Nucleation Of Nanotubes Research Articles

Review of: "The size of catalytic nanoparticles plays an important role in the growth of nanotubes, generally, catalytic nanoparticles with a small size (less than 01 nm) are active for the nucleation and growth of carbon nanotubes"

Review of: "The size of catalytic nanoparticles plays an important role in the growth of nanotubes, generally, catalytic nanoparticles with a small size (less than 01 nm) are active for the nucleation and growth of carbon nanotubes"

Insights into the Nucleation and Structure of Lignin-Based Carbon Nanotubes Synthesized Using Iron via Floating Catalyst Chemical Vapor Deposition

Insights into the Nucleation and Structure of Lignin-Based Carbon Nanotubes Synthesized Using Iron via Floating Catalyst Chemical Vapor Deposition

Nucleation and Growth Mechanisms of Bimetallic Sm-Co Nanowires and Nanotubes

Nucleation and growth mechanisms of bimetallic Sm-Co magnetic nanowires and nanotubes, electrocrystallizing into hard anodic alumina templates, are described. Nanowires are produced at two overpotentials −0.9 V and −3 V, into templates with pore diameters of 20 nm and 40 nm; for larger pores, 200 nm in diameter, nanowires result at −0,9 V while at −3 V nanotubes form. The electrodeposition process mainly develops under diffusional control, with the current monotonically decreasing with time. Experimental current/time curves are described by suitable models adapted to bimetallic phases, considering successive stages in the pore filling process. In membranes with small pore diameter, a linear diffusion zone ahead the growing nanowire surface allows to apply a modified Cottrell equation. Models based on recessed microelectrodes behaviour are proposed, considering the overlap of diffusion zones at the porous mouth. For large pore diameter (>100 nm), current transitory is described by a 1D model for nanowires grown at −0.9 V, while a new expression is derived for nanotubes developing at −3 V, where the hydrogen evolution provides an important contribution to the mechanism. The mechanisms proposed are consistent with nanowires´ and nanotubes´ morphology details observed in SEM images.

Nucleation of Single-Wall Carbon Nanotubes from Faceted Pt Catalyst Particles Revealed by in Situ Transmission Electron Microscopy.

Revealing the nucleation and growth mechanism of single-wall carbon nanotubes (SWCNTs) from faceted solid catalysts is crucial to the control of their structure and properties. However, due to the small size and complex growth environment, the early stages and dynamic process of SWCNT nucleation have rarely been directly revealed, especially under atmospheric conditions. Here, we report the atomic-resolved nucleation of SWCNTs from the faces of truncated octahedral Pt catalysts under atmospheric pressure using a transmission electron microscope equipped with a gas-cell. It was found that the graphene layers were initially formed preferentially on (111) surfaces, which then joined together to form an annular belt and a hemispherical cap, followed by the elongation of the SWCNT. Based on the observations, an annular belt assembly nucleation model and a possible chirality control mechanism are proposed for SWCNTs grown from well-faceted Pt catalysts, which provides useful guidance for the controlled synthesis of SWCNTs by catalyst design.

Temperature-dependent selective nucleation of single-walled carbon nanotubes from stabilized catalyst nanoparticles

• Enriched (6,5) and (7,5) SWCNTs are respectively synthesized at ambient pressure. • Highly stabilized cobalt nanoparticles are generated from catalyst reduction. • Thermodynamic stability of different tube nuclei accounts for SWCNT selectivity. The utilization of metal nanoparticles supported on oxides substrate as a catalyst for rational single-walled carbon nanotube (SWCNT) growth is hindered by particle coarsening at high synthesis temperature, despite many empirical advances in supported catalyst design. In this study, a newly developed MgO-supported cobalt (Co-MgO) catalyst affords the formation of well-stabilized Co nanoparticles upon reduction, which is attributed to the electronic metal-support interaction and electrostatic stabilization at the Co-MgO interface. The highly stabilized Co nanoparticles led to the predominant growth of (6, 5) SWCNTs at 700 °C by CO disproportionation and the major SWCNT species was found to be (7, 5) SWCNTs at a reaction temperature of 800 °C. The temperature-dependent selective growth of the two SWCNT species was found, by density functional theory calculation, to be strongly correlated with the change of the relative thermodynamic stability of the SWCNT nuclei in the chirality assigning process at different temperatures.

