Showing papers by "Wuhan University of Technology published in 2009"

Fabrication and Characterization of Visible-Light-Driven Plasmonic Photocatalyst Ag/AgCl/TiO2 Nanotube Arrays

Abstract: Conventional TiO2 photocatalyst possesses excellent activities and stabilities, but requires near-ultraviolet (UV) irradiation (about 4% of the solar spectrum) for effective photocatalysis, thereby severely limiting its practical application. It is highly desirable to develop a photocatalyst that can use visible light in high efficiency under sunlight irradiation. In this work, we prepare new visible-light-driven plasmonic photocatalyst Ag/AgCl/TiO2 nanotube arrays (NTs) by depositing AgCl nanoparticles (NPs) into the self-organized TiO2 NTs, and then reducing partial Ag+ ions in the surface region of the AgCl particles to Ag0 species under xenon lamp irradiation. The prepared metal−semiconductor nanocomposite plasmonic photocatalyst exhibits a highly visible-light photocatalytic activity for photocatalytic degradation of methyl orange in water and stability. A new plasmonic photocatalytic mechanism, which is proposed on the basis of the fact that the Ag NPs are photoexcited due to plasmon resonance and c...

Preparation, characterization and visible-light-driven photocatalytic activity of Fe-doped titania nanorods and first-principles study for electronic structures

Abstract: Fe-doped TiO 2 (Fe-TiO 2 ) nanorods were prepared by an impregnating-calcination method using the hydrothermally prepared titanate nanotubes as precursors and Fe(NO 3 ) 3 as dopant. The as-prepared samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, N 2 adsorption–desorption isotherms and UV–vis spectroscopy. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air under visible-light irradiation. The results show that Fe-doping greatly enhance the visible-light photocatalytic activity of mesoporous TiO 2 nanorods, and when the atomic ratio of Fe/Ti ( R Fe ) is in the range of 0.1–1.0%, the photocatalytic activity of the samples is higher than that of Degussa P25 and pure TiO 2 nanorods. At R Fe = 0.5%, the photocatalytic activity of Fe-TiO 2 nanorods exceeds that of Degussa P25 by a factor of more than two times. This is ascribed to the fact that the one-dimensional nanostructure can enhance the transfer and transport of charge carrier, the Fe-doping induces the shift of the absorption edge into the visible-light range with the narrowing of the band gap and reduces the recombination of photo-generated electrons and holes. Furthermore, the first-principle density functional theory (DFT) calculation further confirms the red shift of absorption edges and the narrowing of band gap of Fe-TiO 2 nanorods.

Enhancement of Photocatalytic Activity of Mesporous TiO2 Powders by Hydrothermal Surface Fluorination Treatment

Abstract: Mesporous surface-fluorinated TiO2 (F−TiO2) powders of anatase phase with high photocatalytic activity are prepared by a one-step hydrothermal strategy in a NH4HF2−H2O−C2H5OH mixed solution with tetrabutylorthotitanate (Ti(OC4H9)4, TBOT) as precursor. The prepared samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption−desorption isotherms, UV−vis absorption spectroscopy, and transmission electron microscopy. The production of hydroxyl radicals (•OH) on the surface of UV-illuminated TiO2 is detected by a photoluminescence (PL) technique with use of terephthalic acid as a probe molecule. The photocatalytic activity is evaluated by photocatalytic oxidation decomposition of acetone in air under UV light illumination. The results show that the photocatalytic activity of F−TiO2 powders is obviously higher than that of pure TiO2 and commercial Degussa P25 (P25) powders due to the fact that the strong electron-withdrawing ability of the surface ≡Ti−F groups reduces the rec...

Corporate governance structure and firm performance in developing economies: evidence from Nigeria

Abstract: – The purpose of this paper is to examine the link between corporate governance structure and firm performance in Nigeria, – The present study uses the regression model to analyze publicly available data for a sample of 107 firms quoted in the Nigerian Stock Exchange for the fiscal years 1998 to 2002, – The empirical investigations showed that ownership concentration has a positive impact on performance Although the results revealed no evidence to support the impact of board composition on performance, there is significant evidence to support the fact that CEO duality adversely impact firm performance The result also suggests firm size and leverage to impact on firm performance A new variable, identified as more than one family member on the board, is found to have an adverse effect on firm performance, – The study relied much on publicly available data for a sample of 107 listed firms in Nigeria for the fiscal years 1998 to 2002 Thus, effort should be made to look at this study in a more elaborate viewpoint and across borders, – Good corporate governance standards are imperative to every organization and should be encouraged for the interest of the investors and other stakeholders, – Interestingly, from a developing country perspective, especially in sub‐Saharan Africa, the paper is the first of its kind and offers evidence on the impact of corporate governance structure on firm performance The paper provides useful information that is of great value to policy makers, academics and other stakeholders

