DOI:10.30919/esmm5f199

Received: 20 Dec 2018
Revised: 13 Jan 2019
Accepted: 13 Jan 2019
Published online: 14 Jan 2019

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Carbon and Boron Nitride Nanotubes: Structure, Property and Fabrication

 Chang Liu,1 Qichen Fang,1 Daoyuan Wang,2 Chao Yan,3* Faqian Liu,4* Ning Wang,5 Zhanhu Guo6 and Qinglong Jiang2*

1 Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio, USA

2 Department of Chemistry and Physics, University of Arkansas, Pine Bluff, Arkansas, USA

3 School of Material Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu, China

4School of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai, China.

5 State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, Haikou, P. R. China

6Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, USA

*E-mail:

jiangq@uapb.edu; liufq7@mail.sysu.edu.cn; chaoyan@just.edu.cn

 

ABSTRACT:

As an interesting and important material, carbon nanotube (CNT) and boron nitride nanotube (BNNT) have been widely used in various applications such as electrical conductor, thermal management, catalyst, sensing, energy harvest and storage, tissue engineering, drug delivery, bio-imaging and cancer therapy. The special size, geometry, aspect ratio, chemical composition and electronic structure endow them the unique properties. Nanotube basics for CNT and BNNT will be covered in this review, such as structures, properties and synthesis methods.

Table of Content

Nanotube basics for CNT and BNNT will be covered in this review, such as structures, properties and synthesis.

Keywords: Nanotube, CNT, BNNT

1. Introduction

Nanotubes are hollow fibers at the nanoscale. Since the discovery of carbon nanotube (CNT) in late 1990s,1 nanotubes have drawn great interests for its high aspect ratio, high specific surface area and nano-size dependent properties. As a consequence, nanotubes such as CNT, boron nitride nanotube (BNNT), titanium dioxide (TiO2), zinc oxide (ZnO) nanotube and other nanotubes are widely studied in environmental remediation, catalyst application,2-5 energy harvest and storage,6-10 sensors,11,12 bio-medical/tissue engineering,13-16 optoelectric application,17 conductive and thermal management applications18,19 and many other fields.20

As one of the most important nanotubes, CNT has attracted both academia and industry interests for its special size and electronic structure. CNT has been used as nano-electronic element to continue the nearly ended Moore’s Law. However, three major problems are retarding CNT for applications: large scale production, manipulation and chirality separation.21,22 Up to date, the producing capability of CNT for most companies is about a ton per year, which is extremely limiting its application. The chirality separation is the key for CNT to be used as nano-electronic components. Therefore, researchers are looking forward to multi-functional and hybrid composites rather than nano-electronics. The special multi-functional properties are contributed by either composition or structure. For example, hybrid and hierarchical structures.

In this review, we will go through the CNT and BNNT in three sections: structure, property and synthesis methods. In the first section, basic structures of different nanotubes are illustrated. Properties of nanotubes are discussed on mechanical, electrical and thermal aspects. Synthesis method defines the structure/property, which is essential for nanotubes’ application. In this case, we emphasized conventional and emerging fabrication methods in the third section. Modification and functionalization of nanotubes methods are discussed as well. Nanotube based hierarchical structures are introduced in the fourth section. Building hierarchical structure with various synthesis methods is an important approach in designing multifunctional and meta- materials.

2. Structure and property of nanotubes

2.1 Structure of nanotubes

CNT is the most typical model to illustrate the structure of nanotubes. As shown in Fig. 1, CNT can be considered as rolled graphene sheet. The electronic structure of formed CNT differs by rolling orientation. And the corresponding CNT is noted as armchair or zig-zag. The chirality notation is represented by a vector pair (n, m) which is also called chiral vector (Fig. 1c). The chirality becomes one of the most important characteristic for single wall carbon nanotube (SWCNT). The armchair CNT (n, n) is metallic (Fig. 1a). However, the zigzag CNT (n,0) (Fig. 1b) is quasi-metallic. When n-m is a multiple of 3 (n≠m, nm≠0), the SWCNT is also quasi-metallic. All other CNT are semiconductive.23 The match of electronic structure between different walls can change its electronic property as well.24 The structural stress of CNT always exists. Normally, the smaller diameter, the larger internal stress will be. However, when researchers are seeking smaller CNT, they successfully synthesized stable and small CNT with an inner diameter of 0.4 nm.25, 26 CNTs can be classified in two main categories: single wall carbon nanotube (SWCNT)27 and multi-wall carbon nanotube (MWCNT)28 (Fig. 1d, e, f, g). Some studies are using double wall CNT (DWCNT) for functionalization of CNT.29 The outer wall can provide the location for chemical bonding and the inner wall supports the structure. Sorting different CNTs is a significant topic due to the difference of CNT’s electronic property. This difference is also preventing CNT from being used as nano-electronics in large scale production. Most researches are using chromatography related methods which are based on the weak interaction between electron density with chromate fillers.21 The other method is using a special polymer which can wrap the semiconductive CNT for separation.22

Fig. 1 Structure and chirality of CNT. (a) Armchair assemble of SWCNT; (b) Zig-zag conformation of SWCNT; (c) Chirality of CNT. Transmittance electron microscope (TEM) image of SWCNTs; (d) (18, 8) SWCNT; (e) (28, 0) zigzag SWCNT; (f) higher magnification image of (e) (Warner et al. 2011 Adapted with permission of Nature Springer); 27 (g) TEM image of MWCNT shows the loss of five walls (Yuzvinsky et al. 2005 Adapted with permission of AIP publishing).28

By alternatively replacing the carbon atoms in CNT with boron and nitrogen atoms, we can get boron nitride nanotube (BNNT). As it has an identical structure with CNT, BNNT shows a similar outstanding mechanical property. BNNT is also called white CNT due to its white color. Different from full carbon structure, boron nitride (BN) has a much better stability in oxygen (Fig. 2a), especially at high temperature. This allows BN material to be excellent candidate for thermal management and thermal ablation applications. Hexagonal BN (h-BN) nanomaterials, such as BN nanosheet and BNNT, have been widely used as fillers to improve thermal conductivity of polymers. Besides, the electronic structure formed by boron and nitrogen makes BNNT a wide bandgap insulator (~5.5 eV).

Fig. 2 Structure of (a) BNNT and (b) h-BN; (c) Chiral vector of MoS2 nanotubes; (d) armchair MoS2 nanotube; (e) Zig-zag MoS2 nanotube;30 (f) Layer structure of MoS2.

Black phosphorus is new graphite like 2D semi-conductive material. By using exfoliation methods31, phosphorene (single layer black phosphorus: SLBP) can be obtained. As a result, black phosphorus nanotube (BPNT) is expected.32 However, different from CNT, the BPNT has 1 layer of phosphorus atom but aligned in 2 cylindrical planes (Fig. 3). Similarly, MoS2 nanotube consists of two molybdenum layers and one sulfur layer (Fig. 2d, 2e and 2f).30 Besides, there is a large group of 2-dimentional materials can be rolled up to nanotubes.33-35

Fig. 3 Structure of BPNT32. (a) Top view of single layer black phosphorus sheet (SLBP); (b) Zigzag-view of SLBP; (c) Armchair-view of SLBP; (e) Armchair BPNT; (f) Zig-zag BPNT.

Besides these well aligned walls, there is another kind of nanotube consist of stacked Dixie shaped structure.36, 37 Different from the vertical aligned walls in SWCNT and MWCNT, its wall consists of wrapped graphene layers (Fig. 4). Such a material has a hollow core and the diameter is about 200 nm. As a result, this material can be called either MWCNT or vapor grown carbon nanofiber (VGCNF).36 Due to its large diameter, high crystallinity and high roughness surface, the VGCNF is a wonderful material for mechanical reinforcement and electrical conductive nanofiller.

Fig. 4 TEM image of VGCNF. (a) detailed wall structure; (b) Stacked cup structure; (c) dimensions in the stacked cup structure.36

2.2 Properties of nanotubes: mechanical, thermal and electrical

The conductivity of metallic conductive CNT is higher than most metals such as copper.38 Such a high conductivity attribute to the ballistic transportation of electrons. The conductivity of CNTs depends on ambient temperature and isotope composition as well.39 Similar as the transportation of electron, the special structure of CNT also allows ballistic transportation of phonon. This result CNT has an excellent thermal conductivity and Young’s modulus. Both theoretical calculation and experimental results show CNT has the highest mechanical property. For SWCNT, the tubular graphene structure consists of sp2 hybrid C-C bond only. On the other hand, the chirality of CNT defines its mechanical property along its axis as well. As a result, the tensile strength of CNT ranges from 10 GPa to 150 GPa and the Young’s modulus ranges from 0.2 TPa to 5 TPa. However, we have to notice that the different measurement techniques lead to different results.

