Growth Mechanism Of Carbon Nanotubes Research Articles

Experimental and theoretical aspects of the growth of vertically aligned CNTs by CCVD on AZO substrate

An efficient and reproducible growth of vertically aligned carbon nanotubes by CCVD requires accurate and specific setting of the synthesis parameters and the properties of catalyst thin layers. In this work, the growth of vertically aligned carbon nanotubes onto AZO (= aluminum doped zinc oxide) glass substrate covered by Al2O3 and Fe-Co catalyst layer system is presented. Investigation of the effect of catalyst composition and synthesis temperature on CVD growth revealed the optimum condition of the synthesis. The analysis of as-prepared samples by SEM, TEM and Raman spectroscopy was carried out to prove the structure and quality of carbon deposit. Theoretical considerations have supported speculative ideas about the role of the support layer, the transformation of the catalyst layer in the presence of hydrogen gas and the growth mechanism of carbon nanotubes. The mechanism of CNT growth is modelled and the order of magnitude of experimentally observed vertical linear growth rate of CNT (several nm/s) is reproduced.

Influence of platinum content (X) in the LaNi5PtX catalyst and reaction conditions on the properties of ferromagnetic Ni-filled CNTs

This research highlights the synthesis of carbon nanostructures using the catalytic chemical vapor deposition (CCVD) method, a hybrid process combining chemical vapor deposition (CVD) and Gas-Solid Heterogeneous Catalysis (GSHC). Intermetallic catalysts, LaNi5Ptx (x = 0, 0.05, 0.5, 1.0), were fabricated through an arc melting procedure to serve as templates for the catalytic conversion of carbon precursors into solid materials. These catalysts, featuring the ferromagnetic transition metal Ni, tend to aggregate into larger particles, reducing the rate of hydrocarbon cracking at the catalyst surface. Rare earth metals like Lanthanum were introduced to form an alloy with a higher melting point to prevent thermal aggregation. Additionally, Pt was incorporated to modify the catalytic properties of the alloy. The study primarily explores the impact of catalyst composition on carbon nanotube (CNT) production. The introduction of platinum content to the catalyst influences the rate at which Ni is filled. The research aimed to alter the catalyst's composition by varying platinum doping in the Pauli paramagnetic lanthanum nickel alloy (LaNi5) to understand the growth mechanism and morphological variations of Ni-filled CNTs. Platinum and lanthanum oxides significantly influence nickel filling in CNTs, resulting in an increased filling rate as the catalyst's Pt content varies from 0 to 1.0. However, higher Pt doping content disrupts the CNT structure with spontaneous nickel encapsulation.

A substrate constituent Na-catalyzed growth of carbon nanotubes on glass substrate by atmospheric pressure PECVD

A growth mechanism of carbon nanotubes (CNTs) without any externally added catalyst is reported in this study. Instead of any externally added catalyst, the constituents of the used soda lime glass substrates seem to play the pivotal role in the growth of CNTs. XPS analysis of the synthesized CNTs reveal that among the various constituents of soda lime glass, sodium (Na) emerges as the primary catalyst for initiating CNT growth. The adopted PECVD technique involving an especially designed spiral-shaped fused hollow cathode source for generating the required atmospheric pressure plasma makes such synthesis easily feasible. The important key factors influencing CNT growth include substrate temperature and plasma pre-treatment of the substrate. Plasma pre-treatment of the substrate at an elevated temperature leads to the formation of catalyst nanoparticles on the surface of the substrate. This report features a detailed CNT growth mechanism proposed on the basis of optical emission spectroscopy and XPS analyses. To be precise, this study demonstrates a novel Na-catalysed synthetic approach for achieving uniform CNT growth on glass substrates without using any externally added catalyst, facilitating the preparation of clean CNTs.

Mechanism of carbon nanotube growth in expanded graphite via catalytic pyrolysis reaction using carbores P as a carbon source.

