Branched Carbon Nanotubes Research Articles

Interface Design Strategy for the Fabrication of Highly Stretchable Strain Sensors.

Simultaneously achieving high piezoresistive sensitivity, stretchability, and good electrical conductivity in conductive elastomer composites (CECs) with carbon nanofillers is crucial for stretchable strain sensor and electrode applications. Here, we report a facile and environmentally friendly strategy to realize these three goals at once by using branched carbon nanotubes, also known as the carbon nanostructure (CNS). Inspired by the brick-wall structure, a robust segregated conductive network of a CNS is formed in the thermoplastic polyurethane (TPU) matrix at a very low filler fraction, which renders the composite very good electrical, mechanical, and piezoresistive properties. An extremely low percolation threshold of 0.06 wt %, currently the lowest for TPU-based CECs, is achieved via this strategy. Meanwhile, the electrical conductivity is up to 1 and 40 S/m for the composites with 0.7 and 4 wt % CNS, respectively. Tunable piezoresistive sensitivity dependent on CNS content is obtained, and the composite with 0.7 wt % filler has a gauge factor up to 6861 at strain ε = 660% (elongation at break is 950%). In addition, this strategy also renders the composites' attractive tensile modulus. The composite with 3 wt % CNS shows 450% improvement in Young's modulus versus neat TPU. This work introduces a facile strategy to fabricate highly stretchable strain sensors by designing CNS network structures, advancing understanding of the effects of polymer-filler interfaces on the mechanical and electrical property enhancements for polymer nanocomposites.

Piezoresistive thermoplastic polyurethane nanocomposites with carbon nanostructures

Piezoresistive strain sensors for structural health monitoring (SHM) and human body motion detection applications commonly use polymer nanocomposites based on carbon fillers such as carbon black (CB), carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). Here, we report on new nanocomposites from thermoplastic polyurethane (TPU) with branched carbon nanotubes (known as carbon nanostructures (CNS)) as well as hybrid fillers (CNS + CNT or CNS + GNP) with superior electrical conductivity. These composites manufactured by melt mixing show also exceptional piezoresistive sensitivity. As an example, at only 2 wt% filler concentration, the TPU/CNS and TPU/CNS/GNP nanocomposites have a gauge factor (GF) up to 28 and 144, respectively, under 50% strain (very low for elastomers), which is currently the highest reported values for TPU composites with carbon nanofillers. This study sheds light on the effects of filler morphological structure on electrical conductivity and piezoresistive sensitivity of polymer nanocomposites, introducing a new strategy to prepare multifunctional polymer nanocomposites with very high piezoresistive sensitivity for SHM and body motion detection applications.

Ultrathin, highly branched carbon nanotube cluster with outstanding oxygen electrocatalytic performance

Metal-free heteroatom-doped porous carbons such as N, P co-doped nanoporous carbon materials with designed properties are attracting increased attention for metal-air battery applications. Herein, we report a general approach to synthesizing highly branched N, P co-doped carbon nanotube cluster (NPCTC) derived from metal-organic frameworks as a bifunctional electrocatalyst. NPCTC were obtained by treating ZIF-8 with butyl methylphosphinate, followed by two-step pyrolysis. Benefiting from the cross-linking polymerization and self-aggregation between ZIF-8 and the monomer, the resulting NPCTC exhibited higher mechanical stability and strength. Although the wall thickness was <5 nm, no obvious shrinkage and collapse were observed after graphitization, thereby maximizing the exposure of the active sites. Studies of oxygen electrocatalysis demonstrate that the NPCTC can deliver outstanding bifunctional performance with a more positive half-wave potential, higher limiting current density for oxygen reduction reaction (ORR) than Pt/C, and lower onset potential for oxygen evolution reaction (OER) than IrO2. Homemade Zn-air battery exhibited stable charge-discharge durability over 180 cycles, with an overpotential increase of only 0.15 V. The improved electrochemical performance was mainly attributed to the synergistic effect of N, P co-doping and the distinct geometry of NPCTC, i.e., three-dimensionally interconnected hollow ultrathin nanotube branches facilitating electron and mass transfer.

