High-quality Single-walled Carbon Nanotubes Research Articles

Bio-based protic salts as precursors for sustainable free-standing film electrodes

Transforming amines with low boiling points and high volatilities into protic salts is a versatile strategy to utilize low molecular weight compounds as precursors for N-doped carbon structures in a straightforward carbonization procedure. Herein, conventional mineral acids commonly used for the synthesis of protic salts were replaced by bio-derived phytic acid, which, combined with various amines and amino acids, yielded partially or fully bio-derived protic salts. The biomass-based salts showed higher char-forming ability than their mineral acid-based analogs (up to 55.9% at 800°), simultaneously providing carbon materials with significant porosity (up to 1177 m2g−1) and a considerable level of N,P,O-doping. Here, we present the first comprehensive study on the correlation between the structure of the bio-derived protic precursors and the properties of derived carbon materials to guide future designs of biomass-derived precursors for the one-step synthesis of sustainable carbon materials. Additionally, we demonstrate how to improve the textural properties of the protic-salt-derived carbons (which suffer from high brittleness) by simply upgrading them into highly flexible nanocomposites using high-quality single-walled carbon nanotubes. Consequently, self-standing electrodes for the oxygen reduction reaction were created.

Upcycling plastic polymers into single-walled carbon nanotubes from a magnesia supported iron catalyst

Plastic waste has posed an ever-growing environmental threat to the United Nations’ sustainable development goals. Converting plastic polymers into high value chemicals like carbon nanotubes is a promising approach for recycling without carbon dioxide emission. Using a two-stage pyrolysis-catalytic reactor, we herein report the transformation of five types of plastic polymers into high-quality single-walled carbon nanotubes (SWNTs) with the assistance of a rationally designed heterogeneous catalyst, i.e., an iron metal catalyst supported by porous magnesia. Because of the high metal dispersion and the large carbon solubility of the active component, the heterogeneous catalyst affords the formation of uniform metal particles which can sustain high carbon fluxes, resulting in the synthesis of high quality SWNTs. More importantly, the approach is also demonstrated with mixtures of plastic polymers. This work helps gain deep insights into the mechanisms of plastic polymer conversion to SWNTs, accelerating the progress toward a sustainable plastic economy.

(Digital Presentation) Wettability of Carbon Nanostructures – Hydrophobic or Hydrophilic?

Nanocarbon nanostructures have significant potential to be applied in: filtration[1], energy storying[2], thermogenerators[3], electronics[4], and part of composite materials due to their enormous properties[2]. They characterized magnificent electrical, thermal, and mechanical properties. Many people think their surface nature is hydrophobic. However, more and more scientific publications present the opposite statement about carbon nanotubes and graphene[5-7]. The reason for hydrophobicity is undefined hydrocarbons, which are adsorbed on the nanocarbon surface. The surface character is a crucial parameter for such applications as: electrode materials for storage energy and integration degree between a part of composites.The surface of fullerene C60, high quality (ID/IG = 0.01) single-walled carbon nanotubes (SWCNTs), single-layer graphene (SLG) deposed on copper foil have been investigated to understand the phenomenon of hydrophobic surface and prove that there are intrinsic hydrophilic. A coating from C60 was deposed on glass by spin coating and free-standing film from SWCNTs by method described in previous work. SLG on Cu was synthesized by CVD method. The water contact angle (WCA) was used to define character of surface. The sample was annealed in atmosphere H2/Ar (C60 and SLG) and air (SWCNTs) to remove surface impurities. WCA was measured after/before annealing. Initial C60 and SWCNTs have hydrophobic (WCA >90), SLG has slightly hydrophilic (about 80 ºC). After annealing the surface, all of them have a strongly hydrophilic character, which was even superhydrophilic for C60 and SWCNTs. The nanomaterials were characterized after/before annealing by many techniques such as: Raman spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, Atomic force microscopy, and Attenuated total reflectance-Fourier transform infrared spectroscopy. All of them showed that the nanostructures had not been damaged during the surface purification process. Moreover, after a month of exposure to air, the WCA has increased. The samples were again analyzed by the techniques mentioned before and the reason for changing the surface characters was hydrocarbons. To indeficate the them selected groups of organic compound was deposed onto nanocarbon surface and the experimental results manifested that aromatic hydrocarbons are the main reason of hydrophobicity of the surface.

