Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

Fabrication of an electrochemical platform based on the self-assembly of graphene oxide-multiwall carbon nanotube nanocomposite and horseradish peroxidase: direct electrochemistry and electrocatalysis

A novel hybrid nanomaterial (GO-MWNTs) was explored based on the self-assembly of multiwall carbon nanotubes (MWNTs) and graphene oxide (GO). Compared with pristine MWNTs, such a nanocomposite could be well dispersed in aqueous solution and exhibit a negative charge. Driven by the electrostatic interaction, positively charged horseradish peroxidase (HRP) could then be immobilized onto GO-MWNTs at the surface of a glassy carbon (GC) electrode to form a HRP/GO-MWNT/GC electrode under mild conditions. TEM was used to characterize the morphology of the GO-MWNT nanocomposite. UV-vis and FTIR spectra suggested that HRP was immobilized onto the hybrid matrix without denaturation. Furthermore, the immobilized HRP showed enhanced direct electron transfer for the HRP-Fe(III)/Fe(II) redox center. Based on the direct electron transfer of the immobilized HRP, the HRP/GO-MWNT/GC electrode exhibited excellent electrocatalytic behavior to the reduction of H(2)O(2) and NaNO(2), respectively. Therefore, GO-MWNTs could provide a novel and efficient platform for the immobilization and biosensing of redox enzymes, and thus may find wide potential applications in the fabrication of biosensors, biomedical devices, and bioelectronics.     

Synthesis of MnO2/short multi-walled carbon nanotube nanocomposite for supercapacitors

Multi-walled carbon nanotubes (MWNTs) were selectively etched in molten nitrate to produce short MWNTs (s-MWNTs). MnO₂/s-MWNT nanocomposite was synthesized by a reduction of potassium permanganate under microwave irradiation. For comparative purpose, MnO₂/MWNT nanocomposite was also synthesized and investigated for its physical and electrochemical performance. Uniform and conformal MnO₂ coatings were more easily formed on the surfaces of individual s-MWNTs. MnO₂/s-MWNT nanocomposite estimated by cyclic voltammetry (CV) in 0.5 M Na₂SO₄ aqueous solution had the specific capacitance as high as 392.1 F g⁻¹ at 2 mV s⁻¹. This value was more than 48.9% larger than MnO₂/s-MWNT nanocomposite. In addition, MnO₂/s-MWNT nanocomposite was also examined by repeating the CV test at a scan rate of 50 mV s⁻¹, exhibiting an excellent cycling stability along with 99.2% specific capacitance retained after 1000 cycles. Therefore, MnO₂/s-MWNT nanocomposite is a promising electrode material in the supercapacitors.     

Synthesis of multi-walled carbon nanotube/silver nanocomposite powders by chemical reduction in aqueous solution

Carbon nanotube (CNT)/silver nanocomposite powders with different volume fractions of CNTs 2.5, 5 and 10?vol.% were prepared by chemical reduction in solution. Multi-walled CNTs underwent surface modifications for functionalisations by acid treatments. The acid-treated CNTs were investigated by FT-IR and X-ray photoelectron spectroscopy. The spectroscopic investigations of the acid-functionalised CNTs detected that several kinds of functional groups attached with the graphene structure as well as produced short and de-caped CNTs. Acidic stannous chloride solution was used to sensitise the surface of the functionalised CNTs. Silver was deposited on the surface of sensitised CNTs with chemical reduction reaction of alkaline silver nitrate solution by formaldehyde at room temperature and pH?～?9. The morphology of the produced CNT/silver nanocomposite powder was investigated by high-resolution SEM and TEM. It was observed that the produced CNT/silver nanocomposite powders have decorated type of spherical silver particle size 2–5?nm deposited on the surface of CNTs as well as the CNTs were implanted in large spherical silver nanoparticles of particle size ～200?nm. The chemical analysis of the produced powder indicates that some oxygen content is included in the prepared powders which can be reduced by heat treatment at temperatures between 300°C and 400°C under hydrogen atmosphere.     

Preparation,characterization and micromolding of multi-walled carbon nanotube polydimethylsiloxane conducting nanocomposite polymer

We present the preparation, characterization and micromolding of a flexible electrically conducting nanocomposite polymer which has been prepared by ultrasonic agitation with multi-walled carbon nanotubes (MWCNT) in polydimethylsiloxane (PDMS). We demonstrate microfabrication of the conducting nanocomposite through soft lithography micromolding of hole and post structures (minimum feature size of 200 ± 10 μm, with a height of approximately 200 μm) against a polymer master. We characterize and compare the current–voltage characteristics of films 1 mm × 1 mm × 200 µm in size as a function of different weight percentages of MWCNT (ranging from 0.8 to 2.5 wt.%) with the result that the conductivity remains low until approximately 1.5 wt.%.     

