Carbon 101 (2016) 458e464
Contents lists available at ScienceDirect
Carbon
journal homepage: www.elsevier.com/locate/carbon
Group 16 elements control the synthesis of continuous fibers of
carbon nanotubes
Mas a, Bele
n Alema
n a, Ignacio Dopico a, Ignacio Martin-Bragado a,
Bartolome
rez b, Juan J. Vilatela a, *
Teresa Naranjo b, Emilio M. Pe
a
b
IMDEA Materials Institute, Eric Kandel 2, 28906 - Getafe, Madrid, Spain
IMDEA Nanoscience, Faraday 9, Ciudad Universitaria de Cantoblanco, 28049 - Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 December 2015
Received in revised form
26 January 2016
Accepted 1 February 2016
Available online 10 February 2016
We present the use of Selenium (Se) and Tellurium (Te) as promoters in the growth of carbon nanotubes
(CNTs) by chemical vapor deposition (CVD) and direct spinning from the gas phase into a continuous
macroscopic fiber. At low Se concentrations (0.0018 at.%) the tubes are of single-walled type and predominantly armchair chiral angle. Increasing Se content produces an increase in CNT diameter and their
self-collapse or even self-folding. The stability of these morphologies is compared by molecular dynamics
simulations. These results add Se and Te to the list of promoters currently used for CNT growth (Sulfur
(S), Oxygen (O)). Even at very small concentrations, these elements dominate the catalyst surface, where
they contribute to the lowering of the surface tension of molten Iron (Fe), the catalytic decomposition of
the Carbon (C) source and reconstruction of graphitic layers. Preliminary fiber specific strength is up to
0.9 GPa SG1 and toughness of ~80 J g1, resulting in a ballistic protection figure of merit of 760 m s1.
© 2016 Elsevier Ltd. All rights reserved.
1. Introduction
Decades of research on nanomaterials have shown that the
efficient exploitation of their properties relies, first of all, on the
reproducible synthesis of uniform materials, and for many applications, in their organization in a format that enables further assembly as macroscopic structures. In the case of CNTs, their
assembly as macroscopic fibers with preferential orientation parallel to the fiber axis has led to a new generation of highperformance materials with proven performance in structural
composites [1,2], sensors [3] and energy management applications
[4], among others [5,6]. They are currently produced on a kilometer/day scale in the laboratory [7] and much larger quantities in
industrial settings [8].
Methods for spinning fibers of CNTs include wet-spinning from
lyotropic liquid crystalline solutions [9] or polymer dispersions
[10], drawing from an array of vertically aligned CNTs on a substrate
(forest spinning) [11], or spinning directly from the gas phase
during CNT growth by CVD [12]. For both dry-spinning process,
breakthroughs in CVD synthesis were the turning point that
* Corresponding author.
E-mail address: [email protected] (J.J. Vilatela).
http://dx.doi.org/10.1016/j.carbon.2016.02.005
0008-6223/© 2016 Elsevier Ltd. All rights reserved.
enabled continuous spinning of CNTs as macroscopic fibers. For
forest spinning, this consisted in the growth of arrays of denselypacked long CNTs [13]. In some cases, the CVD reaction is assisted
by the presence of small amounts of O [14], which is known to
produce large enhancements in catalyst activity and CNT growth
rate, hence termed supergrowth [15]. In the direct spinning process, the addition of small amounts of S also produced large increases in CNT growth rate and length, which enabled the
association of the in-forming CNTs as an aerogel in the gas phase
and subsequent extraction as a continuous fiber [12]. S was known
to enhance the growth of vapor grown carbon fibers (VGCF), but its
key role in CNT fiber (CNTf) spinning was a priori unexpected.
Although historically the optimization of the CVD reaction in the
direct spinning process would seem to have been largely guided by
the resulting bulk tensile properties of the fiber [16], the role of S as
a promoter in the reaction is now reasonably well understood
[17,18]. S is known to remain at the surface of the catalyst in a liquid
layer that limits solubility of C and restricts it to the surface during
the CVD reaction. It stabilizes the edge of the nascent CNT, but extrudes the graphitic layer due to its high interfacial energy with the
FeeSeC liquid alloy [19]. This role as a promoter is consistent with
metallurgy literature on the growth of fibrillar graphite in cast irons
and with literature on hydrocarbon catalysis on transition metals in
the presence of S [20].
B. Mas et al. / Carbon 101 (2016) 458e464
To put these ideas to test, we tried to spin continuous fibers of
CNTs using Se and Te as promoters, which are in many ways
equivalent to S. In this article we demonstrate that it is not only
possible to produce such fibers, but also to control the number of
layers of the CNTs and preserve the predominantly armchair chiral
angle of single-walled NTs (SWNTs). Because the resulting CNTs
have a larger diameter per number of layers, they lead to fibers with
an interesting combination of high toughness and specific strength,
with potential in high velocity impact shielding, for example.
