Shan-ng Tu

Biodiesel production from waste cooking oil catalyzed by TiO2-MgO mixed oxides.

Mixed oxides of TiO(2)-MgO obtained by the sol-gel method were used to convert waste cooking oil into biodiesel. Titanium improved the stability of the catalyst because of the defects induced by the substitution of Ti ions for Mg ions in the magnesia lattice. The best catalyst was determined to be MT-1-923, which is comprised of an Mg/Ti molar ratio of 1 and calcined at 923 K, based on an assessment of the activity and stability of the catalyst. The main reaction parameters, including methanol/oil molar ratio, catalyst amount, and temperature, were investigated. The catalytic activity of MT-1-923 decreased slowly in the reuse process. After regeneration, the activity of MT-1-923 slightly increased compared with that of the fresh catalyst due to an increase in the specific surface area and average pore diameter. The mixed oxides catalyst, TiO(2)-MgO, showed good potential in large-scale biodiesel production from waste cooking oil.

Intensification of biodiesel synthesis using zigzag micro-channel reactors.

Zigzag micro-channel reactors have been fabricated and used for continuous alkali-catalyzed biodiesel synthesis. The influences of the main geometric parameters on the performance of the micro-channel reactors were experimentally studied. It has been found that the zigzag micro-channel reactor with smaller channel size and more turns produces smaller droplets which result in higher efficiency of biodiesel synthesis. Compared to conventional stirred reactors, the time for high methyl ester conversion can be shortened significantly with the methyl ester yield of 99.5% at the residence time of only 28 s by using the optimized zigzag micro-channel reactor, which also exhibits less energy consumption for the same amount of biodiesel during biodiesel synthesis. The results indicate that zigzag micro-channel reactors can be designed as compact and mini-fuel processing plant for distributive applications.

One-step solvothermal synthesis of nickel selenide series: Composition and morphology control

A one-step oleylamine-mediated solvothermal method was reported for the synthesis of nickel selenide series within a short reaction time. The method provided a suitable nucleation and growth environment in a uniform and transparent solution reaction system. Through adjustment of the Ni/Se raw material ratio and reaction temperature, cubic NiSe2, orthorhombic NiSe2, and hexagonal Ni1−xSe (x = 0–0.15) were obtained. In addition, under an excess nickel source (Niu2006:u2006Se = 2u2006:u20061) and phase change agent, hexagonal NiSe was converted to rhombohedral Ni3Se2, in which the intermediate phase (NiSe) acted as both reactant and template, plus an effect on Ni3Se2 morphology. At a certain reaction temperature of 260 °C, the phase transformation and morphology can be adjusted by changing the solvents (mixture of OLA and ODE). Finally, the conversion mechanism from cubic NiSe2 to orthorhombic NiSe2 at different reaction temperatures was investigated, and the formation process of a nickel selenide series had also been studied through synthetic route controlled experiments. This paper provided a simple and low cost method to control the composition and morphology of nickel selenide series, which would be of great potential for the synthesis of other metal selenides.

Mercaptopropionic acid capped CdSe/ZnS quantum dots as fluorescence probe for lead(II)

MPA stabilized CdSe/ZnS NCs was applied as a fluorescent probe for the sensitive detection of Pb2+ in water. The microreaction was demonstrated as a facile method for the reproducible synthesis of CdSe/ZnS NCs with a high quantum yield. The good stability of CdSe/ZnS NCs was proved by the significant maintaining of photoluminescent (PL) after the ligand exchange with MPA, and was further demonstrated by the excellent PL property in water solution with various pH values. The cation exchange of Zn with Pb led to the linear quenching of PL with the concentration of Pb2+, which provided as an opportunity to apply MPA stabilized CdSe/ZnS NCs as fluorescent probes for Pb2+. A facile method by adjustment of QDs concentration was demonstrated as a suitable way to approach different detection limits. The detection limits of 0.03 and 3.3xa0μM were achieved by setting QDs solutions with the absorbance of the first exciton peak as 0.05 and 0.15, respectively.

One-step synthesis of pure pyrite FeS2 with different morphologies in water

In this study, pyrite FeS2 with novel nanostructures had been obtained via an ethanolamine (ETA)–water binary system. This method provided a uniform and homogenous environment for the nucleation and growth of FeS2. When only pure water was used as the reaction solvent, marcasite FeS2 with a hollow sphere structure was achieved, and then transformed into the pyrite phase with a rod-like structure piled up by nanoparticles with the increase of the reaction time. Moreover, cubic, flake-like, and two types of tetrakaidecahedron structures were obtained via the adjustment of the volume ratio of ETA and H2O. The transformation mechanism from flower-like amorphous to different types of morphologies of pyrite FeS2 crystals was analyzed through the time-dependent controlled experiments. The Raman spectra of the samples with different morphologies were investigated, which were consistent with the XRD analysis. The studies of optical properties indicate that the morphologies had a great influence on the absorption properties. This study provided a very simple and low cost method to control the morphologies of FeS2 crystals, which would be of great potential for the synthesis of other metal chalcogenides and lay the foundation for the development of solar cells.

Measurement of temperature-dependent diffusion coefficients using a confocal Raman microscope with microfluidic chips considering laser-induced heating effect.

Conventional methods for measuring diffusion coefficients (D) are complex and time consuming. This study presents a method for the continuous measurement of temperature-dependent diffusion coefficients using a confocal Raman microscope with microfluidic chips. Concentration information was collected by a Raman microscope to extract D values. An isothermal diffusion process at various temperatures was ensured by coupling the silicon-based microfluidic chip with an isothermal plate. In the simple silicon/glass chip, the heating effect induced by a Raman laser was observed to contribute to abnormally high D values. To eliminate the heating effect, a 200nm-thick aluminum (Al) reflection film was used to coat the channel bottom. The Al film substantially reduced absorption of laser power, thus ensuring precise D values in excellent agreement with literature data. Other potential methods to eliminate the heating effect were also evaluated by computational fluid dynamics (CFD) simulations and were found impractical for implementation. Consequently, this method for the continuous measurement of temperature-dependent diffusion coefficients is proven to be accurate, efficient, and reliable.

Effect of notch position on creep damage for brazed joint

The creep failure is easy generate in surface notch.The far away notch is helpful to reduce the creep damage of filler metal.As H increases, the failure location moves from filler metal to base metal.As H increases, the failure time increases first then keeps stable.The failure time decreases with L increases while it increases with W increases. In this paper, we investigated the effect of notch position on creep damage for Hastelloy C276-BNi2 brazed joint. Three different types of notches locate in edge of base metal (base notch), edge of filler metal (surface notch) and center of filler metal (inside notch) were compared, and the influence of notch geometric parameters on creep damage was also investigated. The results show that the different notch position and dimension generate different creep damage distributions and have a great influence on creep life. The creep failure is the easiest to occur in surface notch, then the base notch, and the last is inside notch. The brazed joint with higher maximum principal stress and von Mises stress generates creep failure easier. For the base notch, the failure time increases with the increase of base notch distance and the creep failure location moves gradually from the center of filler metal to notch tip. The notch locating away from filler metal is beneficial to reduce the creep damage in filler metal and enhance the creep life. For the inside notch, the failure time decreases with notch length increases and the maximum creep damage locates at notch tip. With the increase of inside notch width, the failure time increases first and then keep steadiness, and the failure location moves away from notch tip. The effects of notch position and dimension should be fully considered in creep failure analyses and life assessments of brazed joints.

Quantum-dots-sensitized solar cells based on vertically ranged titanium dioxide nanotubes

ABSTRACT CdS and CdSe quantum-dots-sensitized solar cells (QDSSC) consisted of highly ordered, vertically oriented TiO2 nanotubes were reported. TiO2 nanotubes served both as a large-area support for quantum dots and high-efficiency electron-transporting medium. Anodization method was investigated to fabricate nanotubes directly growing on Ti foil with various anodization time. Under illumination of one sun, the as-obtained QDSSC provided a power conversion efficiency of 1.61%.

Operational Limitation and Instability of a Microwave-Induced Microplasma Enclosed in a Microcavity at Low Gas Pressures

In this paper, operational limitations (the extinguishing of the stable glow discharge) and instabilities [glow-to-arc transition (GAT)] of microwave-induced microplasmas enclosed in microcavities operated at low gas pressures were investigated by experiments, in comparison with unenclosed microplasmas. For enclosed microplasmas, when gas pressure decreased, GAT occasionally occurred, whereas GAT was never detected for unenclosed microplasmas, because the gas temperatures of enclosed microplasmas were higher than those of unenclosed ones. For enclosed microplasmas operated at low gas pressures, an increase in the microcavity dimension is a valid method to avoid GAT. Extinguishing pressure of stable glow-discharge microplasma (pext) for microwave-induced microplasma enclosed in a microcavity microplasma was lower than that for microwave-induced microplasma generator without the PDMS cavity (UEC) microplasmas. The increase in input power decreased pext for UEC microplasmas but showed a slight influence on pext for EC microplasmas. This paper shed some light on understanding of the enclosed microplasmas operated at low gas pressures.

The glass-silicon-glass sandwich structured microplasma chip as the electron source of a micro mass spectrometer

Micro mass spectrometer is one of the most powerful porta-ble analytical instruments. And the micro electron impact (EI) ionization source, which has crucial effects on micro mass spectrometers performance, has been a research focus. In this study, a microplasma source as the electron source of the EI ionization source was developed to solve the difficulty in miniaturization on filament structure for conventional elec-tron source. The microplasma source was fabricated as a three wafer glass-silicon-glass sandwich with all the struc-tures realized in a highly doped silicon wafer via a deep reac-tive ion etch (DRIE) process. The microplasma source is 33 mm wide, 44 mm long, and 1.3 mm high.