Synthesis of ultrafine SiC from rice hulls (husks): A plasma process

Heat-treated rice hulls have been used as precursor material for synthesis of ultrafne SiC in a RF plasma reactor. Rice hulls containing finely distributed silica and active carbon act as a source for SiC formation. The plasma-synthesized powder contained ultrafnc -SiC with excess carbon and some unreacted silica. Post-treatment processes such as oxidation and acid (HF) treatment appear to be effective in removing the excess carbon and silica.     

Thermodynamical modeling of silicon carbide synthesis in thermal plasma

The synthesis process of solid SiC in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixtures involving silicon and carbon in the presence of argon and hydrogen at various silicon/carbon amounts and at two different total pressures in the system, in the temperature range between 1000 and 6000 K. Use is made of the fact that a thermal plasma, by definition, is a plasma in (local) thermodynamical equilibrium, which makes possible the theoretical determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds present in the system. From the calculated compositions of the investigated gas systems the temperature-composition phase diagrams were obtained. Using these data the temperature zones with saturated and/or oversaturated vapour of SiC as well as of Si and C were determined and the possibility of the formation of SiC in the solid state via different reaction routes was analyzed This revised version was published online in July 2006 with corrections to the Cover Date.     

微波合成SrTiO~3的反应机理

研究了微波合成SrTiO~3的合成过程,XRD及电子探针的结果表明这一反应过程是由扩散控制,微波场的存在使扩散过程明显增强,存在有Sr和Ti元素的相互扩散,与常规合成有较大不同。从微波合成和常规合成反应产物的组成及显微结构等方面说明微波合成与常规合成具有不同的反应机理,微波合成在反应过程中没有出现其他的中间相,反应动力学计算表明反应过程的动力学符合Carter方程,反应的活化能为129kJ/mol,约为常规合成的1/2～1/3。     

Studies on the Preparation and Catalyticproperties of Fe-C-Mn Ultrafine particle Catalyst in F-T synthesis

IntroductionThepurposeofthisstudyistosearchforabettercatalystforthesynthesisofolefinsfromCOandH2.SomeresearcheshaveindicatedthatFe-Mnoxideandlron-carbonidecatalystscou1dimproveitsselectivitytoo1efins[I'2].BasedontheFe/Cultrafineparticle(UFP)obtainedbymeansoflaserpyrolysismethod,thispaperreportsthepreparationofaseriesofFe-C-MnUFPcatalysts.ExperimentallCatalystpreparationHighlydispersedamorphousFe/CUFPwaspreparedbymeansoflaserpy-rolysistechnique['1andthenwashedanddried.Certainamountsof…     

Green synthesis of ZnO nanoparticles using aqueous Brassica oleracea L. var. italica and the photocatalytic activity

ABSTRACT

This study reports the synthesis of ZnO nanoparticles using the aqueous solution of broccoli extract. The nanoparticles, represented as broc-ZnO (with broccoli extract) and nb-ZnO (without broccoli extract), were obtained after calcination. The nanoparticles were characterized using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier Transform infra-red (FTIR), Energy dispersive spectroscopy (EDX), UV-visible spectroscopy (UV) and Photoluminescence (PL). Hexagonal phases were identified for both nanoparticles, while average crystallite sizes of 14 and 17?nm for broc-ZnO and nb-ZnO, respectively, were obtained. UV studies indicated the bandgap of the broc-ZnO and nb-ZnO as 4.09 and 3.87?eV, respectively. A plausible mechanism for the synthesis of the nanoparticles was suggested. The photocatalytic efficiency of broc-ZnO, obtained via the broccoli extract, was evaluated by studying its photo-enhanced catalytic activity against methylene blue (MB) and phenol red (PR), under UV light irradiation and 74% and 71% degradation efficiency of the successive dyes were achieved.     

Solid-phase synthesis of benzothiazoles using an alkoxyamine linker

An alkoxyamine linker was applied for the solid-phase synthesis of benzothiazoles. The substrate was anchored by aldoxime linkage and products were cleaved from the solid-support by aldoxime-imine exchange coupled with air-oxidation under the weakly acidic conditions. The tether is highly robust under Mitsunobu reaction, nucleophilic substitution reaction, and Pd-catalyzed reaction conditions.     

