Ultralong Nanotubes Research Articles

Using ultra-thin interlaminar carbon nanotube sheets to enhance the mechanical and electrical properties of carbon fiber reinforced polymer composites

A major shortcoming of carbon fiber reinforced polymer composites (CFRP) is their interlaminar performance. This study provides an inexpensive and readily scalable solution to this problem by incorporating ultra-thin sheets of carbon nanotubes (CNT) between the plies (laminates) of CFRPs. To this end, dry carbon fiber fabrics are first sandwiched between CNT sheets. The fabrics are then stacked and infused with epoxy to form a CFRP with interlaminar CNT sheets. Contrary to the typical approach where microns-long CNTs are distributed randomly within a CFRP for reinforcement, this study uses ~100 nm thick CNT sheets consisting of aligned and ultra-long (0.3 mm) nanotubes. Despite their negligible weight fraction of only 0.016%, the interlaminar CNT sheets enhanced the CFRP's flexural strength by 49%, interlaminar shear strength by 30%, and mode I fracture toughness by 30%. X-ray micro-tomography revealed that samples with interlaminar CNTs are significantly resistant to delamination and crack propagation. Moreover, the in-plane electrical conductivity of these composites increased commensurate with the weight fraction of CNTs, providing a maximum enhancement of 278% over the reference sample for 0.048 wt% of CNT sheets. This study reveals that for almost no change in weight and thickness, interlaminar CNT sheets can enhance the electrical conductivity and interlaminar performance of CFRPs.

UV photoelectric properties of aligned TiO2 nanotubes with different wall thickness

Horizontally ordered TiO 2 nanotubes with different wall thicknesses were fabricated by three processes: electrospinning, pulse laser deposition and annealing. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–vis) absorption were used to characterize the morphology, crystal structure, surface element composition and band gap of the nanotubes. The photodetectors were fabricated by assembling horizontally ordered TiO 2 nanotubes with different wall thickness on the gold interdigital electrode, and their ultraviolet (UV) detection was compared. The results indicated that the TiO 2 nanotubes with a wall thickness of 39 nm have the better UV response and fast response recovery speed under 365 nm illumination with power density of 4.9 mW/cm 2 . The UV response mechanism and advantages of the horizontally ordered TiO 2 nanotubes were also discussed. • Highly ordered centimeter-long TiO 2 nanotubes with different wall thickness were successful preparation. • The planar photodetectors have been fabricated by combining interdigitated gold electrodes and aligned ultra-long nanotubes. • UV photoelectric properties of aligned TiO 2 nanotubes with different wall thickness were investigated.

Ti3+-doped TiO2@C nanorods with enhanced photocatalytic performance under visible light

ABSTRACTTi3+-doped TiO2@C nanorods were prepared through a facile hydrothermal process. Na2Ti3O7 ultralong nanotubes and glucose were used as TiO2 precursor and carbon (C) source, respectively. During hydrothermal treatment, the hydrolysis of Na2Ti3O7 and polymerization of glucose induced the formation of TiO2 nanorods with a coating of carbon complex. At the same time, a part of Ti4+ was reduced to Ti3+ due to the rich hydroxyl groups in glucose. After calcination, an ultrathin carbon shell was formed on the surface of TiO2 nanorods. In this prepared composite, Ti3+ self-doped TiO2 nanorods work as photosensitizer to harvest solar energy to generate electron-hole pairs, the tight-binding interface between TiO2 nanorods and carbon shell works as electron transportation path, and the ultrathin carbon shell acts as electrons trapped and accumulated site. Photocatalytic test results indicate that Ti3+-doped TiO2@C nanorods exhibit higher activity and stability than TiO2 for photodegradation of methylene blue under visible light.

(Invited) Superacid-Surfactant Exchange

Attaining aqueous solutions of individual single-walled carbon nanotubes is the critical first step for harnessing the extraordinary properties of these materials. However, current approaches cause structural damage and cuts the nanotubes into short pieces. In this talk, we will introduce an unexpectedly simple solution to this decade-old challenge by directly neutralizing a nanotube-superacid solution in the presence of a surfactant. This straightforward superacid-surfactant exchange (S2E) involves two simple solution-mixing steps that completely eliminate the need for both ultrasonication and ultracentrifugation. The result allows us to advance multiple fronts, including aqueous sorting of ultralong nanotubes and stretchable thin film transistors with high carrier mobility.

