Yield Of Single-walled Carbon Nanotubes Research Articles

Single-walled carbon nanotube synthesis with RuRhPdIrPt high entropy alloy catalysts

Using high-entropy alloy nanoparticles (HEA NPs) composed of five platinum-group metals (5PGM), Ru, Rh, Pd, Ir, and Pt, as catalysts, we succeeded in growing single-walled carbon nanotubes (SWCNTs) via chemical vapor deposition (CVD). After CVD growth with C2H2 feedstock at 750 ℃ for 10 min, high-density SWCNTs were grown from 5PGM HEA NPs. The diameters of most SWCNTs were in the range of 0.83–1.1 nm, exhibiting the growth of small-diameter SWCNTs. Compared with monometal PGM catalysts, the SWCNT yield with the 5PGM HEA NP catalysts was much higher and was compatible even with those with Fe and Co.

Statistical patterns in high-throughput growth of single-wall carbon nanotubes from Co/Pt/Mo ternary catalysts

Designed alloy catalysts have shown promise in structure-controlled growth of single-wall carbon nanotubes (SWCNTs). However, due to the high-dimensional growth parameter space and low efficiency of the conventional trial-and-error optimizing approach, it is still challenging to explore and to establish the relations between catalyst compositions and the structure of SWCNTs. Here, we present a high-throughput strategy to investigate the statistical patterns in catalyst activity and selective growth of SWCNTs using Co/Pt/Mo ternary catalysts. Statistical analysis reveals that in the Co/Pt/Mo ternary diagram, there is an active region in the Co-rich Co–Mo corner to grow SWCNTs with high yield (≥25 tubes/μm2) and high quality (IG/ID ≥ 40). Enriched semiconducting (s-) SWCNTs with a purity higher than 90% were obtained along the boundary of the high yield region, near the Co–Pt axis. The statistical patterns of the yield, quality and selectivity are associated with the alloy composition, revealing a negative correlation between the yield and enrichment of s-SWCNTs. High-resolution transmission electron microscope characterization shows that a Co–Pt alloy catalyst with a uniform size distribution facilitates the s-SWCNT enrichment. And the separate phases of a Co–Mo/Co catalyst stabilize the active Co phase, leading to long catalyst lifetime and high yield of SWCNTs.

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

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

Catalyst regeneration and multicycle growth of high purity and yield semiconducting single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) with specific electrical types are urgently demanded for future nanoelectronic applications. However, it is still a challenge to simultaneously improve the purity and yield of semiconducting SWCNTs (s-SWCNTs). Herein, we propose a new multicycle approach to directly synthesize s-SWCNTs by chemical vapor deposition (CVD) using Fe0.01Mg0.99O as catalyst regeneration host. The appropriate carbon feedstock used in the first-time growth is CH4. During this process, the lattice oxygen would be released from Fe0.01Mg0.99O catalyst through H2 reduction and then form water vapor. The water vapor could in-situ selectively etch metallic SWCNTs (m-SWCNTs) in the nucleation process. After the termination of the first-time growth stage, the deactivative catalyst was regenerated by oxidation treatment, then it was reused to grow SWCNTs again. Carbon feedstock was changed to C2H5OH for the multicycle growth of SWCNTs and the secondary etching of as-grown m-SWCNTs and smaller-diameter SWCNTs. The selective synthesis of s-SWCNTs through this new multicycle growth process was up to 93.2% abundance, and the yield of SWCNTs was improved from 0.76% to 1.34% (weight ratio to the catalyst powder). It is interesting that there exists a diameter threshold value, which could affect the ∙OH groups etching on m-SWCNTs. According to the DFT simulation, the experimental results are related to the absorption capacity and reaction activity of SWCNTs. It presents a new approach to the massive synthesis of high purity s-SWCNTs and has wide applications in the future.

Combination effect of growth enhancers and carbon sources on synthesis of single-walled carbon nanotubes from solid carbon growth seeds

In the synthesis of highly crystalline single-walled carbon nanotubes (SWCNTs), high growth temperatures are preferred, while the formation of impurity amorphous carbon (a-C) causes the termination of SWCNT growth and degrades its properties. To remove this by-product, H2O and CO2 have been employed in metal-catalyzed SWCNT growth systems because of their oxidizing ability. Recently, nonmetallic nanoparticles have become one of the growth seed candidates because of their high melting points and fewer metal impurities. In this study, by using nanodiamond-derived carbon nanoparticles as the solid growth seeds, we investigated the effect of CO2 and H2O on high-temperature SWCNT growth with two types of carbon-source supplies: C2H2 and C2H4. In this growth system, H2O showed oxidizing ability to etch a-C with either carbon sources. CO2 exhibited a similar a-C formation-preventing role in C2H4-supplied growth and achieved higher-purity SWCNTs with higher concentration of C2H4 than the case of H2O. However, in contrast to the other combinations, CO2 injection in the C2H2-supplied growth significantly enhanced the formation of a-C rather than the removal of it while the yield of SWCNTs was also increased, indicating the occurrence of the dehydration reaction between CO2 and C2H2. The present findings will lead to efficient growth of high-quality SWCNTs from nonmetallic growth seeds with the use of growth enhancers.

