Composites of polyvinyl alcohol and carbon (coils, undoped and nitrogen doped multiwalled carbon nanotubes) as ethanol, methanol and toluene vapor sensors

We investigate the chemical sensing behavior of composites prepared with polyvinyl alcohol and carbon materials (undoped multiwalled carbon nanotubes, nitrogen-doped multiwalled carbon nanotubes and carbon nanocoils). We determine the sensitivity of thin films of these composites for ethanol, methanol and toluene vapor, comparing their conductance and capacitance responses. The composite that exhibits highest sensitivity depends on specific vapor, vapor concentration and measured electrical response, showing that the interactivity of the carbon structure with chemical species depend on structural specificities of the carbon structure and doping.     

Supramolecular assembly and antitumor activity of multiwalled carbon nanotube-camptothecin complexes

The novel supramolecular complexes were prepared with a water-insoluble anticancer drug camptothecin (CPT) loading onto functionalized multiwalled carbon nanotubes via pi-stacking, in order to improve their solubility and antitumor activity. The multiwalled carbon nanotubes were firstly coated with the tri-block copolymer (Pluronic P123) to render high aqueous solubility. The copolymer-coated multiwalled carbon nanotubes can effectively form non-covalent supramolecular complexes with camptothecin. The supramolecular assembly of the complexes (f-MWNTs-CPT) were systematically characterized by transmission electron microscopy (TEM), UV-vis spectrophotometry (UV), fluorescence spectrophotometry, atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). Furthermore, in vitro cytotoxicity studies of f-MWNTs-CPT supramolecular complexes using the MTT assay exhibit enhanced antitumor activity, suggesting that the functionalized multiwalled carbon nanotubes can facilitate intracellular delivery of anticancer drug and improve drug activity.     

Synthesis and characterization of phospholipid-modified multiwalled carbon nanotubes

A simple three-step strategy to functionalize multiwalled carbon nanotubes using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine phospholipids has been described. The resulting phospholipid-modified multiwalled carbon nanotubes were analyzed by TEM, AFM, NMR, IR, UV-vis and TGA techniques. The experimental results show that the use of amine-terminated phospholipids not only improves the dispersity of multiwalled carbon nanotubes in both aqueous and organic solvents greatly, but also results in the significant enhancement of biocompatibility. These findings will serve as a future biological platform for new devices ranging from biosensors to nano-detectors.     

Synthesis and thermoelectric power of nitrogen-doped carbon nanotubes

We have previously shown that high-purity multiwalled carbon nanotubes (pristine MWNTs) can be prepared from a mixture of xylene-ferrocene (99 at% C:1 at% Fe) inside a quartz tube reactor operating at approximately 700 degrees C. In a similar process, approximately 3 g of melamine (C3H6N6) was introduced during the growth of MWNTs to prepare nitrogen-doped nanotubes. The structural and electronic properties of nitrogen-doped MWNTs were determined by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and thermopower measurements. The individual nitrogen-doped nanotube exhibits a bamboo-like structure and comprises 6-16 tube walls, as evidenced by HRTEM studies. The EELS measurements yielded an average nitrogen content of approximately 5 at% in the doped tubes. The thermoelectric power data of nitrogen-doped MWNTs remained negative even after exposure to oxygen for an extended period of time, suggesting that nitrogen doping of MWNTs renders them n-type, consistent with scanning tunneling spectroscopic studies on similar nanotubes.     

Synthesis and characterization of chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites for bone tissue engineering

Chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites were synthesized by a novel in situ precipitation method. The electrostatic adsorption between multiwalled carbon nanotubes and chitosan was investigated and explained by Fourier transform infrared spectroscopy analysis. Morphology studies showed that uniform distribution of hydroxyapatite particles and multiwalled carbon nanotubes in the polymer matrix was observed. In chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites, the diameters of multiwalled carbon nanotubes were about 10 nm. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The elastic modulus and compressive strength increased sharply from 509.9 to 1089.1 MPa and from 33.2 to 105.5 MPa with an increase of multiwalled carbon/chitosan weight ratios from 0 to 5 %, respectively. Finally, the cell biocompatibility of the composites was tested in vitro, which showed that they have good biocompatibility. These results suggest that the chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.     