Meanwhile, BNNT shares a similar structure with CNT, the hexgonal-tubular structure. On the other hand, boron and nitrogen are the two closest elements to carbon. As a result, the structural property of BNNT and CNT is about to be similar. The Young’s modulus of BNNT was measured to be around 500 GPa to 1.2 TPa.40 However, the theoretical value is about 700 to 900 GPa.40 It seems these measured and simulated values are in a smaller range compare to the CNT’s values. This might because the CNT is discovered at an earlier time. With the development of experimental techniques and modeling accuracy, the obtained values of BNNT are more accurate.

Another advantage of CNT and BNNT is their low density. Theoretically, the specific strength of CNT and BNNT is approximately 300 times of high-carbon steel. Pop and Kim measured the thermal conductivity of CNT is up to 3500 W/m K which value approaches to the theoretical one. On the other hand, thermal conductivity of CNT and BNNT are as high as 300 W/m K and isotope affects this value as well.39 Common polymers have low thermal conductivity of 0.1~0.35 W/m K.20 As a result, CNT and BNNT are widely added into polymers for enhancing the thermal conductivity of polymers. Besides chirality difference, such a huge properties’ variance also origins from defects of the structure leading to another shared problem for nanotubes: when a single nanotube is being used, the connection between nanotube structure (two tube ends) and the connected material is always the weak point. This weak point might be a nanotube-metal bonding, or strong internal stress from distorted bonds. Another interesting property of CNT is that the tube can deform to flat belt. Such a behavior allows CNT to be used for collision absorption applications.7

BNNT has an additional advantage for its high atmosphere stability. The BNNT can stand at lease 800 °C in the air while the CNT can only bear 400 °C. This advantage makes BNNT an outstanding candidate for thermal protection and ablation applications such as re-entry vehicle coating. However, the alkaline solution can dissolve BN materials easily including BNNT and boron nitride nano-sheets (BNNS). These special chemical properties are contributed by the B-N bonding while the B-N bonding can be easily dissociated into B-OH group and N-H group. However, B-N bonding is hard to be oxidized directly into B-O and N-O bond without a proper catalyst. This special B-N bonding also brings BNNT a big band gap. BNNT are usually treated as wide band gap or insulating material due to its big band gap of 5.5 eV. With any kind of doping, the band gap is going to be reduced. Additional information is summarized in later sections.

3. Synthesis methods

There are two main synthesis methods for nanomaterials, bottom-up and top-down. The bottom-up method is an assembling process; however the top-down method is about etching or losing of material. Synthesis process is the most important procedure. It defines the morphology of product nanostructure and further controls properties of application. Several conventional and emerging nanotube synthesis methods and technologies are introduced in this section. Modification methods for nanotubes are discussed as well.

3.1 Arc discharge and Laser ablation

CNT was found accidentally in the carbon soot of using arc discharge method for carbon filament and fullerene.1 Arc discharge method usually consists of two graphitic electrodes which are very close to each other (Fig. 5, left). By applying a 100 A current, the arc will be generated and the temperature could reach 2000 K. During this process, the graphitic anode sublimates, then atomic carbon migrates to the cathode, and deposits onto the cathode. This process produces a large amount of carbon soot. Inert gas such as helium and argon are generally used. Metals are used as catalysts, such as Fe, Ni, Co, B and so on. By tuning the arc conditions (electrode distance, inert gas, gas pressure, current and catalyst), the product ranges from SWCNT, MWCNT, C60, carbon nanofiber, amorphous carbon to carbon soot. However, CNT is more like a byproduct since this process produces too many other products.

Laser ablation is the other energetic method for the production of carbon nanomaterials which was firstly introduced by Smally’s group in 1995.40 The basic setting of laser ablation consists of high energy laser, graphitic target, and collector (Fig. 5 right). The setup is usually set in low pressure (500 Torr) inert gas quartz tube at high temperature (~1200 °C).40 This process greatly improved the yield of CNT from 30% of arc discharge method to 70%. Besides the laser parameters (such as wavenumber, photon density, and pulse duration/frequency), other parameters such as furnace temperature, inert gas pressure, target composition, collector temperature, target-collector distance are also important. For example, using Nd: YAG laser shoot a Co/Ni-graphite composite target at 1200 °C could produce a large amount of SWCNT.40, 41 Arc-plasma42 and laser ablation43 were used to produce silicon nanotubes (SiNT) as well. However, for cost-effective fabrication of SiNT, template method is the most widely used. Template synthesis of SiNT will be introduced in the later section.

Fig. 5 Instrumentation for arc discharge method and laser ablation method.

3.2 Plasma torch

Plasma is a useful tool for preparing nanomaterials, such as thin film, nanoparticle and of course nanotubes.44, 45 During the process, the carbon source is heated to a plasma state in a designed reactor and carbonaceous products are deposited on a target. The plasma can be induced either by microwave or radio frequency torch. The diameter of CNTs produced from plasma method is usually very low.46 The large amount of carbon soot around CNTs is hard to be removed, which means the purification of this CNT kind is hard. The advantage of this method is the production rate is high. Keun Su Kim et al. could produce SWCNT at a rate of 100 g/h with a yield of 40 wt.%.47 Energy consumption of plasma methods is lower than the arc discharge method and laser ablation method. Currently, plasma methods are usually applied to assist other methods such as the CVD method.

3.3 Chemical vapor deposition (CVD)

Compare to arc discharge, laser ablation and plasmonic methods, CVD method allows a lower synthesis temperature (400 °C ~ 900 °C), which means a lower energy consumption and simpler instrumentation. With this convenience, CVD becomes the most widely used method to produce CNTs and also some other nanomaterials. CVD methods can produce various nanotubes, such as SWCNT, MWCNT, VGCNF, BNNT etc. A typical CVD instrumentation consists of a gas source, furnace/reactor, and substrate (Fig. 6a). Key parameters are chemical composition of the gas source, flow rate, furnace/reactor temperature/pressure, substrate kind, catalyst composition, and deposition duration. Besides, by changing gas source composition, catalyst, temperature, etc., other nano-materials can simply be synthesize easily, such as carbon coil,48 graphene,49 nanodiamond50 and so on. As shown in Fig. 6a, CVD method also allows the growth of nanotube to be well controlled on the substrate (orientation, location, length, etc.) which makes CNT based nano-electronics become more possible.

The CVD process, as shown in Fig. 6b, there are two mechanisms: tip growth and bottom growth. Both of them consist of 4 steps: decomposition of carbon contained gas source on catalysts, the formation of carbide, the growth of nanotube, deactivation of catalyst. Before synthesis, catalyst (transition metal salt solution, such as Ni(NO3)3.) is usually cast or coated on the substrate (graphite, copper, mica, silicon wafer, etc.). The metal salt decomposes and turns into metallic carbide when touches the carbon source. When the CVD process begins, carbon contained gas source decomposes on the surface of deposit onto catalyst. However, the catalyst can also be contained in the carbon source. For example, ferrocene is an iron contained organic molecule which can be carbon source and catalyst at the same time.51-53 After the carbon source decomposed, the carbon atoms join the carbide and form the initial tube structure. With more carbon atoms depositing, the tube can grow longer and longer. However, catalysts’ activity and lifetime become the limitation for CNT’s length. Sumio Iijima et al.54, 55 enhanced its activity and lifetime by introducing water into the gas source. Rufan et al. applied the principle of Schulz-Flory distribution for polymerization on the growth of CNT.56 They interpreted the relationship between catalyst activity probability and CNT length, an ultra-long CNT (550 mm) was synthesized. On the other hand, the catalyst particle size defines the diameter of CNT. During the growth process, the carbon source self-pyrolyzed and graphitized which may produce amorphous carbon surround the growing CNT. However, Christoph et al. found the existence of amorphous carbon surrounds may not stop the activity of catalytic decomposition and graphitization.57

Fig. 6 CNT CVD instrumentation (a) and growth mechanism (b).

The catalyst can be deposited on the substrate, floating in gas source, and supported on the carrier. Al2O3, SiO2, MgO, zeolite nano-porous particles (Fig. 7a) were used as carriers to support the catalyst nanoparticles. By mixing catalyst precursor solution with these porous materials, after a calcination process, the precursor is transformed into oxide nanoparticles. During the CVD process, the oxide nanoparticle will be reduced by gaseous chemicals (H2, NH3, etc.) firstly. However, due to the use of supporting material, the purity of CNT is limited. Sol-gel and aerogel approaches are used to prepare high specific surface area supports and which can improve the total yield significantly. Cassell et al. prepared SWCNT using a metal nanoparticle on SiO2/Al2O3 sol-gel hybrid material with a yield of 30 wt.%.58 Su et al. improved the yield by 300% with a modified aerogel method.59

Metal-free CVD is becoming focused recently because the metallic species is a big disadvantage for CNT to be used in bio-medical, tissue engineering applications. In some cases, metal free CVD does not require a further purification process. Bilu et al. used scratched Si/SiO2 wafer as a substrate to synthesis SWCNT.60, 61 In his experiment, the scratched edge becomes the nucleation site. Nanodiamond particle was also used for metal-free CVD.62, 63 A thin layer of nanodiamond was spread on a graphite substrate at 600 °C. Ethanol was used as gaseous carbon source for CVD at 850 °C. Isolated CNT was obtained while the nanodiamond particle remained the same compared to its original state. However, the CNT growth mechanism in this procedure is still unclear. Another study suggests oxides might be able to activate the growth of CNT.64, 65 Another study shows the CNT can continuously grow even after the metallic catalyst being capsuled inside the tube, which means the metallic catalyst only initiate the growth process.66 This concept is different from major studies, more in situ observation and theoretical studies are needed.