Carbon nanotubes (CNTs) had potential applications in energy conversion and storage devices, and it could be prepared by expanded graphite loaded with catalyst at high temperature, however, the mechanism of carbon nanotube growth in expanded graphite need further confirmation. In this work, carbon nanotubes' in situ growth in expanded graphite (EG) were prepared via catalytic pyrolysis reaction using carbores P as a carbon source and Co(NO3)3•6H2O as a catalyst. The results of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS) indicated the carbon nanotubes could generate in, EG with the presence of carbores P as a carbon source and cobalt nitrate as a catalyst. More interestingly, the growth mechanism of carbon nanotubes could be concluded by the results of differential thermal analysis-thermogravimetry-mass spectrometry (DTA-TG-MS) and X-ray photoelectron spectroscopy (XPS) analysis. The pyrolysis products of carbores P were mainly hydrocarbon gas such as CH4 gas, which reacts with Co(NO3)3·6H2O catalyst to reduces CoOx to Co particles, then the carbon form pyrolysis was deposited the on the surface catalyst Co particles and, after continuous solid dissolution and precipitation, carbon nanotubes were at last generated in EG at last.

Low temperature multi-catalytic growth and growth mechanism of carbon nanotubes on carbon fiber surfaces

In order to reduce the etching effect of the catalysts to carbon fibers caused by high temperature during the chemical vapor deposition (CVD) process, four multi-element catalysts, Fe–Co, Fe–Ni, Co–Ni and Fe–Co–Ni, were used to realize the low temperature growth of carbon nanotubes (CNTs) on carbon fibers at 350 °C–400 °C. The results show that the growth state of CNTs has a great relationship with the type of catalysts. The catalytic efficiency of Fe–Co catalysts is low, but the graphitization degree of CNTs is relatively high. The Fe–Co–Ni catalysts has high catalytic efficiency but low graphitization degree of CNTs. The tensile strength of carbon fiber/CNTs reinforcements prepared by Fe–Ni catalysts at 400 °C is the highest, reaching 3.99 GPa, which is 11.14% higher than that of desized fiber. The melt drop phenomenon of the catalysts was found by TEM, indicating the formation of the liquid phase catalysts during the growth of CNTs. This phenomenon can change the diffusion mode of carbon atoms in the catalyst and significantly reduce the growth activation energy of CNTs, so that CNTs can grow at lower temperatures. Based on the detailed analysis of the CVD process, a low temperature growth model of CNTs on carbon fibers was proposed.

The base versus tip growth mode of carbon nanotubes by catalytic hydrocarbon cracking: Review, challenges and opportunities

Hydrogen gas production using catalytic hydrocarbon cracking on metal nanoparticles has become a vital bridge technology, as this process, unlike the traditional methane-based reforming process, does not co-produce carbon gasses (e.g., CO, CO2). The major benefit of direct catalytic methane cracking using a nanostructured catalyst is the formation of solid carbon in high-value products, such as carbon nanotubes (CNTs) or filaments. This solid carbon can then be removed physically and valorized. However, it is challenging to design a catalyst capable of sustaining its activity after solid carbon has started to deposit and grow, meanwhile preventing the formation of coke. For CNTs, in particular, the base growth mode of CNTs is the desired pathway, as the catalyst can then be regenerated and re-used. If the CNTs are formed under the tip-growth mode, the catalyst particle will be lifted off the support of the regeneration and reusability is lost. Therefore, the study of CNTs growth modes is a vital topic, both experimentally and theoretically, of designing appropriate catalysts. To date, enormous efforts have been made to investigate conditions where the CNTs base growth mode can be maintained during the carbon deposition process. Several possible correlations and mechanisms regarding the base growth mode have been explored and established. Theoretical calculations and numerical simulations across length scales were conducted to investigate the nucleation mechanism and growth of CNTs. Density functional theory (DFT), classical and quantum-based molecular dynamics (MD) and Monte Carlo (MC) simulations were also carried out to study the initial CNT cap formation and its encapsulation during the catalytic hydrocarbon cracking process. A thermodynamics-based nucleation formula of CNTs for both the base and tip growth modes was also established. However, there is still no consensus on what determines the CNT growth modes and what the roles are of the various influencing factors such as the nanoparticle size, the oxidation state of the catalyst, the mechanical properties of CNT, and the catalyst-support interaction. This paper reviews the current status of CNT's growth mechanism development. The benefits and limitations of theory and modeling approaches concerning CNT growth modes are discussed.

