Separation of surfactant functionalized single-walled carbon nanotubes via free solution electrophoresis method

This work presents the application of the free solution electrophoresis method (FSE) in the metallic / semiconductive (M/S) separation process of the surfactant functionalized single-walled carbon nanotubes (SWCNTs). The SWCNTs synthesized via laser ablation were purified through high vacuum annealing and subsequent refluxing processes in aqua regia solution. The purified and annealed material was divided into six batches. First three batches were dispersed in anionic surfactants: sodium dodecyl sulfate (SDS), sodium cholate (SC) and sodium deoxycholate (DOC). The next three batches were dispersed in cationic surfactants: cetrimonium bromide (CTAB), benzalkonium chloride (BKC) and cetylpyridinium chloride (CPC). All the prepared SWCNTs samples were subjected to FSE separation process. The fractionated samples were recovered from control and electrode areas and annealed in order to remove the adsorbed surfactants on carbon nanotubes (CNTs) surface. The changes of the van Hove singularities (vHS) present in SWCNTs spectra were investigated via UV-Vis-NIR optical absorption spectroscopy (OAS).     

Purification and fractionation of single-walled carbon nanotubes

This study presents the approach to the purification and subsequent metallic/semiconductive (M/S) fractionation of single-walled carbon nanotubes (SWCNTs) with diameter from 1.04 to 1.60 nm produced via laser ablation. SWCNTs were purified through 3-fold refluxing processes in nitric acid followed by the multiple washings with sodium hydroxide and hydrochloric acid. The purified-annealed SWCNTs sample was divided into seven batches. One batch was dispersed in acetone as a reference sample. Each of the remaining batches were dispersed in one of the following surface agents: sodium dodecyl sulfate, sodium cholate acid (SCA), sodium deoxycholate, cetrimonium bromide, cetylpyridinium chloride, and benzalkonium chloride (BKC). SWCNT suspensions were fractionated via free solution electrophoresis technique. The recovered fractions from electrode and control areas were analyzed via optical absorption spectroscopy in UV–Vis–NIR range to evaluate the efficiency of the separation process. Raman spectroscopy was applied to analyze the purity of the samples. The catalyst content was estimated by atomic absorption spectroscopy. The morphology of the investigated samples was observed via high-resolution transmission electron microscopy. This contribution clearly shows that among the investigated surfactants there are two promising candidates (SCA and BKC) which can efficiently enrich the bulk sample in one electronic type of carbon nanotubes when FSE is applied.     

Surfactant-nanotube interactions in water and nanotube separation by diameter: atomistic simulations

A non-destructive sorting method to separate single-walled carbon nanotubes (SWNTs) by diameter was recently proposed. By this method, SWNTs are suspended in water by surfactant encapsulation and the separation is carried out by ultracentrifugation in a density gradient. SWNTs of different diameters are distributed according to their densities along the centrifuge tube. A mixture of two anionic surfactants, namely sodium dodecylsulfate (SDS) and sodium cholate (SC), presented the best performance in discriminating nanotubes by diameter. Unexpectedly, small diameter nanotubes are found at the low density part of the centrifuge tube. We present molecular dynamics studies of the water-surfactant-SWNT system to investigate the role of surfactants in the sorting process. We found that surfactants can actually be attracted towards the interior of the nanotube cage, depending on the relationship between the surfactant radius of gyration and the nanotube diameter. The dynamics at room temperature showed that, as the amphiphile moves to the hollow cage, water molecules are dragged together, thereby promoting the nanotube filling. The resulting densities of filled SWNT are in agreement with measured densities.     

Pt/CNTs电催化剂制备的UV-Vis、FTIR和XRD光谱分析

采用在乙二醇溶液中添加十二烷基硫酸钠(SDS)作为稳定剂的调变乙二醇还原法,制备了高分散的碳纳米管(CNTs)负载Pt电催化剂Pt/CNTs。利用紫外-可见(UV-Vis)、傅里叶变换红外(FTIR)和X射线衍射(XRD)光谱研究了催化剂的制备过程和结构,考察了Pt/CNTs制备过程中SDS的添加对其结构和甲醇电催化氧化活性的影响。结果表明,在乙二醇溶液中PtCl2-₆与SDS形成了配合物,PtCl2-₆能够被乙二醇完全还原;超声处理后的CNTs表面接上了含氧基团,有利于Pt粒子的吸附,催化剂上不残留有SDS;Pt/CNTs电催化剂具有典型的面心立方结构,添加SDS制备的Pt/CNTs-2电催化剂Pt高度分散,粒径更小,达4.5 nm。循环伏安(CV)测试结果表明,添加SDS制备的Pt/CNTs-2电催化剂比传统乙二醇还原法制备的Pt/CNTs-1具有更高的甲醇电催化氧化活性。     

Comparative study on modification of single wall carbon nanotubes by sodium dodecylbenzene sulfonate and melamine sulfonate superplasticiser

In this work, the results of synthesis and characterization of single wall carbon nanotubes (SWCNTs) functionalized by two surfactants (sodium dodecylbenzene sulfonate and melamine sulfonate superplasticiser) have been presented. The properties of pristine and modified SWCNTs have been compared by different techniques: Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Raman analysis reveals the changes in vibrational spectra of SWCNTs after modification by different surfactant molecules. FTIR analysis has shown the presence of sulfonate group which is strong evidence for nanotube modification. AFM analysis has shown separation of big single wall carbon nanotube bundles into thin bundles of them.     

