Walls Of CNTs Research Articles

Sonochemical synthesis of magnetic properties of Fe3O4/CNT nanocomposites

ABSTRACTFe3O4/CNT hybrids have been successfully synthesized through simple one-step methods. The resulting composites were characterized via transmission electron microscopy (TEM), X-ray diffractometry (XRD), Fourier transform infrared (FTIR) and vibration and sample magnetometry (VSM) approaches. It was found that those Fe3O4/CNT nanocomposites were superparamagnetic. TEM observation indicated that the produced Fe3O4 particles were decorated the external walls of CNTs. The increasing of the ultrasonic times result in the changes in the average particle sizes of the Fe3O4 particles. For the Fe3O4/CNT composites, larger particle sizes lead to the greater magnetic responses.

Carbon nanospheres hanging on carbon nanotubes: a hierarchical three-dimensional carbon nanostructure for high-performance supercapacitors

We describe the single-step synthesis of carbon nanospheres hanging on carbon nanotubes (CNs/CNTs), using a simple chemical vapor deposition method.

Mixed-Matrix Membranes Containing Carbon Nanotubes Composite with Hydrogel for Efficient CO2 Separation.

In this study, a carbon nanotubes composite coated with N-isopropylacrylamide hydrogel (NIPAM-CNTs) was synthesized. Mixed-matrix membranes (MMMs) were fabricated by incorporating NIPAM-CNTs composite filler into poly(ether-block-amide) (Pebax MH 1657) matrix for efficient CO2 separation. The as-prepared NIPAM-CNTs composite filler mainly plays two roles: (i) The extraordinary smooth one-dimensional nanochannels of CNTs act as the highways to accelerate CO2 transport through membranes, increasing CO2 permeability; (ii) The NIPAM hydrogel layer coated on the outer walls of CNTs acts as the super water absorbent to increase water content of membranes, appealing both CO2 permeability and CO2/gas selectivity. MMM containing 5 wt % NIPAM-CNTs exhibited the highest CO2 permeability of 567 barrer, CO2/CH4 selectivity of 35, and CO2/N2 selectivity of 70, transcending 2008 Robeson upper bound line. The improved CO2 separation performance of MMMs is mainly attributed to the construction of the efficient CO2 transport pathways by NIPAM-CNTs. Thus, MMMs incorporated with NIPAM-CNTs composite filler can be used as an excellent membrane material for efficient CO2 separation.

Correlation of surface treatment, dispersion and mechanical properties of HDPE/CNT nanocomposites

The effect of carbon nanotube treatment on the mechanical property of polyethylene/carbon nanotube composite (HDPE/CNT) was investigated. CNTs were initially treated with HCl and then with H2SO4/HNO3. Nanocomposites reinforced with untreated and treated CNTs were prepared by a mechanical mixture of the molten polymer. The results demonstrated a correlation among the surface treatment, dispersion and mechanical properties of HDPE/CNT composites. Raman spectroscopy and TGA analysis showed that both acid treatments removed efficiently amorphous carbon and residual metal catalysts of CNTs. However, these treatments not only removed impurities, they also decreased the crystallinity degree of CNTs due to the addition of oxygenated functional groups to the CNTs walls, as observed by XPS analysis. SEM micrographs revealed that the functional groups improved the CNTs dispersion in the polymeric matrix, resulting in an improvement of the mechanical properties of nanocomposites.

Intercalation-assisted longitudinal unzipping of carbon nanotubes for green and scalable synthesis of graphene nanoribbons.

We have demonstrated an effective intercalation of multi-walled carbon nanotubes (MWCNTs) for the green and scalable synthesis of graphene nanoribbons (GNRs) using an intercalation-assisted longitudinal unzipping of MWCNTs. The key step is to introduce an intercalation treatment of raw MWCNTs with KNO3 and H2SO4, making it promising to decrease the strong van der Waals attractions in the MWCNTs bundles and between the coaxial graphene walls of CNTs. Systematic micro Raman, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) characterizations suggest that potassium, nitrate, and sulfate ions play an important role in the CNT intertube and intratube intercalations during the pretreatment. Detailed scanning electron microscopy (SEM), transmission electron microscopy, XRD, and micro Raman characterizations indicate that the developed methodology possesses the ability to synthesis GNRs effectively with an improved CNT concentration in H2SO4 of 10 mg/ml at 70 °C, which is amenable to industrial-scale production because of the decreased amount of strong acid. Our work provides a scientific understanding how to enhance the GNR formation by accelerating the CNT longitudinal unzipping via suitable molecular intercalation.

