Controlled hydrothermal synthesis and structural characterization of a nickel selenide series

A series of nickel selenides (NiSe2 microcrystals, Ni(1-x)Se and Ni3Se2 microspheres) has been successfully synthesized through a convenient, low-temperature hydrothermal method. A good nucleation and growth environment has been created by forming a uniform and transparent solution reaction system. The compositions (including the x value of Ni(1-x)Se), phase structures, as well as the morphologies of nickel selenides, can be controlled by adjusting the Ni/Se ratio of the raw materials, the pH, the reaction temperatures and times, and so forth. The newly produced Se microspheres in the system have been used as both reactant and in situ template to the Ni(1-x)Se microspheres. It is found that Ni(1-x)Se microspheres act as the intermediate precursor during the formation of Ni3Se2 microspheres. Under certain conditions, hexagonal NiSe microspheres can be converted into rhombohedral NiSe nanowires in solution. The formation mechanisms of a series of nickel selenides has been investigated in detail by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. This work has provided a general, simple, and effective method to control the composition, phase structure, and morphology of metal selenides in aqueous solution, which will be important for inorganic synthesis methodology and further applications of selenides.     

Thermal degradation behavior of multi-walled carbon nanotubes/polyamide 6 composites

This paper focuses on the thermal degradation behavior of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites under air and nitrogen atmosphere using thermogravimetric analysis (TGA). The results show that the dispersion of amino-functionalized MWNTs (f-MWNTs) in PA6 is more homogeneous than purified MWNTs (p-MWNTs). The presence of MWNTs improves the thermal stability of PA6 under air obviously, but has little effect on the thermal degradation behavior of PA6 under nitrogen atmosphere. The activation energies for degradation under air, E_a, estimated by Kissinger method, are 153, 165 and 169 kJ/mol for neat PA6, p-MWNTs/PA6 and f-MWNTs/PA6 composites, respectively. The p-MWNTs/PA6 composites show two-step degradation not only under air but also under nitrogen atmosphere, however, neat PA6 and the f-MWNTs/PA6 composites exhibit two-step degradation only under air.     

Determination of the residue of quizalofop-p-tefuryl in soybean by HPLC

A HPLC method was developed for the analysis of quizalofop-P-tefurylof in soybean. The samples were extracted with methanol-water (volume ratio), The extracts were cleaned up with a column of silica gel. The final residue was detected by HPLC, using a UV detector. The recoveries from the analytical method for soybean were 84.32%–89.25%. Variable coefficients were 0.49%∼1.51%. This method proved to be simple, reliable and accurate. __________ Translated from Chinese Journal of Chromatography, 2005, 23(2)(in Chinese)     

不同材料弹体超声速侵彻钢筋混凝土靶的结构破坏对比实验

设计了超声速钻地结构弹,采用203 mm口径的火炮,开展了25 kg量级弹体在1100~1300 m/s速度范围内侵彻钢筋混凝土靶的实验研究,应用数值仿真对弹体侵彻钢筋混凝土靶的过程进行了模拟计算。基于实验和仿真结果,对超声速侵彻条件下两种金属材料弹体的结构响应、质量损失等问题进行了分析。结果表明:在超声速侵彻钢筋混凝土靶的过程中,两种金属材料的弹体结构变形破坏形式主要为头部侵蚀和侧壁磨蚀,头部侵蚀量的大小与弹体壳体材料有关,高强度G50钢材料更适合用于1200 m/s速度量级的超声速侵彻环境。对出现的“径缩”现象作了初步分析,并对今后工程应用的结构弹体设计提出了指导意见。     

高效组合型 Pd/C 催化剂用于 Suzuki 偶联反应

 采用有机金属 Pd2(dba)3 (dba 为二亚苄基丙酮) 还原分解法制得均匀分布的 Pd 纳米颗粒 (粒径为 3~6 nm) 混合液, 并用活性炭直接吸附得到了组合型 Pd/C 纳米催化剂. 采用透射电子显微镜、X 射线光电子能谱和 X 射线衍射等手段测定了催化剂表面 Pd 颗粒大小分布、晶型和化学态等. 将该催化剂用于 Suzuki 碳-碳偶联反应, 其催化活性比浸渍法制备的 Pd/C 催化剂高 2 倍以上. 以溴代芳烃为底物时, 在 80 oC 下 0.5 h 后偶联产物收率可达 98% 以上. 以邻氯硝基苯为底物时, 在 110 oC 下 1 h 后偶联产物收率可达 64%; 延长反应时间, 产物收率可达 90% 以上.     

