Large-diameter Single-walled Carbon Nanotubes Research Articles

Selective synthesis of large diameter single-walled carbon nanotubes on rice husk-derived catalysts

Selective synthesis of large diameter single-walled carbon nanotubes (SWCNTs) is desired for a variety of applications, but most catalysts can only synthesize SWCNTs with a diameter less than 2 nm. Here, a low cost and green catalyst (Co/RH-SiO2) was prepared by using rice husk-derived SiO2 as the catalyst support, which selectively synthesized large SWCNTs (dt > 2 nm) with a percentage of 70.7 % among all tubes grown at the high growth temperature of 950 ℃. The carbon yield produced on this catalyst containing 1 wt% Co was 4.49 wt%. In contrast, commercial SiO2 supported Co catalyst (Co/Cab-SiO2) synthesized smaller SWCNTs with a broad diameter distribution under the same growth condition. The detailed characterizations of catalysts showed that Co/RH-SiO2 catalyst is unique with the abundant small mesopores (2–4 nm) and reducible Co hydrosilicate and surface Co silicates highly dispersed in the pore structures. The reduction of Co hydrosilicate and surface Co silicates facilitates the formation of large Co clusters, which are stabilized by irreducible Co silicates and small mesopores, leading to the growth of large-diameter SWCNTs. Results in this study provide useful insights to develop low cost and green catalysts from biomass waste for the selective growth of SWCNTs.

The effect of elution speed control on purity of separated large-diameter single-walled carbon nanotubes in gel chromatography

Large-diameter single-walled carbon nanotubes (SWNTs) have unique properties compared to small-diameter ones, for example, higher electrical conductivities, higher charge carrier mobilities, smaller bandgaps, and longer lengths, which can broaden SWNT applications. However, because the preparation methods result in mixtures of metallic SWNTs (m-SWNTs) and semiconducting SWNTs (s-SWNTs); such as in the case of small-diameter SWNTs, they must be separated and used for specific applications to obtain optimal performance characteristics. In this study, we show that simple elution speed control can increase the purity of separated large-diameter SWNTs in gel chromatography. According to the results, the flow rate of the eluant (i.e., the elution speed during gel column chromatography) greatly affects the purity of the separated m-SWNTs. We controlled the elution speed by changing the pressure inside the column during the separation process and experimentally investigated the relationship between the purity of the separated m-SWNTs and elution speed. By adjusting the elution speed to 0.13 ml/min, we obtained large quantities of pure m-SWNTs. Moreover, high-purity s-SWNTs were obtained for a wide elution speed range. Thus, highly pure m- and s-SWNTs can simultaneously be prepared by simply controlling the elution speed in single-column gel chromatography.

Comparative study of the extraction selectivity of PFO-BPy and PCz for small to large diameter single-walled carbon nanotubes

Comparative study of the extraction selectivity of PFO-BPy and PCz for small to large diameter single-walled carbon nanotubes

Selective separation of single-walled carbon nanotubes in aqueous solution by assembling redox nanoclusters.

The selective separation of soluble and individual single-walled carbon nanotubes (SWCNTs) in aqueous solution is a key step for harnessing the extraordinary properties of these materials. Manipulating the strong van der Waals intertube interactions between the SWCNT bundles is very important in selective separation, which is a long-standing challenge. Here we reported the ability of redox polyoxometalate clusters to modulate the intertube π-π stacking interaction through electron transfer and achieved the diameter-selective separation of SWCNTs in a surfactant aqueous solution. The large-diameter SWCNTs concentrated at ∼1.3-1.4 nm were selectively separated when ∼1 nm clusters encapsulated within the tube cavity, and the dispersion of subnanometer ∼0.7-0.9 nm SWCNTs was boosted when clusters were adsorbed on the outer surface of small-diameter nanotubes. The mechanism of diameter-selective separation of SWCNTs associated with the size-dependent interaction between cluster-tubes and the steric hindrance effect of clusters was revealed by optical absorption and Raman spectroscopy. This simple method thus enables the selective separation of individual high-quality SWCNTs in aqueous solutions without harsh sonication with the potential for other separation applications.

