Physical consequences of the mitochondrial targeting of single-walled carbon nanotubes probed computationally

Experiments by F. Zhou and coworkers (2010) [16] showed that mitochondria are the main target of the cellular accumulation of single-walled carbon nanotubes (SWCNTs). Our in silico experiments, based on geometrical optimization of the system consisting of SWCNT+proton within Density Functional Theory, revealed that protons can bind to the outer side of SWCNT so generating a positive charge. Calculation results allow one to propose the following mechanism of SWCNTs mitochondrial targeting. SWCNTs enter the space between inner and outer membranes of mitochondria, where the excess of protons has been formed by diffusion. In this compartment SWCNTs are loaded with protons and acquire positive charges distributed over their surface. Protonation of hydrophobic SWCNTs can also be carried out within the mitochondrial membrane through interaction with the protonated ubiquinone. Such “charge loaded” particles can be transferred as “Sculachev ions” through the inner membrane of the mitochondria due to the potential difference generated by the inner membrane. Physiological consequences of the described mechanism are discussed.     

Growth of single-walled carbon nanotubes on porous silicon

Porous silicon is an important and versatile material in the semiconductor industry, and can be achieved by electrochemically etching silicon wafers. Employing porous silicon as substrates, this article presents a new approach to grow single-walled carbon nanotubes on wafers for device applications. Free from support materials, this method is a clean one. At the same time it is feasible and robust, as porous silicon is remarkably superior to polished surface in facilitating the nucleation of catalyst. The superiority of porous silicon over polished surface is attributed to their different dewetting manners.     

Axisymmetric vibration of single-walled carbon nanotubes in water

A double shell-Stokes flow model is developed to study the axisymmetric vibration of single-walled carbon nanotubes (SWCNTs) immerged in water. In contrast to macroscopic solid-liquid system, a submerged SWCNT is coupled with surrounding water via the van der Waals interaction. It is shown that this unique feature substantially reduces viscous damping of the axisymmetric radial, longitudinal and torsional vibrations and significantly up-shifts the frequency of the radial vibration of an SWCNT. The study offers a theoretical explanation for the experimental observation and molecular dynamics simulations available in particular cases, and provides an efficient modelling tool and useful guidance for the study of the general dynamic behaviour of SWCNTs in a fluid.     

单层碳纳米管的磁输运特性

依据磁场中Boltzmann输运方程及单层磁纳米管(SWNTs)的能量色散关系,对单个SWNTs中轴向磁场诱发的低温磁阻进行了数值计算.分析表明:当电子以低能输运时,SWNTs的磁阻有明显的Aharonov-Bohn(A-B)效应,与并SWNTs的能隙相对应.     

Radical functionalization of single-walled carbon nanotubes with azo(bisisobutyronitrile)

The isobutyronitryl groups from thermal decomposition of azobisisobutyronitrile in a 1,2-dichlorobenzene solution were successfully attached to the sidewalls of single-walled carbon nanotubes; thermogravimetic analysis shows a weight loss of 20% (compared to raw SWNTs), which was calculated to be ca. 1 isobutyronitryl group in 23 carbon atoms.     

Effect of alcohol sources on synthesis of single-walled carbon nanotubes

The effect of oxidant species forming an alcohol molecule for hot-filament chemical vapor deposition (HFCVD) on single-walled carbon nanotubes (SWCNTs) growth has been investigated. To use a graphite rod as a filament for HFCVD to decompose alcohol sources, contamination-free sample surface can be obtained and SWCNTs are successively and densely grown at a lower temperature than those by conventional thermal CVD. It is found that the higher the molecule number of alcohol among CH₃OH, C₂H₅OH, and 2-C₃H₇OH is, the lower the initial growth rate of SWCNTs is. As for CH₃OH, diameter distribution of SWCNTs is dynamically changed with the growth time passed, and a negative growth rate is observed at the later stage of growth. The growth kinetics depending on the alcohol sources is discussed on the basis of a capability of the oxidant species to burn away SWCNTs and deactivation of Co catalysts used for the growth.     

Diameter-dependent thermal-oxidative stability of single-walled carbon nanotubes synthesized by a floating catalytic chemical vapor deposition method

In this paper, purified single-walled carbon naotubes (SWCNTs) with three different diameters were synthesized using a floating catalytic chemical vapor deposition method with ethanol as carbon feedstock, ferrocene as catalyst, and thiophene as growth promoter. The thermal-oxidative stability of different-diameter SWCNTs was studied by using thermal analysis (TG, DTA), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. The results indicate that small diameter SWCNTs (∼1 nm) are less stable and burn at lower temperature (610 °C), however, the larger diameter SWCNTs (∼5 nm) survive after burning at higher temperature (685 °C), the oxidation rate varies inversely with the tube diameter of SWCNTs, which may be concluded that the higher oxidation-resistant temperature of larger diameter SWCNTs can be attributed to the lower curvature-induced strain by rolling the planar graphene sheet for the larger diameter, so small tubes will become thermodynamically unstable.     