Multi-nucleation of single-walled carbon nanotubes in floating catalyst chemical vapor deposition

Floating-catalyst CVD (FCCVD) is a highly promising technique for the scalable synthesis of single-walled carbon nanotubes (SWCNTs). The number concentration (NC) of catalyst particles is one of the process parameters which mainly influences yield of as-produced SWCNTs. In the conventional FCCVD methods, catalyst particles are usually synthesized by thermal decomposition of organometallic compounds inside the FCCVD reactor. Being in-situ catalyst formation in conventional FCCVD, it is an open question that how many SWCNTs a single catalyst particle can grow? Herein, we employed our novel spark discharged based FCCVD technique which decouples the formation of catalyst particles and SWCNTs synthesis into two subsequent process to investigate effects of catalyst NC on SWCNTs synthesis. The NC of both catalyst particles and SWCNTs in gas-phase were quantitatively compared using differential mobility analyzer (DMA). The DMA measurements corroborated with atomic force microscopy and X-rays photoelectron spectroscopy revealed that under carefully chosen reaction conditions in FCCVD, a single catalyst particle can grow more than one SWCNTs. We propose that after the growth of 1st SWCNT, the catalyst particle detach itself to start nucleating 2nd SWCNT and this process continues as long as the catalyst remains in the growth region of the FCCVD reactor.

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.

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.

Single-Walled Carbon Nanotube Synthesis Yield Variation in a Horizontal Chemical Vapor Deposition Reactor.

The controlled synthesis of single-walled carbon nanotubes (SWNTs) is essential for their industrial application. This study investigates the synthesis yield of SWNTs, which depends on the positions of the samples on a horizontal chemical vapor deposition (CVD) system. Methane and Fe thin films were used as the feedstock and catalyst for SWNTs synthesis, respectively. A high-resolution scanning electron microscope was used to examine the synthesis yield variation of the SWNTs along the axial distance of the reactor. The morphology and crystallinity of the fabricated SWNTs were evaluated by atomic force microscopy and Raman spectroscopy, respectively. We observed that the highest synthesis yield of the SWNTs was obtained in the rear region of the horizontal reactor, and not the central region. These results can be applied to the synthesis of various low-dimensional nanomaterials, such as semiconducting nanowires and transition metal dichalcogenides, especially when a horizontal CVD chamber is used.

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.

(Invited) Near Infrared Nanosensors to Image Brain Neurochemistry

Neurons communicate through chemical neurotransmitter signals that either terminate at the postsynaptic process (“wired transmission”) or diffuse beyond the synaptic cleft to modulate the activity of larger neuronal networks (“volume transmission”). Molecules such as dopamine belong to the latter class of neurotransmitters, and have been the pharmacological targets of antidepressants and antipsychotics for decades. Owing to the central role of dopamine over a range of behaviors and psychiatric disorders, real-time imaging of the signal’s spatial propagation would constitute a valuable advance in neurochemical imaging. To this end, we present a nanoscale near-infrared fluorescent nanosensor for dopamine and demonstrate its efficacy for imaging dopamine volume transmission in the extracellular space of the brain striatum and prefrontal cortex (Beyene et al. ACS Chem. Neuro. 2017). The sensor is developed from polymers pinned to the surface of single wall carbon nanotubes (SWNT) in which the surface-adsorbed polymer is the recognition moiety and the carbon nanotube the fluorescence transduction element. Excitonic transitions in functionalized SWNT yield up to ΔF/F = 4500% near-infrared fluorescence emission in the presence of dopamine (Beyene et al. Nano Letters 2018). We next demonstrate imaging of evoked dopamine release in acute striatal slices, and show altered dopamine reuptake kinetics when brain tissue is exposed to dopamine receptor agonist and antagonist drugs (Beyene et al. Science Advances 2019). Lastly, we discuss how to evolve synthetic molecular recognition for other neuromodulators of interest, such as serotonin (Jeong et al. Science Advances 2019). We characterize our findings in the context of their utility for high spatial and temporal neuromodulator imaging in the brain, describe nanosensor exciton behavior from a molecular dynamics (MD) perspective, and validate nanosensor for use to elucidate dopaminergic signaling variability with disease or pharmacological perturbations at a synaptic scale.

