Pure Single-walled Carbon Nanotubes Research Articles

Cucurbit[6]uril as a co-catalyst for hydrogen production from formic acid

Cucurbiturils are organic macrocycles, which are only rarely used for catalytic reactions. We studied a composite comprising of single-walled carbon nanotubes (SWCNTs), cucurbit[6]uril (CB6) and Au species and demonstrated that CB6 is a co-catalyst for hydrogen production from formic acid. Thus, insertion of CB6 into SWCNTs with open tips provides a decrease of the reaction temperatures by 60 K as compared to those over pure SWCNTs. This indicates that CB6 is a metal-free catalyst for this reaction. The use of CB6 during the synthesis of Au catalysts supported on SWCNTs leads to even a stronger decrease of the reaction temperature by 110 K as compared to the Au/SWCNTs catalyst. Density functional theory (DFT) calculations show that these effects could be explained by abstraction of the hydrogen atom from the hydroxyl group of the formic acid molecule on the basic carbonyl portal of the CB6 molecule with the formation of the formate containing adduct. Unusual sandwich-like structures of Au were formed inside the SWCNTs channels due to the interaction of Au with CB6. The results create a base for the development of catalysts containing cucurbiturils for the energy related reactions taking place through the hydrogen abstraction from reactant molecules.

Realisation of highly sensitive and selective NO2 detection at room temperature utilizing defect-induced single-walled carbon nanotubes combined with Pt functionalisation

For the discriminative detection of trace amounts of certain gas molecules in ambient environments, the gas response, selectivity, and humidity independence of sensing characteristics should be improved to realise real-time environmental monitoring applications. In this study, we implement a NO2 gas sensor operating at room temperature with excellent selectivity. The fabricated sensor exhibits good NO2 response even under a humid atmosphere between 33% and 76% RH (RH = relative humidity), compared with previously reported carbon-based sensing materials. To synthesise Pt-functionalised defect-induced single-walled carbon nanotubes (SWCNTs), pure SWCNTs are heat treated at 700 °C for 1 h under an Ar atmosphere for defect formation; subsequently, nanosized Pt particles are randomly functionalised on the surfaces of defect-induced SWCNTs via optimal ultraviolet irradiation. The Pt-functionalised defect-induced SWCNTs achieves high NO2 response, low detection limit (67 ppb), strong selectivity, good reversibility, and the ability to detect NO2 under a humid atmosphere. However, they exhibit only moderately improved humidity-immune NO2 sensing characteristics. The NO2 response of both the Pt-functionalised and defect-induced SWCNTs deteriorates significantly in a humid atmosphere (76% RH). These results show that Pt-functionalised defect-induced SWCNTs are a promising sensing material for the detection of NO2 gas in real-time applications.

Carbon Nanotube-Based Thermoelectric Modules Enhanced by ZnO Nanowires.

Carbon nanotubes (CNTs) have a wide range of unique properties, which have kept them at the forefront of research in recent decades. Due to their electrical and thermal characteristics, they are often evaluated as key components of thermogenerators. One can create thermogenerators exclusively from CNTs, without any metal counterpart, by properly selecting dopants to obtain n- and p-doped CNTs. However, the performance of CNT thermogenerators remains insufficient to reach wide commercial implementation. This study shows that molecular doping and the inclusion of ZnO nanowires (NWs) can greatly increase their application potential. Moreover, prototype modules, based on single-walled CNTs (SWCNTs), ZnO NWs, polyethyleneimine, and triazole, reveal notable capabilities for generating electrical energy, while ensuring fully scalable performance. Upon doping and the addition of ZnO nanowires, the electrical conductivity of pure SWCNTs (211 S/cm) was increased by a factor of three. Moreover, the proposed strategy enhanced the Power Factor values from 18.99 (unmodified SWCNTs) to 34.9 and 42.91 µW/m∙K2 for CNTs triazole and polyethyleneimine + ZnO NWs inclusion, respectively.

