The effect of functionalization on structure and electrical conductivity of multi-walled carbon nanotubes

Nanosized powders of Ti-Nb oxide core-shell nanocrystals with atomic ratios of Nb/Ti = 0.11, 0.25, and 0.38 have been prepared by two preparation routes. The first route was co-precipitation, followed by␣annealing, using NbCl₅ as a source of Nb. The second route was coating of pure TiO₂ nanocrystals by Nb-isopropoxide in liquid medium, followed by impregnation of the Nb into the nanoparticles by annealing. Both methods yielded anatase nanocrystals with a Nb-rich shell and a core, which had much lower Nb loadings. The anatase structure solid solution (with Nb incorporated) was stable under annealing up to 760°C. The particle size remained within the nanometric scale (<50 nm) under heat-treatment up to 760°C. It has been shown that the fabricated powders can be redispersed in aqueous media by simple ultrasound treatment, resulting in nanosized dispersions. Using a variety of analytical techniques, including depth profiling of single nanocrystallites by AES combined with sputtering by Ar ions, the mechanism of the core-shell structure creation was studied. It is proposed that the formation of the core-shell structure is governed by solubility limitations in the co-precipitation route and by solubility and diffusion limitations in the coating-incorporation route.     

Sol-Gel Nanosized Semiconducting Titania-Based Powders for Thick-Film Gas Sensors

Pure, 5 at%, and 10 at% Ta- or Nb-doped TiO₂ nanosized powders were prepared by the sol-gel method. The powders heated to 400°C have the crystalline anatase structure. While the pure TiO₂ powder heated to 850°C has the rutile structure, the addition of Ta and Nb inhibited the anatase-to-rutile phase transformation at this temperature. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired at 650°C and 850°C for 1 h. SEM observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO₂. The addition of Ta and Nb is effective to keep the TiO₂ grain size at the nanometric level even at 850°C. Conductance measurements showed that a good gas response is observed only for the nanostructured titania-based films. The CO response of these materials is only slightly affected by humidity.     

Characterization of Pd Blacks by Temperature Programmed Oxidation

Using different reduction conditions Pd powders have been prepared and characterized by chemisorption and TPO (Temperature Programmed Oxidation) measurements. The amount of carbon deposits introduced during preparation seems to be peculiar to the preparation procedure. The O₂ consumption curves attributed to PdO formation have shown two peak minima suggesting strong differences in the accessibility of Pd particles.     

Thermal decomposition of butylindium thiolates and preparation of indium sulfide powders

Thermal properties of organoindium thiolates were investigated by means of thermogravimetric (TG) and differential thermal (DT) analysis. Dibutyl-indium propylthiolates (Buⁿ₂InSPrⁿ, Buⁿ₂InSPrⁱ, Buⁱ₂InSPrⁿ and Buⁱ₂InSPrⁱ) decomposed up to 280°C along with an exothermic DT peak and gave indium(I) sulfide (InS) powders. Although the arylthiolate Buⁿ₂InSPh also afforded InS powders, it decomposed at a slightly higher temperature. In contrast, the dithiolate and the dithiocarbamate complexes [BuⁿIn(SPrⁱ)₂ and In (S₂CNBu₂)₃] gave indium(III) sulfide (In₂S₃) powders.     

纳米SiC蓝光发射的研究

在４．６８ｅＶ的激光激发下，室温ＣＶＤ合成的纳米ＳｉＣ粉体，可发射４７５ｎｍ的蓝光，经６００～１１００℃在Ｎ２气氛下进行快速退火（ＲＴＡ）处理，其荧光强度随退火温度升高而增强，当Ｔ≥９００℃时，荧光强度下降，但发光峰位与退火温度无关．通过ＸＲＤ、ＩＲ、ＴＥＭ、ＸＰＳ等研究，认为纳米ＳｉＣ中与氧有关的缺陷可能是引起４７５ｎｍ蓝光发射的主要原因     

