排序方式: 共有159条查询结果,搜索用时 203 毫秒
151.
Nanocellulose (NC) materials have some unique properties, which make them attractive as organic or inorganic supports for catalytic applications. Nanocatalysts with diameters of less than 100 nm are difficult to separate from the reaction mixture, therefore, magnetic nanoparticles (MNPs) were used as catalysts to overcome this problem. Fe3O4@NCs/BF0.2 as a green, bio‐based, eco‐friendly, and recyclable catalyst was synthesized and characterized using fourier‐transform infrared spectroscopy (FT‐IR), vibrating sample magnetometer (VSM), X‐ray diffraction (XRD), X‐ray fluorescence (XRF), Brunauer–Emmett–Teller (BET), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA) techniques. Fe3O4@NCs/BF0.2 was employed for the synthesis of 2,3‐dihydro‐1H‐perimidine derivatives via a reaction of 1,8‐diaminonaphthalene with various aldehydes at room temperature under solvent‐free conditions. The present procedure offers several advantages including a short reaction time, excellent yields, easy separation of catalyst, and environmental friendliness. 相似文献
152.
Sedigheh Akrami Bahador Karami Mahnaz Farahi 《Journal of heterocyclic chemistry》2020,57(6):2446-2454
A novel, eco-friendly and fast route has been developed for the synthesis of new and known triazolo[1,5-a]pyrimidin fused chromone derivatives via a one pot three-component reaction of 3-amino-1,2,4-triazoles, aromatic aldehydes and 4-hydroxycoumarin in aqueous medium at room temperature. These reactions are catalyzed by MCM-41-HWO4 as a safe and recyclable mesoporous solid acid. It combines successfully the synergistic effect of green chemistry with nanocatalysis. The yields are high and the products were characterized by 1H NMR, 13CNMR spectra and elemental analysis. 相似文献
153.
The centrality dependences of the experimental rapidity as well as transversemomentumversus rapidity spectra of negative pions were analyzed quantitatively in 12C+12C and 12C+181Ta collisions at 4.2 GeV/c per nucleon using fitting the pion spectra by Gaussian distribution function. The experimental results were compared systematically with the predictions of the Quark-Gluon-String Model (QGSM) adapted to intermediate energies. 相似文献
154.
Dynamic three-phase hollow fiber liquid-liquid-liquid microextraction (HF-LLLME) based on two immiscible organic solvents, with automated movement of organic acceptor phase to facilitate mass transfer was introduced for the first time. Polycyclic aromatic hydrocarbons were used as model compounds and extracted from water and soil samples. The extraction involved filling an 8 cm length of hollow fiber with 25 μL of organic acceptor solvent using a microsyringe, followed by impregnation of the pores in the fiber wall with n-dodecane. The fiber was then immersed in 20 mL of aqueous sample solution. During extraction, the organic acceptor phase was repeatedly moved in the lumen of the hollow fiber by movement of the syringe plunger controlled by programmable syringe pump. Following this microextraction, 2 μL of organic acceptor phase was injected into gas chromatography-flame ionization detector. This new technique provided up to 554-fold preconcentration of the analytes under the optimized conditions. Good repeatabilities (with RSDs ≤8.4%) were obtained. Detection limits were in the range of 0.2-0.5 μg/L. The utilization of the proposed method for extraction of the polycyclic aromatic hydrocarbons from different real samples (such as water and soil samples) also gave good precision and recovery. 相似文献
155.
Yadollah Yamini Mahnaz Ghambarian Ali Esrafili Najmeh Yazdanfar Morteza Moradi 《International journal of environmental analytical chemistry》2013,93(13):1493-1505
The objective of the present study was to develop and validate a rapid, highly sensitive, and reliable extraction method to determine acrylamide in water samples. The method was based on the derivatisation of the acrylamide in the presence of KBr, HBr and saturated Br2 solution into 2,3-dibromopropionamide and dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–electron capture detection (GC–ECD) of the analyte. Different parameters that affect the DLLME process such as types and volumes of disperser solvent, ionic strength of aqueous solution and extraction time were investigated and optimised. Under optimal conditions, excellent linearity was obtained between concentration of acrylamide and the response of ECD with correlation of determination (R2) of 0.9999. The precision of the method, which was determined by calculating the relative standard deviations (RSD) of the at least three replicate measurements, was 3.6%. The method presented in this study is sensitive enough for the determination of acrylamide in different water samples with the limit of detection (LOD) value of 1?ng?L?1. The mean percentage recoveries exceeded 91% for all of spiking levels in the real water samples. The results obtained from DLLME method are validated by EPA method 8032A. 相似文献
156.
