碳纳米管管径的可控性研究

为了合理有效控制碳纳米管(CNTs)的管径,比较研究了化学气相沉积(CVD)-模板法与CVD-中毒法.通过透射电镜(TEM)观察碳纳米管形貌及其管径尺寸,分析了不同条件下,碳纳米管的形貌差异,讨论了制备阳极氧化铝(AAO)膜的氧化电压对碳纳米管的管径、管的有序度的影响和碳酸钠毒物对碳纳米管的管径、管形、产率的影响,并且分析了两种制备方法的生长机理.结果表明,在CVD-模板法中,在一定范围内,电压升高可以使AAO膜孔增大,从而控制碳纳米管的外径;在CVD-中毒法中,微量的碳酸钠粉末能增大碳纳米管的内径.     

Synthesis of carbon nanotubes and nanospheres with controlled morphology using different catalyst precursors

Carbon nanotubes and carbon nanospheres have been selectively synthesized in a polypropylene matrix by simply altering the catalyst precursor. When a mixture of ferrocene and cobalt (II) acetate was added to the polypropylene, well-dispersed carbon nanotubes were produced. When only cobalt (II) acetate was added, however, carbon nanospheres were obtained. In a third case, when the added catalyst precursor was ferrocene, no graphitic carbon was formed.     

Direct growth of carbon nanotubes on hydroxyapatite using MPECVD

For the first time carbon nanotubes (CNTs) have been successfully grown directly on hydroxyapatite (HA) by using microwave plasma enhanced chemical vapor deposition (MPECVD). Such integration has potential to capitalize on the merits of both HA and CNTs. This type of coating could be useful to improve the interface between bone and the implant. Scanning electron microscope SEM investigations show that; the surface of the CNTs is relatively clean and free of amorphous carbon. The CNTs diameters lie in the range 30-70 nm. In addition HA encapsulation by carbon was observed at a growth temperature 750 °C. Raman spectroscopy indicates that the CNTs are of high quality and the I_G/I_D ratio lies between 1.243 and 1.774. The changes in the X-ray diffraction (XRD) patterns give an indication that during the plasma deposition the HA-substrate surface is subjected to a temperature sufficient for partial conversion to the β-tricalcium phosphate via dehydroxylation.     

嵌段共聚物修饰多壁碳纳米管

为了改善多壁碳纳米管的分散性,通过丙烯酸和羟基化多壁碳纳米管的酯化反应将双键引入到碳纳米管的表面,同时利用原子转移自由基聚合合成端基为卤素的苯乙烯-b-甲基丙烯酸羟乙酯嵌段共聚物,并通过对双键的加成反应,将嵌段共聚物引入到多壁碳纳米管的表面,实现了碳纳米管的化学修饰。通过FTIR、TGA和TEM技术对产物进行了表征,结果表明:嵌段共聚物通过共价键接枝到碳纳米管表面,其含量为42.9%,平均约277个碳原子接枝一条聚合物链;修饰后的MW CNTs在乙醇中分散良好。     

Controlled growth of carbon nanotubes

Carbon nanotubes have extraordinary mechanical and electronic properties and hold great promise for future applications. The most important aspects of this structure are its low density, high aspect ratio, one dimensionality, high mechanical strength and high electrical and thermal conductivity. We present a short, state-of-the-art account of tailored nanotube growth. To provide these properties in real devices there exists a need for producing nanotubes on substrates. The challenge in the creation of mesoscale nanotube-based architectures and tailored nanotube networks consisting of thousands of tubes in a predefined order is obviously great. Currently, chemical vapour deposition (CVD) appears to be the most powerful method for achieving such required structures. We describe our work on a new synthesis method, based on catalytic CVD using mainly gas-phase catalyst delivery. Gas-phase catalyst delivery allows us to assemble single-walled and multi-walled carbon nanotubes in predetermined multiple orientations on substrates to build one- to three-dimensional architectures. We are able to control, to a large extent, the types of nanotubes produced, their lengths, locations and their orientations. The ability to make mesoscale architectures with nanotubes should lead us to develop applications in areas such as nano-electromechanical systems.     

Multiscale carbon fibre–reinforced polymer (CFRP) composites containing carbon nanotubes with tailored interfaces

Pristine and functionalized multiwalled carbon nanotubes (MWCNTs) with tailored interfaces were efficiently dispersed in an epoxy matrix using a three‐roll mill and further reinforced with carbon fibres. 1.3‐Dipolar cycloaddition of azomethine ylides was used for the chemical modification of MWCNTs by a solvent‐free approach. The influence of different loadings and types of MWCNTs on the final properties of the epoxy matrix was studied. Moreover, the most promising formulations were selected for manufacturing of prepreg sheets. The transversal tensile properties and the interlaminar fracture toughness under mode I loading (G_IC) of multiscale carbon fibre–reinforced polymer (CFRP) composites were characterized. The results point out that it is not straightforward to transfer the remarkable intrinsic properties of MWCNTs to the composite level, although an overall positive trend was found. Double cantilever beam experiments showed that G_IC of CFRP composites was improved 44% at ultralow content of functionalized MWCNTs (0.043 wt%).     