The Impacts of Polyisoprene Physical Interactions on Sorting of Single-Wall Carbon Nanotubes.

Conjugated polymer sorting is currently the best method to select large-diameter single-walled carbon nanotubes (SWCNTs) with tunable narrow chirality in the adaption of highly desired electronics applications. The acceleration on conjugated polymers-SWCNTs interaction with long-term stability through different molecular designs; for example, longer alkyl side-chains or conjugation moieties have been extensively developed in recent years. However, the importance of the macromolecules with abundant van der Waals (VDW) interaction in the conjugated-based block copolymer system acting during SWCNTs sorting is not clearly demonstrated. In this work, a conjugated diblock copolymer involving polyisoprene (PI) and highly dense π-interaction of poly (9,9-dioctylfluorene) (PFO) is utilized to investigate the impact of natural rubber PI physical interaction on sorting effectiveness and stability. Through the rational design of diblock copolymer, PFO with ≈1200 isoprene units can remarkably enhance SWCNTs sorting ability and selected few chiralities with a diameter of ≈0.83-1.1nm and highly stable solution for more than 1 year. The introduction of long-chain PI system is attributed not only to form weak VDW force with SWCNTs and strengthen the wrapping of PFO around the semiconducting SWCNTs but also to act as a barrier among nanotubes to prevent reaggregation of sorted SWCNTs.

Vapor-phase epitaxial re-growth of large diameter single-walled carbon nanotubes

Long single-wall carbon nanotubes (SWCNTs) with a controlled conductivity type or chirality are interesting for fundamental study and are promising in many different technological applications, such as nanoelectronics, optoelectronics, and also upon utilizing them as nanoscale reactors to produce nanomaterials. In this study, the long aligned large diameter SWCNTs and the large diameter nanotube dense networks were synthesized via a vapor-phase epitaxial re-growth method. The nanotubes were re-grown on ST (stable temperature)-cut quartz substrates from short SWCNT seeds using the mixture of ethanol and acetylene as a precursor. The efficient nanotube re-growth was achieved using unsorted SWCNTs with diameters of 1.2–2.0 nm and semiconducting SWCNTs, sorted by an aqueous two-phase extraction method, as seeds. According to our study, the re-grown nanotubes in an array have an average length of 5.5 μm, while the individual re-grown nanotubes can reach up to 20–30 μm. The extensive optical study confirms the preservation of SWCNTs diameter during the re-growth and signifies the high quality of produced nanotubes. We demonstrate the SWCNT chirality selective efficiency of the re-growth, which leads to predominance of the metallic nanotubes.

Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules.

Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest molecules with widely varying static dielectric constants. Filled through simple ingestion of the guest molecule, each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compounds, covering static dielectric constants from 1.8 to 109, are inserted in large diameter SWCNTs (d = 1.104-1.524 nm) and more than 10 compounds in small diameter SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielectric on the nanotube optical properties is a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude of the dielectric constant. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra additionally enables determination of the critical filling diameter for each molecule and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest molecule/SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is observed for low dielectric constants, with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examining higher-order effects, such as due to nonbulk-like molecule stacking, in host-guest interactions in well-controlled nanopore size materials.

Metal-semiconductor sorting of large-diameter single-wall carbon nanotubes by pH-dependent binding to a hydrophobic-interaction adsorbent