Graphene-winged carbon nanotubes as high-performance lithium-ion batteries anode with super-long cycle life

Graphene-winged carbon nanotubes (G-CNTs) have been prepared by the well-controlled outer-wall peeling of the multi-walled carbon nanotubes (MWCNTs). The final hybrid structure features the few layers of graphene nanosheets attaching to the intact inner walls of CNTs. On one hand, the outer branched graphene nanosheets could suppress the aggregation of CNTs and introduce abundant defects and active-edges for easily accessible chemical interaction. On the other hand, the CNTs could bridge the graphene nanosheets for rapid electron transfer and mechanical robustness. As a result, the G-CNTs was used as the electrode materials exhibiting an extremely steady reversible capacity of 603 mAh g−1 over 2200 cycles at a current density of 1 A g−1 (the corresponding area capacity is 0.16 mAh cm−2 at a current density of 0.26 mA cm−2) and owning a high rate capability much superior to those of the pristine MWCNT-based counterparts. The hierarchical G-CNTs architecture provides a new material platform for development of advanced energy-storage devices.

Enhanced Catalytic Activity of Carbon Nanotubes for the Oxidation of Cyclohexane by Filling with Fe, Ni, and FeNi alloy Nanowires

Fe-, Ni-, and alloyed FeNi-filled carbon nanotubes (Fe@CNT, Ni@CNT, and FeNi@CNT) were prepared by a general strategy using a mixture of xylene and dichlorobenzene as carbon source, and ferrocene, nickelocene, and their mixture as catalysts. By tailoring the composition of the carbon precursor, the filling ratio and the wall thickness of metal@CNT could be controlled. For the catalytic oxidation of cyclohexane in liquid phase with molecular oxygen as oxidant, the highest activity was obtained over Fe@CNT synthesized from pure dichlorobenzene. However, Ni filling did not improve the activity of CNTs. The effects of metal filling, wall thickness, and defects on catalytic activity were investigated to determine the structure–activity relationship of the filled CNTs. The enhanced catalytic performance can be attributed to a combined contribution of thin walls of CNTs and confined electron-donating metals, which are favourable to electron transfer on the surfaces of CNTs. The modification of the electronic structure of CNTs upon Fe and Ni fillers insertion was elucidated through density functional theory calculations.

The homogenizing of carbon nanotube dispersion in aluminium matrix nanocomposite using flake powder metallurgy and ball milling methods

In the present work, the flake powder metallurgy as a slurry based method and the ultrasound-assisted then ball milling as a semi-wet based route were applied to modify the carbon nanotube dispersion within the aluminium powder. For this purpose, two types of long and short fiber CNTs-COOH were selected as reinforcement to strengthen the matrix of Al powders with particle sizes of <45 and <20μm. The effects of morphological changes in composite constituents and the variables of each procedure such as time and rotation speed of ball milling, chemical modification of Al powder by a hydrophilic Polyvinyl alcohol, production of nano-flake Al powders and the carboxyl agent on the wall of CNTs were investigated in this research. The Al (20) and Al (45) with 1.5wt. %CNTs well-dispersed nanocomposites were produced in semi-wet based process after medium energy level ball milling at 200rpm in duration of 2 and 4h, respectively. Also, the flaky shape morphologies of pure Al powders with large aspect ratio of 50 and 125 were obtained after the 2h ball milling of <45 and <20μm powders, respectively.In slurry based method, by forming the hydrogen bonding between the –OH groups of PVA and –COOH groups of multi walled CNTs, the suitable dispersion was resulted for both types of CNTs in Al flake powders with large specific surface area. The final products were studied through field emission scanning electron microscopy (FE-SEM).

Functionalization of Multi Wall Carbon Nanotubes Using Nitric Acid Oxidation

Functionalized of Multi Wall Carbon Nanotubes (MWCNTs) were demonstrated using the nitric acid (HNO3) oxidation technique in order to get opened caps, removing carbonaceous and metal particles impurities for carboxylic groups (-COOH). The surface morphology and the existence of the carboxyl-group on the MWCNTs were examined using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), respectively. The carboxylic groups were observed at the peak of 1640.40cm-1 via FTIR and indicate the absorbance intensity of the functionalized MWCNTs is 2.22 A which is higher than raw material. Furthermore, SEM image shows the bundle of structure on the raw MWCNTs signified the Van der Waals interaction between MWCNTs while after functionalized a groovy CNTs wall were observed due to presence of carboxyl group at the defect sites.

Significance of wall number on the carbon nanotube support-promoted electrocatalytic activity of Pt NPs towards methanol/formic acid oxidation reactions in direct alcohol fuel cells

The inner walls of CNTs have a significant effect on the electrocatalytic activity of supported Pt NPs for MOR/FAOR in fuel cells.

