Advanced Materials Research Vols. 306-307

Abstract: Large-sized macroporous TiO₂/SiO₂ catalysts were prepared via filling a novel SiO₂ support with a solution of tetrabutyl titanate in cyclohexane, undergoing subsequent in situ hydrolysis and final calcination to 600 °C. The loaded nano-particles of TiO₂ were uniformly dispersed on the nano-layer of SiO₂ support, the interaction of TiO₂ and SiO₂ was strengthened through the formation of Si-O-Ti bonds. Methyl orange was introduced in the macroporous catalyst as a target compound to investigate the photo-degradation of the loaded nano-TiO₂. Under radiation of 365 nm UV light the highest degradation rate constant of 1.78/h was observed from the as-prepared catalyst containing 54.5 wt.% of TiO₂. Formaldehyde and xylene in gas states can be captured and photo-degraded by the catalyst that was placed in a self-designed air-circulation device equipped with UV lights and electric fans. The high effectiveness of the catalysts in the cleaning of the indoor air should be owing to its special macroporous structure and the long-term photo-catalytic activity of loaded nano-TiO₂.

Abstract: Cornstalk fibers were modified with surface modification and the properties of cornstalk fiber/gypsum composites was studied. The results showed that mechanical properties of cornstalk fiber/gypsum composites were enhanced by adding unmodified cornstalk fibers, but composites waterproof performance was decreased greatly. Through surface modification on cornstalk fibers, composites mechanical properties were further enhanced, and composites waterproof performance was improved obviously. The mechanism of surface modification was discussed, and the model of interfacial zone between modified cornstalk fiber and gypsum matrix was proposed.

Abstract: The field-emission properties of capped(5, 5) single-walled carbon nanotubes with hydrogen adsorbed on the tip with and without an applied electric field have been investigated using first-principles density-functional theory. It is found that the structure of carbon nanotubes with hydrogen molecules is stable under field-emission conditions. The local density of states at the Fermi level increases with the adsorption of hydrogen molecules. These results elucidate that the field-emission properties of carbon nanotubes can be enhanced by the adsorption of hydrogen molecules, and are consistent with the experimental results.

Abstract: Carbon nanotubes(CNTs) films were fabricated by microwave plasma chemical vapor deposition (MPCVD) on stainless steel substrates. In order to study the reason that its emission current weakens, the CNTs films were treated by hydrogen plasma. The research discovered that the hydrogen plasma treatment to the carbon nanotubes films reduced the surface work function of the film and its filed emission current, this mainly due to the etching of hydrogen plasma to sp² carbon on the surface, it leads emission area to decrease.

Abstract: A new pyridinium dye, 2-{2-[9-ethyl-carbazole-3-yl]vinyl}-N-(3-sulfooxypropyl) pyridinium inner salt, has been synthesized. The photophysical properties of the dye in DMF were investigated. The dye exhibits strong orange fluorescence with quantum yield Φ = 0.1. The particles are nano-scale after 30minutes, but it will accumulate to micron-scale after 4h.

Abstract: Thermal conductivities of two kinds of nanofluids (SiO₂-water and SiO₂-ethylene glycol) were measured by transient hot-wire method at different volume fraction and temperature. Influences of volume fraction of particles and temperature on thermal conductivities of nanofluids were analyzed. The Experimental results show that thermal conductivities of nanofluids are higher than those of base fluids, and increase with the increase of volume fraction and temperature. When approximately 0.5% volume fraction of SiO₂ nanoparticles are added into water and ethylene glycol at the temperature 50°C, the thermal conductivities are enhanced 46.2% and 62.8% respectively.

Abstract: Nanocomposites of single-walled carbon nanotubes modified polypyrrole (PPy/SWNTs) were synthesized successfully by in situ oxidative polymerization method in the FeCl₃·6H₂O solution. The morphological structure, electrical conductivity and thermal stability of the nanocomposites were characterized by TEM, SEM, FTIR and TGA. The PPy/SWNTs were 50-100 nm in diameter of PPy coating uniformly on the surface of the SWNTs. FTIR spectra revealed the presence of covalently interaction between the PPy and the carbon nanotubes. The electrical conductivity of PPy/SWNTs composite and pure PPy were 93 and 8.0×10^-3 S/cm, respectively. Meanwhile, the PPy/SWNTs composites possessed higher thermal stability (65.9 wt. % weight loss at 600 °C) compared to pure PPy (81.2 wt. % weight loss at 600 °C), the content of SWNTs was 15.3 wt. %.

Abstract: Nanosized and highly reactive magnesium niobate Mg₄Nb₂O₉ were successfully synthesized by a sol-gel method as potential candidates for use in microwave applications as a low-temperature co-fired ceramic (LTCC). The Nb-Mg-citric acid solution was evaporated resulting in a dry gel that was calcined in the temperature ranging from 550°C to 850°C for crystallization in air atmosphere. The crystallization process from the gel to the crystalline Mg₄Nb₂O₉ was followed by thermal analysis and during calcinations phase evolution of the powders was studied using X-ray diffraction (XRD) technique. Particle size and morphology were examined by high resolution scanning electron microscopy (HR-SEM). At 850°C the corundum-like phase of magnesium niobate was obtained in air atmosphere with an average particle diameter of 80 nm approximately calculated from the HR-SEM images.

Abstract: Cd_xZn_1-xSe alloy nanocrystals (NCs) were successfully synthesized by an organic route using oleic acid as a capping agent. The molar ratio of Cd/Zn strongly impact on the PL properties of the alloy NCs. The PL peak wavelength of the alloy NCs was 565 nm at the Cd/Zn molar ratio of 0.05 while their wavelength became 621 nm in the case of the molar ratio of 1. The average lifetime of the alloy NCs increased with increasing the Cd/Zn molar ratios (26 ns for a ratio of 0.05 and 45 ns for a ratio of 1). The X-ray diffraction analysis indicated that the alloy NCs revealed a cubic structure. The Cd/Zn molar ratio drastically affected the crystal structure of the alloy NCs which located between those of ZnSe and CdSe NCs.

Abstract: Novel hybrid SiO₂-coated CdTe core-shell nanocrystals (NCs) were fabricated by re-dispersing green-emitting CdTe NCs in a solution of Cd²⁺ ions, thioglycolic acid (TGA), tetraethyl orthosilicate and ammonia with a sol-gel reaction at room temperature and a further reflux procedure. The hybrid NCs consisted of a CdTe core and a hybrid SiO₂ shell with CdS-like clusters. The clusters created by the reaction of Cd²⁺ and S^2- generated by the decomposition of TGA during reflux. The hybrid NCs exhibited tunable photoluminescence (PL) color from green to red and high PL quantum yield (PLQY). The CdS-like clusters play an important role for the hybrid NCs with numerous PL properties. Compared with initial CdTe NCs, the PLQY of the hybrid NCs increased from 18% to 47% together with a red-shifted PL peak wavelength of 61 nm. The average lifetime of the hybrid NCs (39 ns) is longer than that of initial CdTe NCs (25 ns). The high PLQY and the hybrid shell make CdTe NCs an important application for biological technique.