Production of CNT with CVD has many derivations, such as plasma enhanced CVD (PECVD) ,67, 68 water-assisted CVD,54, 55, 69 camphor based CVD69, 70 and HiPco CVD (Fig. 7b) ,71, 72 hot filament CVD.73 For example, the PECVD coupled plasma torch (Fig. 7c) and CVD methods. By using high frequency (radio frequency range) source, the electron in gas precursors can be heated to more than 10,000 K while the atom remains hundreds of Kelvin. Such a hot electron can significantly enhance the dissociation reaction and reduce processing temperature. Most of the derivations are developed for massive production purpose.47, 49, 54, 55, 58, 74-78 When researchers face so many kinds of CNTs, apparently, a standard for CNT and the related product is needed. Parameters such as inner wall diameter, outer wall diameter, length, impurity percentage and impurity composition should be included. A standardized CNT regulation is very important for its commercialization.

Fig. 7 (a) TEM images showing CNT by CVD with Fe, Co/Zeolite catalyst;70 (b) SWCNT bundle from HiPco method (Reprinted with permission from AIP publishing);72 (c) CNT forest for chip application from PECVD method.68

BNNT was also produced with arc discharge method and laser ablation method79, 80 after Marvin Cohen theoretically proofed its existence in 1994.81 However, it was in 2010s, plasma and CVD related methods were successfully developed for large volume production of BNNT (Fig. 8c). Such as RF plasma torch, induce-coupled plasma (ICP),44 pressurized vapor/condenser method (PVC)82 and PECVD. The synthesis principle of BNNT is similar to CNT which consist of gas decomposition and tube growth. However, the raw material varies a lot. In the production of CNT, the gas source is always the carbon source. In the production of BNNT, the gas source can be either borazine (B3N3H6) or NH3. When B3N3H6 is used, the substrate catalyst might be nickel boride nanoparticle.83 Other precursor systems are developed due to the high cost of B3N3H6, such as the most common boron/metal oxide powder mixture which is also called boron oxide CVD (BOCVD)84-86. The metal here can be Fe, Mg, Li, and Ni.87 Solid boron reacts with MgO and forms B2O2 when the temperature is over 1200 °C in which B2O2 exists as a gas. The other gas source, such as NH3, decomposes into N2 and H2 at such high temperature. Then, H2 reacts with the oxygen from B2O2 to form H2O; N2 reacts with boron to form BNNT.87, 88 Of course, BNNT can be produced as well with gaseous BxHy and NH3 at lower reaction temperature with increasing cost on instrumentation and procedure complexity.74

Other nanotubes made from CVD methods such as germanium nanotube89 (Fig. 8a, 9b) and silicon nanotube (SiNT) share a similar synthesis principle as CNT and BNNT.90 Especially, Germanium is a member of group IV element which can form hydrogen contained compound easily such as methane, acetylene, silane, germane and stannane. As a result, the existence of corresponding nanotubes is predictable.91 Because these nanotubes are less studied, currently, only electrical properties were explored in experiments or simulations.91

Fig. 8 TEM images of Ni-NR assisted Ge nanotubes showing control of wall thickness by CVD at (a) 330 °C for 0.5 h; (b) 330 °C for 1 h; (c) Large scale production of BNNT. TEM image of double wall BNNT (d) and 4-walled BNNT; (e) SEM image of cloth like BNNT sheet. Reprinted (adapted) with permission from ref.45, 89 Copyright (2011) American Chemical Society.

3.4 Electrochemical methods

CNT is less made from electrochemical methods. MWCNT can be prepared from electrolysis of carbon electrode in molten LiCl.92 The experiment was carried at 600 °C. Ren et al. used low melting point eutectics lithium carbonate (LiNaKCO3: m.p. 399 °C) as electrolytes, CO2 as the carbon source, Ni as electrode and catalyst prepared long carbon nanofiber. Derek Fray explored a lot on molten salt based electrochemical synthesis of carbon nanostructures.76, 77, 93, 94 He found that graphene sheets are peeled off from the graphitic anode in the electrolysis process. Then, the graphene sheets are rolled up in the molten salt and the MWCNT forms at the interface of the cathode and the molten salt. Other carbon nanostructures form at the same time due to the etching and disintegration of graphene sheets/flakes.77

3.5 Template methods

Although CNT, BNNT, SiNT and Germanium nanotube are usually made from CVD methods, template methods will work as well.89, 90 Template method is always companying with other methods such as CVD, sputtering, physical/chemical coating, electrospinning, pyrolysis and electrochemical method. Generally, template methods can be classified into 3 categories: bottom-up, top-down and transformation.

(1) Coat target material on a cylindrical and removable core (Fig. 9a).

(2) By etching the material in a designed pattern, nanotube arrays can be created (Fig. 9b). For example, using the focused ion beam (FIB) etch a silicon substrate.

(3) Transform organic nanostructures to carbonaceous nanotube by pyrolysis or sintering (Fig. 9c). For example, pyrolyzing of core-shell electrospun nanofiber can produce ultra-long carbonaceous nanotube.95

By all means, the template method has to be coupled with other deposition or growth methods. It’s the special geometry of template allow the formation of the nanotube to be easier. Also, the formed nanotube is usually highly uniform and aligned compare to CVD, arc discharge, laser ablation, and hydrothermal method.

Fig. 9 Template methods. (a) Coat the nanowire; (b) anodization and coating method; (c) pyrolysis of polymer nanotube precursor.

3.6 Hydrothermal method

In short, the hydrothermal method can be described as ‘stew’. Many nanostructures can be synthesized from this method, such as quantum dot, nanoparticle, nanowire, nanotube and gel. However, the main problem is yield and purification for the fabrication of nanotube.96 Gogotsi et al. synthesized MWCNT in aqueous environmental.97 They put polyethylene, water, and nickel catalyst into a reactor at 700 °C - 800 °C under 60 MPa -100 MPa. Under this a hydrothermal condition, the water is in the supercritical state and which may promote the carbonization reaction. Firstly, the C-H will be dissolved in the supercritical water. With an increase of pressure, the solubility of carbon decreases and then carbon deposits onto the surface of catalyst particles. Gogotsi et al also suggest that their experiment may explain why CNT can be found in carbonaceous rocks in nature.98

3.7. Mechanical method

Both CNT99 and BNNT78, 99, 100 can be prepared by mechanical methods as well, for example, ball milling. However, the nanotubes cannot be formed with just only the ball milling process. A post-treatment of high-temperature annealing is the key for the growth of nanotubes. Precursors, gas and room temperature are the only requirements for the ball milling process. The process can take up to 150 hours. After the milling, the material anneals between 700 K ~ 2000 K for 6 h. Although the mechanism is still not well understood, it suggests nucleation of nanotubes occurs in the milling process and the nanotube grows during annealing.99 Yu et al. compared the effect of annealing gas. They found that the BNNT grows without a catalyst in NH3. The growth process is slow but the resulting nanotube has fewer defects and the wall is very thin (~7 nm in diameter with 4 walls). However, in N2 or N2-NH3 ambient with catalyst, the BNNT grows fast with lots of defect structures such as bamboo, Dixie cup shapes (20 nm ~ 150 nm in diameter).100 On the other hand, Zhu et al produced BNNT fuzzy SiC fiber using powder boron with N2.101 Their study focused on the formation mechanism of two types of BNNT: tip growth and bottom growth. They found that the flat wall BNNT is from tip growth mechanism and the bamboo-bubble wall BNNT comes from bottom growth mechanism. And the difference is driven by the interaction stress difference between the catalyst nanoparticle and the substrate surface. Since the mechanism on the growth of nanotubes from ball milling method is still unclear, a further experimental and theoretical study on morphology and chemical composition of milled graphite are needed.102, 103

3.8 Modification of nanotubes

The aim of modification of nanotubes is either improving their processing ability or functionalization for special application. By modification, nanotubes can be functionalized with additional chemical groups or nanostructure. Modifying nanotubes into nanostructures is considered to be hierarchization of nanotubes which has been discussed in the previous section. Also, non-covalent functionalization is not involved. In this section, we are going to focus on chemical modification and functionalization.