Construction and differential growth mechanism of uniform and controllable CNTs and CNWs by ZIF-67 precursor

Carbon nanotubes (CNTs) and carbon nanowires (CNWs) have been successfully derived from ZIF-67 nanoparticles which belongs to metal–organic frameworks on carbon cloth surface. Affected by the atmosphere, ZIF-67 nanoparticles derived ZIF-67@CNTs in a melamine environment while derived ZIF-67@CNWs in a C2H5OH environment. SEM, TEM, Raman, and so on were used to explore the construction of the ZIF-67@CNTs/CNWs modification layer on the carbon fiber surface. The macroscopic morphology of ZIF-67@CNTs/CNWs is influenced by ZIF-67 concentration. When the growth temperature rase, CNTs and CNWs’ graphite degrees significantly improved. CNTs and CNWs both adhere to the traditional tip-growth mode, whereas their growth mechanisms differ. “Bamboo-like” CNTs are formatted due to the different precipitation rates of graphite sheets (GSs), which are caused by catalyst particles in the solid and liquid phases. Solid CNWs are constructed with stacked GSs produced by single-phase catalyst particles. It is the phase uniformity of catalyst particles that ultimately determines the catalytic product.

Catalytic carbon-bed sintering of CNTs/calcium aluminate cement and its effects on thermal mechanical properties of refractory castables

To improve the dispersion of carbon nanotubes in refractory castables and exert the strengthening effect of carbon nanotubes on castables, the core-shell CNTs/CAC (carbon nanotubes/calcium aluminate cement) was synthesized by the catalytic carbon-bed sintering method. The effects of catalyst content on the microstructure of CNTs/CAC powders were evaluated by Raman spectroscopy, SEM, and HRTEM. The results suggested that the optimal addition amount of catalyst was 0.75 wt%. The diameter of the bamboo-like carbon nanotubes was ∼50 nm and the length of the carbon nanotubes was ∼120 μm. Carbon nanotubes and small calcium aluminate particles were interspersed with each other and wrapped in a compact calcium aluminate shell with a thickness of 3∼5 μm. Moreover, the DFT calculation was employed to investigate the growth mechanism of carbon nanotubes. Electrons were transferred from Ni to H, O, and C atoms, increasing bond length and weakening the strength of C–H and CO bonds which was conducive to the growth of carbon nanotubes. The formation of the core-shell structure was in direct connection with the liquid-phase eutectic phase. Calcium carbonate and alumina reacted preferentially to form C12A7, and then C12A7 continued to react with alumina to form CA and CA2. With the increase of sintering temperature, a large amount of liquid phase was formed. Carbon nanotubes were wrapped by the liquid phase of calcium aluminate to form a core-shell structure. The CNTs/CAC cement bonded Al2O3–SiC castables had great mechanical properties and thermal shock resistance. Compared with Al2O3–SiC castables bonded with Secar71, the HMOR and thermal shock residual strength ratio of Al2O3–SiC castables bonded with CNTs/CAC cement were increased by 24.7% and 22.1%, respectively.

Activity competition of catalysts and supports materials on the growth of carbon nanotubes with ZrO2/Fe catalyst

Activity competition commonly exist when using multiple catalyst particles for growing carbon nanotubes (CNTs), and the diverse catalysts can compete with the carbon source and affect the growth kinetics and morphology of the nanotubes. However, the existed problem is that whether the support materials themselves also can engage in activity competition with the catalysts, and how this may impact the growth of CNTs. Here, we investigated the influence of hypoactive ZrO2 support material and hyperactive ZrO2/Fe catalysts on the growth of CNTs, and the activity competition relationship between the support and the catalysts. ZrO2/Fe catalysts were prepared via a facile hydrothermal method, and employed both CH4 and C2H5OH as carbon sources for growing CNTs. It is interesting that single-walled carbon nanotubes (SWCNTs) were grown by utilizing CH4 as carbon source, and multi-walled carbon nanotubes (MWCNTs) were synthesized for the use of C2H5OH as carbon source. A combination of experimental data and density functional theory simulations was able to reveal the underlying activity competition mechanism between hyperactive catalysts and hypoactive supports. It would provide new insight into the growth mechanisms of CNTs, and provide new ideas for the rational design and controlled growth of CNTs.

