Chemical functionalization of carbon nanotubes

There are many reasons why one would want to form chemical attachments to the walls or ends of carbon nanotubes: these chemical bonds might be used to tailor the interaction of the nanotube with other entities, such as a solvent, a polymer matrix, or other nanotubes. The chemically functionalized nanotube might have mechanical or electrical properties that are different from those of the unfunctionalized nanotube and thus might be used as a chemical sensor or a nanometer-scale electronic device. The challenge is to find a way to reproducibly and reliably chemically alter carbon nanotubes that, like graphite, are fairly unreactive. The various methods used to date and the possible application of the resulting functionalized nanotubes is discussed in this review paper.     

1.6-己二胺化学修饰多壁碳纳米管

为获得两端具有活性端胺基的碳纳米管,通过化学方法对多壁碳纳米管(MWCNTs)接枝改性,利用氯化亚砜将MWCNTs酸处理产生的羧基转化为酰氯,进一步与1.6-己二胺发生亲核取代反应,将1.6-己二胺接枝到碳纳米管端部.采用X射线光电子能谱(XPS)、透射电镜(TEM)及扫描电镜(SEM)对化学修饰过程中各反应产物进行表征.结果表明:酸的切割作用,使碳纳米管从端帽下及管壁缺陷处打开,碳管长度由十几微米变为500nm左右;1.6-己二胺成功地接枝到碳纳米管端部,能谱分析(EDS)结果表明N元素接枝率达3.29%,接枝后的碳纳米管可以均匀分散在丙酮溶液中,并含有活性端胺基.     

Chemical functionalization of graphene oxide for improving mechanical and thermal properties of polyurethane composites

Graphene oxide (GO) was chemically functionalized to prepare polyurethane (PU) composites with improved mechanical and thermal properties. In order to achieve a well exfoliated and stable GO suspension in an organic solvent (dimethylformamide, DMF), 4, 4′-methylenebis(phenyl isocyanate) and polycaprolactone diol, which were the two monomers for synthesizing PU, were selectively used to functionalize GO. The obtained functionalized GO (FGO) could form homogeneous dispersions in DMF solvent and the PU matrix, as well as provide a good compatibility with the PU matrix. The most efficient improvement of mechanical properties was achieved when 0.4 wt.% FGO was added into the PU matrix, showing increases in the tensile stress, elongation at break and toughness by 34.2%, 27.6%, and 64.5%, respectively, compared with those of PU. Regarding the thermal stability, PU filled with 1 wt.% FGO showed the largest extent of improvement with T_2% and T_50% (the temperatures at which 2% and 50% weight-loss happened) 16 °C and 21 °C higher than those of PU, respectively. The significant improvement in both mechanical properties and thermal stability of FGO/PU composites should be attributed to the homogeneous dispersion of FGO in the PU matrix and strong interfacial interaction between them.     

碳纳米管溶解性及其化学修饰

详细评述了增加碳纳米管在水和有机溶剂中溶解性的途径，包括单一溶剂直接分散、电子供一受体电荷转移、可溶性聚合物或表面活性剂筒状胶束包裹等非共价键相互作用和顶端开口、化学衍生以及侧壁化学修饰等共价化学修饰。指出今后一段时期碳纳米管化学的主要任务为通过非共价的或共价的化学修饰，改善碳纳米管本身的性能和用途，并耦合其他如化学的、生物的或物理的功能扩展其应用范围。进一步深入理解碳纳米管化学(尤其是其溶液化学)反应理论。     

Effect of a multiscale reinforcement by carbon fiber surface treatment with graphene oxide/carbon nanotubes on the mechanical properties of reinforced carbon/carbon composites

An effective carbon fiber/graphene oxide/carbon nanotubes (CF-GO-CNTs) multiscale reinforcement was prepared by co-grafting carbon nanotubes (CNTs) and graphene oxide (GO) onto the carbon fiber surface. The effects of surface modification on the properties of carbon fiber (CF) and the resulting composites was investigated systematically. The GO and CNTs were chemically grafted on the carbon fiber surface as a uniform coating, which could significantly increase the polar functional groups and surface energy of carbon fiber. In addition, the GO and CNTs co-grafted on the carbon fiber surface could improve interlaminar shear strength of the resulting composites by 48.12% and the interfacial shear strength of the resulting composites by 83.39%. The presence of GO and CNTs could significantly enhance both the area and wettability of fiber surface, leading to great increase in the mechanical properties of GO/CNTs/carbon fiber reinforced composites.     