Visible near Infrared Spectroscopic Evidence of the Purification and Dispersion of Single-Walled Carbon Nanotubes

The application of dispersible single-walled carbon nanotubes in water is required in many fields, such as mechanics, thermology, electricity, etc. In this paper, single-walled carbon nanotube samples were dispersed in sodium deoxycholate aqueous solution with the assistance of ultrasonic crushing. The effects of centrifugal time, concentration and centrifugal velocity on dispersion were investigated. After centrifugal separation, the dispersible single-walled carbon nanotubes solution in water was obtained. The dispersion behavior of single-walled carbon nanotubes in sodium deoxycholate aqueous solution was further investigated by Uv-visible near infrared spectrum and electrochemical cyclic voltammetry curve. At the same time, characterization results of Uv-visible near infrared spectrum shew that the purity of single-walled carbon nanotubes was improved. The cyclic voltammetry curves of single-walled carbon nanotubes after purification and dispersion were tested by electrochemical method, and the electron transfer behavior of single-walled carbon nanotubes after purification and dispersion was investigated.

Single-Walled Carbon Nanotube Chiral Selectivity Exhibited by Commercially Available Hydrogels of Varying Composition.

Despite the commercial availability of many different hydrogel formulations, the effective gel-based purification of single-walled carbon nanotubes (SWNT) remains exclusive to the gel Sephacryl S-200. In this study, 12 commercially available gels and two custom-synthesized gels were investigated for their ability to effectively purify SWNT, as determined through quantification of SWNT adsorption, elution, chiral selectivity, and overall process efficiency. The ability of each gel to separate SWNT was found to correlate with physiochemical properties, such as hydrogel pore size, the presence of ionic ligands, and both polysaccharide backbone and cross-linker compositions. While Sephacryl S-200 demonstrated superior separation efficiency and chiral selectivity among the gels studied, Superose 6 was found to adsorb more SWNT than Sephacryl S-200 per cm2 of the gel surface area and exhibited a unique preference for the (7,3) and (7,5) SWNT chiralities, in contrast to the established selectivity of Sephacryl S-200 for the (6,5) chirality. Collectively, this work both identifies gels that exhibit unique SWNT chiral selectivity and provides insights into the rational design of gels tailored for SWNT purification.

En route to single-step, two-phase purification of carbon nanotubes facilitated by high-throughput spectroscopy

Chirality purification of single-walled carbon nanotubes (SWCNTs) is desirable for applications in many fields, but general utility is currently hampered by low throughput. We discovered a method to obtain single-chirality SWCNT enrichment by the aqueous two-phase extraction (ATPE) method in a single step. To achieve appropriate resolution, a biphasic system of non-ionic tri-block copolymer surfactant is varied with an ionic surfactant. A nearly-monochiral fraction of SWCNTs can then be harvested from the top phase. We also found, via high-throughput, near-infrared excitation-emission photoluminescence spectroscopy, that the parameter space of ATPE can be mapped to probe the mechanics of the separation process. Finally, we found that optimized conditions can be used for sorting of SWCNTs wrapped with ssDNA as well. Elimination of the need for surfactant exchange and simplicity of the separation process make the approach promising for high-yield generation of purified single-chirality SWCNT preparations.

Preparation and Thermoelectric Properties of Semiconducting Single-Walled Carbon Nanotubes/Regioregular Poly(3-dodecylthiophene) Composite Films.

