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91.
Uniform, well-dispersed silver particles of various morphologies have been prepared by reducing highly acidic silver nitrate solutions with ascorbic acid in the presence of a sodium naphthalene sulfonate-formaldehyde copolymer as dispersing agent. By varying the temperature of the reaction, the free acid content, the addition rate of the reductant, and the aging time, both isometric and anisotropic silver particles could be obtained. It was found that the latter were formed by aggregation of nanosize subunits, which were identified by electron microscopy and X-ray diffractometry. 相似文献
92.
G. Rasulić Lj. Milanović S. Jovanović G. Novohatni V. Krivokuća Z. Marjanović 《Journal of Thermal Analysis and Calorimetry》1985,30(1):73-82
A study was made of the changes in the active component of a commercial catalyst for methane reforming by means of steam, as a function of its duration of use and of its position in an industrial reactor. The samples for examination were taken after 3, 8, 9 and 20 months of catalyst use, and from seven different levels in the reformer tube, ranging from the top to the bottom.DTA, TG, IR spectroscopy, X-ray diffraction and surface area determination were used to follow the catalyst changes.
Zusammenfassung Veränderungen der aktiven Komponente eines kommerziellen Katalysators zur Methanreformierung mittels Wasserdampf wurden in Abhängigkeit von der Betriebsdauer und der Lage im industriellen Reaktor untersucht. Proben für die Untersuchung wurden nach 3-, 8-, 9- und 20-monatiger Betriebsdauer aus 7 verschiedenen Höhen vom Boden bis zum Kopf des Reformer-Rohres entnommen. Veränderungen des Katalysators wurden mittels DTA, TG, IR-Spektroskopie, Röntgendiffraktometrie und Oberflächenmessungen verfolgt.
, - , @2 . 3, 8, 9 20 -, -. , , , , , .相似文献
93.
Summary When silver iodide, silver bromide and silver chloride solsin statu nascendi are coagulated by thorium nitrate in the presence of potassium nitrate, three coagulation maxima appear. Two of them are
identical with maxima that are found in absence of KNO3, denoted with (II) and (IV) in fig. 1. The new maximum appears in the stability region of recharged sols (III). It is believed
that this maximum is also—as maximum (IV)—caused by the coagulation of recharged silver halide sols by nitrate ions. Appearance
of two nitrate coagulation maxima is explained by different charge densities on sol particles at various concentrations of
Th(NO3)4 where they are formed. The new maximum indicates a lower charge density of sol particles. The possibility that the new maximum
could have been caused by ionic complex species between thorium and nitrate ions has been rejected for data are available
that the equilibrium constant for such complexes is small.
In the presence of K2SO4 the coagulation effects of thorium nitrate on silver halide sols are markedly different. In acidified solutions only one
coagulation maximum appears at rather high thorium nitrate concentrations [∼ 10−3
N Th (NO3)4] and the sol remains negatively charged [up to ∼ 10−2
N Th (NO3)4] This is explained by complex formation of Th-ions and sulfate ions whereby ionic species of lower charge are formed, which
exert a weaker coagulation effect. In neutral solutions another maximum at lower concentration of Th (NO3)4 is formed which appears to be the usual coagulation maximum produced by hydrolyzed thorium ions.
The antagonistic effects of the salt pair Th (NO3)4-K2SO4 upon the coagulation of silver halides has been discussed and we have concluded that the large effects repeatedly reported
can be explained not by simple electrostatic effects of ions in solution but rather by the formation of complexes between
Th- and SO4-ions.
