Evaluation of affinity of molecules for carbon nanotubes

Recent developments of non-covalent functionalization of carbon nanotubes (CNTs) require a systematic understanding of the interaction between molecule and CNTs (CNT-molecular interaction); however, it has been difficult to evaluate the "net" interaction between the CNTs and molecules. We now use silica gel particles coated with the pristine single-walled carbon nanotubes (SWNTs) in a monolayer fashion as the stationary phase of a HPLC column. The newly developed column (SWNT-column) worked as a powerful tool for ranking the interactions between the SWNTs and molecules with a high precision. We describe the binding affinity analysis of polyaromatic hydrocarbons onto the surfaces of SWNTs. The obtained ranking is determined in the order of benzene < naphthalene < biphenyl < fluorene < phenanthrene < anthracene ～ pyrene < triphenylene < p-terphenyl < tetraphene < tetracene.     

Compressive buckling of carbon nanotubes containing polyethylene molecules

The instability of a carbon nanotube containing a polyethylene molecule subjected to compression is investigated using molecular dynamics. A decrease up to 35% in the buckling strain of the (6,6) and (10,10) carbon nanotube/polymer structures due to the attractive van der Waals interaction between the tube wall and the polymer molecule is reported. In particular, the decrease in the buckling strain of the (6,6) carbon nanotube/polymer structure is attributed to the initiation of two flattenings on the tube wall. Simulations show that the buckling strain of the structure is insensitive to the number of units of the polymer molecule.     

Transportation of hydrogen molecules using carbon nanotubes in torsion

The transportation of hydrogen molecules using carbon nanotubes subjected to torsion is studied with molecular dynamics. Molecular dynamics simulations reveal that the transportation in a (10, 0) carbon nanotube is a result of the van der Waals effect through the propagation of the kink initiated at the onset of the tube torsional buckling. In addition, the applied torsional loading rate has an obvious effect on the orientation of the molecular transportation. On the other hand, the motion of the molecules in a (10, 10) carbon nanotube is found to be less oriented. The mechanism of the transportation in the larger carbon nanotube is investigated through the transform of the collapsed wall of the tube in the dynamic process of the torsional buckling.     

Modification of fluorinated single-walled carbon nanotubes with aminosilane molecules

Single-walled carbon nanotubes (SWCNTs) modified with amino groups were prepared via chemical addition of fluorine on the carbon nanotube surface by plasma treatment. The amino termination makes possible to realize hybrid nanostructures made out of SWCNTs and alkoxy-silane (3′-(aminopropyl)tri-ethoxysilane (APTES)) molecules. The functionalization of the SWCNTs was evidenced by transmission electron microscopy, infrared spectroscopy and thermogravimetric measurements. It was found that the application of a dc electric field enhances the assembly of APTES modified SWCNTs into ordered films with rectifying diode behavior.     

Confined adamantane molecules assembled to one dimension in carbon nanotubes

We have encapsulated adamantane (C₁₀H₁₆) in single- and multi-walled carbon nanotubes. Adamantane is a high symmetry cage like molecule with point group symmetry T_d and can be considered as a hydrogen-terminated diamond fragment. We confirmed and identified the successful filling by high resolution transmission electron microscopy, ¹³C nuclear magnetic resonance, infrared and Raman spectroscopy. ¹³C nuclear magnetic resonance of the adamantane filled nanotubes reveals that the adamantane molecules stop rotating after encapsulation. A blue-shift of the Raman active radial breathing modes of the carbon nanotubes supports this and suggests a significant interaction between encapsulated adamantane molecules and the single wall nanotubes. The encapsulated adamantane molecules exhibit red shifted infrared C–H vibration modes which we assign to a slight elongation of the C–H bonds. We observe both a nanotube diameter dependence of the adamantane filling ratio and a release rate of adamantane from the CNTs that depends on the CNT diameters.     

Functionalization of carbon nanotubes with amphiphilic molecules and their Langmuir-Blodgett films

Crown ether-modified full-length multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) have been prepared by a direct heating method. Subsequently, the Langmuir-Blodgett (LB) method was used to prepare a monolayer of modified carbon nanotubes on an air-water interface. The corresponding Langmuir-Blodgett (LB) films appeared to be very stable and could be transferred onto a hydrophilic silicon substrate easily. Scanning electron microscopy (SEM) images revealed the morphology of the films, in which locally aligned structures could be observed.     

Production of carbon nanotubes from coal

We have demonstrated that the production of carbon nanotubes in large quantities is possible with inexpensive coal as the starting carbon source by the arc discharge technique. It has been found that a large amount of carbon nanotubes of good quality can be obtained in the cathode deposits in which carbon nanotubes are present in nest-like bundles. For the growth of carbon nanotubes, the buffer gas pressure in the reactor is one of the crucial factors. The mineral matter in raw coals may also play an important part in the formation process of carbon nanotubes.     

