Raw Single-walled Carbon Nanotubes Research Articles

Highly-Selective Harvesting of (6,4) SWCNTs Using the Aqueous Two-Phase Extraction Method and Nonionic Surfactants.

Monochiral single-walled carbon nanotubes (SWCNTs) are indispensable for advancing the technology readiness level of nanocarbon-based concepts. In recent times, many separation techniques have been developed to obtain specific SWCNTs from raw unsorted materials to catalyze the development in this area. This work presents how the aqueous two-phase extraction (ATPE) method can be enhanced for the straightforward isolation of (6,4) SWCNTs in one step. Introducing nonionic surfactant into the typically employed mixture of anionic surfactants, which drive the partitioning, is essential to increasing the ATPE system's resolution. A thorough analysis of the parameter space by experiments and modeling reveals the underlying interactions between SWCNTs, surfactants, and phase-forming agents, which drive the partitioning. Based on new insight gained on this front, a separation mechanism is proposed. Notably, the developed method is highly robust, which is proven by isolating (6,4) SWCNTs from several raw SWCNT materials, including SWCNT waste generated over the years in the laboratory.

Self-optimizing iron phosphorus oxide for stable hydrogen evolution at high current

Electrocatalytic water splitting have demonstrated an established methodology to generate hydrogen of high purity, attracting lots of attention from industry. However, deficient supplies or poor electrochemical stability of catalysts contributes to unsatisfactory electrocatalytic hydrogen production, particularly while maintaining high current densities. Herein, we develop a robust catalyst by directly phosphating raw single-walled carbon nanotube films which can be self-optimized into O-FePx-SWCNT, P-Fe2O3-SWCNT or P-FeOOH-SWCNT catalysts, depending on the selected electrolytes with different pH values. The electrochemical measurements reveal the excellent electrocatalytic performance of catalytic films in a wide pH range. Notably, there is no observable degradation, even following one-week of continuous electrolysis process, which reached an elevated current density of 125 mA/cm2 at neutral conditions. In order to manifest its cogent applications, the catalyst is employed to stably electrolyze lake water, further indicating potential hydrogen production in inland areas. Our work confirms the feasibility of using structural self-optimization engineering to develop desirable electrocatalysts, providing flexible catalytic films for practical applications and answering the long-standing controversial question about active sites based on X-ray absorption fine structure (XAFS), operando synchrotron radiation Fourier transform infrared (SR-FTIR) spectroscopy and theoretical calculations, which will significantly contribute to the advancement of HER-related basic and applied research.

PEG/PEI-functionalized single-walled carbon nanotubes as delivery carriers for doxorubicin: synthesis, characterization, and in vitro evaluation.

Single-walled carbon nanotubes (SWCNTs) have attracted great interest regarding drug-delivery applications. However, their application has been limited by some inherent disadvantages. In this study, raw SWCNTs were purified with different oxidizing acids, and the resulting shortened CNTs were conjugated with poly(ethylene glycol) (PEG) and polyethylenimine (PEI). The different nanocarriers, that is, CNTs-COOH (CNTs), CNTs-PEG and CNTs-PEG-PEI, were systematically characterized and evaluated in terms of drug loading, in vitro release, cytotoxicity towards MCF-7 cells and cellular uptake. The results showed that all CNT carriers had a high drug loading capacity. In comparison with CNTs-COOH and CNTs-PEG, CNTs-PEG-PEI showed a more rapid drug release under acidic conditions and a higher antitumor activity. Furthermore, fluorescence detection and flow cytometry (FCM) analysis results indicated that the internalization into cells of CNTs-PEG-PEI was significantly enhanced, thus inducing tumor cell death through apoptosis more efficiently. The above series of benefits of CNTs-PEG-PEI may be attributed to their good dispersibility and comparably higher affinity to tumor cells due to the difunctionalization. In summary, the PEG- and PEI-conjugated CNTs may be used as novel nanocarriers and the findings will contribute to the rational design of multifunctional delivery vehicles for anticancer drugs.