Single-walled carbon nanotubes (SWNTs) have been widely used as leading additives for improving the thermoelectric properties of organic materials, due to their unique structure and excellent electronic transport properties. However, the as-synthesized SWNTs are mixtures (mix-SWNT) of semiconducting (sc-SWNT) and metallic (met-SWNT) carbon nanotubes. The significantly different surface character and transport behavior of sc-SWNT and met-SWNT frequently raise the difficulty of modifying microstructures, and tuning transport properties of SWNTs/organic composites, when using mix-SWNTs as dispersion phase. Herein, we prepared high quality sc-SWNTs/rr-P3DDT composite film by presorting pure sc-SWNT from the raw mix-SWNTs using regioregular poly(3-dodecylthiophene) (rr-P3DDT). Both the smoothness and compactness of sc-SWNTs/rr-P3DDT are great improved, as compared with the mix-SWNTs/rr-P3DDT films, and the sc-SWNTs are well-dispersed and uniformly wrapped by rr-P3DDT with diameter less than 50 nm. The significantly enhanced Seebeck coefficients and power factors are obtained in the sc-SWNT/rr-P3DDT samples. As the result, the maximum power factor of 60 μW/mK2 in 50 wt% sc-SWNTs sample is 70% higher than that of mix-SWNTs/P3DDT sample. This work reveals the effectiveness of pure semiconductor SWNTs as fillers to optimize the thermoelectric properties of CNT/polymer nano-composites.

Protective immunity of largemouth bass immunized with immersed DNA vaccine against largemouth bass ulcerative syndrome virus

To reduce the largemouth bass ulcer syndrome (LBUSV) aquatic economic losses, it must take effective preventive measures and coping strategies should be urgently investigated. In this research, the effects of a functionalized single-walled carbon nanotubes (SWCNTs) applied as a delivery vehicle for DNA vaccine administration in largemouth bass (Micropterus Salmoides) against LBUSV were studied. Our results showed that SWCNTs loaded with DNA vaccine induced a better protection to largemouth bass against LBUSV. We found more than 10 times increase in serum antibody levels, enzyme activities and immune-related genes (IL-6, IL-8, IFN-γ, IgM and TNF-α) expression, in the SWCNTs-pcDNA-MCP immunized groups compared with PBS group and the pure SWCNTs group. The survival rates for control group (PBS), pure SWCNTs groups (40 mg L−1), four pcDNA-MCP groups (5 mg L−1, 10 mg L−1, 20 mg L−1 and 40 mg L−1) and four SWCNTs-pcDNA-MCP groups (5 mg L−1, 10 mg L−1, 20 mg L−1 and 40 mg L−1) were 0%, 0%, 0%, 2.77%, 11.11%, 19.44%, 27.78%, 38.89%, 52.78% and 61.11%, respectively. Our results demonstrate that the SWCNTs-DNA vaccine can be used as a new method against LBUSV showing protection following challenge with LBUSV.

Rapid, efficient, and non-destructive purification of single-walled carbon nanotube films from metallic impurities by Joule heating

We demonstrate a simple and resource-efficient approach for rapid purification of single-walled carbon nanotube (SWCNT) films from catalyst impurities by Joule heating in a vacuum. As a result, the catalyst concentration decreases by a factor of 27 (from 17 to <1 wt%) after heating at 1600°C for 2 min. Moreover, the nanotube structure remains almost intact as the purified films show a high ratio of intensities of G to D bands of Raman spectrum IG/ID = 180. The technique perfectly fits for the devices based on free-standing carbon nanotube films such as protective membranes, infrared detectors, and sound generators. For purified SWCNT films, we show the signal-to-noise ratio for the bolometers to increase by a factor of 2.5 and 24% sound pressure gain for the air-coupled thermophones. The method can be easily extended to other applications, for instance, the SWCNT-based devices of limited liquid and harsh reagent tolerance like nanotube aerogels and drug delivery systems.

Nanocomposites with p- and n-Type Conductivity Controlled by Type and Content of Nanotubes in Thermosets for Thermoelectric Applications.

