Catalytic action of gold and copper crystals in the growth of carbon nanotubes

Multi-wall carbon nanotubes are grown in a chemical vapor deposition process by using bulk gold and copper substrates as catalysts. Nanotube growth starts from a nanometer-sized roughness on the metal surfaces and occurs in a mechanism where the catalyst particle is either at the tip (Au) or root (Cu) of the growing nanotube. Whereas Au leads to nanotubes with good structural perfection, nanotubes grown from Cu show a higher density of defects. High-resolution transmission electron microscopy shows the bonding between Au and carbon at the metal-nanotube interface whereas no bonds between Cu and carbon occur. Highly mobile Au or Cu atoms adsorb at the growing edge of a carbon nanotube from where diffusion along the nanotube wall can lead to the formation of Au or Cu nanowires inside the central hollow of carbon nanotubes.     

Synthesis of clay–carbon nanotube hybrids: Growth of carbon nanotubes in different types of iron modified montmorillonite

In the present study, montmorillonite–carbon nanotube hybrids were synthesized by catalytic decomposition of ethylene over iron montmorillonite surfaces modified by different experimental procedures. SEM and STEM analyses reveal the presence of carbon nanotubes attached to the clay layers and X-ray diffraction results indicate that sodium montmorillonite layers were intercalated with iron species during the ion-exchange processes and further delaminated due to the growth of carbon nanotubes. It is expected that montmorillonite–carbon nanotube hybrids will be beneficiary for improvement of mechanical properties in polymer nanocomposites due to their pre-exfoliated internal structure and the presence of surface carbon nanotubes which may significantly enhance reinforcing effect.     

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.     

Nanotubes in a gradient electric field as revealed by STM TEM technique

We have investigated the behavior of two nanotube systems, carbon and boron nitride, under controlled applied voltages in a high-resolution transmission electron microscope (TEM) equipped with a scanning tunneling microscope (STM) unit. Individual nanotubes (or thin bundles) were positioned between a piezomovable gold electrode and a biased (up to ±140 V) STM tip inside the pole-piece of the microscope. The structures studied include double-and multi-walled carbon nanotubes (the latter having diverse morphologies due to the various synthetic procedures utilized), few-layered boron nitride nanotube bundles and multi-walled boron nitride nanotubes (with or without functionalized surfaces). The electrical breakdown, physical failure, and electrostatic interactions are documented for each system. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Influence of surface chemistry on inkjet printed carbon nanotube films

Carbon nanotube ink chemistry and the proper formulation are crucial for direct-write printing of nanotubes. Moreover, the correct surface chemistry of the self-assembled monolayers that assist the direct deposition of carbon nanotubes onto the substrate is equally important to preserve orientation of the printed carbon nanotubes. We report that the successful formulation of two single walled carbon nanotube (SWNT) inks yields a consistent, homogenous printing pattern possessing the requisite viscosities needed for flow through the microcapillary nozzles of the inkjet printer with fairly modest drying times. The addition of an aqueous sodium silicate allows for a reliable method for forming a uniform carbon nanotube network deposited directly onto unfunctionalized surfaces such as glass or quartz via inkjet deposition. Furthermore, this sodium silicate ingredient helps preserve applied orientation to the printed SWNT solution. Sheet resistivity of this carbon nanotube ink formula printed on quartz decreases as a function of passes and is independent of the substrate. SWNTs were successfully patterned on Au. This amine-based surface chemistry dramatically helps improve the isolation stabilization of the printed SWNTs as seen in the atomic force microscopy (AFM) image. Lastly, using our optimized SWNT ink formula and waveform parameters in the Fuji materials printer, we are able to directly write/print SWNTs into 2D patterns. Dried ink pattern expose and help orient roped carbon nanotubes that are suspended in ordered arrays across the cracks.     

The impact of fluorinated MWCNT additives on the enhanced dynamic mechanical properties of e-beam-cured epoxy

Multi-walled carbon nanotubes were embedded into e-beam-cured epoxy resin to improve the mechanical properties of epoxy resin. The surfaces of these carbon nanotubes were modified using a fluorination treatment to improve their dispersion and adhesion in epoxy resin. The dynamic mechanical properties of epoxy/carbon nanotube composites were investigated at various heating rates and frequencies. As an effect of fluorination treatment, the semi-ionic bond of C–F on the surface of multi-walled carbon nanotubes played an important role in the improved dispersion and adhesion of carbon nanotubes into the epoxy resin. The storage modulus and loss modulus of the composites increased with higher applied frequency. The activation energy of the composites was increased by the effects of a higher heating rate due to the slow heat transfer in the epoxy/carbon nanotube composites. Eventually, the dynamic mechanical properties of the investigated epoxy were significantly improved by the carbon nanotubes dispersed therein via the fluorination treatment.     

