三种不同的纳米钴铁氧体热分解过程、结构和磁性的对比研究

为了改善钴铁氧体材料的性能,本研究采用溶胶-凝胶法,制备出三种具有尖晶石结构的纳米钴铁氧体.经前躯体热分解反应过程分析,产品X射线衍射分析,磁性分析测定,结果表明三种钴铁氧体的各个热分解阶段分别是由若干个反应复合而成,各个热分解阶段的活化能各不相同;产品为平均粒径50～60nm左右的尖晶石相:矫顽力及比饱和磁化强度分别呈不同的变化趋势,因为LaCl3.nH2O代替部分CoCl26H20后,稀土离子进入尖晶石晶格导致磁电子的自旋倾斜,材料矫顽力下降,但LaCl3.nH2O代替部分FeCl2.4H2O后这是由于稀土离子4f层电子受到外层电子的屏蔽保护,可通过自旋-轨道偶合对磁各向异性产生贡献,使矫顽力有明显的提高.     

From layered double hydroxide to spinel nanostructures: facile synthesis and characterization of nanoplatelets and nanorods

Mg-Al spinel (MgAl2O4) nanorods and nanoplatelets transformed from Mg-Al layered double hydroxide (Mg-Al-LDHs) were synthesized via a combined hydrothermal method and calcination route using Al(NO3).9H2O and Mg(NO3)2.6H2O as raw materials. The nanorods and nanoplatelets were characterized by means of physical techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microcopy (HRTEM), selected-area electron diffraction (SAED), Fourier transform infrared spectra (FT-IR), thermogravimetric (TG), and nitrogen adsorption-desorption isotherms. XRD patterns reveal that the Mg-Al-LDHs nanostructures were obtained under a hydrothermal reaction temperature of 200 degrees C and Mg-Al spinel nanostructures were fabricated via calcination of the Mg-Al-LDHs nanostructures at 750 degrees C. It can be seen from TEM that the sizes of the Mg-Al-LDHs nanoplatelets were about 20-40 nm and the diameters of the MgAl2O4 nanorods were ca. 6 nm. The HRTEM images indicate that the crystal lattice spaces of the MgAl2O4 nanorods and nanoplatelets are 0.282 and 0.287 nm, respectively.     

pH和温度敏感型聚合物荧光探针的合成及应用

以萘酰亚胺(NI)、N-异丙基丙烯酰胺(NIPAM)和多面体齐聚倍半硅氧烷(POSS)为原料,通过可逆加成断裂自由基聚合(RAFT)方法,设计合成了具有p H响应和温度敏感的聚合物荧光探针Poly(POSS-NINIPAM)。通过核磁共振波谱仪(NMR)、荧光发射光谱仪和质谱仪(MS)等技术手段表征了Poly(POSS-NINIPAM)的p H和温度的响应性能。结果表明,在p H值5.8~8.0范围内,探针Poly(POSS-NI-NIPAM)的荧光强度变化明显,与p H值呈现良好的线性相关(λem=520 nm,p Ka=6.51),对p H和温度的响应均呈现出良好的循环检测性能,可用于检测活细胞He La的p H值变化。探针Poly(POSS-NI-NIPAM)在检测生物样本中p H/温度变化方面具有潜在的应用前景。     

The Structure and Size-effect of Calcium Modified Lead Titanate Nanocrystal,Pb_(0.85)Ca_(0.15)TiO_3

ＩｎｔｒｏｄｕｃｔｉｏｎＰＴＣｉｓａｋｉｎｄｏｆｉｍｐｏｒｔａｎｔｆｅｒｒｏｅｌｅｃｔｒｉｃｍａｔｅｒｉａｌｏｆｍｏｄｉｆｉｅｄｌｅａｄｔｉｔａｎａｔｅ，ｗｈｉｃｈｃａｎｍａｋｅｔｈｅｔｅｔｒａｇｏｎａｌ／ｃｕｂｉｃａｘｉａｌｒａｔｉｏｏｆｌｅａｄｔ...     

Near-infrared cell-permeable Hg2+-selective ratiometric fluorescent chemodosimeters and fast indicator paper for MeHg+ based on tricarbocyanines