Ultrasonically prepared polystyrene/multi-walled carbon nanotube nanocomposites

Polystyrene (PS) and multi-walled carbon nanotube (MWNT) nanocomposites were synthesized via an in situ bulk polymerization by employing an ultrasonicator without adding an initiator, in which the ultrasonication was found to do a favor in producing well-dispersed MWNT in the PS matrix. Morphology of the as-synthesized PS/MWNT nanocomposite was investigated by both scanning electron microscopy and transmission electron microscopy. Electrical conductivity of the PS/MWNT nanocomposite film fabricated by a solvent casting method was also examined to be enhanced with MWNT content, while average molecular weights of the synthesized PS in the PS/MWNT nanocomposites analyzed by a gel permeation chromatography increased and then saturated at 2 wt% MWNT. Rheological properties of MWNT containing PS were enhanced because of improved dispersion of the MWNT through an interaction between MWNT and PS.     

A novel multi-walled carbon nanotube (MWNT)-based nanocomposite for PEFC electrodes

A novel nanocomposite comprising MWNTs and mixed-conducting polymeric components (electronic and ionic) is prepared, characterized and investigated as a support for platinum (Pt). Nanocomposite of MWNTs and poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT?CPSS) is prepared by in situ polymerization and characterized using Fourier?CTransform infrared spectroscopy (FT?CIR), thermogravimetric analysis (TGA) in conjunction with scanning electron microscopy (SEM). Atomic force microscopy (AFM) studies are also carried out to characterize the surface topography of MWNTs/PEDOT?CPSS nanocomposite. X-ray diffraction (XRD) studies reveal that MWNTs/PEDOT?CPSS nanocomposite provides better backbone for the improved dispersion of Pt as evidenced by the reduced Pt crystallite size over MWNTs/PEDOT?CPSS nanocomposite compared to MWNTs. Electrochemical characterization studies performed with Pt/nanocomposite and Pt/MWNTs demonstrate the superior catalytic activity of Pt/nanocomposite under reduced Nafion loadings in relation to Pt/MWNTs. It is observed that mixed conducting nanoporous network of MWNTs/PEDOT?CPSS composite structure promotes the catalytic activity of Pt by enhancing catalyst utilization.     

Stress-strain behavior of multi-walled carbon nanotube/PEEK composites

This study examined the effects of multi-walled carbon nanotube (CNT) dispersion on stress-strain behaviors of poly-ether-ether-ketone (PEEK) at room temperature. Tensile test specimens containing 9 wt.% and 15 wt.% of CNT were fabricated using injection molding. Results of focused ion beam (FIB) observations show that many CNTs in the CNT/PEEK composite are aligned longitudinally. Although the PEEK stress-strain behavior is almost linear up to 1.5% strain, the stress-strain curves of CNT/PEEK composites exhibit considerable nonlinear and hysteretic behaviors from extremely low strain (<0.1%) under both tensile and compressive loading. The experimental results suggest that the viscoelastic deformation effects on nonlinear and hysteresis behaviors are not strong below 1.5% strain. Presumably, the slippage at the CNT-PEEK interface occurs with increasing applied stress because of poor interfacial load-transfer capability.     

AC-impedance response of multi-walled carbon nanotube/cement composites

AC-impedance spectroscopy (AC-IS) was combined with time-domain reflectometry (TDR) to investigate the impedance response of fiber-reinforced cement (FRC) composites with multi-walled carbon nanotubes (MWCNTs). In Nyquist plots (−imaginary impedance vs. +real impedance) three impedance arcs/features were observed, similar to Nyquist plots for macrofiber and microfiber FRCs. The intersection of the electrode arc and the intermediate frequency feature (R_DC(FRC)) corresponds to the DC resistance of the composite. The intersection of the two bulk features (R_cusp) corresponds to the AC resistance of the composite. Reductions in (R_DC(FRC)) from the matrix resistance are indicative of a nanotube percolating network. Reductions in R_cusp from the matrix resistance are indicative of a discontinuous fiber–fiber path. Both shifts increased with fiber loading. AC-IS measurements are therefore able to discriminate percolation vs. discontinuous fiber effects in CNT-FRCs, with the potential for characterizing dispersion issues (e.g., clumping/aggregation) in nanocomposites.     

Mechanical properties of multi-walled carbon nanotube/epoxy composites

Untreated and acid-treated multi-walled carbon nanotubes (MWNT) were used to fabricate MWNT/epoxy composite samples by sonication technique. The effect of MWNT addition and their surface modification on the mechanical properties were investigated. Modified Halpin–Tasi equation was used to evaluate the Young’s modulus and tensile strength of the MWNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. There was a good correlation between the experimentally obtained Young’s modulus and tensile strength values and the modified Halpin–Tsai theory. The fracture surfaces of MWNT/epoxy composite samples were analyzed by scanning electron microscope.     

