Pristine Single-walled Carbon Nanotubes Research Articles

Synthesizing of helical-single walled carbon nanotubes by chemical vapour decomposition for engine

The captivating interest on carbon nanotubes (CNTs) has kindled the research activity after its discovery in 1991. It is due to its fabulous properties which have opened numerous applications like high weight to strength ratio, field emission transistors, and catalysis. Irrespective of the stunning technological development there is still much struggle in the synthesis aspect, which is a great drawback in compliance of these unique materials in the commercial application. Apart from various known method catalytic chemical vapor deposition (CCVD) is more advantages, where SWCNTs can be produced with varying diameters, large scale production, with high purity, variable temperature and most importantly it can be produced economically. In CCVD technique, We have used magnesium metal as a substrate with transition metal like Fe, and Ni, to prepare combustion catalyst. SWCNTs synthesized from FeaNibMg1-(a + b)O (FNM) catalyst had a higher yield than other catalysts with helical structure in the single layer of graphitic carbon (h-SWCNTs). The morphology of the synthesized h-SWCNTs was identified by Field Emission Scanning Electron Microscope and many others. Environmental damage from industries is looking for a prominent candidate to sort out the issues such as high catalytic activity, reusability, and stability norms. With the obtained result a comparative study was done against combustion catalyst, purified and pristine SWCNTs. It is found that the pristine h-SWCNTs had a good photo catalytic activity with this result we have confirmed SWCNTs synthesized from solution combustion technique can be utilized for commercial application.

Porphyrin nanofiber/single-walled carbon nanotube nanocomposite-based sensors for monitoring hydrogen peroxide vapor

Detection of hydrogen peroxide (H2O2) is particularly important in the field of clinical diagnosis for exhaled breath analysis, because H2O2 is closely related to diseases such as cancer, traumatic brain injury, chronic obstructive pulmonary disease, and asthma. Considering this, development of sensors for sensitive and selective real-time monitoring of H2O2 vapor (HPV) is required. In this study, we report the design and fabrication of a high-performance HPV sensor based on nanocomposites of nanofibers of a porphyrin derivative (oxo-[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) (TiOTPyP)) and single-walled carbon nanotubes (SWCNTs) at room temperature. Two types of HPV sensor transducers were fabricated using pristine SWCNTs only and TiOTPyP nanofiber/SWCNT nanocomposite and the sensor responses were compared. The significant differences in reproducibility and selectivity of the two sensors reflected the significant impact of the added TiOTPyP nanofibers on the device performance. The response of the TiOTPyP nanofiber/SWCNT nanocomposite-based sensor to 1 ppm of HPV is 9 times higher than that of the pristine SWCNT-based sensor. In addition, this sensor shows fast response/recovery times in the detection of HPV in the concentration range of 0.1–10 ppm, while showing a weak response to NH3 gas and negligible response to CO, toluene, acetone, hexane, NO, and NO2 gases.

Field-emission properties of sulfur chain-encapsulated single-walled carbon nanotubes

The encapsulation of elemental sulfur inside single-walled carbon nanotube (SWNT) and the consequent formation of sulfur chain-encapsulated SWNT (S@SWNT) is achieved. Raman spectra suggest an enhanced conductivity and electron doping of the SWNT by the sulfur chain encapsulation, which are also consistent with ultraviolet photoelectron spectra and thermoelectric measurements. Owing to the enhanced electron concentration and the reduced work function, an enhanced field-emission (FE) current is observed for S@SWNT. In addition, a gradual recovery of the suppressed FE current is observed for S@SWNT after the O2 purging in the chamber is terminated, while the permanent failure of FE is observed for the pristine SWNT. Further experimental results collectively demonstrate that the enhanced electron concentration of the relatively n-doped SWNT by sulfur chain encapsulation alleviates the damage inflicted to the emitter tip sites from the oxidative environment generated during FE measurement.

A Simple Method for Anchoring Silver and Copper Nanoparticles on Single Wall Carbon Nanotubes.

