Production Of Single-walled Carbon Nanotubes Research Articles

The Low-Temperature Growth of Carbon Nanotubes Using Nickel Catalyst

This study presents the results of a comprehensive investigation into the fabrication of single-walled carbon nanotubes (SWCNTs) employing chemical vapor deposition (CVD) technique, with nickel nanoparticles serving as crucial catalysts. These nanoparticles are synthesized via the reduction of oxide precursors using hydrogen and are strategically incorporated with ethanol vapor as the primary carbon source. The effectiveness and reproducibility of this synthesis method are thoroughly validated using advanced analytical techniques. Particularly noteworthy is the demonstrated ability to conduct the process at relatively low temperatures, not exceeding 500°C, which is of significant importance. Such precise control over synthesis conditions not only augurs well for the scalability of SWCNT production but also carries substantial implications for the advancement of nanomaterial synthesis methodologies.

One-step separation of high-purity single-chirality single-wall carbon nanotubes using sodium hyodeoxycholate

Chirality separation of single-wall carbon nanotubes (SWCNTs) is key to enabling applications in single photon sources, optoelectronic devices and bioimaging, and it generally requires multiple separation steps to obtain single chirality species with the desired purity. In this work, we report the use of a novel sodium hyodeoxycholate (SHC) surfactant for separation of single-chirality SWCNTs. The results demonstrated that chirality-selective adsorption and desorption of SWCNTs on a gel column can be achieved readily by modulating the concentrations of the SHC-based mixed surfactants. Through an optimized one-step procedure, single-chirality (6,5) SWCNTs were successfully separated, and the chirality purity was estimated to be 97% by using a spectroscopic approach, exceeding most reported purities for traditional surfactant-based one- or multiple-step separations. Due to the ultrahigh chirality resolution of the present method, the (6,5) SWCNTs can also be effectively separated from different SWCNT materials with various diameter or chirality distributions, even from materials containing very few (6,5) SWCNTs. The high-purity chirality separation demonstrated in this work lays an important foundation for the industrial production and applications of single-chirality SWCNTs.

The improvement of yield and thermal stability of single-walled carbon nanotubes fabricated by Gd-assisted FCCVD

In this work, single-walled carbon nanotubes (SWNTs) were synthesized by a scalable floating catalyst chemical vapor deposition (FCCVD) method, in which Gd was used as growth promotor to improve the yield and quality of SWNTs. Based on the characterization results of electron microscope, thermogravimetric analysis and Raman spectroscopy, the application of Gd leads to a great increase in the production of large-diameter SWNTs with a narrow diameter distribution and an enhanced thermal stability. The newly developed FCCVD technique makes it possible to produce large-diameter SWNTs at a low cost, and the generated structurally homogenous SWNTs are suitable for their applications in the fields of electronic systems and electromagnetic shielding, etc.

Machine learning methods for aerosol synthesis of single-walled carbon nanotubes

This work is devoted to the strategy towards the optimal development of multiparametric process of single-walled carbon nanotube (SWCNT) synthesis. Here, we examine the implementation of machine learning techniques and discuss features of the optimal dataset size and density for aerosol chemical vapor deposition method with a complex carbon source. We employ the dataset of 369 points, comprising synthesis parameters (catalyst amount, temperature, feed of carbon sources) and corresponding carbon nanotube characteristics (yield, quality, structure, optoelectrical figure of merit). Assessing the performance of six machine learning methods on the dataset, we demonstrate Artificial Neural Network to be the most suitable approach to predict the outcome of synthesis processes. We show that even a dataset of 250 points with the inhomogeneous distribution of input parameters is enough to reach an acceptable performance of the Artificial Neural Network, wherein the error is most likely to arise from experimental inaccuracy and hidden uncontrolled variables. We believe our work will contribute to the selection of an appropriate regression algorithm for the controlled carbon nanotube synthesis and further development of an autonomous synthesis system for an “on-demand” SWCNT production.

