排序方式: 共有76条查询结果,搜索用时 375 毫秒
31.
Recep B?y?k 《Physica B: Condensed Matter》2009,404(20):3483-3486
VO2+ doped l-alanine (C3H7NO2) single crystals and powders are examined by electron paramagnetic resonance (EPR) and optical absorption spectroscopy. Three magnetically different sites are resolved from angular variations of l-alanine single crystal EPR spectra. In some specific orientations each VO2+ line splits into three superhyperfine lines with intensities of 1:2:1 and maximum splitting value of 2.23 mT. The local symmetries of VO2+ complex sites are nearly axial. The optical absorption spectra show three bands. Spin Hamiltonian parameters are measured and molecular orbital coefficients are calculated by correlating EPR and optical absorption data for the central vanadyl ion. 相似文献
32.
Sebahattin Ikikardes Recep Sahin I. Naci Cangul 《Bulletin of the Brazilian Mathematical Society》2009,40(4):479-494
In this paper, first, we determine the quotient groups of the Hecke groups H(λ
q
), where q ≥ 7 is prime, by their principal congruence subgroups H
p
(λ
q
) oflevel p, where p is also prime. We deal with the case of q = 7 separately, because of its close relation with the Hurwitz groups. Then, using the obtained results, we find the principal
congruence subgroups of the extended Hecke groups $
\overline H
$
\overline H
(λ
q
) for q ≥ 5 prime. Finally, we show that some of the quotient groups of the Hecke group H(λ
q
) and the extended Hecke group $
\overline H
$
\overline H
(λ
q
), q ≥ 5 prime, by their principal congruence subgroups H
p
(λ
q
) are M*-groups. 相似文献
33.
Onur Buyukcakir Recep Yuksel Yi Jiang Sun Hwa Lee Won Kyung Seong Xiong Chen Rodney S. Ruoff 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):882-886
The development of different classes of porous polymers by linking organic molecules using new chemistries still remains a great challenge. Herein, we introduce for the first time the synthesis of covalent quinazoline networks (CQNs) using an ionothermal synthesis protocol. Zinc chloride (ZnCl2) was used as the solvent and catalyst for the condensation of aromatic ortho‐aminonitriles to produce tricycloquinazoline linkages. The resulting CQNs show a high porosity with a surface area up to 1870 m2 g?1. Varying the temperature and the amount of catalyst enables us to control the surface area as well as the pore size distribution of the CQNs. Furthermore, their high nitrogen content and significant microporosity make them a promising CO2 adsorbent with a CO2 uptake capacity of 7.16 mmol g?1 (31.5 wt %) at 273 K and 1 bar. Because of their exceptional CO2 sorption properties, they are promising candidates as an adsorbent for the selective capture of CO2 from flue gas. 相似文献
34.
In this research, the herbaceous peat collected from Gavurgolu peatlands, one of the biggest Turkish peatlands, was utilized as an adsorbent for the removal of copper (II) ions from aqueous solution. Adsorption experiments were conducted under various conditions, i.e., initial concentration, temperature, and pH. While the amount of Cu (II) adsorbed on the peat increased with increasing concentration of Cu (II) ions, it was not markedly affected by temperature and pH. Percentage removal was higher at lower concentration. For example, the maximum percentage removal of Cu (II) ions for initial concentration of 3 x 10(-4) M was 97.04% at 21 degrees C and pH 5.5. The adsorption capacity (Q(0)) of the peat was 4.84 mgg(-1) from Langmuir adsorption isotherm for the concentration range of 3 x 10(-4)-6 x 10(-4) M at 21 degrees C and pH 5.5. The equilibrium time of adsorption of Cu (II) ions was 150 min and independent of concentration and temperature. The amount of Cu (II) adsorbed at equilibrium time did not considerably change with temperature and pH. It was also determined that adsorption isotherm followed both Freundlich and Langmuir. Uptake mechanism of Cu (II) ions by the peat occurs via cation exchange (especially by means of Ca(2+) and Mg(2+)) as well as copper/peat complexation. Adsorption kinetic was consistent with the pseudo-second-order model. 相似文献
35.
Recep Isci Dilara Gunturkun Ahsen Sare Yalin Turan Ozturk 《Journal of polymer science. Part A, Polymer chemistry》2021,59(1):117-123
Two novel copolymers of 4-thieno[3,2-b]thiophen-3-ylbenzonitrile (TT-CN), possessing electron withdrawing cyano moiety, with anthracene (P1) and biphenyl (P2) were prepared via Suzuki coupling. Optic, electronic, and thermal properties of the copolymers were investigated through UV–Vis spectroscopy, cyclic voltammetry, gel permeation chromatography, and thermal gravimetric analysis. The polymers with anthracene and biphenyl had electronic band gaps of 2.01 and 1.90 eV, respectively. Both polymers demonstrated excellent large Stokes shifts of 101 (anthracene) and 105 nm (biphenyl) as well as very good thermal properties. As they had good optical, electronic, and thermal properties, they are promising candidates for electronic applications. 相似文献
36.
