Carbon nanotubes/TiO2 nanotubes hybrid supercapacitor

The rational selection and assembly of materials are central issues in the development of energy conversion and storage applications. Incorporating the utilization of carbon nanotubes cathode and TiO2 nanotubes anode in energy storage, a nonaqueous hybrid supercapacitor was developed in order to significantly increase the energy density of the supercapacitor. The electrochemical performance of the hybrid supercapacitor is characterized by charge/discharge test and cyclic voltam-mograms. According to the voltage value, the energy density of the asymmetric supercapacitor, by applying a potential varying from 0 to 2.8 V, is found to be 14.4 Wh/kg at upwards of 10 C, which is twice more than for the conventional symmetric supercapacitor utilizing carbon nanotubes, while maintaining desirable cycling stability and rate capability.     

Use of highly-ordered TiO(2) nanotube arrays in dye-sensitized solar cells

We describe the use of highly ordered transparent TiO(2) nanotube arrays in dye-sensitized solar cells (DSCs). Highly ordered nanotube arrays of 46-nm pore diameter, 17-nm wall thickness, and 360-nm length were grown perpendicular to a fluorine-doped tin oxide-coated glass substrate by anodic oxidation of a titanium thin film. After crystallization by an oxygen anneal, the nanotube arrays are treated with TiCl(4) to enhance the photogenerated current and then integrated into the DSC structure using a commercially available ruthenium-based dye. Although the negative electrode is only 360-nm-thick, under AM 1.5 illumination the generated photocurrent is 7.87 mA/cm(2), with a photocurrent efficiency of 2.9%. Voltage-decay measurements indicate that the highly ordered TiO(2) nanotube arrays, in comparison to nanoparticulate systems, have superior electron lifetimes and provide excellent pathways for electron percolation. Our results indicate that remarkable photoconversion efficiencies may be obtained, possibly to the ideal limit of approximately 31% for a single photosystem scheme, with an increase of the nanotube-array length to several micrometers.     

Alternative approaches to fabrication of gold-modified TiO2 nanotubes

Three approaches, impregnation–reduction, deposition and direct assembly, are used to fabricate gold-modified TiO₂ nanotubes. Prepared materials are characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV–visible absorption spectroscopy and BET, etc. The gold-modified TiO₂ nanotubes prepared via various procedures exhibit distinct difference in structure. By impregnation–reduction approach, gold-modified TiO₂ nanotubes with large gold particles are fabricated. The gold particles are either deposited on or encapsulated in TiO₂ nanotubes. However, by using gold hydrophilic colloidal dispersion as gold precursor, gold particles in the modified TiO₂ nanotubes are very small. Gold particles only adhere to the outer surface of TiO₂ nanotubes after deposition process, whereas adhere to not only the outer but also the inner walls of TiO₂ nanotubes after direct assembly process. A possible mechanism is proposed to illustrate the formation of gold-modified nanotubes that are prepared by direct assembly process.     

Fabrication and characterization of highly-ordered titania nanotubes via electrochemical anodization

Highly ordered titania nanotube arrays are fabricated via anodization process in electrolytes containing HF and acetic acid. Graphite was used as cathode. The size of titania can be controlled by changing anodizing voltage and bath temperature. From FE-SEM images, we observed the microstructure of titania nanotubes. Whereas, these nanotubes were amorphous; to induce crystallinity, the products were annealed at different temperatures. XRD analysis shows that the anatase and rutile phase emerge at different conditions. The optical properties were characterized via UV–vis absorption analysis. On the basis of these work, a discussion on the growth mechanism of nanotube structure was presented in this paper.     

A self-templated approach to TiO2 microcapsules

A self-templated approach has been developed for the synthesis of TiO2 microcapsules with tunable size and wall thickness by heating sol-gel derived TiO2 microspheres with poly(acrylic acid) (PAA) in a diethylene glycol (DEG) solution. PAA plays a crucial role in the formation of microcapsules by crosslinking the surface TiO2 nanoparticles and preventing them from dissolution by DEG. Hollow microcapsules form when DEG molecules penetrate the outer layer and remove the core materials by forming soluble titanium glycolate.     