Vibrational analysis of double-walled carbon nanotubes with inner and outer nanotubes of different lengths

In this study, the Euler-Bernoulli beam model is used to analyze the resonant vibration of double-walled carbon nanotubes (DWCNTs) with inner and outer nanotubes of different lengths. The resonant properties of DWCNTs with different inner and outer nanotube lengths are investigated in detail using this theoretical approach. The resonant vibration is significantly affected by the vibrational modes of the DWCNTs, and by the lengths of the inner and outer nanotubes. For an inner or outer nanotube of constant length, the vibrational frequencies of the DWCNTs increase initially and then decrease as the length of another nanotube increases. A design for nanoelectromechanical devices that operate at various frequencies can be realized by controlling the length of the inner and outer nanotubes of DWCNTs. This investigation may be helpful in applications of carbon nanotubes such as high frequency oscillators, dynamic mechanical analysis and mechanical sensors.     

Effect of carbon nanotubes dispersion on morphology, internal structure and thermal stability of electrospun poly(vinyl alcohol)/carbon nanotubes nanofibers

The current work reports the effect of multi walled carbon nanotubes and single walled carbon nanotubes dispersion on morphological, structural and thermal degradation of electrospun poly(vinyl alcohol) (PVA)/carbon nanotubes (CNTs) dispersed in sodium dodecyl sulfate (SDS) (PVA/CNTs–SDS) composites nanofibers. (PVA/CNTs–SDS) nanocomposites fibers were elaborated using the traditional electrospinning process to disperse and align CNTs into the fibers, especially for low CNTs loading fraction: 0.3 and 0.7 wt%. The morphology of the electrospun fibers was studied using the scanning electronic microscopy. The average diameter of the fibers changes significantly after the incorporation of the CNTs in the PVA. Furthermore, Fourier transform infrared spectroscopy elucidated the effect of CNTs on the crystallization of the PVA which was confirmed by X-ray diffraction analysis. Thermogravimetric analysis showed that the thermal stability of the composite fibers depends on the loading fraction and on the type of carbon nanotubes.     

Modeling on ion rejection using membranes comprising ultra-small radii carbon nanotubes

In this paper, we investigate the complete ion rejection using carbon nanotube membranes comprising ultra-small radii nanotubes. Three acceptance radii for a water molecule, a sodium ion and a chloride ion are determined assuming the continuous approximation. Given the acceptance radii, we may confine the scope of the nanotube radius so that only water molecules can pass through but the heavier sodium and chloride ions are repulsed from the nanotube ends. We assume that the collective motion of water molecules inside a sufficiently long nanotube is driven by atomic vibrations so that classical phonon theory might be used to deduce the average water transit time inside the nanotube for ion rejection. We predict that for carbon nanotube membranes comprising nanotubes of radii lying between 3.4 and 3.9 ?, only water molecules will pass through, and sodium and chloride ions will not, which together using phonon theory, we deduce that the smaller the nanotube radius, the lower the average water transit time and the higher the efficiency of the membrane for ion rejection purposes. The present theoretical approach has the merit of rapid computational times and indicates those nanotube radii where future experimental work might be focussed.     

Mineralization of surfactant functionalized multi-walled carbon nanotubes (MWNTs) to prepare hydroxyapatite/MWNTs nanohybrid

Multi-walled carbon nanotubes (MWNTs) were well dispersed in water and functionalized by adding surface active agent (i.e., sodium dodecyl sulfate, SDS). Subsequently, biomimetic mineralization was carried out on the SDS functionalized MWNTs by using an alternate soaking process (ASP) in the Ca/P solutions. As-prepared samples were characterized by transmission electron microscope, infrared spectrum and X-ray diffraction. The results show that nano-HA crystals were formed on the SDS functionalized MWNTs and the mineralized MWNTs remained a dispersing state. As-prepared HA-MWNTs nanohybrid combining the osteconductive property of HA and the excellent mechanical property of MWNTs will provide a promising material for bone tissue engineering.     