Synthesis and thermal transport studies of nanofluids based on metal decorated photochemically oxidized multiwalled carbon nanotubes

Nanoparticle fluid suspensions were prepared using photochemically functionalized multiwalled carbon nanotubes in polar base fluids. Multiwalled carbon nanotubes prepared by catalytic chemical vapour deposition technique have been functionalized by irradiating with ultraviolet light of wavelength 254 nm. The photochemical oxidation of multiwalled carbon nanotubes under UV irradiation introduces oxygen containing functional groups onto the surface of the nanotubes, generating new defects on their structure. Silver nanoparticles have been deposited over multiwalled carbon nanotubes by chemical method. The enhancement in thermal conductivity of the prepared nanofluids using functionalized multiwalled carbon nanotubes and Ag nanoparticles deposited functionalized multiwalled carbon nanotubes with volume fraction, temperature and aspect ratio has been demonstrated. Silver deposited functionalized multiwalled carbon nanotubes based nanofluids in DI water with 0.02% volume fraction exhibit a thermal conductivity enhancement of 9.9% and 47% at room temperature and at 50 degrees C respectively.     

Spectroscopic investigations on epoxy--multiwall carbon nanotubes composites

Room temperature electron spin resonance spectra of epoxy resins loaded with various concentrations of multiwalled carbon nanotubes of various lengths are analyzed. The resonance spectrum near the free electron line position is dominated by a single almost symmetric line assigned to delocalized electrons residing on multiwalled carbon nanotubes. The experimental research shown that: (1) The dependence of the g-factor on nanotubes length is controlled by the distortions of multiwalled carbon nanotubes. (2) The dependence of the g-factor on the concentration of multi-walled nanotubes reflects the interactions between electrons localized on different nanotubes. In insulating composites, the resonance line width broadens as the length and the concentration of multiwalled carbon nanotubes is increased. (3) For conducting composites, the dependence of the electron spin resonance line width on the length and concentration of multiwalled carbon nanotubes is controlled by Elliott contribution and exchange interactions, respectively. (4) The concentration of conduction electrons increases as the length and the concentration of multiwalled carbon nanotubes are increased.     

SEM/AFM studies of cementitious binder modified by MWCNT and nano-sized Fe needles

Several compositions of cement paste samples containing multiwalled carbon nanotubes were produced using a small-size vacuum mixer. The mixes had water-to-binder ratios of 0.25 and 0.3. Sulfate resistant cement has been used. The multiwalled carbon nanotubes were introduced as a water suspension with added surfactant admixtures. The used surfactant acted as plasticizing agents for the cement paste and as dispersant for the multiwalled carbon nanotubes. A set of beams was produced to determine the compressive and flexural strengths. The scanning electron microscope and atomic force microscope studies of fractured and polished samples showed a good dispersion of multiwalled carbon nanotubes in the cement matrix. The studies revealed also sliding of multiwalled carbon nanotubes from the matrix in tension which indicates their weak bond with cement matrix. In addition to multiwalled carbon nanotubes also steel wires covered with ferrite needles were investigated to determine the bond strength between the matrix and the steel wire. These later samples consisted of 15-mm-high cylinders of cement paste with vertically cast-in steel wires. As reference, plain steel wires were cast, too. The bond strength between steel wires covered with nano-sized Fe needles appeared to be lower in comparison with the reference wires. The scanning electron microscope studies of fractured samples indicated on brittle nature of Fe needles resulting in shear-caused breakage of the bond to the matrix.     

Role of interfacial effects in carbon nanotube/epoxy nanocomposite behavior

The interfacial effects are critical to understand the nanocomposite behavior based on polymer matrices. These effects are dependent upon the morphology of carbon nanotubes, the type of used polymer and the processing technique. Indeed, we show that the different parameters, as the eventual surfactant use, the ultrasonic treatment and shear mixing have to be carefully examined, in particular, for nanotube dispersion and their possible alignment. A series of multiwalled nanotubes (MWNT) have been mixed with a regular epoxy resin under a controlled way to prepare nanocomposites. The influence of nanotube content is examined through helium bulk density, glass transition temperature of the matrix and direct current electrical conductivity measurements. These results, including the value of the percolation threshold, are analyzed in relationship with the mesostructural organization of these nanotubes, which is observed by standard and conductive probe atomic force microscopy (AFM) measurements. The wrapping effect of the organic matrix along the nanotubes is evidenced and analyzed to get a better understanding of the final composite characteristics, in particular, for eventually reinforcing the matrix without covalent bonding.     

Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization

Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.     

Investigation of an optical limiting mechanism in multiwalled carbon nanotubes

We report our investigation of the mechanism that is responsible for the optical limiting behavior in multiwalled carbon nanotubes. We conducted energy-dependent transmission measurements, picosecond time-resolved pump-probe experiment, and nonlinear scattering experiments at 532-nm wavelength on multiwalled carbon nanotube suspension. For comparison, C(60)-toluene solutions and carbon black suspensions were also studied in the same experiments. The similarities that we observed between the multiwalled carbon nanotubes and carbon black suspension suggest that nonlinear scattering, which is known to be responsible for the limiting action in carbon black suspension, should play an important role in the limiting effect in multiwalled carbon nanotubes.     

Ruthenium complex containing block copolymer for the enhancement of carbon nanotube photoconductivity

We report the synthesis of a multifunctional block copolymer incorporated with pyrene and ruthenium terpyridyl thiocyanato complex moieties by reversible addition-fragmentation chain transfer polymerization. The pyrene block in the copolymer facilitates the dispersion of multiwalled carbon nanotubes in DMF solution because of the strong π-π interaction between the pyrene moieties and nanotube surface. On the other hand, the ruthenium complexes greatly enhance the photosensitivity of the functionalized nanotubes in the visible region. The photocurrent responses of the nanotubes at different wavelength measured by conductive AFM spectrum strongly agree with the absorption spectrum of the ruthenium complex. The results demonstrate a new and versatile approach in enhancing and fine-tuning the photosensitivity or other opto-electronic properties of carbon nanotubes by multifunctional block copolymers.     

Thermogravimetric analysis of the interaction of ferromagnetic metal atom and multiwalled carbon nanotubes

This paper describes the thermal oxidative behavior of atomized iron or atomized cobalt in the presence of multiwalled carbon nanotubes (MWCNT). The thermogravimetric analysis shows the atomized iron thermal oxidation starts at about 500 degrees C that is absent when the atomized iron is sintered with multiwalled carbon naonotubes. The thermal oxidation of iron in the sintered samples requires the collapse of the multiwalled carbon nanotubes. A similar behavior is observed with atomized cobalt when its oxidation requires the collapse of the nanotubes. This thermal oxidative shift is interpreted as due to the atomized iron or atomized cobalt atom experiencing extensive overlap and confinement effect with multiwalled carbon nanotubes causing a spin transfer. This confinement effect is suggested to produce a transformation of iron from the outermost electronic distribution of 3d64s2 to an effective configuration of 3d84s0 and for cobalt 3d74s2 to 3d94s0 producing spintronics effect.     

以预锂化多壁碳纳米管为负极的锂离子电容器性能

采用内部短路方式对多壁碳纳米管负极进行不同程度的预嵌锂处理,预嵌锂时间为5,30,60min,以预嵌锂多壁碳纳米管极片作为负极,活性炭极片作为正极,组装成锂离子电容器。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)对多壁碳纳米管及电极极片进行表征分析,采用恒流充放电(GCD)和交流阻抗谱(EIS)研究预嵌锂多壁碳纳米管负极和未预嵌锂处理多壁碳纳米管负极锂离子电容器的性能。电化学测试结果表明,多壁碳纳米管负极预嵌锂大幅提高了电容器充放电性能,对比未嵌锂多壁碳纳米管电容器,在相同的电流密度下(100mA/g),能量密度提高400%。预嵌锂60min,电流密度100mA/g时,其比容量达到57F/g。在电流密度为100～3200mA/g范围内,其最高能量密度与功率密度分别达到90Wh/kg,4130W/kg。1000次充放电循环后,容量保持率维持在85%以上,表现出良好的超级电容器性能。     

In situ nucleation of carbon nanotubes by the injection of carbon atoms into metal particles