Direct electrochemistry of myoglobin in titanate nanotubes film

Titanate nanotubes (TNT) were proven to be efficient support matrixes for the immobilization of myoglobin (Mb). A comparative study was performed using the corresponding analogue, nanocrystalline anatase TiO2 (TNP). UV-visible absorption and FT-IR spectra show that Mb was not obviously denatured in TNT film in contrast to the significant denaturation of Mb in TNP film. Cyclic voltammetry and square wave voltammetry measurements were carried out using the Mb-TNT or Mb-TNP cast film-covered basal plane pyrolytic graphite electrode. The Mb-TNT film gave a well-defined, nearly reversible redox couple with the apparent formal peak potential (Ep) of -0.239 V (vs Ag/AgCl) in pH 5.5 buffer, whereas a relatively smaller, quais-reversible redox pair with Ep of -0.263 V was observed for the Mb-TNP film. The amounts of electroactive Mb in TNT film and TNP film were 15 and 10%, respectively. Moreover, the Mb-TNT film exerted facile direct electron transfer with the apparent heterogeneous electron-transfer rate constant (kET) of 86+/-7 s-1, almost 4 times the 22+/-5 s-1 value for the Mb-TNP membrane and higher than other Mb-entrapped films reported. Additionally, the Mb-TNT film demonstrates good electrocatalytic reduction of hydrogen peroxide with a detection limit of 0.6 microM, much lower than the 3.0 microM value for the Mb-TNP electrode and other Mb-related film-modified electrodes reported so far. The Mb-TNT film exhibits higher peroxidase-like activity with the apparent Michaelis-Menton constant (KM) of 140 microM, significantly lower than the 1300 microM value for the Mb-TNP film. The functional hydroxyl group and the surface charge as well as tubular morphology of TNT are important factors to stabilize the bound protein.     

微过氧化物酶-11在碳纳米管/壳聚糖修饰电极上的直接电化学及电催化(英文)

采用一步法于室温下有选择性地将小管径的单壁碳纳米管(SWCNTs)分散于生物相容性的聚合物--壳聚糖的水溶液中,并将其滴涂于玻碳电极表面,制备出微过氧化物酶-11(MP-11)修饰电极.循环伏安结果表明SWCNq、促进了MP-11在电极表面的直接电子传递,在pH=7.2的磷酸缓冲溶液中,MP-11的式电位为-0.36 V(vs.SCE),MP-11在电极表面的直接电子转移表观速率常数和覆盖度分别为78 s-1和8.76×10-10mol·cm-2.进一步的研究结果显示,固定在SWCNT表面的MP-11能保持其对氧气和过氧化氢还原的生物电催化活性,适合用作生物燃料电池的阴极和过氧化氢传感器.氧气在该修饰电极上的还原经历一个四电子过程;该过氧化氢生物传感器对过氧化氢还原的检测具有响应灵敏度高(响应时间小于4 S),检测线性范围为2.5×10-6～7.0×10-3vM,检测限为0.8 μM,相应的米氏常数和检测灵敏度分别为1.0 mM and 22.4μA/mM.     

Electroconductive properties of zirconia/carbon nanotube aerogel composite

Electroconductive properties of zirconia/multiwalled carbon nanotube aerogel composite are investigated. The composite exhibits bulk percolation cluster-like conductivity at wide range of spatial scales. Conductive atomic force microscopy reveals the localized nature of conductive properties of the composite on the micro(nano)scopic scale and the uniformity of current distribution in all conductive areas independently of their size. The presence of unlinked conductive chains and the possibility of their linking by dissociating ions are demonstrated in experiments on registration of I–V curves during the evacuation of the composite impregnated with distilled water. The experimental data make it possible to describe the electrical properties of the composite as the properties of a circuit formed by the parallel connections of numerous voltage dividers arranged in a bulk porous structure. These features make the synthesized composite a promising candidate for use in catalysis and water vapor sensors.     

Reinforcement efficiency of multi-walled carbon nanotube/epoxy nano composites

Mechanical reinforcement of polymer matrices loaded by carbon nanotubes is expected to benefit by both the high aspect ratio and the very high modulus of such nanofillers and, consequently, it depends not only by their content within the hosting system but also by the state of dispersion. This work analyses the effect on the bending modulus of dispersed multi-walled carbon nanotube (MWCNT) into an epoxy system. Results indicate that reinforcement efficiency is characterised by two limiting behaviours whose transition region coincides with the development of a percolative network of nanotubes. Well below the percolation threshold, the carbon nanotubes, contribute to the composite modulus with their exceptional modulus (in this case a value of 1.780 TPa was found), whereas it dramatically decreases above this limit due to the reduction of the effective aspect ratio and the micron sized cluster formation. An estimate of the maximum reinforcement induced by carbon nanotubes has been proposed based on percolation and stress transfer theory for large aspect ratio fillers.     

