Nitrogen doping of CVD multiwalled carbon nanotubes: Observation of a large g-factor shift

Nitrogen doped multi-walled carbon nanotubes (N-CNTs) and undoped multi-walled carbon nanotubes (MWCNTs) were synthesized by a chemical vapour deposition (CVD) floating catalyst method. The N-CNTs were synthesized by the decomposition of a ferrocene/N-source/toluene (N-source = triethylamine, dimethylamine, acetonitrile) mixture at 900 °C. The undoped MWCNTs were synthesized using a ferrocene–toluene mixture without a nitrogen source under similar reaction conditions. The structure of the N-CNTs and MWCNTs was ascertained using HRTEM, SEM and Raman spectroscopy. Systematic ESR measurements of the carbon products produced, in the temperature range of 293–400 K showed line widths that were in general very large ∼ kOe. Most importantly, a large g-factor shift in samples of N-CNTs from that of the free electron g-factor was observed. Further, the shift increased with increasing temperature. The large g shift has been analysed in terms of Elliott-Wagoner and Bottleneck models. The temperature dependence of the g shift in the N-CNT samples rules out the Elliott-Wagoner type spin–orbit coupling scenario. The large g shift and temperature dependence can be qualitatively explained in terms of the Bottleneck model.     

Optimization of the mechanical properties of calcium phosphate/multi-walled carbon nanotubes/bovine serum albumin composites using response surface methodology

Response surface methodology (RSM) coupled with the central composite design (CCD) was used to optimize the mechanical properties of calcium phosphate cement/multi-walled carbon nanotubes/bovine serum albumin (CPC/MWCNTs/BSA) composites. In this study, CPC composites were reinforced by multi-walled carbon nanotubes (MWCNTs) and bovine serum albumin (BSA) in order to induce high mechanical properties in the CPC/MWCNTs/BSA system. The effect of various process parameters on the compressive strength of CPC/MWCNTs/BSA composites was studied using design of experiments (DOE). The process parameters studied were: wt.% of MWCNTs (0.2–0.5 wt.%), wt.% of BSA (5–15 wt.%) and type of MWCNTs (e.g. as-pristine MWCNT (MWCNT-AP), hydroxyl group functionalized MWCNT (MWCNT-OH) and carboxyl group functionalized MWCNT (MWCNT-COOH)). Based on the CCD, a quadratic model was obtained to correlate the process parameters to the compressive strength of CPC/MWCNTs/BSA composites. From the analysis of variance (ANOVA), the most significant factor affected on the experimental design response was identified. The predicted compressive strength after process optimization was found to agree well with the experimental value. The results revealed that at 0.5 wt.% of MWCNT-OH and 15 wt.% of BSA, the highest compressive strength of 14 MPa was obtained.     

Dielectric, magnetic, and microwave absorbing properties of multi-walled carbon nanotubes filled with Sm2O3 nanoparticles

This study investigates the dielectric, magnetic, and microwave absorbing properties of Sm₂O₃-filled multi-walled carbon nanotubes (MWCNTs) synthesized by wet chemical method. The complex permittivity and permeability were measured at a microwave frequency range of 2-18 GHz. Sm₂O₃ nanoparticles encapsulated in the cavities enhance the magnetic loss of MWCNTs. The calculated results indicate that the bandwith of absorbing peak of the modified MWCNTs is much broader than that of unfilled MWCNTs. The maximum reflectivity (R) is about − 12.22 dB at 13.40 GHz and corresponding bandwidth below − 5 dB is more than 5.11 GHz. With the increase of thickness, the peak of R shifts to lower frequency, and multiple absorbing peaks appear, which helps to broaden microwave absorbing bandwidth.     

Characteristics of multi-walled carbon nanotubes and background aerosols by carbon analysis; particle size and oxidation temperature

