Application Of Carbon Nanotubes Research Articles

A Brief Introduction of Carbon Nanotubes: History, Synthesis, and Properties

Carbon nanotube (CNT) is one of the most widely used nanomaterials recently. Since it was discovered by Iijima in 1991, its various synthesis methods were being mature in the past 30 years. The research of carbon nanotube applications in different fields has never stopped. Since a number of researchers have tested the excellent properties of CNTs, it provides an optimistic expectation about CNT applications in the future. This review summarizes the historical development of CNTs, and briefly introduces three main CNT synthesis methods and their properties.

Research on the dispersion of carbon nanotubes and their application in solution-processed polymeric matrix composites: A review

This review highlights and categorizes the approaches for preparation of CNTs dispersion and polymer/CNTs composites via solution-based strategies. Carbon nanotubes (CNTs) demonstrate unique physical and chemical properties, which allow several exciting potential applications in various fields including nanocomposites. Presently, the commercialized application of CNTs is still quite limited due to the formation of CNTs bundles, which significantly degrade the properties. Therefore, well dispersion of CNTs in nanocomposites is quite important, especially for CNTs/polymer composites, as a small amount of CNTs can improve the composite properties dramatically. This article will review the research on the dispersion of CNTs (including covalent and non-covalent functionalization) and the fabrication of CNTs/polymer composites through solution-based strategies by using the CNT dispersions. Moreover, the factors influencing the properties of CNTs/polymer composites will be discussed as well as the future outlook.

Aligned Collagen-CNT Nanofibrils and the Modulation Effect on Ovarian Cancer Cells.

Fibrillar collagen is a one-dimensional biopolymer and is the most abundant structural protein in the extracellular matrix (ECM) of connective tissues. Due to the unique properties of carbon nanotubes (CNTs), considerable attention has been given to the application of CNTs in developing biocomposite materials for tissue engineering and drug delivery. When introduced to tissues, CNTs inevitably interact and integrate with collagen and impose a discernible effect on cells in the vicinity. The positive effect of the collagen-CNT (COL-CNT) matrix in tissue regeneration and the cytotoxicity of free CNTs have been investigated extensively. In this study, we aimed to examine the effect of COL-CNT on mediating the interaction between the matrix and SKOV3 ovarian cancer cells. We generated unidirectionally aligned collagen and COL-CNT nanofibrils, mimicking the structure and dimension of collagen fibrils in native tissues. AFM analysis revealed that the one-dimensional structure, high stiffness, and low adhesion of COL-CNT greatly facilitated the polarization of SKOV3 cells by regulating the β−1 integrin-mediated cell–matrix interaction, cytoskeleton rearrangement, and cell migration. Protein and gene level analyses implied that both collagen and COL-CNT matrices induced the epithelial–mesenchymal transition (EMT), and the COL-CNT matrix prompted a higher level of cell transformation. However, the induced cells expressed CD44 at a reduced level and MMP2 at an increased level, and they were responsive to the chemotherapy drug gemcitabine. The results suggested that the COL-CNT matrix induced the transdifferentiation of the epithelial cancer cells to mature, less aggressive, and less potent cells, which are inapt for tumor metastasis and chemoresistance. Thus, the presence of CNT in a collagen matrix is unlikely to cause an adverse effect on cancer patients if a controlled dose of CNT is used for drug delivery or tissue regeneration.

(Invited) Tuning the Properties of Luminescent Defects in Carbon Nanotubes for Applications

Luminescent sp3-defects (also called quantum defects or organic color centers) in single-walled carbon nanotubes (SWCNTs) with their characteristic red-shifted emission and long photoluminescence (PL) lifetimes enable higher PL quantum yields and single-photon emission at room temperature. They can be created in a controlled manner on polymer-wrapped semiconducting nanotubes via diazonium chemistry in organic solvents with a variety of functional substituents [ACS Nano 2019, 13, 9259]. Here we show, how attaching the stable and neutral perchlorotriphenylmethyl (PTM) radical to such sp3-defects impacts their emissive properties in dispersion at room temperature as well as under strong magnetic fields at cryogenic temperatures. Furthermore, the type of defect emission (E11* or E11*-) is governed by the precise binding configuration for chiral (6,5) SWCNTs. We introduce a simple synthetic protocol to obtain exclusively the more red-shifted E11*--defect emission with even longer PL lifetime and high single-photon purity. This new functionalization method relies on nucleophilic addition instead of radical-based reactions and can be transferred to other polymer-sorted nanotubes, e.g. (7,5) and (10,5) SWCNTs. The achieved tunability and control of sp3-defect emission facilitates applications in electroluminescent devices, radiative pumping of exciton-polaritons in metal-clad microcavities [ACS Photonics 2020, DOI: 10.1021/acsphotonics.0c01129] or in-vivo imaging in the 2nd biological window.