Subnanometer Single-Walled carbon nanotube growth from Fe-Containing Layered double hydroxides

High-quality single-walled carbon nanotubes (SWNTs) were synthesized on layered double hydroxides (LDHs) containing Fe and FeCo by CO chemical vapor deposition (CVD). Systematic investigations were performed to study the effects of temperature and catalyst composition on the diameter and chirality distributions of SWNTs. It was revealed that both catalysts produced subnanometer SWNTs at low reaction temperatures, correlated with the catalyst performances and reaction parameters. Particularly, SWNTs with enriched (6, 5) species were synthesized at 600 °C from LDHs containing bimetallic FeCo. Besides, the SWNT chirality distribution was further narrowed by a two-phase extraction method and the extracted (6, 5) SWNTs occupy about 57% of all semiconducting species. This work extends the development of robust LDH-based catalysts for chirality-selective synthesis of SWNTs, which paves the way to large scale production of subnanometer SWNTs for potential applications in electronics and optoelectronics.

Precise Catalyst Production for Carbon Nanotube Synthesis with Targeted Structure Enrichment

The direct growth of single-walled carbon nanotubes (SWCNTs) with a narrow distribution of diameter or chirality remains elusive despite significant benefits in properties and applications. Nanoparticle catalysts are vital for SWCNT synthesis, but how to precisely manipulate their chemistry, size, concentration, and deposition remains difficult, especially within a continuous production process from the gas phase. Here, we demonstrate the preparation of W6Co7 alloyed nanoparticle catalysts with precisely tunable stoichiometry using electrospray, which remain solid state during SWCNT growth. We also demonstrate continuous production of liquid iron nanoparticles with in-line size selection. With the precise size manipulation of catalysts in the range of 1–5 nm, and a nearly monodisperse distribution (σg < 1.2), an excellent size selection of SWCNTs can be achieved. All of the presented techniques show great potential to facilitate the realization of single-chirality SWCNTs production.

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.

Electric Property Change of Single-Walled Carbon Nanotube by the Encapsulation of Aliphatic Thiols.

The encapsulation of single-walled carbon nanotubes (SWNTs) with aliphatic thiol compounds with a relatively small amount of ionization energy achieves n-type doping of SWNTs. Thiol compounds encapsulated inside nanotubes in vacuum drastically change the electric properties of SWNTs by a charge transfer between the two species. The simplicity of the synthetic process offers a viable route for large-scale production of SWNTs with controlled doping states by using mat-type SWNTs. Optical characterization (Raman and near-infrared spectrum) and electric property (conductivity) reveals that a charge transfer between the SWNTs and compounds occurs through the difference in the ionization energy and electron affinity. We confirm an electron density change in SWNTs through optical spectroscopy and conductivity measurement in vacuum. X-ray photoelectron spectroscopy also reveals that the compounds are predominantly encapsulated inside SWNTs.

Catalyst effect on the preparation of single-walled carbon nanotubes by a modified arc discharge

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharge furnace using 500 Torr helium as buffer gas at 600 °C. The effect of the catalyst type on the production of SWCNTs was studied by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results indicated that the catalyst composition plays an important role in the production rate and purity of the SWCNTs product. Fe-Ni-Mg and Co-Ni powder catalysts demonstrated excellent catalytic effect at a catalyst content of 3 wt%. The soot production rate was up to 15 g/hr and the mean diameter of SWCNTs was about 1.3 nm.

Flame-assisted chemical vapor deposition for continuous gas-phase synthesis of 1-nm-diameter single-wall carbon nanotubes

Flame synthesis enables the mass-production of carbon black and fullerene but not of carbon nanotubes (CNTs) due to the narrow window for producing CNTs while preventing tar generation. We report a flame-assisted chemical vapor deposition method, in which a premixed flame is used for the instantaneous generation of floating catalysts, the heating of the gas, and the growth of single-wall CNTs (SWCNTs) using a furnace at the downstream of the flame. This method yields high quality SWCNTs with a small average diameter of 0.96 nm, a small diameter deviation of 0.21 nm, and a high carbon purity of ∼90 wt%. Multiple parameters affect the SWCNT production significantly, which are investigated systematically and optimized carefully. The effects and possible mechanisms of the key parameters are discussed.

