Synthesis Of Single-walled Carbon Nanotubes Research Articles

Transparent and Freestanding Single-Walled Carbon Nanotube Films Synthesized Directly and Continuously via a Blown Aerosol Technique.

Single-walled carbon nanotube (SWCNT) films are promising materials as flexible transparent conductive films (TCFs). Here, inspired by the extrusion blown plastic film technique and the SWCNT synthesis approach by floating catalyst chemical vapor deposition (FCCVD), a novel blown aerosol chemical vapor deposition (BACVD) method is reported to directly and continuously produce freestanding SWCNT TCFs at several hundred meters per hour. The synthesis mechanism, involving blowing a stable aerosol bubble and transforming the bubble into an aerogel, is investigated, and a general phase diagram is established for this method. For the SWCNT TCFs via BACVD, both carbon conversion efficiency and SWCNT TCF yield can reach three orders of magnitude higher than those with the conventional FCCVD. The film displays a sheet resistance of 40ohmsq-1 at 90% transmittance after being doped, representing the record performance based on large-scale SWCNT films. Transparent, flexible, and stretchable electrodes based on BACVD films are demonstrated. Moreover, this high-throughput method of producing SWCNT TCFs can be compatible with the roll-to-roll process for mass production of flexible displays, touch screens, solar cells, and solid-state lighting, and is expected to have a broad and long-term impact on many fields from consumer electronics to energy conversion and generation.

Zeolite Nanosheets Stabilize Catalyst Particles to Promote the Growth of Thermodynamically Unfavorable, Small-Diameter Carbon Nanotubes.

A challenge in the synthesis of single-wall carbon nanotubes (SWCNTs) is the lack of control over the formation and evolution of catalyst nanoparticles and the lack of control over their size or chirality. Here, zeolite MFI nanosheets (MFI-Ns) are used to keep cobalt (Co) nanoparticles stable during prolonged annealing conditions. Environmental transmission electron microscopy (ETEM) shows that the MFI-Ns can influence the size and shape of nanoparticles via particle/support registry, which leads to the preferential docking of nanoparticles to four or fewer pores and to the regulation of the SWCNT synthesis products. The resulting SWCNT population exhibits a narrow diameter distribution and SWCNTs of nearly all chiral angles, including sub-nm zigzag (ZZ) and near-ZZ tubes. Theoretical simulations reveal that the growth of these unfavorable tubes from unsupported catalysts leads to the rapid encapsulation of catalyst nanoparticles bearing them; their presence in the growth products suggests that the MFI-Ns prevent nanoparticle encapsulation and prologue ZZ and near-ZZ SWCNT growth. These results thus present a path forward for controlling nanoparticle formation and evolution, for achieving size- and shape-selectivity at high temperature, and for controlling SWCNT synthesis.

Synthesis of (9,8) single-walled carbon nanotubes on CoSO4/SiO2 catalysts: The effect of Co mass loadings

Selective synthesis of single-walled carbon nanotubes (SWCNTs) with narrow chirality distribution at high production yield is critical to realize their applications in electronics and medicine. However, there is a significant trade-off between chirality selectivity and SWCNT yield. In this study, a series of CoSO4/SiO2 catalysts containing from 1 to 9 wt% of Co were prepared to systematically study how Co mass loadings affect the chirality selectivity and carbon production yield. SWCNTs were analyzed by spectroscopies and microscopes, while catalysts at three stages of SWCNT synthesis were studied by multiple characterization tools. Our results show that all CoSO4/SiO2 catalysts can grow (9,8) tubes. Specifically, the catalyst containing 3 wt% Co has the highest yield of (9,8) tubes, which grow from metallic Co particles with a size of around 1.2 nm. These Co particles are in-situ produced by reducing small Co9S8 particles of 2 nm in size, while unreduced Co9S8 particles help to stabilize metallic Co particles. High Co mass loadings lead to the formation of large Co and Co9S8 particles, which favor the formation of graphitic carbon and multi-walled carbon nanotubes. These findings provide useful insights to guide the development of novel catalysts for the chiral selective production of SWCNTs.

Synthesis of single-walled carbon nanotubes in rich hydrogen/air flames

We explore the production of single-walled carbon nanotubes (CNTs) in a stream surrounded by rich premixed laminar H2/air flames using a feedstock containing ethanol and ferrocene. The as-produced nanomaterials were characterised by Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray diffraction. A formation window of equivalence ratios of 1.00–1.20 was identified, and single-walled CNT bundles with individual CNTs of an average diameter of 1 nm were observed. The formation of CNTs was accompanied by the production of highly crystalline Fe3O4 nanoparticles of a size of 20–100 nm. The investigation of the limiting factors for the CNT synthesis was carried out systematically, assisted by numerical modelling. We conclude that the key factors affecting CNT synthesis are the surrounding flame temperatures, and the concentration of carbon available for CNT nucleation.