Supported in part by U.S. Atomic Energy Commission Contract No. AT (30-1)-1801. 相似文献
Zusammenfassung Die Koagulationseffekte des Thoriumnitrats in Anwesenheit von Kaliumnitrat und Kaliumsulfat an Silberhalogenid-Solenin statu nascendi wurden ausführlich untersucht. Wenn Silberhalogenid-Sole durch Thoriumnitrat-L?sungen koaguliert werden, bilden sich zwei Koagulationsmaxima (II und IV, Abb. 1). Bei sehr niedrigen Konzentrationen des Thoriumnitrats koaguliert das Thorium-Ion (oder Komplex) die negativen Silberhalogenid-Sole, w?hrend bei h?heren Thoriumnitrat-Konzentrationen die ungeladenen Sole durch die NitratIonen koaguliert werden. Zwischen den zwei Maxima besteht ein weites Gebiet der stabilen umgeladenen Sole (III). Unter dem Zusatz von konstanten Mengen des Kaliumnitrats wird in diesem Gebiet ein neues (drittes) Maximum gebildet (Abb. 2–5), das auch als Koagulationsmaximum identifiziert wurde. Es wird angenommen, da? dieses Maximum wieder eine Koagulation der umgeladenen Silberhalogenid-Sole durch Nitrat-Ionen darstellt. Das Auftreten von zwei Koagulationsmaxima, verursacht durch Nitrat-Ionen, wird durch die verschiedenen Ladungsdichten an Solteilchen in Gebieten der Thoriumnitrat-Konzentrationen, in denen Maxima erscheinen, erkl?rt. Die M?glichkeit eines Koagulationseffektes der komplexen Ionen zwischen Thorium und Nitrat wurde ausgeschlossen, da die Gleichgewichtskonstante solcher Komplexe ziemlich niedrig ist. In Anwesenheit von Kaliumsulfat sieht die Koagulationskurve für Silberhalogenid Sole sehr unterschiedlich aus (Abb. 6–8). In den mit Salpeters?ure (0,001N) versetzten Solen erscheint nur ein Maximum bei ziemlich hohen Thoriumnitrat-Konzentrationen [∼ 10−3 N Th (NO3)4], wobei die Solteilchen noch immer negativ sind. Da Thorium- und Sulfat-Ionen sehr stabile Ionen-Komplexe bilden, die eine niedrigere Valenz aufweisen, kann das Maximum als Folge der Koagulationseffekte solcher Komplexe an die Silberhalogenid-Sole angesehen werden. In neutralen L?sungen zeigt sich neben dem beschriebenen Maximum noch ein anderes Maximum bei niedrigerer Thoriumnitrat-Konzentration. Dieses Maximum, hervorgerufen durch die hydrolysierten Thorium-Ionen, scheint das „normale“ Koagulationsmaximum zu sein. Dieantagonistischen Effekte des Salzpaares Th (NO3)4-K2SO4 bei der Koagulation der Silberhalogenide wurden diskutiert, und es wurde geschlossen, da? die gro?en Effekte, die wiederholt ver?ffentlicht worden waren, sehr schwer nur durch die elektrostatischen Anziehungen zwischen den Ionen erkl?rt werden k?nnen. Die Komplexbildung zwischen Thorium- und Sulfat-Ionen wird für den sogenannten antagonistischen Effekt in diesem Falle als verantwortlich angesehen.
Supported in part by U.S. Atomic Energy Commission Contract No. AT (30-1)-1801. 相似文献
94.
M. Spasoević M. Cvijović L. Rybić-Zelenović G. Aćamović-Joković 《Russian Journal of Applied Chemistry》2007,80(4):566-570
The possibility of obtaining smooth homogeneous copper coatings with good adhesion and homogeneous copper coatings with poor adhesion by electrochemical deposition of copper on steel from a solution of nontoxic copper(II) complex with the ligands, 1,3-propylenediamine-N,N′-diacetato-N,N′-di-3-propionic acid, was analyzed. For both types of coatings, the optimum composition of the solution and the optimum deposition conditions were determined. 相似文献
95.
Rosenthal SJ Tomlinson I Adkins EM Schroeter S Adams S Swafford L McBride J Wang Y DeFelice LJ Blakely RD 《Journal of the American Chemical Society》2002,124(17):4586-4594
To explore the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters, we explored the ability of serotonin-labeled CdSe nanocrystals (SNACs) to interact with antidepressant-sensitive, human and Drosophila serotonin transporters (hSERT, dSERT) expressed in HeLa and HEK-293 cells. Unlike unconjugated nanocrystals, SNACs were found to dose-dependently inhibit transport of radiolabeled serotonin by hSERT and dSERT, with an estimated half-maximal activity (EC(50)) of 33 (dSERT) and 99 microM (hSERT). When serotonin was conjugated to the nanocrystal through a linker arm (LSNACs), the EC(50) for hSERT was determined to be 115 microM. Electrophysiology measurements indicated that LSNACs did not elicit currents from the serotonin-3 (5HT(3)) receptor but did produce currents when exposed to the transporter, which are similar to those elicited by antagonists. Moreover, fluorescent LSNACs were found to label SERT-transfected cells but did not label either nontransfected cells or transfected cells coincubated with the high-affinity SERT antagonist paroxetine. These findings support further consideration of ligand-conjugated nanocrystals as versatile probes of membrane proteins in living cells. 相似文献
96.