Iron Oxide Nanoparticle‐Encapsulated CNT Branches Grown on 3D Ozonated CNT Internetworks for Lithium‐Ion Battery Anodes

AbstractMultidimensional hierarchical architecturing is a promising chemical approach to provide unique characteristics synergistically integrated from individual nanostructured materials for energy storage applications. Herein, hierarchical complex hybrid architectures of CNT‐on‐OCNT‐Fe are reported, where iron oxide nanoparticles are encapsulated inside carbon nanotube (CNT) branches grown onto the ozone‐treated surface of 3D CNT internetworked porous structures. The activated surface of the 3D ozonated CNT (OCNT) interacts with the iron oxide nanoparticles, resulting in different chemical environments of inner and outer tubes and large surface area. The mixed phases of iron oxide nanoparticles are confined by full encapsulation inside the conductive nanotubes and act as catalysts to vertically grow the CNT branches. This unique hierarchical architecture allows CNT‐on‐OCNT‐Fe to achieve a reasonable capacity of &gt;798 mA h g−1 at 50 mA g−1, with outstanding rate capability (≈72% capacity retention at rates from 50 to 1000 mA g−1) and cyclic stability (&gt;98.3% capacity retention up to 200 cycles at 100 mA g−1 with a coulombic efficiency of &gt;97%). The improved rate and cyclic capabilities are attributed to the hierarchical porosity of 3D OCNT internetworks, the shielding of CNT walls for encapsulated iron oxide nanoparticles, and a proximate electronic pathway for the isolated nanoparticles.

Service performance of nanopins based on branched carbon nanotubes

Service performance of nanopins based on different branched carbon nanotubes (CNTs) including the 45° Y-type CNT, the 45° V-type CNT, the 90° Y-type CNT, and the T-type CNT have been investigated using classical molecular dynamics simulations. The Y-type CNT is the most cost-effective while there is adequate room to improve its service performance. The installed V-type CNT always has a trend of leaving from the silicon hole, and thus it would better be used with another nanopin cooperatively. For the 90° Y-type CNT, the installation resistance and the unloading force are almost in the same order of magnitude while the installation in pushing approach is relatively easier than that in pulling approach. Interestingly, the attraction between the silicon hole and the T-type CNT can mislead the branch, resulting in the failed installation of the T-type CNT consequently.

Photoresponse of a Single Y-Junction Carbon Nanotube.

We report investigation of optical response in a single strand of a branched carbon nanotube (CNT), a Y-junction CNT composed of multiwalled CNTs. The experiment was performed by connecting a pair of branches while grounding the remaining one. Of the three branch combinations, only one combination is optically active which also shows a nonlinear semiconductor-like I-V curve, while the other two branch combinations are optically inactive and show linear ohmic I-V curves. The photoresponse includes a zero-bias photocurrent from the active branch combination. Responsivity of ≈1.6 mA/W has been observed from a single Y-CNT at a moderate bias of 150 mV with an illumination of wavelength 488 nm. The photoresponse experiment allows us to understand the nature of internal connections in the Y-CNT. Analysis of data locates the region of photoactivity at the junction of only two branches and only the combination of these two branches (and not individual branches) exhibits photoresponse upon illumination. A model calculation based on back-to-back Schottky-type junctions at the branch connection explains the I-V data in the dark and shows that under illumination the barriers at the contacts become lowered due to the presence of photogenerated carriers.

Generic Synthesis of Carbon Nanotube Branches on Metal Oxide Arrays Exhibiting Stable High-Rate and Long-Cycle Sodium-Ion Storage.