Facile Fabrication of Semiconducting Single-Walled Carbon Nanotubes Patterns on Flexible Substrate Based on a Photoimmobilization Technique

Single-walled carbon nanotubes (SWCNTs) have attracted significant attention due to their outstanding properties. For their wide applications in electronics and optoelectronics, pure semiconducting SWCNTs (s-SWCNTs) and their precise placement are preconditions. Recent advances have focused on developing effective strategies to separate s-SWCNTs from raw SWCNTs, a mixture of metallic and semiconducting nanotubes, and deposit s-SWCNTs on target substrates. Herein, a polyfluorene-based alternative copolymer (PFBP) containing the benzophenone group was employed. PFBP achieved higher yield for s-SWCNTs than the well-studied poly(9,9-dioctylfluorene) through solution process. Subsequently, the dispersed s-SWCNTs were immobilized on a flexible polyethylene terephthalate in a facile manner by the photoreactive benzophenone group upon exposure to UV irradiation, and chemically robust patterns were fabricated from micro to macro scales through photomasks. Our method accomplished by utilizing photoimmobilization is a simple cleaning procedure and an important step forward in pitch scaling for further applications of conjugated polymer wrapped s-SWCNTs.

Adsorption of mercury ions from synthetic aqueous solution using polydopamine decorated SWCNTs

Mercury is one of the most toxic and unnecessary elements for human body in a way that only slight amount of it can cause serious hygienic problems and environmental pollution. In the present study, magnetized single walled carbon nanotubes (SWCNTs) functionalized by polydopamine was employed for elimination of mercury heavy metal ions from aqueous media. In order to characterize the physical and chemical properties of the SWCNT and to confirm the functionalization steps, different analyses including TEM, SEM, VSM, EDS, FT-IR were utilized. In the present paper, the effects of experimental parameters such as adsorbent dosage, solution pH, metallic ion initial concentration, process thermodynamics and desorption mechanism on batch system were widely studied. In addition, mercury adsorption trend in continuous system was investigated by a fixed bed reactor. Comparison of adsorption process kinetics were done with models of Freundlich, Langmuir and Dubinin–Radushkevich in batch system and consistency with Yan and Thomas models in continuous system by Sigma plot and MATLAB software packs. Isotherm studies and adsorption kinetics revealed that mercury ions follow Freundlich adsorption isotherm and pseudo-second-order kinetic model. Moreover, thermodynamic studies showed that mercury ion adsorption is an exothermic and spontaneous reaction. Although Thomas model was found to predict more exact results for maximum mercury ion adsorption, both Thomas and Yan models had good fitness with fixed bed reactor data. Finally, adsorption process demonstrated that removal efficiency of the prepared adsorbent was so much higher than raw SWCNTs.

ZnO/Ag NANOPARTICLE-DECORATED SINGLE-WALLED CARBON NANOTUBES (SWCNTs) AND THEIR PROPERTIES

Raw single-walled carbon nanotubes (SWCNTs) were oxidized by using sulfuric acid and nitric acid at 3:1 ratio to produce oxygen functional groups attached to SWCNTs surfaces. Then, the oxidized SWCNTs are coated with zinc oxide and silver nanoparticles by chemical precipitation route to synthesize ZnO/Ag-SWCNTs nanocomposite material. The nanocomposite sample was analyzed via zeta potential analyzer, ultraviolet-visible (UV-Vis) spectrophotometer, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy to investigate colloidal stability, optical, morphological, and structural properties. The SWCNT properties were found to be changed after the addition of ZnO/Ag nanoparticles. Hence, the new ZnO/Ag-SWCNTs nanocomposite is a good candidate for photocatalyst applications and biological applications.

