Carbon Nanotube Architectures Research Articles

Bacteria as Bio-Template for 3D Carbon Nanotube Architectures

It is one of the most important needs to develop renewable, scalable and multifunctional methods for the fabrication of 3D carbon architectures. Even though a lot of methods have been developed to create porous and mechanically stable 3D scaffolds, the fabrication and control over the synthesis of such architectures still remain a challenge. Here, we used Magnetospirillum magneticum (AMB-1) bacteria as a bio-template to fabricate light-weight 3D solid structure of carbon nanotubes (CNTs) with interconnected porosity. The resulting porous scaffold showed good mechanical stability and large surface area because of the excellent pore interconnection and high porosity. Steered molecular dynamics simulations were used to quantify the interactions between nanotubes and AMB-1 via the cell surface protein MSP-1 and flagellin. The 3D CNTs-AMB1 nanocomposite scaffold is further demonstrated as a potential substrate for electrodes in supercapacitor applications.

3D Vertically Aligned CNT/Graphene Hybrids from Layer‐by‐Layer Transfer for Supercapacitors

The exceptional electrical, optical, thermal and mechanical properties make graphene and carbon nanotubes (CNTs) promising for a large variety of applications, including energy storage. In practice, it is higly important to translator these properties associated with the low‐dimensional carbon nanomaterials into bulk materials/devices. Recent theoretical studies have proven that three‐dimensional (3D) pillared architectures, consisting of parallel graphene layers intercalated by vertically aligned carbon nanotubes (VA‐CNTs) in between, possess desriable transport and mechanical properties in all dimensions while maintaining the excellent properties of their building blocks. However, it remains challenging to experimentally realize such 3D pillared graphene/VA‐CNT hybrids. Here, tunable 3D pillared graphene/VA‐CNT architectures are formed by chemical vapor deposition, and a template‐free contact transfer process is presented, involving the hydrophobic‐hydrophobic interactions between graphene and VA‐CNTs. The resultant 3D graphene/VA‐CNT hybrids are demonstrated to be efficient electrode materials for supercapacitors with good performance. This newly‐developed methodology holds great potential for fabricating various 3D architectures with many other materials for a wide range of multifunctional applications, including energy storage, electrical and thermal managements, and flexible electronics.

Controlled 3D Carbon Nanotube Architecture Coated with MoOx Material by ALD Technique: A High Energy Density Lithium‐Ion Battery Electrode

Due to its high theoretical capacity, energy density, and excellent reversibility with Li/Li+, molybdenum oxide is one of the vastly studied electrode material in lithium‐ion batteries. However, like most of the oxides, it also suffers from poor cyclic stability because of its low electrical conductivity. In 3D core–shell structure prepared by atomic layer deposition coating, it can provide superiority in nanoscale decoration than other deposition methods because of its extreme conformality and precise thickness control on high aspect ratio surfaces. This report illustrates the electrochemical activity of 3D core–shell type amorphous MoOx material coated by atomic layer deposition technique on conducting carbon nanotubes (CNT) scaffold which exhibits excellent overall cell capacity. The obtained capacity is manifold higher than its planar 2D counterpart and that can become an advanced nanoscale fabrication methodology of such 3D nanostructures for electrode preparation. Such binder free MoOx/CNT core–shell electrode structure shows very high and stable electrochemical activity toward Li/Li+ system. An optimal thickness of MoOx on CNT is also found out in order to attain the most stable cyclic performance of this nanostructure. A stable reversible areal capacity of 645 µAh cm−2 with specific capacity of 915 mAh g−1 is achieved from optimized MoOx/CNT assembly.