A batch adsorption method for sorting large-diameter single-walled carbon nanotubes (SWCNTs) is described that employs a hydrophobic-interaction chromatography (HIC) adsorbent and a single nonionic surfactant. The method is based on the creation of significant differences between metallic and semiconductor SWCNTs in their adsorption affinity to a HIC adsorbent. These differences are then used for the efficient separation of the electronic forms of large-diameter SWCNTs. To gain a better understanding of the mechanism involved, the effects of various HIC adsorbents under different pH conditions were studied. The results obtained demonstrate the importance of the type and density of the hydrophobic functional groups on the adsorbent in determining the relative strength of the adsorptive interactions for various electronic forms of SWCNTs. The results also show the effects of negatively charged adventitious functional groups on the nanotube on the relative hydrophobicity of the nanotubes. The method described here is implemented using widely-available HIC adsorbents, and only requires simple titration with HCl or NaOH to adjust the pH. Furthermore, the method is potentially suitable to be performed using liquid chromatography with a packed adsorbent column and with a liquid-phase pH gradient in order to achieve high-resolution separations.

Charge and Thermoelectric Transport in Polymer-Sorted Semiconducting Single-Walled Carbon Nanotube Networks.

Understanding the charge transport mechanisms in chirality-selected single-walled carbon nanotube (SWCNT) networks and the influence of network parameters is essential for further advances of their optoelectronic and thermoelectric applications. Here, we report on charge density and temperature-dependent field-effect mobility and on-chip field-effect-modulated Seebeck coefficient measurements of polymer-sorted monochiral small-diameter (6,5) (0.76 nm) and mixed large-diameter SWCNT (1.17-1.55 nm) networks (plasma torch nanotubes, RN) with different network densities and length distributions. All untreated networks display balanced ambipolar transport and electron-hole symmetric Seebeck coefficients. We show that charge and thermoelectric transport in SWCNT networks can be modeled by the Boltzmann transport formalism, incorporating transport in heterogeneous media and fluctuation-induced tunneling. Considering the diameter-dependent one-dimensional density of states (DoS) of the SWCNTs composing the network, we can simulate the charge density and temperature-dependent Seebeck coefficients. Our simulations suggest that scattering in these networks cannot be described as simple one-dimensional acoustic and optical phonon scattering as for single SWCNTs. Instead the relaxation time is inversely proportional to energy (τ ∝ (E - EC)s, s = -1, EC being the energy of the first van Hove singularity), presumably pointing toward the more two-dimensional character of scattering events and the necessity to include scattering at the SWCNT junctions. Finally, our observation of higher power factors in trap-free, 1,2,4,5-tetrakis(tetramethylguanidino)benzene-treated (6,5) networks than in the RN networks emphasizes the importance of chirality selection to tune the width of the DoS. To benefit from both higher intrinsic mobilities and a large thermally accessible DoS, we propose trap-free, narrow DoS distribution, large-diameter SWCNT networks for both electronic and thermoelectric applications.

Ultrafast saturable absorption of large-diameter single-walled carbon nanotubes for passive mode locking in the mid-infrared.

We study the saturable absorption properties of single-walled carbon nanotubes (SWCNTs) with a large diameter of 2.2 nm and the corresponding exciton resonance at a wavelength of 2.4 µm. At resonant excitation, a large modulation depth of approximately 30 % and a small saturation fluence of a few tens of µJ/cm2 are evaluated. The temporal response is characterized by an instantaneous rise and a subpicosecond recovery. We also utilize the SWCNTs to realize sub-50 fs, self-start mode locking in a Cr:ZnS laser, revealing that the film thickness is an important parameter that affects the possible pulse energy and duration. The results prove that semiconductor SWCNTs with tailored diameters exceeding 2 nm are useful for passive mode locking in the mid-infrared range.

(Invited) Growth and Characterization of Various Van Der Waals Hetero-Nanotubes Based on Single-Walled Carbon Nanotubes

