Carbon Nanotube Hybrid Structures Research Articles

Ultrasensitive wearable sensor with novel hybrid structures of silver nanowires and carbon nanotubes in fluoroelastomer: Multi-directional sensing for human health monitoring and stretchable electronics

Today, wearable sensors are being developed for personalized human health monitoring for physical motion detection and physiological signal detection, and well-being. These wearable devices need to be extremely flexible, lightweight, and stretchable to be compatible with the contours of the human body, and mechanically and dynamically stable. Their functionality can be assured by simultaneously increasing conductivity, stretchability, and sensitivity for accurate and fast response. The challenge in fabricating stretchable sensors with these functionalities is embracing current wearable fashion. In this work, for the first time, a new 3D hybrid nanonetwork structures of high aspect ratio silver nanowires (AgNW) and carbon nanotubes (CNT) in fluoroelastomer FKM are developed. An optimized solution mixing (SM) and layer by layer (LBL) assembly technique, and LBL drop-coating process are employed to establish the hierarchical and shell-like nanostructures. The sensor films are ultra-thin and show high conductivity up to 2 × 105 S. m−1, high stretchability of up to 300%, and a maximum sensitivity (gage factor) of up to 2.5 × 107. The multifunctional sensor with hybrid nanonetwork shows high performance in various wearable electronic applications including human motion detection and stretchable light-emitting diode (LED) circuits. These ultra-sensitive materials show capability for multidirectional sensing by special configurations for each human body part movement, and small movements for human heartbeat monitoring.

Hybrid structures of Si Nanocrystals-Carbon Nanotubes with bead architecture

In present work, hybrid structures of Si Nanocrystals (Si-ncs) and Carbon Nanotubes (CNTs) with bead-like architecture have been synthesized by exposing pristine CNTs to silane (SiH4) at 200 ºC. The exposed CNTs were annealed in Ar ambient at 500ºC in a catalytic chemical vapor deposition chamber. High-resolution transmission electron microscopy (HRTEM) elucidated that the bead-like architecture has well-defined crystalline nature. X-ray photoelectron spectroscopy (XPS) was used to study the nature of chemical bonding and structural functionalization/defects caused by silane exposure and annealing on the nanotube surface. XPS results indicated in-diffusion of Si in the CNT cavity as well reduction in oxygen content on the top surface of the CNTs. X-ray diffractometry was used to further confirm the formation of the crystalline hybrid structures. From the present work it is inferred that a controlled synthesis of hybrid structures (CNT-Si ncs) with bead-like architecture can be achieved by a simple CVD method for various applications

Hole-supply-rate-controlled methanol-gas-sensing reaction over p-type Co3O4/single-walled carbon nanotube hybrid structures

Co3O4/single-walled carbon nanotube (Co3O4/SWCNT) hybrid structures are fabricated, and their methanol sensing properties and related sensing principles are systematically investigated. A series of Co/SWCNT nanohybrid structures are deposited on silicon dioxide substrates by a co-arc discharge process and converted to Co3O4/SWCNT nanohybrid structures by subsequent methanol treatment and oxidation processes. The morphologies and structures of the nanohybrid composites are investigated by scanning electron microscopy, transmittance electron microscopy, X-ray diffraction, and Raman spectroscopy. The effect of the nanohybrid film thickness and the Co3O4: SWCNT ratio in the films on their physical and gas sensing properties are systematically examined. The best methanol-sensing performance is observed upon measurement at 300 °C for the material fabricated by deposition for 15 min and oxidized at 500 °C. The enhanced gas-sensing performance of the hybrid nanostructures is analyzed to prove that the high carrier supply rate from the transducer determines the reaction rate on the receptor surface (providing the receptor can accommodate the oxygen ionosorption). The hybrid sensor structures also exhibit low detection limit of 50 ppb, good selectivity, repeatability, and long-term stability, demonstrating their potential for practical application to methanol sensing.