Influence of chemical functionalization on the thermoelectric properties of monodispersed single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) networks have attracted great attention for electronic and energy-harvesting applications, including thermoelectric (TE) devices. However, the simultaneous production of metallic SWCNTs (m-SWCTNs) and semiconducting SWCNTs (s-SWCNTs) randomly with distinct electronic structures always hinders the specific usage. The investigation of the influence of different electronic structures by nature or artificially on the TE performances of monodispersed SWCNTs is significative. In this report, high purity of separated m- and s-SWCNTs was chemically functionalized with 4-bromobenzene diazonium tetrafluoroborate, leading to the hybridization of C atoms changed from sp2 to sp3. The influence of the electronic type of SWCNTs on the TE properties as a function of the modifier agent was systematically investigated. As a consequence, the maximum power factor of s-SWCNTs networks was as high as 244.2 μW m−1 K−2 under the optimal condition, whereas it was only 5.3 μW m−1 K−2 for m-SWCNTs networks. In addition, grafting of functional groups onto the sidewall of nanotubes was predicted to further decrease the thermal conductivity, which is beneficial to increment of the ZT values. Based on these results, we believe that the pure s-SWCNTs and a variety of chemically functionalized composites have great potential as candidate for TE applications.

Catalysts for single-wall carbon nanotube synthesis—From surface growth to bulk preparation

Abstract

Perspectives of Single-Wall Carbon Nanotube Production in the Arc Discharge Process

<p>Single-wall carbon nanotubes (SWNTs) promise wide applications in many technical fields. As a result purified SWNT material is sold now on the West market at more than $1000 per 1 gram. Thus developing an effective technology for SWNTs production rises to a very important scientific problem. The perspectives of three existing methods providing raw material in the technology of SWNT production have been analyzed. They are i) pulsed laser evaporation of graphite/metal composites, ii) evaporation of graphite electrodes with metal content in the arc discharge process, and iii) catalytic decomposition of the mixture of CO and metal carbonyl catalyst precursor. The observed dynamics of SWNT market points to replacing the laser method of SWNTs production by the arc process. The conclusion has been made that the technology based on the arc process will be the major one for the fabrication of purified SWNTs at least for the next five years. A reliable estimation of a low price limit of SWNTs was derived from a comparison of two technologies based on the arc discharge process: the first one is the production of SWNTs and the second one is the production of a fullerene mixture С<sub>60</sub> + С<sub>70</sub>. The main conclusion was made that the price of purified SWNTs should always be more by 2-3 times the price of fullerene mixture. The parameters of a lab-scale technology for the production of purified SWNTs are listed. A large-scale application of the developed technology is expected to reduce the price of purified SWNTs by approximately ten times. The methods now employed for the characterization of products containing SWNTs are briefly observed. It is concluded that electron microscopy, thermogravimetric analysis, absorption and Raman spectroscopy, measurement of the specific surface aria, optical microscopy – each in separation is not enough for extensive characterization of a sample containing SWNTs, and all these methods should be used together.</p>

Exposure Assessment in a Single-Walled Carbon Nanotube Primary Manufacturer.

This study was aimed at documenting and characterizing occupational exposure to single-walled carbon nanotubes (SWCNTs) generated in a primary manufacturing plant. It also compared various strategies of exposure monitoring. A 6-day measurement protocol was scheduled (D1-D6) including both (i) quasi-personal monitoring with an array of direct reading instruments (DRIs) and (ii) offline electron microscopy analyses of surface and breathing zone filter-based samples. The first step (D1 and D2) consisted of contamination screenings resulting from the various SWCNT production tasks using a multimetric approach. Surface sampling was also carried out to assess workplace cross-contamination. The second step (D3-D6) focused on the exposure monitoring during recovery/cleaning task, by comparing three personal elemental carbon (EC) measurements [respirable EC using a cyclone following the NIOSH 5040 method (REC-CYC), respirable and thoracic EC using parallel particle impactors [REC-PPI and TEC-PPI, respectively)] and gravimetric mass concentration measurements. DustTrak DRX and electrical low-pressure impactor measurements indicated that particles were released during weighing, transferring, and recovery/cleaning tasks of the manufacturing process. Electron microscopy revealed the presence of agglomerated SWCNTs only during the recovery/cleaning task. REC-CYC concentrations remained under the limits of quantification; REC-PPI showed levels up to 58 µg m-3; and TEC-PPI ranged from 40 to 70 µg m-3. Ratios calculated between gravimetric measurements and estimated DustTrak mass concentrations ranged from 2.8 to 4.9. Cross-contamination appeared to be limited since SWCNTs was only found on surface samples collected close to the reactor in the production room. This case study showed that the DustTrak DRX should be the preferred device among DRIs to identify potential exposure to SWCNTs. However, there is a risk of false positive since it is a non-specific instrument; therefore, the actual release of SWCNTs must be confirmed with scanning electron microscopy/transmission electron microscopy analyses. Besides, using EC measurements as a proxy for SWCNT exposure assessments, as suggested by the NIOSH, is still challenging since interferences can occur with other EC sources such as carbon black, which is also present in the workplace.

