Covalent functionalization of multi-walled carbon nanotubes by lipase

Lipase from Candida rugosa was covalently anchored onto acid-treated multi-walled carbon nanotubes (MWNTs) through a self-catalytic mechanism. A variety of characterization techniques including FTIR, Raman spectroscopy, and XPS were employed to demonstrate the formation of the ester linkage between lipase and MWNTs. The MWNTs-lipase biocomposites showed significantly increased solubility in some common-used organic solvents, such as THF, DMF and chloroform. This study may offer a novel and facile route for covalent modification of carbon nanotubes, and expand the potential utilization of both lipases and MWNTs in the fields of biocatalyst and biosensor.     

170keV质子辐照对多壁碳纳米管薄膜微观结构与导电性能的影响

碳纳米管具有优异的导电性, 是未来电子元器件的理想候选材料, 应用前景广阔. 针对碳纳米管在空间电子元器件的应用需求, 本文研究了170 keV质子辐照对多壁碳纳米管薄膜微观结构与导电性能的影响. 采用扫描电子显微镜(SEM)、拉曼光谱仪(Raman)、X射线光电子能谱仪(XPS)及电子顺磁共振谱仪(EPR)对辐照前后碳纳米管试样的表面形貌和微观结构进行分析; 利用四探针测试仪对碳纳米管薄膜进行导电性能分析. SEM分析表明, 170 keV质子辐照条件下, 当辐照注量高于5×10¹⁵ p/cm² (protons/cm²)时, 碳纳米管薄膜表面变得粗糙疏松, 纳米管发生明显弯曲、收缩及相互缠结现象. 目前, 质子辐照纳米管发生的收缩现象被首次发现. 基于Raman和XPS分析表明, 170 keV质子辐照后碳纳米管的有序结构得到改善, 且随辐照注量增加, 碳纳米管的有序结构改善明显. 结构的改善主要是由于170 keV质子辐照碳纳米管所产生的位移效应导致缺陷重组. EPR分析表明, 随着辐照注量的增加, 碳纳米管薄膜内的非局域化电子减少. 利用四探针测试分析表明, 碳纳米管薄膜的导电性能变差, 这是由于170 keV质子辐照导致碳纳米管薄膜中的电子特性及形态发生改变. 本文研究结果有助于利用质子辐照对碳纳米管膜结构和性能进行调整, 从而制备出抗辐射的纳米电子器件.     

The effect of chemical treatment on the crystallinity of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were chemically treated using nitric acid solution for different time. Quantitative analysis of the crystallinity of the MWCNTs was performed by wide-angle X-ray diffraction (WAXD). The WAXD patterns were deconvoluted into the crystalline diffraction peaks and the amorphous scattering peaks. The introduction of a correction factor for the integrated peak intensity can enhance the computational accuracy of the crystallinity. With increasing the chemical treatment time, the crystallinity of MWCNTs first increases, and then decreases. When the chemical treatment time is equal to 2 h, the crystallinity of MWCNTs reaches the maximum of 85.9%. Moreover, the degree of order in the structures of chemically treated MWCNTs was further studied by thermogravimetric analysis (TGA) and high-resolution transmission electron microscopy (HRTEM). It was found that the external walls of chemically treated MWCNTs with high crystallinity consist of a series of perfectly continuous and straight graphite layers.     

A study on the electrical conductivity of multi-walled carbon nanotube aqueous solution

The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution.     

Modification of multi-walled carbon nanotubes for electric double-layer capacitors: Tube opening and surface functionalization

Multi-walled carbon nanotubes (MWCNTs) obtained opening the closed ends and using surface functionalization by means of a combination of partial oxidation in air and chemical modifications are characterized systematically in 0.3 M H₂SO₄ between 0 and 1.0 V, and these nanotubes were planned to be used as electrode materials in electric double-layer capacitors (EDLCs). Opening of MWCNTs, clearly observed by means of transmission electron microscopy (TEM), can be easily achieved by the partial oxidation in air through a seven-step temperature program identified by thermogravimetric/differential thermal analyses (TG/DTA). An increase in 175% specific capacitance is obtained for the MWCNTs, partially oxidized in air and chemically modified in H₂SO₄+HNO₃. The temperature-programmed desorption (TPD) data showed that evolutions of CO and CO₂ are, respectively, promoted by the application of partial oxidation in air and chemical modification in H₂SO₄+HNO₃. The above increase in specific capacitance for modified MWCNTs is attributed to an obvious increase in the BET surface area (double-layer capacitance) and the density of oxygen-containing surface functional groups (pseudocapacitance).     

