共查询到20条相似文献,搜索用时 515 毫秒
1.
Yuriy Tyvanchuk Volodymyr Svitlyk Yaroslav Kalychak 《Central European Journal of Chemistry》2012,10(2):354-359
The polycrystalline Ho4Ni11In20 was obtained by arc-melting of the elements. The subsequent high temperature procedure was used for single crystal growth. Crystal structure of the compound was investigated by X-ray single crystal method: U4Ni11Ga20 type, C 2/m, a = 22.4528(17), b = 4.2947(3), c = 16.5587(13) Å, β = 124.591(5)°, R1 = 0.0276, wR2 = 0.0493 for 1989 independent reflections with [I>2σ(I)].The structure is composed of three-dimensional network from Ni and In atoms in which Ho atoms fill distorted pentagonal channels. Open image in new window 相似文献
2.
The relative enthalpies of melts in the system KF - K2NbF7 were measured by drop-calorimetry at the temperatures 1058, 1140 and 1208 K as a function of composition. Heat capacities
of melted mixtures and enthalpies of mixing were determined using the experimental data. The molar heat capacity of melts
diverges slightly from additivity. The molar enthalpy of mixing of melts shows small negative deviation from ideality which
decreases with decreasing temperature. The thermal effect at mixing was assigned predominantly to association reactions producing
more complex fluoroniobate anions.
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3.
Tevhide Özkaya Abdulhadi Baykal Muhammet Sadaka Toprak 《Central European Journal of Chemistry》2008,6(3):465-469
Water-soluble Mn3O4 nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final
product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated
as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm.
FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn3O4 nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction
with neighboring particles.
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4.
Nadezhda Rangelova Lachezar Radev Sanchi Nenkova Isabel M. Miranda Salvado Maria H. Vas Fernandes Michael Herzog 《Central European Journal of Chemistry》2011,9(1):112-118
Methylcellulose (MC) / SiO2 organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized
by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO2. AFM depicts surface roughness which depends on the silica precursor and MC content.
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5.
6.
Radina Kralchevska Maria Milanova Petya Kovacheva Jovo Kolev Georgi Avdeev Dimitar Todorovsky 《Central European Journal of Chemistry》2011,9(6):1027-1038
Microcomposites consisting of TiO2 (or Ce-doped TiO2) and ThO2 (0.5–2% of the TiO2 mass) are produced by sol-gel synthesis of TiO2 in presence of ThO2. X-ray diffraction study reveals the effects of ThO2 (compared to the ThO2-free TiO2, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic
tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant.
The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent.
The highest photocatalytic activity is observed for TiO2 obtained at 550°C and containing 1% ThO2. The composite exhibits activity in dark, also. The presence of Ce4+ ions is not an obligatory requirement for the realization of the ThO2 effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors
responsible for the increased photocatalytic activity of TiO2.
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7.
Liquid-liquid partition is used in sample preparation and in countercurrent and liquid-liquid chromatographic separations.
Partition coefficients are widely used in toxicology, environmental, and analytical chemistry. The K
hn
determination procedure for the n-hexane/nitromethane system was optimized and partition coefficients for 99 ketones, esters and trimethylsilyl derivatives
of phenols, aliphatic and aromatic acids were determined. For 130 compounds, K
hn
values were predicted using mathematical relationships between K
hn
and other physicochemical and structural parameters.
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8.
Magnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30
min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a
pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure
of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption
temperature was somewhat higher than needed for practical application.
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9.
Diamond D5 is the name proposed by Diudea for hyper-diamonds having their rings mostly pentagonal. Within D5, in crystallographic terms: the mtn structure, known in clathrates of type II, several substructures can be defined. In the present work, the structural stability
of such intermediates/fragments appearing in the construction/destruction of D5 net was investigated using molecular dynamics simulation. Calculations were performed using an empirical many-body potential
energy function for hydrocarbons. It has been found that, at normal temperature, the hexagonal hyper-rings are more stable
while at higher temperature, the pentagonal ones are relatively more resistant against heat treatment.
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10.
Optimum conditions for synthesizing monoclinic and triclinic Mg2B2O5 compounds by high-temperature solid-state reactions were investigated. Mixtures composed of boric acid and magnesium oxide
at MgO:B2O3 mole ratios of 1:0.25, 1:0.5 and 1:1.5 were heated for 1 hour at temperatures between 600–1050°C and the formed phases were
identified by XRD analysis. Monoclinic Mg2B2O5 was formed by heating at 850°C for 4 hours together with minimum amounts of triclinic Mg2B2O5, while triclinic Mg2B2O5 was formed as a single phase at 1050°C for the same reaction time. The products obtained at optimum conditions were subjected
to a series of tests to determine their chemical compositions, particle size distributions, surface area values, IR spectra
and TG/DTA patterns.