Multi-scale mechanics and electrical transport in a free-standing 3D architecture of graphene and carbon nanotubes fabricated by pressure assisted welding

A free-standing, 3D nanohybrid structure is fabricated by welding 2D graphene (Gr) and 1D carbon nanotubes (CNT) by localized Joule heating under high pressure. Multi-scale mechanical properties and electrical transport behavior of the hierarchical nanostructure are investigated. Nanoindentation revealed anisotropy in mechanical properties with respect to the orientation of the graphene layers. CNTs were found to act as anchors between graphene layers during in situ indentation, enhancing the resistance to failure. Gr-CNT is characterized by excellent damping capability, with loss tangent values as high as 0.8. Anisotropy in loss tangent was observed, indicating the potential to dissipate energy in a desired orientation while allowing unattenuated energy transfer in the other orientation. A two-fold increase in electrical conductivity is observed (∼108 S/cm) as compared to pure graphene monolith (∼55 S/cm) fabricated by the same technique. In addition, out-of-graphene plane conductivity is also improved by 23% due to nanotube addition. CNTs act as conduction pathways and compensate for resistance at interfaces and linkages in the hybrid. Development of a large-scale 3D architecture with strongly bonded nano-constituents and excellent electrical transport opens up scope for numerous applications, such as nano-microelectromechanical systems, sensors, dampers, precision systems, thermal management, and scaffolds for tissue and neural engineering.

Joining cross-stacked carbon nanotube architecture with covalent bonding

Carbon nanotubes (CNTs) have superior mechanical properties that make them highly attractive for high performance bulk structures such as CNT fibers and films; however, the weak wan der Waals interaction between CNTs gives degraded strength and modulus, forming covalent bonding between CNTs which is considered to be highly promising but remains a considerable challenge due to the inert nature of the carbon surface. An appropriate electron-beam, as yet, has been used to introduce covalent bonding but limited to CNT bundles. Here, we used a spinnable CNT array to form a cross-stacked CNT architecture first, a bulk film, and proved that sp3 covalent bonding can be directly formed between cross-stacked CNTs under high pressure at appropriate temperatures via a laser heated diamond anvil cell method. The Raman spectrum and molecular dynamic simulations were used to probe and interpret the bonding formation process, respectively. It was found that under 30 GPa with the temperature of 765–1345 K, sp3 covalent bonding was mainly formed in the cross-stacked region. We anticipate that the formation of sp3 covalent bonding between CNTs under high pressure could offer a general pathway to enhance the performance of nano-carbon based materials.

Synthesis and Nitrogen-Plasma Treatment of Silicon/Carbon Nanotube/Graphene Composites As Anode Materials for Lithium-Ion Batteries

Lithium-ion batteries compared to other batteries (such as Ni-Cd, Lead-Acid, and Ni-MH) possess higher energy densities (100 – 150 Wh/kg), higher voltage, and lower maintenance [1]. To increase the accessibly specific surface area and the stability as well as conductivity between the carbon nanotube bundles as well as the nickel foam, three dimensional few layer graphene/multi-walled carbon nanotube architectures were fabricated on oxygen-plasma treated nickel foam coated with Fe catalysts by e-beam evaporation through a one-step ambient pressure chemical vapor deposition (CVD) process using a mixture of acetylene and hydrogen [2]. Silicon thin films with loose microstructure deposited on Cu foil by radio frequency (RF) magnetron sputtering as well as used as anode materials for Li-ion rechargeable batteries can not only be help to buffering the volume changes of Si films during discharge/charge cycles, but also provide with effective pathways for Li ions transportation and consequently lead to higher energy density as well as good cycling stability of electrodes [3]. Silicon nitride thin films deposited by plasma enhanced chemical vapor deposition (PECVD) as anode materials for Li-ion batteries possessed high reversible capacity since a ductile and conductive Li3N matrix buffered volume expansion of the Si-Li alloy as well as prevented aggregation of the Si nanoparticles, however, the specific capacity of silicon nitride was very sensitive to RF power, the higher the power, the lower the specific capacity [4]. Silicon nitride derived from silicon nanoparticles by vacuum CVD with ammonia within graphene matrixes as anode materials for Li-ion batteries displayed stable electrochemical performance at 500 mA/g rate of cycling due to the improved stress management and conductive Li3N matrix which was primarily derived from SiN0.73 [5].Carbon nanotube/graphene composites were directly grown on cobalt (Co) catalysts-coated nickel foam by one-step ambient pressure CVD. Next, The silicon film was deposited on the carbon nanotube/graphene composites by RF magnetron sputtering at different power levels (150 and 200 W). Finally, the silicon/carbon nanotube/graphene composites were modified by RF nitrogen-plasma treatment at different power levels (50, 75, and 100 W). The silicon film sputtered on the carbon nanotube/graphene composites at a lower power level possessed higher specific capacity and cyclic stability due to the silicon thin film sputtered on the carbon nanotube/graphene composites at 150 W with loose microstructure [3]. Furthermore, the higher the nitrogen-plasma power, the higher the cyclic stability because a conductive Li3N matrix primarily was derived from SiN0.73 [5], the higher the power, the higher the percentage of SiN0.73 as well as then the higher the percentage of ductile and conductive Li3N which buffered volume expansion of the Si-Li alloy as well as prevented aggregation of the Si nanoparticles [4, 5]. However, the higher the nitrogen-plasma power, the lower the specific capacity since the higher the power, the higher the percentage of nonconductive SiN1.33 which led to the lower specific capacity [4]. Moreover, silicon/carbon nanotube/graphene composites modified by nitrogen-plasma showed a stable cyclic performance in comparison to silicon/carbon nanotube/graphene composites since the incorporation of nitrogen improved the cyclic stability of the anode [4, 5].Keywords: silicon/carbon nanotube/graphene composites; chemical vapor deposition; magnetron sputtering; nitrogen-plasma treatment; lithium-ion batteries