Novel carbonaceous nanomaterials such as carbon nanotubes and fullerenes have many beneficial characteristics as industrial materials, but exposure to these nanomaterials also poses health risks. As part of an exposure assessment, we characterized the following carbonaceous nanomaterials, using an aerosol carbon monitor: nine samples of multi-walled carbon nanotubes (MWCNTs), a sample of single-walled carbon nanotubes (SWCNTs), a standard sample of diesel exhaust particles (DEPs), and an ambient particulate matter (APM). The amounts of elemental carbon (EC) determined by the monitor coincided with the mass of MWCNTs calibrated by a microbalance. The carbonaceous nanomaterials were oxidized in three steps of oven temperatures (550, 700 and 920 °C) in this method. The portion of oxidized carbon at each temperature depended on the sample characteristic. We used the monitor to analyze the aerosol samples collected in five stages by a Sioutas cascade impactor (SCI), which collects size-segregated airborne particles having aerodynamic diameters from 6.6 μm to less than 0.25 μm. As MWCNTs aggregate/agglomerate easily, the size was of a good parameter to distinguish the MWCNTs from other materials. Two-dimensional mapping by size and oxidized temperature suggested the origin of the carbonaceous aerosol samples. Based on the results, we reanalyzed our previous data obtained at a factory manufacturing MWCNTs. The characteristics of workplace samples by particle size and carbon analysis were similar to those of MWCNT aerosol particles.     

Chinese ink-facilitated fabrication of carbon nanotube/polyvinyl alcohol composite sheets with a high nanotube loading

Fabricating carbon nanotube-based composites requires high degree of dispersion of carbon nanotubes into a polymer matrix. The widely used approaches reported in open literature for such a purpose are usually complicated and high-cost. Herein, we found that Chinese ink could be used to prepare composites composed of multi-walled carbon nanotubes (MWCNTs) and polyvinyl alcohol (PVA). The Chinese ink acted as a solvent and a dispersant. The MWCNT-ink-PVA ternary composite possessed both high flexibility and high electrical conductivity, with an optimized electrical conductivity of 8.17 S cm⁻¹. This simple method is believed to be applicable to other nanosacle carbon materials.     

Functionalization of multi-walled carbon nanotubes and its application in preparing the 3D graphene/carbon nanotubes hybrid architectures

A facile strategy for the preparation of water-dispersible multi-walled carbon nanotubes (MWCNTs) in aqueous solution for the preparation of the three-dimensional (3D) graphene/carbon nanotube (G/CNT) hybrid architectures is proposed, where MWCNTs were functionalized by simultaneous radiation-induced graft polymerization of acrylic acid under the γ-ray (denoted as MWCNT-g-PAA) for improving its dispersibility. The stability of the aqueous solution of MWCNT-g-PAA in water is highly improved. We also use the MWCNT-g-PAA fabricating three-dimensional cylindrical graphene/carbon nanotube (G/CNT) hybrid architectures by a simple one-step hydrothermal process. We found that the as-prepared MWCNTs-g-PAA showed a very good dispersibility in GO solution with different concentration ratio and a promising precursor for preparing the graphene/CNT hybrid materials.     

Preparation temperature effect on the synthesis of various carbon nanostructures

Various carbon nanostructures (CNs) have been prepared by a simple deposition technique based on the pyrolysis of a new carbon source material tetrahydrofuran (THF) mixed with ferrocene using quartz tube reactor in the temperature range 700–1100 °C. A detailed study of how the synthesis parameter such as growth temperature affects the morphology of the carbon nanostructures is presented. The obtained CNs are investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), electron dispersive scattering (EDS), thermogravimetry analysis (TGA), Raman and transmission electron microscope (TEM). It is observed that at 700 °C, normal CNTs are formed. Iron filled multi-walled carbon nanotubes (MWCNTs) and carbon nanoribbons (CNRs) are formed at 950 °C. Magnetic characterization of iron filled MWCNTs and CNRs studied at 300 K by superconducting quantum interference device (SQUID) reveals that these nanostructures have an enhanced coercivity (Hc = 1049 Oe) higher than that of bulk Fe. The large shape anisotropy of MWCNTs, which act on the encapsulated material (Fe), is attributed for the contribution of the higher coercivity. Coiled carbon nanotubes (CCNTs) were obtained as main products in large quantities at temperature 1100 °C.     

Thermoplastic elastomers with multi-walled carbon nanotubes: Influence of dispersion methods on morphology

PBT-block-PTMO thermoplastic elastomers derived from dimethyl terephthalate (DMT), 1,4-butanediol(BD) and poly(tetramethylene glycol) (PTMG) were synthesized in the presence of oxidized multi-walled carbon nanotubes (MWCNTs) by a two-stage process involving transesterification and in situ polycondensation. Two procedures were applied to nanotubes in the polymer matrices were used. In procedure 1, nanotubes were dispersed in DMT + BD before the transesterification, while in procedure 2 nanotubes were dispersed in PTMG after transesterification. The mole ratio of the starting components was selected to produce copolymers with a constant hard to soft segment weight ratio of 45:55. Characterization of the new nanocomposites was performed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), small- and wide-angle X-ray scattering (SAXS/WAXS). A better nanotube dispersion can be achieved when oxidized MWCNTs are added to the DMT + BD monomers before transesterification (procedure 1). Oxidized MWCNTs exhibit strong interfacial adhesion to the polymer matrix for both procedures.     