Three tricarbocyanine dyes (IR‐897, IR‐877, and IR‐925) with different thiourea substituents that function as dosimeter units through specific Hg²⁺‐induced desulfurization have been demonstrated in a fast indicator paper for Hg²⁺ and MeHg⁺ ions. In comparison with available Hg²⁺‐selective chemodosimeters, IR‐897 and IR‐877 show several advantages, such as convenient synthesis, very long wavelengths falling in the near‐infrared (NIR) region (650–900 nm) with high molar extinction coefficients, a ratiometric response, and quite low disturbance with Ag⁺ and Cu²⁺ ions. They exhibit large redshifts, which result in a clear color change from deep blue to pea green that can be easily monitored by the naked eye for a convenient indicator paper. In emission spectra, they display a characteristic turn‐off mode at 780 nm and turn‐on mode at 830 nm with titration of Hg²⁺ ions. Remarkably, the signal/noise (S/N) ratio with other thiophilic metal ions (Ag⁺ and Cu²⁺) is greatly enhanced with ratiometric measurement of two channels: excitation spectra mode (I_{810 nm}/I_{670 nm}, monitored at 830 nm) and emission spectra mode (I_{830 nm}/I_{780 nm}, isosbestic absorption point at 730 nm as excitation). The distinct response is dependent upon the electron‐donating effect of the thiourea substituents; that is, the stronger the electron‐donating capability of the thiourea substituents, the faster the Hg²⁺‐promoted cyclization. Additionally, experiments with living SW1116 cells show that these three tricarbocyanine dyes with low toxicity can exhibit special characteristics that are favorable for visualizing intracellular Hg²⁺ and MeHg⁺ ions in biological systems, including excellent membrane permeability, minimal interfering absorption and fluorescence from biological samples, low scattering, and deep penetration into tissues.     

Rational design of shortwave infrared (SWIR) fluorescence probe: Cooperation of ICT and ESIPT processes for sensing endogenous cysteine

Cysteine is well-known to be an important biothiol and related to many diseases. However, the in vivo detection of endogenous cysteine still suffers from lacking small-molecule fluorophores with both excitation and emission in the near-infrared (650-900 nm)/shortwave-infrared region. Herein, we report a molecular engineering strategy for shortwave infrared (SWIR, 900-1700 nm) sensing of cysteine, which integrated an excited-state intermolecular proton transfer (ESIPT) building block into the intramolecular charge transfer (ICT) scaffold. The obtained novel fluorophore SH-OH displays a maximum absorption at the NIR region, and emission at the SWIR region. We introduce the cysteine-recognition moiety to SH-OH structure, and demonstrate sensing of endogenous cysteine in living animals, using the SWIR emission as a reliable off-on fluorescence signal. This fluorophore design strategy of cooperation of ICT and ESIPT processes expands the in vivo sensing toolbox for accurate analysis in clinical applications.     

Binding Strength and Oxygen Coordination of the Fe Sites in High TC GdBa2 Cu3O7—δ

The GdBa₂(Cu_1－xFe_x)₃O_7—δ system with x=0.005－0.001 and various oxygen concentrations was investigated by ⁵⁷Fe-Mossbauer spectroscopy in temperature range 20K to 300K.The spectra of the orthorhombic phase were analyzed with four quadrupole doublets.Three of them were attributed to substitutional Cu(1) sites and one (with the smallest quadrupole splitting)to the substitutional Cu(2) site.From an analysis of temperature dependence of the relative site intensities,different local Debye temperature for the Cu(1) sites were derived.Highly texturized absorbers were investigated to study the polarization dependence of the four quadrupole doublets.Measurements at the magic angle gave evidence for a vibrational anisotropy (Goldanskii-Karyagineffect) of the Cu(1) sites.The Cu(1) site with the largest quadrupole splitting exhibited the lowest Debye temperature and the largest vibrational anisotropy.     

气相多组分反应流场的一种新算法

本文提出气相多组分方程组采用时间推进法,把混合气连续方程同状态方程相联系,把密度的调整量转化为压力的调整量,计算绝对压力场,对大温差下的有化学反应的多组分炉内流场进行计算,获得成功．     

超硬B-C-N材料的电子结构、硬度和光学性质的第一性原理计算

本文基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法计算了z-BC₂N和z-B₂CN的4种晶体结构的电子结构、硬度和光学性质。结果表明,z-BC₂N(2)为直接带隙半导体,其禁带宽度2.449 eV,z-BC₂N(1)为间接宽带隙半导体,其禁带宽度为3.381 eV,而z-B₂CN(1)和z-B₂CN(2)为导体;硬度结果显示z-BC₂N(1)、z-BC₂N(2)和z-B₂CN(1)为超硬材料。最后通过计算z-BC₂N基本光学函数与光子能量的关系表征了其光学性质。分析结果表明,z-BC₂N结构可以用作良好的耐磨材料和窗口耐热材料。     

聚丙烯催化合金结构表征

用IR、DSC、NMR分析了聚丙烯催化合金中乙丙共聚物的微结构 ,发现在一定条件下合成的乙丙共聚物主要由两部分组成 :无规乙丙共聚物和各种不同序列长度的乙丙嵌段物组成 .加上丙烯均聚物 ,聚丙烯催化合金是一种具有多分散性结构的混合物 .这种特殊的结构是聚丙烯催化合金具有高抗冲性的主要原因