Mechanical properties of hollow and water-filled graphyne nanotube and carbon nanotube hybrid structure

By performing molecular dynamics simulations, a GNT/CNT hybrid structure constructed via combing (6, 6) graphyne nanotube (GNT) with (6, 6) carbon nanotube (CNT) has been designed and investigated. The mechanical properties induced by the percentage of GNT, water content and electric field were examined. Calculation results reveal that the fracture strain and strength of hollow hybrid structure are remarkably smaller than that of perfect (6, 6) CNT. In addition, the Young’s modulus decreases monotonously with the increase of percentage of GNT. More importantly, the tunable mechanical properties of hybrid structure can be achieved through filling with water molecules and applying an electric field along tensile direction. Specifically, increasing water content from 0.0 to 8.70 mmol g−1 in the absence of electric field could result in fracture strain and strength reducing by 15.09% and 12.87%, respectively. Besides, enhancing fracture strain and strength of water-filled hybrid structure with water content of 8.70 mmol g−1 can also be obtained with rising electric field intensity. These findings would provide a valuable theoretical basis for designing and fabricating a nanodevice with controllable mechanical performances.

Origin and Control of Polyacrylonitrile Alignments on Carbon Nanotubes and Graphene Nanoribbons

AbstractWhile one of the most promising applications of carbon nanotubes (CNTs) is to enhance polymer orientation and crystallization to achieve advanced carbon fibers, the successful realization of this goal has been hindered by the insufficient atomistic understanding of polymer–CNT interfaces. Herein, polyacrylonitrile (PAN)‐CNT hybrid structures are theoretically studied as a representative example of polymer–CNT composites. Based on density functional theory calculations, it is first found that the relative orientation of polar PAN nitrile groups with respect to the CNT surface is the key factor that determines the PAN–CNT interface energetics and the lying‐down PAN configurations are much more preferable than their standing‐up counterparts. The CNT curvature is identified as another important factor, giving the largest binding energy in the zero‐curvature graphene limit. Charge transfer analysis explains the unique tendency of linear PAN alignments on the CNT surface and the possibility of ordered PAN–PAN assembly. Next, performing large‐scale molecular dynamics simulations, it is shown that the desirable linear PAN–CNT alignment can be achieved even for relatively large initial misorientations and further demonstrate that graphene nanoribbons are a promising carbon nano‐reinforcement candidate. The microscopic understanding accumulated in this study will provide design guidelines for the development of next‐generation carbon nanofibers.

Spontaneous hybrids of graphene and carbon nanotube arrays at the liquid-gas interface for Li-ion battery anodes.

We demonstrate that hybrid structures of graphene and single-walled carbon nanotubes (SWNTs) are precisely controlled at the liquid-gas interface. The functionalized SWNT Langmuir monolayers anchor single-layer graphene nanosheets (GNSs) suspended in water via Coulomb interaction at the interface. This GNS/SWNT hybrid multilayer electrode can be a promising anode material for Li-ion batteries, offering high specific capacity, outstanding power capability, and excellent cyclability.

Synthesis of Hybrid Silica-Carbon Tubular Structures by Chemical Vapor Deposition with Methane or Ethene

Silica microtube and carbon nanotube hybrid structures have been synthesized by catalytic chemical vapor deposition using either methane or ethene as the carbon source, and cobalt-grafted or impregnated silica tubes (200–800 nm) as catalyst. The cobalt-grafted catalyst shows a high resistance to reduction (>1000 °C) and selectivity to single-wall carbon nanotubes (SWCNT). While ethene deposition produces more carbonaceous material, methane experiments show higher selectivity for SWCNT. After removing the silica with an excess of HF, the carbon nanostructure endured, resulting in a coaxial carbon nanostructure. The novel hybrid nanostructures obtained consist of a submicron-sized tube, with walls that are formed by a succession of carbon/silica/carbon layers to which multiwall (20–25 nm) and/or single-wall (0.6–2.0 nm) carbon nanotubes are attached. This synthesis approach combines the mechanical properties of carbon nanotubes and the thermal properties of silica tubes into a synergetic nanostructured material, opening further possibilities for polymer reinforcement and potential applications in catalysis.