碳纤维表面原位SiC纳米纤维的合成与生长

基于化学气相反应法,以高纯Si和SiO₂为反应源材料,在碳纤维表面原位生长β-SiC纳米纤维。采用XRD、SEM和TEM 等分析测试手段对SiC纳米纤维进行了表征分析,研究了不同反应温度和时间对生成β-SiC纳米纤维微观形貌和结构的影响,并探讨了β-SiC纳米纤维的生长机制。研究结果表明：采取化学气相反应法能够制备高质量、高纯度的β-SiC纳米纤维,纳米纤维的直径约为100~300 nm。随着反应温度的提高和时间的延长,纳米纤维的产额增加,且微观组织形貌发生了变化。结合制备过程和纳米纤维微观结构的观察分析,表明气-固(VS)机制是SiC纳米纤维生长的主要机理。     

改进的Ugi法应用于胺烷基二茂铁衍生物的合成

选择不同的按或酰胺组分, 利用改进的Ugi法合成了一系歹含有烷胺烷基、芳胺烷基或酰胺烷基的二茂铁衍生物, 研究了反应的投料比, 反应底物, 反应温域等因素对反应的影响, 并对反应机理进行了探讨。     

碳纤维表面原位SiC纳米纤维的合成与生长

基于化学气相反应法,以高纯Si和SiO₂为反应源材料,在碳纤维表面原位生长β-SiC纳米纤维。采用XRD、SEM和TEM 等分析测试手段对SiC纳米纤维进行了表征分析,研究了不同反应温度和时间对生成β-SiC纳米纤维微观形貌和结构的影响,并探讨了β-SiC纳米纤维的生长机制。研究结果表明：采取化学气相反应法能够制备高质量、高纯度的β-SiC纳米纤维,纳米纤维的直径约为100~300 nm。随着反应温度的提高和时间的延长,纳米纤维的产额增加,且微观组织形貌发生了变化。结合制备过程和纳米纤维微观结构的观察分析,表明气-固(VS)机制是SiC纳米纤维生长的主要机理。     

Novel synthesis of perfluoroalkylated indolizinylphosphonates via a DIPEA-promoted one-pot process

DIPEA-promoted one-pot synthesis of perfluoroalkylated indolizinylphosphonates by the reaction of pyridines 1, bromomethyl ketones 2 with perfluoroalkynylphosphonates 3 is described. This procedure is compatible with a broad range of functional groups in both pyridines and ketones with good yields. The reaction proceeds through a tandem CN bond formation followed by an intramolecular cyclization.     

酯交换法合成碳酸甲乙酯研究进展

碳酸甲乙酯(EMC)具有诸多优异的物理和化学性能,作为锂电池电解液溶剂已经被行业广泛认可,酯交换法是中国目前工业生产EMC的主要方法。本研究系统综述了碳酸酯交换反应热力学、动力学、均相及非均相催化剂、反应机理及反应工艺等方面的研究,重点评述了近五年酯交换法制备EMC的最新进展。均相催化剂中以pK_b值(碱度系数)为标准讨论了可溶碱类催化剂碱强度和催化效率之间的关系,探究了咪唑类离子液体阴、阳离子结构对反应效果的影响规律。针对工业上普遍采用的甲醇钠催化剂,描述了其失活现象并阐述了失活机理。详细比较和讨论了非均相催化剂的制备方法、表面酸碱性与催化效率之间的关系,综合评价了不同类别的催化剂催化酯交换反应的优缺点。着眼绿色、高纯、低成本EMC合成技术,高效固体碱催化剂和涉及气、液、固三相的催化精馏技术是今后开发的重点和发展方向。     

New insight into experimental and theoretical mechanistic study on a green synthesis of functionalized 4H-chromenes using magnetic nanoparticle catalyst