Bahador Karami Zahra Haghighijou Mahnaz Farahi Saeed Khodabakhshi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):754-761
Abstract An efficient, simple, and environmentally benign procedure for the one-pot synthesis of 3,4-dihydropyrimidine-2-(1H) thione derivatives that entails the three-component condensation of appropriate aryl aldehydes, β-dicarbonyls, and thiourea in the presence of catalytic amount of tungstate sulfuric acid under solvent-free conditions was reported. This method has many advantages including excellent yields, short reaction time, and simple work-up procedure. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: 1H, 13C NMR and Mass Spectra for 5b, 5g, 5j, 5i, 5l (S2-S16). Additional Characterization Data (S17-18). 相似文献
157.
Saeed Nojavan Zeinab Tahmasebi Tina Bidarmanesh Hamideh Behdad Mahnaz Nasiri‐Aghdam Sozan Mansori Ahmad Pourahadi 《Journal of separation science》2013,36(19):3256-3263
An electromembrane extraction procedure coupled with HPLC and visible detection was applied for the extraction of three textile azo dyes as organic salts. The extraction parameters such as extraction time, applied voltage, pH range, and concentration of salt added were optimized. A driving force of 60 V was applied to extract the analytes through 2‐nitrophenyl octyl ether, used as the supported liquid membrane, into a neutral aqueous solution. This method required 20 min extraction time from a neutral sample solution. The proposed microextraction technique provided good linearity with correlation coefficients from 0.996 to 0.998 over a concentration range of 1.0–1000.0 ng/mL. The LODs of dyes were 0.30–0.75 ng/mL, while the reproducibility ranged from 6.7 to 12.9% (n = 6). Also, enrichment factors of 96–162 that corresponded to the recoveries ranging from 48 to 81% were achieved. Finally, the application of this new method was demonstrated on wastewater samples and some plants grown in contaminated environments. Excellent selectivity was obtained as no interfering peaks were detected. 相似文献
158.
ICl–SiO2 as a new reactive system was prepared by the treatment of iodine monochloride with an activated silica gel in chloroform. ICl–SiO2 in a heterogeneous system efficiently oxidized urazoles to the corresponding triazolinediones under mild conditions in high yields at room temperature. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:389–393, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20444 相似文献
159.
Herein, a novel polyaniline-co-polyindole functionalized magnetic porous carbon derived from MIL-53(Fe) was prepared and employed as an excellent nano-adsorbent to preconcentrate trace amounts of nitro-phenols in water and wastewater samples. Briefly, magnetic MIL-53(Fe) was synthesized by the addition of magnetite nanoparticles, terephthalic acid, and FeCl3 to the reaction medium. The magnetic MIL-53(Fe) was pyrolyzed under nitrogen protection to obtain a magnetic porous carbon nanocomposite, and finally, the nanomaterial was functionalized with polyaniline-co-polyindole via oxidation polymerization. The obtained nano-adsorbent was characterized via X-ray diffraction, Fourier-transform infrared spectroscopy, vibrating sample magnetometry, and transmission and scanning electron microscopies. After that, the fabricated nano-material was utilized as an excellent nano-adsorbent for the preconcentration of trace nitro-phenols (2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol) in environmental water, and wastewater samples. The detection limits were obtained from 0.1 to 0.15 μg/L after performing the optimization process. The new method was in the range of 0.4–300 μg/L. The proposed method exhibited a good precision from 3.2% to 9.6% for within-day assay, and 5.2%–13.2% for between-day assay at three concentration levels (1, 50, and 250 μg/L). Eventually, this method was utilized to preconcentrate/determine the target analytes in three water, and wastewater samples, satisfactory (relative standard deviations, 5.4%–9.3%; relative recovery, 88%–109%). 相似文献