Facile synthesis of homogeneously dispersed carbon nanotubes on TC4 alloy powder by in-situ CVD and its growth behavior

We developed a simple method of in-situ synthesize carbon nanotubes (CNTs) on Ti–6Al–4V (TC4) alloy powder to fabricate CNTs/TC4 compound powders through plasma-enhanced chemical vapor deposition (PECVD). By this approach, CNTs on TC4 alloy powder exhibit better uniform dispersion and morphology compared with the traditional CVD methods. In order to reveal the growth behavior of CNTs during the PECVD process, XRD, SEM, TEM, and Raman spectroscopy were used to analyze the morphology and graphitization of CNTs at different synthesis conditions. The plasma is benefit to the pyrolysis of CH4, but overmuch plasma bombardment also reduces the yield and quality of CNTs. The number of CNTs can be significantly improved with appropriately increasing the temperature and time, but excessive temperature, time and carbon concentration can increase the number of impurities such as amorphous carbon. Significantly, the growth mechanism of CNTs synthesized in TC4 powders is following tip-growth mode in PECVD process. Additionally, the quantity and quality were satisfactory at 600 °C for 30 min with 50 W plasma power. This study about PECVD process lays a foundation for improving the comprehensive properties of CNTs/TC4 composites in the future.

Synthesis of Ultralong Carbon Nanotubes with Ultrahigh Yields.

Ultralong carbon nanotubes (CNTs) are in huge demand in many cutting-edge fields due to their macroscale lengths, perfect structures, and extraordinary properties, while their practical application is limited by the difficulties in their mass production. Herein, we report the synthesis of ultralong CNTs with a dramatically increased yield by a simple but efficient substrate interception and direction strategy (SIDS), which couples the advantages of floating-catalyst chemical vapor deposition with the flying-kite-like growth mechanism of ultralong CNTs. The SIDS-assisted approach prominently improves the catalyst utilization and significantly increases the yield. The areal density of the ultralong CNT arrays with length of over 1 cm reached a record-breaking value of ∼6700 CNTs mm-1, which is 2-3 orders of magnitude higher than the previously reported values obtained by traditional methods. The SIDS provides a solution for synthesizing high-quality ultralong CNTs with high yields, laying the foundation for their mass production.

Thermotropic flash assembly energy of carbon nanotube in liquid phase based on electrical energy

In order to open the black box of carbon nanotube (CNT) growth, a thermotropic flash assembly (TFA) process in liquid phase at room temperature was innovatively proposed. The thermotropic assembly of CNTs via universal CVD method and an innovative TFA process were described in detail. The equivalent space of CNT growth on the surface of carbon fiber (CF) and different energy models were constructed for the TFA process. The growth equation of CNTs in the TFA process was derived for the first time, and the energy required to grow CNTs per unit mass was calculated to be 0.0214 kWh/g based on the growth conditions, which provided a basis for the growth of CNTs in different types of conductive media and the precise control of interface modification. Interestingly, different nanostructures (such as CNTs, nanolamellae, and nanoflower clusters) were found to grow on the CF surface in the TFA process. Moreover, the evolution process and the growth mechanism of CNTs in the TFA process were analyzed in detail. The analysis results were necessary to calculate the energy required for CNT growth. The power spectra of the continuous TFA and CVD processes were obtained online, and the input energy characteristics of the two processes were compared and calculated. It was concluded that the TFA process had superior homogeneity and stability in this respect, and it was an energy-conserving and efficient method of CNT growth. Therefore, the TFA process provided a new model for CNT growth, and the opened black box provided the possibility to deeply explore the mechanism of in situ thermotropic flash assembly of CNTs.

Growth mechanism of carbon nanotubes from Co-W-C alloy catalyst revealed by atmospheric environmental transmission electron microscopy.