TiO2-nanorod decorated carbon nanotubes for high-permittivity and low-dielectric-loss polystyrene composites

Polymer composites with high permittivity and low dielectric loss are highly desirable in electronic and electrical industry. Adding conductive fillers could significantly increase the permittivity of a polymer. However, polymer composites containing conductive fillers often exhibit very high dielectric loss due to their large electrical conduction or leakage currents. In this work, by engineering TiO₂-nanorod-decorated multi-walled carbon nanotubes (TD-CNTs), polystyrene (PS) composite with high permittivity and low dielectric loss have been successfully prepared. The composite containing of 17.2 vol.% TD-CNTs has a permittivity of 37 at 1 kHz, which is 13.7 times higher than that of the pure PS (2.7), while the dielectric loss still remains at a low value below 0.11. The dielectric properties of the composites are closely related to the length of CNTs and the loading level of TiO₂-nanorods on the CNT surfaces.     

碳纳米管共价修饰功能化研究进展

综述了近年来国内外碳纳米管共价修饰功能化的研究进展,功能化后的碳纳米管不仅保持了原有的特异性质,而且还表现出修饰基团参加反应的活性,为碳纳米管的分散、组装及表面反应提供可能。     

Influence of carbon nanotubes structure on the mechanical behavior of cement composites

Cement matrix composites have been prepared by adding 0.5% in weight of multi wall carbon nanotubes (MWCNTs) to plain cement paste. In order to study how the chemical–physical properties of the nanotubes can affect the mechanical behavior of the composite, we compared the specimen obtained by mixing the same cement paste with three different kinds of MWCNTs. In particular, as-grown, annealed and carboxyl functionalized MWCNTs have been used. In fact, while high temperature annealing treatments remove lattice defects from the walls of CNTs, hence improving their mechanical strength, acid oxidative treatments increase chemical reactivity of pristine material, consequently chemical bonds between the reinforcement and the cement matrix are supposed to enhance the mechanical strength.Flexural and compressive tests showed a worsening in mechanical properties with functionalized MWCNTs, while a significant improvement is obtained with both as-grown and annealed MWCNTs.The phase composition of the composites was characterized by means of thermo gravimetric analysis coupled with mass spectroscopy, while the mineralogy and microstructure were analyzed by means of an X-ray diffractometer and scanning electron microscope. The results are interpreted and discussed taking into account the chemical and physical properties of the MWCNTs by means of EDX, TGA, SEM and Raman analysis.     

Effect of functionalized carbon nanotubes on the mechanical properties of epoxy-based composites

Abstract

In this research, composites reinforced with multi-walled carbon nanotubes (MWCNTs) in terms of their capability of absorbing energy during ballistic impact and tensile test were investigated. In order to investigate the effect of functional groups on mechanical properties of multi-wall carbon nanotubes composites, multi-walled carbon nanotubes were functionalized by COOH and NH₂. In order to investigate the penetration resistance of produced composites, the ballistic impact test with the high velocity was used. Results of the ballistic impact test imply that composites which benefit from carbon nanotubes with the carboxylic functional group have the highest value of the energy absorption. Results of the tensile test indicate, the interaction between carbon nanotubes with the carboxylic agent and the polymer matrix is much better. The ultimate stress for the sample containing nanotubes with hydroxyl functional group is 55% higher compared with the sample which does not contain any nanotubes. Reinforced composite samples which contain carbon nanotubes with the carboxylic functional group absorb 57.63% of the projectile energy and represent a better performance compared to the sample without nanotubes and the sample which consists of nanotubes with the amine functional group. The results of this study show that, uniform dispersion of nanotubes in the polymer matrix can profoundly affect mechanical properties especially the tensile strength. By functionalizing nanotubes and creating suitable functional groups, the cohesion between nanotubes and the matrix can be improved.     