In this work, composites based on epoxy resin and various carbon nanotubes (CNTs) were studied regarding their thermoelectric properties. The epoxy composites were prepared by infiltration of preformed CNT buckypapers. The influence of different types of CNTs on the Seebeck coefficient was investigated, namely lab-made and commercially available multi walled carbon nanotubes (MWCNTs), lab-made nitrogen doped MWCNTs (N-MWCNT) and commercially available single walled carbon nanotubes (SWCNTs). It was found that only by varying the lab-made MWCNT content could both n- and p-type composites be produced with Seebeck coefficients between −9.5 and 3.1 µV/K. The incorporation of N-MWCNTs resulted in negative Seebeck coefficients of −11.4 to −17.4 µV/K. Thus, the Seebeck coefficient of pure SWCNT changed from 37.4 to −25.5 µV/K in the epoxy/1 wt. % SWCNT composite. A possible explanation for the shift in the Seebeck coefficient is the change of the CNTs Fermi level depending on the number of epoxy molecules on the CNT surface.

Effect of metallic nanowire encapsulation on the tensile behavior of single-walled carbon nanotubes: a molecular dynamics study

The encapsulation of nanowires (NWs) into single-walled carbon nanotubes (SWCNTs) is of great significance due to the specific mechanical, electrical and magnetic properties of confined NWs as well as application of filled CNTs in nanoelectromechanical systems (NEMS). The tensile behavior of NWs encapsulated-SWCNTs (NWs@SWCNTs) is investigated herein using molecular dynamics (MD) simulations. The results illustrated that Young’s moduli of NWs@SWCNTs decrease as the length of nanotube increases. Moreover, pure SWCNTs show higher Young’s moduli as compared to NWs@SWCNTs. It is also found that NWs@SWCNTs possess higher ultimate forces than those of pure SWCNTs. In addition, at a given length, the ultimate forces of pure SWCNTs and NWs@SWCNTs increase by increasing the radii of nanotubes.

An Electronic and Optically Controlled Bifunctional Transistor Based on a Bio-Nano Hybrid Complex.

We report an electronically and optically controlled bioelectronic field-effect transistor (FET) based on the hybrid film of photoactive bacteriorhodopsin and electronically conducting single-walled carbon nanotubes (SWNTs). Two-dimensional (2D) crystals of bacteriorhodopsin form the photoactive center of the bio–nano complex, whereas one-dimensional (1D) pure SWNTs provide the required electronic support. The redshift in the Raman spectra indicates the electronic doping with an estimated charge density of 3 × 106 cm–2. The hybrid structure shows a conductivity of 19 μS/m and semiconducting characteristics due to preferential binding with selective diameters of semiconducting SWNTs. The bioelectronic transistor fabricated using direct laser lithography shows both optical and electronic gating with a significant on/off switch ratio of 8.5 and a photoconductivity of 13.15 μS/m. An n-type FET shows complementary p-type characteristics under light due to optically controlled, electronic doping by the “proton-pumping” bacteriorhodopsin. The fabricated bioelectronic transistor exhibits both electronically and optically well-controlled bifunctionality based on the functionalized hybrid electronic material.

Effect of purification on the electrical properties of transparent conductive films fabricated from single-walled carbon nanotubes

Transparent conductive films (TCFs) made of single-walled carbon nanotubes (SWCNTs) are usually fabricated using highly pure SWCNTs. Obtaining pure SWCNTs is an important step for harnessing their excellent electrical properties. Herein, we studied the effect of purification of SWCNTs by thermal and acid processes on the electrical properties of TCFs. These purification processes also affected the length and diameter of the SWCNT bundles. The purity of SWCNTs was determined by UV–visible-near-infrared spectroscopy and the metal content by thermogravimetric analysis. TCFs were made by spraying aqueous suspensions of SWCNTs having different purities onto polyethylene terephthalate substrates, and the ratios of dc to optical conductivities of the films were compared. Thermally purified (TP) SWCNT TCFs had a higher ratio than thermally and acid-purified (TAP) ones even though the purity of the TP-SWCNTs was lower than that of the TAP-SWCNTs. The conducting paths of the SWCNT bundle networks in the TP-SWCNT TCFs were well organized, because nanosized graphitic nanoparticles and metal catalysts occupied the spaces between the CNT bundles or networks without hindering the network connections. Although the SWCNT purity affected the conductivity of the SWCNT TCFs, the network property of lower junction resistance with smaller bundle diameter was more influential on film conductivity.