Synthesis of (9,8) single-walled carbon nanotubes on CoSO4/SiO2 catalysts: The effect of Co mass loadings

Selective synthesis of single-walled carbon nanotubes (SWCNTs) with narrow chirality distribution at high production yield is critical to realize their applications in electronics and medicine. However, there is a significant trade-off between chirality selectivity and SWCNT yield. In this study, a series of CoSO4/SiO2 catalysts containing from 1 to 9 wt% of Co were prepared to systematically study how Co mass loadings affect the chirality selectivity and carbon production yield. SWCNTs were analyzed by spectroscopies and microscopes, while catalysts at three stages of SWCNT synthesis were studied by multiple characterization tools. Our results show that all CoSO4/SiO2 catalysts can grow (9,8) tubes. Specifically, the catalyst containing 3 wt% Co has the highest yield of (9,8) tubes, which grow from metallic Co particles with a size of around 1.2 nm. These Co particles are in-situ produced by reducing small Co9S8 particles of 2 nm in size, while unreduced Co9S8 particles help to stabilize metallic Co particles. High Co mass loadings lead to the formation of large Co and Co9S8 particles, which favor the formation of graphitic carbon and multi-walled carbon nanotubes. These findings provide useful insights to guide the development of novel catalysts for the chiral selective production of SWCNTs.

(Invited) Plasmon Induced Near-infrared Fluorescence Enhancement of Single-walled Carbon Nanotubes

The near-infrared emissions of single-walled carbon nanotubes (SWCNTs) falls within the optical transparency window of biological tissue, allowing deep-tissue, in vivo and in vitro imaging. However, the relatively low photoluminescence quantum yield of SWCNTs, which typically lies in the range of 0.1 - 1.5%, limits the penetration depth and sensitivity of these fluorophores when used as imaging agents and optical sensors. In the present work, we enhance the fluorescence emission of SWCNTs up to 10-fold by employing different localized surface plasmon resonance (LSPR) nanostructures. We observe a chirality-dependent enhancement that varies with the nanostructure geometry and material. The proposed mechanism is based on changes in the charge density following nanoparticle conjugation with the SWCNT. In agreement with this mechanism, the enhancement and quenching effects show a strong correlation with the distance between the SWCNTs and the nanostructures. Finally, we demonstrate the applicability of this technology in a single-molecule imaging SWCNT application.

Improvement in growth yield of single-walled carbon nanotubes with narrow chirality distribution by pulse plasma CVD

A pulse plasma chemical vapor deposition (CVD) technique was developed for improving the growth yield of single-walled carbon nanotubes (SWNTs) with a narrow chirality distribution. The growth yield of the SWNTs could be improved by repetitive short duration pulse plasma CVD, while maintaining the initial narrow chirality distribution. Detailed growth dynamics is discussed based on a systematic investigation by changing the pulse parameters. The growth of SWNTs with a narrow chirality distribution could be controlled by the difference in the nucleation time required using catalysts comprising relatively small or large particles as the key factor. The nucleation can be controlled by adjusting the pulse on/off time ratio and the total processing time.

Roles of sulfur in floating-catalyst CVD growth of single-walled carbon nanotubes for transparent conductive film applications

Sulfur is an effective promoter for growing single-walled carbon nanotubes (SWCNTs) and tuning their structural properties. In particular, sulfur has been utilized in the floating-catalyst chemical vapor deposition (FC-CVD) process to fabricate SWCNT-based transparent conductive films (TCFs). However, in-situ catalyst nucleation process in conventional FC-CVD, hinders to correlate the substantial role of sulfur in tuning SWCNTs synthesis and enhancing the performance of SWCNT-based TCFs. Herein, we have for the first time, systematically studied the roles of sulfur on yield, morphology, and structure of SWCNTs grown by FC-CVD, using ex-situ Fe and Co catalyst particles. We found that SWCNT yield is largely dependent on the amount of sulfur introduced into the FC-CVD reactor and on catalyst composition. More importantly, the addition of an optimized amount of sulfur resulted in a three-fold enhancement of the opto-electronic performance of SWCNT-TCFs, by increasing diameter and bundle length along with improving the quality of SWCNTs. Surprisingly, electron diffraction analysis revealed that SWCNTs grown from both Fe and Co display wide chirality distributions spanning from zig-zag to armchair edges, indicating that the sulfur promoter has little influence on the chirality modulating of SWCNTs.

