CoFe2O4纳米颗粒的制备及其磁学性能

采用溶胶凝胶法制备了CoFe2O4纳米颗粒,分别使用聚乙烯醇(PVA)和聚乙二醇(PEG)作为分散、凝胶剂,用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和综合物性测量系统(PPMS)对CoFe2O4纳米颗粒的结构组成及物相、形貌尺寸和磁学性能进行分析研究.对比了两种分散剂制备的CoFe2O4纳米颗粒的磁学性能,并研究了不同量的PEG对CoFe2O4纳米颗粒的磁学性能的影响.结果表明:用PEG制得的CoFe2O4纳米颗粒的饱和磁化强度(143.11 emu/g)比用PVA制备的CoFe2O4纳米颗粒的饱和磁化强度(62.81 emu/g)大很多,其主要原因是Co2+在A位和B位的重新分布;PEG用量不同时,得到的CoFe2O4纳米颗粒尺寸不同,而颗粒尺寸大小又是影响CoFe2O4纳米颗粒的饱和磁化强度的主要因素;用4 gPEG制备的CoFe2O4纳米颗粒的形貌、尺寸和磁学性能最好.     

二次加热法制备单分散性CoFe2O4纳米晶及其磁性研究

本文分别以CoCl2·6H2O,FeCl3·6H2O,NaOH为原料,利用N(CH3)4OH (四甲基氢氧化铵)作为改性剂,对CoFe2O4纳米颗粒进行原位表面改性,采用二次加热法,制备单分散性CoFe2O4纳米晶.利用透射电子显微镜(TEM)、X射线衍射仪(XRD)、能量散射分析仪(EDS)和振动样品磁强计等测试手段对样品的形貌,粒径,结构,以及磁学性能等进行了表征.结果表明,单分散性CoFe2O4纳米晶仍具有较大的饱和磁化强度和矫顽力.     

羟基硅酸镁纳米棒的制备及光吸收性能研究

以Mg(NO3)2·6H2O和纳米SiO2为原料,采用水热法,合成了Mg3Si2O5(OH)4纳米棒.采用X射线衍射(XRD)及场发射扫描电子显微镜(FE-SEM)对样品的物相组成和微观形貌进行了表征.并采用紫外-可见漫反射测试(UV-vis DRS)测定了样品的光吸收性能,DRS结果显示Mg3Si2O5(OH)4纳米棒的光吸收主要集中在紫外光区,结合Kubelka-Munk方程计算得出Mg3Si2O5(OH)4纳米棒的光学带隙为4.98 eV.     

纳米NiCo2O4的两种制备方法比较及其甲醇电氧化性能研究

分别以微乳液法和共沉淀法制备了NiCo2O4纳米棒和纳米片.对比研究了两种方法制备的NiCo2O4纳米材料的物相、形貌、孔道结构及其催化甲醇氧化的性能.结果表明:350℃煅烧5h后,两种方法均能制备出NiCo2O4纳米材料,但共沉淀法制备的纳米片结晶度低于微乳液法制备的NiCo2O4纳米棒.通过扫描电子显微镜、透射电子显微镜和氮气吸脱附测试发现,NiCo2O4纳米棒具有介孔结构,比表面积为116.8 m2·g-1,而NiCo2O4纳米片是六方片状结构,比表面积为36.1 m2·g-1.电化学结果显示,电压为0.6V,扫描速率为50 mV·s-1时,纳米片的电流密度为47.8 mA·cm-2,纳米棒为31.9 mA·cm-2.在0.5V扫描3000 s后,纳米片仍能保持70;的初始电流密度,纳米棒为51;.共沉淀法制备的NiCo2O4纳米片比微乳液法制备的纳米棒具有更好的催化甲醇氧化活性、稳定性.这可能是由于NiCo2O4纳米片的特殊的片层形貌及其一定的无序度导致的.     