Controlled synthesis of N-type single-walled carbon nanotubes with 100% of quaternary nitrogen

Despite significant improvements in the synthesis of nitrogen (N)-doped carbon nanotubes (CNTs) and their versatile applications, there has always been a large difficulty in controlling the bonding configuration of N atoms within CNTs. In the current work, we report an effective chemical strategy to synthesize single-walled carbon nanotubes (SWNTs) with 100% of quaternary N via a chlorosulfonic acid(CSA) treatment. In this process, the pyridinic and pyrrolic groups were selectively and completely removed while retaining the quaternary N atoms. The presence of 2.04 at. % of quaternary N atoms within SWNTs was directly identified from a single sharp peak in the N 1s spectra of XPS, and indirectly supported by the downshift of C 1s peak in XPS, the upshift of G'-band in Raman spectroscopy, and the decrease of the work function from 5.46 to 4.59 eV. The doping effect of the quaternary N atoms on the macroscopic properties of SWNT fibers was verified by a large increase in the electrical conductivity from 0.63 to 2.17 MS/m. In perspective, our chemical approach can now be applied to synthesize carbon materials with controlled N functionalities for different applications.

Efficient Closed-loop Maximization of Carbon Nanotube Growth Rate using Bayesian Optimization

A major technological challenge in materials research is the large and complex parameter space, which hinders experimental throughput and ultimately slows down development and implementation. In single-walled carbon nanotube (CNT) synthesis, for instance, the poor yield obtained from conventional catalysts is a result of limited understanding of input-to-output correlations. Autonomous closed-loop experimentation combined with advances in machine learning (ML) is uniquely suited for high-throughput research. Among the ML algorithms available, Bayesian optimization (BO) is especially apt for exploration and optimization within such high-dimensional and complex parameter space. BO is an adaptive sequential design algorithm for finding the global optimum of a black-box objective function with the fewest possible measurements. Here, we demonstrate a promising application of BO in CNT synthesis as an efficient and robust algorithm which can (1) improve the growth rate of CNT in the BO-planner experiments over the seed experiments up to a factor 8; (2) rapidly improve its predictive power (or learning); (3) Consistently achieve good performance regardless of the number or origin of seed experiments; (4) exploit a high-dimensional, complex parameter space, and (5) achieve the former 4 tasks in just over 100 hundred experiments (~8 experimental hours) – a factor of 5× faster than our previously reported results.

Effect of Plasma Ignition on the Growth Temperature Decrease of Single-Walled Carbon Nanotubes in a Plasma-Coupled Hybrid Chemical-Vapor-Deposition System

We demonstrate the effect of plasma ignition on the growth temperature decrease of single-walled carbon nanotubes (SWNTs) by using a plasma-coupled hybrid chemical-vapor-deposition system. The horizontal reactor is divided into the plasma ignition region and the SWNT synthesis region. The plasma was generated by using an inductively-coupled system and contributed to efficient decomposition of the feedstock gas. The growth temperature for the SWNTs was suppressed to 500 ◦ C at a plasma power of 400 W with a mixture of C2H4 and H2 gases. The result of optical emission spectroscopy showed H2, Hβ, and CH lines with relatively weak intensities favorable for low-temperature growth of SWNTs.

Synthesis and structural characterization of single-walled carbon nanotubes functionalized with fluorinated phosphonate analogues of phenylglycine, as promising materials for synthetic and biomedical applications

Through chemical functionalization the prerequisites for possible applications of such nanostructures as single-walled carbon nanotubes (SWCNTs) are established. In this study, modifications of SWCNTs by fluorinated phosphonate analogue of phenylglycine, compound belonging to important group of natural amino acid mimetics, using two approaches are presented. The first one was based on noncovalent functionalization of SWCNTs with the phosphono-perfluorophenylglycine analogue. In the second approach, SWCNTs were covalently bonded to the fluorinated α-aminophosphonates in one-step or multi-step reactions. The investigation of the functionalization effect on the dispersibility, thermal properties and the structure of SWCNTs was performed by using of X-Ray spectroscopy, TGA and Raman spectroscopy. Both approaches indicated promising methods for fast and efficient modification of carbon nanotubes (CNTs) also with other representatives of previously synthesized fluorinated aminophosphonates. Functionalized with such compounds CNTs can constitute materials for synthetic and biomedical applications. Due to their biological activity and structural analogy to corresponding α-amino acids, fluorinated α-aminophosphonates provide an important source for drug discovery. Therefore functionalization of SWCNTs with such molecules can provide an important platforms for drug delivery applications. Due to the presence of perfluorinated phenyl rings various nucleophiles can be introduced by nucleophilic aromatic substitution reactions to the functionalized SWCNTs leading to obtaining completely new materials.