2. Experimental
CNT fibers were synthesized by the direct spinning of CNTs from
the gas phase during growth by floating catalyst CVD [12], using
butanol as C source, ferrocene as Iron catalyst and selenophene as a
Se catalyst promoter. Butanol was chosen over other possible carbon sources on the basis of a more uniform precursor injection into
the reactor. The reaction was carried out in Hydrogen atmosphere
at 1250 C, using a precursor feed rate of 3 ml h1 and winding rate
of 10 m min1.
Tellurophene was synthesized following the method described
by Sweat and Stephens [21] and showed satisfactory spectroscopic
data.
In this work we follow recommendations by the International
Union of Pure and Applied Chemistry (IUPAC) concerning group
numbering and thus refer to O, S, Se and Te as members of Group
16.
Electron microscopy was carried out with an FIB-FEGSEM Helios
NanoLab 600i (FEI) at 5 kV, a JEOL JEM 3000F TEM at 300 kV and
Tecnai F30 (FEI company) at 300 kV, all equipped with EDS detectors. Catalyst structure was determined from the Fast-FourierTransform of lattice-resolved micrographs.
XPS data were collected in a SPECS GmbH electron spectroscopy
system provided with a PHOIBOS 150 9MCD analyzer. The deconvolution shown is fitted by Gaussian/Lorentzian peak shapes
and Shirley background profile subtraction.
The mechanical tests and the linear density measurements were
performed using a Textechno Favimatþ with a 2 N as maximum
load. The gauge length and the strain speed were 20 mm and
3% min1, respectively.
Raman spectra were acquired with two different spectrometers:
a Renishaw PLC and a Jasco NRS-5100. All the spectra were taken in
the ranges 1203000 cm1, using a 100 objective lens and the
exposition time was 10 s. With the Renishaw spectrometer a
532 nm laser line (2.33 eV) was used as excitation source, taking
three accumulations at 5% of the total power laser (~1.68 mW) was
used (1% for the case with lower Se). A Jasco spectrometer was used
to acquire the spectra with a 785 nm laser (1.57 eV), with a fixed
power of 5.5 mW and a single accumulation. In order to maximize
the Raman signal, the polarization of the excitation signal was kept
parallel to the CNTf axis.
MD simulations were performed with the Large-scale Atomic/
Molecular Massively Parallel Simulator (LAMMPS) [22]. The potential chosen to reproduce the mechanical stability of CNTs was
the Adaptative Intermolecular Reactive Empirical Bond Order
(AIREBO) [23] potential, that has been proven to successfully account for the mechanical behavior of CNTs [24]. The modified
Lennard-Jones contribution to the AIREBO potential was set with a
cut-off distance of 1.02 nm, since its contribution at larger distances
is considered negligible. A recent study proposes that the AIREBO
potential may lack a comprehensive description of the Van der
Waals (vdW) interactions between graphene layers of the collapsed
SWNT, and might also not consider the thermal fluctuations during
this interaction [25]. The suggested solution is to correct the AIREBO potential by slightly decreasing the vdW interaction by 13%
459
from the original one. The corrected values give a threshold
diameter for the armchair SWNTs, D1, consistent with experimental
observations. Then, the correction was applied to both, the
collapsed and the self-folded configuration to obtain the D1, D2
thresholds at standard room temperature conditions (300 K).
The simulations were made in a canonical NVT ensemble ~0 K
and up to 400 ps, after a prior relaxation to minimize the SWNTs
configurations. A set of 30 inputs was prepared in the range between (10,10) and (100,100) armchair configurations, using the
(m,n) notation, with radius varying between 1.36 nm and 13.56 nm
respectively, in three different states: (i) round, (ii) collapsed and
(iii) self-folded. Collapsed and self-folded inputs were prepared
applying forces to the round CNT until the desired configuration
was reached. Periodic boundary conditions were established for the
z axis. The height of the tubes was set to be 10 unit cells, avoiding
finite size effects.
3. Results and discussion
3.1. Synthesis with Se promoter
Continuous spinning of macroscopic fibers of CNTs was achieved
by replacing S with Se as promoter in the CVD reaction without
variation of reactor temperature, Hydrogen carrier gas flow or the
rate of precursor injection. The range of Se concentration in the
reactants was 0.0820.0018 at.%, depending on the type of CNTs
that were targeted, added in the form of selenophene. For comparison, fibers grown using S require a similar promoter concentration of 0.0890.011 at.%. Under these growth conditions the
spinning process was very stable, enabling continuous spinning of
fibers for hours (see video in SOM). Fig. 1a shows an A4 sheet of
material collected over 15 min and Fig. 1b an electron micrograph
of an individual CNTf filament produced at 15 m min1, or a draw
ratio of around 4. The constituent CNTs are highly graphitized and
because of their large diameter and low number of layers, they tend
to autocollapse into ribbons at atmospheric pressure [26,24]. Fig. 1c
shows a high resolution TEM (HRTEM) of a collapsed double-walled
nanotube (DWNT), with equivalent diameter of 8.75 nm. The Moire
interference pattern arises from the superposition of flat graphitic
layers.
