Comparison of photocatalytic performance of anatase TiO2 prepared by low and high temperature route

Anatase TiO₂ was prepared by a facile sol-gel method at low temperature through tailoring the pH of sol-gel without calcination. As a control, anatase TiO₂ was also synthesized by the conventional sol-gel process, in which calcination at 500 °C was required to transform the amorphous oxide into highly crystalline anatase. As-prepared samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). Their photocatalytic activities were evaluated by degradation of methyl orange under UV light irradiation. On the basis of experiment results, it could be concluded that TiO₂ prepared by low temperature route showed more advantages in small particle size, highly dispersion nature, abundance of surface hydroxyl groups, strong PL signal, and high photocatalytic activity over TiO₂ obtained by the conventional sol-gel process. Furthermore, the reason of the former possessing higher photocatalytic activity was discussed.     

Enhanced photocatalytic degradation of Safranin-O by heterogeneous nanoparticles for environmental applications

Nanostructure titanium dioxide (TiO₂) has been synthesized by hydrolysis of titanium tetrachloride in aqueous solution and Ag-TiO₂ nanoparticles were synthesized by photoreduction method. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) and UV-vis absorption spectroscopy. The experimental results showed that the sizes of the synthesized TiO₂ and Ag-TiO₂ particles are in the range of 1.9-3.2 nm and 2-10 nm, respectively. Moreover, Ag-TiO₂ nanoparticles exhibit enhanced photocatalytic activity on photodegradation of Safranin-O (SO) dye as compared to pure TiO₂. The positive effect of silver on the photocatalytic activity of TiO₂ may be explained by its ability to trap electrons. This process reduces the recombination of light generated electron-hole pairs at TiO₂ surface and therefore enhances the photocatalytic activity of the synthesized TiO₂ nanoparticles. The effects of initial dye and nanoparticle concentrations on the photocatalytic activity have been studied and the results demonstrate that the dye photodegradation follows pseudo-first-order kinetics. The observed maximum degradation efficiency of SO is about 60% for TiO₂ and 96% for Ag-TiO₂.     

Diffusion of CO2/CH4 confined in narrow carbon nanotube bundles

ABSTRACT

The diffusion of a CO₂/CH₄ mixture in carbon nanotube (CNT) bundles was studied using molecular simulations. The effect of diameter and temperature on the diffusion of the mixture was investigated. Our results show that the single-file diffusion occurs when CO₂ and CH₄ are confined in CNTs of diameter less than 1.0 nm. In CNTs of diameter larger than 1.0 nm, both molecules diffuse in the Fickian style. The transition from single-file to Fickian diffusion was demonstrated for both CO₂ and CH₄ molecules. A dual diffusion mechanism was observed in the studied (20, 0) CNT bundle, single-file diffusion of CO₂ in the interstitial sites of (20, 0) CNT bundle and Fickian diffusion of CO₂ and CH₄ in the pores. For CO₂, the interaction energies (CO₂–CO₂ and CO₂–CNT) are larger than that of CH₄ in all cases. But only a very small difference in the diffusion coefficient was observed between CO₂ and CH₄. Temperature has a negligible effect on the difference between diffusion coefficients of CO₂ and CH₄ in the studied CNT bundles. The adsorption, diffusion and permeation selectivities are discussed and compared, and the adsorption is demonstrated to be the rate limiting step for the separation of CO₂/CH₄ in CNT bundle membranes.     

Nanostructured carbon nanotube/TiO2 composite coatings using electrophoretic deposition (EPD)

Electrophoretic deposition (EPD) has been used to combine multi-walled carbon nanotubes of diameter in the range 20–30 nm and commercially available TiO₂ nanoparticles (23 nm particle size) in composite films. Laminate coatings with up to four layers were produced by sequential EPD, while composite coatings were obtained by electrophoretic co-deposition of carbon nanotubes and TiO₂ nanoparticles, respectively. Scanning electron microscopy was used to characterize the resultant microstructures. The mechanism of EPD of carbon nanotube/TiO₂ nanoparticle composites is discussed.     

