EFFECT OF N,N,N~'''',N~''''-TETRAALKYL TEREPHTHALAMIDE ON NON-ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYPROPYLENE

The effect of N,N,N',N'-tetraalkyl terephthalamide (TATA) on the non-isothermal crystallization and melting characteristics of polypropylene (PP) was studied. The addition of TATA can lead to the formation of β-crystal PP. With the increase in TATA concentration the degree of crystallinity for β-crystal PP increased significantly, and that for α-crystal PP decreased, which indicated that TATA effectively induced the formation of β-crystal PP. WAXD also revealed the existence of β-crystal PP after the introduction of TATA into PP. PP containing TATA crystallized at a temperature range of 5-10℃ higher than that of pure PP, and the half-crystallization time (t1/2) and Avrami exponent (n) of PP at the same cooling rate were decreased by the addition of TATA, indicating that TATA influenced the crystallization rate and crystallization growth mode of PP. The rate constant of crystallization of PP containing TATA (Zc) was larger than that of pure PP, which further indicated that the crystallization of PP was accelerated by the addition of TATA.     

1.3μmInGaAsP/InP DCC结构半导体激光器

用普通的LPE技术,严格控制两个有源区组分的匹配、各层掺杂浓度及生长条件,获得了1.3μm双载流子限制DCC结构半导体激光器(T0=150K)。此结构中第二有源区形成的势阱对热载流子具有二次限制作用,增加了第一个有源区泄漏和俄歇过程产生的过热载流子在第二有源区内辐射复合参与激射的机会;降低了这些热载流子进入限制层产生损耗的几率,提高了T0值,说明了DCC结构激光器阈值以下特征EL光谱半宽度与注入电流密度的关系并讨论了两个有源区组分匹配及薄夹层厚度对特征温度T0和阈值电流的影响。     

Rutile TiO2 nanowires on anatase TiO2 nanofibers: a branched heterostructured photocatalysts via interface-assisted fabrication approach

A water-dichloromethane interface-assisted hydrothermal method was employed to grow rutile TiO(2) nanowires (NWs) on electrospun anatase TiO(2) nanofibers (NFs), using highly reactive TiCl(4) as precursor. The water-dichloromethane interface inhibited the formation of rutile NWs in water phase, but promoted the selective radial growth of densely packed rutile NWs on anatase NFs to form a branched heterojunction. The density and length of rutile NWs could be readily controlled by varying reaction parameters. A formation mechanism for the branched heterojunction was proposed which involved (1) the entrapment of rutile precursor nanoparticles at water-dichloromethane interface, (2) the growth of rutile NWs on anatase NFs via Ostwald ripening through the scavengering of interface-entrapped rutile nanoparticles. The heterojunction formed at anatase NF and rutile NW enhanced the charge separation of both under ultraviolet excitation, as evidenced by photoluminescence and surface photovoltage spectra. The branched TiO(2) heterostructures showed higher photocatalytic activity in degradation of rodamine B dye solution than anatase NFs, and the mixture of anatase NFs, and P25 powders, which was discussed in terms of the synergistic effect of enhanced charge separation by anatase-rutile heterojunction, high activity of rutile NWs, and increased specific area of branched heterostructures.     

In situ assembly of well-dispersed gold nanoparticles on electrospun silica nanotubes for catalytic reduction of 4-nitrophenol

The tubular nanocomposite with well-dispersed distribution of small gold nanoparticles (AuNPs) assembled on the inside and outside surfaces of silica nanotubes (SNTs) was fabricated by combining the single capillary electrospinning technique and an in situ reduction approach. The AuNPs/SNTs nanocomposite exhibited a good catalytic activity for reduction of 4-nitrophenol (4-NP).     