High-performance and compact-designed flexible thermoelectric modules enabled by a reticulate carbon nanotube architecture

It is a great challenge to substantially improve the practical performance of flexible thermoelectric modules due to the absence of air-stable n-type thermoelectric materials with high-power factor. Here an excellent flexible n-type thermoelectric film is developed, which can be conveniently and rapidly prepared based on the as-grown carbon nanotube continuous networks with high conductivity. The optimum n-type film exhibits ultrahigh power factor of ∼1,500 μW m−1 K−2 and outstanding stability in air without encapsulation. Inspired by the findings, we design and successfully fabricate the compact-configuration flexible TE modules, which own great advantages compared with the conventional π-type configuration modules and well integrate the superior thermoelectric properties of p-type and n-type carbon nanotube films resulting in a markedly high performance. Moreover, the research results are highly scalable and also open opportunities for the large-scale production of flexible thermoelectric modules.

A three‐dimensional carbon nanotube–nanofiber composite foam for selective adsorption of oils and organic liquids

Carbon nanotubes (CNTs) have attracted tremendous research interest area as promising sorbent material due to the large surface area for adsorption, excellent mechanical and chemical properties. To practically employ CNTs as a potential commercial sorbent, it is essential to form loosely packed architecture of CNTs in 3D space. In recent years, a series of CNTs‐based composites have been fabricated. However, these composites showed a highly compact structure and/or junctions with uneven/excessive CNTs deposition, which significantly limit their performance as sorbents. Herein, we report the direct fabrication of three‐dimensional flower‐like CNTs‐nanofibers foams (3D CNTs‐NFs) by freeze‐drying aqueous solutions of electrospun poly‐acetonitrile (PAN) nanofibers and CNTs. As a result, fully expanded multiple layered CNTs nanosheets with sufficient large surface area could be successfully integrated within the 3D nano‐fibrous architecture. The 3D CNFs‐NFs showed excellent mechanical properties and adsorption capacities, which permit this kind of CNTs composite foam could be used in selective adsorption processes and environmental applications. POLYM. COMPOS., 39:E271–E277, 2018. © 2017 Society of Plastics Engineers

Three-dimensional, free-standing polyaniline/carbon nanotube composite-based electrode for high-performance supercapacitors