辣根过氧化物酶在多壁碳纳米管——壳聚糖膜中的电化学和生物传感性质

采用壳聚糖包裹的多壁碳纳米管膜固定辣根过氧化物酶(HaP)于玻碳电极表面,实现了HRP的直接电化学并以此酶膜制备了NO生物传感器.在磷酸缓冲溶液中固定在电极表面的HRP氧化还原式电位为-0.354 V(us.SCE),直接电子转移速率常数为4.24±1.02 s-1.研究结果表明,固定在电极表面的HRP能保持其对一氧化氮还原的生物电催化活性,该传感器在NO浓度为1.0×10-4~1.4×10-3 mol L-1范围内存在线性响应,响应时间小于11 s,NO的检出限为7×10-4 mol L-1.多壁碳纳米管特殊的电学性质和壳聚糖良好的生物相容性性使得构筑的HRP生物传感器呈现了良好的应用前景,尤其适用于痕量NO的检测.     

Lyocell/多壁碳纳米管复合纤维的制备及性能

将多壁碳纳米管(MWCNTs)水悬浮液、N-甲基吗啉-N-氧化物(NMMO)溶液及纤维素共混得到纺丝液,通过干湿法制备了Lyocell/MWCNT复合纤维。采用X-衍射仪(WAXD)、扫描电镜(SEM)、透射电镜(TEM)、强度仪等分析了所得纤维的结构和性能。WAXD图谱显示复合纤维仍然具有纤维素II晶型的结构,同时还保留了MWCNTs的特征衍射峰;二维X衍射结果表明:MWCNTs质量分数为5%的复合纤维中,MWCNTs与纤维轴的取向角为±15.2°,说明复合纤维中MWCNTs基本沿着纤维轴取向。SEM结果显示复合纤维中MWCNTs在Lyocell基体中分布均匀。对纤维的力学性能分析进一步表明:添加适量的MWCNTs可使复合纤维的力学性能提高,MWCNTs质量分数为1%的复合纤维的初始模量和强度分别比Lyocell纤维增加49.4%和15.7%。     

Ethanol-sensing properties of potassium bromide/multi-walled carbon nanotube composites

The work reported in this paper is related to the fabrication and electrical characterization of multi-walled carbon nanotubes (MWNT)-based solid composites pellets with potential application as gas sensor at room temperature, using potassium bromide as supporting material. Results show an electrical conductivity of the composites as a function of the MWNT loading following a power law associated with a percolation phenomenon. A variation of the electrical resistance of the composites as a function of ethanol concentration in a nitrogen atmosphere has also been observed, allowing detection of ethanol from about hundred of ppm. It is also shown the existence of an optimal MWNT loading for which the composite reaches its best ethanol-sensing performances.     

Direct measurements of interfacial shear strength of multi-walled carbon nanotube/PEEK composite using a nano-pullout method

This paper presents a proposal of a simple and easy method to evaluate the interfacial shear strength (IFSS) of CNT-dispersed polymer composites. An individual multi-wall carbon nanotube (MWNT) was pulled out from a MWNT-dispersed/PEEK composite using a nano-pullout testing system installed in an SEM. The tensile load was measured using the elastic deformation of an AFM cantilever. The pull-out length was controlled by making a through-thickness hole near the specimen edge using a focused ion beam (FIB) system. The IFSS of a MWNT/PEEK composite was measured as 3.5-14 MPa, which agrees with the IFSS estimated from the macroscopic stress-strain behavior of the MWNT/PEEK composites.     

Preparation and characterization of carbon nanotube/polyetherimide nanocomposite films

Multi-walled carbon nanotube (MWCNT)/polyetherimide (PEI) nanocomposite films have been prepared by casting and imidization. A homogeneous dispersion of MWCNTs throughout the PEI matrix is observed by scanning electron microscopy of fracture surfaces, which shows not only a fine dispersion of MWCNTs but also strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTs) in the matrix and by the absence of debonding of CNTs from the matrix. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperature of PEI increases by about 10 °C by the addition of 1 wt% MWCNTs. Mechanical testing shows that for the addition of 1 wt% MWCNTs, the elastic moduli of the nanocomposites are significantly improved by about 250% while the tensile strength is comparable to that of the matrix. This improvement is due to the strong interfacial interaction between the MWCNTs and the PEI matrix which favors stress transfer from the polymer to the CNTs.