Single walled carbon nanotubes (SWCNT) were functionalized using the 1,3-dipolar cycloaddition reaction of an azomethine ylide under solvent-free conditions, a one-pot procedure that yields pyrrolidine type of groups at the nanotubes surface. The functionalized SWCNT were further decorated with Ag and Cu nanoparticles by reduction of the corresponding metal salts in dimethylformamide. The extensive reduction of silver from its nitrate was observed, as well as the partial reduction of copper from its acetate. X-ray photoelectron spectroscopy (XPS) confirmed the functionalization of SWCNT with pyrrolidine that provided anchoring sites for the metal nanoparticles. Metal nanoparticles (NP) were formed at the surface of the organically functionalized SWCNT in higher yields as compared to the same procedure carried out with pristine SWCNT. This was observed using scanning electron microscopy (SEM) and quantified by XPS. Raman spectroscopy demonstrated that functionalization and metal decoration of the SWCNT did not induce structural damage to the SWCNT.

Vibrational Spectrocopic Studies of Organic Molecules After Encapsulation Inside Single-Walled Carbon Nanotubes

7,7,8,8-tetracyano-p-quinodimethane (TCNQ), tetrathiafulvalene (TTF), and dodecanethiol (DoSH) were encapsulated inside single-walled carbon nanotubes (SWNTs), (TCNQ@SWNT, TTF@SWNT, and DoSH@SWNT). We measured the Fourier transform infra-red (FTIR) spectra and X-ray diffraction (XRD) patterns to confirm the encapsulation of organic molecules. Slight shifts of the FTIR peaks and the disappearance of an XRD peak at ~6°, corresponding to the SWNT (10) reflection, were observed. From the measurements of the current-voltage curves, it was revealed that the current of TTF@ SWNT and DoSH@SWNT decreased, and the current of TCNQ@SWNT increased compared with that of pristine SWNTs.

Theoretical study on wetting behavior of B-SWNT: Effects of doping concentration

Wettability is a key property of single-walled carbon nanotubes (SWNTs), governed both by the chemical composition and geometrical microstructure of the contact surface. Wettability of SWNTs can be enhanced via doping with heteroatoms such as boron or nitrogen to tune the electronic properties of SWNTs. We investigated the adsorption of the water monomer and dimer on pristine and B-doped (5,5) SWNTs by first-principles calculations. The calculated adsorption energy of the water monomer and dimer on pristine (5,5) SWNTs was low. The water dimer can form BO dative bonds with B-doped (5,5) SWNTs, enhancing interactions among each other. A higher adsorption energy of the water dimer was obtained with higher B-doping concentration. Additionally, electronic property analysis showed electron transfer from the water dimer to the boron of the SWNT, forming a BO dative bond, then from the SWNT to the water dimer through an OH⋯π interaction. The interactions between water dimer and SWNT are strongly cooperative. We further compared the adsorption energies of the water dimer and trimer on B-doped SWNTs with their cohesive energies. The adsorption energies increase due to cooperative effects, thereby enhancing wettability. We can expect that B-doped SWNTs can efficiently improve the wettability of carbon nanotubes.

First Principles Investigation of NH3 and NO2 Adsorption on Transition Metal-Doped Single-Walled Carbon Nanotubes

Density functional theory calculations were carried out to investigate the binding ability of transition metals (TM = Cr, Mo, W, Mn, Tc, and Re) on (5,5) armchair single-walled carbon nanotubes (SWCNTs) and their adsorption ability with ammonia (NH3) and nitrogen dioxide (NO2). The geometric, electronic, and energetic properties of pristine SWCNT doping with TM and their NH3 and NO2 adsorptions were calculated to explore their potentials as gas adsorptions and sensors. The binding abilities of TMs to the SWCNT are found to be in the order: Cr > Mo > Tc > Re > W > Mn. According to the results, compared to the pristine SWCNT, TM atom doping can significantly increase gas adsorption ability in which W-SWCNT has the strongest interaction, and the ability to absorb NO2 is higher than NH3. The density of states and orbital distributions display that the band gaps and electron delocalizations of TM-SWCNTs are significantly changed upon gas adsorption. These observations suggest that the TM-doped SWCNTs can be introduced as promising candidates in gas adsorptions and sensor devices for storage and detecting NH3 and NO2 molecules.