Single-walled carbon nanotubes synthesized by laser ablation from coal for field-effect transistors.

Single-walled carbon nanotubes (SWCNTs) have been attracting extensive attention due to their excellent properties. We have developed a strategy of using coal to synthesize SWCNTs for high performance field-effect transistors (FETs). The high-quality SWCNTs were synthesized by laser ablation using only coal as the carbon source and Co-Ni as the catalyst. We show that coal is a carbon source superior to graphite with higher yield and better selectivity toward SWCNTs with smaller diameters. Without any pre-purification, the as-prepared SWCNTs were directly sorted based on their conductivity and diameter using either aqueous two-phase extraction or organic phase extraction with PCz (poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl]). The semiconducting SWCNTs sorted by one-step PCz extraction were used to fabricate thin film FETs. The transformation of coal into FETs (and further integrated circuits) demonstrates an efficient way of utilizing natural resources and a marvelous example in green carbon technology. Considering its short steps and high feasibility, it presents great potential in future practical applications not limited to electronics.

High-quality single-walled carbon nanotube films as current collectors for flexible supercapacitors

High-quality single-walled carbon nanotube films are promising current collectors for flexible supercapacitors.

Efficient Fabrication of High-Quality Single-Walled Carbon Nanotubes and Their Macroscopic Conductive Fibers.

High-purity and well-graphitized single-walled carbon nanotubes (SWCNTs) with excellent physiochemical properties are ideal building blocks for the assembly of various CNT macrostructures for a wide range of applications. We report the preparation of high-quality SWCNTs on a large scale using a floating catalyst chemical vapor deposition (FCCVD) method. Under the optimum conditions, the conversion rate of the carbon source to SWCNTs reached 28.8%, and 20.4% of the metal nanoparticles were active for SWCNT growth, which are 15% and ∼400 times higher than those previously reported for FCCVD synthesis, respectively. As a result, the prepared SWCNTs have a very low residual catalyst content of ∼1.9 wt % and a high rapid oxidation temperature of 717 °C. Using these high-quality SWCNTs, we spun macroscopic SWCNT fibers by a wet-spinning process. The resulting fibers had a high electrical conductivity of 6.67 MS/m, which is 32% higher than the best value previously reported for SWCNT fibers.

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.

Growth of Single-Walled Carbon Nanotubes from Solid Carbon Nanoparticle Seeds via Cap Formation Engineering with a Two-Step Growth Process and Water Vapor Supply.

Solid carbon nanoparticles are promising growth seeds to prepare single-walled carbon nanotubes (SWCNTs) at high temperatures, at which the SWCNT crystallinity should be improved significantly but conventional metal catalyst nanoparticles are unstable and suffer from aggregation. The noncatalytic nature of solid carbon nanoparticles, however, makes SWCNT growth inefficient, resulting in a limited growth yield. In this study, we develop a two-step chemical vapor deposition process to efficiently synthesize high-crystallinity SWCNTs at high temperatures from solid carbon nanoparticles obtained from nanodiamond. Based on thermodynamic considerations, the growth conditions are separately adjusted to supply different growth driving forces which are suitable for the formation of the initial cap structures and for the stationary elongation of SWCNTs. This process, called cap formation engineering, improves the nucleation density of the cap structures. We examined the changes in crystallinity, amorphous carbon deposition, diameter, and yield of SWCNTs with respect to the synthesis conditions. By controlling the initial growth conditions, high-quality SWCNTs are grown with improved yield. With the addition of water vapor as the etchant, deposition of amorphous carbon at high temperatures was further prevented. The results provide a pathway for precise growth control of SWCNTs from unconventional solid growth seeds.