High performance InxCeyCo4Sb12 thermoelectric materials with in situ forming nanostructured InSb phase

Abstract: n-Type skutterudites InxCeyCo4Sb12 with in situ forming nanostructured InSb phase have been prepared by a melt-quench-anneal-spark plasma sintering method. Doping of In results in a nanostructured InSb phase with the grain size of 10–80 nm that is evenly distributed on the boundaries of the skutterudite matrix. The nanostructured InSb phase has a strong influence on phonon scattering and leads to a notable suppression of the lattice thermal conductivity of InxCeyCo4Sb12. The combined effect of In and Ce doping results in high performance skutterudite materials. The highest thermoelectric figure of merit ZT=1.43 is achieved at 800 K in the In0.2Ce0.15Co4Sb12 compound.

Hydrothermal Synthesis and Visible-light Photocatalytic Activity of Novel Cage-like Ferric Oxide Hollow Spheres

Abstract: Fe2O3 hollow spheres with novel cage-like architectures and porous crystalline shells were successfully fabricated by a controlled hydrothermal precipitation reaction using urea as a precipitating agent and carbonaceous polysaccharide spheres as templates in a mixed solvent of water and ethanol, and then calcined at 500 °C for 4 h. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption−desorption isotherms, and UV−visible diffuse reflectance spectroscopy. The visible-light photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under visible-light illumination in the presence of H2O2. The results indicated that the diameter, shell thickness, average crystallite size, specific surface areas, pore structures, and photocatalytic activity of Fe2O3 hollow spheres could be easily controlled...

Microstructure and mechanical properties of CoCrFeNiTiAlx high-entropy alloys

Abstract: CoCrFeNiTiAl x ( x values in molar ratio, x = 0, 0.5, 1.0, 1.5 and 2.0) high-entropy alloys were prepared using a vacuum arc melting method. The effects of Al addition on microstructure and mechanical properties were investigated. The results show that only a face-centered cubic (FCC) crystal structure phase is observed in the CoCrFeNiTi alloy. The phase composition transforms to stabilized body-centered cubic (BCC) structure phases and typically cast dendrite structure appears when Al is added. The dendrite region is rich in Co, Ni, Ti and Al elements while the interdendrite region is rich in Fe and Cr elements. Subgrains and nanosized precipitates are observed in the as-cast CoCrFeNiTiAl alloy. These CoCrFeNiTiAl x high-entropy alloys exhibit excellent room-temperature mechanical properties. For CoCrFeNiTiAl 1.0 alloy, the compressive strength and elastic modulus reach as high as 2.28 GPa and 147.6 GPa, respectively. High density of dimple-like structure is observed from the fracture surfaces of the Al 0 alloy, while alloys with Al addition show typical cleavage fractures with river-like patterns and cleavage steps.

One-Pot Template-Free Synthesis of Monodisperse Zinc Sulfide Hollow Spheres and Their Photocatalytic Properties

Abstract: Monodisperse wurtzite ZnS hollow spheres with diameters of about 200 nm and shells composed of nanoparticles have been successfully synthesized in high yield by a one-pot template-free hydrothermal route. The reaction duration, reactant species, and reaction temperature have been shown to play important roles in the formation of ZnS hollow spheres. X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption/desorption, UV/Vis diffuse reflectance spectroscopy, and photoluminescence were used to characterize the products. The results show that all the prepared nanospheres have hexagonal wurtzite structures and exhibit good size uniformity and regularity. A mechanism for the formation of the ZnS hollow spherical structure by localized Ostwald ripening has been proposed based on experimental observations. In addition, studies of the photocatalytic properties of the ZnS hollow spheres by exposure to UV irradiation have demonstrated that they have potential photocatalytic applications. Hydroxyl radicals (*OH) were not detected on the surface of UV-illuminated ZnS by the photoluminescence technique, which suggests that *OH is not the dominant photo-oxidant and a photogenerated hole could instead directly participate in the photocatalytic reaction. The prepared ZnS hollow spheres are also of great interest for use in flat displays, sensors, lasers, catalysis, separation technology, biomedical engineering, and nanotechnology.