催化反应制备碳化硅纳米粉体的密度泛函理论计算及实验研究

以Si_(55),Si_(43)M_(12)和Si_(37)M_(18)(M=Fe,Co或Ni)团簇为模型,采用密度泛函理论(DFT)研究了Fe,Co及Ni纳米团簇催化硅粉转化为SiC的机理.计算结果表明,Fe,Co及Ni纳米催化剂先与Si形成合金,拉长并弱化Si—Si键的强度,起到活化Si粉的作用;合金的形成有利于C原子的吸附及Si原子和C原子间的反应;Fe的催化能力强于Co和Ni.在此基础上,以Si粉和酚醛树脂为原料,以Fe,Co及Ni硝酸盐为催化剂前驱体,通过微波加热反应制备了3C-SiC纳米粉体.研究了催化剂种类、反应温度、催化剂用量和反应时间等对制备3C-SiC纳米粉体的影响.结果表明,催化剂Fe,Co和Ni的加入均可显著降低3C-SiC的合成温度.当以2.0%(质量分数)的Fe为催化剂时,Si粉在1100℃下反应30 min后即可全部转化为3C-SiC纳米粉体;而在相同条件下,无催化剂时Si粉的完全转化温度为1250℃;Fe的催化效果优于Co和Ni,与DFT计算结果吻合.     

Al_2O_3包覆Ba_(0.6)Sr_(0.4)TiO_3复合粉体制备及表征

采用液相包覆法制备了Al2O3包覆的Ba0.6Sr0.4TiO3复合粉体。通过SEM,TEM,TG-DSC,XRD,XPS和ζ电位测试对包覆前后粉体的表面形貌、组织结构、等电点进行了测试和分析。结果表明:Al2O3以无定形结构成功的包覆在Ba0.6Sr0.4TiO3粉体表面,形成了Ba-O-Al、Sr-O-Al和Ti-O-Al键,Ba0.6Sr0.4TiO3颗粒的等电点由包覆前的pH=3.2增大至pH=8。     

Synthesis and morphology of nanosized zeolite L

AFM is a powerful tool for imaging nanoscale surface features; it provides two and three dimensional crystal structure images and other information about actual surface of zeolite crystallites. In this paper, nanosized zeolite L is synthesized in different crystallization times and a study of crystal growth of zeolite L is reported using atomic force microscopy (AFM). X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques are used for characterization of the as synthesized samples. TEM and two‐dimensional AFM images indicate that the zeolite particles are in a nano‐range and they have hexagonal structure. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

激光剥蚀-电感耦合等离子体质谱测定植物样品中的元素

采用193 nm准分子激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)对标准植物粉末样品(GBW07602-GBW07603灌木枝叶、GBW07604杨树叶、GBW07605茶叶、GBW08514烟草)中13种元素(Li,B,Na,Mg,Al,K,Ca,Cr,Mn,Fe,Ni,Cu,Ba)进行定量测试.向植物粉末样...     

XPS analysis of bio‐organic systems

A survey of the literature is made for the XPS analysis of food products (mainly spray‐dried powders, which reveal a considerable surface enrichment in lipids) and of microorganisms and related systems (extracellular polymer substances and biofilms). This survey is used as a background for discussions and recommendations regarding methodology. Sample preparation methods reviewed are freeze drying, analysis of frozen hydrated specimens and adsorption of surface‐active biocompounds on model substrates. Peak decomposition is a way to increase the wealth of information provided by the XPS spectra. It should be performed after a check that sample charge stabilization is satisfactory. Moreover, ensuring the precision needed to make comparisons within sets of samples may involve a trade‐off between imposing constraints and generating information. The examination of correlations between spectral data in the light of chemical guidelines is useful to validate or improve peak decomposition and component assignment, and may also upgrade the chemical information regarding speciation. Further upgrading may be achieved by expressing marker XPS data in terms of concentrations of compounds of interest. Different methods of computation are discussed, providing a composition in terms of ingredients, classes of biochemical compounds, or various organic and inorganic compounds. As an alternative or complement to this deterministic approach, multivariate analysis of suitable spectral windows provides spectral components, which may be used for comparing samples, and which may have a direct chemical relevance or be used to identify features of interest. Copyright © 2011 John Wiley & Sons, Ltd.