Showing papers by "Wuhan University of Technology published in 2007"

Template‐Free Fabrication and Enhanced Photocatalytic Activity of Hierarchical Macro‐/Mesoporous Titania

Abstract: Hierarchical macro-/mesoporous titania is prepared without the addition of templates or auxiliary additives at room temperature by the simple dropwise addition of tetrabutyl titanate to pure water, and then calcined at various temperatures. The products are characterized by X-ray diffraction, N 2 -adsorption-desorption analysis, scanning electron microscopy, and the corresponding photocatalytic activity is evaluated by measuring the photocatalytic oxidation of acetone in air. The results reveal that hierarchical macro-/mesoporous structures of titania can spontaneously form by self-assembly in alkoxide-water solutions in the absence of organic templates or auxiliary additives. The calcination temperature has a strong effect on the structures and photocatalytic activity of the prepared titania. At 300 °C, the calcined sample shows the highest photocatalytic activity. At 400 and 500 °C, the photocatalytic activity slightly decreases. When the calcination temperature is higher than 500 °C, the photocatalytic activity greatly decreases because of the destruction of the hierarchical macro-/mesoporous structure of the titania and the drastic decrease of specific surface area. The hierarchically macro-/mesostructured titania network with open and accessible pores is well-preserved after calcination at 500 °C, indicating especially high thermal stability. The macroporous channel structures are even preserved after calcination at 800 °C. This hierarchical macro-/mesostructured titania is significant because of its potential applications in photocatalysis, catalysis, solar-cell, separation, and purification processes.

Effects of hydrothermal temperature and time on the photocatalytic activity and microstructures of bimodal mesoporous tio2 powders

Abstract: Bimodal nanocrystalline mesoporous TiO2 powders with high photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate (TiO(C4H9)4, TBOT) as precursor. The as-prepared TiO2 powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption–desorption measurements. The photocatalytic activity of the as-prepared TiO2 powders was evaluated by the photocatalytic degradation of acetone (CH3COCH3) under UV-light irradiation at room temperature in air. The effects of hydrothermal temperature and time on the microstructures and photocatalytic activity of the TiO2 powders were investigated and discussed. It was found that hydrothermal treatment enhanced the phase transformation of the TiO2 powders from amorphous to anatase and crystallization of anatase. All TiO2 powders after hydrothermal treatment showed bimodal pore-size distributions in the mesoporous region: one was intra-aggregated pores with maximum pore diameters of ca. 4–8 nm and the other with inter-aggregated pores with maximum pore diameters of ca. 45–50 nm. With increasing hydrothermal temperature and time, the average crystallite size and average pore size increased, in contrast, the Brunauer-Emmett-Teller (BET) specific surface areas, pore volumes and porosity steadily decreased. An optimal hydrothermal condition (180 °C for 10 h) was determined. The photocatalytic activity of the prepared TiO2 powders under optimal hydrothermal conditions was more than three times higher than that of Degussa P25.