Chemical functionalization of CNT has been widely studied since its discovery. For example, amidation,104 amination,105 esterification,106, 107 metallization,14, 108 thiolation (Fig. 10a),109, 110  cycloaddition(Fig. 10b),13 and halogenation are well studied.111,112 The easiest method is converting the carbon-carbon structure into carboxylic acid, hydroxyl group and epoxy group.113, 114 There are many methods to induce the oxygen contained organic groups, for example, ozonolysis treatment and aggressive acid method. The caps of CNT can be removed effectively by a mixture of concentrated sulfuric acid and nitric acid. In order to create the curvature of CNT cap, pentagonal carbon rings always exist. However, this pentagonal carbon ring is much less stable comparing with the hexagonal one. As a result, oxygen contained groups can be easily bonded to carbon atoms on the caps. Both experimental and theoretical studies on oxidation mechanism of CNT show the carbon reacts quickly with nitronium and forms carbonyl group and then transforms into phenol or carboxylic groups.75, 115 At a lower temperature, the reaction occurs at the defective place which is the cap; while, the reaction can be initiated at any place at a higher temperature. Usually, the functionalization is processed in aqueous dispersion or gas phase. Dai et al. developed several methods for asymmetric functionalization.116-118 The methods are using compacted and well aligned CNT forests. By immersing one side of the aligned CNT into a chemical solution, the CNT tip can be functionalized (Fig. 10c).116 Masking is another method to obtain asymmetrically functionalized CNT (Fig. 10d).117, 118 High energy methods can be used for oxidation of CNT as well. For example, the ball mill and high energy radiation method were studied.119-121 The advantage of high energy methods is that a large amount of materials can be modified and the method can also be applied to other materials such as graphene, h-BN (hexagonal boron nitride), BNNT, etc.

Fig. 10 Modification methods for CNT. (a) chemical routes; (b) cycloaddition;122 (c) asymmetric functionalization (Reproduced from Ref. 122 with permission from The Royal Society of Chemistry); (d) TEM image of Pt nanotube deposited onto the nanotube tip. Reprinted (adapted) with permission from ref.13, 116, 118 Copyright (2005) American Chemical Society.)

Acids are usually used to initialize the functionalization of CNT. However, BN is very stable against acids. On the other hand, most BNNTs are produced by using NH3 as a reactant from the CVD method the edge of BNNT remains a large amount of N-H groups. In this case, reactions based on the N-H group are used for functionalization of BNNT. For example, Zhi et al. used stearoyl chloride to modify BNNT based on the reaction between -(C=O)-Cl group and N-H group.123 Surface-initiated atom transfer radical polymerization (ATRP) method was used to attach various polymer (polystyrene: PS, polymethylmethacrylate: PMMA) on the surface of BNNT.124 Ionic liquid and Lewis acid were also used as solvent and catalyst to attach alkyl groups onto BNNT surface based on SN2 substitution reaction.125 These modification methods can be used to produce well-dispersed BNNT nanocomposite. It’s easy to notice that the concentration of edge N-H group is relatively low. Thus, for an efficient functionalization, the surface of BNNT has to be broken. One method to introduce extra N-H group is using high energy beam to shoot the BNNT. For example, ammonia plasma can introduce N-H group on the surface of BNNT effectively.126, 127 Besides N-H group, B-OH and B-N group are also attacking points. However, due to the stability of the p-backbonding, B-N and B-O bonds are hard to be attacked. The functionalization through breaking B-N or B-O bonds is still unexplored. The functionalization on BNNT also changes its electronic structure. It’s very interesting that all kinds of functionalization reduce the band gap of BNNT, for example, from 5.80 eV of neat BNNT to 4.20 eV of C10H7CO-BNNT.128 Boron carbonitride (BCN) nanotube can be considered as a kind of carbon doped BNNT as well. It is found that with the addition of carbon atoms, the band gap of BCN material decreases.129

4. Hierarchical structures

Nanotubes are relatively simple compared to the state of material science art.122 Performance of nanotube-only material is also always not satisfactory. For example, the electromagnetic interference (EMI) shielding range of CNT is relatively low.122 A wide band or selected band EMI shielding are required when designing a high performance or multifunctional EMI application. The hierarchical structure is the best solution.

Hierarchical structure means a multi-level and organized structure. Many hierarchical structures are also factual, such as dendritic, branched and layered which usually forms low-density structure either by growth or self-assembly. For example, fuzzy fiber130, 131 (Fig. 11a, 11b, 11c) can be produced by growing carbon nanotube on glass fiber or carbon fiber surface and the substrate fiber can be bundled into larger filament.132 This 3 levels structure has been used for multifunctional applications.133

However, it’s not necessary to be fractal (Fig. 11d, 11e, 11f). A CNT /graphene structure was synthesized for electrochemical and capacitive energy storage application.134, 135 Mickelson136 and Guan137 packed C60 into BNNT/CNT and created one-dimensional crystal of C60 (Fig. 11f).138

Fig. 11 Hierarchy structures. (a) SEM image of cross-sectional view of aligned CNTs grown on a single carbon fiber; (b) SEM image of CNT grown on carbon fiber buddle (Adapted with permission from ref. 131 Copyright (2013) American Chemical Society); (c) Carbon nanotube fuzzy fiber developed at UDRI;130 (d) CNT grown on graphene; (e) BNNT grown on BN nanosheet;139 (f) C60 capsuled in CNT138 (Adapted with permission from Nature Springer).

Nowadays, commercial materials are designed on the molecular level. Besides the choice of elements, structural design affects products’ properties significantly. The primary way to control structure is the synthesis method. As shown in table 1, different synthesis methods are evaluated. As a result, CVD and template method are the best choices for designing a complex structure. For example, stealth vehicles are requiring broadband absorption or transparent material. One stealth material only provides narrow band absorption property. However, the compatibility between different materials becomes a problem when using different kinds of materials, such as carbon nanomaterial, metallic nanoparticle and ferrite. As a result, a good solution is to use coupled various carbon nanomaterials. For example, Fe/Co coated carbon fiber provides considerable electromagnetic absorption in the 1-10 GHz region.140 CNT nanocomposites have excellent electromagnetic shielding in UHF (ballistic missile early warning) and X (marine and airport) radar band.141 Thus, it’s is predictable that a combination of carbon fiber and CNT has a broader electromagnetic shielding range.142 On the other hand, multifunctional composite was developed for structural health monitoring applications by growing CNT on carbon fiber.130, 133 Of course, besides electromagnetic shielding applications, nanotube-based hierarchical structure can be used in many fields such as catalyst, scaffold, flexible electronics, super-capacitors, etc.

Table 1 Evaluation of different nanotube synthesis methods.

Synthesis methods

Uniformity

Designability (structural)

Reproducibility

Productivity

Price

Arc discharge

poor

poor

good

good

low

Laser ablation

poor

poor

good

good

 

Plasma torch

good

fair

good

good

low

CVD

good

good

good

good

fair

Electrochemical method

poor

poor

good

poor

high

Template method

excellent

excellent

good

poor

high

Hydrothermal method

poor

poor

fair

good

fair

Mechanical method

poor

poor

good

good

low

 

Although the cheapest way to combine different materials is mixing, however, grow them in one piece is the most efficient way. Once the materials are grown into one piece, electron, phonon, and load can be transferred in a more effective way. In summary, the hierarchical structure is an important and emerging approach in many fields. The common geometrical characteristics for nanotubes are there high surface area, high aspect ratio, and small diameter. When being designed into hierarchical structures, nanotubes’ advantages can be enhanced exponentially.

5. Summary

Material science plays a critical role in science/technology and the daily life, such as light emitting devices, smart windows, solar cells and so on.143-153 As a rising star in material science, nanomaterials in form of nanoparticle, 150,154 nanofiber/wire, 155-158 nanocomposite159, 160 have been widely used in many areas.161-166 Nanotubes are one of the most interesting nanomaterials due to their special tubular structure. Fabrication of CNT, BNNT like materials are becoming available in many laboratories. While the grown nanotubes have a high crystallinity, the etched nanotubes are more uniform. Additionally, new nanotubes such as stanene nanotube may come out with astonishing properties since two-dimensional stanene was already made. Despite of material aspects, the design of structure is equally important for the performance of nanomaterial. Hierarchical structures based on nanotubes can response in different levels or different energy regions. For example, the hierarchical carbon nanostructure might be the easiest way to achieve a super black body and wide range electromagnetic wave absorber. As a conclusion, coupling of two materials is not to simply synthesize/mix them together, but also to design a proper structure from the aspect of basic physics and chemistry. Such as designs of electronic structure, crystal plane orientation, nanotube aggregation in confined space, hierarchical structure and charge transfer mechanism. Definitely, the nanotubes are always excellent choices.