(Invited) Step-Wise Molecular Self-Assembly on Single-Wall Carbon Nanotube Networks: Towards Development of Delivery Systems of Highly Potent but Difficult to Administer Drugs

Single-walled carbon nanotubes (SWCNTs) are increasingly being investigated for biomedical imaging, sensing, and drug delivery. Individual dispersion and coating with biocompatible molecules of SWCNTs are essential to avoid triggering cytotoxicity and to realize these applications. Perhaps the most common method for generating SWCNT-based drug delivery systems involves individually dispersing SWCNTs in water with various biocompatible molecules such as DNA, biopolymers and proteins followed by linking drugs and targeting moieties to the biocompatible coating. Another relatively less frequently exploited approach entails first attaching drugs to SWCNTs and then dispersing with biocompatible molecules, which may also be targetable. Unfortunately, both approaches suffer from low SWCNT dispersion yield and inadequate control of drug loading process, particularly if the drugs are highly potent and difficult to administer. We have developed an extremely facile scheme to generate SWCNT-based drug delivery systems by controllably depositing biocompatible molecules and drugs on preformed SWCNT hydrogels. We first individually dispersed SWCNTs in water using suitable surfactant molecules, concentrated the dispersion to form freestanding hydrogels, and then removed the surfactant from the hydrogel. These surfactant-free SWCNT hydrogels comprise of three-dimensional, isotropic network of individual nanotubes held together via van der Waals interactions the junctions between nanotubes, and have >99% porosity, which allows unimpeded transport of biocompatible molecules and drugs. Furthermore, since many potent drugs are only soluble in non-aqueous solvents, water in the hydrogel can be easily exchanged with other suitable solvents to facilitate drug loading. As a proof-of-concept, we coated SWCNTs within the hydrogels first with drugs such as Doxorubicin, Bleomycin, and Digoxin, then with proteins such as albumins, and lastly dispersed in water through gentle 5 minutes sonication with little or no loss of SWCNT yield. Optical characterizations and imaging show that the albumin/drug/SWCNTs complexes are individually dispersed that the cells readily uptake. To demonstrate robustness of this approach, we coated SWCNTs with polymers prior to decorating with biomolecules/drug layers; the polymer coating was chosen to assist in rapid drug release after cell uptake. Overall, this approach allows precisely controlled, step-wise molecular self-assembly on SWCNTs of any drug and biomolecule combinations, suggesting high potential for development of multifunctional drug delivery platforms utilizing SWCNTs.

Systematic investigation of the catalyst composition effects on single-walled carbon nanotubes synthesis in floating-catalyst CVD

Enormous technological promise of single-walled carbon nanotubes (SWCNTs) can only be harnessed with the premise of controllable synthesis of SWCNTs, where catalyst composition thermodynamically plays a vital role. Herein, we have systematically investigated the effects of catalyst composition on SWCNTs synthesis, using a novel floating-catalyst chemical vapor deposition (FCCVD) system, consisting of catalyst synthesis via spark generator, FCCVD reactor and a real-time monitor of catalysts and SWCNTs. We synthesized SWCNTs from both monometallic (Fe, Co, Ni), bimetallic (Co-Ni, Co-Fe) catalyst particles and kinetically optimized yield and performance of SWCNTs films. We found that the highest yield of SWCNTs from Fe is 15 times as that of Ni SWCNTs and the Co-Ni SWCNTs film possesses best opto-electronic performance. Interestingly, the mean diameter of SWCNTs was found related to the catalyst particle size distributions, but not composition. Moreover, detailed atomic structures determination revealed that SWCNTs from Fe and Co have a wide chirality distribution spanning from zig-zag to armchair edges. However, Co-Ni SWCNTs have comparatively narrower chirality distribution having 71% SWCNTs in the chiral angle of 15–30°. Our results indicate that catalyst composition can efficiently tune yield and characteristics of SWCNTs, but it does not dramatically shift chirality of FCCVD SWCNTs.