Lithiated MoO3 Nanobelts with Greatly Improved Performance for Lithium Batteries

Abstract: Recently, nanostructured materials have attracted great interest in the field of lithium-ion batteries, essentially because of their substantial advantages, such as short transport path lengths for both electrons and Li ions, a large amount of contact surface area between the electrode and electrolyte, and large flexibility and toughness for accommodating strain introduced by Li insertion/extraction. Among the transition-metal oxides, nanostructured MoO3 has been extensively investigated as a key material for fundamental research and technological applications in optical devices, smart windows, catalysts, sensors, lubricants, and electrochemical storage. There are two basic polytypes of MoO3: orthorhombic MoO3 (a-type) being a thermodynamically stable phase, and the metastable monoclinic MoO3 (b-type) with a ReO3-type structure. The most important structural characteristic of a-MoO3 is its structural anisotropy, which can be considered as a layered structure parallel to (010) (See the inset of Fig. S1, Supporting Information). Each layer is composed of two sub-layers, each of which is formed by corner-sharing octahedra along [001] and [100]; the two sub-layers stack together by sharing the edges of the octahedra along [001]. An alternate stack of these layered sheets along [010] would lead to the formation of a-MoO3, where a van der Waals interaction would be the major binding force between the piled sheets. One might take advantage of the intrinsic structural anisotropy of a-MoO3 for tuning its properties by interlayer structural modification, annealing, and lithiation. In this Communication, we report the electroactivity of a-MoO3 nanobelts after lithiation that show superior performance to nonlithiated a-MoO3 nanobelts. An X-ray diffraction (XRD) measurement was performed using a D/MAX-III X-ray diffractometer. Fourier-transformed infrared (FTIR) absorption spectra were recorded using the 60-SXB IR spectrometer. Raman spectra were taken using a Renishaw RM-1000 laser Raman microscopy system. Scanning electron microscopy (SEM) images were collected with a JSM-5610 and FES-EM LEO 1530. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) were recorded by using a JEOL JEM2010 FEF microscope. The electrochemical properties were studied with a multichannel battery testing system. Batteries were fabricated using a lithium pellet as the negative electrode; 1 M solution of LiPF6 in ethylene carbon (EC)/dimethyl carbonate (DMC) as the electrolyte; and a pellet made of the nanobelts, acetylene black and PTFE in a 10:7:1 ratio as the positive electrode. The fabrication of a single nanobelt-based device has been described in detail elsewhere. XRD measurement was first used to study the phase and lattice modification of the nanobelts before and after lithiation (Fig. 1A). The diffraction peaks of the XRD pattern for both samples can be readily indexed to be orthorhombic with lattice constants of a = 3.962 A, b = 13.85 A, c = 3.697 A (International Centre for Diffraction Data (ICDD) No. 050508). No peaks of any other phases were detected, indicating the high purity of the MoO3 nanobelts. For the non-lithiated MoO3 nanobelts, the stronger intensities of (020), (040), and (060) peaks than those for the bulk MoO3 (Fig. S1, Supporting Information) indicates the anisotropic growth of the nanostructure as well as the preferred orientation of the nanobelts on the substrate. Importantly, in comparison to the nonlithiated sample, there is a small shift of the (020) peak toward a lower diffraction angle for the lithiated sample. This is direct evidence of an expanded b-plane interlayer distance for 0.065 A after lithiation, possibly due to the introduction of Li interstitials between the layers. The morphology and microstructure of the products were observed by using SEM and TEM. Before lithiation (Fig. 1B), C O M M U N IC A TI O N

Template-free hydrothermal synthesis of CuO/Cu2O composite hollow microspheres

Abstract: CuO/Cu2O composite hollow microspheres with controlled diameter and composition were prepared without the addition of templates and additives by hydrothermal synthesis using Cu(CH3COO)2·H2O as a precursor. Increasing the precursor concentration from 0.02 to 0.2 M increased the diameter of the composite hollow microspheres from 500 nm to 5 μm. Moreover, the content of Cu2O in the composite hollow microspheres increased with increasing the reaction time or/and precursor concentration to produce a range of composite hollow microspheres with Cu2O contents from 20 to 80 wt %. A localized Ostwald ripening mechanism was proposed to account for the formation of CuO/Cu2O composite hollow microspheres. The photocatalytic activity experiment indicated that the prepared CuO/Cu2O composite hollow microspheres exhibited a higher photocatalytic activity for the photocatalytic decolorization of methyl orange aqueous solution under the visible-light illumination than the single phase CuO or Cu2O samples.

Hydrothermal Preparation and Photocatalytic Activity of Hierarchically Sponge-like Macro-/Mesoporous Titania

Abstract: Trimodally sponge-like macro-/mesoporous titania was prepared by hydrothermal treatment of precipitates of tetrabutyl titanate (Ti(OC4H9)4) in pure water. Effects of hydrothermal time on the phase composition, porosity, and photocatalytic activity of hierarchically porous titania were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) and N2 adsorption−desorption measurements. All TiO2 powders prepared at 180 °C showed trimodal pore-size distributions in the macro-/mesoporous region: fine intraparticle mesopores with peak pore diameters of ca. 3.7−6.9 nm, larger interparticle mesopores with peak pore diameters of ca. 23−39 nm, and macropore with pore diameter of ca. 0.5−3 μm. With increasing hydrothermal time, crystallinity, and average anatase crystallite size, pore size and pore volume increased, while specific surface area decreased. The hierarchically porous titania prepared ...