Acknowledgement

This work is funded in part by the U. S. Department of Education, Office of Postsecondary Education, Institutional Services (Title III, Part B, HBCU Program)

Conflict of interest

There are no conflicts to declare.

References

  1. S. Iiji`ma, Nature, 1991, 354, 56-58. CrossRef    View Record in Scopus
  2. Y. B. Yan, J. W. Miao, Z. H. Yang, F. X. Xiao, H. B. Yang, B. Liu and Y. H. Yang, Chem. Soc. Rev., 2015, 44, 3295-3346.CrossRef    View Record in Scopus

     3.  S. Wei, X. P. Fu, W. W. Wang, Z. Jin, Q. S. Song and C. J. Jia, J. Phys. Chem. C, 2018, 122, 4928-4936.CrossRef    View Record in Scopus

  1. J. T. Grant, C. A. Carrero, F. Goeltl, J. Venegas, P. Mueller, S. P. Burt, S. E. Specht, W. P. McDermott, A. Chieregato and I. Hermans, Science, 2016, 354, 1570-1573.CrossRef    View Record in Scopus

   5.  M. Aguilar-Romero, R. Camposeco, S. Castillo, J. Marin, V. Rodriguez-Gonzalez, L. A. Garcia-Serrano and I. Mejia-Centeno, Fuel, 2017, 198, 123-133.CrossRef    View Record in Scopus

  1. C. Liu, F. Li, L. P. Ma and H. M. Cheng, Adv. Mater., 2010, 22, E28-E62.CrossRef    View Record in Scopus

   7.  K. Mylvaganam and L. C. Zhang, Appl. Phys. Lett., 2006, 89, 123127.CrossRef    View Record in Scopus

  1. D. Deng, M. G. Kim, J. Y. Lee and J. Cho, Energ Environ. Sci., 2009, 2, 818-837.CrossRef    View Record in Scopus

   9.  K. Y. Xie, J. Li, Y. Q. Lai, W. Lu, Z. A. Zhang, Y. X. Liu, L. M. Zhou and H. T. Huang, Electrochem. Commun., 2011, 13, 657-660.CrossRef    View Record in Scopus

  1. L. M. Sun, X. H. Wang, Y. R. Wang and Q. Zhang, Carbon, 2017, 122, 462-474.CrossRef    View Record in Scopus
  2.  C. Liu, I. Sergeichev, I. Akhatov and K. Lafdi, Compos. Sci. Technol., 2018, 159, 111-118.CrossRef    View Record in Scopus
  3. C. Liu and K. Lafdi, CAMX 2018 – The Composites and Advanced Materials Expo, Dallas, TX, 2018, TP18-0586. View Record in Scopus

13.  H. C. Wu, X. L. Chang, L. Liu, F. Zhao and Y. L. Zhao, J. Mater. Chem., 2010, 20, 1036-1052.CrossRef    View Record in Scopus

  1. T. J. Whitney, T. Gibson, K. Lafdi and B. Welk, International Mechanical Engineering Congress and Exposition, 2012, 3, 929-932.CrossRef    View Record in Scopus

  15.  A. A. Shvedova, A. A. Kapralov, W. H. Feng, E. R. Kisin, A. R. Murray, R. R. Mercer, C. M. St Croix, M. A. Lang, S. C. Watkins, N. V. Konduru, B. L. Allen, J. Conroy, G. P. Kotchey, B. M. Mohamed, A. D. Meade, Y. Volkov, A. Star, B. Fadeel and V. E. Kagan, Plos One, 2012, 7, e30923.CrossRef    View Record in Scopus

  1. A. M. Wen, M. Infusino, A. De Luca, D. L. Kernan, A. E. Czapar, G. Strangi and N. F. Steinmetz, Bioconjugate Chem., 2015, 26, 51-62.CrossRef    View Record in Scopus

17.  Y. Yamamoto, T. Fukushima, Y. Suna, N. Ishii, A. Saeki, S. Seki, S. Tagawa, M. Taniguchi, T. Kawai and T. Aida, Science, 2006, 314, 1761-1764.CrossRef    View Record in Scopus

