Three-dimensionally intercrossing Mn3O4 nanowires

Three-dimensional Mn₃O₄ nanostructures were synthesized by a soft chemistry templating process using a block copolymer as the structure-directing agent. This material has a unique structure of intertwining nanowires which are grown from faceted Mn₃O₄ particles and aligned spatially perpendicular to or along each facet. The magnetic measurements of such nanostructured films show clear signs of magnetic shape anisotropy, indicating that this templating synthesis approach could be a promising method to develop Mn₃O₄ nanostructures with desired anisotropic properties through dimensionality control.     

Hydrogen reduction behavior and microstructural characteristics of WO3 and WO3-NiO powders

The characterization and understanding of the hydrogen reduction and sintering behavior of powder mixtures prepared from WO₃ and WO₃-NiO have been investigated. The nano-sized W and W-Ni powders were prepared by ball milling and hydrogen reduction of oxide powders. The reduction behavior is analyzed by temperature-programmed reduction method with different heating rates in Ar-10% H₂ atmosphere. X-ray diffractometry analysis revealed that the oxide powders are changed to W and W-Ni powders with an average particle size of about 100 nm by hydrogen reduction at 800 °C for 1 h. The hydrogen reduction kinetics was evaluated by the amount of peak shift with heating rates. The activation energies for the reduction of pure WO₃ and WO₃-NiO, estimated by the slope of the Kissinger plot, were measured as 87.4–117.4 kJ/mol depending on reduction steps. The consolidated W-Ni by spark plasma sintering has relatively dense and large grains with neck growth by enhanced mass transport due to the addition of Ni. These results are help to optimize the powder synthesis process and to understand the hydrogen reduction behavior and Ni addition effect related to microstructure of powders and sintered bodies.     

催化剂Co_2B/Nd_2O_3对NaBH_4水解放氢的影响

研究了催化剂Co2B/Nd2O3对NaBH4水解放氢性能的影响。结果显示,随着Co2B/Nd2O3加入量的增加,掺杂NaBH4试样的放氢速率明显加快。当Co2B/Nd2O3的加入量相同时,随着催化剂Co2B/Nd2O3中Nd2O3含量的增加,掺杂试样的放氢速率明显降低。对于放氢量的研究发现,当Co2B/Nd2O3加入量增加时,试样的放氢量有所增加,但是增加幅度不大,在所有的掺杂试样中,掺杂量为4%的掺杂80%Co2B+20%Nd2O3的试样的放氢量最大为520 mL/g。SEM的分析发现,随着NaBH4中掺杂量的增加,试样的放氢速率变化明显,然而试样的放氢量却没有明显变化。     

Pt-decorated NiWO4/WO3 heterostructure nanotubes for highly selective sensing of acetone

The heterostructured NiWO₄/WO₃ nanotubes (Ni/W NTs) were synthesized by using a facile self-assembly method on the sacrificial polystyrene (PS) nanofibers templates. Then, the Pt-decorated NiWO₄/WO₃ (Pt@Ni/W) composite NTs were obtained through using an ultrasonic mixing method. The experimental results display that the order of gas-sensing performance is Pt@Ni/W>Ni/W>WO₃. The 2wt.%Pt@Ni/W-5 NTs indicate the supreme acetone-sensing response (R_air/R_gas=58.4 at 100×10^?6) at 375 °C, which is 10.6 and 1.53 times that of the WO₃ and NiWO₄/WO₃ NTs, respectively. Additionally, the 2wt.%Pt@Ni/W-5 NTs also exhibit the dramatically high selectivity toward acetone against ethanol, methanal, methanol, NH₃ and toluene. The Pt-decorated Ni/W NTs show the excellent responsivity and stability toward acetone, which is ascribed to the construction of heterostructured NiWO₄/WO₃ and the spill-over effect of Pt nanoparticles.     

Facile synthesis of NiO nanowires and their gas sensing performance

The NiO nanowires were prepared by a facile PEG assisted hydrothermal method using NiC₂O₄·2H₂O as a precursor compound. The microstructure of the samples was characterized by SEM and XRD. The gas sensing properties of the NiO nanowires toward ethanol was also investigated. The results show that PEG plays a key role in the synthesis of wire-like NiO. The NiO nanowires show excellent sensing performances to ethanol gas. This morphology holds substantial promise for applying NiO as a potential gas sensing material for future sensor application.     

