水热法制备二氧化钛纳米管:形成机理、影响因素及应用

TiO2纳米管由于具有较大的比表面积、优异的光催化活性以及结构可控的特性,使其在电学、光学、催化剂以及传感器、锂离子电池、染料敏化太阳能电池、能源转换等方面具有非常大的应用潜力。目前采用简单的水热法就能够在较低的温度和压力下制备出二氧化钛纳米管,这使得水热法合成TiO2纳米管受到广泛关注。文章主要综述了水热法制备TiO2纳米管的形成机理以及温度、原料、酸洗、干燥、填充度等因素对纳米管形成的影响。     

Thermoresponsive PEG‐Coated Nanotubes as Chiral Selectors of Amino Acids and Peptides

A series of nanotubes with a dense layer of short poly(ethylene glycol) (PEG) chains on the inner surface are prepared by means of a coassembly process using glycolipids and PEG derivatives. Dehydration of the PEG chains by heating increases the hydrophobicity of the nanotube channel and fluorescent‐dye‐labeled amino acids are extracted from bulk solution. Rehydration of the PEG chains by cooling results in back‐extraction of the amino acids into the bulk solution. Because of the supramolecular chirality of the nanotubes, amino acid enantiomers can be separated in the back‐extraction procedure, which is detectable with the naked eye as a change in fluorescence as the amino acids are released from the nanotubes. The efficiency and selectivity of the chiral separation are enhanced by tuning the chemical features and inner diameter of the nanotube channels. For example, compared with wide nanotube channels (8 nm), narrow nanotube channels (4 nm) provide more effective electrostatic attraction and hydrogen bond interaction environments for the transporting amino acids. Introduction of branched alkyl chains to the inner surface of the nanotubes enables chiral separation of peptides containing hydrophobic amino acids. The system described here provides a simple, quick, and on‐site chiral separation in biological and medical fields.     

TiO2纳米管气敏材料的研究与应用

TiO2纳米管在气体传感、光电转换、光催化、光裂解等方面具有广阔的应用前景.在气体传感器领域,最新的研究数据表明:室温下通入1000×10-6H2,TiO2纳米管气体传感器的灵敏度高达108.7,这是迄今为止所有材料在任意温度下对任意气体的最大灵敏度.综述了TiO2纳米管气体传感器的研究进展,分析了TiO2纳米管的制备方法、微观结构以及TiO2纳米管气体传感器的性能和敏感机理,展望了TiO2纳米管气体传感器的发展方向.     

Interactions and Chemical Transformations of Coronene Inside and Outside Carbon Nanotubes

By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures are prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via π–π interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor‐phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes.     

Formation and Structure of Boron Nitride Nanotubes

Boron nitride (BN) nanotubes were simply synthesized by heating well-mixed boric acid, urea and iron nitrate powders at 1000℃. A small amount of BN nanowires was also obtained in the resultants. The morphological and structural characters of the BN nanostructures were studied using transmission electron microscopy. Other novel BN nanos-tructures, such as Y-junction nanotubes and bamboo-like nanotubes, were simultaneously observed. The growth mechanism of the BN nanotubes was discussed briefly.     

Electronic Property Modification of Single‐Walled Carbon Nanotubes by Encapsulation of Sulfur‐Terminated Graphene Nanoribbons

The use of carbon nanotubes (CNTs) as cylindrical reactor vessels has become a viable means for synthesizing graphene nanoribbons (GNRs). While previous studies demonstrated that the size and edge structure of the as‐produced GNRs are strongly dependent on the diameter of the tubes and the nature of the precursor, the atomic interactions between GNRs and surrounding CNTs and their effect on the electronic properties of the overall system are not well understood. Here, it is shown that the functional terminations of the GNR edges can have a strong influence on the electronic structure of the system. Analysis of SWCNTs before and after the insertion of sulfur‐terminated GNRs suggests a metallization of the majority of semiconducting SWCNTs. This is indicated by changes in the radial breathing modes and the D and G band Raman features, as well as UV–vis–NIR absorption spectra. The variation in resonance conditions of the nanotubes following GNR insertion make direct (n,m) assignment by Raman spectroscopy difficult. Thus, density functional theory calculations of representative GNR/SWCNT systems are performed. The results confirm significant changes in the band structure, including the development of a metallic state in the semiconducting SWCNTs due to sulfur/tube interactions. The GNR‐induced metallization of semiconducting SWCNTs may offer a means of controlling the electronic properties of bulk CNT samples and eliminate the need for a physical separation of semiconducting and metallic tubes.     

