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991.
《Helvetica chimica acta》2017,100(9)
The synthesis and characterization of chitosan‐silica sulfate nano hybrid (CSSNH ) as a novel and efficient heterogeneous nano catalyst involving acid‐base bifunctional activity is described. The catalytic potency and activity of this eco‐friendly catalyst was investigated in regioselective ring opening of epoxides with carboxylic acids to access structurally diverse 1,2‐diol mono‐esters in good to excellent yields. CSSNH catalyst was characterized using different microscopic and spectroscopic techniques encompassing scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, N2 adsorption isotherm, and Fourier transform infrared spectroscopy. The green nature, cheapness, efficiency, ease of preparation, handling and reusability of this new catalyst makes this catalyst to be useful for green industrial processes. 相似文献
992.
Austrian medieval silver/copper coins were investigated at their surfaces by energy dispersive X-ray fluorescence analysis
(EDXRF) and at the cross-sections by X-ray microanalysis in the scanning electron microscope (SEM/EDX) in order to estimate
the error occurring when corroded objects of art and archaeology are analyzed on the surface by non-destructive methods. Additionally,
Ag/Cu-standards were treated in diluted sulphuric acid and the depletion of copper on the surface was measured by EDXRF. By
calculating the ratio of the Ag-K/Ag-L intensity the process of blanching could be studied. 相似文献
993.
César O. Avellaneda Karim Dahmouche Luis O.S. Bulhões Agnieszka Pawlicka 《Journal of Sol-Gel Science and Technology》2000,19(1-3):447-451
Electrochemical lithium intercalation in thin films of CeO2-TiO2 and WO3, prepared by the sol-gel technique was investigated with cyclic voltammetry and spectroelectrochemical techniques in propylene carbonate solutions. A solid state system having the configuration WO3/Ormolyte/CeO2-TiO2 has been assembled. The solid electrolyte, an organically modified electrolyte (ormolyte), was prepared with different [O]/[Li] ratios. The transmittance variation of this system during a potentiostatic step from –0.7 V to 0.8 V was about 35% at 550 nm. 相似文献
994.
纳米复合固体超强酸SO42-/CoFe2O4的制备和表征 总被引:27,自引:0,他引:27
采用纳米化学制备技术合成了新型的纳米复合团体超强酸催化剂SO42-/CoFe2O4。用XRD、TEM、XPS、红
外光谱和比表面测定等技术研究了该催化剂的结构形态,结果表明:所研制的SO42-/CoFe2O4催化剂为晶态纳
米粒子(< 50nm),比表面积很大(157m2· g-1),SO42-与氧化物的金属离子呈无机双齿螯合状配位化合物的结
合形式。以乙酸乙酯合成为模型反应考察了该催化剂的催化活性,比较了酸性和酸强度,推断出该催化剂的酸
强度H0<-14.5。 相似文献
995.
Daisuke Sawai Mika Miyamoto Tetsuo Kanamoto Masayoshi Ito 《Journal of Polymer Science.Polymer Physics》2000,38(19):2571-2579
No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution‐cast films or their drawn products, generally shows no small‐angle X‐ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm−1 ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (ta) and the temperature (Ta). Depending on ta, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (ta = 0.5–3 min, depending on Ta), rapidly increased in stage II (ta = 0.5–8 min), and stayed at a constant value characteristic for each Ta at yet longer ta's in stage III. The lamellar thickness characteristic for Ta increased rapidly with increasing Ta at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (Tm = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the Tm is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide‐angle X‐ray diffraction. The structural changes associated with annealing are also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2571–2579, 2000 相似文献
996.
通过XRD,BET,In-situ XPS等表征技术对Cu/ZnO基甲醇裂解制氢催化剂进行 了详细的研究。XRD结果表明,Cu-Zn合金的生成是Cu/ZnO基催化剂在反应初期快速 失活的主要原因;XRD,BET和N_2O滴定实验结果表明,Ni助剂可能是通过提高 Cu~0活性物种的分散度并维持Cu~0活性物种在催化反应过程中的稳定性而使 Cu/Zn/Ni催化剂的活性及稳定性大幅度提高。In-situ XPS结果表明,Ni助剂的加 入可以诱导Cu/Zn/Ni催化剂表面在甲醇裂解反应过程中出现Cu~+,从而由 Cu~0/Cu~+共同构成催化剂的活性中心,并最终导致Cu/Zn/Ni催化剂的高活性。 相似文献
997.
用量子化学中的密度泛函DFT方法,在B3LYP/6-311G~*水平上研究了不饱和类 卡宾H_2C=CLiF的结构。结果表明,只有1种平衡结构是稳定的。对稳定的平衡结构 ,找到了分子内氢迁移反应的过渡态,并计算了不同温度下不饱和类卡宾 H_2C=CLiF的平均寿命τ,在200 K时,τ = 7.9 d,在300 K仅为τ = 2.4 s。 相似文献
998.
Bruch’s membrane is a layer composed of collagen fibers located just beneath the retina. This study validates a strategy used
to map the morphological and adhesion characteristics of collagen fibers in Bruch’s membrane. Atomic force microscopy tips
were functionalized with different chemical groups and used to map the hydrophilic and hydrophobic regions on the surface
of the eye tissue. The largest adhesion forces were observed when tips functionalized with NH2 groups were used. The trend in the adhesion forces was rationalized based on the distribution of different functional groups
in the triple-helical structure of the collagen fibers. The results of this study can be used to design more effective strategies
to treat eye diseases such as age-related macular degeneration. 相似文献
999.
Results of a quantum-chemical study of the molecular structure of dimerization products of saturated 1,3-butadiene and hexafluoro-1,3-butadiene (tricyclo[3.3.0.02.6]octane, dodecafluorotricyclo[4.2.0.02.5]octane (I), and dodecafluorotricyclo[3.3.0.02.6]octane (II)) are presented. The calculated symmetry of the molecule of I in vacuum (C 2) differs from its symmetry in the single crystal (C b , XRD). The most stable of dimers (II) contains C-C bonds with a length of up to 1.573 Å and a four-atom cycle with angles of 82.3°. 相似文献
1000.
Kristina Starčević Marijana Hranjec Dejana Carić Grace Karminski-Zamola 《Monatshefte für Chemie / Chemical Monthly》2008,139(8):975-983
A series of novel substituted derivatives related to furyl-phenyl-acrylates and naphthofurans, was synthesized and characterized
by UV/Vis and fluorescence spectroscopy. Acyclic compounds can undergo photochemical dehydrocyclization by visible light irradiation
in order to obtain their cyclic derivatives. The interactions of the prepared compounds with calf thymus DNA was investigated by means of electronic absorption and fluorescence spectra. It is intriguing that addition of ct-DNA induced a fluorescence increase of acyclic derivatives, exactly the opposite of the strong fluorescence quenching observed
for cyclic derivatives 10 and 12. Compound 11 showed decreasing fluorescence intensity for lower concentrations of ct-DNA, while increasing of fluorescence is observed for high excess of added ct-DNA.
Correspondence: Grace Karminski-Zamola, Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University
of Zagreb, Marulićev trg 20, HR-10000 Zagreb, Croatia. 相似文献