Automated processing of environmental transmission electron microscopy images for quantification of thin film dewetting and carbon nanotube nucleation dynamics

Scalable production of carbon nanotubes (CNTs) requires catalysts and reaction conditions that provide high nucleation efficiency. In situ characterization methods such as environmental transmission electron microscopy (ETEM) can reveal fundamental mechanisms of synthesis, but to date have primarily provided qualitative observations on small sample sizes. Here, quantitative analysis is performed using high-resolution, high-rate video capture of ETEM experimentation coupled with automated image processing, involving computer vision algorithms and convolutional neural networks. By this approach, we detect distinct nanoparticle formation from an alumina-supported iron thin film and subsequent CNT nucleation from the nanoparticles. The statistical summary of particles in each video shows that, compared to a H2-only atmosphere, pretreatment of the catalyst with carbon added to the H2 atmosphere results in a smaller average particle diameter, a 2-fold increase in particle density (to 5300 particles/μm2), a 3-fold increase in CNT nucleation efficiency (to 92%), and more than a 5-fold increase in CNT density (to 4800/μm2). Addition of carbon during exposure to H2 is also more effective than NH3 at dewetting the catalyst film and increasing the CNT nucleation efficiency, in spite of NH3 being a stronger reducing agent for iron. Insights from this study are applicable to improving CNT yield and productivity in both batch-style and continuous processes.

Joint effect of ethylene and toluene on carbon nanotube growth

This work contributes to the understanding of single-walled carbon nanotube synthesis by an aerosol CVD method using ethylene and toluene as a hybrid carbon source. We evaluated an extensive set of synthesis conditions revealing the role of ferrocene, toluene, and ethylene. We found the fundamental role of ethylene promoting nanotube nucleation and catalyst activation degree at all the concentrations studied, and enhancing nanotube growth at low ethylene content. We observed the interplay effect of toluene and ethylene concentrations on the nanotube growth rate, accompanied by the detrimental effect of toluene on catalyst activation degree. Nevertheless, toluene apparently promotes nanotube crystallinity, increasing the film conductivity while used as an individual carbon source. Adjusting the ethylene and toluene concentrations, we produced carbon nanotube-based transparent and conductive films with an equivalent sheet resistance (at 90% transmittance at 550 nm wavelength) value of 57 Ω/□ at the synthesis yield of 0.24 cm2 L−1, which is at least two times higher than the results reported earlier.

(Invited) In Situ Study on Nucleation and Growth of Single-Walled Carbon Nanotubes on Catalysts

Understanding the growth mechanism is prerequisite to design the methodology for controlled growth of single-walled carbon nanotubes (SWNTs). By using an environmental aberration-corrected transmission electron microscope in combination with in situ synchrotron X-ray absorption spectroscopy, we directly present the structural and composition evolution of cobalt and cobalt-tungsten intermetallic catalysts during the nucleation and growth of SWCNTs under carbon feeding. The co-existence of cobalt and cobalt carbide was generally observed among the pure cobalt catalysts which are active in nucleating tubes. The nucleation and growth behaviors of tubes on solid state cobalt nanoparticles and molten ones have been compared. It was found that the tubes grown from solid state catalysts always present smaller diameter than the catalysts. No structure-correlation between catalyst and nanotube was found. Distinct different from cobalt, no carbides or carbon diffusion induced structural change was observed from the in situ characterization. The atomic structure of Co7W6 was stable when CNTs nucleating. These observations reveal that cobalt-tungsten intermetallic catalysts act as the stable structure template for the chirality controlled growth of SWNTs.