Selective growth of carbon nanotubes using catalyst poisoning and geometric trench

This work suggests catalyst poisoning and geometric patterned approaches to selectively grow multiwall carbon nanotubes. Ferromagnetic particles as a catalyst for CNTs growth vanish when they are deposited over an aluminum thin film. Additionally, geometric features, such as trenches or cavities, are revealed to be capable of selectively ceasing the growth of CNTs even though catalytic thin films were covered on entire samples by an atmospheric thermal chemical vapor deposition technique.     

Microwave plasma enhanced chemical vapor deposition growth of few-walled carbon nanotubes using catalyst derived from an iron-containing block copolymer precursor

The microwave plasma enhanced chemical vapor deposition (MPECVD) method is now commonly used for directional and conformal growth of carbon nanotubes (CNTs) on supporting substrates. One of the shortcomings of the current process is the lack of control of the diameter and diameter distribution of the CNTs due to difficulties in synthesizing well-dispersed catalysts. Recently, block copolymer derived catalysts have been developed which offer the potential of fine control of both the size of and the spacing between the metal clusters. In this paper we report the successful growth of CNTs with narrow diameter distribution using polystyrene-block-polyferrocenylethylmethylsilane (PS-b-PFEMS) as the catalyst precursor. The study shows that higher growth pressure leads to better CNT growth. Besides the pressure, the effects on the growth of CNTs of the growth parameters, such as temperature and precursor gas ratio, are also studied.     

Supported Pt-particles on multi-walled carbon nanotubes with controlled surface chemistry

Multi-walled carbon nanotubes (MWCNTs) were functionalized by HNO₃ hydrothermal oxidation at 200 °C. The degree of surface functionalization was described by an exponential function in terms of HNO₃ concentration. Very small Pt particles, with mean particle size of 1.7 ± 0.3 nm, could be supported on the surface of pristine MWCNTs and also on MWCNTs treated with HNO₃ concentrations up to 0.20 mol L^− 1, while a broader range of particle sizes, and larger Pt particles (3.4 ± 1.3 nm) were obtained on the MWCNTs treated with a higher HNO₃ concentration (0.30 mol L^− 1). Therefore, the amounts of surface groups and Pt particle sizes can be selected by tuning the HNO₃ concentration used in the hydrothermal treatment.     

Pressure effects on bond lengths and shape of zigzag single-walled carbon nanotubes

We investigate structural parameters, i.e., bond lengths and bond angles of isolated uncapped zigzag single-wall nanotubes in detail. The bond lengths and bond angles are determined for several radii tubes by using a theoretical procedure based on the helical and rotational symmetry for atom coordinates generation, coupled with Tersoff potential for interaction energy calculations. Results show that the structure of zigzag tubes is governed by two bond lengths. One bond length is found to have a value equal to that of graphite, while the other one is larger. Furthermore, the tube length is found to have significant effect only on larger bond length in zigzag tubes. With the application of the pressure, only the larger bond length compresses, the other one remaining practically constant. At some critical pressure, this bond length becomes equal to constant bond length. This behavior of bond lengths is different from those of armchair tubes. An analysis regarding the cross sectional shape has also been done. At some higher pressure, transition from circular to oval cross section takes place. This transition pressure is found to be equal 2.06 GPa for (20,0) tube. Some comparison with chiral tubes has also been made and important differences on bond length behavior have been observed.     

Gas-phase growth of diameter-controlled carbon nanotubes

We demonstrate gas-phase (aerosol) generation of diameter-controlled carbon nanotubes (CNTs) by employing size-controlled monodisperse nickel nanoparticles produced by the combination of pulsed laser ablation and electrostatic classification. The electrostatic classifier sorted agglomerated mono-area nickel particles, and then a subsequent heating process at ∼ 1200 °C created sintered single primary particles with very narrow size distribution. These isolated single primary particles were then sent to an aerosol reactor where free-flight CNTs were grown with acetylene and hydrogen mix at temperature of ∼ 750 °C. The resulting CNTs formed in this continuous gas-phase process were found to have a uniform diameter, which is commensurate with the diameter of the size-controlled catalytic nickel particles.     

Continued growth of single-walled carbon nanotubes

We demonstrate the continued growth of single-walled carbon nanotubes (SWNTs) from ordered arrays of open-ended SWNTs in a way analogous to epitaxy. Nanometer-sized metal catalysts were docked to the SWNT open ends and subsequently activated to restart growth. SWNTs thus grown inherit the diameters and chirality from the seeded SWNTs, as indicated by the closely matched frequencies of Raman radial breathing modes before and after the growth.     