Bottom-up growth of carbon nanotube multilayers: unprecedented growth

An unusual growth phenomenon, with no precedent in vapor-phase thin film growth, is described here, for the case of the growth of stacked multiple layers of vertically aligned carbon nanotubes(1-6) on solid substrates. As multiple layers of ordered nanotubes are sequentially deposited from the vapor onto the substrate, each layer nucleates and grows from the original substrate surface at the bottom of the existing multiple stacks of nanotubes. In contrast to conventional understanding of thin film deposition,(7) the mechanism here has similarities to porous oxide film formation on surfaces.(8) The stacked layers of aligned nanotubes act as fully permeable membranes for the downward diffusion of growth precursor vapors, allowing growth to occur at the buried solid interface. The preexisting multiple nanotube stacks lift up to accommodate the vertical growth of fresh layers, allowing the formation of nanotube towers extending in millimeter lengths. Our results provide evidence for a new growth phenomenon, characterized by selective, interface-driven, bottom-up growth of self-assembled nanowires at buried interfaces, covered with weakly adhering thick porous membranes.     

Dye-sensitized solar cells using branched titania nanotube films

Photovoltaic characteristics of dye-sensitized solar cells fabricated from branched titania nanotube arrays are compared with those obtained from unbranched ones. Branched titania nanotubes result in increased efficiency and short circuit current density without any discernible increases in dark current, than in devices with purely unbranched tubes. Adsorption isotherms show that increased inter-tube porosity exposes the outer surfaces of the branched tubes, providing increased access and area for dye adsorption. Our findings indicate that branched titania nanotubes could be attractive for use in many applications.     

基于碳纳米管模板的氮化镓纳米线束合成

通过金属有机物化学气相沉积方法在碳纳米管模板上生长氮化镓纳米线束.对所生长的纳米结构进行了扫描电镜和X射线能谱分析,结果显示氮化镓纳米晶体可以与碳纳米管形成纳米线束状复合物.纳米线束状复合物直径为100～200 nm,长度为1.5～2.5μm,纳米线的两端呈现尖角状.由于氨气很容易吸附在碳纳米管表面,可知所获得的纳米结构的初始生长机制为碳纳米管的表面氮化.该研究也证明金属有机物化学气相沉积将是用于制造化合物纳米结构材料的一项有效的技术.     

聚丙烯腈基碳纳米管复合材料的制备及其表征

碳纳米管添加到聚合物中对其结构和性能都有深远的影响,本文通过浓硝酸对碳纳米管改性后,采用水相沉淀聚合的方法制备了聚丙烯腈/碳纳米管复合材料,同时研究了碳纳米管经过浓硝酸处理后其化学结构的变化;探讨了碳纳米管对聚丙烯腈复合材料热学和结晶性的影响。研究表明,浓硝酸常温处理不仅能除去杂质,还可以在碳纳米管表面引入羧基等含氧基团;加入碳纳米管后,聚丙烯腈的预氧化温度有一定程度的提前,放热量明显降低,同时对聚合物的结晶度也有一定程度的影响。     

The effect of carbon nanotubes on the fracture toughness and fatigue performance of a thermosetting epoxy polymer

Multi-walled carbon nanotubes, with a typical length of 140 μm and a diameter of 120 nm, have been used to modify an anhydride-cured epoxy polymer. The modulus, fracture energy and the fatigue performance of the modified polymers have been investigated. Microscopy showed that these long nanotubes were agglomerated, and that increasing the nanotube content increased the severity of the agglomeration. The addition of nanotubes increased the modulus of the epoxy, but the glass transition temperature was unaffected. The measured fracture energy was also increased, from 133 to 223 J/m² with the addition of 0.5 wt% of nanotubes. The addition of the carbon nanotubes also resulted in an increase in the fatigue performance. The threshold strain-energy release-rate, G _th, increased from 24 J/m² for the unmodified material to 73 J/m² for the epoxy with 0.5 wt% of nanotubes. Electron microscopy of the fracture surfaces showed clear evidence of nanotube debonding and pull-out, plus void growth around the nanotubes, in both the fracture and fatigue tests. The modelling study showed that the modified Halpin–Tsai equation can fit very well with the measured values of the Young’s modulus, when the orientation and agglomeration of the nanotubes are considered. The fracture energy of the nanotube-modified epoxies was predicted, by considering the contributions of the toughening mechanisms of nanotube debonding, nanotube pull-out and plastic void growth of the epoxy. This indicated that debonding and pull-out contribute to the toughening effect, but the contribution of void growth is not significant. There was excellent agreement between the predictions and the experimental results.     