Thermal transport properties of graphyne nanotube and carbon nanotube hybrid structure: nonequilibrium molecular dynamics simulations

By performing nonequilibrium molecular dynamics (NEMD) simulations, a GNT/CNT hybrid structure made by graphyne nanotube (GNT) and carbon nanotube (CNT) has been designed and investigated. The influences of length, percentage of GNT, and tensile strain on the thermal transport properties of GNT/CNT hybrid structure are examined. It reveals that the thermal conductivity of hybrid structure increases linearly with the length. Due to the different phonon properties between GNT and CNT, the thermal conductivity of hybrid structure appears as a sharp drop in comparison with the pure CNT. By controlling the percentage of GNT, this hybrid structure exhibits tunable thermal transport behaviors. Moreover, a dramatically thermal rectification phenomenon is observed when applying a tensile strain along the heat flow direction. As the strain rises from 0.0 to 0.06, the rectification factor increases from 2.62 to 12.94%; however, the thermal conductivities reduce by 23.9 and 16.3% for the heat flow direction from GNT to CNT and the opposite direction, respectively. These findings would provide significant insights into the potential applications of GNT/CNT hybrid material in nanodevices.

High‐Power Graphene–Carbon Nanotube Hybrid Supercapacitors

AbstractThe bulky structure of current power sources is hindering the widespread development of next‐generation electronics. Here, we propose a graphene/single wall carbon nanotube (SWCNT) hybrid structure for the realization of high‐performance supercapacitors. The devices are assembled by using 2 cm2 area hybrid graphene/SWCNT electrodes, designed by combining a scalable solution‐processing method (e.g., liquid phase exfoliation of pristine graphite and de‐bundling of SWCNTs) with dynamic spray‐gun deposition, and an aqueous electrolyte (3 m LiNO3). This architecture allows us to effectively balance the supercapacitors performance achieving remarkable electrode gravimetric capacitance and specific energy at 2 mV s−1 of 104 F g−1, 20.8 Wh kg−1, respectively, and a maximum specific power of 92.3 kW kg−1. Our results, based on industrially scalable materials production and deposition methods, represent a real breakthrough compared to state‐of‐the‐art lab‐scale devices.

Graphene and Carbon Nanotube Hybrid Structure: A Review

Graphene has been reported with record-breaking properties which have opened up huge potential applications. Considerable amount of researches have been devoted to manipulating or modify the properties of graphene to target a more smart nanoscale device. Graphene and carbon nanotube hybrid structure (GNHS) is one of the promising graphene derivate. The synthesis process and the mechanical properties are essential for the GNHS based devices. Therefore, this review will summarise the recent progress of the highly ordered GNHS synthesis/assembly, and discuss the mechanical properties of GNHS under various conditions as obtained from molecular dynamics simulations.

Synthesis of palladium nanoparticle modified reduced graphene oxide and multi-walled carbon nanotube hybrid structures for electrochemical applications

In this work, palladium (Pd) nanoparticles functionalized reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) hybrid structures (Pd/rGO-MWCNTs) were successfully prepared by a combination of electrochemical reduction with electrodeposition method. The morphology, structure, and composition of the Pd/rGO-MWCNTs hybrid were characterized by scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The as-synthesized hybrid structures were modified on the glassy carbon electrode (GCE) and further utilized for hydrazine sensing. Electrochemical impedance spectroscopic, cyclic voltammetry and single-potential amperometry experiments were carried out on Pd/rGO-MWCNTs hybrid structures to investigate the interface properties and sensing performance. The measured results demonstrate that the fabricated Pd/rGO-MWCNTs/GCE sensor show a high sensitivity of 7.09μAμM−1cm−2 in a large concentration range of 1.0 to 1100μM and a low detection limit of 0.15μM. Moreover, the as-prepared sensor exhibits good selectivity and stability for the determination of hydrazine under interference conditions.

Fe3C/helical carbon nanotube hybrid: Facile synthesis and spin-induced enhancement in microwave-absorbing properties

Abstract Exploring effective microwave absorption materials is always a challenge especially in the relatively low frequency range of 2–8 GHz and broad absorption band. Here we developed a Fe 3 C/helical carbon nanotube (HCNT) hybrid structures synthesized via catalytic chemical vapor deposition (CCVD) using Fe 3 O 4 nanoparticles as catalyst. The microwave-absorbing characteristics of such hybrid nanomaterials were investigated based on the transmission line theory through the evaluation of the experimental data including complex permittivity and permeability. Considering the reaction temperature range of 400–750 °C, the as-prepared hybrid synthesized at 700 °C can be adjusted to have effective performance of RL value less than −10 dB in the relatively lower frequency ranged from 2.9 GHz to 9.9 GHz at the thickness range of 2–5 mm. Furthermore, the hybrid in case of 750 °C bears bandwidths with RL lower than −10 dB from 7.3 GHz to 18 GHz and the minimum RL is about −21 dB. The observed advantageous reflection loss was attributed to the pronounced impedance match owing to the reasonable synergistic effect between magnetic nanoparticles and HCNTs.

Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters

We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

A systematic investigation into a novel method for preparing carbon fibre–carbon nanotube hybrid structures

By electrospraying solvent dispersed carbon nanotubes (CNTs) with a binder onto carbon fibre (CF), hybrid structures, with an end aim to improve interfacial bonding in composites, were formed. The electrospray parameters controlling the modification of the CNT morphologies were studied. High-speed camera observations found applied voltage was critical for determining spray mode development. Electric field simulations revealed a concentrated electric field region around each fibre. Both voltage and distance played an important role in determining the CNT morphology by mediating anchoring strength and electric field force. The forming mechanism investigation of different surface morphologies suggested that binder with appropriate wetness gives freedom to the CNTs, allowing them to orientate radially from the CF surface. Linear density (LD) measurements and thermogravimetric analysis revealed that a 10min coating increased the LD of a single CF filament by up to 31.7% while a 1h treatment increased fibre bundle mass by 1%.

Environmentally friendly preparation of nanoparticle-decorated carbon nanotube or graphene hybrid structures and their potential applications

Nanoparticle-modified carbon nanotubes or graphene structures have recently been developed for use in various applications, such as drug delivery systems, biosensors, batteries, energy storage, and nanoelectronics. However, highly hazardous materials may be produced and released during the synthesis reaction and sample preparation of these nanostructures under existing methods. In order to overcome the problem, many scientists are working on the development of environmentally friendly and user-friendly preparation methods for decorating carbon nanostructures with nanomaterials. This review introduces several synthesis strategies that may lead toward more eco-friendly approaches. Potential applications in various fields for nanoparticle-decorated carbon nanotubes or graphene prepared using an environmentally friendly method are also a focus of the article.

Dependence of Thermal Conductivity of Carbon Nanopeapods on Filling Ratios of Fullerene Molecules

Focusing on carbon nanopeapods (CNPs), i.e., carbon nanotubes (CNTs) filled with fullerene C60 molecules, the thermal conductivity and its dependence on the filling ratio of C60 molecules have been investigated by equilibrium molecular dynamics simulations. It turns out that the CNP thermal conductivity increases first, reaches its maximum value at filling ratio of 50%, and then decreases with increasing filling ratio. The heat transfer mechanisms were analyzed by the motion of C60 molecules, the mass transfer contribution, the phonon vibrational density of states, and the relative contributions of tube and C60 molecules to the total heat flux. The mass transfer in CNPs is mainly attributed to the rotational and translational motion of C60 molecules in tubes. As the filling ratio is larger than 50%, the axially translational motion of C60 molecules gets more and more restricted with increasing filling ratio. For either the mass transfer contribution to heat transfer or the phonon coupling between the tube wall and C60, the peaking behavior occurs at a filling ratio of 50%, which confirms the corresponding maximum thermal conductivity of CNP. With the filling ratio increasing, the dominating contribution to heat transfer changes from tube-wall atoms to fullerene atoms. Their relative contributions almost keep stable when the filling ratio is larger than 50% until it reaches 100%, where the contribution from fullerene atoms suddenly drops because of strong confinement of translational motion of C60 molecules. This work may offer valuable routes for probing heat transport in CNT hybrid structures, and possible device applications.

Study of the Structural Changes Undergone by Hybrid Nanostructured Si-CNTs Employed as an Anode Material in a Rechargeable Lithium-Ion Battery

Silicon–carbon nanotube (Si-CNT) hybrid structures have been fabricated in a single step on Cu substrate by hot filament chemical vapor deposition (HFCVD). A mixture of straight chain saturated aliphatic polymer and Si nanoparticles was used as the seeding source. The material was analyzed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), and the Si content in the Si-CNT was estimated to be ∼15% wt % by thermogravimetric analysis (TGA). Thereafter, the films were used for lithium-ion battery (LIB) anodes, whose cyclic voltammetry studies show redox peaks for Si and C consistent with lithium insertion/extraction, indicating good reversibility over extensive cycling. Electrochemical tests showed that Si-CNT electrodes can deliver an initial high discharge capacity of ∼700 mAh/g and a reversible capacity of ∼500 mAh/g over 520 cycles. After electrochemical cycling, the Si-CNTs were analyzed and compared to pristine material. The cycled films showed an increment of Si-CNT...