Improving Charge Collection from Colloidal Quantum Dot Photovoltaics by Single-Walled Carbon Nanotube Incorporation.

Improving charge collection is one of the key issues for high-performance PbS colloidal quantum dot photovoltaics (CQDPVs) due to the considerable charge loss resulting from the low mobility and large defect densities of the 1,2-ethanedithiol-treated PbS quantum dot hole-transporting layer (HTL). To overcome these limitations, single-walled carbon nanotubes (SWNTs) and C60-encapsulated SWNTs (C60@SWNTs) are incorporated into the HTL in CQDPVs. SWNT-incorporated CQDPV demonstrates a significantly improved short-circuit current density (JSC), and C60@SWNT-incorporated CQDPV exhibits an even higher JSC than that of pristine SWNT. Both result in improved power-conversion efficiencies. Hole-selective, photoinduced charge extraction with linearly increasing voltage measurements demonstrates that SWNT or C60@SWNT incorporation improves hole-transporting behavior, rendering suppressed charge recombination and enhanced mobility of the HTL. The enhanced p-type characteristics and the improved hole diffusion lengths of SWNT- or C60@SWNT-incorporated HTL bring improvement of the entire hole-transporting length and enable lossless hole collection, which results in the JSC enhancement of the CQDPVs.

Gas sensing mechanism of sulfur chain-encapsulated single-walled carbon nanotubes

Atomic encapsulation inside single-walled carbon nanotubes (SWNT) has drawn notable attention recently due to the unique strength of an extremely confined, stable 1-dimensional structure. However, the charge transport characteristics of these SWNT species, particularly upon specific gas exposure, have not yet been elucidated. Herein, sulfur atoms are encapsulated inside the SWNT, and the electronic properties of sulfur chain-encapsulated SWNT (S@SWNT) are investigated. In addition, the current responses of both pristine and S@SWNT species upon exposure to gas molecules with distinctly opposite natures, oxygen and ammonia, are demonstrated under high vacuum conditions. While the same trends are observed with ammonia purging, oxygen purging induces opposite trends for the two species. Based on the comparison of gas responses between pristine SWNT and S@SWNT, the gas sensing mechanism of S@SWNT is proposed.

High-Performance N-Type Carbon Nanotube Composites: Improved Power Factor by Optimizing the Acridine Scaffold and Tailoring the Side Chains.

Single-walled carbon nanotubes (SWCNTs)/organic small molecules (OSMs) are promising candidates for application in thermoelectric (TE) modules; however, the development of n-type SWCNT/OSMs with high performance is lagging behind. Only a few structure-activity relationships of OSMs on SWCNT composites have been reported. Recently, we find that the n-type acridone/SWCNT composites display high power factor (PF) values at high temperature but suffer from low PFs at room temperature. Here, the performance of SWCNT composites containing an acridine derivative (AD) as well as its analogues with different counterions (Cl-, SO42- and F-) and lengths of alkyl chains (ADLA1-2 and ADLA4-5) is reported. Among the composites, SWCNT/ADLA4 with no counterions exhibits the highest PF value of 195.2 μW m-1 K-2 at room temperature, which is 4.9 times higher than that of SWCNT/ADTAd (39.8 μW m-1 K-2), indicating that the acridine scaffold and the lengths of alkyl chains contribute to the dramatic changes in the TE performance. In addition, SWCNT/ADLA4 exhibits high PF values at all the temperatures we investigate, which range from 154.7 to 230.7 μW m-1 K-2. Furthermore, a TE device consisting of five pairs of p (the pristine SWCNTs)-n (SWCNT/ADLA4) junctions is assembled, generating a relatively high open-circuit voltage (41.7 mV) and an output power of 1.88 μW at a temperature difference of 74.8 K. Our results suggest that structural modifications might be an effective way to advance the development of TE materials.