RGD peptide immobilized on TiO2 nanotubes for increased bone marrow stromal cells adhesion and osteogenic gene expression

Recently, TiO₂ nanotube layers are widely used in orthopedics and dental applications because of their good promotion effect on bone cells. Furthermore, peptide sequences such as arginine–glycine–aspartic acid are used to modify Ti implant for binding to cell surface integrins through motif. In this study, a cellular adhesive peptide of arginine–glycine–aspartic acid–cysteine (RGDC) was immobilized onto anodized TiO₂ nanotubes on Ti to examine its in vitro responses on rat bone marrow stromal cells (BMSCs). Materials were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy techniques. High-resolution C1s scans suggested the presence of RGDC on the surface and SEM images confirmed the nanotubes were not destroyed after modification. BMSCs adhesion and osteogenic gene expression were detected in TiO₂ nanotube layers with and without RGDC modification by fluorescence microscopy, confocal laser scanning microscopy, SEM, and realtime polymerase chain reaction (Real-time PCR). Results showed that the TiO₂ nanotube layers immobilized with RGDC increased BMSCs adhesion compared to nonfunctionalized nanotubes after 4 h of cultivation. Furthermore, the osteogenic gene expression of BMSCs was dramatically enhanced on the TiO₂ nanotube layers immobilized with RGDC (10 mM) compared to the TiO₂ nanotube layers immobilized with RGDC (1 mM) and non-functionalized anodized Ti. Our results from in vitro study provided evidence that Ti anodized to possess nanotubes and then further functionalized with RGDC should be further studied for the design of better biomedical implant surfaces.     

Titanium oxide nanotubes for bone regeneration

Titanium oxide nanotubes with Ca ions on their surfaces were prepared as 2 mm cylindrical inserts and placed into surgically created bone defects in the femurs of Wistar rats. On day 3, fibroblast-like cells were present on the surface of the nanotube inserts and fibers were observed by scanning electron microscopy (SEM). On day 7, cells with alkaline phosphatase activity were present and identified as osteoblasts by SEM and transmission electron microscopy. New bone matrices were observed in and around the porous nanotube inserts by light microscopy. Compared with clinically used hydroxyapatite and tricalcium phosphate, beta-titanium oxide nanotubes promote faster acquisition and development of osteoblasts and bone tissues and have better bone regenerating ability after one week.     

Covalent Surface Chemistry of Single‐Walled Carbon Nanotubes

In this review article, we explore covalent chemical strategies for the functionalization of carbon‐nanotube surfaces. In recent years, nanotubes have been treated as chemical reagents (be it inorganic or organic) in their own right. Indeed, from their inherent structure, one can view nanotubes as sterically bulky, π‐conjugated ligands, or conversely as electron‐deficient alkenes. Hence, herein we seek to understand, from a structural perspective, the breadth and types of reactions single‐walled nanotubes (SWNTs) can undergo in solution phase, not only at the ends and defect sites but also along the sidewalls. Controllable chemical functionalization suggests that the unique electronic and mechanical properties of SWNTs can be tailored in a determinable manner. Moreover, prevailing themes in nanotube functionalization have been involved with dissolution of tubes.     

MoS_2与TiO_2一维纳米复合材料的制备与表征

本文采用气相还原法制备了MoS2包覆TiO2的一维纳米复合材料,首先用水热法制备TiO2纳米管,并制备前驱体(NH42)MoS4;用浸渍法将(NH4)2MoS4附着于TiO2纳米管表面;然后利用氢气还原前驱体得到MoS2包覆层。用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)表征所得产物的结构及微观形貌。结果表明当还原反应温度较高(≥600℃)时,产物呈烧结状态,而当反应温度为500℃时,可以得到表面均匀包覆MoS2的TiO2纳米管复合材料,其中包覆层MoS2的结晶程度较低。在此基础上,本文提出了该产物的生长模型,并对包覆前后的样品做荧光性能分析。     

Influence of sterilization methods on cell behavior and functionality of osteoblasts cultured on TiO2 nanotubes