Residence time effect on single-walled carbon nanotube synthesis in an aerosol CVD reactor

• Residence time in aerosol CVD was tuned while nanotube nucleation maintained. • Carbon nanotube length and I G /I D ratio increase with a higher residence time. • The increase in length and defectiveness drops equivalent sheet resistance. • Effect of vortices, diffusion, and thermophoresis on nanotube yield was shown. • SWCNT/HAuCl 4 thin films with equivalent sheet resistance of 51 Ω/□ were obtained. We examine an effect of residence time on the growth of single-walled carbon nanotubes (SWCNTs) in an aerosol (floating catalyst) chemical vapor deposition (CVD) process using CO as a carbon source and ferrocene as a catalyst precursor. The key feature of aerosol CVD reactors, namely stabilization of fine nanoparticles by an extreme dilution, limits the method for catalyst evolution studies. We show an approach to examine the role of the residence time while maintaining all the processes preceding the nanotube growth (catalyst formation, nanotube nucleation). Using the diameter distribution of nanotubes as a fingerprint of the SWCNT nucleation stage, we have proven the latter to be unaffected by changes in the residence time. Using SEM observations, we have revealed a quite intuitive but inspiring correlation between the carbon nanotube length and residence time. We have also found a decrease in the SWCNT yield caused by the drop in the aerosol concentration, which could be attributed to the gas-phase losses as well as the shift in the catalyst activation degree. Nevertheless, the trends observed allowed us to reach a tenfold decrease in an equivalent sheet resistance (sheet resistance of a film with 90% transmittance at 550 nm) by a threefold increase in the residence time at optimal CO 2 concentration. SWCNT films with the equivalent sheet resistance as low as 245 Ω/□ and 51 Ω/□ (for pristine and doped carbon nanotubes, correspondingly) ensure the promising future of the proposed strategy for optimization of both aerosol CVD reactors and SWCNT-based films for optoelectronic applications.

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.

Automated Processing of Environmental Transmission Electron Microscopy Images for Quantification of Thin Film Dewetting and Carbon Nanotube Nucleation Dynamics

Automated Processing of Environmental Transmission Electron Microscopy Images for Quantification of Thin Film Dewetting and Carbon Nanotube Nucleation Dynamics

Oxygen evolution activity limits the nucleation and catalytic growth of carbon nanotubes from carbon dioxide electrolysis via molten carbonates

Controlled catalytic synthesis of technologically valuable carbon nanomaterials by the electrochemical capture and conversion of CO2 is bottlenecked by limited understanding of combined electrochemical and catalytic mechanisms at play during conversion. Here, our findings provide new insight that a key factor for the electrochemical two-electrode catalytic growth of carbon nanotubes (CNTs) on the cathode surface is the oxygen evolution activity (OEA) occurring at the anode. Poor OEA can inhibit catalytic CNT formation altogether, while increased anode OEA is correlated to changes in diameter and crystallinity of CNTs with otherwise identical cathode catalyst layers and synthesis conditions. Specifically, comparing Cu, Ni/Al2O3, and Pt anodes with Fe/stainless steel cathodes we observe over 6x smaller CNT diameter distribution and over 2x lower D/G ratio when using Pt anodes with the highest OEA. This is attributed to the role of transport between the cathode and anode during synthesis; in the case of poor anode OEA, a build-up of oxide species near the cathode surface influences the surface tension at the catalyst-carbonate interface to modify CNT diameter and properties. This mechanistic insight opens the door to routes to controllably produce high quality carbon nanomaterials from the electrochemical capture and conversion of carbon dioxide.

Synthesis of bimetallic NiMo/MgO catalyst for catalytic conversion of waste plastics (polypropylene) to carbon nanotubes (CNTs) via chemical vapour deposition method

Non-biodegradable waste plastics constitute huge environmental problem and their effective disposal or beneficiation to value-added products such as carbon nanotubes (CNTs) is imperative for environmental sustainability. However, methods employ in the preparation of the catalysts employed in the catalytic conversion of waste plastics to CNTs play a key role in providing the desired nanoparticle morphology and stability towards increasing the catalytic (active) sites for nucleation and growth of carbon nanotubes (CNTs). It also determines the diameter, nature and alignment of the produced CNTs. In this study, bimetallic NiMo supported on MgO catalyst was prepared by two different synthesis methods: sol–gel and incipient wet impregnation (IWI) methods. Physico-chemical property and catalytic activity of the catalysts obtained from these catalyst preparation methods were evaluated and compared during the synthesis of CNTs from waste polypropylene under similar conditions using a one-step chemical vapour deposition technique (CVD). The physico-chemical properties of the prepared catalysts and those of the produced CNTs were obtained via X-ray diffraction (XRD) and Scanning electron microscopy (SEM) and compared. Results reveal that all prepared catalysts are porous and exhibited catalytic activity, but the catalyst obtained via IWI method is more porous and displayed higher catalytic activity when compared to the one obtained via sol–gel. Furthermore, bulk deposition of multi-walled CNTs (MWCNTs) of different diameters was also observed.