Nitrogen plasma functionalization of carbon nanotubes for supercapacitor applications

Surface modification of carbon nanotubes with a simple and fast plasma treatment allows for the design of new nanomaterials with enhanced electrochemical properties. Both structural disorder and nitrogen concentration of the nanotubes increase after a nitrogen plasma treatment. The effect of plasma power and nitrogen pressure on the charge storage capability of the nanotubes has been investigated in detail. Depending on the plasma conditions, nitrogen functionalities such as quaternary nitrogen in the basal planes, and pyrrolic groups at the edges are introduced in the nanotubes structure. The potential difference between anodic and cathodic peaks of the Fe³⁺/Fe²⁺ redox couple decreases from 102 mV down to 75.7 mV after the nitrogen plasma treatment, which accounts for an increased reversibility of the electron transfer process between nanotubes and electrolyte. Moreover, the treated nanotubes show a significant increase in their specific capacitance from 22 up to 55 F g^?1 at a scan rate of 10 mV s^?1 in a 0.1 M Na₂SO₄ solution. Pyridinic and pyrrolic functionalities are found to play an important role in enhancing the reversibility and specific capacitance of the obtained electrodes.     

碳纳米管对碳纤维/环氧树脂复合材料力学性能的影响

为了探讨碳纳米管(CNTs)对碳纤维/环氧树脂复合材料(CF/ER复合材料)力学性能与疲劳寿命的影响,利用静态拉伸实验和拉-拉疲劳实验沿纤维方向对CF/ER复合材料和CNTs增强CF/ER复合材料(CNTs/CF/ER复合材料)进行了对比研究,同时利用X射线仪与扫描电镜对试样进行了观察.研究结果表明,CNTs的加入,虽然对CF/ER复合材料的拉伸力学性能影响不明显,但可以提高高周疲劳寿命约4倍,使各种实验应力水平下的裂纹密度降低9.5％以上,并可观察到试样中CNTs的拔出、破裂及桥联作用.由此可见,CNTs的加入可明显改善CF/ER复合材料的疲劳寿命.     

The reinforcement role of carbon nanotubes in epoxy composites with different matrix stiffness

This paper systemically evaluates the different reinforcement roles of carbon nanotubes in those nanocomposites with different matrix stiffness while the curing process is controlled. Both mechanical test and microscope observation indicated that such reinforcement would gradually reduce while increasing the stiffness of matrix. However in the soft and ductile composites, carbon nanotubes show a significant reinforcement without fracture strain decreasing. The interface interaction is poor between carbon nanotubes and matrix in the stiff composite, and therefore, they have little contribution to the mechanical properties of composite. This research may help to propose a further positive solution for designing and fabricating carbon nanotube–epoxy nanocomposites.     

Functionalization of multi-wall carbon nanotubes with silane and its reinforcement on polypropylene composites

Multi-wall carbon nanotubes (MWCNTs) were functionalized with a silane coupling agent. The MWCNTs were first coated with inorganic silica by a sol–gel process and then grafted with 3-methacryloxypropyltrimethoxysilane (3-MPTS). The grafting of 3-MPTS onto the MWCNTs surface was confirmed by Fourier-transform infrared spectroscopy, transmission electron microscopy and X-ray photoelectron spectra. Polypropylene (PP) composites filled with raw MWCNTs and functionalized MWCNTs were prepared and characterized. The PP/3-MPTS functionalized MWCNTs composite has higher tensile strength than the PP/raw MWCNTs composite. This is explained by the organic groups of 3-MPTS grafted onto the surface of MWCNTs.     

Sidewall functionalization of carbon nanotubes through electrophilic substitution

We report a general strategy for functionalizing the sidewalls of carbon nanotubes (CNTs), which is based on electrophilic substitution reactions on phenylated CNTs. By using this strategy, four new functionalized CNTs were prepared, including diphenyl ketone, benzenesulfonyl chloride, benzyl chloride and thiophenol modified CNTs. The benzenesulfonyl chloride and benzyl chloride functinalized CNTs could serve as novel initiators for surface-initiated atom transfer radical polymerization. The thiophenol modified CNTs were used in immobilizing Pd nanoparticles on the CNT surface, and the CNT/Pd hybrid produced exhibits good catalytic efficiency for the electrochemical oxidation of methanol.     