The effect of multi-walled carbon nanotube pretreatments on the electrodeposition of Ni-MWCNTs coatings

Two different chemical treatments were performed on multi-walled carbon nanotubes (MWCNTs), namely functionalization, and shortening-functionalization processes. Then, nickel-MWCNTs coatings were co-electrodeposited. The results showed that the chemically shortened nanotubes were behaved as inert particles, and embedded into the nickel matrix, whilst the long functionalized nanotubes showed metallic behavior and during electrodeposition, they were incorporated into the nickel matrix. In similar plating condition, the amount of co-deposited shortened nanotubes was more than elongated ones. Furthermore, it was revealed that the pretreatment of nanotubes significantly affected the microstructure, surface morphology, hardness and corrosion resistance of deposited coatings.     

Effect of plasma treatment on electrical conductivity and Raman spectra of carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were treated with a radio-frequency discharge. We found that MWCNTs showed opposite trends in electrical conductivity when treated with oxygen and hydrogen plasmas. MWCNTs showed enhanced electrical conductivity when placed at cathode with oxygen plasma treatment, whereas MWCNTs treated at positive column did not show such a trend. In contrast, the conductivity of MWCNTs dropped sharply with hydrogen plasma treatment. The measured conductivity trends of MWCNTs are correlated with observed Raman spectral shift. The possible mechanisms of the change in electrical conductivity in plasma-treated MWCNTs are discussed.     

Kondo效应对磁杂质碳纳米管电输运特性的影响

从碳纳米管中Kondo效应的影响出发, 在有限温度下采用Anderson模型表征碳纳米管/磁杂质系统, 利用Landauer公式对磁杂质碳纳米管的电导和热电势进行研究, 得出和实验结果一致结论. 关键词： Kondo效应 碳纳米管 电输运特性     

Effects of corona discharge on the surface structure, morphology and properties of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were modified by corona discharge and then heat treated in the air. The influences of corona discharge parameters such as treatment time and processing power were investigated. The results of energy dispersive X-ray analysis (EDX) and thermogravimetric analysis (TGA) indicated the introduction of oxygen-containing functional groups onto the surface of the MWCNTs after heat treatment. The water contact angle tests showed that the hydrophobicity of the MWCNTs was decreased to some extent. The static water contact angle was reduced from 146° to 122° when the time of the corona discharge treatment reached 3 min at the processing power of 200 W. The enhanced thermomechanical and mechanical properties of epoxy nanocomposites filled with the corona discharge treated MWCNTs were observed. The modified MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between the treated MWCNTs and epoxy.     

Effects of dielectric barrier discharge in air on morphological and electrical properties of graphene nanoplatelets and multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) have been functionalized by dielectric barrier discharge (DBD) in air. The extent of functionalization of MWCNTs and GNPs reaches a maximum at the delivered discharge energy of 720 and 240 J mg⁻¹, respectively. Further exposure to plasma leads to reduction of functional groups from the surface of the treated nanomaterials. It has also been demonstrated that DBD plasma does not produce dramatic structural changes in MWCNTs, while flakes of the treated GNPs become thinner and smaller in the lateral size. Conductive thin films, obtained by drop casting a solution of the treated nanomaterials in N-methyl-1-pyrrolidone on poly(methyl methacrylate) substrate, show significantly lower sheet resistance.     