Supplementary video related to this article can be found at
http://dx.doi.org/10.1016/j.carbon.2016.02.005.
Before discussing in more detail the synthesis and structure of
these fibers, we note that several precautions were taken to ensure
that the reactor and injection system were free of S, and that indeed
the resulting fiber was grown using only Se as promoter. The need
for these experiments follows observations by Gspann et al. suggesting that similar CVD systems can retain S up to 20 min after
stopping its injection into the reactor [18]. To ensure a S-free system we carried out control experiments using a brand new reactor
tube and flushing the entire injection system with alcohol for
30 min before CVD (SOM). Our results also confirm in passing that
spinning of fibers without promoter (either Se or S) is not yet
possible.
3.2. CNT and catalyst characterization
Post-synthesis characterization of the fiber material shows the
presence of Se as part of the catalyst, associated with Fe. Fig. 2a
presents X-ray photoelectron spectroscopy (XPS) emission data in
the 4861 eV binding energy region, showing emission from Iron
3p (Fe3p) and Se 3d (Se3d). The deconvoluted signals from Fe and
Se at 53.2 eV and 55.4 eV, respectively, agree with literature values
[27]. These observations are confirmed by energy dispersive X-ray
spectroscopy (EDX). Measurements in scanning transmission
460
B. Mas et al. / Carbon 101 (2016) 458e464
Fig. 1. Image sequence of CNT fibers from macro- to nano-scale. a) Photograph of a
CNT fiber array produced for 15 min at 10 m min1. b) SEM image of an individual
filament of CNT fibers. c) TEM image of a collapsed DWNT with diameter around
8.75 nm. (A colour version of this figure can be viewed online.)
electron microscopy mode (STEM) shown in Fig. 2b, locate Se in the
vicinity of the catalyst particle. Inspection of the catalyst particle by
HRTEM shows mainly a structure consistent with FCC Fe, as the
example in Fig. 2c shows. Such catalyst structure is also present in
CNT fibers produced using S promoter [7].
In a previous study [19] we demonstrated that at the point of
reaction S is segregated to the surface of the catalyst particle, where
it forms a layer of liquid alloy rich in Fe and S. Upon cooling, this
Fig. 2. a) XPS spectrum of CNT fibers in the range of 4861 eV (solid black line) and
fitting (dotted black line) showing Se3d (blue line) and Fe3p (red line) components and
Shirley background (green line). b) EDX spectra of CNT walls and of a catalyst particle
containing Se, obtained in STEM mode. The inset shows STEM micrographs of the areas
probed. Non-indexed peaks correspond to SiKa,b and CuKa,b, from furnace tube and TEM
grid respectively. c) HRTEM image of a catalyst particle. (Upper inset: FFT analysis of
this particle with the plane reflections labels confirming the FCC structure. Lower
inset: Particle detail). (A colour version of this figure can be viewed online.)
layer evolves into an Fe1xS intermetallic which however, is less
than a nanometer in thickness and therefore elusive to locate or
detect by X-ray or electron diffraction. The thermodynamics of
B. Mas et al. / Carbon 101 (2016) 458e464
FeeSe and FeeS alloy systems are to some extent similar, as can be
observed by inspection of the their equilibrium binary diagrams
(Fig. S1). The similarities that we highlight as particularly relevant
for CNT growth are: the presence of a Se-rich liquid at temperatures
below 1000 C degrees (see for example the monotectic reaction at
46.5 at.%); stable intermetallics with composition close to FeSe
below 1000 C; and the negligible solubility of Se in FCC or BCC.
These features are analogous to the FeeS system and it is thus
expected that the reaction using Se promoter follows the same
thermodynamic path proposed before for the FeeSeC system.
Upon formation of an FCC Fe nuclei, Se is rejected to the surface
where as part of a liquid rich in Fe and Se it assists in the catalytic
decomposition of the C source and the stabilization of the edge of
the nascent CNT, and latter it contributes to the extrusion of the
nanotube via a high interfacial energy of the graphite basal plane
and the FeeSeeC alloy.