多壁碳纳米管/聚醚砜环氧树脂复合材料的制备及力学性能

环氧树脂具有优异的热性能及力学性能,但本身脆性较大。为制备低成本、高性能的环氧树脂体系,使用聚醚砜（PES）和多壁碳纳米管（MWCNT）对环氧树脂进行增韧,制备了不同PES含量的PES-环氧树脂共混物,讨论了PES含量对环氧树脂力学性能的影响;采用熔融法,并配合使用机械搅拌、高剪切分散和超声分散制备了MWCNT/PES-环氧树脂复合材料,测试了其拉伸性能及断裂韧性,用SEM观察了MWCNT在树脂中的分散状态以及拉伸试样的断口形貌。结果表明：MWCNT的加入能够提高PES-环氧树脂体系的综合力学性能,且当MWCNT含量为0.7wt%时,树脂体系的综合力学性能最好;低PES含量下,小于1.0wt%的MWCNT的加入使材料力学性能超过用20.0wt%PES改性的环氧树脂;PES与MWCNT对环氧树脂具有协同增韧作用。     

机械混炼对碳纳米管/丁苯橡胶复合材料的影响

为研究机械混炼对碳纳米管(CNTs)/粉末丁苯橡胶(SBR)复合材料性能的影响,从而获得性能优异的CNTs/SBR复合材料,联合采用喷雾干燥法和机械混炼法,制备高填充量CNTs/SBR复合材料.将喷雾干燥法制备的CNTs/粉末SBR复合材料在开炼机上机械混炼,对比分析混炼前后试样的物理和力学等相关性能,并对其微观形貌进行检测.结果表明,机械混炼使CNTs获得进一步的分散,与SBR基体间作用力得到增强,与混炼前相比,混炼后试样的玻璃化转变温度、交联度和常规力学性能均得到提高,当CNTs加入量为50phr时,混炼后复合材料的拉伸强度和撕裂强度分别为13.1MPa和39.8kN/m,比混炼前试样分别提高了约80%和20%.     

Electrical and mechanical properties of aluminosilicate inorganic polymer composites with carbon nanotubes

The DC electrical conductance of potassium aluminosilicate inorganic polymers (geopolymers) containing up to 6 wt% single-wall carbon nanotubes has been determined as a function of temperature up to 340 °C. After removal of the processing water during the first heating cycle, the conductance in subsequent heating cycles increases as a function of carbon nanotube content and temperature from 9.75 × 10⁻⁴ to 1.87 × 10⁻³ S m⁻¹ in the composites containing 0 and 0.2 wt% carbon nanotubes, respectively, at 290 °C. By comparison, the electrical conductance of potassium inorganic polymer composites containing graphite was generally lower. The conductance activation energies of the carbon nanotube and graphite composites were similar, and decreased from about 55 to 5 kJ mole⁻¹ with increasing carbon content. The tensile strengths of carbon nanotube and graphite-containing potassium geopolymer composites, determined by the Brazil method on 10–12 replicates, were about 2 MPa, and showed little change with increasing carbon nanotube content up to 0.3 wt%. By contrast, the tensile strengths of an analogous set of sodium composites were up to four times greater, possibly reflecting the necessity for less processing water in the synthesis of the sodium samples.     

Microwave-assisted functionalization of single-wall carbon nanotubes through diazonium

Single-wall carbon nanotubes (SWNTs) have been functionalized by a diazonium method through both a classical thermal reaction and a microwave-assisted reaction. The functionalized SWNTs have been characterized by nIR-Vis-UV absorption spectroscopy, Raman spectroscopy, and thermal gravimetric analysis. The results show that SWNTs are covalently functionalized through both reactions and that the microwave-assisted reaction is more rapid. Moreover, optimal choice of the reaction time can prevent the microwave irradiation from the adverse effect of subsequently removing the functional groups on the SWNT surface.     

石墨烯-多壁碳纳米管协同增强环氧树脂复合材料的低温力学性能

为了提高环氧树脂的低温力学性能,采用石墨烯与多壁碳纳米管(MWCNTs)协同改性环氧树脂,系统研究了石墨烯-MWCNTs/环氧树脂复合材料的室温(RT)和低温(77K)力学性能。结果表明:当石墨烯的质量分数为0.1wt%,MWCNTs的质量分数为0.5wt%时,纳米填料的加入可同时改善环氧树脂的低温拉伸强度、弹性模量和冲击强度;在此最佳含量下,石墨烯-MWCNTs/环氧树脂复合材料在RT和77K时的拉伸强度皆达到最大值,比纯环氧树脂的拉伸强度分别提高了11.04%和43.78%。石墨烯和MWCNTs能协同提高环氧树脂的低温力学性能。