A new and generic strategy to construct interwoven carbon nanotube (CNT) branches on various metal oxide nanostructure arrays (exemplified by V2 O3 nanoflakes, Co3 O4 nanowires, Co3 O4 -CoTiO3 composite nanotubes, and ZnO microrods), in order to enhance their electrochemical performance, is demonstrated for the first time. In the second part, the V2 O3 /CNTs core/branch composite arrays as the host for Na(+) storage are investigated in detail. This V2 O3 /CNTs hybrid electrode achieves a reversible charge storage capacity of 612 mAh g(-1) at 0.1 A g(-1) and outstanding high-rate cycling stability (a capacity retention of 100% after 6000 cycles at 2 A g(-1) , and 70% after 10 000 cycles at 10 A g(-1) ). Kinetics analysis reveals that the Na(+) storage is a pseudocapacitive dominating process and the CNTs improve the levels of pseudocapacitive energy by providing a conductive network.

Phonon scattering at SWCNT–SWCNT junctions in branched carbon nanotube networks

In this research article, we analyze phonon scattering in branched single-walled carbon nanotube (SWCNT) networks with SWCNT–SWCNT T- and X- junctions using the wave packet method. Five phonon branches including the longitudinal acoustic, twisting, transverse acoustic, radial breathing, and flexural optical modes are selected to study energy reflection, ramification, and transmission through T- and X-junctions with (6,6) and (4,4) SWCNTs. The results of the simulations indicate that the diameter of SWCNTs affects phonon scattering at carbon nanotube junctions; T-junctions of (6,6) SWCNTs transmit energy more efficiently when compared to T-junctions with (4,4) SWCNTs. In addition, T-junctions of both (6,6) and (4,4) SWCNTs transmit vibrational energy more efficiently when compared to X-junctions in the same phonon frequency range—for example, in the case of the longitudinal acoustic branch, the average energy transmission at T-junctions for low-frequency phonons (lower than 6 THz) was found to be 1.8–2.4 times higher [for the case of (6.6) and (4,4) SWCNTs, respectively] when compared to the X-junctions. It is also observed that energy transmission at the T-junctions shows a dependency on the phonon group velocity with the higher group velocity phonons showing higher energy transmission; however, for the case of the X-junctions, there is little or no correlation observed between the group velocity and energy transmission indicating a complete energy redistribution of the incoming phonons at the junction. Moreover, for the SWCNT–SWCNT branched networks, the energy ramification at the T-junctions was found to be very similar to that at the X-junctions for both (6,6) and (4,4) SWCNTs indicating transverse thermal transport at the X-junctions to be as efficient as the T-junctions.

All-benzene carbon nanocages: size-selective synthesis, photophysical properties, and crystal structure.

The design and synthesis of a series of carbon nanocages consisting solely of benzene rings are described. Carbon nanocages are appealing molecules not only because they represent junction unit structures of branched carbon nanotubes, but also because of their potential utilities as unique optoelectronic π-conjugated materials and guest-encapsulating hosts. Three sizes of strained, conjugated [n.n.n]carbon nanocages (1, n = 4; 2, n = 5; 3, n = 6) were synthesized with perfect size-selectivity. Cyclohexane-containing units and 1,3,5-trisubstituted benzene-containing units were assembled to yield the minimally strained bicyclic precursors, which were successfully converted into the corresponding carbon nanocages via acid-mediated aromatization. X-ray crystallography of 1 confirmed the cage-shaped structure with an approximately spherical void inside the cage molecule. The present studies revealed the unique properties of carbon nanocages, including strain energies, size-dependent absorption and fluorescence, as well as unique size-dependency for the electronic features of 1-3.

Model calculation and empirical investigation of enhanced field emission behavior of branched carbon nanostructures

In this paper, we propose the novel branched carbon nanotubes (B-CNTs) as efficient candidate for field emission applications. We believe that the double-stage structure of B-CNTs, beside formation of multiple thin branches at the apex of each vertical CNT, is responsible for the observed enhanced field emission behavior in B-CNTs. In this regard, we have derived an analytical model to evaluate the field enhancement factor (β) of the B-CNTs in comparison with CNTs, as the most popular cathode for field emission applications in the scientific society. The presented model also allows investigating the effect of different structural parameters on the field emission characteristic. We have also, compared the field emission characteristics of the B-CNTs with vertical CNTs experimentally. We observed a β value for B-CNTs which was around three times higher than CNTs. The observed enhancement in the experimental data was in good agreement with the presented analytical model.