Flowerlike PtCl4/Bi2WO6 composite photocatalyst with enhanced visible-light-induced photocatalytic activity

Flowerlike PtCl₄/Bi₂WO₆ composite photocatalyst was successfully synthesized through a simple two-step method involving a template-free hydrothermal process and the following impregnation treatment. The samples were fully characterized by the study of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis absorption spectra. The results indicated that the doping of Pt species did not affect the crystal structure and the morphology of Bi₂WO₆ photocatalyst, but it had great influences on the photocatalytic activity of Bi₂WO₆ towards rhodamine-B (RhB) degradation. Besides, the Pt species was found to be present as PtCl₄ in the composite samples, and also an optimal Pt species content on the surface of Bi₂WO₆ photocatalyst was discovered with the highest photocatalytic ability. The improved photocatalytic performance could be ascribed to the enhanced interfacial charge transfer and the inhibited recombination of electron-hole pairs. Meanwhile, a possible mechanism for RhB photocatalytic degradation over PtCl₄/Bi₂WO₆ catalyst was also proposed.     

Investigation on mechanism of photocatalytic activity enhancement of nanometer cerium-doped titania

A series of Ce-TiO₂ are prepared by the sol-gel process with ammonium cerium(IV) nitrate and tetra-n-butyl titanium as raw materials and characterized with XRD, TEM, DRS, and XPS. The aberrance (0.355) of anatase(1 0 1) plane of 0.1% Ce/TiO₂ increases compared to that of TiO₂. Cerium is found to be present as a mixture of Ce^3+/4+ oxidation states, that is, the oxidation state of some cerium in Ce-TiO₂ has changed after calcination. Ce/TiO₂ yields a large red shift compared to TiO₂. Moreover, the reflectance decreases in the visible region after cerium doped on TiO₂, and the lower the reflectance the higher the activity. Cerium appears to enhance the photocatalytic activity of Ce/TiO₂ by suppressing electron-hole recombination with electron trapping at Ce⁴⁺. 0.1% Ce/TiO₂ shows highest activity for the degradation of aqueous suspension of formaldehyde.     

Titanium dioxide nanoparticles prepared by laser pyrolysis: Synthesis and photocatalytic properties

TiO₂ nanoparticles were synthesized via the laser pyrolysis of titanium tetrachloride-based gas-phase mixtures. In the obtained nanopowders, a mixture of anatase and rutile phases with mean particle size of about 14 nm was identified. Using the thermal heated laser nanopowders, mechanically stable films were produced by immobilizing titania nanopowders on glass substrates (the doctor blading method followed by compression). The photocatalytic activity of the prepared films was tested by the degradation of 4-chlorophenol in an aqueous solution under UV-illumination. By referring to known commercial samples (Degussa P25) similarly prepared, higher photocatalytic efficiency was found for the laser-prepared samples.     

Fabrication of flower-shaped Bi2O3 superstructure by a facile template-free process

A novel flower-shaped Bi₂O₃ superstructure has been successfully synthesized by calcination of the precursor, which was prepared via a citric acid assisted hydrothermal process. The precursor and Bi₂O₃ were characterized with respect to morphology, crystal structure and elemental chemical state by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was shown that both the precursor and Bi₂O₃ flower-shaped superstructure were constructed of numerous nanosheets while the nanosheets consisted of a great deal of nanoparticles. Furthermore, key factors for the formation of the superstructures have been proposed; a mechanism for the growth of the superstructure has been presented based on the FESEM investigation of different growth stages.     

Preparation of photocatalytic Fe2O3-TiO2 coatings in one step by metal organic chemical vapor deposition