Core–shell TiO2@C ultralong nanotubes with enhanced adsorption of antibiotics

As materials capable of adsorbing antibiotics continue to be developed, composite adsorbents have been shown to offer advantages over mono-material adsorbents.

Facile synthesis of controllable TiO2 composite nanotubes via templating route: Highly sensitive detection of toluene by double driving from Pt@ZnO NPs

Electrospinning is an effective way to fabricate ultralong nanotubes with a large surface area. However, the nanotubes synthesized through this way suffer from difficult controlling of structural parameters. A facile strategy for constructing highly controllable Pt@ZnO nanoparticles (NPs) drive TiO2 nanotubes (NTs) (Pt@ZnO-TiO2 NTs) was developed in this work. First, the polystyrene electrospun nanofibers (∼490 nm) containing Pt@zeolitic imidazolate framework-8 (ZIF-8) was fabricated as a self-sacrificial template and then was decorated by a thinner tetrabutyl orthotitanate layer through soaking. After annealing, the Pt@ZnO NPs were obtained due to the decomposition of Pt@ZIF-8 during calcination. The involving of ZIF-8 can effectively prevent the aggregation of Pt during heat treatment (∼3 nm, monodispersed), and thus highly improves its catalyst property. When Pt@ZnO-TiO2 NTs were evaluated as a sensing material for toluene detection, the obtained sensors exhibited an enhanced sensing response (11.1 to 1 ppm toluene), faster response/recovery times (7.5 and 20.1 s) and a lower detection limit (23 parts per billion) during dynamic measurement, when compared to the pristine TiO2 and directly mixed Pt-TiO2 NTs. This was mainly attributed to the improved oxygen vacancy concentration in the NT composite and resistance modulation effect induced by the unique NT structure, as well as the well-dispersed and small-sized Pt catalyst.

Rice spike-like g-C3N4/TiO2 heterojunctions with tight-binding interface by using sodium titanate ultralong nanotube as precursor and template

A novel rice spike-like g-C3N4/TiO2 nanowire heterojunctions are fabricated by hydrothermal treating Na2Ti3O7 ultralong nanotubes in the presence of g-C3N4. The presence of g-C3N4 promotes the hydrolysis of Na2Ti3O7 ultralong nanotubes. The partially replaced O of TiO2 by N from g-C3N4 leads to the formation of a tight-binding interface between one dimensional TiO2 and two dimensional g-C3N4, which is crucial for fast and effective transfer of photogenerated electrons in heterostructured photocatalysts. As a result, the g-C3N4/TiO2 nanowire heterojunctions exhibit excellent visible-light photocatalytic activity. The kinetic constant (k) of g-C3N4/TiO2 (0.024 min−1) for degradation of methylene blue under visible light irradiation is 1.85 and 4 times than that of pure g-C3N4 and P25, respectively.

Construction of Vesicles, Micro/Nanorods and Ultralong Nanotubes through the Self‐Assembly of Non‐Classical Amphiphiles with Rigid Conformation

AbstractAmphiphilic molecules have long been regarded as an important class of supramolecular building blocks for the fabrication of nanomaterials. While most previous researches have mainly focused on amphiphlies with flexible structures, in this work, four novel amphiphiles possessing wholly‐rigid skeletons have been designed and synthesized. These molecules were built by using 4,4’‐bipyridin‐1‐ium or viologen as hydrophilic moieties and phenyl or biphenyl as hydrophobic segments, bridged by a pyridazine unit. Their self‐assembly behavior has been investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), which revealed they could self‐assemble into well‐ordered nanoarchitectures with various morphologies such as vesicles, micro/nanorods and nanotubes in water or methanol, depending on their hydrophilic/hydrophobic fraction ratios.

Fiber grating compression of giant-chirped nanosecond pulses from an ultra-long nanotube mode-locked fiber laser.

We demonstrate that the giant chirp of coherent, nanosecond pulses generated in an 846m long, all-normal dispersion, nanotube mode-locked fiber laser can be compensated using a chirped fiber Bragg grating compressor. Linear compression to 11ps is reported, corresponding to an extreme compression factor of ∼100. Experimental results are supported by numerical modeling, which is also used to probe the limits of this technique. Our results unequivocally conclude that ultra-long cavity fiber lasers can support stable dissipative soliton attractors and highlight the design simplicity for pulse-energy scaling through cavity elongation.