Enhancing thermoelectric properties of single-walled carbon nanotubes using halide compounds at room temperature and above

Carbon nanotubes (CNTs) are materials with exceptional electrical, thermal, mechanical, and optical properties. Ever since it was demonstrated that they also possess interesting thermoelectric properties, they have been considered a promising solution for thermal energy harvesting. In this study, we present a simple method to enhance their performance. For this purpose, thin films obtained from high-quality single-walled CNTs (SWCNTs) were doped with a spectrum of inorganic and organic halide compounds. We studied how incorporating various halide species affects the electrical conductivity, the Seebeck coefficient, and the Power Factor. Since thermoelectric devices operate under non-ambient conditions, we also evaluated these materials' performance at elevated temperatures. Our research shows that appropriate dopant selection can result in almost fivefold improvement to the Power Factor compared to the pristine material. We also demonstrate that the chemical potential of the starting CNT network determines its properties, which is important for deciphering the true impact of chemical and physical functionalization of such ensembles.

High-throughput screening and machine learning for the efficient growth of high-quality single-wall carbon nanotubes

It has been a great challenge to optimize the growth conditions toward structure-controlled growth of single-wall carbon nanotubes (SWCNTs). Here, a high-throughput method combined with machine learning is reported that efficiently screens the growth conditions for the synthesis of high-quality SWCNTs. Patterned cobalt (Co) nanoparticles were deposited on a numerically marked silicon wafer as catalysts, and parameters of temperature, reduction time and carbon precursor were optimized. The crystallinity of the SWCNTs was characterized by Raman spectroscopy where the featured G/D peak intensity (IG/ID) was extracted automatically and mapped to the growth parameters to build a database. 1,280 data were collected to train machine learning models. Random forest regression (RFR) showed high precision in predicting the growth conditions for high-quality SWCNTs, as validated by further chemical vapor deposition (CVD) growth. This method shows great potential in structure-controlled growth of SWCNTs.

Growth of Semiconducting Single-Walled Carbon Nanotubes Array by Precisely Inhibiting Metallic Tubes Using ZrO2 Nanoparticles.

Synthesis of high-quality single-walled carbon nanotubes arrays with pure semiconducting type is crucial for the fabrication of integrated circuits in nanoscale. However, the naturally grown carbon nanotubes usually have diverse structures and properties. Here the bicomponent catalyst using Au and ZrO2 is designed and prepared. The Au nanoparticle serves as the catalysts for carbon feedstock cracking and facilitating the nucleation of carbon nanotubes, whereas the close-connected ZrO2 forms a localized etching zone around Au by releasing lattice oxygen and to inhibit the nucleation of metallic carbon nanotubes precisely. The obtained single-walled carbon nanotubes array show a high semiconducting content of >96%,on the basis of good performance of field-effect transistor devices. And such building of localized etching zone is compatible with other catalyst systems as a universal and efficient method for the scalable production of semiconducting carbon nanotubes.

Initial competing chemical pathways during floating catalyst chemical vapor deposition carbon nanotube growth

Ferrocene (Fc) is an effective precursor for the direct synthesis of high quality single-walled carbon nanotubes (SWCNTs) via floating catalyst chemical vapor deposition (FCCVD). However, the formation mechanism of the Fe floating catalyst and the SWNCT growth precursors, such as carbon chains, during Fc decomposition are not well understood. Here, we report first principles nonequilibrium quantum chemical molecular dynamics simulations that investigate the decomposition of Fc during FCCVD. We examine the influence of additional growth precursors including ethylene, methane, CO, and CO2 on the Fc decomposition mechanism and show that the dissociation of these species into C2Hx radicals and C atoms provides the key growth agents for the nucleation of carbon chains from Fc-derived species such as cyclopentadienyl rings. Without an additional growth precursor, Fc decomposes via the spontaneous cleavage of Fe–C and C–H bonds, thereby enabling Fe atoms to cluster and form the floating catalyst. On the basis of these simulations, we detail the two competing chemical pathways present during the initial stages of FCCVD: Fe catalyst nanoparticle growth and carbon chain growth. The latter is accelerated in the presence of the additional growth precursors, with the identity of the precursor determining the nature of the balance between these competing pathways.