煤基碳纳米管的制备

碳纳米管是一类新型纳米炭，具有很多潜在的应用价值，用煤为碳源制备碳纳米管可以降低其成本，本文介绍了电弧放电法和等离子体法制备煤基碳纳米管研究情况，以及相应的煤基碳纳米管生长机制。     

Synthesis of carbon nanotubes from acetone

The process of synthesizing carbon nanotubes (CNTs) using the method of catalytic gas-phase pyrolysis has been studied using acetone as a source of carbon. CNTs with outer diameters of 8–10 nm were prepared. The highest yield of the CNTs with the best quality is achieved when (Co, Mo)/MgO-Al₂O₃ catalyst is used. When (Fe, Co, Mo)/Al₂O₃ is used, the yield and quality of CNTs are lower. For comparison, CNTs obtained on the same catalysts but with propylene as the source of carbon have been investigated. It has been shown that, in this case, the best yield is achieved if (Fe, Co, Mo)/Al₂O₃ catalyst is used. According to the thermogravimetric data, CNT prepared at optimal conditions from acetone have fewer structural defects than those prepared from polypropylene. The optimal temperature and concentration conditions of the CNT synthesis from acetone have been determined. Based on the kinetic data, it has been assumed that the growth of CNTs takes place due to the ketene formed under the thermal decomposition of acetone. The ecological aspects of the CNT preparation from hydrocarbons and acetone are considered.     

Vacuum annealing of carbon nanotubes produced from amorphous carbon

In the vacuum annealing of carbon nanotubes formed by the mechanical activation of amorphous carbon (from sphagnum moss), the yield of purified nanotubes is 19–75 wt %. The potential of materials derived from sphagnum moss as enteric sorbents is considered.     

Synthesis and characterization of double-walled carbon nanotubes from multi-walled carbon nanotubes by hydrogen-arc discharge

Double-walled carbon nanotubes (DWNTs) were synthesized in a large scale by a hydrogen arc discharge method using graphite powders or multi-walled carbon nanotubes/carbon nanofibers (MWNTs/CNFs) as carbon feedstock. The yield of DWNTs reached about 4 g/h. We found that the DWNT product synthesized from MWNTs/CNFs has higher purity than that from graphite powders. The results from high-resolution transmission electron microscopy observations revealed that more than 80% of the carbon nanotubes were DWNTs and the rest were single-walled carbon nanotubes (SWNTs), and their outer and inner diameters ranged from 1.75 to 4.87 nm and 1.06 to 3.93 nm, respectively. It was observed that the ends of the isolated DWNTs were uncapped and it was also found that cobalt as the dominant composition of the catalyst played a vital role in the growth of DWNTs by this method. In addition, the pore structures of the DWNTs obtained were investigated by cryogenic nitrogen adsorption measurements.     

Electrochemical lithium ion storage properties of single-walled carbon nanotubes containing organic molecules

The Li ion storage properties of single-walled carbon nanotube peapods containing one of three organic molecules (9,10-dichloroanthracene, β-carotene, coronene) were measured. It was found by electrochemical charge-discharge measurements that the reversible storage capacity of the SWCNTs significantly increased as a result of the inclusion, although unfortunately the samples are still not appropriate for the practical use as an anode material in Li ion battery because of the high irreversible capacity (>900 mAh/g). In the most effective case, the tube containing the organic molecule can store about 2.5 times more Li ions compared to an empty tube.     

Optimising DNA binding to carbon nanotubes by non-covalent methods

The use of carbon nanotubes as a gene delivery system has been extensively studied in recent years owing to its potential advantages over viral vectors. To achieve this goal, carbon nanotubes have to be functionalized to become compatible with aqueous media and to bind the genetic material. To establish the best conditions for plasmid DNA binding, we compare the dispersion properties of single-, double- and multi-walled carbon nanotubes (SWCNTs, DWCNTs and MWCNTs, respectively) functionalized with a variety of surfactants by non-covalent attachment. The DNA binding properties of the functionalized carbon nanotubes were studied and compared by electrophoresis. Furthermore, a bilayer functionalization method for DNA binding on SWCNTs was developed that utilized RNA-wrapping to solubilize the nanotubes and cationic polymers as a bridge between nanotubes and DNA.     

The separation of carbon nanotubes from chlorides

Carbon nanotubes (CNTs) were synthesized by molten chloride electrolysis, resulting in the suspension of CNTs in the molten chloride. After the chloride was cooled down to room temperature it was dissolved in water. As a result of this investigation, ethyl acetate was found to be the most efficient extracting agent, which was able to extract more than 90% of CNTs from the aqueous salt solution within 5 s. After additional seven washing cycles by water and evaporating the remaining ethyl acetate-water solution, pure CNTs were obtained, i.e. their separation from the chloride phase was complete.     

Field emission from carbon nanotubes on a graphitized carbon fabric

Multi-walled carbon nanotubes (MWCNTs) have been directly grown over a flexible graphitized carbon fabric by water assisted chemical vapor deposition. Field emission properties are compared with randomly oriented multi-walled and single walled carbon nanotube field emitters obtained by spin coating on to carbon fabric. The MWCNTs and single walled carbon nanotubes (SWCNTs) used in spin coating were characterized by X-ray diffraction (XRD) and Raman spectroscopy. High resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) were used to characterize the field emitters. The use of graphitized carbon fabric as substrate has brought in flexibility in the fabrication of carbon nanotube field emitters. The samples show good field emission properties with a fairly stable emission current. Analysis of field emission based on the Fowler-Nordheim theory reveals current saturation effects at high applied fields for all the samples.     

Quantum-mechanical simulations of field emission from carbon nanotubes

We present simulations of field emission from 2-nm long open (5,5), closed (5,5) and open (10,0) carbon nanotubes. Besides usual effects associated with the field-emission process, the total-energy distributions of the field-emitted electrons present peaks that are shifted by the electric field. Their sharpness and the evolution of their amplitude when changing the electric field depend on the semiconducting or metallic character of the nanotube.