Growth Kinetics and Structure Controlled Synthesis of Single-Walled Carbon Nanotubes

Growth Kinetics and Structure Controlled Synthesis of Single-Walled Carbon Nanotubes

Highly Exfoliated and Functionalized Single-Walled Carbon Nanotubes as Fast-Charging, High-Capacity Cathodes for Rechargeable Lithium-Ion Batteries.

Compared with traditional metal-oxide lithium-ion battery (LIB) cathodes, nanocarbon-based cathode materials have received much attention for potential application in LIBs because of their superior power density and long-term cyclability. However, their lithium-ion storage capacity needs further improvement for practical applications, and the trade-off between capacity and conductivity, when oxygen functional groups as lithium-ion storage sites are introduced to the nanocarbon materials, needs to be addressed. Here, we report a sequential oxidation-reduction process for the synthesis of single-walled carbon nanotubes (SWCNTs) for LIB cathodes with fast charging, long-term cyclability, and high gravimetric capacity. A LIB cathode based on highly exfoliated (dbundle < 10 nm) and oxygen-functionalized single-walled carbon nanotubes is obtained via the modified Brodie's method using fuming nitric acid and a mild oxidant (B-SWCNTs). Post treatment including horn sonication and hydrogen thermal reduction developed surface defects and removed the unnecessary C-O groups, resulting in an increase in the Li-ion storage capacity. The B-SWCNTs exhibit a high reversible gravimetric capacity of 344 mA h g-1 at 0.1 A g-1 without noticeable capacity fading after 1000 cycles. Furthermore, it delivers a high gravimetric energy density of 797 W h kgelectrode-1 at a low gravimetric power density of 300 W kgelectrode-1 and retains its high gravimetric energy density of ∼100 W h kgelectrode-1 at a high gravimetric power of 105 W kgelectrode-1. These results suggest that the highly exfoliated, oxygen-functionalized single-walled carbon nanotubes can be applied to LIBs designed for high-rate operations and long cycling.

High-performance transparent conducting films of long single-walled carbon nanotubes synthesized from toluene alone

Single-walled carbon nanotube (SWCNT) transparent conducting films (TCFs) are attracting increasing attention due to their exceptional optoelectronic properties. Toluene is a proposed carbon source for SWCNT synthesis, but the growth parameters of SWCNTs and their TCF optoelectronic performance (i.e., sheet resistance versus transmittance) have been insufficiently evaluated. Here, we have for the first time reported a systematic study of the fabrication of high-performance SWCNT TCFs using toluene alone as the carbon source. The mechanisms behind each observed phenomenon were elucidated using optical and microscopy techniques. By optimizing the growth parameters, high yields of SWCNT TCFs exhibiting a considerably low sheet resistance of 57 Ω/sq at 90% transmittance were obtained. This competitive optoelectronic performance is mainly attributable to long SWCNT bundles (mean length is 41.4 μm) in the film. Additionally, a chirality map determined by electron diffraction displays a bimodal distribution of chiral angles divided at 15°, which is close to both armchair and zigzag edges. Our study paved the way towards scaled-up production of SWCNTs for the fabrication of high-performance TCFs for industrial applications.

Stability of iron-containing nanoparticles for selectively growing single-walled carbon nanotubes

The structure and composition of catalyst particles play crucial roles in growing carbon nanotubes (CNTs) during chemical vapor deposition. Particularly, some bimetallic catalysts have been previously reported to synthesize single-walled carbon nanotubes (SWCNTs) with selective chirality. However, the active phase of such bimetallic catalysts has been rarely investigated and the origin of the SWCNT chirality selectivity remains controversial. To fill this gap, we herein study the evolution of an MgO supported FeCu catalyst with the assistance of environmental transmission electron microscopy. It is revealed that the introduction of CO at 600 °C could reduce the catalyst in which the active phase is determined to be Fe2.5C. Large-diameter Fe2.5C particles fluctuate strikingly and catalyze the synthesis of multi-walled CNTs by a tip-growth mode. Whereas small-diameter Fe2.5C particles exhibit high stability and grow SWCNTs with a base-growth mode. Theoretical simulations reveal that the interfacial formation energy between (6, 5) SWCNT and the popular Fe2.5C (311) surface is the lowest, partially accounting for the high selectivity of (6, 5) SWCNTs. This work sheds more lights on the CNT growth mechanisms and could guide the design of novel catalysts for controlled synthesis of CNTs.