Preparation and properties of montmorillonite modified asphalts

Abstract: Modified asphalts were prepared by melt blending with different contents of montmorillonite (MMT) and organomodified montmorillonite (OMMT). The X-ray diffraction (XRD) results show that the MMT modified asphalt may form an intercalated structure, whereas the OMMT modified asphalt may form an exfoliated structure. The addition of MMT and OMMT to asphalt increases both the softening point and viscosity of the modified asphalts at high temperatures. Furthermore, the modified asphalts exhibited higher complex modulus, lower phase angle. As a consequence, the MMT and OMMT modified asphalts displays enhanced viscoelastic properties, which improve its resistance to rutting at high temperatures. Compared with MMT, OMMT showed better effect in improving softening point and rutting resistance of asphalt, which contributes to the formation of exfoliated structure in OMMT modified asphalt. Storage stability tests disclose that the asphalts modified with MMT or OMMT are very stable when montmorillonite content is less than 3 wt%.

From Copper Nanocrystalline to CuO Nanoneedle Array: Synthesis, Growth Mechanism, and Properties

Abstract: In the present work, a novel method for synthesizing a one-dimensional CuO nanoneedle array was introduced; that is, first, a pure copper nanocrystalline layer was plated by using a periodic revers...

Effect of montmorillonite on properties of styrene–butadiene–styrene copolymer modified bitumen

Abstract: Clay/styrene–butadiene–styrene (SBS) modified bitumen composites were prepared by melt blending with different contents of sodium montmorillonite (Na-MMT) and organophilic montmorillonite (OMMT). The structures of clay/SBS modified bitumen composites were characterized by XRD. The XRD results showed that Na-MMT/SBS modified bitumen composites may form an intercalated structure, whereas the OMMT/SBS modified bitumen composites may form an exfoliated structure. Effects of MMT on physical properties, dynamic rheological behaviors, and aging properties of SBS modified bitumen were investigated. The addition of Na-MMT and OMMT increases both the softening point and viscosity of SBS modified bitumens and the clay/SBS modified bitumens exhibited higher complex modulus, lower phase angle. The high-temperature storage stability can also be improved by clay with a proper amount added. Furthermore, clay/SBS modified bitumen composites showed better resistance to aging than SBS modified bitumen, which was ascribed to barrier of the intercalated or exfoliated structure to oxygen, reducing efficiently the oxidation of bitumen, and the degradation of SBS. POLYM. ENG. SCI., 47:1289–1295, 2007. © 2007 Society of Plastics Engineers

Low-temperature preparation and visible-light-induced catalytic activity of anatase F–N-codoped TiO2

Abstract: This paper reports a new process to prepare the F–N-codoped TiO2 photocatalysts with anatase at 100 ◦ C using TiCl4 and NH4F as titanium and fluorine, nitrogen sources, respectively. The as-prepared yellow or white yellow photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen adsorption/desorption measurements (BET), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (UV–vis DRS). The results showed that the F–N-codoping extended the absorbance spectra of TiO2 into visible region. The BET surface area of the as-prepared F–N-codoped TiO2 photocatalyst was high up to 191 m 2 g −1 . The results of degradation of methyl orange (MO) solution showed that the F–N-codoped samples exhibit much higher visible-light-induced catalytic activities than that of Degussa P25 and the as-prepared pure TiO2. This property can be attributed to the synergetic effects of absorption in the visible-light region, red shift in adsorption edge, good crystallization, porous structure and large surface area of the F–N-codoped TiO2. © 2007 Elsevier B.V. All rights reserved.

Multiwall boron carbonitride/carbon nanotube junction and its rectification behavior.

Abstract: Theoretical calculations have predicted that the band gap of boron carbonitride (BCN) nanotubes can be tailored over a wide range by chemical composition rather than by geometrical structure. The following attempts toward the fabrication of BCN nanotube devices should be of great importance both to further understand their electronic properties and to develop their prospective applications for nanoscale electronic and photonic devices. Here, the direct synthesis of massive BCN/C nanotube junctions has been realized via a bias-assisted hot-filament chemical vapor deposition method. The electrical transport measurements of individual nanotube junctions were performed on a conductive atomic force microscopy. It is found that the BCN/C nanotube junction shows a typical rectifying diode behavior.