Growth and Formation Mechanism of Branched Carbon Nanotubes by Pyrolysis of Iron(II) Phthalocyanine

Abstract In this letter, a route for synthesizing vertically aligned multi-walled carbon nanotubes (MWCNTs) with branched nanotubes in large area was reported. The branched MWCNTs up to about 30% can be generated by the pyrolysis of iron(II) phthalocyanine in presence of thiol under Ar/H2 at 800∼900°C. The growth mechanism of the branched nanotubes was proposed and the possible reason that thiol enhanced branched nanotubes growth is discussed. The as-prepared samples provide a suitable candidate to investigate the special electrical or thermal properties of CNTs with branched structures further.

Growth and Formation Mechanism of Branched Carbon Nanotubes by Pyrolysis of Iron(II) Phthalocyanine

In this letter, a route for synthesizing vertically aligned multi-walled carbon nanotubes (MWCNTs) with branched nanotubes in large area was reported. The branched MWCNTs up to about 30% can be generated by the pyrolysis of iron(II) phthalocyanine in presence of thiol under Ar/H2 at 800∼900°C. The growth mechanism of the branched nanotubes was proposed and the possible reason that thiol enhanced branched nanotubes growth is discussed. The as-prepared samples provide a suitable candidate to investigate the special electrical or thermal properties of CNTs with branched structures further.

Synthesis and characterization of unbranched and branched multi-walled carbon nanotubes using Cu as catalyst

Unbranched and branched carbon nanotubes (CNTs) were synthesized by catalytic chemical vapor deposition from methane at 900 °C over a Cu/MgO catalyst. Morphology and structure of the CNTs were characterized by scanning and transmission electron microscopy, and Raman spectroscopy. The effect of methane flow rate on the CNT growth was investigated. The results suggest that the products were transformed from unbranched to branched CNTs with an increase in methane flow rate. The simplicity and controllability of such a preparation technique make it a promising method to synthesize different carbon nanotube structures.

Growth of branched carbon nanotubes with doped/un-doped intratubular junctions by one-step co-pyrolysis

Branched CNTs with nitrogen doped/un-doped intratubular junctions have been synthesized by a simple one-step co-pyrolysis of hexamethylenetetramine and benzene. The difference in the vapor pressure and the insolubility of the precursors are the keys for the formation of the branched intratubular junctions. The junctions behave like Schottky diodes with nitrogen-doped portion as metal and un-doped portion as p-type semiconductor. The junctions also behave like p-type field effect transistors with a very large on/off ratio.

Synthesis and properties of all-benzene carbon nanocages: a junction unit of branched carbon nanotubes

The first synthesis of an all-benzene carbon nanocage 1, which represents a junction unit of branched carbon nanotubes, has been achieved. A stepwise assembly of six L-shaped units [cis-di(p-bromophenyl)cyclohexane derivative] and two three-way units (1,3,5-triborylbenzene) by cross-coupling and homocoupling provided the unstrained cyclic precursor. Acid-mediated aromatization of cyclohexane moieties in the precursor resulted in the formation of carbon nanocage 1. Photophysical measurements and DFT studies revealed the unique properties of 1, such as D3 symmetry with degenerate HOMO/HOMO − 1 and LUMO/LUMO + 1, high fluorescence quantum yield (ΦF = 0.87), and a relatively large two-photon absorption cross section (500 GM at 590 nm), which are attractive for various applications.