  1. Z. D. Han and A. Fina, Prog. Polym. Sci., 2011, 36, 914-944.CrossRef    View Record in Scopus
  2.  Y. X. Lin, Y. T. Jia, G. Alva and G. Y. Fang, Renew. Sust. Energ. Rev., 2018, 82, 2730-2742.CrossRef    View Record in Scopus
  3. Z. Han and A. Fina, Prog. Polym. Sci., 2011, 36, 914-944.CrossRef    View Record in Scopus
  4. M. Zheng, Topics Curr. Chem., 2017, 375, 13.CrossRef    View Record in Scopus
  5. H. W. Lee, Y. Yoon, S. Park, J. H. Oh, S. Hong, L. S. Liyanage, H. L. Wang, S. Morishita, N. Patil, Y. J. Park, J. J. Park, A. Spakowitz, G. Galli, F. Gygi, P. H. S. Wong, J. B. H. Tok, J. M. Kim and Z. A. Bao, Nat. Commun., 2011, 2, 541.CrossRef    View Record in Scopus
  6.  E. A. Laird, F. Kuemmeth, G. A. Steele, K. Grove-Rasmussen, J. Nygard, K. Flensberg and L. P. Kouwenhoven, Rev. Mod. Phys., 2015, 87, 703-764.CrossRef    View Record in Scopus
  7. T. W. Ebbesen, H. J. Lezec, H. Hiura, J. W. Bennett, H. F. Ghaemi and T. Thio, Nature, 1996, 382, 54-56.CrossRef    View Record in Scopus
  8. L. C. Qin, X. L. Zhao, K. Hirahara, Y. Miyamoto, Y. Ando and S. Iijima, Nature, 2000, 408, 50.CrossRef    View Record in Scopus
  9. C. Qin and L. M. Peng, Phys. Rev. B, 2002, 65, 155431.CrossRef    View Record in Scopus
  10. J. H. Warner, N. P. Young, A. I. Kirkland and G. A. D. Briggs, Nat . Mater., 2011, 10, 958-962.CrossRef    View Record in Scopus
  11. T. D. Yuzvinsky, W. Mickelson, S. Aloni, S. L. Konsek, A. M. Fennimore, G. E. Begtrup, A. Kis, B. C. Regan and A. Zettl, Appl. Phys. Lett., 2005, 87, 083103.CrossRef    View Record in Scopus
  12. C. Shen, A. H. Brozena and Y. H. Wang, Nanoscale, 2011, 3, 503-518.CrossRef    View Record in Scopus
  13. J. Xiao, M. Q. Long, X. M. Li, H. Xu, H. Huang and Y. L. Gao, Sci. Rep., 2014, 4, 4327.CrossRef    View Record in Scopus
  14. V. Sresht, A. A. H. Padua and D. Blankschtein, ACS Nano, 2015, 9, 8255-8268.CrossRef    View Record in Scopus
  15. J. Shi, K. Cai, L. N. Liu and Q. H. Qin, Sci. Rep., 2017, 7, 12951.CrossRef    View Record in Scopus
  16. W. Jiang, X. X. Li, A. B. Guo, H. Y. Guan, Z. Wang and K. Wang, J. Magn. Magn. Mater., 2014, 355, 309-318.CrossRef    View Record in Scopus
  17. J. L. C. Fajin, M. N. D. S. Cordeiro and J. R. B. Gomes, Phys. Chem. Chem. Phys., 2017, 19, 19188-19195.CrossRef    View Record in Scopus
  18. J. K. Chen, W. T. Chen, C. C. Cheng, C. C. Yu and J. P. Chu, Mater. Today, 2018, 21, 178-185.CrossRef    View Record in Scopus
  19. L. Guadagno, M. Raimondo, V. Vittoria, L. Vertuccio, K. Lafdi, B. De Vivo, P. Lamberti, G. Spinelli and V. Tucci, Nanotechnology, 2013, 24, 305704.CrossRef    View Record in Scopus
  20. A. C. Yilmaz, M. S. Ozen, E. Sancak, R. Erdem, O. Erdem and N. Soin, J. Compos. Mater., 2018, 52, 1423-1432.CrossRef    View Record in Scopus
  21. S. Hong and S. Myung, Nat. Nanotechnol., 2007, 2, 207-208.CrossRef    View Record in Scopus
  22. E. Pop, D. Mann, Q. Wang, K. E. Goodson and H. J. Dai, Nano Lett., 2006, 6, 96-100.CrossRef    View Record in Scopus
  23. R. Arenal, M. S. Wang, Z. Xu, A. Loiseau and D. Golberg, Nanotechnology, 2011, 22, 265704.CrossRef    View Record in Scopus
  24. A. Thess, R. Lee, P. Nikolaev, H. J. Dai, P. Petit, J. Robert, C. H. Xu, Y. H. Lee, S. G. Kim, A. G. Rinzler, D. T. Colbert, G. E. Scuseria, D. Tomanek, J. E. Fischer and R. E. Smalley, Science, 1996, 273, 483-487.CrossRef    View Record in Scopus
  25. P. Castrucci, M. Scarselli, M. De Crescenzi, M. Diociaiuti, P. S. Chaudhari, C. Balasubramanian, T. M. Bhave and S. V. Bhoraskar, Thin Solid Films, 2006, 508, 226-230.CrossRef    View Record in Scopus
  26. S. Yamada and H. Fujiki, Jpn. J. Appl. Phys. 2, 2006, 45, L837-L839.CrossRef    View Record in Scopus
  27. A. Fathalizadeh, T. Pham, W. Mickelson and A. Zettl, Nano Lett., 2014, 14, 4881-4886.CrossRef    View Record in Scopus
  28. K. S. Kim, C. T. Kingston, A. Hrdina, M. B. Jakubinek, J. W. Guan, M. Plunkett and B. Simard, ACS Nano, 2014, 8, 6211-6220.CrossRef    View Record in Scopus
  29. O. Smiljanic, B. L. Stansfield, J. P. Dodelet, A. Serventi and S. Desilets, Chem. Phys. Lett., 2002, 356, 189-193.CrossRef    View Record in Scopus
  30. K. S. Kim, G. Cota-Sanchez, C. T. Kingston, M. Imris, B. Simard and G. Soucy, J. Phys. D Appl. Phys., 2007, 40, 2375-2387.CrossRef    View Record in Scopus
  31. M. Hikita, R. L. Bradford and K. Lafdi, Crystals, 2014, 4, 466-489.CrossRef    View Record in Scopus
  32. A. N. Obraztsov, Nat. Nanotechnol., 2009, 4, 212-213.CrossRef    View Record in Scopus
  33. J. E. Butler and A. V. Sumant, Chem. Vapor Depos., 2008, 14, 145-160.CrossRef    View Record in Scopus
  34. K. E. Kim, K. J. Kim, W. S. Jung, S. Y. Bae, J. Park, J. Choi and J. Choo, Chem. Phys. Lett., 2005, 401, 459-464.CrossRef    View Record in Scopus
  35. K. Kuwana and K. Saito, P. Combust. Inst., 2007, 31, 1857-1864.CrossRef    View Record in Scopus
  36. K. Kuwana and K. Saito, Carbon, 2005, 43, 2088-2095.CrossRef    View Record in Scopus
  37. K. Hata, D. N. Futaba, K. Mizuno, T. Namai, M. Yumura and S. Iijima, Science, 2004, 306, 1362-1364.CrossRef    View Record in Scopus
  38. D. N. Futaba, K. Hata, T. Yamada, K. Mizuno, M. Yumura and S. Iijima, Phys. Rev. Lett., 2005, 95, 056104.CrossRef    View Record in Scopus
  39. R. F. Zhang, Y. Y. Zhang, Q. Zhang, H. H. Xie, W. Z. Qian and F. Wei, ACS Nano, 2013, 7, 6156-6161.CrossRef    View Record in Scopus
  40. C. Schunemann, F. Schaffel, A. Bachmatiuk, U. Queitsch, M. Sparing, B. Rellinghaus, K. Lafdi, L. Schultz, B. Buchner and M. H. Rummeli, ACS Nano, 2011, 5, 8928-8934.CrossRef    View Record in Scopus
  41. A. M. Cassell, J. A. Raymakers, J. Kong and H. J. Dai, J. Phys. Chem. B, 1999, 103, 6484-6492.CrossRef    View Record in Scopus
  42. M. Su, B. Zheng and J. Liu, Chem. Phys. Lett., 2000, 322, 321-326.CrossRef    View Record in Scopus
  43. B. L. Liu, W. C. Ren, C. Liu, C. H. Sun, L. B. Gao, S. S. Li, C. B. Jiang and H. M. Cheng, ACS  Nano, 2009, 3, 3421-3430.CrossRef    View Record in Scopus
  44. B. L. Liu, W. C. Ren, L. B. Gao, S. S. Li, S. F. Pei, C. Liu, C. B. Jiang and H. M. Cheng, J. Am. Chem. Soc., 2009, 131, 2082-2083.CrossRef    View Record in Scopus
  45. D. Takagi, Y. Kobayashi and Y. Hommam, J. Am. Chem. Soc., 2009, 131, 6922-6923.CrossRef    View Record in Scopus
  46. D. Sarangi, C. Godon, A. Granier, A. Goullet, G. Turban and O. Chauvet, Chem. Phys. Lett., 2004, 397, 516-519.CrossRef    View Record in Scopus
  47. M. H. Rummeli, E. Borowiak-Palen, T. Gemming, T. Pichler, M. Knupfer, M. Kalbac, L. Dunsch, O. Jost, S. R. P. Silva, W. Pompe and B. Buchner, Nano Lett., 2005, 5, 1209-1215.CrossRef    View Record in Scopus
  48. S. Han, X. L. Liu and C. W. Zhou, J. Am. Chem. Soc., 2005, 127, 5294-5295.CrossRef    View Record in Scopus
  49. M. H. Rummeli, F. Schaffel, C. Kramberger, T. Gemming, A. Bachmatiuk, R. J. Kalenczuk, B. Rellinghaus, B. Buechner and T. Pichler, J. Am. Chem. Soc., 2007, 129, 15772-15773.CrossRef    View Record in Scopus