Metallurgy literature on the FeeSeeC system is scarce, and
there are no reports on the contact angle of molten FeeSeeC alloys
on graphite (as there are for FeeSeC [28]) or on the equilibrium
ternary phase diagram. But Se, and group 16 elements (including O)
in general, are known to lower the surface energy of molten Fe
upon its migration to the surface. Using the GibbseLangmuir model
for adsorption isotherms and segregation of solutes, for example, it
has been shown that surface coverage of the catalyst occurs for bulk
concentrations of group 16 elements below 0.03% [29e31]. H2S, for
example, adsorbs on Nickel and covers half of its surface at concentrations of parts per billion [32]. Hence the extended view that
group 16 elements including Se ‘poison’ hydrocarbon cracking reactions on transitions metals even when present at impurity levels.
But their poisoning mechanism involves in fact the formation of
graphitic deposits, often of tubular morphology (see for example
Figure 12 in Ref. [32]), i.e. CNT growth. It should thus be no surprise
that Se (and in general group 16 elements) can be used as promoters in the growth of CNTs and their spinning into continuous
fibers. We confirmed this hypothesis by spinning continuous fibers
of CNT using Te in form of tellurophene as promoter (see video in
SOM).
3.3. Se effect on CNT morphology
By increasing the ratio of Se/C in the CVD reaction, it is possible
to increase the diameter and number of layers of the CNTs. This
effect can be directly observed by Raman spectroscopy measurements, which probe a large number of CNTs on the fiber surface and
thus provide a reasonable average composition of the sample. Examples of Raman spectra obtained with a 785 nm laser and
normalized by the intensity of the G band are presented in Fig. 3a
(data for 532 nm laser line is shown in Fig. S2). The plot shows that
for small Se amounts (0.008 at.%), the CNTs correspond to the
SWNT type, as indicated by the radial breathing modes (RBMs), for
this example at 157, 203, 231, 267 cm1, as well as the split of the G
band into its G and Gþ components. Furthermore, these SWNTs
are predominantly of armchair type (Fig. S4), although this is a
consequence of the liquid state of the catalyst and not specific to
the use of Se as promoter [19]. In adidtion, the metallic nature of the
CNTs can be analyzed by the lineshape of low frequency band
component [33]. The Breit-Wigner-Fano (BWF) fit yields an asymmetric factor (1/q) around 0.6 (Fig. S3), comparable to 0.14
to 0.4 for fibers of SWNTs grown with S as promoter and literature
values of 0.2 [33], and confirming the intrinsic metallic character
of CNT fibers grown by high temperature CVD [19]. At higher Se
contents, the Raman spectra are indicative of CNTs with few layers,
with the disappearance of RBMs, yet with a G band still showing the
Gþ, G split. Further increase in Se concentration leading to multiwalled NTs (MWNTs) is observed by a well defined G* and the loss
461
Fig. 3. a) Evolution of the Raman spectra of CNT fibers produced with different amount
of Se. The inset shows the 2D peak upshift due to increased in number of layers and
decreased curvature at higher Se concentration during synthesis. The measurement
was carried out with a 785 nm laser. b) Plot of the ratio of CNT number of layers (n) to
CNT diameter (D) versus the atomic ratio of promoter to C for CNT fibers produced
with S (black) and Se (red) as promoter, respectively. The ratio n/D remains constant
for different promoter concentrations. This ratio is expected to be proportional to
surface solubility of C in the catalyst. (A colour version of this figure can be viewed
online.)
of resonance of the G band increasing the D/G ratio. The increase in
CNT diameter and number of layers also produces an upshift in the
2D band [7]. This shift is somewhat similar to that observed in
graphene [34], but reflects in addition the decrease in curvature of
the CNTs.
The control over CNT diameter and number of layers by
increasing the Se/C ratio was confirmed by observation of constituent CNTs under TEM. Interestingly, these CNTs are of unusually
large diameter for their number of layers, at least compared with
fibers produced using S promoter. Fig. 3b shows this behavior as a
plot of number of layers/diameter (n/D) for different atomic ratio of
promoter/C. In spite of the relatively large error bars, reflecting
uncertainty in extracting precise values of diameter and number of
layers from HRTEM observation in addition to sample polydispersity, Se samples clearly lie on a lower line. At 3$104 atomic
ratio of promoter/Carbon the SWNTs grown from Se have a diameter of 6.2 nm whereas those grown using S have a diameter of
2.45 nm. The parameter n/D is actually of interest to understand the
CVD reaction and optimize CNT morphology for bulk fiber applications. We assume that the rate of incoming C into the catalyst
462
B. Mas et al. / Carbon 101 (2016) 458e464
scales with the catalyst surface times its C solubility ((D2$p/2)$s),
whereas the rate of extruded C as number of layers times particle
circumference ((D$p)$n). If these rates are equal, then the ratio of
incoming to extruded C must be constant, and solubility proportional to n/D. Fig. 3b shows indeed approximately a constant value
for both promoters, with Se leading to nearly half the C solubility in
the catalyst. This is consistent with Se producing a faster drop in
surface tension of molten Fe [29] and implying a lower enthalpy of
adsorption.
tubes up to around 5 nm, collapsed tubes between 5 nm and
around 7.3 nm and self-folding for larger diameters. The presence of
neighboring CNTs strongly affects the morphology of CNTs, favoring
polygonization or collapse as a way of also maximizing inter-tube
contact. In addition to bundle composition, chemical environment and temperature will also affect the different stability ranges,
thus, the prediction in Fig. 4b is to be taken as a first model to
describe the unusual morphology observed in Se-grown CNTs.