There are two major difficulties in the TiO₂ liquid-solid photocatalytic system: effective immobilization of the TiO₂ particles; and improving the catalytic activity under visible light. To simultaneously solve these two problems, Fe₂O₃-TiO₂ coatings supported on activated carbon fiber (ACF), have been prepared in one step by a convenient and efficient method—metal organic chemical vapor deposition (MOCVD). XRD results revealed that Fe₂O₃-TiO₂ coatings mainly composed of anatase TiO₂, α-Fe₂O₃ phases and little Fe₂Ti₃O₉. The pore structure of ACF was preserved well after loading with Fe₂O₃-TiO₂ coatings. UV-vis diffuse reflectance spectra showed a slight shift to longer wavelengths and an enhancement of the absorption in the visible region for Fe₂O₃-TiO₂ coatings, compared to the pure TiO₂ sample. A moderate Fe₂O₃-TiO₂ loading (13.7 wt%) was beneficial to mineralizing wastewater because the intermediates could be adsorbed onto the surface of photocatalyst following decomposition. The stable performance revealed that the Fe₂O₃-TiO₂ coatings were strongly adhered to the ACF surface, and the as prepared catalysts could be reused showing potential application for wastewater treatment.     

From ‘core-shell’ to composite mixed cathode materials for rechargeable lithium batteries by mechanochemical process

Solid state mechanical activation method was applied for surface modification of LiMn₂O₄ by Li-M-O (M = Co, Co+Ni) and for preparation of composite mixed LiMn₂O₄/LiCoO₂ cathode materials. Pristine LiMn₂O₄ was ground with correspondent precursors (for coating) or with LiCoO₂ (for composites) in high-energy planetary mills and then heat treated at different temperatures. As prepared materials were studied by XRD, ⁷Li MAS NMR spectroscopy, XPS, SEM and electrochemical cycling. It has been shown that both ‘core-shell’ and composite materials prepared by mechanochemical process are characterized by superior electrochemical performance due to smaller particles and chemical modification of LiMn₂O₄.     

Tribological Properties of Thermosetting Polyimide/TiO2 Nanocomposites Under Dry Sliding and Water-Lubricated Conditions

Thermosetting polyimide(PI)-based nanocomposites containing various contents of nano-TiO₂ were fabricated via an in situ polymerization of monomer reactants (PMR) process. Under dry sliding and water-lubricated conditions the friction and wear behaviors of the PMR PI and its nanocomposites were evaluated and compared. The addition of nano-TiO₂ in PI contributed to improving the friction and wear behavior considerably under dry sliding. The highest change ratio of wear rate was 61% with the optimum nano-TiO₂ content of 3%, while the highest change of friction coefficient was 60% with the optimum nano-TiO₂ content of 9%. Under water-lubricated condition, contrarily, the addition of nano-TiO₂ in PI does harm to the tribological properties. Namely, the friction coefficient of the nanocomposites increased with increasing the nano-TiO₂ content. These results may be caused by the following facts: the hardness of the PI matrix would be increased by adding the nano-TiO₂ reducing the ability of elastic deformation of the nanocomposites; accordingly, the poor elastic deformation hindered the formation of a water-lubrication film on the surface. An investigation on the wear tracks indicated that the wear mechanism of PI/TiO₂ nanocomposites under dry sliding condition proceeded from fatigue wear to a combination of fatigue wear and abrasive wear with increasing the mass fraction of nano-TiO₂.     

Characterization and photocatalytic activity of Zn–TiO2/AC composite photocatalyst

Activated carbon (AC) supported Zn²⁺–TiO₂ photocatalyst was prepared by sol–gel method. The prepared samples were characterized by X-ray diffraction, scanning electron micrograph, nitrogen absorption, diffuse reflectance UV/VIS and X-ray photoelectron spectroscopy. Using toluene as a pollution target, the photocatalytic activity of photocatalyst was evaluated. The results showed that prepared photocatalyst was obviously helpful for the removal of toluene in air. The photocatalytic degradation of toluene by Zn²⁺–TiO₂/AC reached 100% for 40 min and remained 75% after 160 min, while degradation by TiO₂ was only 30%. It indicated that the photocatalytic activity of prepared photocatalyst was enhanced. It is due to Zn²⁺-doping increased the oxidation and reduction of hole–electron pairs, which was the important factor in heterogeneous photocatalysis.     

