Controlled Growth of Single-Walled Carbon Nanotube Films by Iron-assisted Floating Solid Catalyst Chemical Vapor Deposition

Single-walled carbon nanotube (SWNT) films, with exciting electronic properties are increasingly important for next-generation technologies. Here, an Iron-assisted floating solid catalyst chemical vapor deposition (IA-FSCCVD) method is developed for the controlled growth of high-quality and high-purity SWNT films. Titanium carbide nanoparticles with a high melting point are used as the solid catalysts, which provide a stable template for SWNT growth through the perpendicular growth mode. Trace amounts of iron are introduced to increase the efficiency of SWNT growth. Gas chromatography measurements and density functional theory show that the gas-phase iron acts as a pre-cracking assistance for the carbon source, promoting the growth of SWNTs. Carbon nanotube films with a high quality (average IG/ID = 166) are successfully prepared, a small diameter deviation (mean diameter of 1.6 nm), and a high content of SWNTs (97%) using the IA-FSCCVD platform. This work provides a powerful way to prepare the carbon nanotube aggregates with a controlled structure.

Multifunctional MXene/Carbon Nanotube Janus Film for Electromagnetic Shielding and Infrared Shielding/Detection in Harsh Environments

Multifunctional, flexible, and robust thin films capable of operating in demanding harsh temperature environments are crucial for various cutting-edge applications. This study presents a multifunctional Janus film integrating highly-crystalline Ti3C2Tx MXene and mechanically-robust carbon nanotube (CNT) film through strong hydrogen bonding. The hybrid film not only exhibits high electrical conductivity (4250 S cm-1), but also demonstrates robust mechanical strength and durability in both extremely low and high temperature environments, showing exceptional resistance to thermal shock. This hybrid Janus film of 15 μm thickness reveals remarkable multifunctionality, including efficient electromagnetic shielding effectiveness of 72 dB in X band frequency range, excellent infrared (IR) shielding capability with an average emissivity of 0.09 (a minimal value of 0.02), superior thermal camouflage performance over a wide temperature range (- 1 to 300 °C) achieving a notable reduction in the radiated temperature by 243 °C against a background temperature of 300 °C, and outstanding IR detection capability characterized by a 44% increase in resistance when exposed to 250 W IR radiation. This multifunctional MXene/CNT Janus film offers a feasible solution for electromagnetic shielding and IR shielding/detection under challenging conditions.

JA, Nasibulin AG. Bithiophene as a Sulfur-Based Promotor for the Synthesis of Carbon Nanotubes and Carbon-Carbon Composites

We assess bithiophene (C8H6S2) as a novel sulfur-based promotor for the growth of single-walled carbon nanotubes (SWCNTs) in the aerosol (floating catalyst) CVD method. Technologically suitable equilibrium vapor pressure and an excess of hydrocarbon residuals formed under its decomposition make bithiophene an attractive promoter for the production of carbon nanotubes in general and specifically for ferrocene-based SWCNT growth. Indeed, we detect a moderate enhancement in the carbon nanotube yield and a decrease in the equivalent sheet resistance of the films at a low bithiophene content, indicating the improvement of the product properties. Moreover, the relatively high concentrations and low temperature stability of bithiophene result in non-catalytical decomposition, leading to the formation of pyrolytic carbon deposits; the deposits appear as few-layer graphene structures. Thus, bithiophene pyrolysis opens a route for the cheap production of hierarchical composite thin films comprising carbon nanotubes and few-layer graphene, which might be of practical use for hierarchical adsorbents, protective membranes, or electrocatalysis.