The performances of modified single-walled carbon nanotubes/poly(ether ether ketone) composites prepared by solution blending and melt blending

The modified single-walled carbon nanotubes (m-SWCNTs)/poly(ether ether ketone) (PEEK) composites were prepared by solution blending and melt blending, respectively. The mechanical, dielectric, and frictional performances of the m-SWCNTs/PEEK composites obtained by different processing technic were investigated. The poly(aryl ether ketone)s with pyrene (PAEK-Pys) were synthesized through iridium-catalyzed C−H borylation followed by Suzuki coupling. PAEK-Pys were characterized using ultraviolet–visible spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The polymers were then used for surface modification of pristine SWCNTs. Finally, the m-SWCNTs were used to prepare m-SWCNTs/PEEK composites via co-blending in solution or melt. The mechanical, frictional, and dielectric performance of the m-SWCNTs/PEEK composite by solution blending were better than these in m-SWCNTs/PEEK composite by melt blending. These results suggest that the method of solution blending is more favorable for the dispersion of the SWCNTs in PEEK.

ZnO Nanocluster-Functionalized Single-Walled Carbon Nanotubes Synthesized by Microwave Irradiation for Highly Sensitive NO2 Detection at Room Temperature

To improve the NO2-sensing performance of single-walled carbon nanotube (SWCNT)-based sensors, zinc oxide (ZnO) nanoclusters (NCs) were functionalized by a microwave (MW)-assisted synthesis technique. Gas sensors based on pristine SWCNTs and ZnO NC–SWCNT composites synthesized using different weight ratios (ZnO/SWCNTs = 0.5:1, 1:1, 2:1, and 3:1) were fabricated, and their ability to sense various gases at room temperature (25 °C) was investigated. The results showed that the sensing performance of the ZnO NC–SWCNT composite synthesized with a weight ratio of 1:1 (denoted as Z-SWCNTs) was significantly enhanced with respect to NO2 response and selectivity. This enhanced sensing performance is thought to be a result of both the modulation of the conduction channel at the ZnO NC–SWCNT heterointerfaces and the generation of defects (or holes) by MW irradiation that act as active sites for the target gases. The results obtained in this work provide not only a facile method of cofunctionalizing oxide NCs and defects but also a new methodology for improving the sensing capabilities of SWCNT-based gas sensors.

Solar-Light-Driven Efficient ZnO–Single-Walled Carbon Nanotube Photocatalyst for the Degradation of a Persistent Water Pollutant Organic Dye

An efficient photocatalyst, ZnO–single-walled carbon nanotube (ZnO–SWCNT) nanocomposite was successfully fabricated through a straightforward one-pot–two-chemical recrystallization technique followed by thermal decomposition. The photocatalytic efficiency of the prepared ZnO–SWCNT composite was investigated by assessing the degradation of a persistent water-pollutant dye (methylene blue, MB) under visible-light irradiation. We found that the synthesized photocatalyst is an effective and recyclable agent for the decomposition of an MB solution. Its photocatalytic performance was substantially better than that of pristine ZnO nanorods or pristine SWCNTs. The reusability of the photocatalyst was also examined, affirming that it could be used repeatedly for five cycles without conspicuous loss of morphology or catalytic performance.