Carbon and Core Shell like Molecular Nanostructures in Cancer diagnosis and Therapy

During the past years, carbon nanotubes (CNTs) have attracted considerable interest since their first discovery. Great progress has been made in the field of nanomaterials given their great potential in biomedical applications. Carbon nanotubes (CNTs), due to their unique physicochemical properties, have become a popular tool in cancer diagnosis and therapy. They are considered one of the most promising nanomaterials with the capability of both detecting the cancerous cells and delivering drugs or small therapeutic molecules to these cells because of the unique structure, extremely high specific surface area to-volume ratio enable them to use in an intense real time applications such as detection and treatment of cancerous cells, nervous disorders, tissue repair. and excellent electrical and mechanical properties carbon nanotubes composed of excellent mechanical strength, electrical and thermal conductivities makes them a suitable substance toward developing medical devices., CNTs have been explored in almost every single cancer treatment modality, including drug delivery with small nanomolecules, lymphatic targeted chemotherapy, thermal therapy, photodynamic therapy, and gene therapy and demonstrate a great promise in their use in targeted drug delivery systems, diagnostic techniques and in bio-analytical applications. Majority of the biomedical applications of CNTs must be used after successful functionalization for more potential applications than pristine CNTs. There are several approaches to modify pristine CNTs to potentially active. CNTs poised into the human life and exploited in medical context. Here in, we reviewed the following topics (i) Functionalization of CNTs (ii) CNTs in real time applications such as drug delivery, gene therapy, biosensors and bio imaging; (iii) CNTs 3D printed scaffolds for medicine and (iv) Biocompatability and Biodegradability. Single-walled carbon nanotubes (SWCNTs) were synthesized using the high-pressure carbon monoxide disproportionation process (HiPCO). The SWCNT diameter, diameter distribution and yield can be varied depending on the process parameters. The obtained HiPCO product present an iron nanoparticle encapsulated heteronanocarbon (core-shell nanoparticles) at low pressure (1 bar) after removing of iron metal catalyst nanoparticle and amorphous carbon by acid immersion and oxidation. The resulting therapeutic molecule in the form of coreshell nanoparticles and single walled carbon nanotubes after functionalization by filling of iron can be use as therapeutic nanomaterials in nanomedicine in diagnosis and treatment of cancer tumor. This paper describes the synthesis method and role of multifunctional nanoparticle in diagnosis and treatment of cancer. Therefore, the aim of this review is to provide basic information on nanoparticles, describe previously developed methods to functionalize nanoparticles and discuss their potential applications in nanobiomedical and mention the therapeutic nanoparticle large scale production and commercialization challenges. In the final part of the review, emphasis is given on the pharmacokinetic aspects of carbon nanotubes including administration routes, absorption mechanisms, distribution and elimination of carbon nanotubes based systems. Lastly, a comprehensive account about the potential biomedical applications has been given followed by insights into the future carbon nanotubes from synthesis to in vivo biomedical applications.

Tuning Geometry of SWCNTs by CO2 in Floating Catalyst CVD for High‐Performance Transparent Conductive Films

AbstractOptimized geometry of single‐walled carbon nanotubes (SWCNTs) is vital to high‐performance transparent conductive films (TCFs). Herein, the geometry of SWCNTs, i.e., tube diameter, bundle length, and bundle diameter, are successfully tuned by introducing carbon dioxide (CO2) into floating catalyst chemical vapor deposition (FC‐CVD), where carbon monoxide (CO) is used as a carbon source and ferrocene as a catalyst precursor. Both tube diameter and bundle length increase with an increment of CO2 concentration, and the yield of SWCNTs can be significantly promoted with the appropriate amount of CO2. The role of CO2 in this behavior is further rationalized as enhancing CO decomposition or carbon dissolution into catalysts. The TCFs based on SWCNTs with optimized geometry by CO2 exhibit improved performance up to 86.8 Ω sq−1 at 90% transmittance after AuCl3 doping, achieving about 50% reduction of sheet resistance compared to the TCFs without CO2. The use of CO2 for directly tuning growth of SWCNTs blazes a new trail in the field of SWCNT based TCFs.

A Comparison Between Reduced and Intentionally Oxidized Metal Catalysts for Growth of Single‐Walled Carbon Nanotubes

In this article, the authors report a detailed comparative study on the growth of single‐walled carbon nanotubes (SWNTs) from monometallic and its oxide (intentionally oxidized) catalysts. The difference and findings are summarized in the following three aspects. 1) High‐quality SWNTs are also grown from intentionally oxidized Co nanoparticles, but the yield of SWNTs significantly decreases, resulting in random network rather than vertically aligned SWNT arrays. 2) The authors clarify from in‐plane transmission electron microscopy that Co oxide nanoparticles grow SWNTs through an in situ reduction process, which means Co oxide becomes metallic Co after the introduction of ethanol; direct growth from an oxide phase is not observed. 3) Compared to the SWNTs grown by pre‐reduced catalysts, SWNTs grown from intentionally oxidized catalysts show narrower diameter distribution and smaller average diameter from Raman spectra. The strategy also shows similar results in the Ni catalysts. The findings are helpful to improve the controllability of SWNT diameter and morphology, as well as the reproducibility and robustness of CVD process.