3.5. Mechanical properties
3.4. CNTs self-collapse and fold
The self-collapse of CNTs into ribbons is favored by a low n/D
ratio. In the case of CNTs grown using Se promoter, the unusually
large diameter of SWNT and DWNTs over 10 nm implies that they
can self-fold and remain stable due to the additional layer contact
and relatively small bending energy penalty. An example of such a
morphology is shown in Fig. 4a, corresponding to a HRTEM
micrograph of a collapsed SWNT of equivalent 7.6 nm diameter that
is folded. This geometry is commonly observed in graphene samples and accurately described by MD [35]. We carried out a similar
MD study to analyze the theoretical stability of self-folding of CNT.
Average total energy per atom was calculated for individual SWNTs
with diameters ranging from 1.36 nm to 13.56 nm in the different
states: non-collapsed, collapsed and self-folded. The results are
presented in Fig. 4b. The simple model predicts stability of round
Fig. 4. Self-folding of large diameter collapsed SWNTs. a) HRTEM micrograph of a
SWNT folded over itself. The inset shows a higher magnification view of the folding
area. b) Comparison of energy per atom of individual SWNT as a function of diameter
in round, collapsed and self-folded morphologies. The theoretically stable regions are
marked in color, and examples of tubes included: (30,30) round CNT of 4.03, (60,60)
collapsed CNT of 8.13 and self-folded (100,100) of 13.4 nm diameter. (A colour version
of this figure can be viewed online.)
With the view that mass-normalized tensile properties of CNT
fibers benefit from collapsed tubes of few layers, we present preliminary data for fibers grown with Se promoter. Specific stressestrain curves for fibers spun at 15 m min1, corresponding roughly
to a draw ratio of 4, are included in Fig. 5a. The curves show a
modest initial modulus in the range 2630 GPa SG1 up to around
1% strain, but followed by a large deformation and a specific
strength up to 0.9 GPa SG1 (or N tex1). Further optimization of the
fiber structure for tensile properties by applying higher draw ratios
that increases CNT alignment, and the removal of residual catalyst
Fig. 5. a) Stress-strain curves of individual filaments of CNT fibers grown with Se
promoter. b) Comparison of specific strength and specific toughness of CNT fibers
produced with different promoters in this work (blue). The graph includes also conventional high-performance fibers: Kevlar 49 [36], T1000G carbon fiber [37], AS4
carbon fiber (measured), Dyneema SK75 [38], S2 glass fiber [39], Zylon (HM) [40] and
Spider Silk [41], as well as literature data for CNT fibers from different precursor:
Toluene-S [18]), CH4-S [18] and CNTf (acetone/ethanol) [42]. Fibers spun from liquid
crystal phases [43] included for reference. Inset: values of figure of merit for ballistic
protection. (A colour version of this figure can be viewed online.)
B. Mas et al. / Carbon 101 (2016) 458e464
impurities, are in progress and will be reported in a separate work.
But this preliminary assessment already shows an interesting
combination of tensile strength and toughness (energy-to-break).
Fig. 5b presents a comparison of specific strength and specific
toughness of CNT fibers produced with different precursors. It also
includes data for spider silk and conventional high-performance
fibers such as aramid (Kevlar 49), ultrahigh-molecular weight
polyethylene (UHMWPE-Dyneema SK 75), poly(p-phenylene-2,6benzobisoxazole) (PBO-Zylon HM) and S2 glass. In CNT fibers,
toughness benefits form a large interface between elements, either
by shear stress transfer in the elastic regime (conservative) or by
CNT sliding (dissipative) when shear strength is exceeded. Thus, the
increase in toughness observed by replacing S with Se as promoters
is a consequence of maximizing CNT diameter per number of layers,
which increases the contact between load-bearing elements and
therefore the total overlap surface. Further improvements are expected by combining Se with other C sources, for example toluene,
which has been reported to produce fibers with very high strength
[18], possibly due to a longer CNT length related to the a more
efficient thermal decomposition compared to butanol. As an
example of a property that benefits from high specific properties
we highlight protection against high energy impact, whose figure
* 1/3
of
pmerit
ffiffiffiffiffiffiffiffi ((U ) ) is the cubed root of the product of sonic modulus
( E=r) times specific toughness [44]. The inset in Fig. 5b compares
values for (U*)1/3, with CNT fibers grown using Se above S2 glass
and aramid.