Thermodynamic and kinetic studies sorption of 5-fluorouracil onto single walled carbon nanotubes modified by chitosan

Single-walled carbon nanotubes (SWCNTs) were functionalized by chitosan and their application was examined in adsorbing an anti-cancer drug, 5-fluorouracil (5Fu). Surface, physical and morphological characteristics of raw SWCNTs and Chitosan-functionalized SWCNTs (Ch-SWCNTs) were extensively characterized by Fourier transform spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Brunauer-Emmet-Teller (BET) and X-ray diffraction (XRD). The effects of various variables such as pH, initial drug concentration, temperature, and contact time on adsorption capacity were also investigated. Thermodynamic parameters such as ΔSo, ΔHo, and ΔGo were estimated. Isotherm and kinetic studies of drug adsorption indicated that the adsorption process followed Langmuir isotherm model and pseudo-second-order kinetic, respectively. The maximum adsorption capacity (qm) of 5Fu on Ch-SWCNTs was 31.77 mg g−1 at 298 K, pH 4.0, and 120 min, which is higher than adsorption capacity of SWCNTs (4.12 mg g−1) in the same conditions. The adsorption was spontaneous and exothermic process in nature, with a slight decreasing in entropy.

Synthesis of Ag-doped TiO2 nanoparticles coated with carbon nanotubes by the sol–gel method and their antibacterial activities

In this study, raw single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were chemically treated with sulfuric acid (H2SO4) and nitric acid (HNO3) in a ratio (3:1). These carbon nanotubes (CNTs) have been coated with Ag-doped TiO2 nanoparticles (NPs) by using the sol–gel method. All samples have been studied by X-ray diffraction (XRD), Fourier transform-infrared (FTIR) spectroscopy, UV–vis spectroscopy, field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and zeta potential analyzer. X-ray diffraction analysis revealed that the polycrystalline structure of silver (Ag) embedded with anatase titanium (TiO2) nanoparticles, while SWCNTs and MWCNTs were verified by EDS spectra due to covering of the (002) peak of carbon nanotubes (CNTs) by the (101) diffraction peak of the TiO2. The FTIR results confirmed the formation of oxygen functional groups onto the SWCNTs and MWCNTs. FESEM results indicated that TiO2/Ag nanoparticles (NPs) successfully loaded onto SWCNTs and MWCNTs. UV–vis absorbance results show a decrease in the energy band gap of MWCNTs-Ag/TiO2 and SWCNTs-Ag/TiO2 in comparison with pure TiO2. Antibacterial activities of nanocomposite samples against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were evaluated by an international recognized test (ASTM E2149). The results showed that nanocomposite samples have a strong bacterial inhibition against E. coli and S. aureus. Gram-negative bacteria appeared to be more resistant to nanocomposite materials than Gram-positive bacteria under illumination by UV light.

Electronically Pure Single Chirality Semiconducting Single-Walled Carbon Nanotube for Large Scale Electronic Devices

Abstract Carbon nanotube thin film transistors (TFTs) with characteristics resembling those of TFTs constructed on amorphous silicon, low-temperature polycrystalline silicon and metal oxides were fabricated on (6,5) single chirality single-walled carbon nanotube (SWCNT) thin film deposited from electronically pure semiconducting (6,5) single chirality single-walled carbon nanotube (SWCNT) ink. This ink was extracted in industrial scale from raw SWCNTs produced using high pressure carbon monoxide conversion, and deposited on pretreated substrates to form uniform and consistent (6,5) HiPCO SWCNT thin film using solution process. The (6,5) HiPCO SWCNT thin films were characterized as pure semiconductor without metallic impurities showing classic nonlinear current-bias curves in Schottky-type diodes. Both N-type and P-type (6,5) HiPCO SWCNT TFTs were fabricated with femto Ampere off-current and ION/IOFF ratio of 108 by depositing SiNx and HfO2 dielectrics on the top of (6,5) HiPCO SWCNT thin films, respectively. The (6,5) HiPCO SWCNT inverter with voltage gain of 52 was also demonstrated by wire-bonding one P-type HiPCO SWCNT TFT to one N-type HiPCO SWCNT TFT.

