Cup-stacked Carbon Research Articles

Catalytic carbonization of polypropylene into cup-stacked carbon nanotubes with high performances in adsorption of heavy metallic ions and organic dyes

Abstract A one-pot approach was demonstrated to effectively synthesize cup-stacked carbon nanotubes (CS-CNTs) through carbonization of polypropylene (PP) under the combined catalysis of halogenated compound and NiO at 700 °C. The effect of halogenated compound on the morphology, microstructure, phase structure and thermal stability of the resultant CS-CNTs was studied by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. Long, straight and surface-smooth CS-CNTs with graphene nanosheets oblique to CS-CNT axis at the angle of 21–25° were obtained when a low content of halogenated compound was added. The synergetic catalytic efficiency of combined catalysts in the carbonization of PP into CS-CNTs followed in the sequence: fluorinated compound/NiO ≪ chlorinated compound/NiO

Electrochemical properties of oxygenated cup-stacked carbon nanofiber-modified electrodes.

Oxygenated cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were investigated as electrode materials by using typical redox species in electrochemistry, Fe(2+/3+), [Fe(CN)6](3-/4-), and dopamine. The electron transfer rates for these redox species at oxygenated CSCNF electrodes were higher than those at edge-oriented pyrolytic graphite and glassy carbon electrodes. In addition, the oxygen-containing functional groups also contributed to the electron transfer kinetics at the oxygenated CSCNF surface. The electron transfer rate of Fe(2+/3+) was accelerated and that of [Fe(CN)6](3-/4-) was decelerated by the oxygen-containing groups, mainly due to the electrostatic attraction and repulsion, respectively. The electrochemical reaction selectivities at the oxygenated CSCNF surface were tunable by controlling the amount of nanofibers and the oxygen/carbon atomic ratio at the nanofiber surface. Thus, the oxygenated CSCNFs would be useful electrode materials for energy-conversion, biosensing, and other electrochemical devices.

Striking Influence about HZSM-5 Content and Nickel Catalyst on Catalytic Carbonization of Polypropylene and Polyethylene into Carbon Nanomaterials

A one-pot approach was established to effectively convert polypropylene (PP) and linear low density polyethylene (LLDPE) into carbon nanomaterials (CNMs) including cup-stacked carbon nanotubes and carbon nanofibers under the combined catalysis of HZSM-5/NiO or HZSM-5/Ni2O3 at 700 degrees C. The effects of HZSM-5 content, a nickel catalyst, and the carbon precursor on the morphology, microstructure, phase structure, and thermal stability of CNMs were investigated with scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, and thermal gravimetric analysis. The effect of HZSM-5 content on the degradation products of PP and LLDPE was analyzed by gas chromatography and gas chromatography mass spectrometry. With increasing HZSM-5 content, the yields of light hydrocarbons and aromatics increased due to proton acid sites on the surface of HZSM-5 catalyzing cracking of PP or LLDPE degradation products. This one-pot approach provides a novel potential way to largely transform mixed waste polyolefin into high value-added CNMs.

Striking influence of chain structure of polyethylene on the formation of cup-stacked carbon nanotubes/carbon nanofibers under the combined catalysis of CuBr and NiO

A one-pot approach was used to convert polyethylene (PE) with different chain structures into carbon nanomaterials (CNMs) under the combined catalysis of CuBr and NiO at 700°C, including linear low density polyethylene (LLDPE), low density polyethylene (LDPE) and high density polyethylene (HDPE). The effect of chain structure of PE on the yield, morphology, microstructure, phase structure and thermal stability of CNMs, including cup-stacked carbon nanotubes (CS-CNTs) and carbon nanofibers (CNFs), were investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. In addition, the degradation products from different chain structures of PE under the catalysis of CuBr were analyzed by gas chromatography and gas chromatography–mass spectrometry. It was demonstrated that the branched structure played an important effect in the degradation products of PE. The dehydrogenation and aromatization of LLDPE were remarkably promoted by Br radicals from the decomposition of CuBr to form a large amount of light hydrocarbons and a relatively small amount of aromatics, favoring the formation of long and straight CS-CNTs. However, the degradation of LDPE was not obviously influenced by Br radicals due to its high extent of branched structure, while the random cleavage of HDPE was accelerated with the formation of a lot of olefins with long chains, resulting in the formation of short and winding CNFs. This work will contribute to the conversion of mixed waste polyolefin into high value-added CNMs.