Frkanec L Jokić M Makarević J Wolsperger K Zinić M 《Journal of the American Chemical Society》2002,124(33):9716-9717
The photoinduced gelation system based on 1 (non-gelling) to 2 (gelling) molecular photoisomerization in water results by microspheres (1) to gel fibers (2) transformation at the supramolecular level. 相似文献
97.
π-electron energies and bond orders of benzenoid hydrocarbons with up to five fused hexagons have been considered by the simple
Bond Orbital Resonance Theory (BORT) approach. The corresponding ground states were determined according to four BORT models.
In the first three models a diagonalisation of the Hückel-type Hamiltonian was performed in the bases of Kekulé, of Kekulé
and mono-Claus and of Kekulé and Claus resonance structures, respectively. In the fourth model a simple BORT ansatz was used.
According to this ansatz, the ground state is a linear combination of the positive Kekulé structures, all with equal coefficients.
It was shown that π-electron energies and bond orders obtained by these models correlate much better with the PPP energies
and bond orders than with the Hückel energies and bond orders. This indicates that a simple BORT approach is quite reliable
in predicting the more sophisticated PPP results. Concerning the relative performance of the four BORT models, the best results
were obtained with the BORT ansatz. The performance deteriorates with the expansion of the basis set. This is attributed to
the fact that in these models the improvement of the basis set is not accompanied with the corresponding improvement of the
Hamiltonian. Comparing the BORT-ansatz bond orders with the Pauling bond orders, it was shown that BORT-ansatz bond orders
correlate much better with the PPP bond orders.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
Summary The effect of pre-adsorbed benzene and ethanol on the adsorptive properties of natural zeolite (clinoptilolite) has been studied
by gas-solid chromatography. It has been shown that modification of the solid surface by volatile organics has a significant
influence on the adsorptive properties. The modification is of the same order as the more difficult modification by inorganics,
as illustrated here by clinoptilolite modification with Co2+. Energy distribution of surface adsorptive sites appears to be continuous and confirms previous finding that only a small
proportion of active sites is responsible for most adsorbate retention.
Part II reference [4] 相似文献
99.
The hybridization in several cyclic polyacetylene compounds has been calculated by the maximum overlap method, assuming planar and non-planar geometries of the molecules. In the planar configuration the hybrids describing the molecular skeleton deviate from the corresponding bond directions. We have a few “bent” bonds, but in contrast to the situation in small rings, here the deviation angles are negative, i.e., the hybrids point toward the inside of the ring. Non-planar structures in which acetylene groups are kept in a plane and CCH2 or CH2 groups are displaced out of the plane show less deviation from the bond directions of bent bonds. Furthermore, the deviation angles decrease with an increase in the out-of-plane displacement of methylene groups. Finally, when the angle of bending of the molecules approaches 50°, the deviation vanishes, predicting a puckered conformation for the molecules. Correlation between CC stretching vibration frequencies and the corresponding CC bond overlap is discussed. 相似文献
100.
Martinez-López S Morales-Noé A Pastor-Garcia A Morales-Rubio A de la Guardia M 《Journal of AOAC International》2005,88(4):1247-1254
The determination of 15 polycyclic aromatic hydrocarbons (PAHs) in olive oil samples has been improved in order to obtain a fast methodology with a low limit of detection through the combination of liquid-liquid extraction with acetonitrile and preparative gel permeation chromatography (GPC) prior to the injection of purified extracts into a C18 column. Acetonitrile-water was used as the mobile phase with a gradient from 50 to 95%, w/w, acetonitrile in 30 min. The oven temperature was maintained at 15 degrees C, and fluorometric detection was made at a fixed excitation wavelength of 264 nm and variable, optimal emission wavelength for each analyte ranging from 352 nm for 11-H-benzo(b)fluorene to 500 nm for indeno(1,2,3-cd)pyrene. Recovery for all the compounds studied varied from 75 to 111%, and limit of detection values from 0.05 ng/g for benzo(k)fluoranthene to 0.48 ng/g for indeno(1,2,3-cd)pyrene, corresponding to 0.09 ng/g benzo(a)pyrene. Results were compared with those obtained by liquid-liquid extraction followed by a cleanup on silica and a direct GPC treatment of oil samples diluted in dichloromethane, 2 other methodologies that are appropriate for quantifying PAHs in olive oils. However, the proposed method improves the determination limits, reduces the time of analysis, and provides a highly stable baseline for sample chromatograms. 相似文献