Vertically aligned Carbon Nanotube (CNT) arrays are synthesized directly on CNT sheets used as substrates by plasma enhanced chemical vapor deposition (PECVD) in NH3 plasma environment. The resulting 3-D nanostructured, N-doped CNT (NCNT) architecture combines high conductivity and superior mechanical properties of CNT sheets with porous structure and high electrochemical activity of CNT arrays. NCNT sheets are then used as scaffolds for polyaniline (PANI) deposited by electrodeposition. PANI coating thickness is optimized to create a core-shell morphology with PANI shell supported by CNT core. Freestanding and flexible PANI/NCNT electrodes are fabricated without using any metal supports/foil or binders with the CNT sheets serving as current collectors. PANI/NCNT electrodes with 56 wt% polymer content demonstrate a gravimetric capacitance of 359 F/g at a current density of 1.56 mA/cm2. The electrode also shows high rate capabilities and retains 82% of original capacitance after current density is increased 30-fold to 46.87 mA/cm2. PANI/NCNT electrodes are used to assemble a symmetric supercapacitor device with PVA/H2SO4 hydrogel as separator and electrolyte. The flexible PANI/NCNT supercapacitor showed a specific capacitance of 128 F/g at 2.47 A/g current density and retained over 92% of initial capacitance after 10000 cycles of charge-discharge at 24.7 A/g current density.

High Aspect Ratio Machining of Nanocarbon Materials by Reactive Ion Etching

AbstractWe demonstrate anisotropic, vertical deep etching of graphite and densely packed carbon nanotube (CNT) thick layer beyond the micrometer scale, which representing the first step toward nanocarbon bulk micromachining. This micromachining process is compatible with standard lithography and therefore allows the fabrication of graphite and CNT architectures with 1 μm lateral resolution and up to 10 μm scale depth.

Tuning electric field aligned CNT architectures via chemistry, morphology, and sonication from micro to macroscopic scale.

Electric-field alignment of carbon nanotubes (CNT) is widely used to produce composite materials with anisotropic mechanical, electrical, and optical properties. Nevertheless, consistent results are difficult to achieve, and even under identical electric field conditions the resulting aligned morphologies can vary over μm to cm length scales. In order to improve reproducibility, this study addresses (1) how solution processing steps (oxidation, sonication) affect CNT properties, and (2) how CNT chemistry, morphology, and dispersion influence alignment. Aligned CNT were deposited onto PVDF membranes using a combination of electric-field alignment and vacuum-filtration. At each step in solution processing, the CNT chemistry (oxygen content) and morphology (length/diameter) were characterized and compared to the final aligned morphology. Well-dispersed CNT with high oxygen content (>8.5%O) yielded uniform membrane coatings and microscopically aligned CNT, whereas CNT with low oxygen CNT (<2.2%O) produced aligned bundles visible at a macroscopic level, but microscopically the individual CNT remained disordered. Based on regression analysis, CNT with larger mean length and diameter, smaller length and diameter variation, and higher oxygen content yielded increased electrical anisotropy, and bath sonication was slightly preferable to probe sonication for initial dispersion.

Electrically Conductive Hierarchical Carbon Nanotube Networks with Tunable Mechanical Response.

Small diameter carbon nanotube (CNTs) are synthesized directly from a parent CNT forest using a floating catalyst chemical vapor deposition (CVD) method. To support a new CNT generation from an existing forest, an alumina coating was applied to the CNT forest using atomic layer deposition (ALD). The new generation of small diameter CNTs (8 nm average) surround the first generation, filling the interstitial regions. The hierarchical forests exhibit a 5-10-fold increase in stiffness, and the two generations are electrically addressable in spite of the interfacial alumina layer between them. This work enables the design of complex CNT architectures with hierarchical features that bring tailored properties such as high specific surface area and robust mechanical properties that can benefit a range of applications.

Conductivity and electromagnetic interference shielding of graphene-based architectures using MWCNTs as free radical scavenger in gamma-irradiation

In this work, we reported a green approach for synthesis of large-scale and low cost three dimensional graphene/polyacrylamide/multi-walled carbon nanotubes (3DGPW) architectures by γ–ray irradiation. Multi-walled carbon nanotubes were used to reduce free radicals and avoid defects brought into graphene during irradiation process. Meanwhile two kinds of conductive networks in the architecture were made up by graphene sheets and multi-walled carbon nanotubes. With the help of free radical scavenger and two kinds of conductive network structures, a remarkable conductivity of 3344.5S/m was achieved for 3DGPW, which was 20 folds higher than that achieved for three dimensional graphene/ polyacrylamide architectures. In addition, the average value of the electromagnetic interference shielding increased from 9.8 to 24.6dB. Therefore, the designed 3DGPW architectures could be considered as promising candidates for applications electromagnetic interference shielding materials.