  50. L. Szymanski, Z. Kolacinski, S. Wiak, G. Raniszewski and L. Pietrzak, Nanomaterials, 2017, 7, 45.CrossRef    View Record in Scopus
  51. C. C. Yap, C. Brun, D. L. Tan, H. Li, E. H. T. Teo, D. Baillargeat and B. K. Tay, Nanoscale Res. Lett., 2012, 7, 1-18.CrossRef    View Record in Scopus
  52. M. Kumar and Y. Ando, J. Nanosci. Nanotechno., 2010, 10, 3739-3758.CrossRef    View Record in Scopus
  53. M. Kumar, X. L. Zhao, Y. Ando, S. Iijima, M. Sharon and K. Hirahara, Mol. Cryst. Liq. Cryst., 2002, 387, 341-345.CrossRef    View Record in Scopus
  54. P. Nikolaev, M. J. Bronikowski, R. K. Bradley, F. Rohmund, D. T. Colbert, K. A. Smith and R. E. Smalley, Chem. Phys. Lett., 1999, 313, 91-97.CrossRef    View Record in Scopus
  55. M. J. Bronikowski, P. A. Willis, D. T. Colbert, K. A. Smith and R. E. Smalley, J. Vac. Sci. Technol. A, 2001, 19, 1800-1805.CrossRef    View Record in Scopus
  56. H. J. Jeong, S. Y. Jeong, Y. M. Shin, J. H. Han, S. C. Lim, S. J. Eum, C. W. Yang, N. G. Kim, C. Y. Park and Y. H. Lee, Chem. Phys. Lett., 2002, 361, 189-195.CrossRef    View Record in Scopus
  57. C. Y. Su, W. Y. Chu, Z. Y. Juang, K. F. Chen, B. M. Cheng, F. R. Chen, K. C. Leou and C. H. Tsai, J. Phys. Chem. C, 2009, 113, 14732-14738.CrossRef    View Record in Scopus
  58. I. Gerber, M. Oubenali, R. Bacsa, J. Durand, A. Goncalves, M. F. R. Pereira, F. Jolibois, L. Perrin, R. Poteau and P. Serp, Chem-Eur J., 2011, 17, 11467-11477.CrossRef    View Record in Scopus
  59. A. R. Kamali and D. J. Fray, Carbon, 2014, 77, 835-845.CrossRef    View Record in Scopus
  60. A. R. Kamali, J. Feighan and D. J. Fray, Faraday Discuss, 2016, 190, 451-470.CrossRef    View Record in Scopus
  61. E. Song, R. Geng, Z. Zhu, L. Xie, W. Lu, C. Li and Y. Yao, Ceramics Internat., 2018, 44, 22794-22799.CrossRef    View Record in Scopus
  62. D. P. Yu, X. S. Sun, C. S. Lee, I. Bello, S. T. Lee, H. D. Gu, K. M. Leung, G. W. Zhou, Z. F. Dong and Z. Zhang, Appl. Phys. Lett., 1998, 72, 1966-1968.CrossRef    View Record in Scopus
  63. C. H. Lee, S. Bhandari, B. Tiwari, N. Yapici, D. Y. Zhang and Y. K. Yap, Molecules, 2016, 21, 922.CrossRef    View Record in Scopus
  64. A. Rubio, J. L. Corkill and M. L. Cohen, Phys. Rev. B, 1994, 49, 5081-5084.CrossRef    View Record in Scopus
  65. M. W. Smith, K. C. Jordan, C. Park, J. W. Kim, P. T. Lillehei, R. Crooks and J. S. Harrison, Nanotechnology, 2009, 20, 505604.CrossRef    View Record in Scopus
  66. O. R. Lourie, C. R. Jones, B. M. Bartlett, P. C. Gibbons, R. S. Ruoff and W. E. Buhro, Chem. Mater., 2000, 12, 1808-1810.CrossRef    View Record in Scopus
  67. C. Tang, Y. Bando, T. Sato and K. Kurashima, Chem. Commun., 2002, 12, 1290-1291.CrossRef    View Record in Scopus
  68. Y. Huang, J. Lin, C. C. Tang, Y. Bando, C. Y. Zhi, T. Y. Zhai, B. Dierre, T. Sekiguchi and D. Golberg, Nanotechnology, 2011, 22, 145602.CrossRef    View Record in Scopus
  69. L. Li, X. W. Liu, L. H. Li and Y. Chen, Microelectron Eng., 2013, 110, 256-259.CrossRef    View Record in Scopus
  70. P. Ahmad, M. U. Khandaker, Z. R. Khan and Y. M. Amin, RSC. Adv., 2015, 5, 35116-35137.CrossRef    View Record in Scopus
  71. Y. Chen, L. T. Chadderton, J. F. Gerald and J. S. Williams, Appl. Phys. Lett., 1999, 74, 2960-2962.CrossRef    View Record in Scopus
  72. X. D. Li, G. W. Meng, Q. L. Xu, M. G. Kong, X. G. Zhu, Z. Q. Chu and A. P. Li, Nano Lett., 2011, 11, 1704-1709.CrossRef    View Record in Scopus
  73.  H. Wu, G. Chan, J. W. Choi, I. Ryu, Y. Yao, M. T. McDowell, S. W. Lee, A. Jackson, Y. Yang, L. B. Hu and Y. Cui, Nat. Nanotechnol., 2012, 7, 310-315.CrossRef    View Record in Scopus
  74. C. Z. Wang, X. N. Fu, Y. Y. Guo, Z. X. Guo, C. X. Xia and Y. Jia, Nanotechnology, 2017, 28, 115202.CrossRef    View Record in Scopus
  75. W. K. Hsu, J. P. Hare, M. Terrones, H. W. Kroto, D. R. M. Walton and P. J. F. Harris, Nature, 1995, 377, 687.CrossRef    View Record in Scopus
  76. A. T. Dimitrov, G. Z. Chen, I. A. Kinloch and D. J. Fray, Electrochim Acta, 2002, 48, 91-102.CrossRef    View Record in Scopus
  77. A. R. Kamali and D. Fray, J. Mater. Sci., 2016, 51, 569-576.CrossRef    View Record in Scopus
  78. C. Liu and K. Lafdi, J. Appl. Polym. Sci., 2017, 134, 45388.CrossRef    View Record in Scopus
  79. Y. Gogotsi, T. Kraft, K. G. Nickel and M. E. Zvanut, Diam. Relat. Mater., 1998, 7, 1459-1465.CrossRef    View Record in Scopus
  80. Y. Gogotsi, J. A. Libera and M. Yoshimura, J. Mater. Res., 2000, 15, 2591-2594.CrossRef    View Record in Scopus
  81. C. Velasco-Santos, A. L. Martinez-Hernandez, A. Consultchi, R. Rodriguez and V. M. Castano, Chem. Phys. Lett., 2003, 373, 272-276.CrossRef    View Record in Scopus
  82. Y. Chen, J. D. Fitz Gerald, J. S. Williams and S. Bulcock, Chem. Phys. Lett., 1999, 299, 260-264.CrossRef    View Record in Scopus
  83.  J. Yu, B. C. P. Li, J. Zou and Y. Chen, J. Mater. Sci., 2007, 42, 4025-4030.CrossRef    View Record in Scopus
  84.  G. X. Zhu, S. M. Dong, J. B. Hu, Y. M. Kan, P. He, L. Gao, X. Y. Zhang and H. J. Zhou, RSC Adv., 2016, 6, 14112-14119.CrossRef    View Record in Scopus
  85.  Y. Chen, M. J. Conway and J. D. Fitz Gerald, Appl. Phys. A-Mater., 2003, 76, 633-636.CrossRef    View Record in Scopus
  86.  Santra, H. Y. Ko, Y. W. Yeh, F. Martelli, I. Kaganovich, Y. Raitses and R. Car, Nanoscale, 2018, 10, 22223-22230.CrossRef    View Record in Scopus
  87.  K. Kan, T. L. Xia, L. Li, H. M. Bi, H. F. Fu and K. Y. Shi, Nanotechnology, 2009, 20, 185502.CrossRef    View Record in Scopus
  88. Y. L. Cheng, B. B. Xia, C. Q. Fang and L. Yang, J. Mater. Sci. Technol., 2017, 33, 1187-1194.CrossRef    View Record in Scopus
  89. K. F. Fu, W. J. Huang, Y. Lin, L. A. Riddle, D. L. Carroll and Y. P. Sun, Nano Lett., 2001, 1, 439-441.CrossRef    View Record in Scopus
  90. Y. P. Sun, W. J. Huang, Y. Lin, K. F. Fu, A. Kitaygorodskiy, L. A. Riddle, Y. J. Yu and D. L. Carroll, Chem. Mater., 2001, 13, 2864-2869.CrossRef    View Record in Scopus
  91. Y. D. Yang, L. T. Qu, L. M. Dai, T. S. Kang and M. Durstock, Adv. Mater., 2007, 19, 1239-1243.CrossRef    View Record in Scopus
  92. J. K. Lim, W. S. Yun, M. H. Yoon, S. K. Lee, C. H. Kim, K. Kim and S. K. Kim, Synthetic Met., 2003, 139, 521-527.CrossRef    View Record in Scopus
  93. N. O. V. Plank, R. Cheung and R. J. Andrews, Appl. Phys. Lett., 2004, 85, 3229-3231.CrossRef    View Record in Scopus
  94. D. Janas, S. Boncel and K. K. K. Koziol, Carbon, 2014, 73, 259-266.CrossRef    View Record in Scopus
  95. Z. S. Qian, J. J. Ma, J. Zhou, P. Lin, C. C. Chen, J. R. Chen and H. Feng, J. Mater. Chem., 2012, 22, 22113-22119.CrossRef    View Record in Scopus
  96. V. Datsyuk, M. Kalyva, K. Papagelis, J. Parthenios, D. Tasis, A. Siokou, I. Kallitsis and C. Galiotis, Carbon, 2008, 46, 833-840.CrossRef    View Record in Scopus
  97. Y. P. Sun, K. F. Fu, Y. Lin and W. J. Huang, Accounts Chem. Res., 2002, 35, 1096-1104.CrossRef    View Record in Scopus
  98. Y. Kanai, V. R. Khalap, P. G. Collins and J. C. Grossman, Phys. Rev. Lett., 2010, 104, 066401.CrossRef    View Record in Scopus