Carbon Nanotube Assemblies for Neuroscience Applications

Assembling carbon nanotubes (CNTs) into macroscopic materials allows multiple applications that takes advantage of their physical properties. Specifically, the synthesis, fiber assembly, polymer coating and application of CNTs as microelectrodes has allowed us explore physiological applications as well as sensor development. This talk will summarize our research in CNT microelectrode development, neural recording and stimulation, and neurotransmitter detection and quantification through voltammetric techniques. Recordings and stimulations of neuronal electrical activity is a topic of great interest in neuroscience. Current commercial electrodes for transferring charges from solid electrode materials to and from biological tissue still have some limitations. A microelectrode that is flexible, chemically inert, electrically conducting, and preferentially transfers electrons via capacitive charge-injection is needed to treat multiple neurological disorders. This talk will compare charge transport capabilities from carbon nanotube fibers, noble metals Au and Ag wire microelectrodes to biological tissue. The recording ability of microelectrodes is demonstrated through Electroretinography (ERG) on Sarcophaga bullata fly eyes, where light stimulation generates potential changes that were detected by our microelectrodes. Stimulation is demonstrated through Au wire and carbon nanotube fiber implants in Madagascar hissing cockroach (Gromphadorhina portentosa) antennas to control their locomotion directions. In addition, CNT microelectrodes has been found to detect neurotransmitters dopamine (DA), serotonin (5-HT), epinephrine (Epn) and nor-epinephrine (Nor-epn) using voltammetric techniques with excellent limits of detection in the range of ~10-11 M. For practical applicability, the electrodes can detect in real time DA release from culture rat pheochromocytoma (PC12) cells upon concentrate K+stimulation.

Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application

As the world human population and industrialization keep growing, the water availability issue has forced scientists, engineers, and legislators of water supply industries to better manage water resources. Pollutant removals from wastewaters are crucial to ensure qualities of available water resources (including natural water bodies or reclaimed waters). Diverse techniques have been developed to deal with water quality concerns. Carbon based nanomaterials, especially carbon nanotubes (CNTs) with their high specific surface area and associated adsorption sites, have drawn a special focus in environmental applications, especially water and wastewater treatment. This critical review summarizes recent developments and adsorption behaviors of CNTs used to remove organics or heavy metal ions from contaminated waters via adsorption and inactivation of biological species associated with CNTs. Foci include CNTs synthesis, purification, and surface modifications or functionalization, followed by their characterization methods and the effect of water chemistry on adsorption capacities and removal mechanisms. Functionalized CNTs have been proven to be promising nanomaterials for the decontamination of waters due to their high adsorption capacity. However, most of the functional CNT applications are limited to lab-scale experiments only. Feasibility of their large-scale/industrial applications with cost-effective ways of synthesis and assessments of their toxicity with better simulating adsorption mechanisms still need to be studied.

Common Defects Accelerate Charge Separation and Reduce Recombination in CNT/Molecule Composites: Atomistic Quantum Dynamics.

Carbon nanotubes (CNTs) are appealing candidates for solar and optoelectronic applications. Traditionally used as electron sinks, CNTs can also perform as electron donors, as exemplified by coupling with perylenediimide (PDI). To achieve high efficiencies, electron transfer (ET) should be fast, while subsequent charge recombination should be slow. Typically, defects are considered detrimental to material performance because they accelerate charge and energy losses. We demonstrate that, surprisingly, common CNT defects improve rather than deteriorate the performance. CNTs and other low dimensional materials accommodate moderate defects without creating deep traps. At the same time, charge redistribution caused by CNT defects creates an additional electrostatic potential that increases the CNT work function and lowers CNT energy levels relative to those of the acceptor species. Hence, the energy gap for the ET is decreased, while the gap for the charge recombination is increased. The effect is particularly important because charge acceptors tend to bind near defects due to enhanced chemical interactions. The time-domain simulation of the excited-state dynamics provides an atomistic picture of the observed phenomenon and characterizes in detail the electronic states, vibrational motions, inelastic and elastic electron-phonon interactions, and time scales of the charge separation and recombination processes. The findings should apply generally to low-dimensional materials, because they dissipate defect strain better than bulk semiconductors. Our calculations reveal that CNT performance is robust to common defects and that moderate defects are essential rather than detrimental for CNT application in energy, electronics, and related fields.