We have synthesized a new coaxial nanotube structure, in which mono- or few-layer hexagonal boron nitride nanotube (BNNT) seamlessly wrap around a single-walled carbon nanotube (SWCNT); SWCNT@BNNT [1]. We named these as one-dimensional van der Waals hetero-nanotubes, because we found no correlation between chiral angle of inner SWCNT and outer BNNT for ‘double-walled’ SWCNT@BNNT. We have further developed the 1D coating CVD of transition metal dichalcogenide nanotubes (TMD-NT), such as MoS2 nanotubes and WSe2 nanotubes. We can grow MoS2 nanotubes around relatively large diameter SWCNT or SWCNT@BNNT. These nanotubes can be labelled as SWCNT@TMD-NT or SWCNT@BNNT@TMD-NT as shown in Fig. 1. Because BNNT is thermally more stable than SWCNT, we can remove SWCNT from SWCNT@BNNT by the gentle oxidation process. Hence, we can produce BNNT with inner diameter determined by the original SWCNT. Then, the MoS2 CVD can result BNNT@TMD-NT or TMD-NT@BNNT as shown in Fig. 1. Recently, CVD growth of carbon nanotubes over SWCNT@BNNT is realized, resulting SWCNT@BNNT@SWCNT. These hetero-nanotubes are characterized by HR-TEM, STEM-EELS, optical absorption, FT-IR, Raman scattering, Photoluminescence spectroscopy.Part of this work was supported by JSPS KAKENHI Grant Numbers JP15H05760, JP18H05329.Reference:[1] R. Xiang, T. Inoue, Y. Zheng, A. Kumamoto, Y. Qian, Y. Sato, M. Liu, D. Gokhale, J. Guo, K. Hisama, S. Yotsumoto, T. Ogamoto, H. Arai, Y. Kobayashi, H. Zhang, B. Hou, A. Anisimov, Y. Miyata, S. Okada, S. Chiashi, Y. Li, E. I. Kauppinen, Y. Ikuhara, K. Suenaga, S. Maruyama, arXiv:1807.06154 (2019). Figure 1

Sodium deoxycholate surfactant selected large-diameter single-walled carbon nanotubes (~1.6 nm): Characterization and nonlinear optical properties

Abstract In the present work, we proposed a strategy to select the single-walled carbon nanotubes (SWCNTs) with a relatively large diameter (~1.6 nm) with a sodium deoxycholate (SDC) surfactant. Both the Raman spectrum and the transmission electron microscopy (TEM) image confirmed the successful sorting of the large diameter (~1.6 nm). In addition, the prepared large-diameter SWCNTs exhibited the wide absorption band, implying the possible wideband nonlinear optical properties. A conventional open-aperture Z-scan measurement was implemented to investigate typical saturable absorption performance at 1.3 and 1.9 μm. As a proof of the excellent nonlinear saturable absorption, passively Q-switched lasers were demonstrated with the prepared large-diameter SWCNTs based saturable absorber, producing the minimum pulse duration of 335 ns. Our work reversed that the saturable absorption of SWCNTs can extend to the Mid-IR regime by sort the proper diameter.

One-Dimensional Pnictogen Allotropes inside Single-Wall Carbon Nanotubes.

The discovery of phosphorene, a single layer of black phosphorus, has accelerated the investigation of pnictogen nanomaterials, leading to the recent identification of arsenene and antimonene. These two-dimensional nanomaterials display physical properties superior to those of graphene for some applications. Recently, single-wall carbon nanotubes (SWCNTs) have been filled with P4 molecules from the melt and As4 molecules from the vapor phase. Confined within SWCNTs, polymerization reactions yielded new one-dimensional pnictogen allotropes. Here, we show using high-resolution electron microscopy that such nanostructures can also be observed upon filling SWCNTs from the vapor phase using red phosphorus as the source material. Using larger-diameter SWCNTs, the vapor phase favors the formation of double-stranded phosphorus zigzag ladders observed here for the first time. Overall, however, SWCNTs were generally found to fill more efficiently with liquid phosphorus; substantial decreases in the filling yields were observed for both phosphorus and arsenic filling of narrow SWCNTs using the vapor route. Attempts to extend the pnitogen series using molten antimony gave very low filling yields. However, the antimony zigzag ladder was observed on two occasions, suggesting that this structural motif dominates across the pnictogens. Computational predictions of the encapsulation energies of the various pnictogen nanostructures are consistent with the observed experimental trends, and band gap calculations predict that the single-stranded zigzag chains of all investigated pnictogens are fully metallic. Using SWCNTs with diameters of >1.5 nm revealed a plethora of complex new phosphorus nanostructures, which highlights an exciting new avenue for future work in this area.