Synthesis and carbothermal nitridation mechanism of ultra-long single crystal α-Si3N4 nanobelts

One-dimensional Si3N4 nanostructures are desirable for constructing nanoscale electric and optoelectronic devices due to their peculiar morphologies. Herein, a facile and environmentally friendly catalyst-free method is proposed to synthesize ultra-long single crystal α-Si3N4 nanobelts via carbothermal nitridation of carbon nanotubes at 1750 °C. The obtained α-Si3N4 nanobelts with a flat surface (thickness of ∼150 nm, length of several millimeters) exhibited an extremely high aspect ratio, perfect crystal structure, and high specific surface area of 7.34–10.09 m2 g−1. In addition, the width was increased from approximately 80 nm to 8 μm by increasing the holding time from 1 to 3 h. The nanobelt formation was governed by the vapor–solid (VS) reaction between SiO vapor, N2 and carbon nanotubes, and the vapor–vapor reaction between SiO, CO and N2. The former was responsible for the initial nucleation and successive base-growth of α-Si3N4 nanotubes. The latter additionally contributed to the nanorod and subsequent proto-nanobelt formation and to the growth of the nanobelts. During high-temperature annealing at 1750 °C, the original Si3N4 nanotubes gradually transformed into nanorods, and, finally, nanobelts with stable shapes as a result of surface energy minimization.

A theoretical indicator of transition-metal nanoclusters applied in the carbon nanotube nucleation process: a DFT study.

Knowledge about the appropriate indicators to point out the best components in a catalytic process is a basic prerequisite for obtaining insights into optimized reactions as, for example, in the chemical vapour deposition method, which enables the growth of carbon nanotubes. In this work, we report a density functional theory study of 13-atom transition-metal nanoclusters interacting with (5,0) zigzag and (3,3) armchair carbon nanotube fragments, considering all transition-metal species from the periodic table as possible candidates for the chemical vapour deposition method. The icosahedral configuration was found to be a good model to simulate the seed of nucleation in the case of the short carbon nanotube fragments that are initially formed during the growth process. From full geometric optimizations, without any constraints, we found that the energetic and structural nanocluster properties change as a function of the occupation of the bonding and anti-bonding d-states. The center of gravity of the occupied d-states for nanoclusters is found to be a good indicator to reveal the best candidates for the interaction with the carbon nanotubes, namely, Sc-Cu, Y-Nb, Pd, Lu, Hf, and Pt. The interaction between all transition-metal nanoclusters with both armchair and zigzag segments is favorable in terms of the adhesion energy, where the adhesion is larger for systems with smaller occupation of the d-states. The bond strength is more pronounced for systems with zigzag fragments than those with armchair fragments, which is confirmed by the smaller average bond length between the metal atoms of the nanocluster and the C atoms of the zigzag segment. Our prediction about the best 13-atom transition-metal candidates is reinforced by the linear relationship between the adhesion energy and the center of gravity of the occupied d-states. Thus, the adhesion energy presents increased intensity for the interaction between carbon nanotube fragments and nanoclusters in relation to the smaller occupation of the d-states. Consequently, our model is able to provide a good descriptor for indicating the best 13-atom transition-metal candidates in the chemical vapour deposition process.

Atomic Self‐reconstruction of Catalyst Dominated Growth Mechanism of Graphite Structures

AbstractUnderstanding the nucleation and growth process of carbon nanotubes (CNTs) is important for guiding their efficient and controllable synthesis in industry. However, the intrinsic mechanism that controls the formation of carbon nanotubes is still controversial. Here, using in‐situ transmission electron microscopy (TEM), we demonstrate the dynamic catalytic growth of multilayered graphite crystallites and single‐walled carbon nanotubes (SWCNTs) from the Co2C catalyst nanoparticles (NPs) at the atomic resolution. The dissociative carbon atoms arrive at the nucleation sites on the surface of small and large NPs by the surface and bulk diffusion, respectively. These two different diffusion modes are found to be the essential prerequisite for growing single‐walled carbon nanotubes (SWCNTs) or multilayered graphite crystallites. The small NPs utilize crystal self‐rotation to expose the (111) plane for efficiently capturing carbon atoms, while the large NPs use self‐reshaping on (111) facets to provide atomic steps as active nucleation sites. Density functional theory (DFT) calculations indicate that the observations are in good agreement with the growth mechanism of graphite structures involving the preferential selectivity of crystal facets. Our results may open up the possibility of adjusting the size and crystal orientation of cobalt‐based catalyst particles to efficiently synthesize the SWCNTs with high quality.