(Invited) Microenvironment Effects on Photoluminescent Doped Sites of Locally Functionalized Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) with semiconducting features emit photoluminescence (PL) in near infrared (NIR) regions. Owing to their unique one dimensional nanostructures, strong quantum confinement and weak dielectric screening affect Coulombic interactions between electron and electron or hole and, therefore, the PL properties are sensitively changed by effects of microenvironments that are composed of surrounding surfactants and solvent molecules. [1] Recently, defect doping to SWNTs by local chemical functionalization is gathering great attention due to emergence of new PL properties. Namely, in the locally functionalized SWNTs (lf-SWNTs), additional PL (E 11*) appears with redshifted wavelengths and enhanced quantum yields compared to original PL (E 11) of pristine SWNTs.[2-9] Moreover, it is found that chemical structures of the modified molecules on the doped sites play an important role to determine and modulate the E 11* PL wavelengths.[4-9] Thus, their molecularly-tunable properties of the doped sites need to be clarified not only for fundamentals but also for advanced optical applications using the NIR PL. Here, we examine microenvironment effects on the E 11* PL of lf-SWNTs for characterization of the doped site properties by comparing those of the pristine sites. Nitroaryl-functionalized lf-SWNTs (lf-SWNTs-NO2) were synthesized using diazonium chemistry, which were solubilized in D2O containing sodium dodecylbenzenesulfonate (SDBS). For microenvironment creation using organic solvents[10], water immiscible organics such as o-dichlorobenzene (oDCB) was added and mixed in order to inject the organic solvent into the hydrophobic domains between the lf-SWNTs-NO2 and the coating SDBS micelles. In PL spectrum of lf-SWNTs-NO2 after the treatment using oDCB, PL peaks of E 11* and E 11 were redshifted from 1.085 eV and 1.269 eV to 1.069 eV and 1.257 eV, respectively. Other organic solvents also induced different spectral redshifts depending on their chemical structures. Importantly, the shifted energy values of the E 11* PL were larger than those of the E 11 PL when aromatic solvents were used. The energy shifts were analyzed by using a solvent parameter and a linear correlation was found. Details of these results will be discussed in this presentation together with effects of molecular structure differences in the doped sites of lf-SWNTs.

(Invited) Pristine Carbon Nanowires: Are They Five-Fold Symmetry C90, C100 and C120 Fullerenes or [5,5] End-Capped Carbon Nanotubes?

In contrast to the ubiquitous studies on C60 and C70 fullerenes, few experimental studies have been reported that describe pristine samples of higher fullerenes beyond 90 carbon atoms. Likewise, very few single-walled carbon nanotube reports have focused on pristine SWCNTs studies because of the lack of pristine nanotubes of either zigzag (n,n) or armchair (n,0) forms with respect to diameter and chirality. In this presentation, we describe a series of pristine molecules that can be described as either five-fold symmetry C90, C100 and C120 fullerenes or [5,5] End-Capped Carbon Nanotubes. The isolation, characterization, and physical properties of this pristine carbonaceous series will be the focus of this presentation.

Characterization of thermal transport and laser absorption properties of an individual pristine SWCNT

Determination of thermal transport properties and optical absorption cross-section of nanowires is of central importance for designing nano-optoelectronics and nano-photovoltaics. Experimental study of these properties is challenging because of the very small size of a typical sample. In this study, we present a steady-state Raman method for determining the temperature (T)-dependent thermal conductivity (λ) and laser absorption cross-section (Cabs) for an individual nanowire. This method was verified and then applied to determine λ and Cabs of an individual pristine single-walled carbon nanotube (SWCNT, L = 22 μm, d = 1.29 nm). The results show that λ decreases with increasing T in this experimental temperature range, indicating that higher temperature induces a larger scattering rate of three-phonon Umklapp processes. By measuring the temperature increase at the sample center induced by a 0.284 mW focused polarized Gaussian laser spot (514.5 nm, re = 1.0 μm), we derived the absorbed laser power (Pα) and Cabs to be 3.98 × 10−5 mW and 5.46 × 10−15 m2 for this individual SWCNT. The laser absorption cross-section per carbon atom (σc) was determined to 1.64 × 10−17 cm2 with an uncertainty lower than 10.6%.

Solution-Processed Hybrid Ambipolar Thin-Film Transistors Fabricated at Low Temperature

We demonstrate solution-processed hybrid ambipolar thin-film transistors (TFTs) employing a stack structure composed of indium–gallium–zinc-oxide (IGZO) and single-wall carbon nanotube (SWCNT) as an active channel fabricated at low temperature. With an optimized deep-ultraviolet (DUV) photo annealing process for sol–gel based IGZO thin film on SWCNT random networks, the ambipolar transport of both electrons and holes with good electrical characteristics was realized. We also investigate the effect of DUV photo annealing on the material characteristics of solution-processed hybrid stack films and on the device performance of solution-processed hybrid ambipolar TFTs compared to those of samples thermally annealed at 500 °C, which is required for solution-processed high-quality IGZO thin films. The Raman spectra show that DUV photo annealing ensures hole transport in SWCNT random networks of a hybrid stack film, where the intensity of the 2D peak to the G peak was not changed compared to that of pristine SWCNT random networks. We believe that these analytical investigations reveal that DUV photo annealing is a promising method by which to realize hybrid ambipolar SWCNT/IGZO TFTs fabricated at low temperature.