Dr. Recep Kas Onagie Ayemoba Nienke J. Firet Joost Middelkoop Prof. Wilson A. Smith Prof. Angel Cuesta 《Chemphyschem》2019,20(22):2904-2925
The field of electrochemical CO2 conversion is undergoing significant growth in terms of the number of publications and worldwide research groups involved. Despite improvements of the catalytic performance, the complex reaction mechanisms and solution chemistry of CO2 have resulted in a considerable amount of discrepancies between theoretical and experimental studies. A clear identification of the reaction mechanism and the catalytic sites are of key importance in order to allow for a qualitative breakthrough and, from an experimental perspective, calls for the use of in-situ or operando spectroscopic techniques. In-situ infrared spectroscopy can provide information on the nature of intermediate species and products in real time and, in some cases, with relatively high time resolution. In this contribution, we review key theoretical aspects of infrared reflection spectroscopy, followed by considerations of practical implementation. Finally, recent applications to the electrocatalytic reduction of CO2 are reviewed, including challenges associated with the detection of reaction intermediates. 相似文献
37.
Recep Akkaya 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(2):771-775
In this research, a new composite, poly (hydroxyethylmethacrylate-hydroxyapatite) [P(HEMA-Hap)], was synthesized and its adsorptive
features for natural radionuclides (TI+, Ra2+, Bi3+and Ac3+ in a leaching solution) were investigated at differing initial pH, concentration and temperature ranges. The natural radionuclides
were counted by gamma spectrometer using a type NAI (Tl) detector. The adsorption data obtained were well represented by Langmuir
and Freundlich type isotherms. The magnitude of determined monolayer adsorption capacities (X
L) for the adsorbed radionuclides were TI+ = Ac3+ > Ra2+ = Bi3+. These results demonstrated that P(HEMA-Hap) had high affinity to the natural radionuclide. The thermodynamic parameters
indicated that the adsorption mechanisms were spontaneous (ΔG < 0) in terms of adsorption free enthalpy, and changes in the enthalpy and entropy values showed that the overall adsorption
process was endothermic (ΔH > 0), thus increasing entropy (ΔS > 0). 相似文献
38.
Hayriye Aral Tarık Aral K. Serdar Çelik Berrin Ziyadanoğulları Recep Ziyadanoğulları 《Chromatographia》2014,77(11-12):771-781
Retention behaviors of an amide-embedded silica base stationary phase, which was recently developed by our group, were studied by using six different groups of small polar compounds including phenolic compounds, substituted anilines, chlorinated herbicides, Sudan dyes and some nucleotides and nucleosides in HPLC. The chromatographic behaviors of the prepared stationary phase for these analytes were compared with those of a commercially available reversed-phase column ACE C18 under same conditions. Among the six groups of analytes studied, the amide-silica stationary phase showed enhanced selectivity towards phenolic compounds, substituted anilines, Sudan dyes and herbicides under reversed-phase conditions and satisfactory selectivity towards nucleosides and nucleotides which could not be separated with ACE C18 column under HILIC conditions. Experimental data provided some evidence that functional groups on the stationary phases might have certain degrees of influence on selectivity possibly through secondary interactions with the model compounds. The retentions of the moderately polar compounds such as phenolic acids, anilines and herbicides on the stationary phase are higher than highly polar compounds such as nucleotides and nucleosides due to both the hydrophobic and hydrophilic interactions between the stationary phase and analytes. The quantitative determination of Sudan dyes (I, II, III, and IV) in red chilli peppers was performed. Many red chilli peppers were screened and three of them contained Sudans dyes. 相似文献
39.
Gary S. Groenewold Gary L. Gresham Recep Avci Muhammedin Deliorman 《Surface and interface analysis : SIA》2009,41(3):244-250
The presence of organic compounds as surface contaminants on particles can provide valuable data about the particles environment, but identification can be analytically challenging. This is true particularly for compounds that have the potential for strong surface binding, such as compounds capable of multidentate attachment. Direct analysis using time‐of‐flight secondary ion mass spectrometry was evaluated for characterization of soil particles contaminated with low concentrations of two bidentate organophosphoryl compounds, diphenyl‐N,N‐di‐n‐butylcarbamoylmethylphosphine oxide and tetraphenylmethylene diphosphine dioxide. Molecular ions were formed by cationization with H+ and alkali elements Na+ and K+ that are indigenous to the particle surface chemistry. Spectra generated from a contaminated calcareous soil were dominated by K+‐containing ions, whereas spectra from a sandy loam had more abundant Na+‐species. Cation‐bound dimers were also formed which favored incorporation of K+, and a unique aluminosilicate‐phosphoryl conjugate cation was also formed when the diphosphoryl ligand was present on the surface. The phosphoryl ligands also underwent fragmentation reactions, the course of which varied depending on the cation that was bound. Minimum detectable surface concentrations were evaluated and were in the 0.04–0.2 monolayer range, depending on the compound and soil particle matrix they was bound to. The ion signature was detected on soil particle surfaces for time periods exceeding six months, suggesting that the characterization approach could be used for environmental exposure history at times well beyond initial exposure. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
40.
Single crystal of gammairradiated 2,6-di-tert-butyl-4-methylphenol (BHT) was investigated using an electron paramagnetic resonance (EPR) technique at different orientations in the magnetic field at room temperatures. Taking into consideration the chemical structure and the experimental spectra of the irradiated single crystal of BHT, we assumed that one phenoxyltype paramagnetic species was produced having an unpaired electron localized at the methyl fragment side of the phenyl ring. Depending on this assumption, one possible radical was modeled using the B3LYP/6-311+G(d) level of density-functional theory. EPR parameters were calculated for these modeled radical using the B3LYP/TZVP and B3LYP/EPR-III level. The averaged value of isotropic hydrogen hyperfine coupling constants of rotating methyl functional group of phenoxyl radical is calculated for the first time. Theoretically calculated values of the modeled radical are in reasonably good agreement with the experimental data determined from the spectra (differences in averaged coupling constant values smaller than 5%, and differences in isotropic g values fall into 1 ppt). 相似文献