Lower limits of detection in using carbon nanotubes as thermoluminescent dosimeters of beta radiation

World-wide, on-going intensive research is being seen in adaptation of carbon nanotubes (CNTs) for a wide variety of applications, particular interest herein being in the thermoluminescent (TL) properties of CNTs and their sensitivity towards energetic radiations. Using beta radiation delivering dose levels of a few Gy it has been observed in previous study that strain and impurity defects in CNTs give rise to significant TL yields, providing an initial measure of the extent to which electron trapping centres exist in various qualities of CNT, from super-pure to raw. This in turn points to the possibility that there may be considerable advantage in using such media for radiation dosimetry applications, including for in vivo dosimetry. CNTs also have an effective atomic number similar to that of adipose tissue, making them suitable for soft tissue dosimetry. In present investigations various single-wall carbon nanotubes (SWCNT) samples in the form of buckypaper have been irradiated to doses in the range 35–1.3Gy, use being made of a 90Sr beta source, the response of the CNTs buckypaper with dose showing a trend towards linearity. It is shown for present production methodology for buckypaper samples that the raw SWCNT buckypaper offer the greatest sensitivity, detecting doses down to some few tens of mGy.

Influence of PEG Molecular Weight on the Drug Release and In vitro Cytotoxicity of Single-Walled Carbon Nanotubes-PEG-Gemcitabine Conjugates.

Gemcitabine (GEM) is a highly hydrophil anticancer drug which extensively used in the clinic for the treatment of a range of solid tumors, including pancreatic and lung cancers. We have designed a drug delivery system based on single-walled carbon nanotubes (SWCNTs) for the anticancer drug GEM, which has limitations under biological conditions, by using polyethylene glycol (PEG) to obtain nanoconjugates with high loading capacity, controlled drug release and effective cytotoxicity. Raw SWCNTs were functionalized through carboxylation, acylation, PEGylation and finally GEM conjugation via a cleavable ester bond. Different characterization techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectrometer (NMR) and differential scanning calorimetry analysis (DSC) were performed to confirm the successful functionalization. Next, the influence of molecular weight (MW) of PEG on the drug loading capacity, drug release and cytotoxicity was studied. Experimental results showed that the drug loading capacity was dependent on the MW of PEG, but the drug release was independent. Also, the results revealed that the nanoconjugates with lower PEG MW caused higher cytotoxicity in A549 and MIA PaCa-2 cancer cells. Our studies indicated which of PEG MWs could be useful for this drug delivery system.

Influence of PEG Molecular Weight on Drug Delivery of Gemcitabine Conjugated to SWCNT-PEG

Gemcitabine (GEM) is a highly hydrophil anticancer drug which extensively used in the clinic for the treatment of a range of solid tumors, including pancreatic and lung cancers. We have designed a drug delivery system based on single-walled carbon nanotubes (SWCNTs) for the anticancer drug GEM, which has limitations under biological conditions, by using polyethylene glycol (PEG) to obtain nanoconjugates with high loading capacity, controlled drug release and effective cytotoxicity. Raw SWCNTs were functionalized through carboxylation, acylation, PEGylation and finally GEM conjugation via a cleavable ester bond. Different characterization techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectrometer (NMR) and differential scanning calorimetry analysis (DSC) were performed to confirm the successful functionalization. Next, the influence of molecular weight (MW) of PEG on the drug loading capacity, drug release and cytotoxicity was studied. Experimental results showed that the drug loading capacity was dependent on the MW of PEG, but the drug release was independent. Also, the results revealed that the nanoconjugates with lower PEG MW caused higher cytotoxicity in A549 and MIA PaCa-2 cancer cells. Our studies indicated which of PEG MWs could be useful for this drug delivery system.