Three-dimensional porous graphene-based ultra-lightweight aerofoam exhibiting good thermal insulation

Three-dimensional (3D) architectures of graphene and carbon nanotubes (CNTs) were prepared via the in situ self-assembly of graphene oxide and carboxyl-functionalized CNTs by mild chemical reduction and freeze-drying. The prepared 3D architectures exhibited densities of 7.35–9.68 mg/mL and thermal conductivities of 0.0192–0.0414 W/mK. These features were created by a highly porous structure, including millimeter-, micrometer-, and nanometer-scale pores. A number of analytical techniques were used to characterize the 3D architectures of graphene. The highly porous graphene-based aerofoams exhibited low densities, good thermal stabilities, and low thermal conductivities, making them excellent candidates for application in thermal protection materials, as well as in super capacitors and energy storage systems.

Novel Three-Dimensional Carbon Nanotube–Graphene Architecture with Abundant Chambers and Its Application in Lithium–Silicon Batteries

So far, the fabrication of three-dimensional (3D) architectures of carbon nanotubes (CNTs) and graphene-based materials remains a significant challenge. In this work, one facile and template-free strategy for fabricating a novel 3D carbon hybrid architecture was reported, which is comprised of CNTs and few-layer graphene (FLG) through carbonizing the solvent-free CNT fluids at 700 °C. In this architecture, FLG served as walls and CNTs acted as backbones forming abundant chambers. The results of transmission electron microscopy, electron diffraction patterns, and Raman spectra all proved that FLG was produced from the long-chain organic ions grafted on the CNT surface through carbonization. The analysis of atomic force microscopy showed the thickness of FLG was about 1 nm. The charge–discharge experimental result of the Si/CNT–FLG battery shows that the reversible capacity still remained approximately 1350 mAh g–1 with 96% capacity retention after 300 cycles at 0.5 C, demonstrating an outstanding cycling s...

Synthesis and Nitrogen-Plasma Treatment of Carbon Nanotube/Graphene Composites As Anode Materials for Lithium-Ion Batteries

Lithium ion batteries compared to other batteries (such as Ni-Cd, Lead-Acid, and Ni-MH) possess higher energy densities (100 – 150 Wh/kg), higher voltage, and lower maintenance [1]. Hybrid CNTs and graphene nanostructures applied in lithium ion batteries were directly grown by ambient pressure chemical vapor deposition (CVD); methane was introduced to form graphene on copper foils at 950 oC, then Fe catalysts were deposited on graphene/copper foils by e-beam evaporation, and ethylene was next introduced to grow pillar CNTs on graphene/copper foil at 750 oC [2]. To increase the accessibly specific surface area and the stability as well as conductivity between the carbon nanotube bundles as well as the nickel foam, three dimensional few layer graphene/multi-walled carbon nanotube architectures were fabricated on oxygen-plasma treated nickel foam coated with Fe catalysts by e-beam evaporation through a one-step ambient pressure CVD process using a mixture of acetylene and hydrogen [3]. N-doped multiwall carbon nanotubes prepared by a plasma enhanced chemical vapor deposition process contain wall defects through which lithium ions can diffuse so as to occupy a large portion of the interwall space as storage regions and then improve the Li storage capability [4]. N-doped graphene nanosheets prepared by heat treatment (800 oC and 2 h) of graphite oxide under an ammonia atmosphere exhibited a high reversible capacity due to N-doping inducing a large number of defects on the graphene layer as well as forming a disordered carbon structure (further enhancing Li intercalation properties) and enhanced cycling stability, which demonstrated the N-doped graphene nanosheets to be a promising candidate for anode materials of lithium ion batteries [5]. The effects of the electron-deficiency (making the defect graphenes have an electron-accepting tendency) of N-doped (pyridinic, pyrrolic, and graphitic) graphenes on their application in lithium ion batteries were investigated and the pyridinic graphene possessed the best as anode materials of lithium ion batteries, while graphitic graphene would be the weakest of the three defect structures [6]. To simultaneously synthesize carbon nanotubes and graphene on nickel foam without additional catalysts, it is tried to grow using one-step ambient pressure chemical vapor deposition (CVD) at different temperatures (700, 800, and 900 oC). Next, in order to add nitrogen-doped defects to the surface of carbon nanotube/graphene composites, it is modified by RF (radio frequency) nitrogen-plasma at different power levels (50, 100, and 150 W) and time periods (5, 15, and 30 min). Carbon nanotubes and graphene are simultaneously synthesized by CVD at 800 oC. Furthermore, the specific capacity (618.32 mAh/g) reached a maximum at the better nitrogen-plasma treatment conditions (power = 100 W and time = 15 min) due to the highest percentage of the pyridinic defect structure which is the most suitable for Li storage with a high storage capacity [6]. Moreover, it also shows higher electrochemical stability after carbon nanotube/graphene composites being treated by nitrogen-plasma.