Carbon Nanotubes Decrease the Negative Impact of Alternaria solani in Tomato Crop.

The diseases that attack the tomato crop are a limiting factor for its production and are difficult to control or eradicate. Stem and fruit rot and leaf blight caused by Alternaria solani causes severe damage and substantial yield losses. Carbon nanotubes (CNTs) could be an alternative for the control of pathogens since they have strong antimicrobial activity, in addition to inducing the activation of the antioxidant defense system in plants. In the present study, multi-walled carbon nanotubes were evaluated on the incidence and severity of A. solani. Moreover, to the impact they have on the antioxidant defense system and the photosynthetic capacity of the tomato crop. The results show that the application of CNTs had multiple positive effects on tomato crop. CNTs decreased the incidence and severity of A. solani. Furthermore, CNTs increased the fruit yield of tomato crop and dry shoot biomass. The antioxidant system was improved, since the content of ascorbic acid, flavonoids, and the activity of the glutathione peroxidase enzyme were increased. The net photosynthesis and water use efficiency were also increased by the application of CNTs. CNTs can be an option to control A. solani in tomato crop, and diminish the negative impact of this pathogen.

Applicability of CNT as support candidate for thiophene hydrodesulfurization and 1-octene hydrogenation catalyst

The application of carbon nanotubes (CNT) as a support candidate for hydrotreating catalysts for FCC (fluid catalytic cracking) gasoline was researched in the microreactor with a fixed bed at experimental conditions. The CNT synthesized using the AC arc discharge method was functionalized by chemical treatment with nitric acid. Scanning electron spectroscopy (SEM), X-ray diffraction (XRD) and X-photoelectron spectroscopy (XPS) of the functionalized CNT show that during the functionalization of it, HNO3 impurities unwanted for further application were removed and carbon nanostructures haveoxidized, and therefore they have oxide functional groups attached to those walls. At all the conditions observed, the Ni-Mo/CNT catalysts and Co-Mo-0.25 catalyst showed better hydrodesulfurization activities in comparison with the conventional Ni-Mo/γ-Al2O3. As shown in the XRD analysis, the Ni–W/CNT catalysts showed lowest thiophene hydrodesulfurization activity in the temperature range observed, but they showed very good hydrogenation activity on model compounds used.Catalytic performance tests of different catalysts showed that good applicability of the CNT as support candidate for the hydrotreating catalysts. It also was experimentally demonstrated that the Ni-Mo/CNT and Co-Mo/CNT can be the best hydrotreating catalysts.

Carbon-Nanotube-Coated Surface Electrodes for Cortical Recordings In Vivo.

Current developments of electrodes for neural recordings address the need of biomedical research and applications for high spatial acuity in electrophysiological recordings. One approach is the usage of novel materials to overcome electrochemical constraints of state-of-the-art metal contacts. Promising materials are carbon nanotubes (CNTs), as they are well suited for neural interfacing. The CNTs increase the effective contact surface area to decrease high impedances while keeping minimal contact diameters. However, to prevent toxic dissolving of CNTs, an appropriate surface coating is required. In this study, we tested flexible surface electrocorticographic (ECoG) electrodes, coated with a CNT-silicone rubber composite. First, we describe the outcome of surface etching, which exposes the contact nanostructure while anchoring the CNTs. Subsequently, the ECoG electrodes were used for acute in vivo recordings of auditory evoked potentials from the guinea pig auditory cortex. Both the impedances and the signal-to-noise ratios of coated contacts were similar to uncoated gold contacts. This novel approach for a safe application of CNTs, embedded in a surface etched silicone rubber, showed promising results but did not lead to improvements during acute recordings.

Whole-Transcriptome Responses to Environmental Stresses in Agricultural Crops Treated with Carbon-Based Nanomaterials.

