Room-temperature ionic liquids/multi-walled carbon nanotubes/chitosan composite electrode for electrochemical analysis of NADH

An electrochemical sensing platform was developed based on the integration of room-temperature ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, BMIM·BF₄) and multi-walled carbon nanotubes (MWNTs) with polymeric matrix (chitosan, CHIT). The resulting composite were investigated and characterized by FTIR, TEM, SEM, EDS and electrochemical methods. The BMIM·BF₄/MWNTs/CHIT have good dispersibility in aqueous solution and can form a relative uniform film with unique structure. Electrochemical studies suggested that the BMIM·BF₄/MWNTs/CHIT composite system provided a synergistic augmentation on the voltammetric and amperometric behaviors of electrochemical oxidation of NADH, which indicated by the decrease of the peak potential of NADH oxidation and the improvement of amperometric response. Additionally, the BMIM·BF₄/MWNTs/CHIT/GC electrode shows good analytical performance such as low detection limit (0.06 μM), good regeneration and anti-fouling properties for determination of NADH. This nanomaterials-based composite may be used as electrochemical transducers and have potential application for designing a variety of NAD⁺-dependent electrochemical biosensors.     

Effect of the synthetic strategy on the non-covalent functionalization of multi-walled carbon nanotubes with polymerized ionic liquids

Multiwalled carbon nanotubes (MWCNTs) have been non covalently functionalized with various imidazolium-based polymerized ionic liquids (PILs). Two functionalization methods, starting from ionic liquid (IL) monomers containing a vinyl group, have been explored: a simple solution mixing of MWCNTs and PILs and the in situ polymerization. The resulting hybrid materials have been characterized by infrared and Raman spectroscopy, transmission electron microscopy, zeta potential measurement, thermogravimetric analysis and differential scanning calorimetry, and their dispersibility in various solvents has been evaluated to access the effect of the functionalization. The particle size analysis of MWCNTs/PILs agglomerates in various solvents is also reported. The in situ method allows a homogeneous coating of the MWCNT surface and thus a better dispersion of the nanotubes. The solution mixing method, for which diffusion limitations of the PILs into MWCNT aggregates should exist, does not allow a uniform surface functionalization. Finally, with protic IL monomers showing a tendency for hydrogen bonding, we have produced stable CNT/PIL organo- or hydrogel composites.     

Direct electrochemistry of guanosine on multi-walled carbon nanotubes modified carbon ionic liquid electrode

A multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was fabricated and used to investigate the electrochemical behavior of guanosine. CILE was prepared by mixing hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄), graphite powder and liquid paraffin together. The fabricated MWCNTs/CILE showed great electrocatalytic ability to the oxidation of guanosine and an irreversible oxidation peak appeared at 1.067 V (vs. SCE) with improved peak current. The electrochemical behavior of guanosine on the MWCNTs/CILE was carefully studied by cyclic voltammetry and the electrochemical parameters such as the charge transfer coefficient (α) and the electrode reaction standard rate constant (k_s) were calculated with the result as 0.66 and 2.94 × 10⁻⁴ s⁻¹, respectively. By using differential pulse voltammetry (DPV) as the detection method, a linear relationship was obtained between the oxidation peak current and the guanosine concentration in the range from 1.0 × 10⁻⁷ to 4.0 × 10⁻⁵ mol/L with the detection limit as 7.8 × 10⁻⁸ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine detection and the modified electrode showed good ability to distinguish the electrochemical response of guanosine and adenosine.     

离子液体在碳纳米管功能化及复合材料中的应用研究进展

离子液体具有低毒性、不易挥发、高的离子传导率、高的化学和热稳定性等特殊的性质,近几年在碳纳米管中的应用研究引起了广泛的关注.本文作者综述了离子液体近年来在碳纳米管的共价功能化、非共价功能化和聚合物复合材料中的应用研究进展,重点论述了其优势及展望.     

多壁碳纳米管的功能化及其应用研究

首先用混合酸纯化了原料碳纳米管,然后使用有机胺对碳纳米管进行了共价功能化。拉曼光谱和元素分析结果表明,烷基胺通过共价键接合于碳纳米管表面。从热重分析结果可知,碳纳米管表面附着有质量分数为6.9%～16.4%的有机物。透射电镜照片显示,在碳纳米管的外壳上覆盖有厚度为几纳米的无定形的材料,形成核—壳结构。力学性能结果表明,加入质量分数为1%的功能化纳米碳管可使环氧树脂的断裂韧性提高35%。     

Reduction of solubilized multi-walled carbon nanotubes

In this paper, the chemical reduction of solubilized multi-walled carbon nanotubes by LiAlH₄ was investigated. The amide groups on the nanotubes could be reduced to hydroxyl groups, which was confirmed by FTIR and XPS studies. The Raman spectroscopic investigation showed that the morphology of the nanotubes did not change after the reduction.     