Development of conducting polychloroprene rubber using imidazolium based ionic liquid modified multi-walled carbon nanotubes

A simplified and an eco-friendly approach to develop polychloroprene rubber composites with high electrical conductivity is reported. The usage of room temperature ionic liquid, 1-butyl 3-methyl imidazolium bis(trifluoromethylsulphonyl)imide and a low concentration (5 phr) of commercial grade multi-walled carbon nanotubes (MWCNTs) in polychloroprene rubber exhibited an electrical conductivity of 0.1 S/cm with a stretchability >500%. The physical (cation-pi/pi-pi) interaction between the ionic liquid and the MWCNTs is evidenced by Raman spectroscopy. Transmission electron microscopy images exhibit an improved dispersion of the BMI modified tubes in matrix at various magnification scales. The dependency of dynamic properties on the concentration of ionic liquid at constant loading of nanotubes supports the fact that ionic liquid assists in the formation of filler-filler networks. The tensile modulus of 3 phr loaded modified MWCNT/CR composite is increased by 50% with regard to that of the unmodified MWCNT/CR composite. Mooney-Rivlin plot displays the existence of rubber-filler interactions.     

Microwave-assisted synthesis and highly photocatalytic activity of MWCNT/ZnSe heterostructures

The multi-walled carbon nanotubes (MWCNTs) coated with the face-center cubic ZnSe nanoparticles with a uniform and small diameter have been prepared to form MWCNT/ZnSe heterostructures by microwave irradiation. The morphology, loading quantity and size of the ZnSe nanoparticles in the range of 15–50 nm can be controlled easily by adjusting the microwave power, pH value of the initial solution, the molar ratios of the Zn(AC)₂/MWCNTs and the appropriate complexing agent. The photoluminescence measurement indicates that the MWCNT/ZnSe heterostructures are blue-shifted compared to reported bulk ZnSe. The UV–vis absorption spectra of the heterostructures appears two sharp absorption peaks at 336 and 344 nm, respectively. It was demonstrated that the heterostructures could photodegrade the fuchsine acid in the solution with highly photocatalytic activity.     

Electrical and optical properties of reduced graphene oxide and multi-walled carbon nanotubes based nanocomposites: A comparative study

Graphene and multi-walled carbon nanotubes have attracted interest for a number of potential applications. One of the most actively pursued applications uses graphene and carbon nanotubes as a transparent conducting electrode in solar cells, displays or touch screens. In this work, in situ reduced graphene oxide/Poly (vinyl alcohol) and multi-walled carbon nanotubes/Sodium Dodecyl Sulfate/Poly (vinyl alcohol) composites were prepared by water dispersion and different reduction treatments. Comparative studies were conducted to explore the electrical and optical properties of nanocomposites based on graphene and multi-walled carbon nanotubes. A thermal reduction of graphene oxide was more effective, producing films with sheet resistances as low as 10²–10³ Ω/square with 80% transmittance for 550 nm light. The percolation threshold of the thermally reduced graphene oxide composites (0.35 vol%) was much lower than that of the chemically reduced graphene oxide composites (0.57 vol%), and than that of the carbon nanotubes composites (0.47 vol%). The Seebeck coefficient of graphene oxide films changes from about 40 μV/K to −30 μV/K after an annealing of three hours at 200 °C. The optical absorption of the nanocomposites showed a high absorbance in near UV regions and the photoluminescence enhancement was achieved at 1 wt% graphene loading, while the carbon nanotubes based composite presents a significant emission at 0.7 wt% followed with a photoluminescence quenching at higher fraction of the nanofillers 1.6 wt% TRGO and 1 wt% MWCNTs.     