Biodegradation of Single-Walled Carbon Nanotubes in Macrophages through Respiratory Burst Modulation.

The biodegradation of carbon nanotubes (CNTs) may be one of major determinants of the toxic outcomes in exposed individuals. In this study, we employed a macrophage/monocyte model, Raw264.7, to investigate the feasibility of regulating the biodegradation of three types of single-walled carbon nanotubes (SWCNTs) (pristine, ox-, and OH-SWCNTs) by respiratory burst modulation. An artificial fluid mimicking the enzymatic reactions of respiratory burst was constituted to reveal the role of respiratory burst played in SWCNT biodegradation. The biodegradation of SWCNTs were characterized by Raman, ultraviolet-visible-near-infrared spectroscopy, and transmission electron microscopy. Our results showed significantly accelerated biodegradation of ox-SWCNTs and OH-SWCNTs in macrophages activated by phorbol myristate acetate (PMA), which could be prevented by N-acetyl-l-cysteine (NAC), whereas p-SWCNTs were resistant to biodegradation. Similar tendencies were observed by using the in vitro enzymatic system, and the degradation rates of these SWCNTs are in the order of OH-SWCNTs > ox-SWCNTs >> p-SWCNTs, suggesting a pivotal role of respiratory burst in accelerating the biodegradation of SWCNTs and that defect sites on SWCNTs might be a prerequisite for the biodegradation to occur. Our findings might provide invaluable clues on the development of intervention measurements for relieving the side effects of SWCNTs and would help to design safer SWCNT products with higher biodegradability and less toxicity.

Phototransformation-Induced Aggregation of Functionalized Single-Walled Carbon Nanotubes: The Importance of Amorphous Carbon.

Single-walled carbon nanotubes (SWCNTs) with proper functionalization are desirable for applications that require dispersion in aqueous and biological environments, and functionalized SWCNTs also serve as building blocks for conjugation with specific molecules in these applications. In this study, we examined the phototransformation of carboxylated SWCNTs and associated amorphous carbon impurities in the presence or absence of H2O2 under simulated sunlight conditions. We found that while carboxylated SWCNTs were rather unreactive with respect to direct solar photolysis, they photoreacted in the presence of H2O2, forming CO2 and strongly aggregated SWCNT products that precipitated. Photoreaction caused SWCNTs to lose oxygen-containing functionalities, and interestingly, the resulting photoproducts had spectral characteristics similar to those of parent carboxylated SWCNTs whose amorphous carbon was removed by base washing. These results indicated that photoreaction of the amorphous carbon was likely involved. The removal of amorphous carbon after indirect photoreaction was confirmed with thermogravimetric analysis (TGA). Further studies using carboxylated SWCNTs with and without base washing indicate that amorphous carbon reduced the extent of aggregation caused by photoreaction. The second-order rate constant for carboxylated SWCNTs reacting with (•)OH was estimated to be in the range of 1.7-3.8 × 10(9) MC(-1) s(-1). The modeled phototransformation half-lives fall in the range of 2.8-280 days in typical sunlit freshwaters. Our study indicates that photosensitized reactions involving (•)OH may be a transformation and removal pathway of functionalized SWCNTs in the aquatic environment, and that the residual amorphous carbon associated with SWCNTs plays a role in SWCNT stabilization.