A green synthesis of functionalized 4H-chromenes using one-pot, three-component reaction of salicylaldehyde ( 1 ), active methylene ( 2 ), and carbon-based nucleophile ( 3 ) using Fe₃O₄@CONa nanoparticles in water has been performed at 60°C. The Fe₃O₄@CONa nanoparticle as an efficient, green, and magnetically reusable heterogeneous catalyst was applied in these reactions up to the nine runs. Green catalyst and solvent, short reaction time, high product yields, as well as simple work-up procedure were found as some advantages of this methodology. The density functional theory calculations were applied to all-inclusive perception of the one-pot, three-component reaction mechanism. The most reactions progressed through the following route: (a) nucleophilic addition of 2 to 1 ; (b) ring closing, dehydration; (c) nucleophilic substitution of 3 (2-naphtol, 4-hydroxycumarin) to intermediate. Sometimes mechanism mutated to: (a) nucleophilic addition of 3 (indole, 2-methylindole) to 1 , and dehydration; (b) nucleophilic addition of 2 to intermediate; and (c) ring closing, and dehydration. The frontier molecular orbitals, NBO analyses, molecular electrostatic potential of reactants, and intermediates confirmed the proposal mechanisms. Theoretical study could be so helpful to pick out suitable reactants of the reaction.     

Highly enantioselective synthesis of organic compound using right- and left-handed helical silica

Highly enantiomerically enriched (up to 96-97% ee) 5-pyrimidyl alkanol was obtained by the addition of diisopropylzinc to pyrimidine-5-carbaldehyde in the presence of the artificially designed chiral inorganic material, right- and left-handed helical silica.     

Part II: NiMoO4 Nanostructures Synthesized by the Solution Combustion Method: A Parametric Study on the Influence of Material Synthesis and Electrode-Fabrication Parameters on the Electrocatalytic Activity in the Hydrogen Evolution Reaction

Earth-abundant NiMo-oxide nanostructures were investigated as efficient electrocatalytic materials for the hydrogen evolution reaction (HER) in acidic media. Synthesis and non-synthesis parameters were thoroughly studied. For the non-synthesis parameters, the variation in Nafion loading resulted in a volcano-like trend, while the change in the electrocatalyst loading showed that the marginal benefit of high loadings attenuates due to mass-transfer limitations. The addition of carbon black to the electrocatalyst layer improved the HER performance at low loadings. Different carbon black grades showed a varying influence on the HER performance. Regarding the synthesis parameters, a calcination temperature of 500 °C, a calcination time between 20 and 720 min, a stoichiometric composition (Ni/Mo = 1), an acidic precursor solution, and a fuel-lean system were conditions that yielded the highest HER activity. The in-house NiMoO₄/CB/Nafion electrocatalyst layer was found to offer a better long-term performance than the commercial Pt/C.     

Isoconversional method to explore the cure reaction mechanisms and curing kinetics of DGEBA/EMI‐2,4/nano‐SiC system

The curing kinetics of the diglycidyl ether of bisphenol‐A (DGEBA)/2‐ethyl‐4‐methylimidazole (EMI‐2,4)/nano‐sized carborundum (nano‐SiC) system was studied by means of nonisothermal differential scanning calorimetry (DSC). An isoconversional method of kinetic analysis yields a dependence of the effective activation energy E on the extent of conversion that decreases initially, and then increases as the cure reaction proceeds. The variations of E were used to study the cure reaction mechanisms, and the Shrinking Core Model was used to study the resin–particle reaction. The results show that the presence of nano‐SiC particles prevents the occurrence of vitrification, as well as inhibits the cure reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 371–379, 2006     

2,4-噻唑烷二酮的合成方法、路线与机理研究进展

2,4-噻唑烷二酮是一种重要的医药中间体,已经被广泛应用于抗高血糖、抗癌、抗菌、抗病毒等方面,具有广阔的市场前景。首先,通过逆合成法对2,4-噻唑烷二酮五元环的构建方式进行系统分析,按照硫源的引入方式将合成方案分为硫脲法、硫氰酸盐法、羰基硫法和罗丹宁法四类,并对2,4-噻唑烷二酮合成过程中的取代、环化、水解反应机制进行探讨。其次,探究了不同合成方法的反应机理,阐明不同反应原料的反应速率、原子经济性,并针对各自的优缺点进行了评价。最后,根据逆合成分析结果提出两种潜在的合成策略,为开发绿色高效、环境友好、适合工业化生产的2,4-噻唑烷二酮及其类似结构药物的合成方法提供理论基础和研究思路。     

A green methodology for one-pot synthesis of polysubstituted-tetrahydropyrimidines using PEG

Abstract

Polyethylene glycol (PEG)-mediated facile one-pot synthesis of polysubstituted-tetrahydropyrimidines have been developed under mild and green reaction conditions. The obtained products are interesting nitrogen heterocyclic molecules that contain α- and β-amino acid blocks. PEG can be reused with minimum loss of its activity.     