The importance of H2 in the controlled growth of semiconducting single-wall carbon nanotubes

H2 is considered an indispensable component of the atmosphere for the growth of high-quality single-wall carbon nanotubes (SWCNTs) by chemical vapor deposition. However, details of the roles H2 playing are still unclear due to the complex conditions of SWCNT growth. In this study, we elucidate the functions of H2 in the selective growth of semiconducting SWCNTs (s-SWCNTs) by using monodispersed uniform Fe nanoparticles as a catalyst. High-quality s-SWCNTs were synthesized by finely tuning the concentration of H2 and the other growth parameters. Experimental data combined with atomistic simulations indicate that H2 not only adjusts the concentration of the carbon source, but also serves as a mild etchant that selectively removes small carbon caps grown by a perpendicular mode from the Fe nanoparticles. These results provide useful hints for the controlled growth of SWCNTs with a semiconducting or metallic conductivity, and even a specific chirality.

Carburization of Fe/Ni Catalyst for Efficient Growth of Single‐Walled Carbon Nanotubes

Scale-up production of single-walled carbon nanotubes (SWNTs) with high quality and purity is in pursuit, since the subsequent post purification treatment of residual metal or amorphous carbon is complicated and restricts further applications. Here, a compatible method to efficiently synthesize pure SWNTs on various supporters by using the precarburized Fe/Ni catalysts is reported. The preparation of catalysts is achieved by gas phase deposition together with CO gas at proper temperature, and the carburization of metal particles occurring simultaneously contributes to the size limitation of catalysts. By using micro-quartz sand as a recyclable supporter, high-quality SWNTs with a yield of 50 mg h-1 are prepared with 60% metal precursor utilization, 81% carbon source utilization, and only 0.12% (m/m) metal residues. Taking advantage of carburized Fe/Ni catalysts and appropriate supports makes it possible to balance the quantity, purity, and quality among SWNTs growth. Furthermore, this method provides a straightforward pathway to strongly combine SWNTs and diverse composite materials for further potential applications.

Dry-transfer technique for polymer-free single-walled carbon nanotube saturable absorber on a side polished fiber

We fabricate single-walled carbon nanotube saturable absorbers on a side-polished fiber by a dry transfer technique. We demonstrate that this method allows for the easy and robust implementation of polymer-free carbon nanotube film for an evanescent field interaction in the fiber laser cavity. The high-quality single-walled carbon nanotubes are synthesized by the aerosol CVD method with absorption maximum tuned to an erbium doped fiber laser emission line. The Q-switch and mode-lock regimes as well as the harmonic mode-lock regime with the 79th order are successfully demonstrated with this approach. Critical power for damage threshold is estimated.

Single-wall carbon nanotube based electrochemical immunoassay for leukemia detection

A label-free electrochemical immunosensor is fabricated using high quality single-walled carbon nanotube for early detection of leukemia cells. It is based on P-glycoprotein (P-gp) expression level detection; by effective surface immune-complex formation with the monoclonal anti-P-glycoprotein antibodies bound to an epoxy modified nanotube surface. The expression level of P-gp on the leukemia cell surface detected by cyclic voltammetry is in good agreement with immunofluorescence microscopy studies. The proposed biosensor could be used for the detection of P-gp expressing cells within a linear range of 1.5 × 103 cells/mL – 1.5 × 107 cells/mL where lowest detection limit is found to be 19 cells/mL. A calibration plot of peak current v/s the logarithm of concentration of leukemia K562 cells is found linear with a regression coefficient of 0.935. This strategy promises high sensitivity, low-cost, fast, and repeatable recognition of cancer cells. The immunosensor was stable for three weeks and showed good precision with the relative standard deviation (RSD) of 3.57% and 2.12% assayed at the cell concentrations of 1.5 × 103 and 1.5 × 105 cells mL−1 respectively. The proposed single-wall carbon nanotube based immunosensor showed better analytical performance in comparison to similar leukemia electrochemical sensors reported.