Mechanical and shape recovery properties of shape memory polymer composite embedded with cup-stacked carbon nanotubes

This study investigated the mechanical and shape recovery properties of a styrene-based shape memory polymer composite reinforced by cup-stacked carbon nanotubes. Due to their unique morphology, cup-stacked carbon nanotubes could be well dispersed in the polymer matrix and offer remarkable benefits in the load transfer between the reinforcement fillers and shape memory polymer. Under the same amount of fillers, shape memory polymer composites embedded with cup-stacked carbon nanotubes exhibit superior mechanical properties in comparison with those embedded with multiwalled carbon nanotubes and carbon nanofibers. The elastic modulus, tensile strength, and flexural strength of the 2 wt% cup-stacked carbon nanotube–reinforced shape memory polymer composite increased by 61%, 66%, and 84%, respectively. It was also found that the glass transition temperature of shape memory polymer composite decreased from 61.9°C to 52.8°C by introducing 2 wt% cup-stacked carbon nanotubes, indicating that the shape recovery process could be triggered more easily by external stimulus due to the role of reinforcement fillers. Finally, under the external resistance load, the developed shape memory polymer composite was successfully driven to recover their shapes under thermal stimulus. The cup-stacked carbon nanotubes were proved to be a promising candidate for the polymer reinforcement.

Role of cone angle on the mechanical behavior of cup-stacked carbon nanofibers studied by atomistic simulations

Classical molecular dynamics simulations are used to study the effects of cone angle on mechanical properties and failure mechanisms in thermally-treated cup-stacked CNFs. We find a 22-fold reduction in elastic modulus and 4-fold decrease in tensile strength of cup-stacked CNFs with a wide range of cone angles between 19.2° and 180°. Our results show significant elastic stiffening for intermediate angles between 38.9° and 112.9°, as well as a minimum in tensile strength at a critical cone angle, due to the competition between weak van-der-Waals forces between layers and strong strengthening mechanisms from surface bonds introduced during thermal treatment. Different failure modes in CNFs subjected to tensile deformation are also predicted as a function of cone angle. This study constitutes an important step toward understanding the origin of strength dispersions observed experimentally in CNFs, and suggests that the design of high-strength CNFs can be optimized structurally by appropriately tuning the cone angle.

Growth of a cup-stacked carbon nanotube carpet with a superhydrophobic surface

Growth of a cup-stacked carbon nanotube carpet with a superhydrophobic surface

Growth of a cup-stacked carbon nanotube carpet with a superhydrophobic surface

A carpet structure composed of high purity cup-stacked carbon nanotubes (CSCNTs) was synthesized by a catalytic chemical vapor deposition method. In a 15-min growth time, the CSCNT carpet with a height up to ∼300 μm and carbon purity above 99.9 wt% was prepared. Transmission electron microscopy observations indicated that the CSCNTs with diameters ranging from 80 nm to 230 nm consist of truncated conical graphene layers. Based on the experimental results, a possible “base growth” mechanism was proposed for the CSCNTs. The CSCNT carpet is highly flexible and superhydrophobic, showing a contact angle of ∼155o. It can be easily harvested from the original growth substrate and be transferred to target substrates. It may therefore find applications as a water-proof and self-cleaning coating layer.

Effect of the added amount of organically-modified montmorillonite on the catalytic carbonization of polypropylene into cup-stacked carbon nanotubes

For the first time, cup-stacked carbon nanotubes (CS-CNTs) with high quality were efficiently synthesized by a one-pot approach through the carbonization of polypropylene (PP) under the combined catalysis of organically-modified montmorillonite (OMMT)/NiO. The effects of the added amount of OMMT on the yield, morphology, microstructure, phase structure and thermal stability of carbon nanomaterials (including CS-CNTs and carbon nanofibers (CNFs)) were fully investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. Furthermore, the effects of OMMT on the degradation products of PP and the coalescence and reconstruction of NiO nanoparticles before the growth of CS-CNTs and CNFs were analyzed by gas chromatography, gas chromatography–mass spectrometry and HRTEM. It was found that after adding a low amount of OMMT, a relatively large amount of light hydrocarbons and a small amount of aromatics were produced during the degradation of PP, which promoted the coalescence and reconstruction of NiO nanoparticles into rhombic shape. Subsequently, the reshaped NiO catalysts catalyzed the light hydrocarbons and aromatics into long, straight and smooth-surface CS-CNTs with narrow length and diameter distributions. This approach offers a new potential way to largely transform waste polymer materials into valuable CS-CNTs.