Bath sonication for the scalable separation of semiconducting single walled carbon nanotubes

Commercially available single-walled carbon nanotubes (SWNTs) consist of a mixture of metallic (m-SWNTs) and semiconducting SWNTs (sc-SWNTs), and therefore cannot be used as they are for applications where pure semiconductors or metallic materials are needed. Hence, the separation of sc-SWNTs from pristine SWNT mixtures is an essential process that precedes the evaluation of SWNTs. The polymer wrapping method, which is one of the well-known methods for separating sc-SWNTs, can separate sc-SWNTs by forming a sc-SWNT/polymer complex in which sc-SWNTs are selectively wrapped with a conductive polymer over metallic SWNTs. This process is generally realized using a tip sonicator, which enables the polymer wrapping and dispersion for SWNTs. However, this conventional tip sonication has several drawbacks, such as difficulties with respect to mass production, contamination, and high cost of equipment. In this work, the selective dispersion and separation of sc-SWNTs were achieved using bath sonication, which can overcome the drawbacks related to conventional tip sonication process. It was confirmed that bath sonication can achieve a similar level of sc-SWNT dispersion efficiency to that of tip sonication. The variation in the dispersion efficiencies with respect to the dispersion time, SWNT concentration, SWNT types, polymer concentration, and solvent types and concentrations was investigated. Furthermore, the dispersion stability was compared by measuring the particle sizes of the sc-SWNT/conductive polymer composites obtained using the bath sonication and tip sonication methods via electrophoretic light scattering as a function of time.

A Facile and Efficient Protocol for Preparing Residual-Free Single-Walled Carbon Nanotube Films for Stable Sensing Applications.

In this article, we report on an efficient post-treatment protocol for the manufacturing of pristine single-walled carbon nanotube (SWCNT) films. To produce an ink for the deposition, the SWCNTs are dispersed in an aqueous solution with the aid of a carboxymethyl cellulose (CMC) derivative as the dispersing agent. On the basis of this SWCNT-ink, ultra-thin and uniform films are then fabricated by spray-deposition using a commercial and fully automated robot. By means of X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), we show that the CMC matrix covering the CNTs can be fully removed by an immersion treatment in HNO3 followed by thermal annealing at a moderate temperature of 100 °C, in the ambient air. We propose that the presented protocols for the ink preparation and the post-deposition treatments can in future serve as a facile and efficient platform for the fabrication of high-quality and residual-free SWCNT films. The purity of SWCNT films is of particular importance for sensing applications, where residual-induced doping and dedoping processes distort the contributions from the sensing specimen. To study the usability of the presented films for practical applications, gas sensors are fabricated and characterized with the CNT-films as the sensing material, screen printed silver-based films for the interdigitated electrode (IDE) structure, and polyimide as a flexible and robust substrate. The sensors show a high and stable response of 11% to an ammonia (NH3) test gas, at a concentration of 10 ppm.

Cover Feature: Controlling Size‐Dispersion of Single Walled Carbon Nanotubes by Interaction with Polyoxometalates Armed with a Tryptophan Tweezer (Eur. J. Inorg. Chem. 3‐4/2019)

The Cover Feature shows how tryptophan tweezers, anchored on a polyoxometalate (POM) scaffold, intercalate into single-walled carbon nanotube (SWCNT) bundles, leading to a selective dispersion and enrichment of nanotubes with a small diameter range. The engineering of the POM tweezer and of its supramolecular surface interactions can be used to evaluate the impact of the amino acid terminals on the recognition of pristine SWCNTs. This information can address possible SWCNT/peptide interactions and their impact on the cellular level for drug delivery and CNS-based therapy. This work opens new possibilities for the fabrication of nanohybrid functional interfaces. More information can be found in the Communication by M. Calvaresi, M. Prato, M. Bonchio et al.