Carbon-based nanomaterials (CBNs) such as carbon nanotubes (CNTs) and graphene can be beneficial to crops exposed to abiotic stresses such as drought and high salinity. Our findings suggest that the improvement observed in stressed crops treated with CBNs can be associated with CBN-induced restoration of gene expression. When subjected to salt stress, sorghum seedlings showed modified expression in 51 stress-related genes. The introduction of CNTs or graphene into the salty growth medium resulted in the restoration of the expression of 29 affected genes, resembling that of untreated sorghum seedlings. RNA-Seq approach allowed us to analyze the total gene expression of CBN-treated rice exposed to water-deficit stress and gene expression of CBN-treated tomato plants exposed to salt stress. The application of CNTs or graphene resulted in full or partial restoration of expression of 458 and 1620 genes, respectively, affected by water-deficit stress in rice. Similarly, CBN treatment of NaCl-exposed tomato seedlings led to full or partial restoration of 1639 and 1391 salt-affected transcripts, respectively. Of the genes with restored expression, many of them were identified as major stress-response genes and major transcriptional factors (aquaporins, dehydrins, and heat shock proteins/co-chaperons, NAC, WRKY) and were associated with key stress-signaling pathways (ABA-signaling, InsP3 signaling, and MAPK signaling) in all three tested plant species. These findings provide evidence that CBNs can provide halotolerance and drought tolerance by normalizing the expression of affected stress genes.

Facile synthesis and applications of carbon nanotubes in heavy-metal remediation and biomedical fields: A comprehensive review

Carbon nanotubes (CNTs) have drawn great attention due to the rich science underpinning their applications coupled with a unique combination of properties like large aspect ratios, superior thermal and electrical conductivity, excellent optical characteristics and high surface area. Through chemical modification, re-engineering and functionalization, control of parameters such as surface chemistry, size distribution, surface area, agglomeration and structure have been made possible leading to improved functionality. CNTs not only holds promise in a wide range of applications in medicine, nano and microelectronics, and environmental remediation but can also be used for laboratory experimental tenacities. More particularly, CNTs serve as an excellent adsorbent in the removal of heavy metal ions (HMI) from wastewater. Equally, they are capable of coupling with many therapeutic and diagnostic agents hence being used in biomedical applications such as tissue engineering, cancer therapy, drug delivery, biosensing and imaging. These two distinguished and noble applications have offered improved human health services and ensured a safer environment thus momentously revolutionizing human life. In that regard, this article has reviewed the advancements in the applications of CNTs in the treatment of heavy metal-contaminated water and biomedical applications drawn from several research articles and other publications.

Using Wet Electrospun PCL/Gelatin/CNT Yarns to Fabricate Textile-Based Scaffolds for Vascular Tissue Engineering.

Incorporating conductive materials in scaffolds has shown advantages in regulating adhesion, mitigation, and proliferation of electroactive cells for tissue engineering applications. Among various conductive materials, carbon nanotubes (CNTs) have shown great promises in tissue engineering because of their good mechanical properties. However, the broad application of CNTs in tissue engineering is limited by current methods to incorporate CNTs in polymers that require miscible solvents to dissolve CNTs and polymers or CNT surface modification. These methods either limit polymer selections or adversely affect the properties of polymer/CNT composites. Here, we report a novel method to fabricate polymer/CNT composite yarns by electrospinning polycaprolactone/gelatin into a bath of CNT dispersion and extracting electrospun fibers out of the bath. The concentration of CNTs in the bath affects the thermal and mechanical properties and the yarns' degradation behavior. In vitro biological test results show that within a limited range of CNT concentrations in the bath, the yarns exhibit good biocompatibility and the ability to guide cell elongation and alignment. We also report the design and fabrication of a vascular scaffold by knitting the yarns into a textile fabric and combining the textile fabric with gelatin. The scaffold has similar mechanical properties to native vessels and supports cell proliferation. This work demonstrates that the wet electrospun polymer/CNT yarns are good candidates for constructing vascular scaffolds and provides a novel method to incorporate CNTs or other functional materials into biopolymers for tissue engineering applications.