Preparation and Purification of Single-Walled Carbon Nanotubes

Preparation and Purification of Single-Walled Carbon Nanotubes

Fabrication of Surfactant-Dispersed HiPco Single-Walled Carbon Nanotube-Based Alginate Hydrogel Composites as Cellular Products.

In this study, we designed, synthesized, and characterized ultrahigh purity single-walled carbon nanotube (SWCNT)-alginate hydrogel composites. Among the parameters of importance in the formation of an alginate-based hydrogel composite with single-walled carbon nanotubes, are their varying degrees of purity, their particulate agglomeration and their dose-dependent correlation to cell viability, all of which have an impact on the resultant composite’s efficiency and effectiveness towards cell-therapy. To promote their homogenous dispersion by preventing agglomeration of the SWCNT, three different surfactants-sodium dodecyl sulfate (SDS-anionic), cetyltrimethylammonium bromide (CTAB-cationic), and Pluronic F108 (nonionic)-were utilized. After mixing of the SWCNT-surfactant with alginate, the mixtures were cross-linked using divalent calcium ions and characterized using Raman spectroscopy. Rheometric analysis showed an increase in complex viscosity, loss, and storage moduli of the SWCNT composite gels in comparison with pure alginate gels. Scanning electron microscopy revealed the presence of a well-distributed porous structure, and all SWCNT-gel composites depicted enhanced electrical conductivity with respect to alginate gels. To characterize their biocompatibility, cardiomyocytes were cultured atop these SWCNT-gels. Results comprehensively implied that Pluronic F108 was most efficient in preventing agglomeration of the SWCNTs in the alginate matrix, leading to a stable scaffold formation without posing any toxicity to the cells.

Hydrogen storage in platinum loaded single-walled carbon nanotubes

To study the hydrogen storage capacity, platinum (Pt) nanoparticles were deposited on single-walled carbon nanotubes (SWNT) using hexachloroplatinic acid (H2PtCl6·6H2O) as a precursor. To verify Pt deposition on the surface of the SWNT, a Transmission Electron Microscope (TEM) was used to obtain surface morphology. The TEM images show that Pt nanoparticles were homogeneously distributed on the surface of SWNT. Commercial SWNT were also used to compare the results. Thermal Gravimetric Analysis at heating rate of 5 °C/min is measured for pure SWNT and Pt loaded SWNT. Before hydrogen storage measurements these samples were reduced in 10% of H2 in Ar, flowing at 900 °C in a tubular furnace for 1 hour. Hydrogen storage capacity of these SWNT was investigated under 25 bar pressure and room temperature as well as liquid nitrogen temperature.

Effect of Functional Groups on the Thermoelectric Performance of Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs) have received much attention in the past decade due to their excellent electric and mechanical properties. The quantum confinement effect of charge carriers in an individual carbon nanotube (CNT), together with the flexible topology and high tensile strength, make it a potential candidate thermoelectric (TE) material. However, the low Seebeck coefficient and high thermal conductivity of SWCNTs limits further development for a good TE material with high performance. Although many efforts have been focused on the improvement of TE performance for SWCNTs by doping and composites, few works have been devoted to investigation of functional groups in SWCNTs. In this work, we investigated the TE performance of SWCNT films in detail with different functional groups (hydroxyl, carboxyl, and amino). It is found that the Seebeck coefficient of SWCNTs with different functional groups have an obvious improvement with the decrease in electrical conductivity. An optimal power factor of 47.8 μW m−1 K−2 was obtained for SWCNTs with a hydroxyl group comparable to pure SWCNTs. Significantly, the introduction of functional groups results in a marked reduction in thermal conductivity and an enhanced TE figure of merit (ZT). This work provides an alternative strategy to optimize the TE performance of SWCNTs.