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11.
Jinzhang Gao Yingying Zhang Jie Ren Ming Li Wu Yang 《Central European Journal of Chemistry》2010,8(3):602-606
A sensitive and convenient method for the determination of trace europium ions using an oscillating chemical reaction involving
Ce(IV) - KBrO3 - acetone - oxalic acid - H2SO4 was proposed. The results indicated that the changes in oscillating period (T) was linearly proportional to the negative
logarithmic concentration of Eu3+ (-log C) in the range of 1.41 × 10−8 ˜ 1.41 × 10−4 mol L−1 (r = 0.9982) with a detection limit of 1.04 × 10−9 mol L−1. The recoveries were limited to the range of 99.5% to 100.8%. Under the same conditions, other rare earth ions did not interfere
with the determination of Eu3+. In addition, a perturbation mechanism was also discussed briefly.
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12.
Ana-Maria Ungureanu Ovidiu Oprea Bogdan Stefan Vasile Corina Andronescu Georgeta Voicu Ioana Jitaru 《Central European Journal of Chemistry》2014,12(9):909-917
We successfully synthesized tin dioxide nanoparticles with polyhedral morphology via an ethylene glycol assisted sol-gel approach. The structural characteristics of three tin dioxide samples were investigated after being thermally treated at 400°C, 600°C and 800°C. X-ray diffraction (XRD) patterns clearly show the formation of single phase tin dioxide nanoparticles, with crystallite size of 6–20 nm, in good correlation with Fourier transform infrared (FTIR) spectra. Transmission electron microscopy (TEM) analysis confirms the formation of 6nm polyhedral nanoparticles for the 400°C sample. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectra suggest a high concentration of oxygen vacancies. The oxygen vacancy concentration increases with temperature, due to the combined action of the formation of VO and the energetic O compensation. X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of single phase tin dioxide and the presence of oxygen vacancies in good agreement with UV-VIS and PL data. 相似文献
13.
Ali Hassanzadeh Behrang Moazzez Hossein Haghgooie Mohsen Nasseri Mir Maqsood Golzan Hassan Sedghi 《Central European Journal of Chemistry》2008,6(4):651-656
A simple sol-gel process is proposed for synthesizing SnO2 nanopowders utilizing normal propanol and isopropanol mixture instead of just using normal alcohols such as ethanol, propanol
or butanol for Sol preparation. No surfactant was used in this Sol preparation process. The structure of sol is studied by
FT-IR-ATR technique. On altering propanol to isopropanol ratio, three different nanopowders were obtained. X-ray powder diffraction,
high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction pattern (SAED) and BET techniques
were used to characterize prepared powders. Results show that smaller grain size was obtained via altering alcohols ratio.
In addition, Merck commercial SnO2 powder was also used as a reference material for comparing purposes; because it has nanometer scale (ca. 60 nm). HRTEM images
show that obtained nanopowders were polycrystalline and their average diameters fall into the range of 6–80 nm. Finally, the
effect of alkoxide ligand size through sol-gel synthesis on product particle size is discussed.
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14.
Iwona E. Malka Tomasz Czujko Jerzy Bystrzycki Leszek R. Jaroszewicz 《Central European Journal of Chemistry》2011,9(4):701-705
The hydrogenation properties of magnesium hydride mechanically milled with iron fluorides (FeF2 and FeF3), were investigated by Temperature Programmed Desorption (TPD) and volumetric methods using a Sieverts-type apparatus, as
prepared upon dehydrogenation and finally upon subsequent hydrogenation. The activation energy of hydrogen desorption (Ea), calculated from the Kissinger formula using TPD measurements obtained with different heating rates, showed significant
decreases of Ea in comparison to that of milled MgH2 without any dopants. Moreover, the influence of these metal fluorides on the thermodynamics of the decomposition process
was also examined. In the case of the FeF2 dopant, rehydrogenation following desorption caused the complete decomposition of the iron fluoride to BCC iron and the formation
of a predominant MgH2 phase. In contrast to FeF2, the addition of FeF3 led to the formation of β-MgH2 as a major phase coexisting with Mg2FeH6 and MgF2 compounds. The presence of pure Fe in the MgH2+FeF2 composite, as opposed to MgH2+FeF3 containing Mg2FeH6 and MgF2, did not cause any significant influence on the sorption properties of MgH2. Moreover, the original material doped with FeF3 predominantly showed iron in the Mg2FeH6 compound, while the FeF2 dopant iron mostly showed the nearly pure BCC metallic phase
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15.