Pressure and discharge current dependence of production rate of single-walled carbon nanotubes by the bipolar pulsed arc-discharge method

ABSTRACTBipolar pulsed arc-discharge method has been studied for the efficient production of high quality single-walled carbon nanotubes (SWNTs). Gas pressure and discharge current dependence of this method has been carried out to obtain the optimum production condition. The experimental results show no cathode deposition, and almost all the sublimated carbon becomes soot containing SWNTs. The production rate increases with increasing gas pressure and discharge current. The high production rate with high quality SWNTs is obtained around the conditions of helium gas pressure, p (He) = 50 – 70 kPa and discharge current, Id ≃ 55 A. The morphology of the SWNTs is measured by a TEM and the quality is analyzed by a Raman spectrometer.

CVD Growth of Carbon Nanotube Forest with Selective Wall-Number from Fe–Cu Catalyst

We reported herein the chemical vapor deposition (CVD) growth of vertically aligned carbon nanotubes (CNTs) with selective wall-number using binary Fe–Cu catalysts. High quality single-walled carbon nanotube (SWNT) and double-walled carbon nanotube (DWNT) forests were predominantly produced with selectivity of ∼92% and ∼85%, respectively. Formation of small catalyst nanoparticles with high areal density and fully reduced state was found key for efficient SWNT growth. Characterization of the catalysts by atomic force microanalysis (AFM) and high resolution transmission electron microscope (HRTEM) showed that the introduction of the proper amount of Cu into the Fe/Al2O3 catalyzing system inhibited diffusion of Fe NPs and facilitated the full reduction of Fe catalyst, thus facilitating the selective growth of SWNTs. DWNTs were also obtained by introducing a thick layer of Cu catalyst onto Fe/Al2O3. Our work provides a rational way for selective growth of vertically aligned SWNTs and DWNTs, whose remarkable e...

Growth of high quality, high density single-walled carbon nanotube forests on copper foils

We demonstrate the growth of high quality single-walled carbon nanotube (SWCNT) forests on commercial Cu foils by cold-wall chemical vapor deposition. Time-of-flight secondary ion mass spectrometry was employed to study the effect of annealing on the catalyst evolution with or without an AlOx barrier layer. X-ray photoelectron spectroscopy was used to investigate the chemical states of the catalyst and the barrier layer. SWCNT forests can be reproducibly grown on Cu foils sputter-coated with Al and Fe layers as thin as 6 nm and 0.4 nm, respectively. Al transforms into AlOx on exposure to air and during annealing. Most importantly, such a thin AlOx barrier layer ensures not only the growth of SWCNTs but also an Ohmic contact between the as grown SWCNTs and the Cu base as measured by a two-point probe station. The as-grown SWCNTs exhibit a bimodal distribution of diameters ranging from 0.6 to 4.5 nm, with two peaks centered at 0.8 nn and 2.6 nm, respectively.

Uncovering the ultimate performance of single-walled carbon nanotube films as transparent conductors

The ultimate performance—ratio of electrical conductivity to optical absorbance—of single-walled carbon nanotube (SWCNT) transparent conductive films (TCFs) is an issue of considerable application relevance. Here, we present direct experimental evidence that SWCNT bundling is detrimental for their performance. We combine floating catalyst synthesis of non-bundled, high-quality SWCNTs with an aggregation chamber, in which bundles with mean diameters ranging from 1.38 to 2.90 nm are formed from identical 3 μm long SWCNTs. The as-deposited TCFs from 1.38 nm bundles showed sheet resistances of 310 Ω/□ at 90% transparency, while those from larger bundles of 1.80 and 2.90 nm only reached values of 475 and 670 Ω/□, respectively. Based on these observations, we elucidate how networks formed by smaller bundles perform better due to their greater interconnectivity at a given optical density. Finally, we present a semi-empirical model for TCF performance as a function of SWCNT mean length and bundle diameter. This gives an estimate for the ultimate performance of non-doped, random network mixed-metallicity SWCNT TCFs at ∼80 Ω/□ and 90% transparency.