Effect of a nerve graft substitute single-walled carbon nanotubes on rat pheochromocytoma cells

Carbon nanotubes (CNTs) were extensively explored for their beneficial use in nervous system tissue engineering. However, an important concern regarding the use of CNTs is their toxicity during the interaction between cells and the nano particles. The rat pheochromocytoma cell line (PC12) was co-cultured with three types of single-walled carbon nanotubes (SWNTs), purified raw SWNTs (C), hydroxyl purified SWNTs (C-OH) and carboxyl purified SWNTs (C-COOH) at 25 µg/mL and 100 µg/ml. The experimental results revealed that SWNTs at the concentration below 100 µg/mL did not affect the cell viability. Notably, powerful antioxidant system in nerous system tissue is able to counteract with the toxicity of CNTs, which is characterized by the prominently enhanced expression of main antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST)). Therefore, we believe that CNTs can be good candidates for the fabrication of biomedical scaffolds for the nerve tissue repair.

Toxicity of Raw and Purified Single-Walled Carbon Nanotubes in Rat's Lung Epithelial and Cervical Cancer Cells.

The increased applications of carbon nanotubes in the field of drug delivery, bioimaging and biosensors demand nanotubes to be of highest purity, free from metallic impurities and amorphous carbon. All of these sectors require a profound investigation about the toxic effects on human and the environment. Many attempts have been made to purify and surface modify the carbon nanotubes, however a detailed study on the raw and purified material has yet to be conducted. Here we present the toxicity studies of raw and the purified single-walled carbon nanotubes in rat's lung epithelial cell and cervical cancer cells (HeLa). These cells were treated with increasing concentration of 0.5 µg/mL to 50 µg/mL and the various biocompatibility assays were performed. The results showed an increased cell death with purified single-walled carbon nanotubes followed by the depletion of antioxidant levels and activation of the caspase cascade at a rapid rate compared to raw single-walled carbon nanotubes. This suggests that purified single walled carbon nanotubes are more toxic to the cells and exhibit ultra-fine particulate matter like toxicity.

Improved thermoelectric power output from multilayered polyethylenimine doped carbon nanotube based organic composites

By appropriately selecting the carbon nanotube type and n-type dopant for the conduction layers in a multilayered carbon nanotube composite, the total device thermoelectric power output can be increased significantly. The particular materials chosen in this study were raw single walled carbon nanotubes for the p-type layers and polyethylenimine doped single walled carbon nanotubes for the n-type layers. The combination of these two conduction layers leads to a single thermocouple Seebeck coefficient of 96 ± 4 μVK−1, which is 6.3 times higher than that previously reported. This improved Seebeck coefficient leads to a total power output of 14.7 nW per thermocouple at the maximum temperature difference of 50 K, which is 44 times the power output per thermocouple for the previously reported results. Ultimately, these thermoelectric power output improvements help to increase the potential use of these lightweight, flexible, and durable organic multilayered carbon nanotube based thermoelectric modules in low powered electronics applications, where waste heat is available.

Effective Nondestructive Purification of Single-Walled Carbon Nanotubes Based on High-Speed Centrifugation with a Photochemically Removable Dispersant

A purification method for raw single-walled carbon nanotubes (SWCNTs) without damage to their intrinsic structures has been desired in many applications. We investigated the purification of SWCNTs based on high-speed centrifugation of water-dispersed SWCNTs using the photoreactive dispersant we previously investigated. SWCNTs wrapped with the dispersant were separated from impurities, such as an amorphous carbon and metal particles by centrifugation, similarly to conventional physical purification using surfactants. In contrast to general surfactants that form micelles to disperse SWCNTs in aqueous solutions, the photoreactive dispersant did not form micelles. Therefore, an excess amount of the dispersant, which did not adsorb onto the SWCNT surfaces, was removable by dialysis of the supernatant. Since the amount of the dispersant was minimized by dialysis, we tuned the UV-irradiation time to eliminate the dispersibility of SWCNTs in water to as low a value as ∼2 h. The SWCNT precipitates were collected, ...