ZnFe2O4纳米棒的制备和性能研究

以硫酸锌、氯化亚铁和草酸铵为原料,采用水热法和热分解法成功制备了ZnFe2O4纳米棒,并利用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、X射线能量色散分析谱仪(XEDS)、高分辨透射电子显微镜(HRTEM)、选区电子衍射(SAED)和振动样品磁强计(VSM)等测试手段对样品的化学成分、形貌、晶体结构和磁性能进行了表征.结果表明,制备的ZnFe2O4为结晶良好的单相尖晶石型结构,没有杂峰出现.样品形貌为一维纳米棒状结构,分散性良好.ZnFe2O4纳米棒直径约为200nm,长度约为1～2 μm,纳米棒由晶粒尺寸在15 ～ 20 nm范围内的ZnFe2O4单晶颗粒构成.ZnFe2O4纳米棒在室温下具有超顺磁特性.     

盐酸对共沉淀法合成单分散性纳米四氧化三铁的改性研究

采用共沉淀法合成了粒径为6～10 nm的Fe3O4粒子.借助X射线衍射、红外光谱分析和透射电子显微镜等对其进行了表征.盐酸对纳米Fe3O4分散性的影响通过透射电镜和紫外可见吸收光谱进行表征.结果表明:盐酸对纳米Fe3O4的分散性有很大影响.这种作用机理通过Zeta电位进行验证,表明颗粒的分散性和稳定性随扩散双分子层的厚度而变化,而且,改性后的纳米Fe3O4显示了更好地超顺磁性.     

微波辐射低温固相反应法制备NiFe2O4纳米片晶

采用FeO4·7H2O、NiSO4·6H2O和NaOH作为反应物,充分研磨制备前驱体,对前驱体进行微波辐射制备NiFe2O4纳米粉体.通过X射线衍射分析和扫描电子显微镜分析等手段,研究了微波辐射功率、辐射时间、研磨时间对NiFe2O4纳米粉体尺寸、均匀性及团聚情况的影响.结果表明:采用微波辐射低温固相反应法能够快速且均匀地制备出结构单一的NiFe2O4尖晶石纳米晶,当微波辐射功率为700 W、辐射时间为16 min、研磨时间为20 min时,所制备的NiF2O4尖晶石纳米晶,其晶粒呈圆片状,晶粒尺寸约为30 nm,颗粒均匀性最好,且粉体不易团聚.     

离子交换树脂均匀沉淀法制备MgO纳米粒子

以(Mg(NO3)2·6H2O, (NH4)2CO3 和NH3·H2O为原料,采用两种离子交换树脂均匀沉淀法分别制备MgO纳米粒子.用热分析、X射线粉末衍射(XRD)、透射电子显微镜(TEM)、高分辨电子显微镜(HR TEM)、选区电子衍射(SAED)和BET等对所制备的MgO粒子进行了表征.结果表明:经700 ℃焙烧后制备的MgO纳米晶体属六方晶系,样品分散性较好,平均粒径约为25 nm;MgO纳米晶体清晰、有序的电子衍射点阵,表明晶体的结晶度较好;纳米粒子a和b的比表面积分别为31 m2/g and 32 m2/g.     

碳纳米管负载氧化铋的制备及催化二硝酰胺铵热分解的研究

采用微波辐射法制备了沉积于碳纳米管(CNTs)表面的氧化铋(Bi2O3)纳米粒子(Bi2O3/CNTs),用扫描电子显微镜(SEM)、光电子能谱(XPS)和X射线衍射(XRD)对制备的Bi2O3/CNTs纳米粒子进行了表征。研究了Bi2O3/CNTs纳米粒子对二硝酰胺铵(ADN)的催化热分解。结果表明,纳米Bi2O3均匀沉积在CNTs表面,平均粒径为8nm;添加3%Bi2O3/CNTs纳米粒子的ADN的初始热分解温度降低了12.8℃,热分解终止温度降低了29.3℃;NH4N(NO2)2→NH4NO3 N2O为ADN初始热分解的主导反应。     

Zn2SiO4纳米材料的可控制备及光吸收性能研究

以Zn(NO2)2·6H2O和纳米SiO2为原料,采用水热法,通过控制反应体系pH值制备了Zn2SiO4纳米颗粒、纳米棒及海胆形微米球.采用X射线衍射(XRD)及场发射扫描电子显微镜(FE-SEM)对样品的物相组成和微观形貌进行了表征.并采用紫外-可见漫反射测试(UV-vis DRS)测定了样品的光吸收性能,DRS结果显示Zn2SiO4纳米材料的光吸收主要集中在紫外光区,与Zn2SiO4纳米棒和纳米颗粒相比,海胆形Zn2SiO4微米球的吸收峰更宽,表明其对光的利用范围要大于纳米棒和纳米颗粒.     

CsI-LiCl共晶材料的坩埚下降法生长与闪烁性能研究

本文采用坩埚下降法,在真空密封的石英坩埚中成功生长出CsI-LiCl与CsI-LiCl:Na共晶闪烁体。通过扫描电子显微镜(SEM)观察晶体微结构表明该共晶中LiCl相与CsI相存在周期性的层状排列,CsI相的厚度在5 μm左右。共晶样品的X射线激发发射谱显示在CsI-LiCl和CsI-LiCl:Na共晶样品存在缺陷发光,在CsI-LiCl样品中还观察到了纯CsI的自陷激子(STE)发光。CsI-LiCl样品在α粒子激发下的多道能谱中观察到明显的全能峰,这一结果证明CsI-LiCl共晶可用于热中子探测的潜力。     

静电纺丝法制备CeO2微纳米纤维及其除氟性能

以聚丙烯腈(PAN)为载体,六水合硝酸铈[Ce(NO₃)₃·6H₂O]为原料,采用静电纺丝法制备了Ce(NO₃)₃/PAN纤维,在空气中热处理得到CeO₂微纳米纤维,通过XRD、BET和SEM对CeO₂微纳米纤维进行表征。采用静态吸附实验探讨了CeO₂微纳米纤维去除水溶液中氟离子的性能,考察了溶液pH值、初始氟离子浓度及共存阴离子等对吸附性能的影响。结果表明,pH=3时,CeO₂微纳米纤维对F^-的吸附性能最佳,CeO₂吸附量随着F^-浓度的增大呈上升趋势。CeO₂微纳米纤维对F^-的吸附等温线遵循Langmuir模型,二级动力学模型能很好地描述CeO₂微纳米纤维对F^-的吸附过程。CeO₂微纳米纤维的除氟性能优良,可为其实际应用提供理论参考。     

X-ray analysis of sideroxol from <Emphasis Type="Italic">Sideritis leptoclada</Emphasis>

Sideroxol (1), a kaurane diterpene which has the ent-7α,18-dihydroxy-15β,16β-epoxykaurane structure (MW = 320.47, C₂₀H₃₂O₃) was obtained from the acetone extract of Sideritis leptoclada plant as well as from some other Sideritis species. It crystallizes in the orthorhombic space group P2₁, 2₁, 2₁ with a = 10.967(3), b = 24.555(5), c = 6.372(4) Å, Dc = 1.240 g cm⁻³, Z = 4, and refines to R = 0.065 for 721 independent reflections. The skeleton consists of three fused six-membered rings and a five-membered ring with fused epoxide. The six membered rings exhibited slightly distorted chair conformation. In addition to sideroxol, two kaurane and five kaurene diterpenes were isolated from the hexane and acetone extracts of the studied plant.     

New zeotype borophosphates with chiral tetrahedral topology: (H)0.5M1.25(H2O)1.5[BP2O8]·H2O (M = Co(II) and Mn(II))

Two new isostructural open‐framework zeotype transition metal borophosphate compounds, (H)_0.5M_1.25(H₂O)_1.5[BP₂O₈]·H₂O (M = Co(II) and Mn(II)) were synthesized by mild hydrothermal method. The structure of compounds were characterized by single‐crystal X‐ray diffraction which have ordered, alternating, vertex‐sharing BO₄, PO₄, and (MO₄)OM(H₂O)₂ groups with hexagonal, P 6₁ 2 2 (No 178) space group and unit cell parameters for Co a = 9.4960(6) Å, c = 15.6230(13) Å, for Mn a = 9.6547(12) Å, c = 15.791(3) Å, Z = 1 for both of them. TGA/DTA analysis, IR spectroscopy were used for characterization. Magnetic susceptibility measurements for both of the compound indicate strong antiferromagnetic interaction between metal centers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence characteristics of Mg- and Si-doped GaN thin films grown by MOCVD technique

We have studied the optical, structural and surface morphology of doped and undoped GaN thin films. The p- and n-type thin films have been successfully prepared by low-pressure MOCVD technique by doping with Mg and Si, respectively. The different carrier concentrations were obtained in the GaN thin films by varying dopant concentrations. Photoluminescence (PL) studies were carried to find the defect levels in the doped and undoped GaN thin films at low temperature. In the undoped GaN thin films, a low intensity and broad yellow band peak was observed. The donor–acceptor pair (DAP) emission and its phonon replicas were observed in both the Si or Mg lightly doped GaN thin films. The dominance of the blue and the yellow emissions increased in the PL spectra, as the carrier concentration was increased. The XRD and SEM analyses were employed to study the structural and surface morphology of the films, respectively. Both the doped and the undoped films exhibited hexagonal structure and polycrystalline nature. Mg-doped GaN thin films showed columnar structure whereas Si-doped films exhibited spherical shape grains.     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.     

Considerations on the structure and physical properties of B2O3-SiO2 and GeO2-SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B₂O₃-SiO₂ and GeO_2-SiO₂ glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B₂O₃, GeO₂ and SiO₂. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO₃, GeO₄ and SiO₄ units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si-O-B or Si-O-Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B₂O₃ or GeO₂ in the concerned glasses.     

Molecular structure and crystal packing of uncomplexed 1,6-bis(N-cyano-p-methoxy-anilino)-2,4-hexadiyne, C22H18N4O2

The X-ray crystal structure of 1,6-bis(N-cyano-p-methoxy-anilino)-2,4-hexadiyne, C₂₂H₁₈N₄O₂, is determined. The crystal packing is dominated by phenyl stacking interactions. Weak C–H···N hydrogen bonds help align the molecules. C–H··· hydrogen bonding is not apparent.     

Structural and electrical properties of vapour phase grown Cd1 − xFexTe single crystals

Cd_1 − xFe_xTe single crystals were prepared by vapour phase growth method in the composition range of 0 ≤ x ≤ 0.03. Chemical analysis, surface morphology, structural investigations and electrical properties were carried out by EDAX, SEM, XRD, TEM and transport technique, respectively. Microscopic variations between the target and actual compositions were noticed. Morphology studies revealed that dislocation aided growth is active in the present crystals. TEM and XRD studies confirmed that the samples of all compositions crystallized in zinc blende structure, and the lattice parameters varied almost linearly decreases with Fe content. At room temperature, the resistivity of the Cd_1 − xFe_xTe crystals of all compositions (x = 0.01, 0.015, 0.02, 0.025 and 0.03) lies in the range of 3.5-6.5 M Ω, the activation energies lie in the range of 63-133 meV, and the samples were show the ‘p’ type conductivity.     

空位浓度对纤锌矿CdS电子结构和光学性质影响的第一性原理研究

本文基于密度泛函理论的平面波超软赝势方法,采用第一性原理研究了含Cd空位缺陷CdS和含S空位缺陷纤锌矿CdS的几何结构、能带结构、电子态密度及光学性质。通过计算分析可知,含Cd空位缺陷的CdS体系均为p型半导体,含S空位缺陷的CdS体系跃迁方式均由直接跃迁变为间接跃迁。Cd、S空位缺陷的CdS体系的态密度总能量降低。空位CdS体系相较于本征CdS体系的静介电常数均有提高,并随着空位浓度的增大而增大,Cd空位缺陷体系更为明显,极化能力得到显著提升。空位Cd的CdS体系相较于本征CdS体系在红外波段存在明显的吸收,空位S的CdS体系相较于本征CdS体系在可见光波段存在明显的吸收。