Synergistic strengthening effect of graphene-carbon nanotube hybrid structure in aluminum matrix composites

High-performance reinforcement and tailored architecture are currently explored to develop advanced metal matrix composites. In this work, aluminum (Al) matrix composite reinforced by hybrid carbon nanofillers was fabricated by a composite flake assembly process. It was found that for various carbon nanofiller volume fractions, a striking synergistic strengthening effect was achieved by employing graphene (reduced graphene oxide, RGO) and carbon nanotube (CNT) hybrid structure as reinforcement in the Al matrix. Particularly, a tensile strength of 415 MPa was achieved with the addition of 1.5 vol.% of RGO-CNT hybrid, which is significantly higher than those reinforced by individual CNT or RGO (326 and 331 MPa, respectively). The synergistic strengthening effect was attributed to the formation of a planar network of RGO and CNT, which improves the load transfer efficiency between the matrix and the reinforcement in composites. Our study highlights the importance of reinforcement architecture for enhancing the strengthening ability in composites, and provides an effective route to fully take the advantage of the superior properties of various reinforcements.

Magnetically aligned iron oxide/gold nanoparticle-decorated carbon nanotube hybrid structure as a humidity sensor.

Functionalized carbon nanotubes (f-CNTs), particularly CNTs decorated with nanoparticles (NPs), are of great interest because of their synergic effects, such as surface-enhanced Raman scattering, plasmonic resonance energy transfer, magnetoplasmonic, magnetoelectric, and magnetooptical effects. In general, research has focused on a single type of NP, such as a metal or metal oxide, that has been modified on a CNT surface. In this study, however, a new strategy is introduced for the decoration of two different NP types on CNTs. In order to improve the functionality of modified CNTs, we successfully prepared binary NP-decorated CNTs, namely, iron oxide/gold (Au) NP-decorated CNTs (IA-CNTs), which were created through two simple reactions in deionized water, without high temperature, high pressure, or harsh reducing agents. The physicochemical properties of IA-CNTs were characterized by ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy, a superconducting quantum interference device, scanning electron microscopy, and transmission electron microscopy. In this study, IA-CNTs were utilized to detect humidity. Magnetic IA-CNTs were aligned on interdigitated platinum electrodes under external magnetic fields to create a humidity-sensing channel, and its electrical conductivity was monitored. As the humidity increased, the electrical resistance of the sensor also increased. In comparison with various gases, for example, H2, O2, CO, CO2, SO2, and dry air, the IA-CNT-based humidity sensor exhibited high-selectivity performances. IA-CNTs also responded to heavy water (D2O), and it was established that the humidity detection mechanism had D2O-sensing capabilities. Further, the humidity from human out-breathing was also successfully detected by this system. In conclusion, these unique IA-CNTs exhibited potential application as gas detection materials.

Carbon Nanotube Thin Films and Hybrid Structures for Supercapacitor and Fuel Cell Applications

The development of low cost and environmentally friendly energy conversion andstorage systems is currently of the utmost priority. Here we discuss the impact of chemical design of carbon nanomaterials on their performance as active materials for supercapacitor and catalyst support for fuel cell applications.Chemical modification of single-walled carbon nanotubes (SWNTs) and graphene, is a powerful means to improve the charge capacitance of the materials. By introducing oxygen-containing groups the gravimetric capacity of SWNTs and graphene can be doubled. Furthermore, the combination of 1D SWNTs and 2D graphene affords hybrid structures with enhanced synergistic electrochemical performance.We also demonstrate the advantages of functionalized SWNTs for the fabrication of SWNT thin film catalyst support layers in polymer electrolyte membrane fuel cells (PEMFCs). Introducing an optimum level of carboxylic groups in the SWNTs allows the fabrication of SWNT-based PEMFC with efficient Pt catalyst utilization. This offers an attractive route to the manufacture of highly efficient fuel cells that meet some of the US DOE 2017 technical targets.