Scientometric analysis of geostatistics using multivariate methods

Abstract: Multivariate methods were successfully employed in a comprehensive scientometric analysis of geostatistics research, and the publications data for this research came from the Science Citation Index and spanned the period from 1967 to 2005. Hierarchical cluster analysis (CA) was used in publication patterns based on different types of variables. A backward discriminant analysis (DA) with appropriate statistical tests was then conducted to confirm CA results and evaluate the variations of various patterns. For authorship pattern, the 50 most productive authors were classified by CA into 4 groups representing different levels, and DA produced 92.0% correct assignment with high reliability. The discriminant parameters were mean impact factor (MIF), annual citations per publication (ACPP), and the number of publications by the first author; for country/region pattern, CA divided the top 50 most productive countries/regions into 4 groups with 95.9% correct assignments, and the discriminant parameters were MIF, ACCP, and independent publication (IP); for institute pattern, 3 groups were identified from the top 50 most productive institutes with nearly 88.0% correct assignment, and the discriminant parameters were MIF, ACCP, IP, and international collaborative publication; last, for journal pattern, the top 50 most productive journals were classified into 3 groups with nearly 98.0% correct assignment, and its discriminant parameters were total citations, impact factor and ACCP. Moreover, we also analyzed general patterns for publication document type, language, subject category, and publication growth.

Effects of fibers on the dynamic properties of asphalt mixtures

Abstract: The dynamic characteristics of fiber-modified asphalt mixture were investigated. Cellulose fiber, polyester fiber and mineral fiber were used as additives for asphalt mixture, and the dosage was 0.3%, 0.3%, 0.4%, respectively. Dynamic modulus test using SuperPave simple performance tester (SPT) was conducted to study the dynamic modulus (E*) and phase angle (δ) for the control asphalt mixture and fiber-modified ones at various temperatures and frequencies. Experimental results show that all fiber-modified asphalt mixtures have higher dynamic modulus compared with control mixture. The dynamic modulus master curves of each type of asphalt mixtures are determined based on nonlinear least square regression in accordance with the timetemperature superposition theory at a control temperature (21.1°C). The fatigue parameter E*×sinδ and rutting parameter E*/sinδ of asphalt mixture are adopted to study the fatigue and rutting-resistance properties, and experimental results indicate that such properties can be improved by fiber additives.

Pressureless Sintering of α-Si3N4 Porous Ceramics Using a H3PO4 Pore-Forming Agent

Abstract: A new method for preparing high bending strength porous silicon nitride (Si3N4) ceramics with controlled porosity has been developed by using pressureless sintering techniques and phosphoric acid (H3PO4) as the pore-forming agent. The fabrication process is described in detail and the sintering mechanism of porous ceramics is analyzed by the X-ray diffraction method and thermal analysis. The microstructure and mechanical properties of the porous Si3N4 ceramics are investigated, as a function of the content of H3PO4. The resultant high porous Si3N4 ceramics sintered at 1000°–1200°C show a fine porous structure and a relative high bending strength. The porous structure is caused mainly by the volatilization of the H3PO4 and by the continous reaction of SiP2O7 binder, which could bond on to the Si3N4 grains. Porous Si3N4 ceramics with a porosity of 42%–63%, the bending strength of 50–120 MPa are obtained.

Dynamics in microbial immobilization and transformations of phosphorus in highly weathered subtropical soil following organic amendments

Abstract: To improve knowledge on the role of microbial processes in phosphorus (P) transformations in highly weathered subtropical soil, dynamics in microbial biomass C (BC) and P (BP), and Olsen-P in a subtropical Ultisol following amendments with glucose at 2 g C kg−1 soil (G2) and rice straw at 2 and 4 g C kg−1 soil (RS2 and RS4) was studied during a 43-day incubation period at 25°C and 45% of soil water-holding capacity. By 3 days, the amount of soil BC had increased about 3.2, 1.7, and 2.6 times for G2, RS2, and RS4, respectively. The amount of soil BC significantly decreased between 3 and 7 days for G2 and 3 and 14 days for RS4, and thereafter remained almost steady throughout the 43-day incubation period, at levels about 1.6–2.4 times larger than for the control (no organic amendment; CK). The amount of soil BP for G2 and RS4 almost doubled by 3 or 7 days, then remained relatively steady, and for RS2, maintained relatively constant (6.7–8.2 mg kg−1 soil) throughout 43-day incubation period, whereas it declined by about 50% for CK. A significant decrease (3.5 mg kg−1 soil) in Olsen-P occurred in G2 by 3 days; indicating a close response of available P to microbial immobilization. Also, the amounts of Al- and Fe-bound P in G2 and Fe-bound-P in RS4 decreased significantly, as determined at 43 days. In conclusion, organic amendment enhances microbial immobilization and transformations of P, but the turnover of BP behaves in different patterns as BC in highly weathered subtropical soil.