Direct evidence for lip-lip interactions in multi-walled carbon nanotubes

The stability of open edged multi-walled carbon nanotubes has been investigated by using in situ high resolution transmission electron microscopy at elevated temperatures. Formation of inter-shell structures was experimentally observed for the first time and attributed to a robust interaction between adjacent concentric shells (so-called lip-lip interaction). The fl uctuating behavior of the inter-shell structures suggests a mechanism by which the carbon atoms can pass in or out through the inter-shell edges during carbon nanotube growth or shrinkage processes. This article is published with open access at Springerlink.com     

Dispersion of functionalized multi-walled carbon nanotubes in multi-walled carbon nanotubes/liquid crystal nanocomposites and their thermal properties

A novel liquid crystal functionalized multi-walled carbon nanotubes (LC-MWNTs)/2-methyl-N,N′-bis(4′-methoxy benzoyloxy)-terephthalamide liquid crystal (LC) nanocomposite (LC-MWNTs/LC) was prepared via solution blend. The dispersion and thermal property of the nanocomposites with different loadings of LC-MWNTs (0.1-1 wt.%) were investigated using SEM, TGA and DSC. The results show that the dispersion of LC-MWNTs in LC matrix is more homogeneous than purified MWNTs. The decomposition temperature of nanocomposites exhibits obvious decrease at first and then increase with increasing concentration of LC-MWNTs, which is lower than that of LC for 0.1-0.4 wt.% LC-MWNT loadings and higher than that of LC for 0.5-1 wt.% LC-MWNT loadings. The addition of LC-MWNTs has little effects on the texture of smectic mesophase. These results illustrate the LC-MWNTs/LC nanocomposites, which have lower melting point and higher decomposition temperature than those of LC by adding adequate amount of LC-MWNTs, show a wide temperature range of mesophase and high thermostability. The increased mesophase temperature region of LC materials will be beneficial to their practical applications.     

Observation of the superstructural diffraction peak in the nitrogen doped carbon nanotubes: Simulation of the structure

A superstructural peak at ～12° in X-ray diffraction patterns of nitrogen-doped carbon nanotubes compared to the undoped carbon nanotubes was observed and assigned to the formation of spatially ordered defects. The simulation of the N-CNT structure using the graphitic g-C₃N₄ phase and turbostratic ordering made it possible to propose a new model of the spatially ordered defects in the N-CNT layer, which consist of clusters of carbon vacancies and pyridine-like nitrogen. A correlation between this type of defects and electrical conductivity of the N-CNTs is defined.     

Evaluating the effects of multi-walled carbon nanotubes on the mechanical properties of chopped strand mat/polyester composites

In this research, the influence of adding multi-walled carbon nanotubes at various contents on the mechanical properties of chopped strand mat/polyester composites was investigated. Initially, the effect of the sonication time on the dispersion of carbon nanotube at the highest weight ratio (0.5 wt.%) was inspected. To achieve this goal, a new technique based on scanning electron microscopy, which utilizes the burn-off test, was introduced to visualize the dispersion state of carbon nanotubes. Subsequently, the effect of addition of multi-walled carbon nanotube on the tensile and flexural properties of the fiber reinforced composites was studied. The results of mechanical tests showed that adding only 0.05 wt.% carbon nanotube enhanced the flexural strength of the hybrid composite by 45% while the tensile strength was not changed significantly. Improvements in the tensile and flexural moduli were also observed. Moreover, theoretical relations between the tensile, flexural and compressive moduli based on the classical beam theory were employed to determine the effect of carbon nanotube on the compressive modulus of composites. The theoretical result showed 31% enhancement in the compressive modulus.     

Fabrication of humidity sensors by multi-walled carbon nanotubes

Humidity sensors have multi-walled carbon nanotubes (MWNTs) as the sensing material is demonstrated. The sensor was fabricated on a silicon dioxide coated silicon wafer with metal electrodes. MWNTs were deposited and interlinked with the electrodes by means of the dielectrophoresis technique. The sensing device has the function of a hygrometer when measuring resistance variations to the local relative humidity percentage (RH%) through MWNTs. By measuring the MWNT resistances, we find that higher RH% results in a decrease of conductivity. The results indicate that electron transports in MWNTs are affected by water molecules adsorption on the outermost nanotube surface. A miniature thermocouple sensor was also fabricated and integrated with the humidity sensor. This allowed us to simultaneously sense environmental humidity and temperature. Hence, accurate humidity measurements were achieved with this prototype by calibrating the electrical resistance and temperature levels to carry out the tests with the humidity percentages.     