A reversible strain-induced electrical conductivity in cup-stacked carbon nanotubes

We have used in situ current-voltage measurements of cup-stacked carbon nanotubes (CSCNTs) to establish reversible strain induced (compressive bending) semiconducting to metallic behavior. The corresponding electrical resistance decreases by two orders of magnitude during the process, and reaches values comparable to those of highly crystalline multi-walled carbon nanotubes (MWCNTs) and graphite. Joule heating experiments on the same CSCNTs showed that the edges of individual cups merge to form "loops" induced by the heating process. The resistance of these looped CSCNTs was close to that of highly deformed CSCNTs (and crystalline MWCNTs), thus suggesting that a similar conduction mechanism took place in both cases. Using a combination of molecular dynamics and first-principles calculations based on density functional theory, we conclude that an edge-to-edge interlayer transport mechanism results in conduction channels at the compressed side of the CSCNTs due to electronic density overlap between individual cups, thus making CSCNTs more conducting. This strain-induced CSCNT semiconductor to metal transition could potentially be applied to enable functional composite materials (e.g. mechanical sensors) with enhanced and tunable conducting properties upon compression.

Preparation and Damping Properties of Cups-Stacked Carbon Nanotubes(CSCNTs)/Prime 20

CSCNT is a new type carbon nanotube, which has better physical and mechanical properties than the traditional materials. In this study, the effect of the dispersion and concentration of cup-stacked carbon nanotubes on mechanical properties of the CSCNTs/epoxy nanocomposites were investigated. The epoxy resin system used in this study was a two component (resin and harder) Prime 20. The CSCNTs were dispersed into the Prime 20 by ultrasonic agitation and mechanical mixing together. And the morphologies of the fracture surface of CSCNTs/Prime 20 nanocomposites were observed by scanning electron microscope (SEM); damping behaviors of the nanocomposites were studied by DMA at frequency domain.

Influence of the carbon surface on cathode deposits in non-aqueous Li–O2 batteries

Cup-stacked carbon nanotubes (CSCNT) with different surface properties were used for the non-aqueous Li–O2 battery cathodes, and then examined at high magnification to understand how the discharge products were deposited on the cathode. As-prepared CSCNT based cathode had many reactive edges consisting of truncated conical graphene layers. After discharge, discharge products with average particle size 50nm covered a nanotube, resulting in a layer-like texture. On the other hand, a heat-treated CSCNT based cathode was composed of edges terminated by graphitization of several graphene layers. After discharge, the size of the products was almost the same but the products were agglomerated, forming a bulky morphology. It was, thus, found that the carbon surface structure was closely related with the morphology of the cathode deposits after discharge. First principles calculations also indicated that no terminated edges acted as preferential active sites in adsorbing and storing the reaction species. It was, therefore, concluded that the active edges of the carbon surface were indispensable for controlling the morphology of cathode deposits and improving the battery performance.

Electrochemical Characterization of Cup-Stacked Carbon Nanofiber-Modified Electrodes and its Application to Biosensing

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Direct Synthesis of Cup-Stacked Carbon Nanofiber Microspheres by the Catalytic Pyrolysis of Poly(ethylene glycol)

Uniformly sized microspheres tangled with cup-stacked carbon nanofibers (CSCNFs) were directly synthesized by the pyrolysis of poly(ethylene glycol) (PEG) with a nickel catalyst. A PEG/Ni membrane was prepared on a silicon wafer surface by heating it to 750 °C at a heating rate of 15 °C min(-1). The wafer was heated to a temperature of 400 °C and was held at that temperature for 1 h before raising the temperature to 750 °C for 10 min to form the CSCNF microspheres. The final CSCNF microspheres and the intermediates were evaluated using scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and Raman spectroscopy to elucidate the growth mechanism. Furthermore, the CSCNF microspheres were successfully dispersed and maintained their spherical shape in an aqueous solution containing 0.5% Nafion. The CSCNF microspheres have the potential to work as a sophisticated carrier with high adsorption and fast electron-transfer exchange properties based on the graphene edges of the nanofiber surface.