Multi-barrier layer-mediated growth of carbon nanotubes

Variation in the height of carbon nanotubes (CNTs) grown has been co-related to the type of multi-barrier-layer used. Initially, various types of barrier-layers such as Al, Al₂O₃, Al/SiO₂, Al₂O₃/SiO₂ were prepared onto a n-type Si (100) substrate. The thickness of SiO₂ was ∼ 550 nm, where as, Al₂O₃ and Al were ∼ 15 nm thick. These samples were covered with ∼ 1 nm thick Fe catalyst layer. The coated samples were subjected to the thermal chemical vapor deposition (T-CVD) process. SEM analysis showed that, for Al₂O₃/SiO₂ barrier layers, the average height of the CNTs was ∼ 10 μm, where as, for other types of samples it was less than ∼ 1 μm. To investigate this, multi-barrier layers were characterized by dynamic secondary ion mass spectrometry (D-SIMS). The observed variation in height of CNTs is attributed to the variation in diffusivity of Fe atoms into multi-barriers-layers. The results showed that, diffusion of Fe catalyst atoms could severally affect height of CNTs.     

两亲性嵌段共聚物改性单壁碳纳米管的制备

以具备生物相容性的两亲性三嵌段共聚物Pluronic F108为分散剂,超纯水为溶剂,在超声作用下对混酸处理的单壁碳纳米管(SWNTs)进行非共价改性,制备均匀、稳定的SWNTs分散液.运用紫外-可见吸收光谱(UV-vis)、透射电子显微镜(TEM)、傅立叶变换红外光谱(FI-TR)、拉曼光谱(Raman)等对不同处理的SWNTs分散液进行表征比较.实验结果表明,分散剂F108的最佳使用浓度为1wt%,经混酸处理后的SWNTs成功带上了羧基官能团,在分散剂F108溶液中呈现单根或小管束的分散状态,分散液可稳定保存30天以上.利用混酸处理和超声解离单壁碳纳米管团聚体、F108保持单壁碳纳米管分散状态等多种处理方法的综合使用,实现了单壁碳纳米管在水中的高效、稳定分散.     

两亲性嵌段共聚物改性的多壁碳纳米管的制备

通过对碳纳米管进行表面改性制得具有引发ATRP反应活性的碳纳米管(MWNT-Br),以MWNT-Br作引发剂经过两次ATRP反应将聚乙烯基吡咯烷酮(PVP)和聚甲基丙烯酸特丁酯(PtBMA)先后接枝到多壁碳纳米管表面制得两亲性嵌段共聚物接枝的碳纳米管(MWNT-PVP-b-PtBMA),用红外光谱、热失重和透射电镜对两亲性碳纳米管进行了表征.并考察了修饰前弱亲油性的纯碳纳米管、酸化后亲水性的碳纳米管和修饰后两亲性碳纳米管这3种碳纳米管在水和氯仿形成的两相体系中的分散情况,观察到所制备的两亲性碳纳米管能够均匀分散在油水两相界面上.     

Titanium oxide nanotubes with controlled morphology for enhanced bone growth

An array of vertically aligned titanium oxide nanotubes was grown on the surface of titanium substrate by anodization. A chemical treatment with NaOH solution to make them more bioactive with a formation of nanoscale sodium titanate structure. The presence of such treated TiO₂ nanotubes significantly accelerated the kinetics of hydroxyapatite growth by a factor of as much as 7. The adhesion/growth of osteoblast cells is also significantly accelerated by the topography of the TiO₂ nanotubes with the filopodia of the growing cells actually going into the nanotube pores, producing a locked-in cell structure. The number of the adhered cells on the TiO₂ nanotubes increases by as much ∼400% as compared to the Ti metal, most likely caused by the pronounced topological feature, significantly increased surface area, as well as the in-between-nanotube pathways for fluid. Such an array of TiO₂ nanotubes well adherent on Ti implant surface can be useful for accelerated bone growth in orthopaedic/dental applications.     

Cadmium-catalyzed surface growth of single-walled carbon nanotubes with high efficiency

We demonstrate that cadmium (Cd) can catalyze the growth of single-walled carbon nanotubes (SWNTs) with high efficiency. The Cd nanocatalysts, prepared using a diblock copolymer templating method, were uniformly spaced over a large deposition area with an average diameter of 1.9 nm and narrow size distribution. By using the normal-heating and fast-heating method, random and horizontally aligned arrays of SWNTs can be generated. The density of the SWNTs can be altered by the chemical vapor deposition conditions. The morphology and microstructure of the SWNTs characterized by scanning electron microscopy, Raman spectroscopy, atomic force microscopy, and high-resolution transmission electron microscopy revealed that the grown nanotubes do not have carbonaceous particles and have good crystallinity. In addition, after careful check with superlong nanotubes 735 out of 790 nanotubes were found to be deposited with Ag (93%) and only 7% SWNTs without Ag deposition. While for superlong SWNT arrays from Fe, 32% long SWNTs without Ag deposition was found, the high percentage of SWNTs with Ag deposition from Cd indicates that the SWNTs have better conductivity and better structural uniformity with less defects.