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active, Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

AbstractA facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom‐doped carbon (CNT/HDC) core–sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom‐containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom‐containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom‐doped nanocarbon catalysts in terms of half‐wave potential and kinetic current density. The four‐electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long‐term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active, Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

A facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom-doped carbon (CNT/HDC) core-sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom-containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom-containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom-doped nanocarbon catalysts in terms of half-wave potential and kinetic current density. The four-electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long-term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.

Nickel Oxide Coated on Pretreated MWCNTs as an Electrode for Supercapacitor

Nickel oxide/carbon nanotubes (NiO/CNTs) composite materials for supercapacitor are prepared by chemically depositing of nickel hydroxide onto CNTs pretreated by ultrasonication and followed by thermal annealing at 200-300°C. A series of NiO/CNTs composites with different weight ratios of CNTs and different annealing temperature are synthesized via the same route. The scanning electron microscope (SEM) images show that the nucleation of the nickel hydroxide formed on the outer walls of CNTs due to ultrasonic cavitations, and then nickel oxide coated uniformly on the outer surface of the individual CNTs after thermal annealing. The NiO/CNTs electrode presents a maximum specific capacitance of 254 F/g as well as a good cycle life in 2 M KOH electrolyte. The good electrochemical characteristics of NiO/CNTs composite can be attributed to the three-dimensionally interconnected nanotubular structure with a thin film of electroactive materials.

Functionalization of Carbon Nanotubes and Polymer Compatibility Studies

Multiwalled carbon nanotubes (MWNTs) were oxidated and functionalized in order to determine the structural and chemical changes on their atomic bonding. MWNTs were oxidized in an aqueous solution of HNO3 (70%) and H2SO4 (95%) at 25 °C. Pristine and oxidized carbon nanotubes (ox-MWNTs) were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetrical analysis (TGA). MWNTs and ox-MWNTs were silane-functionalized and incorporated into a polymethyl-methacrylate (PMMA) matrix. The dispersion properties and interface interactions were studied for the composite materials. MWCNTs oxidation was performed and supported by Raman spectroscopy and FTIR results of disorder and defects in the carbon lattice; as well as change in the amount and type of chemical groups attached to the CNTs walls. Roughness areas visible in SEM images indicate Van der Waals interactions between CNTs and functionalization reagents. Control of the oxidation state can effectively direct molecular functionalization of a CNT sidewall. Composites showed good dispersion of filler; with the best one for oxidized-silane functionalized CNTs.

CoFe2O4 nanoparticles as a catalyst: synthesis of a forest of vertically aligned CNTs of uniform diameters by plasma-enhanced CVD

Controlling actively the structures of carbon nanotubes such as the alignment, length, diameter, chirality and the number of walls still remains a crucial challenge. The properties of CNTs are highly structure sensitive and particularly dependent on the diameter and number of walls. In this brief communication, we synthesise monodisperse CoFe2O4 nanoparticles of uniform diameters, i.e. 4.8 and 6.9 nm, which are modified with oleic acid as a catalyst for the growth of CNTs. We show that a forest of vertically aligned CNTs of uniform diameters and lengths can be grown using CoFe2O4 nanoparticles. The internal diameters and lengths of CNTs grown using CoFe2O4 nanoparticles of 4.8 and 6.9 nm diameters are, respectively, 4.4 and 6.2 nm and 10 and 15 μm. It is clearly shown that the number of walls of CNTs can be engineered changing the materials of the catalytic nanoparticles. The present results may well encourage further systematic studies on the growth of CNTs using various combinations of elements for the catalytic nanoparticles under different external conditions, which may provide not only the possibilities of controlling the properties of CNTs but also an insight into the nucleation and growth mechanisms.

A new fabrication method of uniformly distributed TiO2/CNTs composite film by in-situ chemical vapordeposition

A uniformly distributed TiO2/CNTs composite film was fabricated by an in-situ chemical vapor deposition (CVD) method. CNTs are directly grown from the prepared TiO2 film by the spray pyrolysis deposition method doped with nickel oxide on Ni substrate. The nano-size TiO2 particles are uniformly distributed on the side walls of CNTs. The TiO2/CNTs composite exhibits high photocatalytic activity in the degradation of methyl orange (MO) and 95% of MO (10mg/L) could be removed within 150min under UV light irradiation. The results of the present study are promising for the development of a new method for the fabrication of well-distributed TiO2/CNTs compositefilm.