  99. K. M. Lee, L. C. Li and L. M. Dai, J. Am. Chem. Soc., 2005, 127, 4122-4123.CrossRef    View Record in Scopus
  100. L. T. Qu and L. M. Dai, Chem. Commun., 2007, 37, 3859-3861.CrossRef    View Record in Scopus
  101. L. T. Qu, L. M. Dai and E. Osawa, J. Am. Chem. Soc., 2006, 128, 5523-5532.CrossRef    View Record in Scopus
  102. M. H. Miao, S. C. Hawkins, J. Y. Cai, T. R. Gengenbach, R. Knott and C. P. Huynh, Carbon, 2011, 49, 4940-4947.CrossRef    View Record in Scopus
  103. J. X. Guo, Y. G. Li, S. W. Wu and W. X. Li, Nanotechnology, 2005, 16, 2385-2388.CrossRef    View Record in Scopus
  104. M. C. Evora, D. Klosterman, K. Lafdi, L. Li and J. L. Abot, Carbon, 2010, 48, 2037-2046.CrossRef    View Record in Scopus
  105. N. Li, Y. Huang, F. Du, X. B. He, X. Lin, H. J. Gao, Y. F. Ma, F. F. Li, Y. S. Chen and P. C. Eklund, Nano Lett., 2006, 6, 1141-1145.CrossRef    View Record in Scopus
  106. C. Y. Zhi, Y. Bando, C. C. Tang, S. Honda, K. Sato, H. Kuwahara and D. Golberg, Angew. Chem. Int. Edit., 2005, 44, 7932-7935.CrossRef    View Record in Scopus
  107. C. Y. Zhi, Y. Bando, C. C. Tang, H. Kuwahara and D. Golberg, J. Phys. Chem. C, 2007, 111, 1230-1233.CrossRef    View Record in Scopus
  108. C. Y. Zhi, Y. Bando, W. L. Wang, C. C. Tang, H. Kuwahara and D. Golberg, J. Phys. Chem. C, 2007, 111, 18545-18549.CrossRef    View Record in Scopus
  109. T. Ikuno, T. Sainsbury, D. Okawa, J. M. J. Frehet and A. Zettl, Solid State Commun., 2007, 142, 643-646.CrossRef    View Record in Scopus
  110. T. Sainsbury, T. Ikuno, D. Okawa, D. Pacile, J. M. J. Frechet and A. Zettl, J. Phys. Chem. C, 2007, 111, 12992-12999.CrossRef    View Record in Scopus
  111. C. Y. Zhi, Y. Bando, C. C. Tang and D. Golberg, Phys. Rev. B, 2006, 74, 153413.CrossRef    View Record in Scopus
  112. C. Y. Zhi, J. D. Guo, X. D. Bai and E. G. Wang, J. Appl. Phys., 2002, 91, 5325-5333.CrossRef    View Record in Scopus
  113. M. Bouchard, K. Lafdi, N. Schehl, J. Sebastian and Y. Yoon, Ed. U. S. A. Force, Defense Technical Information Center, Wright-Patterson Air Force Base, 2010, FRL-RX-WP-TR-2011-4122.
  114. S. A. Steiner, R. Li and B. L. Wardle, ACS Appl. Mater. Inter., 2013, 5, 4892-4903.CrossRef    View Record in Scopus
  115. Q. H. Zhang, J. W. Liu, R. Sager, L. M. Dai and J. Baur, Compos. Sci. Technol., 2009, 69, 594-601.CrossRef    View Record in Scopus
  116. M. Boehle, P. Pianca, K. Lafdi and F. Chinesta, Adv. Aircr. Spacecr. Sci., 2015, 2, 263-273.CrossRef    View Record in Scopus
  117. L. C. Li and K. Lafdi, Sensor Actuat B-Chem., 2008, 132, 202-208.CrossRef    View Record in Scopus
  118. D. S. Yu, K. Goh, H. Wang, L. Wei, W. C. Jiang, Q. Zhang, L. M. Dai and Y. Chen, Nat. Nanotechnol., 2014, 9, 555-562.CrossRef    View Record in Scopus
  119. W. Mickelson, S. Aloni, W. Q. Han, J. Cumings and A. Zettl, Science, 2003, 300, 467-469.CrossRef    View Record in Scopus
  120. L. H. Guan, K. Suenaga, Z. J. Shi, Z. N. Gu and S. Iijima, Phys. Rev. Lett., 2005, 94, 045502.CrossRef    View Record in Scopus
  121. B. W. Smith, M. Monthioux and D. E. Luzzi, Nature, 1998, 396, 323-324.CrossRef    View Record in Scopus
  122. Y. X. Song, B. Li, S. W. Yang, G. Q. Ding, C. R. Zhang and X. M. Xie, Sci. Rep., 2015, 5, 10337.CrossRef    View Record in Scopus
  123. L. Wang, F. He and Y. Z. Wan, J. Alloy Compd., 2011, 509, 4726-4730.CrossRef    View Record in Scopus
  124. A. Kolanowska, D. Janas, A. P. Herman, R. G. Jedrysiak, T. Gizewski and S. Boncel, Carbon, 2018, 126, 31-52.CrossRef    View Record in Scopus
  125. M. G. Jang, S. C. Ryu, K. J. Juhn, S. K. Kim and W. N. Kim, J. Appl. Polym. Sci., 2019, 136, 47302.CrossRef    View Record in Scopus
  126. X. Tu, X. Fu and Q. Jiang , Displays, 2010, 31, 150-154.CrossRef    View Record in Scopus
  127. Y. F. Gong, X. K. Fu, S. P. Zhang and Q. Jiang , Chin. J. Chem., 2007, 25, 1743-1747.CrossRef    View Record in Scopus
  128. Q. Jiang, M. Chen, J. Li, Y. Xin, X. Shan, B. Pan, C. Wang, S. Lin, T. Siegrist, Q. Xiao and Z. Yu, ACS Nano, 2017, 11, 1073-1079.CrossRef    View Record in Scopus
  129. Q. Jiang, X. Zeng, N. Wang, Z. L. Xiao, Z. Guo and J. Lu, ACS Energy Lett., 2018, 3, 264-269.CrossRef    View Record in Scopus
  130. Q. Jiang, L. Wang, C. Yan, C. Liu and Z. Guo, Eng. Sci., 2018, 1, 64-68.
  131. Q. Jiang and T. Xu, Comments Inorg. Chem., 2016, 36, 200-214.CrossRef    View Record in Scopus
  132. J. Zhao, L. Wu, C. Zhang, B. Zeng, Y. Lv, Z. Li, Q. Jiang and Z. Guo, J. Mater. Chem. C, 2017, 5, 3903-3907.CrossRef    View Record in Scopus
  133. Q. Jiang, Y. Yeh, N. Lu, H. Kuo, M. Lesslie and Tao Xu, J. Renew. Sustain. Ener., 2016, 8, 013701.CrossRef    View Record in Scopus
  134. Y. Wang，J. Li，J. Li，C. Duan，H. Zhang，H. Jian，L.He，G. Tao，C. Yan and T. Jiu, Solar Energy, 2018, 160, 353-359.CrossRef    View Record in Scopus
  135. Y. Wang，C. Duan，J. Li，W. Han，M. Zhao，L. Yao，Y. Wang，C. Yan and T. Jiu, ACS Appl. Mater. Inter., 2018, 10, 20128-20135.CrossRef    View Record in Scopus
  136. Q. Du，Y. Zhou，X. Pan，J. Zhang，Q. Zhuo，S. Chen，G. Chen，T. Liu，F. Xu and C. Yan, RSC Advances, 2016, 6, 54589-54596.CrossRef    View Record in Scopus
  137. Q. Jiang, F. Liu, T. Li and T. Xu, J. Mater. Chem. C, 2014, 2, 618-621.CrossRef    View Record in Scopus
  138. E. Ghafari, X. Jiang and N. Lu, Adv. Compos. Hybr. Mater., 2018, 1, 332-340.CrossRef   
  139. Y. Ma, M. Ma, X. Yin, Q., N. Lu, Yi., Y. Lu, E. Wujcik, X. Mai, C. Wang and Z. Guo, Polymer, 2018, 156, 128-135.CrossRef    View Record in Scopus
  140. E. Ghafari and N. Lu, Compos. B Eng., 2019, 160, 1-9. CrossRef    View Record in Scopus
  141. Q. Jiang, X. Sheng, Y. Li, X. Feng and T. Xu, Chem. Commun., 2014, 50, 14720-14723.CrossRef    View Record in Scopus
  142. E. Wujcik, L. Lyu, J. Liu, H. Liu, C. Liu, Y. Lu, K. Sun, R. Fan, N. Wang, N. Lu and Z. Guo, Eng. Sci., 2018, 2, 26–42.
  143. M. Idrees, S. Batool, J. Kong, Q. Zhuang, H. Liu, Q. Shao, N. Lu, Y. Feng, E. Wujcik, Q. Gao, T. Ding, R. Wei and Z. Guo, Electrochim. Acta, 2019, 296, 925-937.CrossRef    View Record in Scopus
  144. Y. Guo, T. Liu, N. Wang, Q. Luo, H. Lin, J. Li, Q. Jiang, L. Wu and Z. Guo, Nano Energy, 2017, 38,193-200.CrossRef    View Record in Scopus
  145. F. Q. Liu, G. H. Li, S. W. Luo, W. Li, Z. G. Huang, W. Li, F. Su, C. Q. Li, Z. B. Ding and Q. Jiang, ACS Appl. Mater. Interfaces, 2019, 11, 691-698.CrossRef    View Record in Scopus
  146. J. Zhao, L. Wu, C. Zhang, T. Li, Q. Jiang, F. Wang, P. Zhao, J. Ryu and Z. Guo, Mater. Res. Bull., 2018, 103, 19-24.CrossRef    View Record in Scopus
  147. Q. Jiang, X. Zeng, L. Ge, X. Luo and L. He, Multifunctional Nanocomposites for Energy and Environmental, 2018, John Wiley Publisher.
  148. T. Tong, D. Fu, A. X. Levander, W. J. Schaff, B. N. Pantha, N. Lu, B. Liu, I. Ferguson, R. Zhang, J. Y. Lin, H. X. Jiang, J. Wu and D. G. Cahill, Appl. Phys. Lett., 2013, 102, 121906CrossRef    View Record in Scopus
  149. Q. Hao, D. Xu, N. Lu and H. Zhao, Phys. Rev. B, 2016, 93, 205206. CrossRef    View Record in Scopus

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