Chemical Functionalization of Carbon Nanotubes with Polymers: A Brief Overview

Carbon nanotubes (CNTs), the one-dimensional allotropes of carbon, have attracted noteworthy research interest since their discovery in 1991 owing to their large aspect ratio, low mass density, and unique chemical, physical, and electronic properties that provide exciting possibilities for nanoscale applications. Nonetheless, two major issues should be considered when working with this sort of nanomaterial: their strong agglomerating tendency, since they are typically present as bundles or ropes of nanotubes, and the metallic impurities and carbonaceous fragments that go along with the CNTs. The successful utilization of CNTs in a wide variety of applications—in particular, in the field of polymer composites—depends on their uniform dispersion and the development of a strong chemical interaction with the polymeric matrix. To achieve these aims, chemical functionalization of their sidewalls and tips is required. In this article, a brief overview of the different approaches for CNT modification using polymers is provided, focusing on the covalent functionalization via “grafting to” or “grafting from” strategies. The characteristics and advantages of each approach are thoroughly discussed, including a few typical and recent examples. Moreover, applications of polymer-grafted CNTs as biosensors, membranes, energy storage substances, and EMI shielding are briefly described. Finally, future viewpoints in this vibrant research area are proposed.

Advantages and challenges of carbon nanotubes as bone repair materials

With the in-depth research on bone repair process, and the progress in bone repair materials preparation and characterization, a variety of artificial bone substitutes have been fully developed in the treatment of bone related diseases such as bone defects. However, the current various natural or synthetic biomaterials are still unable to achieve the structure and properties of natural bone. Carbon nanotubes (CNTs) have provided a new direction for the development of new materials in the field of bone repair due to their excellent structural stability, mechanical properties, and functional group modifiability. Moreover, CNTs and their composites have broad prospects in the design of bone repair materials and as drug delivery carriers. This paper describes the advantages of CNTs related to bone tissue regeneration from the aspects of morphology, chemistry, mechanics, electromagnetism, and biosafety, as well as the application of CNTs in drug delivery carriers and reinforcement components of scaffold materials. In addition, the potential problems and prospects of CNTs in bone regenerative medicine are discussed.

Salting-out aided dispersive extraction of Mn3O4 nanoparticles and carbon nanotubes for application in supercapacitors

In this study, results from a conceptually new method for the preparation of Mn3O4-multiwalled carbon nanotube (MCNT) composites are presented. High active mass (HAM) Mn3O4-MCNT cathodes are prepared and tested for supercapacitors. The method is based on a salting-out aided dispersive extraction of Mn3O4 particles precipitated in an aqueous phase to isopropanol and their co-dispersion with MCNT. The use of lauryl gallate as an extractor is a key factor for the phase transfer. Lauryl gallate is used as a co-dispersant for Mn3O4 and MCNT. The mechanisms of lauryl gallate adsorption on Mn3O4 and MCNT and the salting-out aided extraction mechanism are discussed. Enhanced electrochemical performance of the electrodes with HAM of 41 mg cm−2 is achieved due to enhanced mixing and co-dispersion of Mn3O4 and MCNT. The electrodes show a high capacitance of 6 F cm−2 in aqueous Na2SO4 and low electrical resistance. The obtained areal capacitance is substantially higher than that for Mn3O4-MCNT composites, prepared by other methods. The capacitance increase during initial cycling is linked to the microstructure changes. The salting-out aided extraction method overcomes the limitations of other extraction techniques and opens a new strategy for the manufacturing of nanocomposites with advanced functional properties.

Medium-term response of the natural grassland soil biota to multiwalled carbon nanotube contamination.

Although the soil environment can potentially be exposed to contamination by carbon nanotubes (CNT), its impact on soil biology is poorly understood. In this study, we investigated the effect of the multiwalled CNT (MWCNT) contamination on different groups of soil organisms (microbial, micro- and mesofaunal communities) as well as the soil enzyme activity. The experimental mesocosms included the intact soil cores that were collected from a natural grassland. The MWCNTs that were pristine (pCNTs) and functionalised (fCNTs) at a concentration of 500μgg-1 of soil were applied in the form of water suspensions to the surface of the mesocosms, while ensuring the soil was not mixed after the treatment. Soil samples were taken at 3, 6, and 15weeks after CNT application. The CNT soil contamination highlighted differences in the community dynamics within the studied groups when compared to the control (non-contaminated soil). Among the faunal groups, nematodes were found to be more sensitive to the CNT impact than mites. The most pronounced response of the nematodes was observed in the subsoil at week 6, when their numbers were 3- (pCNTs) and 4-fold (fCNTs) higher than the control mesocosms. Both types of CNTs influenced the relative abundance of the bacterial- and hyphal-feeding nematodes, where pCNTs significantly and negatively affected the predatory nematodes. Moreover, CNTs temporarily, but significantly, decreased the diversity of the nematode communities. In addition, the values of the nematode Structure Index confirmed a strong transitional disturbance effect of CNTs in the soil food web, while the Channel Index in the pCNTs indicated an increasing share of fungi in the decomposition pathway. Hence, we can infer that although the impact of CNTs seems to be temporary, the shifts in the soil community abundance and structure that it induced may have long-term consequences for soil functioning, including nutrient cycling.