Microstructure changes of polyurethane by inclusion of chemically modified carbon nanotubes at low filler contents

The surface of multi-walled carbon nanotubes (MWCNTs) was modified to introduce acidic groups in either covalent or van der Waals interaction bonding environments to establish cross-linking sites with a host polymer. Nanocomposites based on a polyurethane matrix (PU) containing chemically functionalised multi-walled carbon nanotubes (MWCNTs) have been shown to alter its mechanical performance depending on the nature of the surface functional groups on MWCNTs, which correlates to the type of bonding interaction of the surface group and also the dispersibility of MWCNTs and their influence on the domain structure of polyurethane. The stress at break for nanocomposites containing 0.25 wt% of acid-oxidised MWCNTs (MWCNT-ox), bearing covalently attached carboxylic, lactone and phenolic groups, was twice that of the native PU and Young’s Modulus for the nanocomposites increased by four times. Whereas when hemin, which contains carboxylic functionality, was immobilised to the surface of pure MWCNTs, the improvement in Young’s Modulus was only around twice that of pure PU. Differences in the disaggregation of MWCNTs into PU were observed between the samples as well as variation of the native domain structure of PU. The results also infer that the purification of MWCNTs from acid-oxidative lattice fragments (fulvic acids) is vital prior to conducting surface chemistry and polymerisation in order to ensure maximum mechanical performance enhancement in their reinforcement of the host polymer.     

纳米纤维素/碳纳米管/纳米银线柔性电极的制备

目的以竹粉为原料制备纳米纤维素,并将其作为基底材料制备纳米纤维素/碳纳米管/纳米银线复合电极,应用于柔性超级电容器。方法采用化学机械处理法,将竹粉通过化学处理以及研磨、超声等处理,制备成纳米纤维素悬浮液;分别将多壁碳纳米管和纳米银线超声分散于溶剂中;最后,通过层层自组装制备纳米纤维素/碳纳米管/纳米银线复合电极,同时,作为对照组,制备纳米纤维素/碳纳米管复合电极。结果纳米纤维素纤丝的直径大约为30~100 nm,相互之间缠绕成网状结构,是很好的支撑材料,纳米纤维素/碳纳米管/纳米银线复合电极具有很好的成膜性和电化学性能,在扫描速率为30 m V/s时,面积比电容达到77.95 m F/cm~2。结论以纳米纤维素为基底,通过层层自组装方法制备的纳米纤维素/碳纳米管/纳米银线复合电极具有较好的电化学性能,可作为柔性超级电容器的电极。     

Synergetic effect of hybrid boron nitride and multi-walled carbon nanotubes on the thermal conductivity of epoxy composites

This study investigates the synergistic effect of combining multi-walled carbon nanotubes (MWCNTs) and boron nitride (BN) flakes on thermally conductive epoxy composite. The surface of the two fillers was functionalized to form covalent bonds between the epoxy and filler, thereby reducing thermal interfacial resistance. The hybrid filler provided significant enhancement of thermal conductivity, adding 30 vol% modified BN and 1 vol% functionalized MWCNTs achieving a 743% increase in thermal conductivity (1.913 W mK⁻¹, compared to 0.2267 W mK⁻¹ of neat epoxy).     

Synthesis and characterization of well-dispersed multi-walled carbon nanotube/low-bandgap poly(3,4-alkoxythiophene) nanocomposites

In this study, we prepared nanocomposites of multi-walled carbon nanotubes (MWCNTs) and low-energy-bandgap conjugated polymers incorporating 3,4-alkoxythiophene monomers. Poly(3,4-dihexyloxythiophene) (PDHOT) and poly(3,4-dimethoxythiophene-co-3,4-dihexyloxythiophene) [P(DMOT-co-DHOT)] have relatively low-energy-bandgaps (ca. 1.38 and 1.34 eV, respectively), determined from the onsets of absorbances in their UV–Vis spectra, because of the electron-donating effects of their alkoxy groups. MWCNTs have poor solubility in common organic solvents; after surface modification with alkyl side chains using the Tour reaction, however, the p-hexylaniline modified MWCNT derivative (MWCNT-HA) was readily dispersed in CHCl₃ and could be mixed with the low bandgap polymers. Scanning electron microscopy images revealed that MWCNT-HA was dispersed well in each polythiophene derivative; only a few MWCNT-HA bundles could be observed at a high MWCNT-HA content (≧20 wt.%). The electrical conductivities of the MWCNTs/PDHOT composites were dependent on their MWCNT content, reaching 16 S/cm at 30 wt.% MWCNT-HA. We suspect that the two hexyloxy chains of PDHOT enhanced its solubility and allowed it to wrap around the surfaces of the MWCNTs more readily.     

