Young’s modulus of crystalline C60 nanotubes studied by in situ transmission electron microscopy

Bending tests of crystalline nanotubes composed of fullerene C₆₀ molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C₆₀ nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C₆₀ nanowhiskers. The result concerning the increase in the Young’s modulus of the C₆₀ nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C₆₀ nanowhiskers.     

Efficient usage of highly dispersed Pt on carbon nanotubes for electrode catalysts of polymer electrolyte fuel cells

A Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in polymer electrolyte fuel cells (PEFCs) below 500 mA/cm². K₂PtCl₄ and H₂PtCl₆·6(H₂O) are used for the Pt deposition onto multi-walled CNTs (MWCNTs), which are produced by the catalytic decomposition of hydrocarbons. The electric power densities produced using the Pt/CNT electrodes are greater than that of the Pt/CB by a factor of two to four on the basis of the Pt load per power. CNTs are thus found to be a good support of Pt particles for PEFC electrodes. TEM images show 2–4-nm Pt nanoparticles dispersed on the CNT surfaces. These high performances are considered to be due to the efficient formation of the triple-phase boundaries of gas–electrode–electrolyte. The mechanisms of Pt deposition are discussed for these Pt-deposited CNTs.     

Self-organized porous TiO2 and ZrO2 produced by anodization

The present work investigates the electrochemical formation of self-organized high aspect ratio TiO₂ and ZrO₂ nanotube layers. The formation and growth of a self-organized porous layer can be achieved directly by anodization without any templates in fluoride containing electrolytes. The morphology of the porous layers is affected by the electrochemical conditions such as the electrolyte composition, the pH and the exact polarization treatment (such as the potential sweep rate from the open-circuit potential to the anodizing potential). For Ti, nanotube layers are formed with diameters varying from approx. 20 nm to 100 nm and lengths from approx. 0.25 μm to 2.5 μm depending on the electrolytes and pH. On the other hand, for Zr, tubes of 50 nm in diameter and up to approx. 17 μm in length can be grown—a key parameter in this case is the potential sweep rate. The large difference between Ti and Zr in the achievable thickness of nanotube layers indicates a difference in the growth mechanism which may be based on the different chemical dissolution rates of electrochemically formed oxides.     

Flexible Triboelectric Nanogenerator Based on High Surface Area TiO2 Nanotube Arrays

Triboelectric nanogenerators (TENGs) can harvest mechanical energy through coupling triboelectric effect and electrostatic induction. Typically, TENGs consist of organic materials, however on account of the potentially wide range of applications of TENGs as the self‐powered portable/wearable electronics, biomedical devices, and sensors; semiconductor metal oxide materials can be promising candidates to be incorporating in TENG structure. Here, flexible TENG based on self‐organized TiO₂ nanotube arrays (TNTAs) is fabricated via anodization method. The introduced flexible large area nanotubular electrode is employed as the moving electrode in contact with Kapton film in vertical contact separation mode of TENG. The fabricated TENG can deliver output voltage of 40 V with the current density of 1 μA cm^?2. To evaluate the role of nanostructured interface, its performance has been compared to the thin film flat compact TiO₂ electrode. The results of extracted charge measurements under short circuit condition indicate that larger triboelectric charge density formed in TNTA‐based electrode (about 110 nC per cycle of press and release) is in comparison to 15 nC in flat TiO₂ electrode. Due to the extensive range of applications of TiO₂, the introduced structure can potentially be applicable in various types of self‐powered systems such as photo‐detectors and environmental gas and bio‐sensors.

     

Enhanced photoelectrochemical current response of titania nanotube array

Self-organized and highly-ordered TiO₂ nanotube array with disjunctive wall-hole structure has been synthesized from titanium foil by potentiostatic–galvanostatic anodization process. The morphology and microstructure of the TiO₂ layer depend greatly on the electrolyzing parameters and electrolyte components. TiO₂ formation mechanism by anodization oxidation is discussed. The crystallized TiO₂/Ti nanotube electrode exhibited a significant enhancement of photoelectrochemical current response in comparison with micrometer-sized TiO₂/Ti multiporous electrode. Such kind of TiO₂ nanotube will have many potential applications in various areas as an outstanding photoelectrochemical material.     