Viscoelasticity of Single-Walled Carbon Nanotubes in Unsaturated Polyester Resin: Effects of Purity and Chirality Distribution

The recent commercialization of single-walled carbon nanotubes (SWNT) with controlled chirality distributions has created new opportunities for producing SWNT materials with tailored electrical properties. However, there has been relatively little research on understanding the effects of chirality distribution and SWNT purity on the two main determinants of nanocomposite mechanical properties: dispersion microstructure and nanotube–resin interactions. To establish a framework for comparing dispersion and interactions, we investigated the viscoelasticity of four SouthWest NanoTechnologies’ SWNT products: a low and high purity semiconducting grade and a low and high purity metallic grade. Optical microscopy of the dispersions did not show any significant differences between the SWNT types. However, analysis of the dispersions’ viscoelastic properties revealed the difference in dispersion microstructure and the relative strength of SWNT–resin interactions. While all four products had a similar percolation th...

Chemisorbed nickel catalyst for the production of SWCNTs with a very narrow size distribution

The synthesis of single-walled carbon nanotubes (SWCNTs) with the narrowest possible diameter distribution is a challenging undertaking in carbon nanoscience, which can be overcome through the fabrication of monodisperse catalytic nanoparticles. A technique is presented here to approach the diameter control of SWCNTs using a chemisorbed nickel acetylacetonate monolayer at the surface of silica. We show by Fourier transform infrared spectroscopy and thermogravimetry coupled with mass spectroscopy that a monolayer of nickel acetylacetonate is anchored with the silanol groups at the surface of the substrate. After thermal decomposition, the nickel remains bonded with these silanol groups, resulting in a good dispersion of the nickel over the silica surface. Using this catalyst, SWCNTs with a narrow diameter distribution were synthesized at moderate temperature. This opens new perspectives for the fabrication of uniform-diameter carbon nanotubes.

Effect of ammonia gas addition to the synthesis environment of single-walled carbon nanotubes on their surface chemistry

This study evaluates the effect of ammonia gas addition on synthesis environment and surface chemistry of single-walled carbon nanotubes (SWCNTs) produced by induction thermal plasma system (ITP). The experiments were carried out based on the opposed-flow injection of ammonia into the ITP reactor used for mass production of SWCNTs containing soot. The influence of in situ ammonia injection on the SWCNT final products was closely examined by Raman spectroscopy at three wavelengths, coupled thermogravimetry-infrared spectroscopy (TG-FTIR) and solid-phase infrared spectroscopy. The results clearly indicated the surface modification of SWCNTs where the metallic tubes had a greater tendency than the semiconducting tubes to react with ammonia at high temperature. To better understand the reaction system and predict the concentration profile of the intermediates and the product species from thermal decomposition of ammonia in the ITP reactor, a numerical simulation was developed including both the detailed kinetic of ammonia decomposition and turbulent mixing in the reaction system. By comparing the experimental and simulation results, a two-step reaction mechanism is suggested for this in situ SWCNTs chemistry in which the reaction of atomic hydrogen and amidogen radicals with SWCNTs, is followed by the ammonia chemisorption.

Biological impact of as‐produced and purified Single Wall Carbon Nanotube in Kidney epithelial cells.

Single Wall carbon nanotubes (SWCNT), due to their unique and outstanding properties, have generated extraordinary interest and expectations for industrial and biomedical applications. The increasing mass production of SWCNT requires their biocompatibility studies to prevent the possible health hazards among workers involved in the research, manufacturing of these materials and in the general public. The as‐produced and purified SWCNT were characterized by FESEM, TEM, FTIR and the purity was checked by TGA and EDS. Kidney epithelial cell lines were used to investigate the biological impact induced by as‐produced and purified SWCNT. Our results showed a significant amount of incorporation of dUTPs in the nucleus in the as‐produced single wall carbon nanotube confirming the induction of apoptosis, which was also validated by DNA fragmentation assay. The activity of caspases‐3 and caspase‐8 in as‐produced SWCNT increased in a dose and time dependent manner in comparison with the purified SWCNT parallel to the morphological apoptosis. Also the decrease in the antioxidants levels like SOD, GSH was in a higher ratio with the as‐produced SWCNT compared to purified SWCNT. Together, we present a complete evaluation of stress levels induced, antioxidants depletion, activation of caspase cascade by as‐produced and purified SWCNTs.