水溶性聚合物与十二烷基硫酸钠相互作用的1H NMR研究

用¹H NMR方法研究了分别在2 g/L聚乙烯吡咯烷酮(PVP)和2 g/L聚乙烯醇（PVA）存在下，一系列不同浓度的十二烷基硫酸钠(SDS)溶液. 二维NOESY实验表明，SDS在浓度为2.5 mmol/L时形成胶束，且PVP被增溶到胶束内部；当SDS浓度低于2.5 mmol/L时，PVP与SDS之间没有明显的相互作用. 自旋-自旋弛豫时间的测量结果支持这一结论. 实验中没有检测到PVA与SDS之间的相互作用.     

Facile fabrication and optical properties of novel Pb(OH)Cl nanotubes

Uniform Pb(OH)Cl nanotubes were synthesized for the first time through a reverse micelles system. The system was consisting of C₁₂E₉ as a surfactant, n-pentanol as a cosurfactant, hexamethylene as the continuous oil phase and lead acetate or sodium chloride solution as the dispersed aqueous phase. The obtained Pb(OH)Cl nanotubes have an average outer diameter of 60 nm, inner diameter of about 40 nm, and an length up to 3 μm as TEM picture showed. And the range of the nanotube diameter is from 50 nm to 70 nm. XRD result indicated that Pb(OH)Cl crystallized in an orthorhombic phase. Photoluminescent (PL) spectrum showed that the product emit in near ultraviolet region and visible region at 335 nm and 439 nm respectively. The experimental results show that reaction temperature have effect on the shape of Pb(OH)Cl nanotubes. A possible formation mechanism was also discussed.     

高度有序的TiO2纳米管在有机电解液中的制备及碳掺杂TiO2纳米管的性能

"采用电化学阳极氧化法,在含有氟离子的有机电解液中,使纯钛表面形成一层高度有序的TiO2纳米管阵列．通过控制不同的阳极氧化电压和时间,可以得到形貌不同的TiO2纳米管．最长的TiO2纳米管接近60 1m,长径比约为600．TiO2纳米管在不同的温度(450、550和650 ℃)下焙烧2 h,采用SEM、XRD、EDS和UV-Vis分光光度仪对样品进行表征．X射线衍射仪测试结果表明制备的TiO2纳米管是无定型的,当在较高的温度下焙烧时,其结构由无定型转变为锐钛型和金红石型．EDS微量分析表明TiO2纳米管中     

The kinetics of solvolysis of phosphorus acid esters in the ternary sodium dodecyl sulfate-ethylene glycol -La micellar system

By methods of conductivity measurements, micellization of sodium dodecyl sulfate in ethylene glycol at the concentration above 0.18 M is shown. The La³⁺ ion catalysis of solvolysis of phosphorus acid ester both in the absence of surfactant and in the micellar sodium dodecyl sulfate solution in ethylene glycol is found. The influence of the other lanthanide ions on the kinetics is also studied. The La³⁺ and Pr³⁺ are found to exert an identical effect while Sm³⁺ is less effective. By methods of polarizing microscopy, the formation of liquid crystalline mesophase at high lanthanum (tris(dodecyl)sulfate concentrations in ethylene glycol is revealed. The investigation of the catalytic effect of the sodium dodecyl sulfate -La³⁺ (3 : 1 molar) composition has shown a sharp acceleration of the reaction at high surfactant concentration.     

Synthesis and characterization of highly-ordered barium-strontium titanate nanotube arrays fabricated by sol—gel method

Highly uniformed barium-strontium titanate nanotube arrays were fabricated using a porous anodic aluminum oxide template from a barium-strontium titanate sol--gel solution. Electron microscope results showed that nanotubes with uniform length and diameter were obtained. The diameters and lengths of these nanotubes were dependent on the pore diameter and the thickness of the applied anodic aluminum oxide template. High resolution transmission electron microscopy and the selected-area electron diffraction pattern investigations demonstrated the perovskite structure and the polycrystalline of the fabricated barium-strontium titanate nanotubes. The characterization of the electrical and dielectric properties had also been made. Compared to thin film material, the intrinsic leakage current density is almost the same. Besides, at 30~℃, the dielectric constant and dielectric loss of the fabricated nanotube is 80 and 0.027 at 1~MHz respectively.     

碳纳米管复合吸波涂层微波吸收性能的模拟计算

如何利用碳纳米管复合吸波涂层的参数进行吸波性能优化是电磁屏蔽研究的热点之一.涂层参数对吸波性能影响的研究主要停留在实验探索阶段,而碳纳米管的结构参数对吸波性能影响的研究鲜有报道.因此,从微观结构层次研究涂层参数对吸波性能的影响有重要意义.基于多壁碳纳米管的等效电路,利用碳纳米管结构参数与等效电路各元件参数的关系,研究了碳纳米管损耗微波的机理,建立了碳纳米管结构参数与微波反射率的关系式.根据此关系式,利用Matlab软件模拟计算了碳纳米管管长、管径、涂层中碳纳米管的含量以及涂层厚度对微波反射率的影响.模拟计算结果表明:涂层的微波反射率随碳纳米管含量变化的模拟曲线与实验结果符合;碳纳米管含量和厚度是影响吸收峰位置和吸收强度的重要参量,而碳纳米管直径和长度是主要影响吸收峰强度的参量.     