Large-Scale, Lightweight, and Robust Nanocomposites Based on Ruthenium-Decorated Carbon Nanosheets for Deformable Electrochemical Capacitors

Despite the increase in demand for deformable electrochemical capacitors as a power source for wearable electronics, significant obstacles remain in developing these capacitors, including their manufacturing complexity and insufficient deformability. With recognition of these challenges, a facile strategy is proposed to fabricate large-scale, lightweight, and mechanically robust composite electrodes composed of ruthenium nanoparticles embedded in freestanding carbon nanotube (CNT)-based nanosheets (Ru@a-CNTs). Surface-modified CNT sheets with hierarchical porous structures can behave as an ideal platform to accommodate a large number of uniformly distributed Ru nanoparticles (Ru/CNT weight ratio of 5:1) while improving compatibility with aqueous electrolytes. Accordingly, Ru@a-CNTs offer a large electrochemically active area, showing a high specific capacitance (∼253.3 F g^-1) and stability for over 2000 cycles. More importantly, the exceptional performance and mechanical durability of quasi-solid-state capacitors assembled with Ru@a-CNTs and a PVA-H₃PO₄ hydrogel electrolyte are successfully demonstrated in that 94% of the initial capacitance is retained after 100 000 cycles of bending deformation and a commercial smartwatch is charged by multiple cells. The feasible large-scale production and potential applicability shown in this study provide a simple and highly effective design strategy for a wide range of energy storage applications from small- to large-scale wearable electronics.

High Purity Single Wall Carbon Nanotube by Oxygen-Containing Functional Group of Ferrocene-Derived Catalyst Precursor by Floating Catalyst Chemical Vapor Deposition

Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst’s exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (−OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate (SO42−) than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal−sulfur bonds (such as S2− and Sn2−). The hydroxyl group (−OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.

Waste NR Latex Based-Precursors as Carbon Source for CNTs Eco-Fabrications

In this work, the potential of utilizing a waste latex-based precursor (i.e., natural rubber glove (NRG)) as a carbon source for carbon nanotube (CNT) fabrication via chemical vapor deposition has been demonstrated. Gas chromatography-mass spectroscopy (GC-MS) analysis reveals that the separation of the lightweight hydrocarbon chain from the heavier long chain differs in hydrocarbon contents in the NRG fraction (NRG-L). Both solid NRG (NRG-S) and NRG-L samples contain >63% carbon, <0.6% sulfur and <0.08% nitrogen content, respectively, as per carbon-nitrogen-sulfur (CNS) analysis. Growth of CNTs on the samples was confirmed by Raman spectra, SEM and TEM images, whereby it was shown that NRG-S is better than NRG-L in terms of synthesized CNTs yield percentage with similar quality. The optimum vaporization and reaction temperatures were 350 and 800 °C, respectively, considering the balance of good yield percentage (26.7%) and quality of CNTs (I_D/I_G = 0.84 ± 0.08, diameter ≈ 122 nm) produced. Thus, utilization of waste NRG as a candidate for carbon feedstock to produce value-added CNTs products could be a significant approach for eco-technology.

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.

The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promising method for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) method is a rapid process that achieves catalyst formation, CNT nucleation and growth, and aerogel-like sock formation within a few seconds. However, the formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalyst composition to CNT fiber synthesis and their structural properties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposes and generates various secondary hydrocarbon species, such as CH₄ , C₂ H₄ , C₂ H₂ , C₃ H₆ , and C₄ H₁₀ whereas monometallic catalysts generate only CH₄ and C₂ H₄ on decomposition. CNT fiber formation with Fe₁ Ni₀ begins about 400 mm from the reactor entrance, whereas CNT formation with Fe_0.8 Ni_0.2 and Fe_0.5 Ni_0.5 begins at about 500 and 300 mm, respectively. The formed CNT bundles and individual CNTs are oriented along the gas flow at these locations. The enhanced rate of fiber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effects between the two metals. The synthesized CNTs become predominantly semiconducting with increasing Ni contents.