Simple electrochemical synthesis of ultra-long silver telluride nanotubes

Ultra-long Ag2Te nanotubes could be electrochemically synthesized by post-electrodeposition of Te on electro-spun Ag nanofibers, in which Ag atoms diffuse into layers of Te and results in a morphology change from nanofibers to hollow nanotubes.

Ultrasonication-Assisted Hydrothermal Synthesis of Ultralong TiO2 Nanotubes

Abstract Ultralong titanate nanotubes were synthesized by treating general anatase TiO2 in alkaline solution using a facile sonication-assisted hydrothermal method. The as-synthesized products via sonication and sonication-hydrothermal treatment were characterized by SEM, TEM, OM and XRD. The effects of sonication power, sonication frequency and sonication temperature on the morphology and the crystal structure of the products were investigated. The results show that in the range of ultrasonic power (200, 300, 400, 500 W) and frequency (20, 40, 80 kHz), titanium dioxide particles were swelled in alkali aqueous solution to get the hedgehog flocculent intermediate products by ultrasonic irradiation when the ultrasonic temperature was equal or higher than 60 °C; several tens of microns long titanate nanotubes were achieved using the intermediate products as raw materials under the mild hydrothermal conditions of 90 °C and 5 h. The possible formation mechanism for ultralong titanate nanotubes was also discussed. The hedgehog floccules synthesized by sonication play an important role to synthesize the several tens of micrometers long nanotubes.

Efficient suppression of nanograss during porous anodic TiO 2 nanotubes growth

When Ti foil was anodized in fluoride-containing electrolyte for a long time, undesired etching-induced “nanograss” would inevitably generate on the top of porous anodic TiO2 nanotubes (PATNTs). The nanograss will hinder the ions transport and in turn yield depressed (photo) electrochemical performance. In order to obtain nanograss-free nanotubes, a modified three-step anodization and two-layer nanostructure of PATNTs were designed to avoid the nanograss. The first layer (L1) nanotubes were obtained by the conventional two-step anodization. After washing and drying processes, the third-step anodization was carried out with the presence of L1 nanotubes. The L1 nanotubes, serving as a sacrificed layer, was etched and transformed into nanograss, while the ultralong nanotubes (L2) were maintained underneath the L1. The bi-layer nanostructure of the nanograss/nanotubes (L1/L2) was then ultrasonically rinsed in deionized water to remove the nanograss (L1 layer). Then much longer nanotubes (L2 layer) with intact nanotube mouths could be obtained. Using this novel approach, the ultralong nanotubes without nanograss can be rationally controlled by adjusting the anodizing times of two layers.

Synthesis and characterization of ultralong single-walled carbon nanotubes

Ultarlong aligned single-walled carbon nanotubes (SWNTs) are very useful for high performance nanoelectronics because they have uniform properties along tube axis. In this study, ultralong and well-aligned SWNT arrays were synthesized via an ultralow gas flow chemical vapor deposition (CVD) system using ethanol as the carbon source. Raman spectroscopy was employed to comprehensively characterize the as-grown SWNTs. The intensity ratio of D band and G band (I D /I G ) of the SWNTs was extremely low, indicating the nanotubes are of high quality. The frequencies of RBM and G band acquired along one isolated tube axis maintained constant over a large length scale, which reveals that the SWNT is structural and chiral uniform. Field-effect transistors (FETs) were fabricated with such ultralong single nanotube as conduction channel, exhibiting excellent performances. Our results show possibility of large scale fabricating SWNT-based electronic devices and perspective of creating integrated circuits on individual SWNTs.

Self‐Assembled Ultralong Chiral Nanotubes and Tuning of Their Chirality Through the Mixing of Enantiomeric Components

Enantiomeric L- or D-glutamic acid based lipids were designed and their self-assembly was investigated. It was found that at a certain concentration, either L- or D-enantiomeric derivatives could self-assemble in absolute alcohol to form a white organogel, which was composed of ultralong nanotubes with an aspect ratio higher than 1000. Further investigations revealed that these nanotubes were in chiral forms. The chirality of the nanotubes was determined by that of the enantiomers employed. In addition, when D and L enantiomers were mixed in different ratios, the nanotube could be tuned consecutively from nanotubes with a helical seam to nanotwists, the chirality of which being determined by the excess enantiomer in the mixed systems. In the case of an equimolar mixture of the enantiomers, flat nanoplates instead of helical nanotubes or nanotwists were obtained. The FTIR vibrational data and XRD layer-distance values showed a consecutive change as a function of the enantiomeric excess. It was further revealed that the slightly stronger interaction between D-L enantiomeric pairs than that between D-D or L-L pairs was responsible for the formation of the diverse self-assembled nanostructures.