Alternative Synthesis Method for Carbon Nanotubes

It is demonstrated that carbon nanotubes (CNTs) can be synthetized on the surface of an example carbon background, activated carbon, using the thermal conversion of poly(furfuryl alcohol) (PFA). This newly discovered CNTs synthesis method is an alternative solution to previously known methods, e.g., chemical vapor deposition, arc discharge, and laser ablation. Scanning electron microscopy and high‐resolution transmission electron microscopy images deliver direct evidence of CNT formation through the thermal degradation of PFA in a temperature range of 500–700 °C. The discovered process consists of the free growth of CNTs from PFA without any mechanical patterning, casting, or molding. CNTs obtained in this manner resemble MWCNTs in size, though according to microscopic investigation the tubes do not possess the well‐developed layered structure of MWCNTs. Nonetheless, X‐ray photoelectron spectroscopy and Raman spectroscopy studies fully confirm that carbon (C) is the main elemental constituent of the tubes (C atomic content above 85%) and C atoms are structured in a manner typical of defected CNTs (D, G, and G' intensity ratios).     

Nanoelectromagnetics: Circuit and Electromagnetic Properties of Carbon Nanotubes

This Review presents a discussion of the electromagnetic properties of nanoscale electrical conductors, which are quantum mechanical one‐dimensional systems. Of these, carbon nanotubes are the most technologically advanced example, and are discussed mainly in this paper. The properties of such systems as transmission electron microscopy waveguides for on‐chip signal propagation and also the radiation properties of such systems are discussed. This work is primarily aimed at microwave, nanometer‐wave, and THz electronics. However, the use of nanotubes as antennas in the IR and optical frequency range is not precluded on first principles and remains an open research area.

     

氧化钒纳米管的自组装合成机理

以V₂O₅和十六胺为原料在水热条件下合成了氧化钒纳米管, 采用XRD、SEM、TEM、FTIR、ESR等手段分析研究了氧化钒纳米管的形成机理. 结果表明, 氧化钒纳米管的形成主要基于“卷曲机理”, 其形成过程包括: 表面活性剂分子嵌入到钒氧化物层间, 形成新层状化合物前驱体; 水热驱动下层状化合物边缘松动, 并开始卷曲, 降低体系能量; 合适的水热反应时间下最终形成钒氧化物纳米管. 模板剂嵌入到钒氧化物层间形成一定大小的层间距以及V⁴⁺的存在对从层状化合物卷曲成纳米管起到了积极的作用.     

Unique Tube–Ring Interactions: Complexation of Single‐Walled Carbon Nanotubes with Cycloparaphenyleneacetylenes

Carbon nanotubes (CNTs) interlocked by cyclic compounds through supramolecular interaction are promising rotaxane‐like materials applicable as 2D and 3D networks of nanowires and disease‐specific theranostic agents having multifunctionalities. Supramolecular complexation of CNTs with cyclic compounds in a “ring toss'' manner is a straightforward method to prepare interlocked CNTs; however, to date, this has not been reported on. Here, the “ring toss” method to prepare interlocked CNTs by using π‐conjugated carbon nanorings: [8]‐, [9]‐, and [10]cycloparaphenyleneacetylene (CPPA) is reported. CPPAs efficiently interact with CNTs to form CNT@CPPA complexes, while uncomplexed CPPAs can be recovered without decomposition. CNTs, which tightly fit in the cavities of CPPAs through convex–concave interaction, efficiently afford “tube‐in‐ring”‐type CNT@CPPA complexes. “Tube‐in‐ring”‐type and “ring‐on‐tube”‐type complexation modes are successfully distinguished by spectroscopic, thermogravimetric, and microscopic analyses.