4. Conclusions
Our results show the possibility to use Se or Te as promoters in
the growth of CNTs by floating catalyst CVD and direct spinning
from the gas phase as continuous macroscopic fibers. The addition
of two more group 16 elements to the list of CNT growth promoters
reinforces the view that they play an equivalent role in the CVD
reaction. Even at impurity concentrations they strongly adsorb on
the catalyst surface, reducing its surface tension, assisting in stabilizing the edge of the nascent tubes and promoting the growth of
graphitic tubular layers. Low concentrations of Se lead to SWNTs,
which have a chiral angel distribution biased towards armchair.
Increasing Se precursor content produces larger diameter tubes and
a higher number of layers. The ratio n/D is fairly constant across Se
contents, though around half that of S-grown CNTs. This ratio is
closely related to the ability of the promoter to assist in the catalytic
decomposition of the C source and can thus be seen as a solubility,
but future work should provide a more specific description of this
parameter and its relation to the enthalpy of adsorption of the
promoter and its activity, among other parameters at the FeeSeC
boundary.
The resulting CNTs have an unusually large diameter for their
number of layers. They thus collapse into ribbons and self-fold. MD
simulation confirm that the self-folded morphology is thermodynamically stable for individual SWNTs with diameter above 7.3 nm.
Finally, replacing S with Se is shown to substantially increase
tensile properties, particularly those benefiting from a high
toughness. Further improvements in tensile properties are expected by increasing draw ratio at the point of assembly or using
other C sources known to enhance strength/stiffness.
Acknowledgment
J.J.V. is grateful for discussions with A. Windle and for financial
support from MINECO (RyC-2014-15115, Spain), MAD2D project
(S2013/MIT-3007, Comunidad de Madrid), and FP7-People- Marie
Curie Action-CIG (322129). I.M.-B. acknowledges funding by
n y Cajal fellowship RYC-2012-10639. E.M.P.
MINECO under Ramo
463
gratefully acknowledges funding from the European Research
Council (ERC-StG-307609) and the MINECO of Spain (CTQ201460541-P).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.carbon.2016.02.005.
References
[1] X. Wang, Z.Z. Yong, Q.W. Li, P.D. Bradford, W. Liu, D.S. Tucker, W. Cai,
F.G. Yuan, Y.T. Zhu, H. Wang, F.G. Yuan, Y.T. Zhu, Ultrastrong, stiff and
multifunctional carbon nanotube composites, Mater Res. Lett. 1 (1) (2013)
19e25, http://dx.doi.org/10.1080/21663831.2012.686586.
[2] J.J. Vilatela, D. Eder, Nanocarbon composites and hybrids in sustainability: a
review, ChemSusChem 5 (3) (2012) 456e478, http://dx.doi.org/10.1002/
cssc.201290009.
[3] A. Hehr, Y. Song, B. Suberu, J. Sullivan, V. Shanoc, M. Schulz, Embedded carbon
nanotube sensor thread for structural health monitoring and strain sensing of
composite materials, in: Nanotube Superfiber Materials, 2014, pp. 671e712.
[4] J.J. Vilatela, R. Marcilla, Tough electrodes: carbon nanotube fibers as the ultimate current collectors/active material for energy management devices,
Chem. Mater. 27 (5495) (2015) 6901e6917, http://dx.doi.org/10.1021/
acs.chemmater.5b02783.
[5] J.J. Vilatela, Nanocarbon based composites, in: Nanocarbon-inorganic Hybrids:
Next Generation Composites for Sustainable Energy Applications, 2014, pp.
227e254.
[6] A. Lekawa-Raus, J. Patmore, L. Kurzepa, J. Bulmer, K. Koziol, Electrical properties of carbon nanotube based fibers and their future use in electrical wiring,
Adv. Funct. Mater. 24 (25) (2014) 3661e3682, http://dx.doi.org/10.1002/
adfm.201303716.
[7] V. Reguero, B. Alem
an, B. Mas, J.J. Vilatela, Controlling carbon nanotube type in
macroscopic fibers synthesized by the direct spinning process, Chem. Mater.
26 (11) (2014) 3550e3557, http://dx.doi.org/10.1021/cm501187x.
[8] M.W. Schauer, M.A. White, Tailoring industrial scale cnt production to specialty markets, in: Symposium MM e Carbon Nanotubesesynthesis, Properties, Functionalization, and Applications, vol. 1752, 2015, pp. 103e109.