Effect of ultrasonication time on microstructure,thermal conductivity,and viscosity of ionanofluids with originally ultra-long multi-walled carbon nanotubes

The stability along with thermal and rheological characteristics of ionanofluids (INFs) profoundly depend on the protocol of preparation. Therefore, in this work, the effect of ultrasonication time on microstructure, thermal conductivity, and viscosity of INFs containing 0.2 wt% of originally ultra-long multi-walled carbon nanotubes (MWCNTs) and four different ILs, namely 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium thiocyanate, or 1-ethyl-3-methylimidazolium tricyanomethanide, was studied. The INFs were obtained by a two-step method using an ultrasonic probe. The ultrasonication process was performed for 1, 3, 10, or 30 min at a constant nominal power value of 200 W. The obtained results showed that for the shortest sonication time, the highest thermal conductivity enhancement of 12% was obtained. The extended sonication time from 1 to 30 min caused the cutting of MWCNTs and breaking the nanoparticle clusters, leading to a decrease in the average length of the nanotube bundles by approx. 70%. This resulted in a decline in thermal conductivity even by 7.2% and small deviations from the Newtonian behavior of INFs.     

The effect of carbon nanotubes on the corrosion and tribological behavior of electroless Ni-P-CNT composite coating

In this study, Ni-P-CNT composite coating was successfully deposited on the surface of copper by electroless plating. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the coatings. The wear behavior of the coatings was investigated using a pin-on-disk test rig and subsequently friction coefficient data were reported. The corrosion behavior of the Ni-P and Ni-P-CNT coated specimen were evaluated through polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl aqueous solution at the room temperature. The results indicated that the incorporation of carbon nanotubes (CNTs) in the coating improved both tribological behavior and corrosion resistance. These improvements have been attributed to superior mechanical properties, unique topological structure and high chemical stability of nanotubes.     

Grafting modification and structural degradation of multi-walled carbon nanotubes under the effect of ultrasonics sonochemistry

Polyvinyl pyrrolidone (PVP) grafted multi-walled carbon nanotubes (MWCNTs) were prepared by the degradation effect of ultrasonics sonochemistry. PVP macroradicals formed by sonochemical degradation of a PVP solution were trapped by MWCNTs and grafted onto the surface of MWCNTs. It was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis that the PVP was covalently bonded on the MWCNTs. Transmission electron microscopy showed nanotubes in the grafted samples were shorter than the original MWCNTs due to the crushing effect of ultrasonics sonochemistry. Both the decrease in length of the MWCNTs and the PVP grafted onto them are beneficial for their dispersion in solvents.     

The effect of catalyst nanoparticle preparation techniques on the structure of carbon nanotubes

The effect of the composition, deposition method, and preliminary annealing temperature of catalyst thin films on the structure of catalyst nanoparticles and carbon nanotubes synthesized by CVD with a single acetylene burst was studied. A catalyst preparation technique was found that yields the narrowest distribution of the diameters of nanoparticles and of single-wall carbon nanotubes grown on them.     

Behavior of multi-walled carbon nanotubes on the porosity and microstructure of cement-based materials

The porosity and microstructure of a Portland cement-multi-walled carbon nanotube composite were investigated. Multi-walled carbon nanotubes (CNTs), up to 1 wt.% of cement, synthesized by infusion chemical vapor deposition, and Portland cement type I (PC) were used to produce pastes with a water to cement ratio of 0.5. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to characterize Portland cement-CNTs systems. MIP analysis of the results indicates that total porosity of the mixes with CNTs was found to decrease with increasing CNTs content. Moreover, an important effect of additional CNTs was a reduction in the number of mesopores, while SEM technique showed dispersion of CNTs between the hydration phases of Portland cement pastes.     