A novel Li2Mn2.9Ni0.9Co0.2O8spinel composite interweaved with carbon nanotube architecture as a lithium battery cathode

Custom designed Li2Mn2.9Ni0.9Co0.2O8/MWCNT spinel composite, prepared through a template assisted co-precipitation method demonstrates its suitability for lithium battery applications by exhibiting high capacity and high rate capability.

Controllable and Predictable Viscoelastic Behavior of 3D Boron‐Doped Multiwalled Carbon Nanotube Sponges

3D carbon nanotube (CNT)‐based macrostructures are the subject of extensive attention because the outstanding properties of 1D and 2D nanostructures have not been fully translated into key engineering applications. Generation of 3D CNT architectures with covalent junctions could endow the new materials with extraordinary mechanical properties. In this study, detailed experimental characterization and statistical comparison are carried out on 3D boron‐doped multiwalled CNT (CBxMWNT) sponges with covalent junctions and undoped multiwalled CNT (undoped‐MWNT) sponges without junctions. By investigating the plastic, elastic, viscoelastic, and dynamic viscoelastic properties of both sponges, as well as the dependency of these mechanical properties on material morphology, the CBxMWNT sponge is found to be a more predictable and stable material than the undoped‐MWNT sponge. Statistical comparison proves that the excellent properties of the CBxMWNT are attributed to its “elbow‐like” junctions inside the 3D networks, which prevent permanent buckling and bundling of the CNTs under extreme loading. Thus, by optimizing the covalent junctions in 3D CNT sponges, their functional behavior can be controlled and regulated. These findings may promote applications of 3D CNT sponges in various fields, including biomedical or high‐precision devices in which lightweight, controllable, and reliable mechanical properties are always desirable.

Shape-controlled carbon nanotube architectures for thermal management in aerospace applications

Abstract

Hyperelasticity of three-dimensional carbon nanotube sponge controlled by the stiffness of covalent junctions

To expand the applications of carbon nanotubes (CNTs) at macroscale, a heteroatom doping technique has been employed to fabricate isotropic 3-D CNT architectures by inducing elbow-like covalent junctions into multiwalled CNTs. As the junctions modify the topology of each CNT by favoring the stable bends in CNTs, junction stiffness and the consequence of junction-related morphology changes in sponge's hyperelasticity remain largely elusive. In this study, two types of 3-D multiwalled CNT sponges were fabricated by inducing boron-doped or nitrogen-doped covalent junctions into CNTs. Hyperelastic properties of the sponges were experimentally quantified as the functions of CNT morphology. A novel microstructure informed continuum constitutive law was developed specifically for such isotropic CNT sponges with junctions. Analyzing the experimental data with the new theory demonstrated that, for the first time, the effective modulus of boron-doped junctions (∼100 GPa) is higher than that of nitrogen-doped junctions (∼20 GPa), and the junction stiffness is a key factor in regulating the hyperelastic compressive modulus of the material. Theoretical analysis further revealed that increased number of junctions and shorter segments on each individual CNT chain would result in stronger hyperelastic 3-D CNT networks. This study has established a fundamental knowledge base to provide guidance for the future design and fabrication of 3-D CNT macrostructures.