Imaging and Raman Spectroscopy of Individual Single-Wall Carbon Nanotubes on a Large Substrate

A beam-scanning confocal Raman microscope system capable of large-area imaging is developed for characterizing single-wall carbon nanotubes at the single tube level. Individual ultralong nanotubes grown on a large silicon substrate are systematically imaged by both confocal Raman microscopy and scanning electron microscopy. Raman spectra for more than 200 nanotubes, consisting of both semiconducting and metallic nanotubes, are obtained. A large variation in the nanotube radial breathing mode (RBM) Raman intensity is observed for different tubes and can be understood in terms of resonance enhancement and nanotube structure-dependent electron−phonon coupling strength. Nanotube diameters determined from RBM frequencies reveal a broad distribution from 0.8 to ∼2 nm for nanotubes grown by chemical vapor deposition. The tangential mode (G band) Raman spectra of individual metallic nanotubes are found to exhibit a variety of different line shapes, with the Breit−Wigner−Fano feature diminished for most of the observed spectra.

Quasi-Continuous Growth of Ultralong Carbon Nanotube Arrays

We report the growth of ultralong (>10 cm) multi-walled and single-walled carbon nanotubes such that the length is limited by the size of the furnace rather than by the termination of growth. The disturbance of microscale laminar flows results in disordered or shorter growth of carbon nanotubes. By downsizing reaction pipes, reaction gas flows are stabilized with low Reynolds numbers. In this way, the catalyst nanoparticles at the end of growing carbon nanotubes can travel a longer distance to grow ultralong nanotubes.

Raman Studies of New Carbon Nanotube Sample Types

Generation of new carbon nanotube sample types, including individualized nanotubes suspended in surfactant solutions and recently synthesized ultralong nanotubes, has enabled new experimental studies that provide useful insight into nanotube structure and photophysical behavior. We present a review of Raman studies performed in our laboratory on these newly available sample types. Results from Raman excitation profile studies of individualized HiPco-produced nanotubes have confirmed fluorescence-based chirality assignments and have revealed chiral-dependences in the Raman scattering cross-sections. These studies have also enabled a direct evaluation of the effects of nanotube bundling on electronic and vibrational structure. Confocal Raman imaging is demonstrated as a useful technique for probing vibrational structure of ultralong nanotubes over large length scales and has resulted in the detection and imaging of a semiconductor-to-metallic nanotube intramolecular junction.

Raman Spectroscopy and Imaging of Ultralong Carbon Nanotubes

Raman spectroscopy and confocal Raman imaging with 514 nm excitation was performed on recently developed ultralong carbon nanotubes grown by the "fast-heating" chemical vapor deposition (CVD) method. The ultralong nanotubes are found to consist of both semiconducting and metallic types, with spectra that are consistent with the nanotubes being single walled. Characterization of nanotube diameters shows that short nanotubes appearing near the sample catalyst region have a broader distribution than is observed for the ultralong nanotubes. The narrow diameter distribution is determined by uniformity of catalyst particle size and gives additional evidence for the proposed "kite" mechanism for long nanotube growth. Raman imaging was performed over large length scales (up to 140 microm). Imaging reveals the ultralong nanotubes to be of high quality, with a very low defect density. Variations in G-band frequencies and intensity demonstrate the occurrence of minor structural changes and variations in nanotube-substrate interaction along the length of the nanotubes. Evidence also demonstrates that larger structural changes resulting in a full chirality change can occur in these nanotube types to produce a metal-to-semiconductor intramolecular junction.

Ultralong single-wall carbon nanotubes.

Since the discovery of carbon nanotubes in 1991 by Iijima, there has been great interest in creating long, continuous nanotubes for applications where their properties coupled with extended lengths will enable new technology developments. For example, ultralong nanotubes can be spun into fibres that are more than an order of magnitude stronger than any current structural material, allowing revolutionary advances in lightweight, high-strength applications. Long metallic nanotubes will enable new types of micro-electromechanical systems such as micro-electric motors, and can also act as a nanoconducting cable for wiring micro-electronic devices. Here we report the synthesis of 4-cm-long individual single-wall carbon nanotubes (SWNTs) at a high growth rate of 11 microm s(-1) by catalytic chemical vapour deposition. Our results suggest the possibility of growing SWNTs continuously without any apparent length limitation.