High-melting point alloy catalysts have been reported to be effective for the structure-controlled growth of single-wall carbon nanotubes (SWCNTs). However, some fundamental issues remain unclear because of the complex catalytic growth environment. Here, we directly investigated the active catalytic phase of Co-W-C alloy catalyst, the growth kinetics of CNTs, and their interfacial dynamics using closed-cell environmental transmission electron microscopy at atmospheric pressure. The alloy catalyst was precisely identified as a cubic η-carbide phase that remained unchanged during the whole CNT growth process. Rotations of the catalyst nanoparticles during CNT growth were observed, implying a weak interfacial interaction and undefined orientation dependence for the solid catalyst. Theoretical calculations suggested that the growth kinetics are determined by the diffusion of carbon atoms on the surface of the η-carbide catalyst and through the interface of the catalyst-CNT wall.

Two birds with one stone: Simultaneous fabrication of HfC nanowires and CNTs through efficient utilization of polymer-derived ceramics

• Carbon nanotubes (CNTs) were fabricated by using the waste gasses when preparing hafnium carbide nanowires (HfC NWs ) through thermal pyrolysis of Hf-containing precursor. • The CO and CH 4 released by Hf-containing precursor are the main carbon source for the growth of CNTs. • The in situ growth of HfC NWs increased the flexural strength of carbon/carbon (C/C) composites, and CNTs/carbon cloth displayed enhanced electrochemical performance. Carbon nanotubes (CNTs) are fabricated in carbon cloth by ultilizing the waste gasses when fabricating hafnium carbide nanowires (HfC NWs ) through thermal pyrolysis of Hf-containing polymer precursor. The formed HfC NWs are distributed uniformly on the surface of the carbon fibers in carbon/carbon (C/C) composites and display perfect single crystal appearance. The pyrolysis of the Hf-containing organic precursor provides hafnium and carbon source for the growth of HfC NWs . The released waste gasses containing CO, CH 4 and CO 2 are the main carbon source for the growth of CNTs. Specifically, the flexural strength of HfC NWs reinforced carbon/carbon (HfC NWs -C/C) composites is enhanced by ∼105% compared with pure C/C, and the CNTs/carbon cloth also displays improved electrochemical performance with respect to capacitor applications. The present study introduces a novel sustainable and eco-friendly process related to polymer-derived ceramics to form advanced ceramic nanocomposites and proposes a deep understanding of the growth mechanism of CNTs.

Platinum supported on hydroxyl-grafted poly (3,4-ethylenedioxythiophene)-modified RuCo, N-tridoped bamboo-like carbon nanotubes for direct methanol fuel cell

The development of highly active and efficient heterogeneous catalytic oxidation system has become an attractive research field. In this paper, a catalyst (RuCo/N-CNT@PEDOT-OH/Pt) from platinum nanoparticles (Pt NPs) supported on hydroxyl-grafted poly(3,4-ethylenedioxythiophene) (PEDOT–OH)-modified RuCo, N-tridoped bamboo-like carbon nanotubes (RuCo/N-CNT) are used for direct methanol fuel cell (DMFC). The electrocatalytic activity of RuCo/N-CNT@PEDOT-OH/Pt is systematically compared with RuCo/N-CNT/Pt (Pt NPs supported on RuCo/N-CNT without PEDOT-OH) in the methanol oxidation reaction (MOR). The growth mechanism of carbon nanotubes and the role of heteroatom doping in the electrocatalytic process is explored. The catalysts show excellent electrocatalytic performance with high stability for MOR. It is found that the mass activity (MA) of the RuCo/N-CNT@PEDOT-OH/Pt (1961.3 mA mg−1Pt) for MOR was higher than that of RuCo/N-CNT/Pt (1470.1 mA mg−1Pt) and the commercial Pt/C catalysts (281.0 mA mg−1Pt), indicating the positive effect of the PEDOT-OH in the electrocatalytic MOR. In addition, density functional theory (DFT) calculations verify the possible mechanism pathways of the obtained RuCo/N-CNT@PEDOT-OH/Pt catalyst. This presented catalyst offers new inspiration for designing efficient electrocatalysts for methanol oxidation.

Is the Carbon Nanotube-Catalyst Interface Clean during Growth?