Carburization of Fe/Ni Catalyst for Efficient Growth of Single‐Walled Carbon Nanotubes

Scale-up production of single-walled carbon nanotubes (SWNTs) with high quality and purity is in pursuit, since the subsequent post purification treatment of residual metal or amorphous carbon is complicated and restricts further applications. Here, a compatible method to efficiently synthesize pure SWNTs on various supporters by using the precarburized Fe/Ni catalysts is reported. The preparation of catalysts is achieved by gas phase deposition together with CO gas at proper temperature, and the carburization of metal particles occurring simultaneously contributes to the size limitation of catalysts. By using micro-quartz sand as a recyclable supporter, high-quality SWNTs with a yield of 50 mg h-1 are prepared with 60% metal precursor utilization, 81% carbon source utilization, and only 0.12% (m/m) metal residues. Taking advantage of carburized Fe/Ni catalysts and appropriate supports makes it possible to balance the quantity, purity, and quality among SWNTs growth. Furthermore, this method provides a straightforward pathway to strongly combine SWNTs and diverse composite materials for further potential applications.

Application of a simple and highly efficient nanoparticle surface modification method to single-walled carbon nanotubes and formation of an interfacial organized film

A simple and highly efficient surface modification method for inorganic nanoparticles is applied to single-walled carbon nanotubes (SWCNTs), and morphological control of the organized films at the air/water interface is achieved. Prolonged ultrasonic treatment with a mixed acid leads to hydrophilization of the SWCNTs. Amphiphilic organo-modified SWCNTs are prepared by reacting an ionic surfactant on the hydrophilized surface. The organo-modified SWCNTs are well dispersed in organic solvents, resulting in a spreading solvent for the monolayer on the water surface. When it precipitates as a solid at the interface, the surface-modified chain is eliminated, and a pure SWCNT film is obtained by transferring the films to the substrate via firing. The distribution of the tube length in the SWCNT monolayer changes depending on the ultrasonic treatment time. In addition, the monolayer on the SWCNT surface becomes dense and is less defected by the “repeated compression–expansion method.” Furthermore, when a lysozyme is allowed to act as a subphase, it is adsorbed and immobilized in the SWCNT monolayer nanosheets. Introduction of the SWCNTs at the air/water interface leads to interfacial organization, thus facilitating nanostructural control and strong interaction with biomolecules.

Exploiting the Physiochemical Interactions between Single-Walled Carbon Nanotubes and Hydrogel Microspheres To Afford Chirally Pure Nanotubes

Single-walled carbon-nanotubes (SWNTs) exhibit unique electronic, optical, and mechanical properties; however, a narrow availability of chirally pure (single electronic structure) material can limit effective integration within novel devices and schemes. This work focuses on understanding, modeling, and advancing methodology used to generate preparative quantities of single-chirality SWNT: the iterative adsorption/desorption of SWNT from aqueous surfactant suspensions to/from hydrogel microspheres. Commercially available hydrogel microspheres (Sephacryl S200) were sorted by radius and exposed to SWNT, affording a direct correlation between microsphere surface area and quantity of SWNT adsorbed using differential absorbance spectroscopy. This relationship elucidates a SWNT/gel purification scheme interaction mechanism exclusively involving the gel surface. High-concentration surfactant was used to elute SWNT from the gel with desorption efficiencies dependent on both SWNT chirality and hydrogel microsphere radius, ranging from 25–45%. A thermodynamic model for SWNT desorption that accounts for hydrogel microsphere curvature effects is presented and suggests that (when compared with experimental data) SWNT with greater than ∼41% of their length adsorbed to a hydrogel surface bind irreversibly, while others are desorbed in the presence of high-concentration surfactant. These findings inspired the generation and application of mechanically fractured hydrogel microspheres (exhibiting greater surface area) for use as SWNT purification media in per-iteration quantities far less than traditional gels. A 10-iteration SWNT purification procedure demonstrated a marked improvement in process efficiency, as mechanically fractured gels afford a 10-fold reduction in gel-media use (the major expense of the process) while yielding equivalent SWNT purification.