多壁碳纳米管吸附异甘草苷的热力学研究

多壁碳纳米管可选择性地吸附结构相似的两种黄酮类化合物甘草苷和异甘草苷,研究了异甘草苷被多壁碳纳米管吸附的吸附热力学特征。结果表明:多壁碳纳米管吸附异甘草苷的量随着异甘草苷浓度的增加而增加,随着温度升高而降低。异甘草苷的吸附过程符合Freundlich方程。其ΔH0和ΔG0值表明该吸附反应是自发进行的放热反应。     

Physical activation and characterization of multi-walled carbon nanotubes catalytically synthesized from methane

A series of treatment processes were employed to purify and then physically activate the multi-walled carbon nanotubes obtained using catalytic decomposition of methane. In order to characterize and compare the activation effect, the carbon fibers were also treated by the same activation processes. The results showed that the normal physical activation by CO₂ or steam has not too much effect on the surface area of purified multi-walled carbon nanotubes, in particular, the carbon nanotubes were burned when using the poignant activation conditions. However, the surface area of carbon fibers availably etched in the same activation processes is much increased. In addition, the mechanisms of physical activation on multi-walled carbon nanotubes and carbon fibers have been investigated.     

Highly conductive, transparent flexible films based on open rings of multi-walled carbon nanotubes

Open rings of multi-walled carbon nanotubes were stacked to form porous networks on a poly(ethylene terephthalate) substrate to form a flexible conducting film (MWCNT-PET) with good electrical conductivity and transparency by a combination of ultrasonic atomization and spin-coating technique. To enhance the electric flexibility, we spin-coated a cast film of poly(vinyl alcohol) onto the MWCNT-PET substrate, which then underwent a thermo-compression process. Field-emission scanning electron microscopy of the cross-sectional morphology illustrates that the film has a robust network with a thickness of ~ 175 nm, and it remarkably exhibits a sheet resistance of approximately 370 Ω/sq with ~ 77% transmittance at 550 nm even after 500 bending cycles. This electrical conductivity is much superior to that of other MWCNT-based transparent flexible films.     

Solvent-free microwave-assisted synthesis of tenorite nanoparticle-decorated multi-walled carbon nanotubes

Copper-decorated carbon nanotubes (CNTs) have important applications as precursors for ultra-conductive copper wires. Tenorite-decorated CNTs (CuO-CNTs) are ideal candidates and are currently developed using laborious processes. For this reason, we have developed a facile and scalable method for the synthesis of CuO-CNTs from copper acetate. It was found that the optimal loading of copper acetate onto the CNTs was 23.1 wt% and that three 1-minute microwave treatments were sufficient for the decomposition of copper acetate to copper oxide. The loading of copper oxide onto the nanotubes was confirmed using X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis. The materials were characterised using X-ray diffraction and scanning electron microscopy.     

Cyclodextrin polyurethanes polymerized with multi-walled carbon nanotubes: Synthesis and characterization

Insoluble cyclodextrin polymers co-polymerized with multi-walled carbon nanotubes were synthesized by polymerizing β-cyclodextrin with acid-functionalized multi-walled carbon nanotubes and diisocyanate linkers; hexamethylene- and toluene-2,4-diisocyanate. The polymers are useful in removing some organic pollutants from water, and we now report the full characterization of these polymers using infrared spectroscopy (IR), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and thermal techniques such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).The polymers could be synthesized as either powders or amorphous solids. Results of the IR analysis showed the presence of functional groups such as CO, CC, CH and CO, indicating that polymerization indeed took place. Characterization of the polymers by scanning electron microscopy and BET analysis showed that these polymers had a spongy appearance indicating a hierarchical pore structure. Incorporation of small amounts (<5%) of multi-walled nanotubes (MWNTs) improved the thermal stability of the polymers. This observation was further confirmed by differential scanning calorimetry (DSC) measurements.     