Wave characteristics of single-walled fluid-conveying carbon nanotubes subjected to multi-physical fields

Wave propagation in single-walled carbon nanotubes (SWCNTs) conveying fluids and placed in multi-physical fields (including magnetic and temperature fields) is studied in this paper. The nanotubes are modelled as Timoshenko beams. Based on the nonlocal beam theory, the governing equations of motion are derived using Hamilton's principle, and then solved by Galerkin approach, leading to two second-order ordinary differential equations (ODEs). Numerical simulations are carried out to verify the analytical model proposed in the present study, and determine the influences of the nonlocal parameter, the fluid velocity and flow density, the temperature and magnetic field flux change, and the surrounding elastic medium on the wave behaviour of SWCNTs. The results show that the nonlocal parameter has a considerable influence on dynamic behaviour of the nanotube and the fluid flow inside it. The results also show that the magnetic and temperature fields play an important role on the wave propagation characteristics of SWCNTs.     

Filling of single-walled carbon nanotubes by CuI nanocrystals via capillary technique

The present study is focused on the synthesis and investigation of the nanocomposite CuI@SWNT obtained by the filling of metallic single-walled carbon nanotubes (SWNTs) (inner diameter 1–1.4 nm) by wide-gap semiconducting CuI nanocrystals using so-called capillary technique. The method is based on the impregnation of pre-opened SWNTs by molten CuI in vacuum with subsequent slow cooling to room temperature. SWNTs and CuI@SWNT nanocomposites were studied by nitrogen capillary adsorption method, EDX microanalysis, HRTEM microscopy and Raman spectroscopy. The changing of electronic properties of CuI@SWNT as compare to row nanotubes was observed.     

高效循环电弧放电法制备大量单壁纳米碳管的研究

介绍一种利用电弧放电法高效率制备大量单壁纳米碳管的新方法.以钨代替传统的石墨棒作为放电阴极，采取循环式往返放电法.同时利用高分辨透射电子显微镜及拉曼光谱对制备的单壁纳米碳管进行了观察、表征.实验证明：以钨为阴极的循环电弧放电法可以初步实现单壁纳米碳管的高效率、大批量生产. 关键词： 单壁纳米碳管 钨电极 拉曼光谱     

Surface growth of single-walled carbon nanotubes from ruthenium nanoparticles

In this paper, we report that ruthenium is an active and efficient catalyst for growth of single-walled carbon nanotubes (SWNTs) by a chemical vapor deposition (CVD) process for the first time. High density random and horizontally superlong well-oriented SWNTs on substrate can be fabricated via CH₄ or EtOH as carbon source under suitable conditions. Scanning and transition electron microscopy investigations, Raman spectroscopy and atomic force microscopy measurements show the tubular structure, the high crystallinity, and the properties of the grown nanotubes. The results show that the SWNTs from ruthenium have better structural uniformity with less defects and provides an alternative catalyst for SWNTs growth. The successful growth of SWNTs by Ru catalyst provides new experimental information for understanding the growth mechanism of SWNTs, which may be helpful for their controllable synthesis.     

Random telegraph noise in carbon nanotubes and peapods

The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs) and C₆₀-filled SWNTs (the so-called peapods). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with ballistic electrons. On the other hand, the noise for peapods can be attributed to the motion of C₆₀ molecules in hollow space of SWNTs.     

Field—ion microscopy observation of single—walled carbon nanotubes

Field-ion microscopy(FIM),a tool for surface analysis with atomic resolution,has been employed to observe the end structure of single-walled carbon nanotubes(SWCNTs).FIM images revealed the existence of open SWCNT ends,Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them.Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles.Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.     

Synthesis of single-walled carbon nanotubes in oxy-fuel inverse diffusion flames with online diagnostics

A novel technique for synthesis of single-walled carbon nanotubes (SWNTs) in diffusion flames is presented, as is a diagnostic tool that can provide online information about nanotube size, number density, and purity. An inverse diffusion flame with a high stoichiometric mixture fraction (Z_st) is used to produce SWNTs with an average length of 1 μm. The high Z_st flame allows nanotubes to be produced in a fuel-rich region that is void of soot and polycyclic aromatic hydrocarbons (PAH). In addition, by operating as an inverse diffusion flame the carbon nanotubes (CNTs) are not exposed to oxygen and thus, can be collected downstream. Consequently, this flame provides a potential approach to large-scale synthesis of pure SWNTs. In addition, a differential mobility analyzer (DMA) is employed as an online diagnostic tool. The DMA can distinguish between excess catalyst particles and CNTs due to the differences in their electrical mobilities. Thus, the presence of CNTs as well as their size, number density, and purity relative to excess catalyst particles can be identified from the size distribution of the aerosol sampled downstream of the flame. This tool allows for rapid identification of the effect of changing process variables on nanotube growth and thus, the production process can be quickly optimized.     