A magnetic metal-organic framework as a new sorbent for solid-phase extraction of copper(II), and its determination by electrothermal AAS

We report on the synthesis of Fe₃O₄-functionalized metal-organic framework (m-MOF) composite from Zn(II) and 2-aminoterephthalic acid by a hydrothermal reaction. The magnetic composite is iso-reticular and was characterized by FTIR, X-ray diffraction, SEM, magnetization, and TGA. The m-MOF was then applied as a sorbent for the solid-phase extraction of trace levels of copper ions with subsequent quantification by electrothermal AAS. The amount of sorbent applied, the pH of the sample solution, extraction time, eluent concentration and volume, and desorption time were optimized. Under the optimum conditions, the enrichment factor is 50, and the sorption capacity of the material is 2.4 mg g^?1. The calibration plot is linear over the 0.1 to 10 μg L^?1 Cu(II) concentration range, the relative standard deviation is 0.4 % at a level of 0.1 μg L^?1 (for n?=?10), and the detection limit is as low as 73 ng L^?1. We consider this magnetic MOF composite to be a promising and highly efficient material for the preconcentration of metal ions.

Controllable synthesis and enhanced visible photocatalytic degradation performances of Bi2WO6–carbon nanofibers heteroarchitectures

Bi₂WO₆–carbon nanofibers (Bi₂WO₆–CNFs) heteroarchitectures were fabricated by two steps consisting of the preparation of CNFs by electrospinning and growth of Bi₂WO₆ on the CNFs through ethylene glycol solvothermal processing. The results showed that the loading amounts of Bi₂WO₆ on the surface of CNFs could be controlled by adjusting the precursor concentration for the fabrication of Bi₂WO₆–CNFs heteroarchitectures during the solvothermal process. The photocatalytic tests revealed that the obtained Bi₂WO₆–CNFs heteroarchitectures showed higher photocatalytic property under visible light to degrade Rhodamine B than pure Bi₂WO₆ synthesized by solvothermal process in the absence of CNFs owing to improved separation efficiency of photogenerated electrons and holes. Moreover, the Bi₂WO₆–CNFs heteroarchitectures could be separated easily by sedimentation due to their one-dimensional nanostructural property. Meanwhile, the photocatalytic activity of Bi₂WO₆–CNFs heteroarchitectures was stable during the recycling due to the strong interactions between Bi₂WO₆ nanosheets and CNFs. Trapping experiment suggested that ${\text{O}}_{ 2}^{ \cdot - }$ , instead of OH·, was the main active species during the photocatalytic process of the Bi₂WO–CNFs heteroarchitectures.     

MODIFICATION OF CeO2 AND ITS EFFECT ON THE HEAT-RESISTANCE OF SILICONE RUBBER

By means of the wet chemical surface modification,the surface of CeO_2 was modified by vinyltrimethoxysilane (VTMS).Infrared spectroscopy was used to investigate the structure of the modified CeO_2 and the result showed that VTMS has been attached onto the surface of CeO_2.Effect of VTMS concentration on the active index of the modified CeO_2 was also studied,and the result indicated that the active index of the modified CeO_2 increases with the increase of VTMS concentration and the optimal concentratio...     

Biocompatible ZnO/Au nanocomposites for ultrasensitive DNA detection using resonance Raman scattering

A novel method for identifying DNA microarrays based on ZnO/Au nanocomposites functionalized with thiol-oligonucleotide as probes is descried here. DNA labeled with ZnO/Au nanocomposites has a strong Raman signal even without silver acting as a surface-enhanced Raman scattering promoter. X-ray photoelectron spectra confirmed the formation of a three-component sandwich assay, i.e., constituted DNA and ZnO/Au nanocomposites. The resonance multiple-phonon Raman signal of the ZnO/Au nanocomposites as a spectroscopic fingerprint is used to detect a target sequence of oligonucleotide. This method exhibits extraordinary sensitivity and the detection limit is at least 1 fM.     

Local bond average for the thermally induced lattice expansion

An approach of local bond average (LBA) has been developed by extending the bond-order-length-strength correlation (Sun, C. Q. Prog. Solid State Chem. 2007 , 35, 1- 159 ) to temperature domain for the mechanism of the thermally driven bond expansion in a solid specimen. It is shown that the detectable quantities of a solid can be connected directly to the bonding identities and the response of the bonding identities to the stimulus of temperature change, being free from using the concepts in classical thermodynamics or hypothetical constants. The success of the LBA approach has been evidenced by fitting the observations from a number of specimens with derived information of atomic cohesive energy, which may go beyond the currently available approaches.