Renata Farkas Mercedesz Törincsi Pal Kolonits Jenö Fekete Oscar Jimenez Alonso Lajos Novak 《Central European Journal of Chemistry》2010,8(2):300-307
During the diazo-coupling reaction, nucleophilic displacement of a nitro group was also observed. This was the main reaction
(1→7) when the starting amine bore either a chlorine or methoxy group at the para position (1b–c). The newly prepared compounds (7) might serve as convenient building blocks in synthesis of some heterocycles.
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16.
Raúl Terrazas Reza Carlos A. Martínez Pérez Claudia A. Rodríguez González Humberto Monreal Romero Perla E. García Casillas 《Central European Journal of Chemistry》2010,8(5):1041-1046
In this work, the synthesis of magnetite nanoparticles by two variant chemical coprecipitation methods that involve reflux
and aging conditions was investigated. The influence of the synthesis conditions on particle size, morphology, magnetic properties
and protein adsorption were studied. The synthesized magnetite nanoparticles showed a spherical shape with an average particle
size directly influenced by the synthesis technique. Particles of average size 27 nm and 200 nm were obtained. When the coprecipitation
method was used without reflux and aging, the smallest particles were obtained. Magnetite nanoparticles obtained from both
methods exhibited a superparamagnetic behavior and their saturation magnetization was particle size dependent. Values of 67
and 78 emu g−1 were obtained for the 27 nm and 200 nm magnetite particles, respectively. The nanoparticles were coated with silica, aminosilane,
and silica-aminosilane shell. The influence of the coating on protein absorption was studied using Bovine Serum Albumin (BSA)
protein.
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17.
Marco A. S. de Abreu Edisson MorgadoJr. Paula M. Jardim Bojan A. Marinkovic 《Central European Journal of Chemistry》2012,10(4):1183-1198
Hydrogen titanate nanotubes (H-TTNT) were synthesized by the alkali hydrothermal method followed by proton exchange and then submitted either to thermal treatment or to acid hydrothermal reaction to generate TiO2-anatase nanocrystals of different morphologies. The samples were characterized by XRPD, TGA, sulfur analysis, N2 physisorption, UV-Vis spectroscopy and TEM. Their photocatalytic activities were determined by measuring the NO conversion in inert gas stream passed through the powder catalyst bed under UV radiation. Incomplete transformation into anatase resulted in nanomaterials with low activity due to coexistence with H-TTNT or TiO2-B precursors. Anatase specimens derived from H-TTNT aged in strong sulfuric acid media contained equidimensional nanoparticles, but retention of sulfate negatively affected their photocatalytic activity. Combining milder acidic pH with higher aging temperature, allowed synthesis of a sulfate free anatase with the same optical properties and specific surface area as the counterpart produced by calcination of H-TTNT at 550°C; however, the former exhibited truncated bi-pyramid nanocrystals and the other adopted the form of nanorods. This latter showed the highest photocatalytic activity for NO abatement, outperforming the benchmark photocatatyst TiO2-P25; this improved activity was tentatively ascribed to the maximization of high energy {001} facets in anatase nanorods formed during calcination of H-TTNT.
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18.
Gheorghe Roman 《Central European Journal of Chemistry》2012,10(5):1516-1526
Benzimidazole, benzimidazoles diversely substituted at position 2, and 5,6-dimethylbenzimidazole have been alkylated at N
1 with ketonic Mannich bases derived from acetophenones, acetylnaphthalenes, 2-acetylthiophene and 1-tetralone to afford a
series of novel 1-(3-oxopropyl)benzimidazoles. The reduction of these transamination products with NaBH4 in methanol produced the corresponding 1-(3-hydroxypropyl)benzimidazoles in excellent yields.
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19.
A novel hydroxyamino phosphane was synthesised through the reaction of 2-imidazolidinone with ClPPh2 and subsequently reaction
of the resulting bisphosphino derivative with the Grignard reagent BrMgC5H11. The interaction of the pentyl substituent with one of the two phosphino groups and the structure in solution is shown by
multinuclear NMR-spectroscopy..
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20.
Nikolai N. Kolesnikov Elena B. Borisenko Dmitrii N. Borisenko Boris A. Gnesin 《Central European Journal of Chemistry》2011,9(4):619-623
In the present study newly produced semiconductor ceramic nanopowder materials made of CdTe and Cd1−xZnxTe (CZT) are considered. Common features and differences in microstructures, phase transformations, grain growth and properties
of the ceramic materials of the binary and ternary compositions are studied.
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