镍纳米线的简易合成及其气敏性能(英文)

采用水热法,以聚乙二醇(PEG)作为辅助剂,通过先驱物NiC2O4·2H2O合成氧化镍纳米线,并通过SEM和XRD对样品的微观结构进行分析。实验结果显示:PEG对镍线的合成起重要作用,镍纳米线表现出良好的气敏性能。该形态使得氧化镍(NiO)可作为传感器的气敏材料得到应用。     

Nanocrystalline Co3O4 fabricated via the combustion method

A facile and rapid combustion method has been used to prepare nano-crystalline Co₃O₄ spinel employing urea as a combustion fuel. The fabrication was carried out by refluxing a mixture of cobalt nitrate and urea followed by calcination, for 3 h in static air atmosphere, at 400 °C. The thermal genesis of the Co₃O₄ was explored by means of thermogravimetric and differential thermal analyses in air atmosphere in the temperature range 25–1000 °C. X-ray diffraction, Fourier transform infrared spectra, and scanning electron microscopy were used to characterize the structure and morphology of the Co₃O₄. The obtained results conrmed that the resulting oxides were comprised of pure single-crystalline Co₃O₄ nanoparticles. Moreover, various comparison experiments showed that several experimental parameters, such as the reflux time and the urea/cobalt nitrate molar ratio, play important roles in the crystallite size as well as the morphological control of Co₃O₄ powders. Consequently, the minimum crystallite size can be obtained at 12 h reflux and a urea/cobalt nitrate molar ratio of 5.     

Crystal Structures of Dy_2(WO_4)_3 and GdY(WO_4)_3

Two compounds, Dy2(WO4)3 and GdY(WO4)3, were synthesized by using the standard solid state reaction technique. The crystal structure was determined by powder X-ray diffraction and Rietveld refinement method. It is found that both compounds have Eu2(WO4)3-type monoclinic structure, with space group C 2/c, Z = 4. The unit cell parameters of Dy2(WO4)3 are a = 0.75981(1) nm. b = 1.13220( 1) nm, c = 1.13254( 1) nm, and β= 109.8001(3)°, and those of GdY(WO4)3 are a = 0.76175(1) nm, b = 1.13543(1) nm, c = 1.13496(2) nm, and bbbbbbbbbβwhile each rare-earth atom is surrounded by eight oxygen atoms. WO4 tetrahedra share their four vertices with REO8 (RE = Dy, Gd, or Y) trigondodecahedra and some REO8 trigondodecahedra share an edge with each other. The phase transition and the magnetic properties were investigated by differential thermal analysis (DTA) and dc superconducting quantum interference device (SQUID) magnetometer.     

前驱体对四氧化三钴形貌的影响与表征

以Co(CH3COO)2.4H2O为钴源,聚乙二醇(PEG)20 000为表面活性剂,在水-正丁醇溶剂体系中,分别以氢氧化钾、碳酸铵和草酸为沉淀剂,采用沉淀法制备氢氧化钴、碱式碳酸钴和草酸钴前驱体。氢氧化钴前驱体于160℃通过水热氧化法,可制得立方体状四氧化三钴(Co3O4);碱式碳酸钴和草酸钴前驱体采用水热-热分解法分别于450℃和400℃煅烧3 h可制得球链状和棒状Co3O4。用热重分析、红外光谱、X射线衍射和透射电镜对所制得前驱体和产物Co3O4的形貌和结构进行表征,并对所制备的不同形貌Co3O4进行电化学性能测试。研究结果表明:产物Co3O4的形貌与其前驱体和制备方法有关,当采用氢氧化钴前驱体可制备平均晶粒度约为15 nm的立方体状Co3O4;当采用碱式碳酸钴和草酸钴前驱体可分别制得直径约为40 nm、长约为100 nm的球链状Co3O4和直径约为0.1μm、长度可达1μm的棒状Co3O4。通过对不同形貌的Co3O4进行循环充放电测试,可知纳米级Co3O4的电化学性能优于微米级Co3O4的;立方体状Co3O4的电化学性能优于其他形貌Co3O4的电化学性能,其循环10次后的充电比容量为406 mA.h/...     