The State of HiPco Single-Walled Carbon Nanotubes in 2019

High-pressure carbon monoxide (HiPco)-synthesized single-walled carbon nanotubes (SWCNTs) have been a widely studied carbon nanomaterial for nearly two decades. It has been the de facto standard for SWCNT research, be it functionalization, separation and purification, or composites, as a result of the consistent, high-quality material that was made available at an affordable price to researchers worldwide. The recent shutdown of the HiPco reactor at Rice University has resulted in a scarcity of HiPco material available to the research community, and a new source of similar SWCNTs is desperately needed. Continued research and development on the design, materials used, and the overall process have led to a new HiPco material, referred to as NoPo HiPCO®, as an alternative to the erstwhile Rice HiPco SWCNTs. In this work, we have compared the two HiPco materials, and aim to provide more clarity for researchers globally on the state of HiPco SWCNTs for research and applications alike in 2019.

Fine-tuning of spark-discharge aerosol CVD reactor for single-walled carbon nanotube growth: The role of ex situ nucleation

We report a development of recently designed apparatus equipped with a spark discharge generator of catalytic nanoparticles for robust aerosol CVD synthesis of single-walled carbon nanotubes. We achieve a profound control over the diameter distribution and the defectiveness of carbon nanotubes produced. By providing a justified comparison of the apparatus with the most abundant aerosol CVD reactor utilizing ferrocene as a catalyst precursor, we reveal the role of the activation procedure: while spark-discharge generator provides aerosol of nanoparticles (ex situ route), the ferrocene vapor decomposes in the nanotube growth zone providing an in situ formation of the catalyst. With other parameters being equal, we reveal the differences in the nanotube growth (diameter and length distribution, yield, defectiveness) employing a comprehensive set of methods (the analysis of differential mobility of the aerosol particles, optical spectroscopy, scanning and transmission electron microscopy, Raman spectroscopy, and atomic force microscopy). We show the ex situ activation in the spark discharge reactor to provide a lower utilization degree of the nanoparticles due to over-coagulation. However, the same method provides an independence of the key performance parameters of the nanotubes opening a room for scaling the apparatus.

Structural characterization of interaction between SWCNTs and 6-phenyl-2-thiouracil by molecular spectroscopic methods

Chemical vapor decomposition (CVD) method is used to synthesize single wall carbon nanotubes (SWCNTs), after purification process COOH functional group modified SWCNTs are obtained via oxidation reaction by using H2SO4/HNO3. 6-Phenyl-2-thiouracil (6P2T) molecule is bonded on the surface of functionalized SWCNTs. Raman spectroscopy was used to characterize bands of SWCNTs and differences among raw SWCNT, functionalized SWCNTs and 6P2T bonded SWCNTs are shown. FT-IR spectra have been used to determine vibrations of SWCNTs and the interaction sites between SWCNTs and 6P2T molecule. XRD and EDX methods indicate removing catalyst materials and amorphous carbon during the purification process.

Diameter-Selective Synthesis of Single-Walled Carbon Nanotubes on Supported Cobalt Catalysts

Supported Co catalysts were prepared by impregnating the support (MgO, SiO2 and Al2O[Formula: see text] with Co(acac)2 solution, and diameter-selective growth of single-walled carbon nanotubes (SWCNTs) by ethanol chemical vapor deposition has been assessed on these Co catalysts. In contrast to Co/SiO2 and Co/Al2O3 catalysts with relatively high surface areas, Co/MgO catalyst with a low surface area demonstrates the best performances in the diameter-selective growth of SWCNTs under an optimal growth condition. Multiple characterizations on catalysts and SWCNTs revealed that Co(acac)2 was absorbed on MgO by ligand exchange and anhydrous solvent CH2Cl2 strengthened the anchoring of Co(acac)2 on the MgO surface, which resulted in well-dispersed Co species upon calcination in air. Under a modest reduction temperature, the reduction of Co oxides provided Co clusters, which were anchored by the unreacted Co ions in the interior of MgO support, leading to the synthesis of SWCNTs with a narrow diameter distribution.