Influence of functionalization on mechanical and electrical properties of carbon nanotube-based silver composites

In this study, we have extended the molecular-level mixing method to fabricate multiwall carbon nanotube (CNT)-reinforced silver nanocomposites. The multiwall nanotubes used in the synthesis process were dispersed by two ways viz. covalent and non-covalent functionalization techniques. To elucidate the comparative effects of functionalization, structural, mechanical and electrical properties of nanocomposites were evaluated before and after sintering. The structural characterization revealed that the nanotubes were embedded, anchored and homogenously dispersed within the silver matrix. Hardness and Young’s modulus of nanotube-reinforced nanocomposite were increased by a factor of 1–1.6 times than that of pure silver, even before and after the sintering. Covalently functionalized nanotube-based composites have shown more enhanced mechanical properties. The CNT reinforcement also improved the electrical conductivity of low-conducting nanosilver matrix before sintering. Non-covalently functionalized nanotube-based nanosilver composites showed more increased electrical conductivity before sintering. But a negative reinforcement effect was observed in high-conducting bulk silver matrix after the sintering. Thus, covalent functionalization might be appropriate for mechanical improvement in low-strength materials. However, non-covalent functionalization is suitable for electrical enhancement in low-conducting nanomaterials.     

The growth of multi-walled carbon nanotubes on natural clay minerals (kaolinite, nontronite and sepiolite)

The suitability of clay minerals - kaolinite, nontronite and sepiolite - is studied for synthesis of nanocomposites based on carbon nanotubes. Particles of iron were used as catalysts. Prior to synthesis, kaolinite and sepiolite were doped by the catalytically active metal, whereas in the case of nontronite the presence was used of this metal in the matrix of this mineral. Synthesis of CNTs was performed by hot filament chemical vapor deposition method. The produced nanocomposites were examined by transmission and scanning electron microscopies and energy dispersive X-ray spectroscopy. The experiment verified the potential of the three microcrystalline phyllosilicates for the growth of carbon nanotubes. Under the same technology conditions, the type of catalyst carrier affects the morphology and structure of the nanotube product markedly.     

Coating of carbon nanotubes on flexible substrate and its adhesion study

The primary goal of this project was to develop a flexible transparent conductor with 100 Ω/sq and 90% transmittance in the wavelength range of 400-700 nm on a flexible substrate. The best result achieved so far was 110 Ω/sq at 88% transmittance using purified single-walled carbon nanotubes (SWNTs) coated on a polyethylene naphthalate (PEN) substrate. The secondary goal was to simplify the overall coating procedure; we successfully reduced the process from five (prior art method) to three steps utilizing a sonication method. We also found that the use of metallic SWNTs significantly improved the conductivity and transmittance compared with the use of mixed SWNTs, i.e., unseparated SWNTs. Furthermore, a possible adhesion mechanism between SWNTs and the surface of PEN was studied; we concluded that a π-π stacking effect and a hydrophobic interaction are the major contributing factors for SWNTs to adhere to the surface of the substrate.     

镍离子对DNA结构和导电性的影响

在碱性环境下,向DNA溶液中加入较低浓度的镍离子制备了金属DNA （M-DNA）,并分别对单根DNA和M-DNA的导电性进行了测量.结果表明,二者均表现出半导体性质;随镍离子浓度的增加导电性明显增强,伏特间隙减小;当镍离子浓度超过0.1 mmol/L时,DNA的电导几乎不随镍离子浓度变化.在中性环境下向DNA溶液中加入较高浓度的镍离子,实现了DNA从右手到左手螺旋结构的转变.利用STM观察到了左手螺旋结构的Z-DNA,Z构象可以分辨出大沟与小沟,并且螺旋结构不均匀,伴有局部的解旋和无序化;单根Z-DNA的导电性明显减弱.DNA,M-DNA,Z-DNA的电导大小关系为G_M-DNA>G_DNA>G_Z-DNA.通过紫外吸收和Raman光谱测量发现,使DNA发生右手到左手螺旋结构转变的镍离子浓度约为1.7 mol/L. 关键词： 镍离子 M-DNA Z-DNA 导电性     

The thermal effect on vibration and instability of carbon nanotubes conveying fluid

Based on the theory of thermal elasticity mechanics, an elastic Bernoulli–Euler beam model is developed for vibration and instability analysis of fluid-conveying single-walled carbon nanotubes (SWNTs) considering the thermal effect. Results are demonstrated for the dependence of natural frequencies on the flow velocity as well as temperature change. The influence of temperature change on the critical flow velocity at which buckling instability occurs is investigated. It is concluded that the effect of temperature change on the instability of SWNTs conveying fluid is significant.