Revealing a "true" picture of the carbon nanotube (CNT) growth front at the catalyst surface is critical to understanding the mechanism of CNT growth. If the CNT-catalyst interface is clean or messy, which will greatly affect the mechanism of controlled CNT growth, has never been properly solved either experimentally or theoretically. Here, this issue by ab initial calculation-based kinetic analysis and classical molecular dynamic (MD) simulations is revisited. It is found that the appearance of carbon chains at the CNT-catalyst interfaces or the "messy" interfaces in MD simulations is a consequence of the very short simulation time, and a "clean" CNT-catalyst interface will emerge if the simulation time is close to that in real experiments. This study reveals that, during real CNT experimental growth, a "clean" CNT-catalyst interface with zigzag, armchair, and/or kink sites dominates the growth kinetics, and therefore, the controllable CNT growth by tuning the CNT-catalyst interface is feasible.

Synthesis, Sorting, and Applications of Single-Chirality Single-Walled Carbon Nanotubes.

The synthesis of high-quality chirality-pure single-walled carbon nanotubes (SWCNTs) is vital for their applications. It is of high importance to modernize the synthesis processes to decrease the synthesis temperature and improve the quality and yield of SWCNTs. This review is dedicated to the chirality-selective synthesis, sorting of SWCNTs, and applications of chirality-pure SWCNTs. The review begins with a description of growth mechanisms of carbon nanotubes. Then, we discuss the synthesis methods of semiconducting and metallic conductivity-type and single-chirality SWCNTs, such as the epitaxial growth method of SWCNT (“cloning”) using nanocarbon seeds, the growth method using nanocarbon segments obtained by organic synthesis, and the catalyst-mediated chemical vapor deposition synthesis. Then, we discuss the separation methods of SWCNTs by conductivity type, such as electrophoresis (dielectrophoresis), density gradient ultracentrifugation (DGC), low-speed DGC, ultrahigh DGC, chromatography, two-phase separation, selective solubilization, and selective reaction methods and techniques for single-chirality separation of SWCNTs, including density gradient centrifugation, two-phase separation, and chromatography methods. Finally, the applications of separated SWCNTs, such as field-effect transistors (FETs), sensors, light emitters and photodetectors, transparent electrodes, photovoltaics (solar cells), batteries, bioimaging, and other applications, are presented.

In-situ preparation of carbon nanotubes on CuO nanowire via chemical vapor deposition and their growth mechanism investigation

In-situ growth of carbon nanotubes (CNTs) on CuO nanowires is realized by chemical vapor deposition method, in which hydrogen/argon mixed gas and acetylene are used as pretreatment gas and carbon source, respectively. CuO nanowires are formed uniformly on the surface of copper wire (CW) through thermal oxidation method, which generates CW@CuO@CNTs with a good hierarchical structure. Also, many copper nanoparticles are formed on the surface of CNTs. The growth mechanisms of CNTs and copper nanoparticles are investigated in this paper.

Development of Carbon Nanotubes (CNTs) Membrane from Waste Plastic: Towards Waste to Wealth for Water Treatment

Plastic, a non-biodegradable material has always been a concern to the environment and people. This single-use item generates waste to landfills and it persists for centuries once disposed. The urge of transforming such material into a highly valuable product has sought attention from many researchers. This study emphasizes on a nanotechnological approach to synthesize vertically-aligned carbon nanotubes (CNTs) on a substrate template using commercially available plastic bags as carbon precursor. CNTs are grown inside a hexagonally arranged nanoporous anodic alumina membranes (NAAMs). CNTs are liberated by wet chemical etching to dissolve the alumina matrix. The resulting CNTs are used as adsorption media filters for water treatment purpose. The high adsorption affinity towards heavy metals, organic matters and microbes, ability to antifouling and self-cleaning function have made CNTs a better choice over others. This article briefly discusses the catalyst-free synthesis, growth mechanism, characterization and functionalization of CNTs for water treatment application.

Advances in Precise Structure Control and Assembly toward the Carbon Nanotube Industry (Adv. Funct. Mater. 11/2022)

Controlled Synthesis The commercialization of carbon nanotubes (CNTs) depends on rapid development in precise structure control and morphological assembly technology. In article number 2109401, Weizhong Qian, Fei Wei, and co-workers summarize the catalytic growth mechanism of defect-free CNTs. The template-assisted morphological assembly is subsequently introduced as an efficient route towards their mass production. Finally, more cutting-edge applications are presented with potential breakthroughs in fibers, energy, and electronics.