonably stable even in the presence of air. Raman spectroscopic studies show the usual features observed in doped trans polyacetylene. 相似文献