Sol-gel assisted ZnO nanorod array template to synthesize TiO(2) nanotube arrays

A TiO(2) nanotube array with a large surface area is fabricated on a glass substrate using a ZnO nanorod array and sol-gel process, and the structural characteristics of the TiO(2) nanotube array are investigated. The well-aligned ZnO nanorod array, which is deposited on ZnO seed layer coated glass substrates by the wet-chemical route, is used as a template to synthesize TiO(2)/ZnO composite nanostructures through the sol-gel process. Then, by selectively removing the ZnO template, a TiO(2) nanotube with contours of the ZnO nanorods is fabricated on the ZnO seed layer coated glass. The resultant TiO(2) nanotubes are 1.5?μm long and 100-120?nm in inner diameter, with a wall thickness of ～10?nm. In addition, by adjusting the experimental parameters, such as the dip-coating cycle number or heating rate, porous TiO(2) thick films can also be obtained.     

The fabrication of the antibacterial paste based on TiO2 nanotubes and Ag nanoparticles-loaded TiO2 nanotubes powders

ABSTRACT

We successfully synthesised TiO₂ nanotubes (TNTs) and silver nanoparticles (Ag NPs)-loaded TiO₂ nanotubes paste. These were coated on a glass substrate by spin coating method, and their antibacterial activities were surveyed. The morphology of materials was defined by transmission electron microscopy (TEM) image; the crystalline structure and the composition of the materials were determined by X-ray diffraction (XRD) pattern and X-ray photoelectron spectroscopy (XPS). Vibrational properties of the molecules existing in the sample were investigated by Fourier transform infrared (FTIR) spectroscopy, and the transmittances of films were determined by UV–Vis transmittance spectroscopy. This research shows that the structure and morphology of TNTs did not change after they underwent the processes of paste preparing and film coating on a glass substrate. Furthermore, the transmittance of TNTs film (about 75%) is higher than Ag NPs-loaded TiO₂ nanotubes (Ag/TNTs) film (about 65%) in the visible region. Moreover, the antibacterial property of Ag/TNTs film shows its effectiveness against Escherichia coli bacteria, and the antibacterial efficiency is 99.06% for 24 h-incubation period in the dark condition.     

Fast one-step method to synthesize TiO2 nanoparticle clusters for dye sensitized solar cells

We have successfully designed a rapid method for producing dye sensitized solar cells (DSSC) using TiO2 films prepared by a modified dielectric barrier discharge jet (m-DBD jet) method which uses a DBD jet with elevated substrate temperatures from room temperature (RT) to 500 degrees C for approximately 10 min. This facile process has several advantages over other methods such as (1) eliminating additional coating and annealing steps, (2) creating films with high speed electron mobility via hierarchical pore clusters, and (3) allowing controlled TiO2 bandgap by N doping using atmospheric nitrogen instead of supplying N2 gas. Depending on reaction conditions, the resulting nanostructured materials have various sizes and shapes, with those deposited at the highest substrate temperatures displaying hierarchical walnut-shaped morphology as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A possible growth mechanism of TiO2 nanoparticle clusters (TNC) is presented and discussed. Finally, this m-DBD jet method produces TNC films that exhibit approximately 4 times higher photo-conversion efficiency than the nanoparticle films by the unmodified DBD jet method.     

Self-rising approach to synthesize hierarchically porous metal oxides

Hierarchically porous metal oxides are prepared using a novel self-rising approach. The method is ‘hard-template’ free and relatively easy to perform, utilizes inexpensive precursors and processing conditions, and is versatile, thus offering tremendous opportunities with a wide variety of conditions to explore to synthesize single or mixed metal oxides with hierarchically porous structures. Fe₂O₃, Sm_0.2Ce_0.8O_1.9, LaFeO₃, LaCoO₃, and La_0.5Sr_0.5Co_0.5Fe_0.5O₃ have been successfully synthesized while Fe₂O₃ and La_0.5Sr_0.5Co_0.5Fe_0.5O₃ as examples for single and mixed metal oxides have been studied in detail. Sm_0.2Ce_0.8O_1.9 has been applied as electrolyte for solid oxide fuel cells, showing good sinterability and high conductivity. A tentative scheme is provided to illustrate the pore formation mechanism using the self-rising approach.     

复合TiO2纳米管制备与表征

首次采用温和的制备方法制得Al2O3-TiO2纳米管.TiO2粉体在700℃下熔融、110℃水热反 应,制备了管径约为数纳米、单层管壁厚约为0.2纳米,管长约为数微米的复合Al2O3-TiO2纳米管.组织形貌和特性使用TEM、DRS和XRD进行表征.由于Al2O3的沉积在TiO2纳米管上,导致纳米管对紫外光的吸收蓝移40 nm.并对其形成机理进行了讨论.     