[9] L.M. Ericson, H. Fan, H. Peng, V.A. Davis, W. Zhou, J. Sulpizio, Y. Wang,
R. Booker, J. Vavro, C. Guthy, A.N.G. Parra-Vasquez, M.J. Kim, S. Ramesh,
R.K. Saini, C. Kittrell, G. Lavin, Schmidt, W.W. Adams, W.E. Billups, M. Pasquali,
W.F. Hwang, R.H. Hauge, J.E. Fischer, R.E. Smalley, Macroscopic, neat, singlewalled carbon nanotube fibers, Science 305 (5689) (2004) 1447e1450,
http://dx.doi.org/10.1126/science.1101398.
nicaud, C. Coulon, C. Sauder, R. Pailler, C. Jornet, P. Bernier,
[10] B. Vigolo, A. Pe
P. Poulin, Macroscopic fibers and ribbons of oriented carbon nanotubes, Science
290
(5495)
(2000)
1331e1334,
http://dx.doi.org/10.1126/
science.290.5495.1331.
[11] M. Zhang, K.R. Atkinson, R.H. Baughman, Multifunctional carbon nanotube
yarns by downsizing an ancient technology, Science 306 (5700) (2004)
1358e1361, http://dx.doi.org/10.1126/science.1104276.
[12] Y.L. Li, I.A. Kinloch, A.H. Windle, Direct spinning of carbon nanotube fibers
from chemical vapor deposition synthesis, Science 304 (5668) (2004)
276e278, http://dx.doi.org/10.1126/science.1094982.
[13] C.P. Huynh, S.C. Hawkins, Understanding the synthesis of directly spinnable
carbon nanotube forests, Carbon 48 (4) (2010) 1105e1115, http://dx.doi.org/
10.1016/j.carbon.2009.11.032.
[14] S. Zhang, L. Zhu, M.L. Minus, H.G. Chae, S. Jagannathan, C.P. Wong, J. Kowalik,
L.B. Roberson, S. Kumar, Solid-state spun fibers and yarns from 1-mm long
carbon nanotube forests synthesized by water-assisted chemical vapor
deposition, J. Mater. Sci. 43 (13) (2008) 4356e4362, http://dx.doi.org/10.1007/
s10853-008-2558-5.
[15] K. Hata, D.N. Futaba, K. Mizuno, T. Namai, M. Yumura, S. Iijima, Water-assisted
highly efficient synthesis of impurity-free single-walled carbon nanotubes,
Science 306 (5700) (2004) 1362e1364, http://dx.doi.org/10.1126/
science.1104962.
[16] M.S. Motta, Y.L. Li, I.A. Kinloch, A.H. Windle, Mechanical properties of
continuously spun fibers of carbon nanotubes, Nano Lett. 5 (8) (2005)
1529e1533, http://dx.doi.org/10.1021/nl050634þ.
[17] M.S. Motta, A. Moisala, I.A. Kinloch, A.H. Windle, The role of sulphur in the
synthesis of carbon nanotubes by chemical vapour deposition at high temperatures, J. Nanosci. Nanotechnol. 8 (5) (2008) 2442e2449, http://dx.doi.org/
10.1166/jnn.2008.500.
[18] T.S. Gspann, F.R. Smail, A.H. Windle, Spinning of carbon nanotube fibres using
the floating catalyst high temperature route: purity issues and the critical role
of sulphur, Farad Discuss. 173 (2014) 47e65, http://dx.doi.org/10.1039/
C4FD00066H.
rez, V. Reguero, X. Guanglong, Y. Cui,
[19] B. Aleman, M. Bernal, B. Mas, E. Pe
J.J. Vilatela, Inherent predominance of high chiral angle metallic carbon
nanotubes in continuous fibers grown from molten catalyst, Nanoscale 8 (7)
(2016) 4236e4244, http://dx.doi.org/10.1039/C5NR07455J.
464
B. Mas et al. / Carbon 101 (2016) 458e464
[20] B. Delmon, G.F. Froment, in: Catalyst Deactivation 1980: International Symposium Proceedings, first ed., 1980, pp. 1e600.
[21] D.P. Sweat, C.E. Stephens, A modified synthesis of tellurophene using nabh4 to
generate sodium telluride, J. Organomet. Chem. 693 (14) (2008) 2463e2464,
http://dx.doi.org/10.1016/j.jorganchem.2008.04.022.
[22] S. Plimpton, Fast parallel algorithms for short e range molecular dynamics,
J. Comput. Phys. 117 (1) (1995) 1e19, http://dx.doi.org/10.1006/
jcph.1995.1039.
[23] S.J. Stuart, A.B. Tutein, J.A. Harrison, A reactive potential for hydrocarbons with
intermolecular interactions, J. Chem. Phys. 2000 (112) (2000) 6472e6486,
http://dx.doi.org/10.1063/1.481208.
[24] J.A. Elliott, J.K.W. Sandler, A.H. Windle, R.J. Young, M.S.P. Shaffer, Collapse of
single-wall carbon nanotubes is diameter dependent, Phys. Rev. Lett. 92 (9)
(2004), http://dx.doi.org/10.1103/PhysRevLett.92.095501, 095501(4pp).