Copper‐catalyzed asymmetric 1,4‐conjugate addition of dialkylzinc to enones

Asymmetric 1,4‐conjugation addition of dialkylzinc (diethylzinc and dimethylzinc) to cyclic enones, chalcone and nitroalkenes was achieved by a 25 mol% (R)‐6,6′‐Br₂‐BINOL( 1f ), 25 mol% CuSPh and 100 mol% dicyclohexylmethylamin(Cy₂NMe) catalyst system. The Cu(I) catalyst system enables the cyclic enone, chalcone and nitroalkene generality with high enantioselectivity (up to 84% ee) and isolated yield (up to 94%) under mild reaction conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Modular amino acid amide chiral ligands for enantioselective addition of diethylzinc to aromatic aldehydes

Enantioselective addition of diethylzinc to a series of aromatic aldehydes was developed using a modular amino acid amide chiral ligand (2S)‐3‐phenyl‐N‐((R)‐1‐phenyl‐ethyl)‐2‐(tosylamino)propanamide without using titanium complex. The catalytic system employing 10 mol% of 1g was found to promote the addition of diethylzinc (ZnEt₂) to a wide range of aromatic aldehydes with electron‐donating and electron‐withdrawing substituents, giving up to 82% ee of the corresponding secondary alcohol under mild conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Modular amino acids and β‐amino alcohol‐based chiral ligands for enantioselective addition of diethylzinc to aromatic aldehydes

Enantioselective addition of diethylzinc to a series of aromatic aldehydes was developed using a modular amino acids and ${\bf \beta}$ ‐amino alcohol‐based chiral ligand (2R)‐N‐[(1R,2S)‐1‐hydroxy‐1‐phenylpropan‐2‐yl]‐3‐phenyl‐2‐(tosylamino) propanamide ( 1f ) without using titanium complex. The catalytic system employing 15 mol% of 1f was found to promote the addition of diethylzinc (ZnEt₂) to a wide range of aromatic aldehydes with electron‐donating and electron‐withdrawing substituents, giving up to 97% ee of the corresponding secondary alcohol under mild conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

A facile "dispersion-decomposition" route to metal sulfide nanocrystals

In this paper, we demonstrate a simple and general "dispersion-decomposition" approach to the synthesis of metal sulfide nanocrystals with the assistance of alkylthiol. This is a direct heating process without precursor injection. By using inorganic metal salts and alkylthiol as the raw materials, high-quality Ag(2)S, Cu(2)S, PbS, Ni(3)S(4), CdS, and ZnS nanocrystals were successfully synthesized. The mechanism study shows that the reaction undergoes two steps. A key intermediate compound, metal thiolate, is generated first. It melts and disperses into the solvent at a relatively low temperature, and then it decomposes into metal sulfide as a single precursor upon heating. This method avoids using toxic phosphine agent and injection during the reaction process. The size and shape of the nanocrystal can be also controlled by the concentration of the reactant and ligands. Furthermore, the optical properties and assembly of the nanocrystals have also been studied. This report provides a facile, direct-heating "dispersion-decomposition" approach to synthesize metal sulfides nanocrystals that has potential for future large-scale synthesis.     

Chelating template-induced encapsulation of NiO cluster in mesoporous silica via anionic surfactant-templated route

In this study, we develop a novel one-step method for synthesis of nickel oxide/silicon dioxide (NiO/SiO(2)) mesoporous composites by using N-hexadecyl ethylenediamine triacetate (HED3A) as structure-directing agent. Besides playing a role in directing the mesophase formation, the anionic surfactant also functions as a chelating agent that binds nickel ions. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopic analyses were undertaken to determine the chelating ability between HED3A and nickel ions. By adjusting the molar ratio of Ni(2+)/HED3A in the template solution, a series of mesoporous composites with various NiO contents were obtained after calcination. These composites were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and nitrogen adsorption/desorption. The results showed that the generated NiO nanoparticles were aggregated into clusters with the size less than 20 nm, and the composites retained mesoporous characteristics even with high NiO contents. HRTEM images also revealed the migration and aggregation for NiO nanoparticles during the sintering process. Moreover, the energy-dispersive X-ray spectrum (EDX) results showed a close linear relationship between Ni/Si in the composites and Ni(2+)/HED3A in the templates. This chelating surfactant-assistant encapsulation route has the potential to synthesize diversiform metal oxide/silica mesoporous composites with designated compositions.