The synthesis of carbon nanotubes (CNTs) of desired chiralities and diameters is one of the most important challenges in nanotube science and achieving such selectivity may require a detailed understanding of their growth mechanism. We report the formation of CNTs in an entirely condensed phase process that allows us, for the first time, to monitor the nucleation of a nanotube on the spherical surface of a metal particle. When multiwalled CNTs containing metal particle cores are irradiated with an electron beam, carbon from graphitic shells surrounding the metal particles is ingested into the body of the particle and subsequently emerges as single-walled nanotubes (SWNTs) or multiwalled nanotubes (MWNTs) inside the host nanotubes. These observations, at atomic resolution in an electron microscope, show that there is direct bonding between the tubes and the metal surface from which the tubes sprout and can be readily explained by bulk diffusion of carbon through the body of catalytic particles, with no evidence of surface diffusion.     

Sorption capacity of carbon nanotubes prepared by mechanochemical processing of amorphous carbon

We have studied the sorption properties of nanofibrous carbon (multiwalled nanotubes) produced by milling amorphous carbon prepared through sphagnum moss pyrolysis. The results demonstrate that the sorption capacity of the carbon nanotubes depends on storage time and that their oxidation behavior depends on nanotube preparation conditions.     

Evaluating industrial grade functionalized multiwalled carbon nanotubes by X-ray photoelectron spectroscopy

Utilization of carbon nanotubes in various applications is a function of their dispersion in respective matrix which effectively depends on the functionalization employed. Functional group distribution on Carbon Nanotube surface is usually a complex mixture of groups depending on the oxidizing agent employed. In this regard, nine varieties of Industrial grade multiwalled carbon nanotubes belonging to 10–30, 20–40 and 50–80?nm outer diameter ranges but differing in functionality (carboxyl and hydroxyl) were analyzed. X-ray photoelectron spectroscopy was employed to quantify the different functionalities on pristine, hydroxyl and carboxyl functionalized multiwalled carbon nanotubes and high-resolution transmission electron microscopy was used to image the internal structure including the side wall damage in functionalized varieties. X-ray photoelectron spectroscopy measurements on nine batches have suggested the presence of carbonyl, carboxyl and hydroxyl functional groups on all multiwalled carbon nanotubes in different proportions. This implies that it is not possible to have exclusive hydroxyl or carboxyl functionalization on a CNT surface Additionally, comparison is drawn between already existing deconvolution procedures from literature.     

Deflection of nanotubes in response to external atomic collisions

The mechanical response of single-walled and multiwalled carbon nanotubes to a series of external Ar atom impacts is examined with classical molecular dynamics simulations. The extent to which the carbon nanotubes deform in the direction perpendicular to their axis is found to depend on the amount of momentum transferred during the collisions. The details of the mechanical response and recovery of the nanotubes after release are also found to depend on the nanotube configurations.     

Chemical functionalization of carbon nanotubes for the mechanical reinforcement of polystyrene composites

An organometallic approach was used to functionalize multiwalled carbon nanotubes with n-butyllithium. This procedure was repeated two more times to achieve a higher degree of multiwalled carbon nanotube functionalization. The functionalized nanotubes have been characterized by Fourier transform infrared and Raman spectroscopy, thermogravimetrical analysis, scanning electron microscopy and sedimentation studies. It was possible to form stable suspensions of the functionalized nanotubes in tetrahydrofuran and they were used to make nanotube polymer composites. The mechanical properties of these new nanotube polymer composites were tested and they were found to show an increase of up to 25% in their Young's moduli and up to 50% in their tensile strength over pure polystyrene.     

Undoped, nitrogen-doped and boron-doped multiwalled carbon nanotube/poly(vinyl alcohol) composite as active layer in simple hydrostatic pressure sensors

We report on hydrostatic pressure sensors prepared using 10 % w/w multiwalled carbon nanotube (MWCNT)/poly(vinyl alcohol) composites. Three types of carbon nanotubes were used in the composites: undoped MWCNTs, nitrogen-doped MWCNTs and boron-doped MWCNTs (B-MWCNTs). The sensor response was tested using an alternating current input, measuring the capacitance and conductance outputs. The sensors based on the three composites show a linear capacitance and conductance sensitivity pressure dependence in the range 50–120 kPa, but a higher sensitivity to pressure dependence above this interval. The highest angular coefficient of the sensitivity, which reached 0.092 kPa^?1, was observed for the capacitance sensitivity of the B-MWCNT based composite.