The kinetics of solvolysis of phosphorus acid esters in the ternary sodium dodecyl sulfate-ethylene glycol -La3+ micellar system

By methods of conductivity measurements, micellization of sodium dodecyl sulfate in ethylene glycol at the concentration above 0.18 M is shown. The La³⁺ ion catalysis of solvolysis of phosphorus acid ester both in the absence of surfactant and in the micellar sodium dodecyl sulfate solution in ethylene glycol is found. The influence of the other lanthanide ions on the kinetics is also studied. The La³⁺ and Pr³⁺ are found to exert an identical effect while Sm³⁺ is less effective. By methods of polarizing microscopy, the formation of liquid crystalline mesophase at high lanthanum (tris(dodecyl)sulfate concentrations in ethylene glycol is revealed. The investigation of the catalytic effect of the sodium dodecyl sulfate -La³⁺ (3 : 1 molar) composition has shown a sharp acceleration of the reaction at high surfactant concentration.     

A study on photo-generated charges property in highly ordered TiO2 nanotube arrays

In this study TiO₂ nanotube arrays were fabricated by potentiostatic anodization of titanium sheet. The X-ray diffraction (XRD) pattern and field emission scanning electron microscopy (FE-SEM) image indicated the TiO₂ nanotube arrays were of pure anatase form and highly ordered. The properties of the photo-generated charges in the nanotube arrays were investigated by transient photovoltage (TPV) technique and surface photovoltage (SPV) technique based on lock-in amplifier with dc bias, in comparison with the commercial powder derived film. The separation processes of the photo-induced charges in the system of TiO₂ nanotubes on Ti have been demonstrated to be correlated with the incident light intensity, surface trapping states, and the interfacial electric field between Ti and TiO₂. The results also show that the highly ordered nanotube film could generate much stronger SPV responses under external electric field than the commercial powder derived film.     

Altering the catalytic activity of thin metal catalyst films for controlled growth of chemical vapor deposited vertically aligned carbon nanotube arrays

The growth rate and terminal length of vertically aligned carbon nanotube arrays (VANTAs) grown by chemical vapor deposition have been dramatically improved through pulsed KrF excimer laser pretreatments of multilayer metal catalyst films. Silicon wafers coated with Al, Mo, and Fe layers were laser processed in air with single laser shots of varying fluence through circular apertures, then heated to ∼750°C and exposed to acetylene and ferrocene containing gas mixtures typically used to grow vertically aligned nanotube arrays. In situ videography was used to record the growth kinetics of the nanotube arrays in both patterned and unpatterned regions to understand the changes in catalytic activity, growth rates, and termination of growth. The height of the patterned regions varied with fluence, with the most successful treatment resulting in 1.4 cm tall posts of nanotubes embedded in a 0.4 cm tall nanotube carpet. High-resolution transmission electron microscopy images from the nanotubes in the posts revealed fewer walls, smaller diameters, and a much narrower distribution of diameters compared to the nanotubes grown in the carpet. This information, along with data obtained from weighing the material from each region, suggests that pulsed laser processing can also significantly increase the areal density of VANTAs. Research sponsored by the Division of Materials Sciences and Engineering, U.S. Department of Energy.     

Length dependence of linear and nonlinear optical properties of finite-length BN（5,0） nanotube

In this paper, we investigate the length dependence of linear and nonlinear optical properties of finite-length BN nanotubes. The recently predicted smallest BN(5,0) nanotube with configuration stabilization is selected as an example. The energy gap and optical gap show the obvious length dependence with the increase of nanotube length. When the length reaches about 24 {\AA}, the energy gap will saturate at about 3.2 eV, which agrees well with the corrected quasi-particle energy gap. The third-order polarizabilities increase with the increase of tube length. Two-photon allowed excited states have significant contributions to the third-order polarizabilities of BN(5,0) nanotube.     

Growth of vertically aligned single crystal ZnO nanotubes by plasma-molecular beam epitaxy

Highly oriented and vertically aligned single crystalline ZnO nanotubes were fabricated on Al₂O₃ (0001) substrates by plasma-molecular beam epitaxy without employing any external metal catalysts or templates. Field emission scanning electron microscope images indicate that the regularly aligned ZnO nanotubes with uniform size distribution were obtained. The chimney-like single crystal ZnO nanotube was confirmed by the transmission electron microscope and selected area electron diffraction pattern of the single nanotube. The formation mechanism of the nanotubes was also described briefly.