[25] M. He, J. Dong, K. Zhang, F. Ding, H. Jiang, A. Loiseau, J. Lehtonen,
E.I. Kauppinen, Precise determination of the threshold diameter for a singlewalled carbon nanotube to collapse, ACS Nano 8 (9) (2014) 9657e9663,
http://dx.doi.org/10.1021/nn5042812.
[26] N.G. Chopra, L.X. Benedict, V.H. Crespi, M.L. Cohen, S.G. Louie, A. Zettl, Fully
collapsed carbon nanotubes, Nature 377 (6545) (1995) 135e138, http://
dx.doi.org/10.1038/377135a0.
[27] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-Ray
Photoelectron Spectroscopy: a Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, 1992.
[28] C. Wu, V. Sahajwalla, Influence of melt carbon and sulfur on the wetting of
solid graphite by fe-c-s melts, Metall. Mater. Trans. B 29 (2) (1998) 471e477,
http://dx.doi.org/10.1007/s11663-998-0126-7.
[29] K. Nakashima, K. Mori, Interfacial properties of liquid iron alloys and liquid
slags relating to iron- and steel-making processes, ISIJ Int. 32 (1) (1992)
11e18, http://dx.doi.org/10.2355/isijinternational.32.11.
[30] M.J. Mcnallan, T. Debroy, Effect of temperature and in Fe-Ni-Cr alloys containing sulfur, Metall. Trans. B 22 (4) (1991) 557e560, http://dx.doi.org/
10.1007/BF02654294.
[31] Svein Stolen, Tor Grande, Neil L. Allan, Chemical Thermodynamics of Materials: Macroscopic and Microscopic Aspects, 2003.
[32] C.H. Bartholomew, Mechanisms of catalyst deactivation, Appl. Catal. A Gen.
212 (1e2) (2001) 17e60, http://dx.doi.org/10.1016/S0926-860X(00)00843-7.
[33] S.D.M. Brown, A. Jorio, P. Corio, M.S. Dresselhaus, G. Dresselhaus, R. Saito,
K. Kneipp, Origin of the Breit-Wigner-Fano lineshape of the tangential G-band
feature of metallic carbon nanotubes, Phys. Rev. B 63 (15) (2001), http://
dx.doi.org/10.1103/PhysRevB.63.155414, 155414(8pp).
[34] A. Ferrari, J. Meyer, C. Scardaci, C. Casiraghi, M. Lazzeri, Raman spectrum of
graphene and graphene layers, Phys. Rev. Lett. 97 (18) (2006), http://
dx.doi.org/10.1103/PhysRevLett.97.187401, 187401(4pp).
[35] X. Meng, M. Li, Z. Kang, X. Zhang, J. Xiao, Mechanics of self-folding of singlelayer graphene, J. Phys. D Appl. Phys. 46 (5) (2013), http://dx.doi.org/10.1088/
0022-3727/46/5/055308, 055308(6pp).
[36] Dupont, KEVLAR Aramid Fiber: Technical Guide, 2011.
[37] Toray, T1000G Data Sheet, 2008.
[38] D.S.M. Dyneema, Technical Brochure: Dyneema in Marine and Industrial
Applications, 2008.
[39] P. Morgan, Carbon Fibres and Their Composites, 2005.
[40] Toyobo, PBO Fiber-zylon, 2005.
[41] F. Vollrath, D.P. Knight, Liquid crystalline spinning of spider silk, Nature 410
(6828) (2001) 541e548, http://dx.doi.org/10.1038/35069000.
[42] X.H. Zhong, Y.L. Li, Y.K. Liu, X.H. Qiao, Y. Feng, J. Liang, J. Jin, L. Zhu, F. Hou,
J.Y. Li, Continuous multilayered carbon nanotube yarns, Adv. Mater. 22 (6)
(2010) 692e696, http://dx.doi.org/10.1002/adma.200902943.
[43] N. Behabtu, C.C. Young, D.E. Tsentalovich, O. Kleinerman, X. Wang, A.W.K. Ma,
E.A. Bengio, R.F. ter Waarbeek, J.J. de Jong, R.E. Hoogerwerf, S.B. Fairchild,
J.B. Ferguson, B. Maruyama, J. Kono, Y. Talmon, Y. Cohen, M.J. Otto,
M. Pasquali, Strong, light, multifunctional fibers of carbon nanotubes with
ultrahigh conductivity, Science 339 (6116) (2013) 182e186, http://dx.doi.org/
10.1126/science.1228061.
[44] P.M. Cunniff, M.A. Auerbach, High performance ‘M5’ fiber for ballistics/
structural composites, in: 23rd. Army Science Conference, 2002, pp. 1e8.