Formation of COx-Free H2 and Cup-Stacked Carbon Nanotubes over Nano-Ni Dispersed Single Wall Carbon Nanohorns

Transitional metals (M) were dispersed on single-wall carbon nanohorns (M/SWCNHs, M = Fe, Co, Ni, Cu) by simple thermal treatment of the deposited metal nitrate without H(2) reduction. Nanometallic Ni particles on SWCNH were evidenced by high-resolution transmission electron microscopic observation and X-ray photoelectron spectroscopy. The nano-Ni dispersed on SWCNH showed the highest CH(4) decomposition activity; the activity of used transitional metals decreases in the order Ni ≫ Co > Fe ≫ Cu. On the other hand, the reaction rate over Ni/SWCNH was much larger than that over Ni/Al(2)O(3), and the former provided CO(x)-free H(2) and cup-stacked carbon nanotubes, while Ni/Al(2)O(3) produced CO(x) in addition to H(2). SWCNH was superior to Al(2)O(3) as the catalyst support of Ni for the CH(4) decomposition reaction.

Peroxidase-modified cup-stacked carbon nanofiber networks for electrochemical biosensing with adjustable dynamic range

Cup-stacked carbon nanofibers (CSCNFs) were treated with ozone to introduce oxygen-containing groups to the edges of the graphene cups. The O/C atomic ratio at the surface was estimated to be 5.3 × 10−2. The hydrophilic CSCNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Horseradish peroxidase (HRP) molecules were immobilized onto the network for amperometric sensing of H2O2 and inhibition-based sensing of cyanide. Both the upper sensing limit of H2O2 and the upper and lower sensing limits of cyanide were controlled by about two orders of magnitude by changing the HRP coverage.

Introducing carbon nanotubes into living walled plant cells through cellulase-induced nanoholes

Carbon nanotubes can intracellularly transport through different cellular barriers. However, their use in plant cells is limited by the cellulosic cell wall surrounding these cells. Here we show that cup-stacked carbon nanotubes with cellulase immobilized on their sidewalls and tips penetrate the cell wall and transport intracellularly through cellulase-induce nanoholes.

The plant cell uses carbon nanotubes to build tracheary elements

Since their discovery, carbon nanotubes (CNTs) have been eminent members of the nanomaterial family. Because of their unique physical, chemical and mechanical properties, they are regarded as new potential materials to bring enormous benefits in cell biology studies. Undoubtedly, the first step to prove the advantages of CNTs is to understand the basic behavior of CNTs inside the cells. In a number of studies, CNTs have been demonstrated as new carrier systems for the delivery of DNA, proteins and therapeutic molecules into living cells. However, post-uptake behavior of CNTs inside the cells has not received much consideration. Utilizing the plant cell model, we have shown in this study that the plant cells, differentiating into tracheary elements, incorporate cup-stacked carbon nanotubes (CSCNTs) into cell structure via oxidative cross-linking of monolignols to the nanotubes surface during lignin biosynthesis. This finding highlights the fate of CNTs inside plant cells and provides an example on how the plant cell can handle internalized carbon nanomaterials.

Assemblies of artificial photosynthetic reaction centres

Nature harnesses solar energy for photosynthesis in which one reaction centre is associated with a number of light harvesting units. The reaction centre and light-harvesting units are assembled by non-covalent interactions such as hydrogen bonding and π–π interactions. This article presents various strategies to assemble artificial photosynthetic reaction centres composed of multiple light harvesting units and charge-separation units, which are connected by non-covalent bonding as well as covalent bonding. First light-harvesting units are assembled on alkanethiolate-monolayer-protected metal nanoparticles (MNPs), which are connected with electron acceptors by non-covalent bonding. Light-harvesting units can also be assembled using dendrimers and oligopeptides to combine with electron acceptors by π–π interactions. The cup-shaped nanocarbons generated by the electron-transfer reduction of cup-stacked carbon nanotubes have been functionalized with a number of porphyrins acting as light-harvesting units as well as electron donors. In each case, the photodynamics of assemblies of artificial photosynthetic reaction centres have revealed efficient energy transfer and electron transfer to afford long-lived charge-separated states.

Electromagnetic Interference Shielding Efficiency in the Range 8.2-12.4 GHz of Polymer Composites with Dispersed Carbon Nanoparticles

In the present work, electromagnetic interference shielding properties of polymer composites with dispersed cup-stacked carbon nanotubes, graphite nanoparticles and carbon black were investigated. The polymer composites with carbon nanoparticles content from 1 to 5 w% were successfully prepared by the coagulation method, and composite sheets with thickness from 0.25 to 0.77 mm were formed by the hot press technique. The electromagnetic interference shielding efficiency measured in the frequency range of 8.2~12.4 GHz (X-band) of cup-stacked carbon nanotubes/polymer composite was considerably higher than that of carbon black and graphite nanoparticles polymer composites at the same contents of carbon nanoparticles, and contribution of absorption to the shielding efficiency was found to be higher than that of reflection.