Regeneration and reuse of the carbon nanotubes for the adsorption of selected anticancer drugs from water matrices

Effective methods of water and wastewater purification are still being investigated. Among several methods, sorption onto carbon nanotubes (CNTs) is very promising solution. CNTs possess high potential to remove a wide range of chemicals from water, including pharmaceuticals, which are frequently found in various aqueous samples. Crucial aspect of the application of CNTs as adsorbents is the possibility to use the material multiple times with the material maintaining its sorption potential and capacity. For this reason, thermal and chemical regeneration of Multi-Walled Carbon Nanotubes (MWCNTs) was investigated in our study. The conditions of thermal regeneration were set at 300 °C for 2 h. Higher temperatures caused large losses of MWCNTs. Next, the adsorbent was put in a cycle of contamination – regeneration, where it was mixed with wastewater treatment plant influent for 16 h, then dried and thermally regenerated. After thermal treatment, the sorption level (%) of three anticancer drugs — cyclophosphamide, ifosfamide and 5-fluorouracil — was determined. The obtained results proved that there was no negative influence on the sorption level of any investigated pharmaceuticals after 5 cycles of contamination – thermal regeneration. An additional regeneration method of MWCNTs with 3 M HNO3 was proposed, but the sorption level of cyclophosphamide after such treatment decreased from around 50 % (for untreated and thermally regenerated MWCNTs) to around 30 %. It suggests that contact with acid changed MWCNTs, probably by introducing additional functional groups onto their surface. The performed elemental analysis, Raman spectroscopy and both SEM and TEM images, confirm these predictions.

Fenton-like reaction driving the degradation and uptake of multi-walled carbon nanotubes mediated by bacterium

Carbon nanotubes (CNTs) have been widely studied because of their potential applications. The increasing applications of CNTs and less known of their environmental fates rise concerns about their safety. In this study, the biotransformation of multi-walled carbon nanotubes (MWCNTs) by Labrys sp. WJW was investigated. Within 16 days, qPCR analysis showed that cell numbers increased 4.92 ± 0.36 folds using 100 mg/L MWCNTs as the sole carbon source. The biotransformation of MWCNTs, which led to morphology and functional group change, was evidenced by transmission electron microscopy and X-ray photoelectron spectroscopy analyses. Raman spectra illustrated that more defects and disordered carbon appeared on MWCNTs during incubation. The underlying biotransformation mechanism of MWCNTs through an extracellular bacterial Fenton-like reaction was demonstrated. In this bacteria-mediated reaction, the OH production was induced by reduction of H2O2 involved a continuous cycle of Fe(II)/Fe(III). Bacterial biotransformation of MWCNTs will provide new insights into the understanding of CNTs bioremediation processes.

Natural Materials—Interesting Candidates for Carbon Nanomaterials

This review sums up the techniques used for the synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon nanospheres (CNSs) by employing catalysts of natural origin. Establishing large-scale production and commercial applications of CNTs for a sustainable society is still of high apprehension. In this regard, one of the major factors is the starting materials such as precursors and catalyst sources. However, natural materials contain a minor quantity of metals or metal oxides and could be employed as a catalyst source for the synthesis of CNTs, providing the possibility to replace expensive catalyst sources. A large number of successful studies have been completed so far and confirm that these developed methods for carbon nanomaterials synthesis exhibiting high quality from common natural materials are not only possible but, most importantly, promising and scalable. This review also highlights purification methods and recent promising applications of as-synthesized CNTs.