Electromagnetic absorption properties of Sn-filled multi-walled carbon nanotubes synthesized by pyrolyzing

Multi-walled carbon nanotubes (MWCNTs) filled with Sn nanocrystals were synthesized by metal-organic chemical vapour deposition at relatively lower pyrolysis temperature. Their electromagnetic parameters and microwave absorbing properties were investigated in the frequency range of 2-18 GHz. An obvious increase in the complex permittivity and electric loss tangent of the Sn-filled MWCNTs has been observed. The dielectric and magnetic properties were significantly improved. The Sn nanocrystals encapsulated in MWCNTs modify the electromagnetic parameters of the MWCNTs. The variation of the normalized input impedance induces the enhancement of absorbing properties. The modified MWCNTs exhibit much broader absorbing bandwidth and larger reflectivity than those of unfilled MWCNTs. The calculated results indicate that the Sn-filled MWCNTs have excellent absorbing properties and potential applications in thin thickness and light weight microwave absorbers.     

Synthesis and characterization of conductive polypyrrole/multi-walled carbon nanotubes composites with improved solubility and conductivity

High conductivity and solubility of polypyrrole (PPy)/multi-walled carbon nanotubes (MWCNT) composites has been successfully synthesized by in situ chemical oxidation polymerization using various concentrations of cationic polyelectrolyte poly(styrenesulfonate) (PSS) and ammonium peroxodisulfate (APS). Raman spectroscopy, FTIR, EPR, FESEM and HRTEM were used to characterize their structure and morphology. These images of FESEM and HRTEM showed that the fabricated PPy/MWCNT composites are one-dimensional core-shell structures with the average thickness of the PPy/MWCNT composites without PSS is about 250 nm and considerably decreases to 100–150 nm by adding the PSS content. The results of Raman spectrum, FTIR and UV–Vis indicate the synthesized PPy/MWCNT composites are in the doped state. The conductivities of PPy/MWCNT composites synthesized with the weight ratio of PSS/pyrrole monomer at 0.5 are about two times of magnitude higher than that of PPy/MWCNT composites without PSS. These results are perhaps due to the part of cationic electrolyte served as a dopant can be incorporated to the PPy structure to improve the conductivity of fabricated PPy/MWCNT composites.     

多壁纳米碳管的制备与表面改性处理

以Co-MCM-41作催化剂,采用化学气相沉积(CVD)法催化热解无水乙醇制备纳米碳管(CNTs),然后将纳米碳管在120℃下用浓硝酸回流,进行纯化及表面酸氧化改性处理。通过XRD、FT-IR、TEM、N2吸附-脱附和Raman光谱等分析手段对酸处理前后的纳米碳管进行了表征。结果表明制备出品质较好、管径均匀、管壁较厚、顶端开口的多壁纳米碳管。浓硝酸氧化处理后在纳米碳管的表面存在羧基和羟基等官能团。     

Removal of vanadium from wastewater by multi-walled carbon nanotubes

Nitric acid heating reflux modified multi-walled carbon nanotubes (HMWCNTs) were used for the removal of vanadium(V) in aqueous solution. The removal rate of vanadium(V) decreased with the increase of the initial vanadium(V) concentration and the solution pH, and increased with the increase of reaction time, HMWCNTs amount and solution temperature. The adsorption equilibrium and dynamic kinetics fitted the Langmuir adsorption isotherm and pseudo-second order models. The results obtained by scanning electron micrography and Fourier transform infrared spectroscopy analysis revealed that the hydroxyl and carboxyl functional groups are mainly responsible for the vanadium adsorption. This study showed that the HMWCNTs proved to be a considerable adsorbent for the removal of vanadium from wastewater.     

多壁碳纳米管/PCL-b-PNIPAM复合材料的制备

通过对多壁碳纳米管（MWCNTs）表面修饰合成羟基化的MWCNTs,利用羟基化的MWCNTs催化己内酯开环聚合,接着与溴代异丁酰溴反应,合成MWCNTs接枝聚己内酯（PCL）的大分子引发剂,利用该大分子引发剂引发N-异丙基丙烯酰胺单体进行原子转移自由基活性聚合（ATRP）,成功制备了MWCNTs/PCL-b-PNIPAM复合材料。利用FTIR、TGA、XRD、NMR及TEM对产物进行表征。考察了MWCNTs/PCL-b-PNIPAM复合材料的结晶性能及在氯仿中的溶混性。XRD结果表明:MWCNTs/PCL-b-PNIPAM复合材料的结晶峰与PCL-b-PNIPAM嵌段共聚物基本一致,并且MWCNTs/PCL-b-PNIPAM复合材料在氯仿溶液中有很好的混溶性。