Evidence for electro-chemical interactions between multi-walled carbon nanotubes and human macrophages

Carbon multi-walled nanotubes (MWCNTs) may have several dangerous effects on different cell systems, but the mechanisms responsible for their cytotoxicity are not well known yet. At present, very little is known about the electrical interactions between nanomaterials and cells. We aimed to verify whether MWCNT electrical properties could affect the so called “charge-sensitive” cell parameters, interacting with cellular electrical activity. Human macrophages were challenged with two fully characterised MWCNT samples, one tested as-prepared (MWCNT), the other one purified (by annealing at 2400 °C) and better electro-conductive (a-MWCNT). Our findings show that a-MWCNTs are less cytotoxic but possess a higher inflammatory potential, as compared to MWCNTs. Moreover, only annealed and better conductive MWCNTs affect significantly the mitochondrial membrane polarity, the intracellular pH and the reorganisation of cytoskeleton actin filaments, cell functions strictly dependent on electro-chemical mechanisms. Based on our results, there is evidence for electro-chemical interactions taking place between cell membranes and electro-conductive MWCNTs. Such a specific behaviour could have wide-range applications in the biomedical field, not only concerning those cellular systems (neuronal and bone cells) sensitive to electrical stimuli, but also other cell systems.     

Ni-deposited multi-walled carbon nanotubes by electrodeposition

Multi-walled carbon nanotubes (MWNTs), having a diameter around 100-200 nm, were used as host material for electrodeposition of Ni using a Ni plating bath containing homogeneously dispersed MWNTs. Ni-deposited or coated MWNTs with a skewered dumpling shape accumulated on the Cu cathode electrode. A model representing the growth process of these electrodeposits, which possess such a skewered dumpling shape, is presented. These electrodeposits were separated easily from the cathode electrode by ultrasonic irradiation in an acetone bath to yield a Ni-deposited or coated MWNTs powder. The amount of Ni deposited on the MWNTs can be controlled by selecting the appropriate electroplating conditions.     

Extraordinary aspects of bromo-functionalized multi-walled carbon nanotubes as initiator for polymerization of ionic liquid monomers

Two ionic liquid monomers, 1-(2-acryloyloxy-ethyl)-3-methyl-imidazol-1-ium iodide (AMImI) and 1-(2-acryloyloxy-ethyl)-3-methyl-benzoimidazol-1-ium iodide (AMBImI), were synthesized and polymerized through atom transfer radical polymerization (ATRP). Poly(AMImI)-grafted multi-walled carbon nanotubes (denoted as MWCNT-poly(AMImI)) could also be fabricated through “grafting from” method of ATRP using bromo-functionalized MWCNT (denoted as MWCNT–Br) as initiator but MWCNT-poly(AMBImI) could not. Based on the thermogravimetric analysis and high resolution transmission electron microscopy, AMBImI monomer has encapsulated the MWCNT–Br probably through the π-π and cation-π interactions invalidating the initiation capability of MWCNT–Br. Besides, by mixing AMBImI with MWCNT–Br directly at room temperature, the MWCNT–Br was coated with a thin layer of AMBImI, whereas MWCNT–Br could not physisorb AMImI. Both MWCNT-poly(AMImI) and AMBImI-encapsulated MWCNT were dispersed well in 1-methyl-3-propylimidazolium iodide ionic liquid.     

Characterization and application of hydrophobin-dispersed multi-walled carbon nanotubes

Hydrophobins are amphiphilic proteins with high surface activity, which can readily adsorb on interfacial surfaces, especially on hydrophobic surfaces. Based on their properties, we used the class I hydrophobin isolated from Grifola frondosa (HGFI) to disperse multi-walled carbon nanotubes (MWCNTs) in water. MWCNTs could be effectively dispersed by 30-min sonication in a 0.1 mg/ml HGFI solution. Optical absorption and transmission electron microscopy provide evidence for individually stable dispersed MWCNTs. X-ray photoelectron, Fourier transform infrared, and Raman spectroscopies and thermogravimetric analysis suggest that HGFI can non-covalently bind to MWCNTs through hydrophobic interaction, rendering them hydrophilic. A quartz crystal microbalance and immunological sandwich assay were used to demonstrate that the HGFI-coated MWCNTs can be used to immobilize human immunoglobulin G in solution.     