Drug-loading capacity and nuclear targeting of multiwalled carbon nanotubes grafted with anionic amphiphilic copolymers

In this study, three types of hybrid nanotubes (NTs), ie, oxidized multiwalled carbon NTs (COOH MWCNTs), heparin (Hep)-conjugated MWCNTs (Hep MWCNTs), and diblock copolymer polyglycolic acid (PGA)-co-heparin conjugated to MWCNTs (PGA MWCNTs), were synthesized with improved biocompatibility and drug-loading capacity. Hydrophilic Hep substituents on MWCNTs improved biocompatibility and acted as nucleus-sensitive segments on the CNT carrier, whereas the addition of PGA enhanced drug-loading capacity. In the PGA MWCNT system, the amphiphilic copolymer (PGA-Hep) formed micelles on the side walls of CNTs, as confirmed by electron microscopy. The PGA system encapsulated the hydrophobic drug with high efficiency compared to the COOH MWCNT and Hep MWCNT systems. This is because the drug was loaded onto the PGA MWCNTs through hydrophobic forces and onto the CNTs by π–π stacking interactions. Additionally, most of the current drug-carrier designs that target cancer cells release the drug in the lysosome or cytoplasm. However, nuclear-targeted drug release is expected to kill cancer cells more directly and efficiently. In our study, PGA MWCNT carriers effectively delivered the active anticancer drug doxorubicin into targeted nuclei. This study may provide an effective strategy for the development of carbon-based drug carriers for nuclear-targeted drug delivery.

Facile encapsulation of nanosized SnO2 particles in carbon nanotubes as an efficient anode of Li-ion batteries

An efficient anode with a superior high-rate capability and stability remains a challenge for development of high performance Li-ion batteries. We present a new concept by encapsulating 2 nm-sized SnO2 nanocrystals in the channels of carbon nanotubes (SnO2-in-CNTs). Characterization shows that the confined space does not only stabilize the small nanoparticles but also alleviates the stress caused by the large volume change of tin species during the charging–discharging process. In addition, well crystallized graphitic structure of CNTs with a positive curvature provides a good contact between SnO2 nanoparticles and graphene layers, and excellent electronic conductivity. As a result, SnO2-in-CNTs as an anode of lithium ion battery exhibit stable cyclability and superior high-rate capability relative to SnO2 nanoparticles dispersed on the outer walls of CNTs particularly under a high current density. The charge capacity remains about 560 mA h g−1 after 50 cycles at 50 mA g−1, and even around 400 mA h g−1 at 1000 mA g−1. Additionally, the facile preparation method we have developed makes such encapsulates appealing for further optimization and applications.

Silanization and silica enrichment of multiwalled carbon nanotubes: Synergistic effects on the thermal-mechanical properties of epoxy nanocomposites

In this paper the synergistic effects of both 3-amminopropryltriethoxy silane (APTES) functionalization and silica enrichment of carbon nanotubes on thermal and thermal-mechanical properties of epoxy based composite materials were investigated. Pristine multiwalled carbon nanotubes were oxidized, functionalized with APTES and then modified with silica nanoparticles preformed through the Stober process. The FTIR, XPS and TGA analysis confirmed the occurrence of the silane functionalization and surface silica enrichment. TEM analysis showed the presence of a “bunches” morphology where silica nanoparticles aggregated around both the CNTs wall and their ends. Thermo-mechanical, thermal and flammability properties of nanocomposite containing 1wt% of different fillers were determined and results compared to neat epoxy resin.Results showed that both the elastic and rubbery modulus increase with the addition of filler. In particular, in the rubbery region, the storage modulus of composites with silanized and silica enriched carbon nanotubes were about 240% and 285% higher than modulus of neat epoxy system. In the glassy region, a modest increment of 25% for the storage modulus was recorded. The glass transition temperature increased of about 20°C with silica enriched carbon nanotubes alongside with a significant enhancement of the damping behavior.

Study on the Controllable Scale-Up Growth of Vertically-Aligned Carbon Nanotube Arrays

Vertically aligned carbon nanotubes (VA-CNTs) with high purity have been grown on quartz substrate via the gas phase catalytic chemical vapour deposition (CVD) by using ferrocene as the catalyst source and camphor as the carbon source. The effects of catalyst concentration, flow rate and water assistance on the morphology and structure of VA-CNTs are investigated by SEM, TEM, Raman and XPS characterizations. Under the optimized CVD conditions with modest ferrocene concentration and flow rate, dense and well VA-CNT arrays have been obtained. The water concentration should be controlled to improve CNTs alignment and impurity without damaging the walls of CNTs.