745 research outputs found
Effects of hydrothermal temperature and acid concentration on the transition from titanate to titania
No full textNanostructured titanates were prepared by alkaline hydrothermal processing. The titanates were transformed to the anatase particles at low concentrations of acid, whereas the rutile rods were produced from the titanates at high concentrations of acid. These changes were more retarded in the titanate nanofiber product than in titanate nanotubes product, which could be attributed to the stability and high crystallinity of the titanate nanofiber product prepared at a high hydrothermal temperature. The photocatalytic activities of the acid treated nanostructured titanates for MB degradation and gaseous CH 3CHO oxidation were strongly dependent on the presence of the anatase crystalline phase. © 2012 The Korean Society of Industrial and Engineering Chemistry.1
Enhancement of photocatalytic activity of titania-titanate nanotubes by surface modification
No full textHydrothermally prepared titanate nanotubes are known to be thermodynamically unstable and to be easily transformed to the titania phase by heat or acid treatment, which is accompanied by the destruction of the nanotube structures. Surface modification of titanate nanotubes is expected to retard the phase-transition reactions from titanate nanotubes to titania nanoparticles. In this study, we investigated the effects of surface modifications, such as fluorination or phosphation, on the phase-transition reactions of hydrothermally prepared titanate nanotubes under acidic conditions. After acid treatment, surface-modified titanate nanotubes maintained their nanotube structures, and spherical nanoparticles were partially formed in the titanate nanotubes. Unmodified titanate nanotubes, however, changed to elongated nanostructures and spherical nanoparticles. The surface modifications also strongly affected the crystalline phases and increased the BET surface area. The photocatalytic activities for methylene blue degradation and gaseous CH 3CHO oxidation were strongly enhanced by the surface modifications. These effects were attributed to the anatase crystalline phase and the high surface area. Therefore, these surface modifications are useful methods to improve the photocatalytic activities of titanate nanotubes. © 2012 Elsevier B.V.1
Preparation of hybrid silicon wire and planar solar cells having ZnO antireflection coating by all-solution processes
No full textThis report proposes newly designed all-solution based processes for fabricating hybrid silicon (Si) wire-planar solar cells having conformal zinc oxide (ZnO) nanorod anti-reflection coating (ARC). The all-solution processes were composed of three steps. First, metal-assisted chemical etching combined with natural lithography was used to fabricate ordered Si wire arrays. Second, spin-on-dopant (SOD) diffusion was introduced to make a pn junction in the Si wire arrays and bulk Si substrate. Finally, using hydrothermal synthesis, ZnO nanorods were grown on hybrid Si wire-planar solar cells to create an efficient ARC. Currentvoltage (IV) results show that the hybrid solar cells with ZnO ARC lead to increased power conversion efficiency by more than 25% compared to the planar solar cells. This is mainly attributed to the enhanced light absorption and reduced light reflection by the combination of Si wire geometry and ZnO ARC. This research demonstrates a new approach for lowering the cost of Si wire-based solar cells and making them applicable to photovoltaic devices with large areas. © 2011 Elsevier B.V. All rights reserved.
Metal nanoparticles decorated PET/PET-TiO2 bi-component filaments by photocatalytic deposition
No full textGold, silver, and platinum nanoparticles were immobilized on the surface of TiO2 in the sheath part of bi-component filaments. The processes involved include the spinning process used to prepare polyethylene terephthalate (PET)/PET-TiO2 bi-component filaments and the photocatalytic deposition process of gold, silver and platinum nanoparticles. The core part and the sheath part consist of virgin PET and 4 wt.% of TiO2 compounded PET, respectively. The sheath: core ratio of the filament was 50:50. For the photo-deposition of metal nanoparticles, adsorption of the metal ions on the surface of the fabrics was performed by immersing them in AgNO3, HAuCl4, and H2PtCl6 aqueous solutions, with simultaneous addition of methanol as a sacrificial agent. Photo-deposition was then carried out under UV light with an irradiation time of 60 seconds. The structural and antibacterial properties of the bi-component filaments were characterized. The nano-sized noble metal particles in a polka dot form were observed around the surface of the TiO2 particles in sheath region of bi-component filaments after photocatalytic deposition. Ag, Au, and Pt metal photo-deposited fabrics showed excellent antimicrobial effect against the two types of bacteria Staphylococcus aureus and Klebsiella pneumoniae under dark conditions. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.