Removing Aggregates from Single-Walled Carbon Nanotube Samples by Magnetic Purification

Purification of raw single-walled carbon nanotube (SWCNT) material remains an important challenge in nanotube research and applications. We describe here a simple but effective purification method that uses permanent magnets to remove many nanotube aggregates, as well as residual metallic catalyst, from aqueous suspensions of surfactant-coated SWCNTs. Samples have been characterized by optical absorption, fluorescence, and Raman spectroscopies; atomic force microscopy and near-infrared fluorescence microscopy; and thermogravimetric analysis. It is found that magnetic purification reduces absorption backgrounds and increases average fluorescence efficiencies to levels comparable to those in ultracentrifuged samples. The ratio of individualized SWCNTs to aggregates in magnetically processed HiPco samples is estimated to be approximately 4:1. As compared to ultracentrifugation, magnetic processing promises major advantages in cost, simplicity, energy consumption, and scalability.

Removal and Adsorption ofp-Nitrophenol from Aqueous Solutions Using Carbon Nanotubes and Their Composites

In an attempt to explore the possibility of using carbon nanotubes (CNTs) as efficient adsorbents for removal of pollutants from the contaminated water, the adsorption ofp-nitrophenol (PNP) on raw multiwalled carbon nanotubes (r.MWNTs) with different outer diameters, various functionalized multiwalled carbon nanotubes (f-MWNTs), raw single-walled carbon nanotubes (r.SWNTs) and oxidized single-walled carbon nanotubes (ox-SWNTs) has been investigated. The ox-SWNTs showed better adsorption ability for PNP with different concentrations, while lower uptake capacity was found for all of the r.MWNTs andf-MWNTs. The removal efficiency of PNP by ox-SWNTs was around 98%, indicating that ox-SWNTs possess a great potential application prospect for removing PNP from aqueous solutions.

Effects of Purity on the Mechanical Properties of Single-Walled Carbon Nanotubes-Polymer Nanocomposites

This study investigated the superior mechanical properties of single-walled carbon nanotubes (SWCNTs), its polymer nanocomposites using 0.5% and 1% loading of raw and purified SWCNTs in an epoxy matrix and the degree of dispersion. The extent of load transfer between the nanotubes and the matrix was studied by analysing the second order G’-band ( �2550 cm -1 ) of Raman Spectroscopy. The samples have been characterised from structural (Raman spectroscopy), mechanical (tensile test), physical and microstructural (SEM) point of view. Purified SWCNTs give a better reinforcing potential compared to raw SWCNTs. We found an increase in Young’s Modulus (3780 MPa-4263 MPa) and toughness (62 MPa-68.8 MPa) for the nanocomposites prepared from purified SWCNTs.

The synthesis of covalent bonded single-walled carbon nanotube/polyvinylimidazole composites by in situ polymerization and their physical characterization

Single-walled carbon nanotube (SWCNT) polyvinylimidazole (PVI) composites have been prepared by in situ emulsion polymerization. Dispersion of raw SWCNTs in the PVI matrix was improved by surface modification of the SWCNTs using nitric acid treatment and air oxidation. The carbonyl-terminated SWCNTs were covalently bonded to PVI by in situ polymerization and the SWCNT/PVI composite was thus obtained. The morphological and structural characterizations of the surface-functionalized SWCNTs and SWCNT/PVI composites were carried out by Fourier transform infrared spectroscopy, X-ray diffraction, conductivity measurements, scanning, and transmission electron microscopy. Thermograms of the materials were determined by the differential scanning calorimetry technique. The characterization results indicate that PVI was covalently bonded to SWCNTs and a new material was then obtained. The functionalized SWCNTs showed homogenous dispersion in the composites, whereas purified SWCNT resulted in poor dispersion and nanotube agglomeration. SWCNT/PVI composites exhibited chemical stability enhancement in many common solvents. I–V curves of the samples exhibit an ohmic character. Conductivity values for pure SWCNTs, pure PVI and SWCNT/PVI composite were measured to be 3.47, 2.11 × 10−9, and 2.3 × 10−3 S/m, respectively. Because of resonance, a large dielectric constant is obtained for SWCNT/PVI composite, which is not observed for ordinary materials. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers