聚乙烯醇用于碳纳米管的开口及修饰研究

在低温(250 ℃)下,用聚乙烯醇(polyvinyl alcohol, PVA)和提纯后的碳纳米管(carbon nanotubes, CNTs)的混合物在空气中加热,以研究聚乙烯醇对碳纳米管的修饰作用,并采用TEM对不同条件下所得的产物进行了形态分析.结果发现,碳纳米管的顶端被打开,随着时间的增加,弯曲的碳纳米管断裂成较短的碳纳米管.聚乙烯醇对碳纳米管的氧化及修饰在实验中得到证实.讨论分析了氧化和修饰机理,认为可能是聚乙烯醇在空气中分解所得的产物的一种或几种在氧化和修饰过程中起主要作用.     

A DFT study of the amination of fullerenes and carbon nanotubes: reactivity and curvature

The first principles density functional theory (DFT) approach (GGA-PW91/DNP) was used to study the addition reaction of methylamine to fullerenes C(50) and C(60) or single-walled carbon nanotubes (SWNTs) (5,5) and (10,0). To understand the relationship between reactivity and curvature, various addition sites have been investigated for comparisons. The DFT calculation results showed that the reaction energy of the addition of methylamine onto C(60) or the closed caps of (5,5) and (10,0) is rather low. Moreover, the reaction at a few sites even appears exothermic. However, the reaction on the perfect sidewall of the nanotubes is always endothermic, and the reaction energy is much higher than that on the caps. The energetically preferable addition sites are the carbon atoms located at the vertexes formed with five-, five-, six-membered rings on C(50) or five-, five-, seven-membered rings on defects of nanotubes. The systematic theoretical study revealed that the pyramidalization and pi-orbital misalignment could result in an increased reactivity of these pentagon-pentagon fusion sites. The reactivity depends on the pyramidalization angle, which is a quantitative measurement of the local curvature and strain of the reaction center.     

Layer-by-layer fabrication and characterization of DNA-wrapped single-walled carbon nanotube particles

Carbon nanotubes have been proposed as support materials for numerous applications, including the development of DNA sensors. One of the challenges is the immobilization of DNA or other biological molecules on the sidewall of carbon nanotubes. This paper introduces a new fabrication of DNA-carbon nanotubes particles using the layer-by-layer (LBL) technique on single-walled carbon nanotubes (SWCNTs). Poly(diallyldimethylammonium) (PDDA), a positively charged polyelectrolyte, and DNA as a negatively charged counterpart macromolecule are alternatively deposited on the water-soluble oxidized SWCNTs. Pure DNA/PDDA/SWCNTs particles can be prepared and separated by simple unltracentrifugation. The characterization of DNA/PDDA/SWCNTs particles was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy, Raman spectroscopy, and thermogravimetric analysis (TGA). An electrode modified by the DNA/PDDA/SWCNTs particles shows a dramatic change of the electrochemical signal in solutions of tris(2,2'-bipyridyl)ruthenium(II) ((Ru(bpy)(3)2+) as a reporting redox probe. A preliminary application of the DNA-modified carbon nanotubes in the development of DNA sensors used in the investigation of DNA damage by nitric oxide is presented.     

Cover Picture

The cover picture shows a single-walled carbon nanotube (SWNT) functionalized with nucleophilic carbenes at the sidewall. Normally, single-walled nanotubes exist in the form of insoluble bundles. The sidewall addition of reactive organic groups such as radicals, nitrenes, or carbenes such as the ones shown in the cover picture disrupts the bundles. The background of the picture shows a typical AFM image of such derivatized SWNTs. The isolated SWNTs are soluble in organic solvents giving black solutions. This enables a spectroscopic characterization of nanotubes in solution. With this versatile sidewall functionalization the decisive requirements for the development of technological applications such as the production of ultrathin films or the processing to polymer composites with new electronic and mechanic properties have been compiled. Details about this new chemical funtionalization of SWNTs is described by Hirsch et al. on pp. 4002 ff.     

碳纳米管微结构的改变对其容量性能的影响

以KOH为活性剂，通过在高温下将碳纳米管进行活化处理来实现对碳纳米管管壁结构的改变，得到了比表面积和孔容分别是活化处理前约3倍和1.5倍的活性碳纳米管.将活化处理前后两种碳纳米管分别制作成电化学超级电容器电极，在充满氩气的无水手套箱组装成模拟电化学超级电容器，在恒流充放电模式下进行电化学可逆容量的测试，发现活性碳纳米管的电化学容量远高于活化前碳纳米管，是它的2倍.从而发现碳纳米管被打断，管壁变粗糙的活性碳纳米管比一般碳纳米管更适合用于电化学超级电容器电极材料.     

Vacancy-induced chemisorption of NO2 on carbon nanotubes: a combined theoretical and experimental study

The role of structural defects on the adsorption of NO2 on carbon nanotubes (CNTs) is analyzed here by means of both statical density functional theory calculations and Car-Parrinello molecular dynamics and further confirmed by X-ray photoelectron spectroscopy measurements. The interaction of a NO2 molecule with an active site produced by a single vacancy on the sidewall follows two possible reaction routes, leading to the formation of a C-N bond or to dissociation of NO2. Accounting for defective adsorption sites allows a better understanding of microscopic mechanisms involved in technological applications of CNTs, e.g., gas-sensing devices.     

Functionalization and Dissolution of Single-Walled Carbon Nanotubes by Chemical-Physical and Electrochemical Treatments

Single-Walled Carbon Nanotubes (SWCNTs) possess a wealth of exceptional structural, mechanical and electronic properties. These have made them potentially useful for applications in nanotube-reinforced materials, nanoelectronic devices, field emitters, probe tips for SPM, as well as for sensors, biosensors, and actuators. However, manipulation and processing of SWCNTs has been limited by their insolubility in most common solvents, although some dissolution has recently been obtained. Their chemical modification might pave the way to many useful applications, including the preparation of composite materials or the immobilization of biological molecules as enzymes (i.e., for biosensors and electrochemical sensors). Attachment of oxygen-containing functional groups (i.e., carboxy groups, carbonyl groups, hydroxy groups, etc.) on the surface of the carbon nanotubes could be achieved using different pretreatments of the nanostructured material. These involved (a) chemical and physical procedures; and (b) electrochemical functionalization. Different attempts at sidewall modification have been hampered by the presence of significant contaminants as graphitic and amorphous carbon or have required solubilization via chemical reactions on the ends of cut nanotubes. A more accommodating and direct approach to functionalize nanotubes is therefore required. We report here the sidewall functionalization of purified SWCNTs, obtained by different approaches and finally, we can discuss possible applications of functionalized SWCNTs in the sensing area.     

Surfactant-free nanofluids containing double- and single-walled carbon nanotubes functionalized by a wet-mechanochemical reaction

Single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) have been functionalized through the wet-mechanochemical reaction method. Results from the infrared spectrum and zeta potential measurements show that the hydroxyl groups have been introduced onto the treated SWNT and DWNT surfaces. Transmission electron microscope observations revealed that the SWNTs and DWNTs were cut short after being milled. SWNTs and DWNTs with optimized aspect ratio can be obtained by adjusting the ball milling parameters. Thermal conductivity enhancement of water-based nanofluids containing treated carbon nanotubes (CNTs) shows augmentation with the increase of temperature mainly due to the effects of an ordering liquid layer forming around the chemical surfaces of CNTs. Moreover, the thicker interfacial layer of water molecules on the surfaces of CNTs with smaller diameter, such as SWNTs, is in favor of greater thermal conductivity enhancement compared with the thinner one on the surfaces of DWNTs or MWNTs with larger diameter.     

Immobilizing shortened single-walled carbon nanotubes (SWNTs) on gold using a surface condensation method

We propose a surface condensation method for assembling single-walled carbon nanotubes (SWNTs) on gold. The as-prepared long and randomly tangled SWNTs were cut into short pipes by chemical oxidation, allowing the nanotubes to be terminated by carboxyl functionalities. A surface condensation reaction was then performed by immersing an amino self-assembled monolayer (SAM)-modified gold substrate into the dimethylformamide suspension of carboxylic nanotubes with the aid of dicyclohexylcarbodiimide condensation agent. Raman spectroscopy and atomic force microscopy (AFM) results show that a highly aligned assembly of SWNTs has been formed on gold, with the nanotubes standing on the surface stable enough for a long ultrasonication. In combination with the microcontact printing (muCP) technique, we have fabricated patterned nanotube assemblies using this surface condensation method. Moreover, we found that the "giant" carbon nanotubes tend to form bundles on an amino-terminating surface, likely following a nucleation-growth model.     

Interaction of a transition metal atom with intrinsic defects in single-walled carbon nanotubes

Interaction of a transition metal atom with defects in single-walled carbon nanotubes (SWNTs) were investigated through density functional theory calculations. For three kinds of intrinsic defects (single vacancies, double vacancies and Stone-Wales defects) in (5,5) armchair and (10,0) zigzag SWNTs, stable configurations were analyzed. The orientation of the specific bonds of the defects is related to the most stable configuration among several possible configurations. The stable adsorption sites and binding energies of a Ni atom on three intrinsic defects were calculated and compared to those on perfect side walls. All defects enhance Ni adsorption, and the single vacancy shows the most exothermic binding. These results shed light on the nature of the interaction of the transition metal with defects in SWNT, an important topic to the many aspects of carbon nanotubes interacting with transition metals. Particularly, this is useful for the fabrication of nanosized transition metal particles supported on carbon nanotubes.     

Solvent-free functionalization of carbon nanotubes

A fundamentally new single-walled and multiwalled carbon nanotube sidewall functionalization technique has been developed in which solvent is not required and the reaction times are greatly shortened (1 h at 60 degrees C). Exploiting the long linear dimension of the nanotube ropes by macroscopic mechanical deformation, reactive sites are generated merely by mechanically deforming the tubes using a stir bar. This approach eliminates the need for large volumes of solvent ( approximately 2 L/g), which were formerly considered essential due to the insolubility of carbon nanotubes. Using a series of 4-substituted anilines and a nitrite, the aryl diazonium intermediates were generated in situ and permitted to react with the tubes. Raman, IR, and UV spectroscopies, coupled with thermogravimetric analyses and solubility studies, support the assignments.     

The adsorption kinetics of cadmium by three different types of carbon nanotubes

Oxidized nitrogen-doped multiwall carbon nanotubes (ox-N-MWCNTs), oxidized multiwall carbon nanotubes (ox-MWCNTs), and oxidized single-wall carbon nanotubes (ox-SWCNTs) were evaluated via batch adsorption kinetic experiments to determine the effect of nanotube morphology on the adsorption rate of cadmium. The nanotubes were characterized by HRTEM, XRD and Raman spectroscopy. Cadmium adsorption isotherms were determined at pH 6. Analyses of the kinetic data with an external mass transport model and an intraparticle diffusion model considered two cases: (1) single nanotubes suspended in aqueous solution and (2) agglomerates of nanotubes suspended in aqueous solution. The intraparticle diffusion model produced the best fit to the experimental data. However, only the diffusivity coefficients for single nanotubes suspended in solution were similar to literature values: about 4×10(-9), 1×10(-9) and 2.4×10(-11) cm(2)/s for ox-N-MWCNTs, ox-MWCNTs and ox-SWCNTs, respectively. The morphology of the various carbon nanotubes might determine cadmium diffusivity. The high amount of sidewall pores observed in the single-walled carbon nanotubes could limit cadmium diffusion and account for the slow diffusion rate of 180 min. Conversely, the short length, small surface area and bamboo-type morphology observed with nitrogen-doped multiwall carbon nanotubes may account for the relatively fast adsorption rate of 15 min as this morphology prevents cadmium diffusion through the internal tubular space of these nanotubes.     

Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates

Mono and binary transition metal oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air. The transition metal oxide nanotubes were composed of nano-crystallites of metal oxides. The functional groups on the carbon nanofiber templates were essential for the coating of these templates: they acted as adsorption sites for the metal nitrates, ensuring a uniform metal oxide coating. During the removal of the carbon nanofiber templates by calcination in air, the metal oxide coatings promoted the combustion reaction between the carbon nanofibers and oxygen.     

High-yield synthesis of single-wall carbon nanotubes on MCM41 using catalytic chemical vapor deposition of acetylene

High-quality single-wall carbon nanotubes (SWNTs) with narrow diameter distribution have been grown on Fe/Co-loaded MCM41 by using acetylene as the carbon source within a short reaction period, typically 10 min or less. The optimum temperature for SWNTs synthesis is 850 degrees C. Longer reaction time (i.e., 30 min) favors the formation of multiwall carbon nanotubes (MWNTs) and graphitic carbon. When the reaction time is reduced to less than 10 min, formation of MWNTs and graphitic carbon is greatly suppressed, and high-quality SWNTs dominates the yield. The surface of the as-grown SWNTs is found to be free from amorphous carbon, as observed from high-resolution transmission electron microscope (HRTEM) analysis. Raman spectral data show a G/D ratio above 10, indicating that the as-grown SWNTs have very few defects. Furthermore, radial breathing mode (RBM) analysis reveals that the diameter distribution of the current SWNTs is narrow and ranges from 0.64 to 1.36 nm.     