多壁碳纳米管/聚丙烯复合材料热导率研究

用Pt细丝代替已有3ω方法中的薄膜热线,并设计了基于Labview程序的虚拟测量系统,准确、方便地测量了聚丙烯复合材料的热导率. 测量结果发现,多壁碳纳米管/丁苯橡胶/聚丙烯三元复合材料的热导率随着多壁碳纳米管/丁苯橡胶粉末含量的增加变化不大;多壁碳纳米管/聚丙烯复合材料的热导率随着多壁碳纳米管含量增加而增大;复合材料热导率远小于简单混合规则预测的结果,而与有效介质理论符合很好. 关键词： ω法')" href="#">3ω法 多壁碳纳米管 聚丙烯复合材料 热导率     

Plasma sprayed Al2O3/FeCrAl composite coatings for electromagnetic wave absorption application

Al₂O₃/FeCrAl composite coatings were fabricated by atmosphere plasma spraying technique. Microstructure and dielectric properties in the frequency range from 8.2 to 12.4 GHz were investigated. The microstructure of composite coatings shows a uniform dispersion of metal particles with litter pores and microcracks in the composite coatings. The relaxation polarization and interfacial polarization in the coatings would contribute to enhance ?′ with rising FeCrAl content, and the associated loss could be considered as a dominating factor enhancing ?″. By calculating the microwave-absorption as a single-layer absorber, for the composite coatings with 41 wt.% FeCrAl content, the reflection loss values exceeding −10 dB are achieved in the frequency range of 9.1-10.6 GHz when the coating thickness is 1.3 mm.     

Te/TeO2-SiO2复合薄膜的吸收和非线性光学特性研究

应用分光光度计测量Te/TeO₂-SiO₂复合薄膜的透射光谱和吸收光谱, 在480nm附近观察到Te颗粒引起的等离子体共振吸收峰; 采用Z扫描技术研究了共振(激发波长为532 nm)和非共振情况下(激发波长1064 nm) 不同电位制备薄膜的Te颗粒状态与复合薄膜的三阶非线性极化率的关系. 基于有效介质理论对复合薄膜的三阶非线性效应进行分析, 研究Te颗粒大小对Te/TeO₂-SiO₂复合薄膜的非线性光学性质的影响及其产生机理. 结果表明薄膜制备过电位增大, Te的粒径减小, 颗粒数量多, 颗粒分布趋于均匀, 使得金属颗粒的表面等离子体共振峰红移, 吸收强度增强, 导致三阶非线性光学效应增强, χ⁽³⁾由1064 nm的5.12×10^-7 esu增大为532 nm的8.11×10^-7 esu. 关键词： 碲 二氧化碲 复合薄膜 三阶非线性     

The control of the diameter of the nanorods prepared by dc reactive magnetron sputtering and the applications for DSSC

The TiO₂ nanorod arrays, with about 1.8 μm lengths, have been deposited on ITO substrates by dc reactive magnetron sputtering at different target-substrate distances. The average diameter of these nanorods can be modified from about 45 to 85 nm by adjusting the target-substrate distance from 90 to 50 mm. These nanorods are highly ordered and perpendicular to the substrate. Both XRD and Raman measurements show that the nanorods prepared at different target-substrate distances have only an anatase TiO₂ phase. The nanorods prepared at the target-substrate distance less than 80 mm have a preferred orientation along the (2 2 0) direction. However, this preferred orientation disappears as the target-substrate distance is more than 80 mm. These TiO₂ nanorods have been used as the electrodes for dye-sensitized solar cells (DSSCs). The highest conversion efficiency, about 4.78%, has been achieved for TiO₂ nanorods prepared at 80 mm target-substrate distance.     

Transport properties and mechanism of C60 coupled to carbon nanotube electrode

By applying non-equilibrium Green's functions in combination with density-functional theory, we investigate electronic transport properties of C₆₀ coupled to carbon nanotubes and Li electrodes. The results show that electronic transport properties of CNT-C₆₀-CNT and Li-C₆₀-Li systems are completely different. Nonlinear I-V characteristic, varistor-type behavior and negative differential resistance (NDR) phenomenon are observed when electrodes are carbon nanotubes. We discuss the mechanism of I-V characteristics of CNT-C₆₀-CNT systems in details. Our results suggest conductance, energy level of Frontier molecular orbitals, energy gap between HOMO and LUMO, the coupling between molecular orbitals and electrodes are all playing critical roles in electronic transport properties.     