One Dimensional Van Der Waals Heterostructures Wrapped Around Single-Walled Carbon Nanotubes

We have synthesized a new coaxial nanotube structure, in which mono- or few-layer hexagonal boron nitride nanotube (BNNT) seamlessly wrap around a single-walled carbon nanotube (SWCNT), and result in an atomically smooth coaxial tube consisting two different materials, as shown in Fig. 1(a). TEM-EELS clearly demonstrated the BNNT-SWCNT coaxial structure. We have tried various morphologies of SWCNTs as starting material, e.g. vertically aligned array, horizontally aligned array, suspended SWCNTs, and dry-deposited random network films. We can clearly observe the coaxial structure from originally isolated SWCNTs. We found no correlation between chiral angle of inner SWCNT and outer BNNT for ‘double-walled’ SWCNT-BNNT shown in Fig. 1(b). We concluded that these are one-dimensional van der Waals heterostructure. We have further developed the 1D coating CVD for transition metal dichalcogenide nanotubes, such as MoS2 nanotube as shown in Fig. 1 (c). We can grow MoS2 nanotubes around relatively large diameter SWCNT or SWCNT@BNNT [1]. We will discuss properties of the 1D heterostructures though optical absorption, Raman scattering, photoluminescence, FT-IR, and cathode luminance. Reference: [1] Rong Xiang et al., arXiv:1807.06154 (2018). Figure 1

Manufacture of Networks from Large Diameter Single-Walled Carbon Nanotubes of Particular Electrical Character.

We have demonstrated that the aqueous two-phase extraction (ATPE) can differentiate between large diameter single-walled carbon nanotubes (CNTs) by electrical character. Introduction of “hydration modulators” to the ATPE machinery has enabled us to isolate metallic and semiconducting CNTs with ease. We have also shown that often there is a trade-off between the purity of the obtained fractions and the ability to separate both metallic and semiconducting CNTs at the same time. To isolate the separated CNTs from the matrices, we have proposed a method based on precipitation and hydrolysis, which can eliminate the need to use lengthy dialysis routines. In the final step, we prepared thin free-standing films from the sorted material and probed how electrical charge is transported through such macroscopic ensembles.

Probing the mechanics of aqueous two-phase extraction using large diameter single-walled carbon nanotubes

We have demonstrated that large diameter (1.8 ± 0.4 nm) carbon nanotubes (CNTs) can be separated by means of the aqueous two-phase extraction (ATPE). This rapid and convenient tool has enabled us to isolate fractions of particular CNT diameter distribution. We have shown how a range of parameters can be used to fine tune the characteristics of the isolated material. Interestingly, by varying the pH of the medium, we have suppressed the extraction of low diameter CNTs and only large diameter CNTs were obtained. A number of other factors such as selected surfactant concentration steps, temperature or amount of starting CNT material have been found to have a significant effect on the end result of the CNT differentiation. The findings have provided us with more insight regarding the underlying mechanics of ATPE for processing polydisperse CNT mixtures.

Structure factors of carbon nanotubes on the thermal conductivity of carbon nanotube/epoxy composites

The structure factors of carbon nanotubes such as the dispersion, morphology and size have effects on the thermal conductivity of carbon nanotube/epoxy composites (kc). However, the behavior how these structure factors affect the kc has still not been fully understood. To seek the answer, three-dimensional computational models containing various dispersion of bending single wall carbon nanotubes (SWCNTs) are developed using the finite element method. A conjecture is proposed based on these models that the dispersion and the number of the overlapping heat-affected zones (OHAZs) of heat conduction networks play an important role on the kc. To prove the conjecture, a feature parameter–a dispersion coefficient is proposed to quantify the dispersion uniformity. The kc is calculated in models with different dispersion coefficients. The results show that the kc increases with the dispersion coefficient. The effects of the morphology and the size of SWCNTs on the kc could also be explained using this conjecture. SWCNTs with a larger length efficiency and diameter are found to be beneficial to a higher kc. Because a larger length efficiency increases the number of OHAZs and a larger diameter SWCNT has a wider heat-affected zone which also increases the number of OHAZs.