Combinatorial design of molecular seeds for chirality-controlled synthesis of single-walled carbon nanotubes

The chirality-controlled synthesis of single-walled carbon nanotubes (SWCNTs) is a major challenge facing current nanomaterials science. The surface-assisted bottom-up fabrication from unimolecular CNT seeds (precursors), which unambiguously predefine the chirality of the tube during the growth, appears to be the most promising approach. This strategy opens a venue towards controlled synthesis of CNTs of virtually any possible chirality by applying properly designed precursor molecules. However, synthetic access to the required precursor molecules remains practically unexplored because of their complex structure. Here, we report a general strategy for the synthesis of molecular seeds for the controlled growth of SWCNTs possessing virtually any desired chirality by combinatorial multi-segmental assembly. The suggested combinatorial approach allows facile assembly of complex CNT precursors (with up to 100 carbon atoms immobilized at strictly predefined positions) just in one single step from complementary segments. The feasibility of the approach is demonstrated on the synthesis of the precursor molecules for 21 different SWCNT chiralities utilizing just three relatively simple building blocks.

Roles of sulfur in floating-catalyst CVD growth of single-walled carbon nanotubes for transparent conductive film applications

Sulfur is an effective promoter for growing single-walled carbon nanotubes (SWCNTs) and tuning their structural properties. In particular, sulfur has been utilized in the floating-catalyst chemical vapor deposition (FC-CVD) process to fabricate SWCNT-based transparent conductive films (TCFs). However, in-situ catalyst nucleation process in conventional FC-CVD, hinders to correlate the substantial role of sulfur in tuning SWCNTs synthesis and enhancing the performance of SWCNT-based TCFs. Herein, we have for the first time, systematically studied the roles of sulfur on yield, morphology, and structure of SWCNTs grown by FC-CVD, using ex-situ Fe and Co catalyst particles. We found that SWCNT yield is largely dependent on the amount of sulfur introduced into the FC-CVD reactor and on catalyst composition. More importantly, the addition of an optimized amount of sulfur resulted in a three-fold enhancement of the opto-electronic performance of SWCNT-TCFs, by increasing diameter and bundle length along with improving the quality of SWCNTs. Surprisingly, electron diffraction analysis revealed that SWCNTs grown from both Fe and Co display wide chirality distributions spanning from zig-zag to armchair edges, indicating that the sulfur promoter has little influence on the chirality modulating of SWCNTs.

Selective synthesis of metallic and semi-conducting single-walled carbon nanotube by floating catalyst chemical vapour deposition

Selective synthesis of both metallic and semi-conducting single-walled carbon nanotubes (SWCNTs) has been performed using floating catalyst chemical vapour deposition (FC-CVD). It was observed that partial pressure of hydrogen determined the selectivity of SWCNTs being predominantly metallic at lower hydrogen concentration (20 vol%) and predominantly semiconducting at higher hydrogen concentration (80 vol%). The qualitative and quantitative analysis on type of SWCNTs was performed based on UV–vis-NIR, Raman spectra at different wavelengths and SWCNT-based field effect transistor device performance. Transmission electron microscopy was used to get diameter distribution of SWCNTs. Detailed analysis showed that the type of SWCNTs was decided at the nucleation stage that was governed by the collision frequency between hydrogen molecules and iron nanoparticles.

Atomic-scale structural identification and evolution of Co-W-C ternary SWCNT catalytic nanoparticles: High-resolution STEM imaging on SiO2.

Recently, W-based catalysts have provided a promising route to synthesize single-walled carbon nanotubes (SWCNTs) with specific chirality, but the mechanism of the growth selectivity is vaguely understood. We propose a strategy to identify the atomic structure as well as the structure evolution of the Co-W-C ternary SWCNT catalyst. The key is to use a thin SiO2 film as the catalyst support and observation window. As the catalyst is uniformly prepared on this SiO2 film and directly used for the SWCNT synthesis, this method has an advantage over conventional methods: it creates an opportunity to obtain original, statistical, and dynamic understanding of the catalyst. As a technique, atomic-scale imaging directly on SiO2 serves as a powerful and versatile tool to investigate nanocrystals and high-temperature reactions; for the synthesis of SWCNTs, this work successfully visualizes the structure and evolution of the catalyst and illuminates the possible nucleation sites of the chirality-specific growth.