Fabrication of open-ended TiO2 nanotube arrays by anodizing a thermally evaporated Ti/Au bilayer film

Fabrication of TiO₂ nanotube arrays (TNAs) with through-hole morphology is practical significance to enhance the photocatalytic activity of TNAs, as well as expanding their applications. In present work, open-ended TNAs are synthesized on a conductive Au layer by anodizing a thermally evaporated Ti/Au bilayer film. In the anodizing process, the upper Ti layer is transformed into well-aligned TNAs. The barrier layer under the growing TNAs ultimately touches the Au layer and is completely dissolved by the electrochemical etching. In order to avoid the bubble disruption of TNAs caused by the water electrolysis after the Au layer is exposed to the electrolyte, a specific non-aqueous electrolyte is used. The XRD results reveal that the as-formed open-ended TNAs are amorphous and can be transformed into anatase by annealing at 350 °C.     

Sunlight photocatalytic activity of CdS modified TiO2 loaded on activated carbon fibers

To improve the photocatalytic application performances of TiO₂, in this work, firstly CdS modified Degussa P25 TiO₂ (CdS/TiO₂) composites were prepared by two methods, sol-gel method and precipitation method. Next they, sol-gel-CdS/TiO₂ (sg-CdS/TiO₂) and precipitation-CdS/TiO₂ (pp-CdS/TiO₂), were loaded on activated carbon fibers (ACFs) by dip-coating method using the sodium carboxymethyl cellulose as adhesives. The composites were characterized by XRD, UV-vis absorbance spectra, SEM, EDS and BET. The photocatalytic activities under sunlight were investigated by the degradation of methylene blue. The results showed that CdS/TiO₂ composites were mainly composed of anatase-TiO₂ and little CdS cubic phases. The absorption wavelengths of sg-CdS/TiO₂ and pp-CdS/TiO₂ composites were extended to 590 nm and 740 nm, respectively. The absorption edge had a pronounced ‘red shift’. From EDS analysis, the elemental contents of CdS/TiO₂ were mainly Ti and O and a small quantity of S and Cd. CdS/TiO₂ loaded on ACFs were in the form of small clusters, but not very uniform; compared with the original ACFs, the surface area and pore volume of CdS/TiO₂/ACFs decreased slightly, respectively, while the average pore diameter was not changed. The photodegradation rate of methylene blue under sunlight with CdS/TiO₂/ACFs composites was markedly higher than that of P25-TiO₂/ACFs, and the effect of pp-CdS/TiO₂/ACFs composites was better than that of sg-CdS/TiO₂/ACFs, when irradiated for 180 min, and the photodegradation rate of methylene blue reached to 90.1%. The photodegradation kinetics of the methylene blue fitted with the Langmuir-Hinshelwood equation. The apparent reaction rate constants of sg-CdS/TiO₂/ACFs and pp-CdS/TiO₂ were 0.0105 min⁻¹ and 0.0146 min⁻¹, respectively, which were about 1.3-1.7 times as large as that of P25-TiO₂/ACFs.     

Photoelectrochemical property and photocatalytic activity of N-doped TiO2 nanotube arrays

N-doped TiO₂ nanotube arrays (NTN) were prepared by anodization and dip-calcination method. Hydrazine hydrate was used as nitrogen source. The surface morphology of samples was characterized by SEM. It showed that the mean size of inner diameter was 65 nm and wall thickness was 15 nm for NTN. The ordered TiO₂ nanotube arrays on Ti substrate can sustain the impact of doping process and post-heat treatment. The atomic ratio of N/Ti was 8/25, which was calculated by EDX. Photoelectrochemical property of NTN was examined by anodic photocurrent response. Results indicated the photocurrent of NTN was nearly twice as that of non-doped TiO₂ nanotube arrays (TN). Photocatalytic activity of NTN was investigated by degrading dye X-3B under visible light. As a result, 99% of X-3B was decomposed by NTN in 105 min, while that of TN was 59%.