Shape-controlled synthesis of nanocubic Co3O4 by hydrothermal oxidation method

The nanocubic Co3O4 was synthesized by hydrothermal oxidation method. The effects of cobalt salt, precipitating agent, surfactant, solvent, pH value of the suspension and the amount of oxidant H2O2 on the morphology and structure of Co3O4 were investigated. The Co3O4 powders were characterized by transmission electron microscope and X-my diffraction. The results show that the morphology of Co3O4 is closely dependant on the anion in cobalt salts, but it is not so sensitive to the precipitating agents and solvents. The amount of H2O2 is the key factor to obtain Co3O4 with spinel crystal structure. The optimum synthetic conditions of uniform shape-controlled Co3O4 nanocubes are as follows： Co（CH3COO）2·4H2O as cobalt salt, KOH as precipitating agent, polyethylene glycol with relative molecular mass of about 20 000 as surfactant, water-n-butanol as solvent system, pH value of 8-9, the molar ratio of H2O2 to Co^2＋ above 2.5：1.0, hydrothermal temperature of 160 ℃ and hydrothermal holding time of 10 h. The tap density and apparent density of nanocubic Co3O4 obtained with the average particle size of 20 nm are 1.01 g/cm^3 and 0.70 g/cm^3, respectively.     

非晶态Ag表面修饰NiFe2O4的制备及对丙酮气体的气敏性能

采用微波诱导低温固相反应法合成NiFe2O4纳米粉体,并通过浸渍法在其表面修饰Ag,通过X射线衍射分析(XRD)、扫描电镜(SEM)和X射线光电子能谱(XPS)研究修饰前、后粉体的结构及形貌,并对修饰不同含量Ag的旁热式气敏元件的气敏性能进行测试.结果表明:表面修饰的Ag为非晶态,能够有效阻止NiFe2O4纳米颗粒的团聚及长大,当表面修饰1.5％Ag后,NiFe2O4气敏元件的最佳工作电压为4.5 V,对丙酮气体具有较高的灵敏度,达到43,且响应(l s)和恢复(～l0 s)时间快,优于直接固相反应法掺杂1.5％Ag所得的NiFe2O4气敏元件的气敏性能.     

锂离子电池纳米Co3O4-PTFE复合负极材料的循环性能

采用在加温的水溶液中电沉积然后烧结方法制备锂离子电池的纳米Co3O4-PTFE复合负极材料.XRD分析表明,电沉积的物质在245℃真空热处理后转变为Co3O4-PTFE.SEM观察可以发现,Co3O4-PTFE中的Co3O4呈现蜂窝结构,其厚度为30～50nm;PTFE则形成交联的柱状体吸附在片状Co3O4两侧,其直径为50～100nm.这种纳米Co3O4-PTFE复合沉积层具有结构稳定、抗粉化的特点.充放电实验结果表明,Co3O4掺杂PTFE可明显提高负极材料的可逆比容量和循环性能,其首次放锂比容量为920.1mAh·g-1,20次循环后放锂比容量为685.6mAh·g-1;而没有掺杂PTFE的试样对应的数据分别为865.1mAh·g-1和180.4mAh·g-1.     

Influences of Y2O3 Doping on Hydrogen Release Property of LiAlH4

主要通过PCT设备研究了掺杂Y2O3的LiAlH4试样的放氢性能。结果显示,随着Y2O3掺杂量的增加,LiAlH4的放氢量增加,然而,当掺杂量达到某一值时,LiAlH4的放氢量随着掺杂量的增加而降低。和LiAlH4原样相比,掺杂Y2O3的试样初始放氢时间提前。此外,关于Y2O3对LiAlH4放氢速率影响的研究还发现,所有掺杂试样的放氢速率都比未掺杂原样的放氢速率快。并且所有掺杂试样的放氢速率的变化趋势都是相似的,即:随着时间的延长,放氢速率快速增大之后逐步降低。     

Improved sensing performance of WO3 nanoparticles decorated with Ag and Pt nanoparticles

Gas sensors built with metal oxide semicon-ductors have attracted tremendous attention due to the growing demand for the detection of inflammable,explo-sive and...     