Branched carbon nanotube reinforcements for improved strength of polyethylene nanocomposites

A bio-inspired design of polyethylene nanocomposites is presented in this letter using branched carbon nanotubes (BCNTs) as reinforcements. Using coarse-grained molecular dynamics simulations, we demonstrate that the pullout strength of the proposed BCNT nanofibers can be an order of magnitude higher than that of CNT reinforcements. The drastically improved interfacial shearing strength is found to be strongly dependent on the geometry of nanofibers, the molecular weight of matrix polymers, and the pullout velocity. By analyzing the time-evolving molecular configurations of BCNT nanofibers and surrounding polymer chains, the underlying strengthening mechanisms are discussed and strategies for further improvement are suggested.

Growth of carbon nanotube branches by electrochemical decoration of carbon nanotubes

Recently we have proposed to electrochemically deposit Ni catalyst particles on conducting surfaces in order to grow carbon nanotube (CNT) interconnects by chemical vapor deposition (CVD). In this paper, we propose to reiterate the electrochemical deposition of Ni particles in order to decorate as grown CNTs and produce CNT branches by a second CVD step. Ni particles with diameters in the order of 30nm are able to nucleate secondary CNTs, thus forming CNT branches by CVD at temperatures of about 600°C. Our method may be used to produce novel three terminal devices such as switches and frequency generators.

Fabrication and Modeling of a Novel SAW-Like Transducer Device Based on Branched Carbon Nanotubes

A novel interdigital sensor and actuator device based on branched carbon nanotubes (B-CNTs) on silicon-based membranes with a high capacitance value is reported. The presence of B-CNTs leads to a high overlap between interdigital (ID) fingers and the resulted capacitance value. The formation of a sensor/actuator system is based on ID patterns on silicon-based membranes, and the branched carbon nano-structures have been grown selectively on the electrodes. The actuation behavior of the device has been investigated in a SAW-like sensor and actuator device which has been placed on a flexible membrane.

Investigating the antifungal activity of TiO2 nanoparticles deposited on branched carbon nanotube arrays

Branched carbon nanotube (CNT) arrays were synthesized by plasma-enhanced chemical vapour deposition on a silicon substrate. Ni was used as the catalyst and played an important role in the realization of branches in vertically aligned nanotubes. TiO2 nanoparticles on the branched CNTs were produced by atmospheric pressure chemical vapour deposition followed by a 500 °C annealing step. Transmission and scanning electron microscopic techniques were used to study the morphology of the TiO2/branched CNT structures while x-ray diffraction and Raman spectroscopy were used to verify the characteristics of the prepared nanostructures. Their antifungal effect on Candida albicans biofilms under visible light was investigated and compared with the activity of TiO2/CNT arrays and thin films of TiO2. The TiO2/branched CNTs showed a highly improved photocatalytic antifungal activity in comparison with the TiO2/CNTs and TiO2 film. The excellent visible light-induced photocatalytic antifungal activity of the TiO2/branched CNTs was attributed to the generation of electron–hole pairs by visible light excitation with a low recombination rate, in addition to the high surface area provided for the interaction between the cells and the nanostructures. Scanning electron microscopy was used to observe the resulting morphological changes in the cell body of the biofilms existing on the antifungal samples.

Branched carbon nanotubes to realize a novel capacitive sensor and actuator device

Novel, high capacitance interdigital structures based on branched carbon nanotubes (B-CNTs) are realized using plasma enhanced chemical vapor deposition. Extensive overlapping between parallel fingers due to the branched carbon nanostructures leads to high capacitance values in the fabricated interdigital structures. A significant rise in the capacitance up to 100 times is reported by means of branched carbon nanotubes. The high electron emission of such nanostructures over regular CNTs can be applied to realize high sensitivity sensors. To investigate the functionality of fabricated B-CNT-based actuator, both sensor and actuator configurations have been designed on a silicon-based membrane and the electro-mechanical response of the whole structure has been investigated. These structures show a superior actuation behavior owing to their high capacitance due to extensive overlapping fingers.