Antibacterial and photocatalytic activities of TiO2 nanotubes

TiO₂ nanotubes have been prepared by anodisation of titanium foil and their antibacterial activities have been tested against Gram-positive bacteria (Bacillus atrophaeus) while photocatalytic activity was tested for the degradation of the methyl orange dye. We found that the annealing temperature strongly affected antibacterial activity and photocatalytic dye degradation, as well as the production of reactive oxygen species under illumination. However, different trends were observed for dye degradation and antibacterial activity dependence on the annealing temperature. The relationship between annealing conditions, crystal structure, reactive oxygen species generation, dye degradation and antibacterial activity is discussed.     

Self-organized regular arrays of anodic TiO2 nanotubes

The formation of self-organized regular arrays of oxide nanotubes lies in a delicate balance between the oxide growth rate and the oxide etching rate and a lattice mismatch between the grown metal oxide and the underlying valve metal. The requisites for their fabrication are the electropolishing and a two-step anodization. The most uniform and self-organized regular arrays of anodic TiO2 nanotubes among those known so far are reported as another example of valve metal oxide nanotube arrays since regular arrays of anodic aluminum oxide nanochannels were produced. Our findings can be generalized to fabricate self-organized regular arrays of other valve metal oxides.     

氮掺杂二氧化钛纳米管制备与光催化性能

以多孔氧化铝为模板,采用溶胶凝胶法制备出二氧化钛纳米管,在氨气气氛下进行了氮掺杂。用TEM、XRD、DRS等对其进行了表征,并通过降解碱性藏花红溶液研究了其光催化的性能。结果表明,用模板法制备的二氧化钛纳米管管径均匀、可控且排向一致,从DRS光谱可以推测出氮掺杂后的二氧化钛纳米管在可见光区有较强的吸收,并且与二氧化钛纳米管相比氮掺杂的二氧化钛纳米管的降解碱性藏花红溶液的效率更高。     

Wide-range hydrogen sensing with Nb-doped TiO2 nanotubes

Anatase-type titania nanotubes doped with Nb element were fabricated through an anodization of Ti35Nb alloy substrate and further annealing at 450 °C. Hydrogen sensitivity of the Nb-doped TiO(2) nanotubes at room temperature was investigated through exposure of the nanotube samples to different hydrogen atmospheres. At room temperature, the Nb-doped nanotubes demonstrated a good sensitivity for wide-range detection of both dilute and high-concentration hydrogen atmospheres ranging from 50 ppm to 2% H(2). The Nb-doped nanotubes also presented remarkable reversibility and repeatability as well as a quick response to the hydrogen atmosphere. The Nb-doped titania nanotubes have great advantages as robust and wide-range hydrogen sensors operating at room temperature.     

TiO2纳米管与纳米线的光电化学研究

利用在钛箔表面沉积一层TiO2纳米粒子作为晶种,与NaOH反应,通过改变反应温度制备了TiO2纳米管与纳米线.制备了TiO2纳米管和纳米线膜电极,并进行了光电化学测试.光电化学实验表明,混晶结构TiO2纳米管和纳米线显示出优良的光电转化性能.     

Self-rising approach to synthesize porous hollow metal oxides

Porous hollow metal oxides are prepared using a novel self-rising approach. The method is 'hard-template' free and relatively easy to perform, utilizes inexpensive precursors and processing conditions, and is versatile, thus offering tremendous opportunities with a wide variety of conditions to explore to synthesize materials with hollow structures. Co3O4 and amorphous Sm(0.5)Sr(0.5)CoO3 as a model has been successfully synthesized, showing hollow structure with porous shell and possessing high BET surface areas. A tentative scheme is given to illustrate its synthetic mechanism.     

An X-ray absorption approach to mixed and metallicity-sorted single-walled carbon nanotubes

Carbon based structures have been widely studied by X-ray absorption (XAS), also called NEXAFS, which is a very useful bulk probing method that allows examining the unoccupied density of states (DOS) and the site selective bonding environment. Two very well known spectral features in the XAS core level spectrum are the σ* and π* bands, and both have been analyzed in several studies for graphitic-like systems. However, among all the carbon materials, the unique one-dimensional electronic properties attributed to single-walled carbon nanotubes (SWCNTs) exhibit features that reveal clearly their electronic structure in the core level XAS spectrum. In this article, we outline the C1s response in XAS, which is related to the DOS of the conduction band in SWCNTs and its fine structure, revealed by experiments performed on metallicity-sorted SWCNT material. The progress in the identification of changes in the site selective conduction band electronic structure with XAS is discussed in detail.