Au/Co_3O_4的制备、表征及加氢催化性能研究

采用化学浸渍法制备出Au/Co_3O_4纳米复合材料,用透射电子显微镜(TEM)、X射线能谱(EDS)和X射线粉末衍射(XRD)等对其结构和组成进行了表征,并考察了其在对硝基苯酚加氢反应中的催化性能。表征结果表明,Au纳米粒子很好地分散在Co_3O_4载体上。催化性能测试表明,Au/Co_3O_4纳米复合材料对于对硝基苯酚加氢反应表现出优异的催化活性,TOF值为5.01 min~(-1);此外,催化剂经过5次循环仍然保持优异的催化性能。     

由草酸钴热分解制备Co3O4及其物性表征

根据草酸钴的热重/差热分析曲线,利用热分解法,在不同条件下由草酸钴制备了各种Co3O4微粉,并对其进行了X射线衍射分析和扫描电镜表征.结果表明:在低温下制得了具有标准Co3O4晶形结构的树枝状Co3O4;在高温下,尤其是采用两段升温制得了具有标准活性Co3O4晶形结构的球形Co3O4,其中位粒径为1.35μm,松装密度为0.83 g/cm3,并由此获得了由草酸钴热分解制备活性球型Co3O4的分解条件.     

Controllable synthesis of Zn0.95Co0.05O nanowires and nanotubes by electrophoretic deposition method

Zn_0.95Co_0.05O nanotubes, as well as nanowires, were controllably synthesized by electrophoretic deposition method using anodic aluminum oxide (AAO) as template, and the mechanism of electrophoretic deposition was discussed. Careful characterization indicates that the prepared nanotubes and nanowires are of poly-crystal wurtzite structure and composed with 8–15 nm nano-crystals. The doped Co²⁺ occupied the Zn²⁺ sites in the ZnO lattice. Magnetic investigation indicates that the obtained nanotubes and nanowires are of room-temperature ferromagnetic. The magnetism of the nanotubes is much higher than that of the nanowires for the surface-preferential Co distribution.     

LiNi1/3Co1/3Mn1/3O2和LiNi3/8Co1/4Mn3/8O2纳米纤维的合成与电化学性能

以溶胶前驱体为纺丝液,通过静电纺丝法合成锂离子电池正极材料LiNi1/3Co1/3Mn1/3O2和LiNi3/8Co1/4Mn3/8O2纳米纤维.采用原子力显微镜(AFM)、X射线衍射(XRD)、充放电实验对纳米纤维的形貌、结构和电化学性能进行研究.结果表明,纳米纤维的直径在150～200 nm之间,且具有典型的α-NaFeO2层状结构.LiNi1/3Co1/3Mn1/3O2和LiNi3/8Co1/4Mn3/8O2纳米纤维的首次放电容量均超过170 mAh·g-1,50次循环后容量保持率在90%以上.     

K+掺杂改性的Ca3Co4O9基氧化物热电性能

用溶胶-凝胶法和放电等离子烧结(SPS)制备了层片状结构的(Ca1-xKx)3Co4O4陶瓷,烧结块体相对密度可达97%～99%.XRD(X-ray Diffraction)和SEM(Scanning Electronic Microscope)分析结果表明当K的掺杂量x＜0.08时为单一的Ca3Co4O9相,SPS烧结可以使样品带有一定的织构取向.在室温至700℃的范围内测量了不同K掺杂量时样品电导率和Seeback系数,测试结果表明,当K的掺入量小于0.06时,随着掺入量的增加,可以显著提高样品的电导率(400℃～700℃)和Seebeck系数.其中,700℃时(K0.06Ca0.94)3Co4O9样品的功率因子P=4.43×10-4W·m.-1K-2,与Ca3Co4O9(P=3.51×10-4W.m.-1K-2)相比提高了26.2%,表明K掺杂是改善Ca3Co4O9高温热电性能的有效途径之一.