Nanotube morphology changes for Ti-Zr alloys as Zr content increases

Nanotube morphology changes in Ti-Zr alloys as Zr content increases have been investigated. Ti-Zr (10, 20, 30 and 40 wt.%) alloys were prepared by arc melting and heat treated for 24 h at 1000 °C in an argon atmosphere. TiO₂ nanotubes were formed on the Ti-Zr alloys by anodization in H₃PO₄ containing 0.5 wt.% NaF. Electrochemical experiments were performed using a conventional three-electrode configuration with a platinum counter electrode and a saturated calomel reference electrode. Samples were embedded in epoxy resin, leaving an area of 10 mm² exposed to the electrolyte. Anodization was carried out using a scanning potentiostat, and all experiments were conducted at room temperature. Microstructures of the alloys were examined by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). The Ti-Zr alloy microstructures observed by OM and FE-SEM changed from a lamellar structure to a needle-like structure with increasing Zr content. The microstructures also changed from β phase to increasing amounts of α phase as the Zr content increased. The number of large nanotubes formed by anodization decreased, and the number of small nanotubes increased, as the Zr content increased. The mean inner diameter ranged from approximately 150 to 200 nm with a tube-wall thickness of about 20 nm. The interspace between the nanotubes was approximately 60, 70, 100 and 130 nm for Zr contents of 10, 20, 30 and 40 wt.%, respectively.     

Development of high oxidation resistant coating of nanostructured MgO on carbon nanotubes via simple precipitation technique in Mg/CO gas system

The synthesis of oxide-coated carbon nanotubes (CNTs) by a simple precipitation reaction in Mg/CO gaseous system was studied. The results showed that nanostructured MgO could be uniformly coated on the surface of CNTs via inhomogeneous Mg_(g) and CO_(g) precipitation reaction. Furthermore, we have developed a mixing procedure based on simultaneous agitation and ultra-sonication in order to break CNT bundles and prepare highly dispersed starting materials. By applying such mixing procedure, dispersed and distinct nano-oxide coated CNTs were synthesized which can be efficiently utilized in different composite matrices. Oxidation resistance of samples was investigated by DSC/TG thermal analysis. The results showed that oxide-coated CNTs present superior resistance against oxidation even at rather elevated temperature of 1000 °C and total weight loss of coated CNTs was measured to be less than 1 wt% during heat treatment at such temperature. Finally, coating adhesion was evaluated employing ultrasonic waves (as mechanical force) and subsequent weight loss measurement at temperature of 1000 °C.     

用掺杂法改进碳纳米管气敏传感器的机理

碳纳米管气敏传感器在敏感性、选择性、操纵性等性能上，远胜于传统的金属氧化物膜传感器。但由于受本征碳纳米管(纯净碳纳米管)吸附能力的限制，碳纳米管气敏传感器能检测的气体种类很少。斯坦福大学的Shu Peng等人的实验发现，掺杂了B、N原子的碳纳米管第一次成功地检测出了CO和H2O分子。在详细阐述碳纳米管传感器工作机理的基础上，用半导体杂质理论和离子对吸附模型对这一最新实验结果作出理论解释。这种掺杂方法，很有可能从根本上解决碳纳米管气敏传感器检测范围小的问题。     

碳、硅及氮化硼纳米管轴向拉伸的分子动力学研究

基于Tersoff势的分子动力学方法模拟(5,5)型单壁碳、硅及氮化硼纳米管的轴向拉伸过程.根据模拟结果,讨论三种纳米管拉伸时的构形、能量、载荷、径向收缩率等的变化及其差异.研究结果表明,(1)小应变时,系统能量随变形增大而增大,各纳米管截面构形基本保持圆形不变.(2)碳、硅及氮化硼纳米管的断裂应变值分别为42.8%、33.4% 和49.1%.(3)碳纳米管的能量吸收能力最好,承载最大,径向收缩率最小.