Photocatalytic deposition of silver nanoparticles onto organic/inorganic composite nanofibers
No full textIn this work, silver nanoparticles were embedded in electrospun organic/inorganic composite nanofibers consisting of PAN and TiO2 through photocataly tic reduction of the silver ions in silver nitrate solutions under UV irradiation. The morphology and diameter of PAN/TiO2 composite nanofibers could be controlled by varying the initial contents of TiO2 in the spinning solution. From TEM images and UV-Vis spectra, it has been confirmed that monodisperse silver nano-particles with a diameter of ≈2 nm were deposited selectively upon the titania of the as prepared composite nanofibers. The amount of Ag nanoparticles embedded on composite nano-fibers was greatly influenced by the amount of TiO2 in composite nanofibers, reflecting the role of titania as the inorganic stabilizer and photocatalyst. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.1
Adaptive redundancy control for systematic erasure code based real time data transmission in Internet.
No full textProceedings of IEEE International Conference on Communications (18-22 June 2000 : New Orleans, LA, USA
A new active clamping non-dissipative snubber for ZVS PWM current-fed half-bridge converter
No full textA new active clamping zero-voltage switching (ZVS) pulse-width modulation (PWM) current-fed half-bridge converter (CFHB) is proposed in this paper. Its active clamping snubber (ACS) can not only absorb the voltage surge across the turned-off switch, but also achieve the ZVS of all power switches. Moreover, it can be applied to all current-fed power conversion topologies and its operation as well as structure is very simple. Since auxiliary switches in the snubber circuit are switched in a complementary way to main switches, an additional PWM IC is not necessary. In addition, it does not need any clamp winding and auxiliary circuit besides additional two power switches and one capacitor while the conventional current-fed half bridge converter has to be equipped with two clamp windings, two ZVS circuits, and two snubbers. Therefore, it can ensure the higher operating frequency, smaller-sized reactive components, lower cost of production, easier implementation, and higher efficiency. The operational principle, theoretical analysis, and design considerations are presented. To confirm the operation, validity, and features of the proposed circuit, experimental results from a 200-W, 24-200Vdc prototype are presented
Colorimetric hydrogen gas sensor based on PdO/metal oxides hybrid nanoparticles
No full textWe have synthesized new colorimetric hydrogen-sensing materials, PdO/metal oxide hybrid nanoparticles, in which palladium oxide was loaded upon surface of substrate materials via an acid-base reaction between a H2PdCl4 solution and substrate materials, ZnO, MgO, TiO2, and SiO2 respectively at 25 °C. The colorimetric hydrogen gas sensing properties of all the samples, PdO/ZnO, PdO/MgO, PdO/TiO2 and PdO/SiO2, were characterized and compared in order to investigate how hydrogen gas sensitivity would be affected by surface property of substrate materials. It was confirmed that the amount of the loaded PdO, which was thought to be closely related with the colorimetric hydrogen sensitivity, was quite different according to the substrate materials and was increased with increasing of the basicity of substrate materials (ZnO > MgO > TiO2 > SiO2). Consequently, among the PdO/metal oxide hybrid nanoparticles, the largest amount of PdO was observed to be loaded on ZnO substrate nanoparticles due to its highest basicity. The best colorimetric hydrogen gas sensing properties (color difference, ΔE = 71.57) was observed in PdO/ZnO hybrid nanoparticles, showing the most prominent color change from brown to black, when the sample was exposed to hydrogen gas of 4 vol% balanced with nitrogen for 2 min. © 20181
Optical and photovoltaic properties of silicon wire solar cells with controlled ZnO nanorods antireflection coating
No full textWe introduce a new type of silicon micro-wire (SiMW) solar cell with a conformal zinc oxide (ZnO) nanorods anti-reflection coating (ARC) and discuss the optical and photovoltaic properties of the SiMW solar cells with controlled ZnO nanorods. The fabrication processes were composed of metal-assisted electroless etching combined with photolithography, spin-on-dopant diffusion, and hydrothermal synthesized ZnO nanorods growth. We found that the combination of Si wire geometry and ZnO ARC was able to maximize the light absorption and to minimize the light reflectance. Illuminated current-voltage (I-V) results show that the photovoltaic efficiency of SiMW solar cells with optimized ZnO ARC was enhanced more than 50% and the short-circuit current density was improved by over 43% compared to SiMW solar cells without ZnO ARC. This is mainly attributed to the reduced light reflectance and enhanced photon absorption. These hybrid structures are promising for making low-cost Si wire solar cells and making them applicable to photovoltaic devices with large areas. © 2012 Springer Science+Business Media, LLC.
Synthesis of Al-doped ZnO Nanorods via Microemulsion Method and Their Application as a CO Gas Sensor
No full textAluminum doped ZnO (AZO) nanorods were synthesized by microemulsion method with different types of surfactants. The phase and the morphology of the above nanorods were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM observations showed that the ZnO nanorods had diameters around about 50-200nm and lengths up to several micrometers. The CO gas sensing properties of the AZO nanorods were tested at operating temperatures of 200, 300, 350 and 400°C. It was found that AZO nanorods based sensor exhibited the highest sensitivity to CO at 350°C. © 2015 .
- …