Selective synthesis of single walled carbon nanotubes on metal (iron, nickel or cobalt) sulfate-based catalysts

Selective synthesis of single-walled carbon nanotubes (SWCNTs) is highly desirable for various applications. Among the strategies proposed for achieving this, the method involving sulfur-containing compounds is a promising approach showing the conversion of common cobalt/silica catalysts (Co/SiO2) into chirality selective catalysts. However, the possible influence of sulfur-containing compounds in promoting the selectivity of non-cobalt-based metal/silica catalysts has not been studied. Here three metal sulfate based catalysts (MSO4/SiO2, M=Fe, Ni, or Co) were prepared for SWCNT synthesis under the same growth condition. Detailed SWCNT and catalyst characterizations show that well-dispersed Fe oxides and silicates are formed on Fe2(SO4)3/SiO2, favoring the formation of small diameter (6,5) nanotubes. NiSO4/SiO2 contains a portion of NiSO4 together with Ni silicate and relatively large NiO particles, leading to a wider diameter distribution centered around (8,7) nanotubes. CoSO4/SiO2 consists of dominantly well-dispersed CoSO4 and a small amount of Co silicates, showing the good selectivity toward the relatively larger diameter (9,8) nanotubes with an abundance of 40.6% among the semiconducting nanotubes. Sulfur retained on the catalysts influences the selectivity toward relatively larger diameter SWCNTs. Current work highlights the potential of using metal sulfates with varied decomposition temperatures to achieve the selective growth of SWCNTs.

Quinone molecules encapsulated in SWCNTs for low-temperature Na ion batteries

We have performed Li and Na ion charge–discharge experiments of 9,10-phenanthrene quinone (PhQ) molecules encapsulated in single-walled carbon nanotubes (SWCNTs) with mean tube diameters of 1.5 and 2.5 nm at room temperature and also at low temperatures. The Na ion reversible capacity of PhQ encapsulated in the larger diameter SWCNTs, measured at a low temperature of 0 °C, remained as high as that measured at room temperature (RT), while the capacity of PhQ in the smaller diameter SWCNTs at 0 °C was about a half of that at RT. The diameter dependence of the capacity should be attributed to the difference in the interactions between the encapsulated PhQ molecules and the host SWCNTs, which was revealed by Raman peak profile analysis. Charge-transfer reaction from metallic tubes to PhQ molecules encapsulated in the smaller diameter SWCNTs was detected by Raman measurements. The electrostatic interaction between charged SWCNTs and PhQ molecules, induced by the charge-transfer reaction, would partly contribute to the stabilization of PhQ molecules in the smaller diameter SWCNTs, while only van der Waals interaction stabilizes PhQ molecules in the larger diameter SWCNTs. The difference in stability was confirmed by thermogravimetric, x-ray photoelectron spectroscopy, and Raman measurements. Charge–discharge curves of PhQ encapsulated in SWCNTs were also discussed based on the stability difference.

Anomalous Carrier Transport in Ambipolar Field‐Effect Transistor of Large Diameter Single‐Walled Carbon Nanotube Network

A demonstration of ambipolar transistors of polymer-wrapped single-walled carbon nanotubes (SWNTs) provides an opportunity to scrutinize transport mechanism of electrons and holes in this system. Anomalous temperature-dependent nonlinear transport behavior is observed in large diameter SWNTs. This suggests an interplay between the intrinsic transport of individual tubes and the percolative network properties, highlighting the nature of polymer-wrapped SWNTs as a complex hybrid material. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.