Sonocatalytical degradation enhancement for ibuprofen and sulfamethoxazole in the presence of glass beads and single-walled carbon nanotubes

Sonocatalytic degradation experiments were carried out to determine the effects of glass beads (GBs) and single-walled carbon nanotubes (SWNTs) on ibuprofen (IBP) and sulfamethoxazole (SMX) removal using low and high ultrasonic frequencies (28 and 1000 kHz). In the absence of catalysts, the sonochemical degradation at pH 7, optimum power of 0.18 W mL⁻¹, and a temperature of 15 °C was higher (79% and 72%) at 1000 kHz than at 28 kHz (45% and 33%) for IBP and SMX, respectively. At the low frequency (28 kHz) H₂O₂ production increased significantly, from 10 μM (no GBs) to 86 μM in the presence of GBs (0.1 mm, 10 g L⁻¹); however, no enhancement was achieved at 1000 kHz. In contrast, the H₂O₂ production increased from 10 μM (no SWNTs) to 31 μM at 28 kHz and from 82 μM (no SWNTs) to 111 μM at 1000 kHz in the presence of SWNTs (45 mg L⁻¹). Thus, maximum removals of IBP and SMX were obtained in the presence of a combination of GBs and SWNTs at the low frequency (94% and 88%) for 60 min contact time; however, >99% and 97% removals were achieved for 40 and 60 min contact times at the high frequency for IBP and SMX, respectively. The results indicate that both IBP and SMX degradation followed pseudo-first-order kinetics. Additionally, the enhanced removal of IBP and SMX in the presence of catalysts was because GBs and SWNTs increased the number of free OH radicals due to ultrasonic irradiation and the adsorption capacity increase with SWNT dispersion.     

单壁碳纳米管中的金属-半导体转变与对称性

报道了最近作者对受压扶手椅形单壁碳纳米管中的金属-半导体转变机理的理论研究。这种转变在两种因素的共同作用下得以发生，即外加压力造成碳纳米管镜像对称破缺，以及被压碳纳米管两侧原子发生成键相互作用．作者还进一步揭示了发生这种转变的普遍机制：只要将单壁碳纳米管中两套原来等价的子晶格变得可以区分(对称性破缺)，在费米能附近就会产生能隙．     

On the size of small single-walled carbon nanotubes

We derive a formula relative to the diameter/length ratio of a small single-walled carbon nanotube by means of calculations referring to Fermi energy. These calculations arise from the consideration of the Fermi's velocity for a multiwalled carbon nanotube.     

Well-defined single-walled carbon nanotube fibers as quantum wires: Ballistic conduction over micrometer-length scales

We report quasi-ballistic conduction in single-walled carbon nanotube (SWNT) fibers at room temperature, with a measured mean free path of 1.0–2.6 μm. The dynamic submersion of vertical SWNT fibers into liquid mercury (Hg) electrode shows plateaus and steps indicative of quasi-ballistic electron transport. This response is described with a newly developed network model that uses surface impurities to simplify the parallel conducting channels. The quasi-ballistic SWNT fibers exhibit a resistance per unit length of 2.5–6.5 kΩ/μm and a mean free path exceeding 1 μm, a length longer than typical via dimensions in existing Si-chip technologies. These results highlight that SWNT fiber conductivity can be enhanced by increasing the metallic to semiconducting SWNT ratio and reducing the surface impurities.     

Flame synthesis of single-walled carbon nanotubes

Flames offer potential for synthesis of carbon nanotubes in large quantities at considerably lower costs than that of other methods currently available. This study aims to examine conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single-walled nanotubes have been observed in the post-flame region of a premixed acetylene/oxygen/15 mol% argon flame operated at 6.7 kPa with Fe(CO)₅ vapor used as a source of metallic catalyst necessary for nanotube growth. Thermophoretic sampling and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), giving a resolution of formation dynamics within the flame system. Catalyst particle formation and growth is observed to dominate the immediate post-flame region (10–40 mm HAB). Nanotubes were observed to be present after 40 mm HAB with nanotube inception occurring as early as 30 mm HAB. Between 40 and 70 mm HAB, nanotubes are observed to coalesce into clusters. A nanotube formation ‘window’ is evident with formation limited to fuel equivalence ratios between 1.5 and 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material is observed between these lower and upper limits. High-resolution TEM and Raman spectroscopy revealed nanotube bundles with each nanotube being single-walled with diameters between 0.9 and 1.5 nm.