Boron Nitride Nanotube Nucleation during Ni-Catalyzed Boron Oxide Chemical Vapor Deposition

Boron oxide chemical vapor deposition (BOCVD) has proved to be a valuable synthetic technique for the catalytic synthesis of boron nitride nanotubes (BNNTs) for almost two decades. However, the nuc...

Boron Nitride Nanotube Nucleation via Network Fusion during Catalytic Chemical Vapor Deposition.

Despite boron nitride nanotubes (BNNTs) first being synthesized in the 1990s, their nucleation mechanism remains unknown. Here we report nonequilibrium molecular dynamics simulations showing how BNNT cap structures form during Ni-catalyzed chemical vapor deposition (CVD) of ammonia borane. BN hexagonal ring networks are produced following the catalytic evolution of H2 from the CVD feedstock, the formation and polymerization of B-N chain structures, and the repeated cleavage of homoelemental B-B/N-N bonds by the catalyst surface. Defect-free BNNT cap structures then form perpendicular to the catalyst surface via direct fusion of adjacent BN networks. This BNNT network fusion mechanism is a marked deviation from the established mechanism for carbon nanotube nucleation during CVD and potentially explains why CVD-synthesized BNNTs are frequently observed having sharper tips and wider diameters compared to CVD-synthesized carbon nanotubes.

A spark discharge generator for scalable aerosol CVD synthesis of single-walled carbon nanotubes with tailored characteristics

We have designed and built an exhaust-free spark discharge generator for robust aerosol CVD synthesis of single-walled carbon nanotubes. The systematic study has shown the generator to provide a facile and repeatable route to precisely control the size of the catalyst particle and, therefore, carbon nanotube growth. Using a comprehensive set of methods (the analysis of differential mobility of the aerosol particles, optical spectroscopy, scanning and transmission electron microscopy, Raman spectroscopy, and atomic force microscopy) we have revealed the relation between the defectiveness, length, diameter distribution of carbon nanotubes and specific features of a generator such as electrode characteristics (breakdown voltage, composition, and current) as well as the nature of the surrounding media (carrier gas nature, flow rate). The design used has resulted in separation of the nanoparticle formation and carbon nanotube nucleation processes. This provides a mutual independence of the growth parameters and the diameter distribution of the single-walled carbon nanotubes enhancing the scalability of the process. For instance, the breakdown voltage has been shown to have nearly zero effect on diameter and length distribution of carbon nanotubes produced while strictly governing the yield. We focus here on producing specifically short carbon nanotubes (l < 500 nm) of pronounced defectiveness for drug delivery and transistor applications.

Catalyst- and Etchant-Dependent Mechanisms of Single-Walled Carbon Nanotube Nucleation during Chemical Vapor Deposition

Recent experiments have shown that single-walled carbon nanotube (SWCNT) chirality and diameter can be modulated by adjusting the carbon/hydrogen chemical potentials at the catalyst surface and also by adding chemical etchants, such as ammonia, to the chemical vapor deposition (CVD) feedstock. Here, we present nonequilibrium quantum chemical molecular dynamics simulations showing how these factors control the SWCNT nucleation mechanism in different ways on Fe and Ni catalyst nanoparticles. Polygonal carbon rings form on Ni catalysts via the collapse of extended, partially saturated carbon chains that are adsorbed weakly to the catalyst surface, while SWCNT nucleation on Fe is strongly mediated by the catalyst surface. The weaker Ni–C interaction here means that the carbon desorption rate, and hence carbon chemical potential, on Ni is consistently lower than it is on Fe. Ni also activates adsorbed C–H and N–H bonds more effectively than Fe. Nevertheless, the hydrogen chemical potential is consistently lowe...