From MoO3 Nanobelts to MoO2 Nanorods: Structure Transformation and Electrical Transport

Abstract: The MoO2nanorods (NRs) were synthesized by simple hydrogen reduction using the MoO3 nanobelts (NBs) as the templates. The growth mechanism of one-dimensional (1D) MoO2nanostructure can be explained by the cleavage process due to the defects in the MoO3NBs. DifferentI/Vcharacteristics of individual MoO2 NRs were obtained at different bias voltages, which can be explained by Ohmic and Schottky conduction mechanisms,andtheresistivityincreasedathighbiasvoltageprobablybecauseoftheoxidationofMoO2NRswith large specific surface area.

Enhanced thermoelectric performance in barium and indium double-filled skutterudite bulk materials via orbital hybridization induced by indium filler.

Abstract: Maximizing the thermoelectric figure-of-merit (ZT) is a challenge owing to the conflicting combination of material properties. We explored simultaneously enhancing the power factor and reducing the thermal conductivity through filling In in Ba-filled skutterudite (Ba(0.3)Co(4)Sb(12)). Two large ZT values of 1.33 and 1.34 have been achieved for Ba(0.15)In(0.16)Co(4)Sb(11.83) and Ba(0.14)In(0.23)Co(4)Sb(11.84) at 850 K, respectively. The excellent thermoelectric transport properties for Ba(r)In(s)Co(4)Sb(12) are supposed to be due to the orbital hybridizations induced by In filler. It was found that the In filler made the [Sb(4)](4-) rings become bigger and squarer because of an electron transition from Sb to In brought out by the orbital hybridization between In and Sb and that the Ba filler caused the [Sb(4)](4-) rings to get smaller and squarer because of a reverse electron transition from Ba to Sb induced by a large difference in electronegativities between Ba and Sb. A model of how to form the rectangular [Sb(4)](4-) ring is presented, and the five chemical states of Sb in CoSb(3) are reasonably assigned to different chemical bonds in the model.

Synthesis of Boehmite Hollow Core/Shell and Hollow Microspheres via Sodium Tartrate-Mediated Phase Transformation and Their Enhanced Adsorption Performance in Water Treatment

Abstract: A variety of boehmite hollow core/shell and hollow microspheres with high adsorption affinity toward organic pollutants in water were prepared via a facile one-pot hydrothermal method using aluminum sulfate as a precursor and urea and sodium tartrate as precipitating and mediating agents, respectively. These microspheres were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption. In addition, the aforementioned microspheres were examined as potential adsorbents for Congo red and phenol from aqueous solutions. This study shows that the crystallinity, specific surface area, and pore structure of the resulting microspheres can be controlled by varying the concentration of sodium tartrate and reaction time. The reported experiments allowed us to propose the mechanism of formation of hollow core/shell and hollow microspheres, which involves sodium tartrate-mediated phase transformation, followed by a subsequent self-assembly process. ...

Synthesis of Hierarchical Flower-like AlOOH and TiO2/AlOOH Superstructures and their Enhanced Photocatalytic Properties

Abstract: Hierarchical flower-like boehmite superstructures (HFBS) composed of intermeshed nanoflakes were synthesized by hydrothermal treatment from as-formed aluminum hydroxide microspheres, which were prepared by adding aluminum spheres into a sodium metaaluminate solution. A two-step mechanism for the formation of HFBS is proposed, which involves initial formation of Al(OH)3 microspheres followed by their transformation to AlOOH. The as-prepared HFBS superstructures can be easily transformed into γ-Al2O3 superstructures without morphology change by calcination at 500 °C for 2 h. Furthermore, the TiO2 nanoparticles can homogeneously deposited on the surface of HFBS by the vapor-thermal method. The TiO2 nanoparticles coated on HFBS showed higher photocatalytic activity for photocatalytic decolorization of rhodamine B (RhB) aqueous solution than Degussa P25 (P25) and TiO2 powders prepared at the same experimental conditions. A significant enhancement of the photocatalytic activity can be related to several factors...

Effects of polymer-grafted natural nanocrystals on the structure and mechanical properties of poly(lactic acid): A case of cellulose whisker-graft-polycaprolactone