Surface chemistry in the process of coating mesoporous SiO2 onto carbon nanotubes driven by the formation of Si-O-C bonds

The deposition of mesoporous silica (SiO(2)) on carbon nanotubes (CNTs) has opened up a wide range of assembling possibilities by exploiting the sidewall of CNTs and organosilane chemistry. The resulting systems may be suitable for applications in catalysis, energy conversion, environmental chemistry, and nanomedicine. However, to promote the condensation of silicon monomers on the nanotube without producing segregated particles, (OR)(4-x)SiO(x)(x-) units must undergo nucleophilic substitution by groups localized on the CNT sidewall during the transesterification reaction. In order to achieve this preferential attachment, we have deposited silica on oxidized carbon nanotubes (single-walled and multiwalled) in a sol-gel process that also involved the use of a soft template (cetyltrimethylammonium bromide, CTAB). In contrast to the simple approach normally used to describe the attachment of inorganic compounds on CNTs, SiO(2) nucleation on the tube is a result of nucleophilic attack mainly by hydroxyl radicals, localized in a very complex surface chemical environment, where various oxygenated groups are covalently bonded to the sidewall and carboxylated carbonaceous fragments (CCFs) are adsorbed on the tubes. Si-O-C covalent bond formation in the SiO(2)-CNT hybrids was observed even after removal of the CCFs with sodium hydroxide. By adding CTAB, and increasing the temperature, time, and initial amount of the catalyst (NH(4)OH) in the synthesis, the SiO(2) coating morphology could be changed from one of nanoparticles to mesoporous shells. Concomitantly, pore ordering was achieved by increasing the amount of CTAB. Furthermore, preferential attachment on the sidewall results mostly in CNTs with uncapped ends, having sites (carboxylic acids) that can be used for further localized reactions.     

Highly visible-light luminescence properties of the carboxyl-functionalized short and ultrashort MWNTs

Luminescence of the short multiwalled carbon nanotubes (MWNTs) conjugated with carboxylic acid groups has been studied. The results show that the carboxyl-functionalized short MWNTs could emit luminescence and the emission peak appears at 500 nm with a corresponding optimal excitation wavelength centering at 310 nm. When the short MWNTs are filtered through 0.15 μm polytetrafluoroethylene (PTFE) membrane, the ultrashort MWNTs are obtained from the filtrate. An interesting feature for the ultrashort MWNTs is that the emission intensity is strengthened and the peak is slightly blue shifted to 460 nm. This result indicates that the luminescence properties of MWNTs are strongly affected by the tube length. After chemical oxidization cutting, defects and carboxylic acid groups at the tube end and/or sidewall can be produced; the more shorten of MWNTs, the better dispersion and carboxylic passivation of the nanotubes, and the more intense luminescence emissions. The broad emissions are logically attributed to the trapping of excitation energy by defect sites in the carboxyl-functionalized nanotube structure.     

Improved hydrothermal synthesis of MoS2 sheathed carbon nanotubes

MoS₂ sheathed carbon nanotubes have been successfully synthesized using a hydrothermal route under controlled conditions. The resultant material was studied by XRD, EDS, HRTEM, and Raman spectroscopy. Advantages of the preparation presented here compared to other methods are: a) lower reaction temperature, b) high yield of sheathed nanotubes including ends and full body, c) simple process with non-toxic materials, and d) no damage inflicted to nanotubes.     

单壁碳纳米管与卤代烷的亲电加成反应

主要考察了以路易斯酸为催化剂,几种卤代烷烃为反应试剂的单壁碳纳米管侧壁的亲电加成反应,并通过傅立叶红外光谱、热失重分析和拉曼光谱验证了实验所得产物。此反应的目的是在单壁碳纳米管的侧壁连上烷基基团以提高其溶解性和分散性,并可使其更好地与聚烯烃相结合从而提高复合材料的性能,因而具有较高的研究和应用价值。     

Sidewall epoxidation of single-walled carbon nanotubes: a theoretical prediction

[reaction: see text] By means of a two-layered ONIOM approach, we predict that sidewall epoxidation of single-walled carbon nanotubes (SWNTs) with dioxiranes is viable. The SWNT epoxides thus produced could be precursors for further chemical modification of SWNTs, given the abundant and well-established chemistry of organic epoxides. This opens the door for routine chemical manipulation of SWNTs.     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe-MgO、Co-MgO和Ni-MgO为催化剂,CH4为碳源气,H2为还原气,在873、973和1073 K制备出碳纳米管,通过TEM和拉曼光谱表征,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响.结果表明:不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异.其中Fe-MgO催化剂制备的碳纳米管管径粗,且大小不均匀,而Ni-MgO催化剂制备的碳纳米管管径较细、较均匀.碳纳米管的产率随着裂解温度的变化而改变.Fe-MgO催化剂制备碳纳米管的产率随制备温度的升高而提高,而Ni-MgO催化剂制备碳纳米管的产率随制备温度的升高而降低.Fe-MgO催化剂制备碳纳米管,在1073K甚至更高的制备温度才能达到其最高产率.Co-MgO催化剂制备碳纳米管的产率在973 K左右产率较高,而用Ni-MgO催化剂制备碳纳米管,则在873 K甚至更低的制备温度就能达到最高产率.反应时间与碳纳米管的产率不成正比,有一最佳反应时间,如Ni-MgO催化剂的最佳反应时间为2 h.