Advanced Materials Research Vols. 306-307

Abstract: A simple route to the production of high-quality CdSe quantum dots (QDs) is presented. The characterization of CdSe QDs was measured by Zetasizer Nano ZS, ultraviolet-visible spectoscopy and fluorospectrophotometer. The CdSe QDs were decorated by 3-Aminobenzeneboronic acid to obtain good fluorescent characteristic. Under the optimal conditions, the decreased normalized absorbance was linear to the concentration of glucose from 1.0×10−7 to 2.9×10−6 mol·L^-1 with a detection limit of 5.0´10^-8 mol·L^-1. The relative standard deviation (RSD) for the determination of 1.0×10^-7 mol·L^-1 was 1.4 % by 11 replicate determination. In this paper, the fluorescent behavior of glucose with the decorated CdSe QDs was studied, and it is found that the system has a high sensitivity and selectivity for analysis of glucose.

Abstract: La_1-xSr_xMnO_3+σ perovskite/ySBA-15(x=0, 0.1, 0.2, 0.3、y=0, 1, 2, 3) catalyzers were prepared by two different methods, which are the hard-templating and sol-gel methods. The catalysts were characterized by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), energy-dispersive spectroscopy(EDS), X-ray fluorescence spectroscopy(XRD) and N₂ adsorption/desorption(BET). Their catalytic activity in the oxidation of CO was evaluated. BET and SEM results showed that the repeated template samples had higher surface area(143.7m2/g) and smaller particle size(18nm). The catalytic activity for CO reached the highest value when x=0.2 and y=2. The repeated template samples had higher activity than the sol-gel samples due to the higher surface area.

Abstract: This paper describes the synthesis of CdTe and CdTe/CdS core-shell quantum dots (QDs) in aqueous solution. The quantum dots are prepared by using thioglycolic acid (TGA) as stabilizers. The synthesis procedure is simple and controllable. Different sized CdTe QDs with tuned PL wavelengths from 550 to 640 nm was synthesized by controlling reaction time within 5 h in aqueous solutions at a temperature of 100 °C. We also investigated the influence of precursor Cd/Te molar ratio for the prepared QDs. It was showed that the core-shell CdTe/CdS QDs have larger photoluminescence (PL) emission intensity than the original CdTe QDs. The synthesized core-shell CdTe/ZnS QDs have high quality, water-soluble and will be useful in applications of biolabeling, biosensing, and imaging.

Abstract: A general method was developed for determination of interdiffusion coefficient in nanolayered structures by Auger electron spectroscopical (AES) sputter depth profiling. The procedures of this method are as follows: (1) the concentration depth profile of annealed sample is calculated from its as-grown layered structure by adopting a suitable diffusion model; (2) this diffusion concentration depth profile is convoluted with a resolution function provided by the mixing-roughness-information depth (MRI)-model and as a result a calculated AES depth profile is obtained; (3) the interdiffusion coefficient is determined by fitting the calculated AES depth profile to the measured one. As an example, the interdiffusion coefficient parameters, the pre-exponential factor and the activation energy, were determined as 4.7×10-18 m2/s and 0.76 eV, respectively, for a GexSi1-x/Si multilayered nanostructure with Ge-Si alloyed layers of 2.2, 4.3 and 2.2 nm thickness in Si matrix.

Abstract: Graphene has weak interface compatibility to its solvent, and it is easy to get agglomeration in the solvent. In this paper, graphehe is modified by grafting method to improve the aqueous dispersion. Oxidized graphene is firstly prepared by modified Hummer’s method and supersonic exfoliation. Then oxidized graphene is grafted by hydrophilic polymer polyacrylamide (PAM) and deoxidized into modified graphene. The product is characterized by TEM, FTIR, Raman spectroscopy and sedimentation test. And the result demonstrates a modified graphene is successfully synthesized and its compatibility to the media is enhanced as assumption. When the ratio between PAM and graphene is 1:10, the suspension absorbance is improved as twice as common graphene’s. Meanwhile the concentration of graphene in suspension can reach 0.05mg/ml without any agglomeration.

Abstract: A series of techniques, including field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and energy dispersive X-ray spectroscopy were employed to investigate three types of Y-shaped carbon fibers that were synthesized by the thermal decomposition of acetylene using an atmospheric pressure catalytic chemical vapor deposition process and copper tartrate as a catalyst precursor. On the basis of electron microscopy analysis, we propose that the simultaneous growth of three pieces of carbon fibers on the same copper catalyst particle results in the formation of Y-shaped carbon fibers. When several copper catalyst particles became positioned in a stratified arrangement, other types of Y-shaped carbon fibers were obtained. Our study indicates that the morphology of various Y-shaped carbon fibers can be controlled by tailoring the configuration of the copper catalyst particles used to generate them.

Abstract: The synthesis of complexional ultrafine zinc oxide powders by controlled-release precipitation method, which is a precipitation process of precursor by controlling ammonia distillation rate in ammonia solution under the combination effect of microwave heating and ultrasonic cavitating, and followed by subsequent heat treatment was investigated. The characteristic of precursor and zinc oxide powders were studied using X-ray diffraction, scanning electron microscopy, TG-DTA-DTG, FT-IR, and ultraviolet-visible pectrophotometer. The coloring mechanism of complexional zinc oxide is discussed. This has shown that a tentative composition of the precursor is likely Zn₃CO₃(OH)₄·H₂O. Complexional zinc oxide particles of an average particle size of 200 nm with narrow size distribution, good dispersibility and hexagonal appearance could be obtained after annealing at 350°C for 1.5 hour. ZnO particles are complexional, probably due to nitrogen atom or N-H bond entering into crystal lattice of zinc oxide. Complexional zinc oxide has fine capacity of shielding UV and absorbing wide range of wavelength.

Abstract: BCN–TiO₂ was prepared by doping Ti(OH)₄ with graphite-like structure BCN in an annealing process at 400[°C] for 2[h]. The catalyst samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). Graphite-like structure BCN was detected by XRD. The results showed that with graphite-like structure BCN doped in, the crystal size became smaller than pure TiO₂. Also B, C, N were detected in crystal lattice of TiO₂, in which Boron was in the form of B_x+, Carbon substituted some of the lattice oxygen atoms as Ti-C, and Nitrogen was in the form of Ti-N and Ti-O-N.

Abstract: The amorphization and crystallization of mechanical alloyed Cu₅₀Zr₄₀Ag10 alloy have been investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results demonstrate that a full amorphous phase of Cu₅₀Zr₄₀Ag₁₀ can be obtained through mechanical alloying. The amorphous phase begins to show the initial mechanical crystallization when the milling time is 108 h and subsequently the main milling product is still amorphous structure with increasing milling time up to 208 h. Therefore, the amorphous alloy exhibits the excellent mechanical stability during mechanical alloying. The nearest-neighbor distance of atoms firstly increases then reduces with the increasing milling time, indicating that there is a closely correlation between the initial crystallization behavior and short range ordering.

Abstract: A series of the carbon nanotubes were synthesized on quartz substrates in a chemical vapor deposition (CVD) process. Ethylene was used as the carbon source, and ferrocene used as the catalyst. The scanning electron microscope (SEM) and Raman spectrum were employed to investigate the effects of reaction temperature on the structure and components of the carbon nanotubes. The results showed that, when the reaction temperature is 860°C , the best synthesis of the well-distributed carbon nanotubes with less of non-carbon impurity was achieved. At this condition, The length of the CNTs was 95 μm and the diameter was 104 nm.