High throughput production of single-wall carbon nanotube fibres independent of sulfur-source

Floating catalyst chemical vapor deposition (FC-CVD) methods offer a highly scalable strategy for single-step synthesis and assembly of carbon nanotubes (CNTs) into macroscopic textiles. However, the non-uniform axial temperature profile of a typical reactor, and differing precursor breakdown temperatures, result in a broad distribution of catalyst particle sizes. Spun CNT fibres therefore contain nanotubes with varying diameters and wall numbers. Herein, we describe a general FC-CVD approach to obtain relatively large yields of predominantly single-wall CNT fibres, irrespective of the growth promoter (usually a sulfur compound). By increasing carrier gas (hydrogen) flow rate beyond a threshold whilst maintaining a constant C : H2 mole ratio, CNTs with narrower diameters, a high degree of graphitization (G : D ratio ∼100) and a large throughput are produced, provided S : Fe ratio is sufficiently low. Analysis of the intense Raman radial breathing modes and asymmetric G bands, and a shift in the main nanotube population from thermogravimetric data, show that with increasing flow rate, the fibres are enriched with small diameter, metallic CNTs. Transmission electron microscopy corraborates our primary observation from Raman spectroscopy that with high total flow rates, the fibres produced consist of predominantly small diameter SWCNTs.

Influence of the Sulfur Content Catalyst on the Packing Density of Carbon Nanotube Forests

For the fabrication of high-performance carbon nanotube (CNT) composites with practical applicability, the development of new methods for the controlled growth of high-aspect-ratio CNTs still constitutes a challenge. With the aim of gaining a deeper understanding of the catalytic CNT growth, in this study, the effect of the catalyst composition is investigated using different mixtures of Fe₂(SO₄)₃ and FeCl₂ as catalysts. The relationship between the catalyst chemical state and the growth behavior of CNT forests is demonstrated by evaluating the alignment, diameter, length, and areal density of the CNT forests. When the Fe₂(SO₄)₃ content is increased, the area density, the I_G/I_D ratio, and the crystallite size of the CNTs increase. Additionally, the obtained CNT forests exhibit good spinnability with increasing the sulfur content.

The Dependence of CNT Aerogel Synthesis on Sulfur-driven Catalyst Nucleation Processes and a Critical Catalyst Particle Mass Concentration

The floating catalyst chemical vapor deposition (FC-CVD) process permits macro-scale assembly of nanoscale materials, enabling continuous production of carbon nanotube (CNT) aerogels. Despite the intensive research in the field, fundamental uncertainties remain regarding how catalyst particle dynamics within the system influence the CNT aerogel formation, thus limiting effective scale-up. While aerogel formation in FC-CVD reactors requires a catalyst (typically iron, Fe) and a promotor (typically sulfur, S), their synergistic roles are not fully understood. This paper presents a paradigm shift in the understanding of the role of S in the process with new experimental studies identifying that S lowers the nucleation barrier of the catalyst nanoparticles. Furthermore, CNT aerogel formation requires a critical threshold of Fe_xC_y > 160 mg/m³, but is surprisingly independent of the initial catalyst diameter or number concentration. The robustness of the critical catalyst mass concentration principle is proved further by producing CNTs using alternative catalyst systems; Fe nanoparticles from a plasma spark generator and cobaltocene and nickelocene precursors. This finding provides evidence that low-cost and high throughput CNT aerogel routes may be achieved by decoupled and enhanced catalyst production and control, opening up new possibilities for large-scale CNT synthesis.

Accurate measurement of specific tensile strength of carbon nanotube fibers with hierarchical structures by vibroscopic method

Since carbon nanotube (CNT) fibers have a hierarchical structure, the specific strength of CNT fibers can be estimated to be much higher than its real value when the linear density of the fiber is measured using the vibroscopic method.

Carbon nanotube fibers and films: synthesis, applications and perspectives of the direct-spinning method

The direct-spinning method of creation of CNT macroassemblies has received a lot of attention because of its simplicity to produce high-performance material without apparent limits to its size. CNT fibers or films have shown unparalleled properties and opened new areas of research and commercial development. The process designed more than a decade ago has already given interesting information about the basic science of nanomaterials, which in parallel led to the creation of the first prototypes with high potential of implementation in everyday life. Because of this, there has been growing interest in this technique with research articles coming into view from all around the world on a frequent basis. This review aims to summarize all the progress made in the direct-spinning process on a spectrum of fronts ranging from the study of complex synthesis parameters, material properties to its viable applications. The strong and weak points of the "Cambridge process" are carefully evaluated to put forward what challenges are most pressing. The future overlook puts the state of the art into perspective and suggests the prospective research directions.