Abstract: In this work, polysaccharide nanocrystals—rodlike cellulose whiskers (CWs)—were surface-grafted with polycaprolactone (PCL) via microwave-assisted ring-opening polymerization, and filaceous cellulose whisker-graft-polycaprolactone (CW-g-PCL) nanoparticles were produced. Moreover, the resultant nanoparticles were incorporated into poly(lactic acid) (PLA) as a matrix, and they showed superior function for enhancing the mechanical performance of PLA-based materials in comparison with platelet-like nanoparticles of starch nanocrystal-graft-PCL. The optimal loading level of CW-g-PCL was 8 wt %, and this resulted in simultaneous enhancements of the strength and elongation of approximately 1.9- and 10.7-fold, respectively, over those of the neat PLA material. In this case, the rigid CW nanoparticles contributed to the endurance of higher stress, whereas the grafted PCL chains improved the association between the PLA matrix and the CW-g-PCL filler and hence facilitated the transfer of stress to the rigid CW nanoparticles. Furthermore, such a fully biodegradable PLA-based nanocomposite shows great potential for environmentally friendly materials because of its high mechanical performance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Monitoring temperature effect on a long suspension bridge

Abstract: The Tsing Ma Bridge in Hong Kong is a long suspension bridge. A wind and structural health monitoring system (WASHMS) has been installed in the bridge and operated by the Hong Kong Highways Department since 1997. The WASHMS is devised to carry out the monitoring of environmental status, traffic loads, bridge features and bridge responses. The environmental status includes temperature environment monitored by temperature sensors, whereas the bridge responses contain displacement responses recorded by displacement transducers, level sensing stations, and global positioning systems (GPS). Bridge displacement responses are, however, induced by a combination of four major types of loadings due to wind, temperature, highway, and railway. This investigation focuses on the temperature environment and the predominating temperature effect on the Tsing Ma Bridge. The main features and the pertinent monitoring system of the Tsing Ma Bridge are first introduced. The data collected from the four types of sensors are pre-processed. The statistics of ambient air temperature, effective temperature and displacement response of the bridge are then figured out based on the measurement data. The statistical relationship between the effective temperature and the displacement of the bridge is finally established. These results are useful for monitoring temperature effects on the Tsing Ma Bridge. Copyright © 2009 John Wiley & Sons, Ltd.

An improved binary particle swarm optimization for unit commitment problem

Abstract: This paper proposes a new improved binary PSO (IBPSO) method to solve the unit commitment (UC) problem, which is integrated binary particle swarm optimization (BPSO) with lambda-iteration method. The IBPSO is improved by priority list based on the unit characteristics and heuristic search strategies to repair the spinning reserve and minimum up/down time constraints. To verify the advantages of the IBPSO method, the IBPSO is tested and compared to the other methods on the systems with the number of units in the range of 10-100. Numerical results demonstrate that the IBPSO is superior to other methods reported in the literature in terms of lower production cost and shorter computational time.

Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances

Abstract: Single-crystalline ZnO nanowires were synthesized, and further modified with Pd nanoparticles through self-assemblies. The self-assembly strategy shows advantages of tailoring the surface modification of ZnO nanowires with monodispersed Pd nanoparticles and further tuning of the functionalities of nano-architectures. It was found that poly(vinylpyrrolidone) (PVP) plays a key role in loading Pd nanoparticles onto the surfaces of ZnO nanowires. Having been turned into chemical sensors, the nano-architectures constructed from ZnO nanowires and Pd nanoparticles exhibit a highly enhanced response to H2S gas, compared to the devices from pure ZnO nanowires.

Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin films as sensing materials

Abstract: Different from usually-used bulk magnetostrictive materials, magnetostrictive TbDyFe thin films were firstly proposed as sensing materials for fiber-optic magnetic field sensing characterization. By magnetron sputtering process, TbDyFe thin films were deposited on etched side circle of a fiber Bragg Grating (FBG) as sensing element. There exists more than 45pm change of FBG wavelength when magnet field increase up to 50 mT. The response to magnetic field is reversible, and could be applicable for magnetic and current sensing.

Protein adsorption on poly(N-vinylpyrrolidone)-modified silicon surfaces prepared by surface-initiated atom transfer radical polymerization.

Abstract: Well-controlled poly(N-vinylpyrrolidone) (PVP)-grafted silicon surfaces were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) with 1,4-dioxane/water mixtures as solvents and CuCl/5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6TATD) as a catalyst. The thickness of the PVP layer on the surface increased with reaction time, suggesting that the ATRP grafting of N-vinylpyrrolidone (NVP) from the silicon surfaces was a well-controlled process. The water contact angle and X-ray photoelectron spectroscopy (XPS) were used to characterize the modified surfaces. The protein adsorption property of the PVP-grafted surfaces was evaluated using a radiolabeling method. Compared with unmodified silicon surfaces, a Si−PVP60 surface with a PVP thickness of 15.06 nm reduced the level of adsorption of fibrinogen, human serum albumin (HSA), and lysozyme by 75, 93, and 81%, respectively. Moreover, the level of fibrinogen adsorption decreases gradually with an increase in PVP thicknes...