Multi-scale electrical response of silicon nitride/multi-walled carbon nanotubes composites

Dense silicon nitride (Si₃N₄) composites with various amounts (0-8.6 vol%) of multi-walled carbon nanotubes (MWCNTs) are electrically characterised by combining macroscopic dc-ac and nanoscale conductive scanning force microscopy (C-SFM) measurements. In this way, a coherent picture of the dominant charge transport mechanisms in Si₃N₄/MWCNTs composites is presented. A raise of more than 10 orders of magnitude in the electrical dc conductivity compared to the blank specimen is measured for MWCNTs contents above 0.9 vol%. Semiconductor and metallic-like behaviours are observed depending on both the temperature and the MWCNTs content. Macroscopic measurements are further supported at the nanoscale by means of C-SFM. The metallic-type conduction is associated to charge transporting along the nanotube shells, whereas the semiconductor behaviour is linked to hopping conduction across nanotube-nanotube contacts and across intrinsic defect clusters within the nanotubes.     

Effect of block-copolymer dispersants on properties of carbon nanotube/epoxy systems

The effects of the addition of eight different block copolymers on the dispersion stability of multi-walled carbon nanotubes (MWCNTs) are reported. Suspensions of CNTs in different components of an epoxy system have been prepared using a tip sonicator and different amounts of block copolymers. The resistance to sedimentation of MWCNTs in various media was systematically investigated by using a centrifugation technique. Block copolymers that result in dispersions of MWCNTs in epoxy and hardener stable for more than 1 week have been obtained. Dispersions using a single or a combination of two different dispersing agents have been used for the fabrication of MWCNT nanocomposites. The effect of different preparation routes and use of block copolymers on the tensile properties and surface resistivity of the composites have been evaluated. The results obtained have been related with the dispersion stability of the MWCNTs in the epoxy components.     

Enhanced dielectric and ferroelectric properties induced by TiO2@MWCNTs nanoparticles in flexible poly(vinylidene fluoride) composites

Flexible polymer based composites containing multi-walled carbon nanotubes (MWCNTs) have been reported to present high dielectric constant. However, the composites generally exhibit high dielectric loss and low dielectric breakdown strength, which prohibits their practical use in electronic and electric industry. MWCNTs were coated with a continuous layer of TiO₂ nanoparticles (TiO₂@MWCNTs) by a simple hydrothermal process and TiO₂@MWCNTs/poly(vinylidene fluoride) (PVDF) composites were prepared by a solution casting method. Compared to the pristine MWCNTs/PVDF composites, the TiO₂@MWCNTs/PVDF composites presented enhanced dielectric constant and lower dielectric loss. Additionally, the breakdown strength of the TiO₂@MWCNTs/PVDF composites was also improved, which is favorable for enhanced ferroelectric properties in the composites.     

Magnetic removal of dyes from aqueous solution using multi-walled carbon nanotubes filled with Fe2O3 particles

The Fe₂O₃ nanoparticles have been introduced into the multi-walled carbon nanotubes (MWCNTs) via wet chemical method. The resulting products are characterized by TEM, EDX, XRD and VSM. The magnetic MWCNTs have been employed as adsorbent for the magnetic separation of dye contaminants from water. The adsorption test of dyes (Methylene Blue and Neutral Red) demonstrates that it only takes 60 min to attain equilibrium and the adsorption capacities for Methylene Blue and Neutral Red in the concentration range studied are 42.3 and 77.5 mg/g, respectively. The magnetic MWCNTs can be easily manipulated in magnetic field for desired separation, leading to the removal of dyes from polluted water. The integration of MWCNTs with Fe₂O₃ nanoparticles has great potential application to remove organic dyes from polluted water.     

多壁碳纳米管改性InVO4光催化剂的制备及性能

以酸处理的多壁碳纳米管(MWCNTs)为载体,采用水热合成法制备了InVO4/MWCNTs光催化剂.利用场发射扫描电镜、X射线粉末衍射、BET-N2吸附、傅里叶红外光谱和紫外-可见漫反射吸收光谱等技术对样品的形貌、晶相组成、比表面积和吸光性能等物理性质进行了表征,并以气相的苯作为模型污染物,研究催化剂样品在可见光(λ>420 nm)照射下的光催化氧化能力.结果表明,InVO4颗粒均匀附着于MWCNTs,表面粒径约100 nm.与纯InVO4相比,InVO4/MWCNTs的比表面积和可见光吸收性能显著提高.在可见光照射下,InVO4/MWCNTs具有良好的光催化活性,反应4 h光催化降解苯的转化率和矿化率分别为41.0%和43.4%,其转化率分别是InVO4的1.5倍和掺氮TiO2的3倍,InVO4/MWCNTs光催化活性的提高与载体MWCNTs良好的电子传输特性有关.