Oxidative biodegradation of single- and multi-walled carbon nanotubes

In this study we compare the biodegradation of both single-walled (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) using two different oxidative conditions. In particular, we demonstrate that oxidized multi-walled carbon nanotubes are highly degraded, although not to completeness when treated with horseradish peroxidase (HRP) in the presence of hydrogen peroxide.     

多壁碳纳米管的有机修饰与表征

为了增加多壁碳纳米管(MWCNTs)表面活性,通过浓H2SO4和浓HNO3处理过的MWCNTs与SOCl2回流进而与合成的N-乙基-3,6-二氨基咔唑反应,得到了有机修饰的MWCNTs.用傅立叶变换红外(FTIR)光谱对有机修饰的MWCNTs结构进行研究.研究结果结构表明:有机修饰的MWCNTs红外光谱在1617和16...     

Enhanced interactions between multi-walled carbon nanotubes and polystyrene induced by melt mixing

The effect of melt mixing on the interaction between multi-walled carbon nanotubes (MWNTs) and polystyrene (PS) matrix has been investigated. The interaction between pristine MWNTs and PS in solution was found to exist but not strong enough to allow MWNTs to be soluble in solvent. In contrast, this interaction between MWNTs and PS was significantly enhanced by melt mixing, which led to increased amount of PS-functionalized MWNT exhibiting good solubility in some solvents. The mechanism of melt mixing on this enhanced interaction was attributed to both chemical bonding and physical interaction during the melt mixing.     

Low-temperature catalytic oxidation of multi-walled carbon nanotubes

When in a pure form, carbon nanotubes are known to be stable in air up to ∼800 K making them attractive for a large variety of applications. In this work, we report a significant decrease of ignition temperature (in some cases occurring at ∼500 K) and a reduction in the apparent activation energy for oxidation in air as a result of impregnation with nanoparticles (<2 nm) of metal (Pt, Pd, Ni and Co) acetylacetonates or by decoration with corresponding oxides. Surprisingly, defects introduced by partial oxidation of the carbon nanotubes do not in practice have any influence on the enhancement of further oxidation. Reduction temperatures of metal oxides with H₂ were close to those of other carbon supported catalyst materials. However, the carbon nanotubes showed a tendency for low temperature gasification in the presence of hydrogenation catalyst metals (Pt, Pd).     

Thermal oxidative cutting of multi-walled carbon nanotubes

Commercially available, multi-walled carbon nanotubes grown by CVD are usually inherently entangled, but can be separated by cutting. However, most cutting methods both cause damage to the nanotubes and involve a lengthy work-up procedure. The use of abrupt, repeated exposure to oxidising conditions in air proved to be an efficient (68% yield) means of producing material with open ends, moderate functionalisation, and enhanced solvent dispersibility; the average lengths were reduced from over 5 μm to approximately 650 nm. Additionally, the character of the surface oxides can be tuned to have either an acidic or basic character by using a simple thermal treatment. These approaches could be deliberately integrated into conventional CVD processes, but also have implications for the products of standard nanotube syntheses. Raman spectroscopy and electron microscopy were used to study the impact of cutting on the intrinsic graphitic structure and the length distribution. X-ray photoelectron spectroscopy was used to determine the extent of functionalisation. The cut carbon nanotubes were dispersed in dimethylformamide (DMF), a Lewis basic solvent, and chloroform, a Lewis acidic solvent, using mild sonication. Through the use of an experimentally determined extinction coefficient (ε = 35.10 ml mg⁻¹ cm⁻¹), the relative dispersibility of the cut and functionalised carbon nanotubes in DMF and chloroform was determined.     

Image analysis characterization of multi-walled carbon nanotubes

An original image analysis method is presented to characterize multi-walled carbon nanotubes from transmission electron microscopy images. The analysis is performed in three steps: (i) image preprocessing in order to isolate the nanotubes from the background, (ii) image segmentation, aiming at keeping only the measurable sections of nanotubes, and finally (iii) tube characteristics measurement. The measurement is based on a Lambert-like electron absorption law and is performed on the original gray level image itself. Two geometrical and one physical characteristics are determined for each tube, namely, its outer and inner radius and a linear electron absorption coefficient. The method is illustrated by comparing a pristine and an annealed carbon nanotube samples. The compaction of the tube walls during annealing is shown to result from a lowering of the external radius while the inner radius is left unchanged.