Comparative studies on excitation of nickel ionic lines between argon and krypton glow discharge plasmas

The emission characteristics of nickel ionic lines in a glow discharge plasma are investigated when argon or krypton was employed as the plasma gas. Large difference in the relative intensities of nickel ionic lines which are assigned to the 3d⁸4p–3d⁸4s transition is observed between the krypton plasma and the argon plasma. Different intense Ni II lines appear in the krypton spectrum and in the argon spectrum, such as the Ni II 231.601 nm for Kr and the Ni II 230.009 nm for Ar. The excitation energy of these Ni II emission lines can give a key in considering their excitation mechanisms. The explanation for these experimental results is that charge-transfer collisions between nickel atom and the plasma gas ion play a major role in exciting the 3d⁸4p excited levels of nickel ion. The conditions for energy resonance in the charge-transfer collision determine particular energy levels having much larger population; for example, the 3d⁸4p ⁴D_7/2 level (6.39 eV) for Kr and the 3d⁸4p ⁴P_5/2 level (8.25 eV) for Ar.     

A highly sensitive electrochemical sensor for simultaneous determination of hydroquinone and bisphenol A based on the ultrafine Pd nanoparticle@TiO2 functionalized SiC

A titanium dioxide–silicon carbide nanohybrid (TiO₂–SiC) with enhanced electrochemical performance was successfully prepared through a facile generic in situ growth strategy. Monodispersed ultrafine palladium nanoparticles (Pd NPs) with a uniform size of ∼2.3 nm were successfully obtained on the TiO₂–SiC surface via a chemical reduction method. The Pd-loaded TiO₂–SiC nanohybrid (Pd@TiO₂–SiC) was characterized by transmission electron microscopy and X-ray diffractometry. A method for the simultaneous electrochemical determination of hydroquinone (HQ) and bisphenol A (BPA) using a Pd@TiO₂–SiC nanocomposite-modified glassy carbon electrode was established. Utilizing the favorable properties of Pd NPs, the Pd@TiO₂–SiC nanohybrid-modified glassy carbon electrode exhibited electrochemical performance superior to those of TiO₂–SiC and SiC. Differential pulse voltammetry was successfully used to simultaneously quantify HQ and BPA within the concentration range of 0.01–200 μM under optimal conditions. The detection limits (S/N = 3) of the Pd@TiO₂–SiC nanohybrid electrode for HQ and BPA were 5.5 and 4.3 nM, respectively. The selectivity of the electrochemical sensor was improved by introducing 10% ethanol to the buffer medium. The practical application of the modified electrode was demonstrated by the simultaneous detection of HQ and BPA in tap water and wastewater samples. The simple and straightforward strategy presented in this paper are important for the facile fabrication of ultrafine metal NPs@metal oxide–SiC hybrids with high electrochemical performance and catalytic activity.     

Formal total synthesis of (+)-wortmannin using catalytic asymmetric intramolecular aldol condensation reaction

A catalytic process for the synthesis of optically active C4-substituted tetrahydroindandiones using an asymmetric intramolecular aldol condensation reaction was developed. When 30 mol% of phenylalanine and 50 mol% of pyridinium p-toluenesulfonate were used under highly concentrated conditions, a variety of C4-substituted tetrahydroindandiones and octahydronaphthalenediones were obtained in high yield (up to 89% yield) and high enantiomeric excess (up to 94% ee). One of the products was successfully transformed into the key intermediate for the synthesis of the phosphatidylinositol 3-kinase inhibitor wortmannin, achieving formal total synthesis of (+)-wortmannin.