We investigated the adhesion, proliferation and osteogenic functionality of osteoblasts cultured on titanium dioxide (TiO₂) nanotubes in response to different sterilization methods (dry autoclaving vs. wet autoclaving). We prepared various sizes (30–100 nm diameter) of TiO₂ nanotubes on titanium substrates by anodization, sterilized nanotubes by different conditions, and seeded osteoblast cells onto the nanotube surfaces with two different cell seeding densities (10,000 vs. 50,000 cells/well in 12-culture well). The result of this study indicates that the adhesion, proliferation and alkaline phosphatase activity of osteoblasts cultured on only the larger 70 and 100 nm TiO₂ nanotube arrays were dramatically changed by the different sterilization conditions at a low cell seeding density. However, with a higher cell seeding density (50,000 cells/well in 12-cell culture well), the results revealed no significant difference among altered nanotube geometry, 30–100 nm diameters, nor sterilization methods. Next, it was revealed that the nanofeatures of proteins adhered on nanotubular TiO₂ morphology are altered by the sterilization method. It was determined that this protein adhesion effect, in combination with the cell density of osteoblasts seeded onto such TiO₂ nanotube surfaces, has profound effects on cell behavior. This study clearly shows that these are some of the important in vitro culture factors that need to be taken into consideration, as well as TiO₂ nanotube diameters which play an important role in the improvement of cell behavior and functionality.     

Characteristic of Waves in A Multi-Walled Carbon Nanotube

A multi-walled carbon nanotube is modeled as a multiple-elastic cylindrical structure. The numerical-analytical method is adopted to analyze the characteristics of harmonic waves propagating along an anisotropic carbon nanotube. Each wall of the carbon nanotube is divided into three-nodal-line layer elements. The deflections of two adjacent tubes are coupled through the van der Waals. The governing equation of element is obtained from Hamilton's principle. A set of system equation of dynamics equilibrium for the entire structure is obtained by the assembling of all the elements. From solution of the eigenvalue equations, the dispersive characteristics, group velocities of multi-walled carbon nanotubes are achieved, and these properties of the six characteristic wave surfaces are also obtained.     

Gold Nanowire Fabrication with Surface‐Attached Lipid Nanotube Templates

A high‐throughput approach to fabricate gold nanowires on surfaces with a lipid nanotube template is demonstrated. Streptavidin‐coated gold nanoparticles are attached to the biotin‐tagged lipid nanotubes. After the chemical fixation, the samples are dried and treated with oxygen plasma to remove the organic template and connect the particles. The created nanowires are characterized by cryo‐transmission electron microscopy, atomic force microscopy, and electrical measurements.     

Novel vapor phase reactions for the synthesis and modification of carbon nanotubes and inorganic nanowires

Several vapor phase methods have been developed for the preparation and modification of carbon nanotubes and inorganic nanowires. Thus, nebulized spray pyrolysis has been employed for the synthesis of carbon nanotubes and metal nanowires. Multi-walled carbon nanotubes (MWNTs) with fairly uniform diameters and aligned nanotube bundles have been obtained by nebulized spray pyrolysis using solutions of organometallics such as ferrocene in hydrocarbon solvents. Single-crystalline nanowires of zinc, cadmium, cobalt, and lead are obtained by the decomposition of metal acetates. By reacting acid-treated carbon nanotubes with vapors of metal halides, followed by reaction with water and calcination chemically-bonded oxide layers can be obtained on the nanotubes. A similar procedure has been employed to prepare chemically-bonded oxide layers on Al2O3, ZnO, and silicon nanowires by the reaction of the metal halides with the surface hydroxyl groups present on these nanowire surfaces.     

Nanosize and vitality: TiO2 nanotube diameter directs cell fate

We generated, on titanium surfaces, self-assembled layers of vertically oriented TiO2 nanotubes with defined diameters between 15 and 100 nm and show that adhesion, spreading, growth, and differentiation of mesenchymal stem cells are critically dependent on the tube diameter. A spacing less than 30 nm with a maximum at 15 nm provided an effective length scale for accelerated integrin clustering/focal contact formation and strongly enhances cellular activities compared to smooth TiO2 surfaces. Cell adhesion and spreading were severely impaired on nanotube layers with a tube diameter larger than 50 nm, resulting in dramatically reduced cellular activity and a high extent of programmed cell death. Thus, on a TiO2 nanotube surface, a lateral spacing geometry with openings of 30-50 nm represents a critical borderline for cell fate.