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排序方式: 共有370条查询结果,搜索用时 31 毫秒
81.
In this work, a green approach is reported for efficient synthesis of biologically active tetrazole and pyranopyrazole derivatives in the presence of Cu-Cytosine@MCM-41 and Ni-Cytosine@MCM-41 (copper (II) and nickel (II) catalyst on the modified MCM-41 using cytosine). The synthesis of tetrazoles and pyranopyrazoles in the presence of these catalysts was performed in green solvents such as water or poly (ethylene glycol) (PEG). All products were obtained in high TOF (turnover frequency) numbers in the presence of these catalysts, which indicate the high efficiency of these catalysts in the synthesis of tetrazole and pyranopyrazole derivatives. The prepared catalysts were characterized by various techniques such as BET, TGA, XRD, FT-IR, SEM, EDS, WDX, TEM, and AAS. Mesoporous structure of these catalysts was confirmed by nitrogen adsorption–desorption isotherms. These catalysts can be recovered and reused for several runs without significant change in their catalytic activity or metal capacity. The recovered catalysts have been characterized by XRD, SEM, EDS, WDX, FT-IR and AAS techniques, by which their heterogeneous nature has been confirmed. 相似文献
82.
83.
Production of fibroin nanopowder through electrospraying 总被引:1,自引:0,他引:1
Fibroin is a biomaterial and in the powder form, has found applications such as food and cosmetic additive as well as drug
delivery. Various methods have been employed to produce fibroin powder with different particle size range. In this study,
a novel and original application of electrospraying technique capable of producing fibroin nanopowder is presented. Our technique
is based on electrospraying of dilute fibroin solution in formic acid. Moreover, the effect of variables in electrospraying,
namely, concentration of fibroin solution, voltage, feed rate, and needle–collector distance, on average particle size of
fibroin nanopowder has been studied. The result of this study showed that electrospraying is capable of producing fibroin
nanopowder with average particle size as low as 80 nm. In fact in comparison to other methods reported in the literature,
electrospraying alongside with the precipitation method produce fibroin nanopowder with the lowest particle size. However,
nanopowder obtained through electrospraying technique enjoys a more uniform spherical shape and size. As far as the variables
are concerned, it was ascertained that lower concentrations, lower feed rates and longer needle–collector distances lead to
a decrease in the average particle size of fibroin nanopowder. Increasing voltage up to 20 kV decreases the particle size;
but with higher voltages the average particle size increases. FT-IR and XRD studies showed that the fibroin nanopowder has
a β-sheets structure, similar to fibroin filaments but with a lower crystallinity index. 相似文献
84.
A new high efficient and green protocol for the preparation of dihydropyrimido[4,5‐b]quinolinetrione derivatives using magnetically solid acid catalyst was presented. High performance solid acid catalyst was prepared through a three‐step reaction. Firstly, CoFe2O4 nano particles were synthesized using co‐precipitation method. In second step, CoFe2O4 nano particles were coated with SiO2 shell through treatment with tetraethyl orthosilicate (CoFe2O4@SiO2). Finaly, CoFe2O4@SiO2 was modified with polyphosphoric acid (CoFe2O4@SiO2/PPA) in a simple manner. Green reusable catalyst was characterized in details using FTIR, VSM, TEM, FESEM, EDX and used as catalyst for the synthesis of dihydropyrimido[4,5‐b]quinolinetrione derivatives. Reaction was performed under ultrasonic irradiation as green, effective and mild conditions and products were achieved in high to excellent yields. Green and eco‐friendly conditions, short reaction times with high yield of products in addition to easy workup are some merits of presented method. 相似文献
85.
Afshin Moradi 《Photonics and Nanostructures》2013,11(1):85-88
Propagation of surface plasmon–polariton modes in metallic single-walled carbon nanotubes is investigated within the framework of the classical electrodynamics. Electronic excitations on the nanotube's surface are modeled by an infinitesimally thin layer of free-electron gas which is described by means of the linearized hydrodynamic theory. General expression of surface modes dispersion is obtained by solving Maxwell and hydrodynamic equations with appropriate boundary conditions. It is shown that the system generally disallows the separation of the transverse electric (TE) modes and transverse magnetic (TM) modes, except for the case of modes with no angular dependence. 相似文献
86.
Hydrogen peroxide/MoO3, as an efficient and clean oxidizing system was used to afford diasteroselective oxidative cyclization of bisnaphthols to spirans in ethanol at 60 °C with high yields. Bisnaphthols were prepared by the reaction of a series of aldehydes and 2-naphthol in the presence of a catalytic amount of H3[P(Mo3O10)4].nH2O (HPa) in refluxing dichloromethane. 相似文献
87.
Arabali Vahid Karimi-Maleh Hassan Beitollahi Hadi Moradi Reza Ebrahimi Mahmoud Ahmar Hamid 《Ionics》2015,21(4):1153-1161
Ionics - In this study, a carbon paste electrode (CPE) was chemically modified with Pt/carbon nanotubes (CNTs) nanocomposite and 8,9-dihydroxy-7-methyl-12H-benzothiazolo [2,3-b] quinazolin-12-one... 相似文献
88.
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90.
Somayeh Moradi 《代数通讯》2020,48(6):2699-2712
AbstractThe present work is concerned with characterizing some algebraic invariants of edge ideals of hypergraphs. To this aim, first, we introduce some kinds of combinatorial invariants similar to matching numbers for hypergraphs. Then we compare them to each other and to previously existing ones. These invariants are used for characterizing or bounding some algebraic invariants of edge ideals of hypergraphs such as graded Betti numbers, projective dimension and Castelnouvo–Mumford regularity.Communicated by Jason P. Bell 相似文献