Untreated Multi-walled Carbon Nanotubes Research Articles

Facile preparation of a novel high performance benzoxazine–CNT based nano-hybrid network exhibiting outstanding thermo-mechanical properties

Untreated multi-walled carbon nanotubes (MWCNTs) have been dispersed in two benzoxazine precursors following an easy procedure. The strong intrinsic interactions of CNTs with a selected precursor give rise to the formation of a reinforced network with outstanding thermo-mechanical properties.

Surface modification of multiwalled carbon nanotubes via gliding arc plasma for the reinforcement of polypropylene

AbstractTo increase the applicability of multiwalled carbon nanotubes (MWCNTs), functional groups were generated on the generally inert surface of MWCNTs using gliding arc (GA) plasma. MWCNTs were modified using plasma polymerization with styrene (St) as monomer. The surface compositional and structural changes that occur on MWCNTs were investigated using FT‐IR, Raman spectroscopy, BET surface area, and elemental analysis. Dispersion of the treated MWCNTs in different solvents was evaluated. Transmission electron microscopy images showed that the plasma‐treated MWCNTs had a better dispersion than the untreated ones in nonpolar solvents. Subsequently, MWCNTs‐reinforced polypropylene (PP) composites were prepared by internal batch mixing with the addition of 1.0 wt % MWCNTs. The morphology of MWCNTs/PP nanocomposites was studied through scanning electron microscopy. Observations of SEM images showed that the plasma‐treated MWCNTs had a better dispersion than the untreated MWCNTs either on the composite fracture surfaces or inside the PP matrix. Moreover, the mechanical tests showed that the tensile strength and elongation at break were improved with the addition of polystyrene‐grafted MWCNTs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Electrical conductivity and thermal stability of polypropylene containing well-dispersed multi-walled carbon nanotubes disentangled with exfoliated nanoplatelets

The morphology, crystallization behavior, electrical conductivity, and thermal stability of polypropylene (PP) modified with disentangled multi-walled carbon nanotubes (MWCNTs) is reported. Slightly oxidized MWCNT clusters were disentangled in solution by mild sonication in the presence of exfoliated α-zirconium phosphate nanoplatelets. The disentangled MWCNTs were isolated using acid-induced coagulation to precipitate the nanoplatelets, and were subsequently reacted with octadecylamine. The recovered functionalized MWCNTs (F-MWCNTs) are disentangled and easily dispersed in a commercial PP matrix, and serve as more efficient nucleating agents than the untreated MWCNTs. The PP/F-MWCNT composites exhibit an extremely low percolation-like transition in electrical conductivity, which is attributed to the preservation of a random dispersion of disentangled F-MWCNTs upon cooling from the melt. The thermal stability of PP in air is also substantially enhanced at loadings below the percolation threshold due to the tremendous interfacial area between the polymer chains and the free radical scavenging F-MWCNTs. The present approach provides an efficient and potentially scalable route for commercial production of conductive semi-crystalline thermoplastics. The method may be adapted to uniformly disperse MWCNTs in other polymer matrices by appropriate selection of surface functionality.

Plasma Treated Multi-Walled Carbon Nanotubes (MWCNTs) for Epoxy Nanocomposites

Plasma nanocoating of allylamine were deposited on the surfaces of multi-walled carbon nanotubes (MWCNTs) to provide desirable functionalities and thus to tailor the surface characteristics of MWCNTs for improved dispersion and interfacial adhesion in epoxy matrices. Plasma nanocoated MWCNTs were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), surface contact angle, and pH change measurements. Mechanical testing results showed that epoxy reinforced with 1.0 wt % plasma coated MWCNTs increased the tensile strength by 54% as compared with the pure epoxy control, while epoxy reinforced with untreated MWCNTs have lower tensile strength than the pure epoxy control. Optical and electron microscopic images show enhanced dispersion of plasma coated MWCNTs in epoxy compared to untreated MWCNTs. Plasma nanocoatings from allylamine on MWCNTs could significantly enhance their dispersion and interfacial adhesion in epoxy matrices. Simulation results based on the shear-lag model derived from micromechanics also confirmed that plasma nanocoating on MWCNTs significantly improved the epoxy/fillers interface bonding and as a result the increased composite strength.

Supramolecular bionanocomposites 3: Effects of surface functionality on electrical and mechanical percolation

AbstractPercolation phenomena in bionanocomposites composed of the bioplastic polylactide and surface decorated supramolecular multiwalled carbon nanotubes (MWCNTs) are investigated. MWCNTs with three distinct surface chemistries—a native surface, a hydroxyl functionalized surface, and a short hydrocarbon functionalized surface—are prepared and studied. Two experimental methods are used to determine percolation thresholds; melt rheology provides a measure of the mechanical percolation threshold and electrical impedance spectroscopy provides values of the electrical percolation threshold. The MWCNT‐loading level required to obtain mechanical percolation is systematically found to be lower than the loading level needed to achieve electrical percolation. Hydroxylated MWCNTs have the highest percolation thresholds of 1.8 (mechanical) and 6.7 wt % (electrical), which is attributed to aggregation caused by hydrogen bonding. Alkane‐grafted MWCNTs have lower percolation thresholds of 0.76 (mechanical) and 2.8 wt % (electrical). However, untreated MWCNTs have the lowest thresholds of 0.16 (mechanical) and 1.5 wt % (electrical). The reduced percolation threshold observed upon conversion of the hydroxylated surface to the alkylated surface is attributed to morphological differences—functionalization disrupts hydrogen bonding and leads to better nanotube dispersion. The combination of higher inherent conductivity and more favorable nanotube‐polylactide interactions implies that unmodified MWCNTs are preferred to produce electrically conductive bionanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Adsorption of toluene, ethylbenzene and xylene isomers on multi-walled carbon nanotubes oxidized by different concentration of NaOCl

Multi-walled carbon nanotubes (MWCNTs) were fabricated and oxidized by different concentrations of sodium hypochlorite (NaOCl) solutions. The untreated MWCNTs and modified MWCNTs were employed as adsorbents to study their characterizations and adsorption performance of toluene, ethylbenzene and xylene isomers (TEX) in an aqueous solution. The physicochemical properties of MWCNTs were greatly affected after oxidation, which influences TEX adsorption capacity. The 3% NaOCl-oxidized MWCNTs shows the greatest enhancement in TEX adsorption, followed by the 30% NaOCl. More interestingly, the 15% NaOCl-oxidized MWCNTs has lower adsorption capacities than untreated MWCNTs. The adsorption mechanism of TEX on treated MWCNTs is attributed to the combined action of hydrophobic interaction, π-π bonding interaction between the aromatic ring of TEX and the oxygen-containing functional groups of MWCNTs and electrostatic interaction. 3% NaOCl solution could not only introduce much oxygen-containing functional groups on MWCNTs, but also lead to less damage for the pore structure. This suggests that the CNTs-3% NaOCl is efficient adsorbent for TEX and that they may possess good potential for TEX removal in wastewater treatment.

Preparation and thermal properties of multiwalled carbon nanotube/polybenzoxazine nanocomposites

AbstractIn this study, we prepared nanocomposites comprising multiwalled carbon nanotubes (MWCNTs) and polybenzoxazine (PBZ). The MWCNTs were purified through microwave digestion to remove most of the amorphous carbon and metal impurities. After purification, MWCNTs were treated with H2SO4/HNO3 (3 : 1) to introduce hydroxyl and carboxyl groups onto their surfaces. Raman spectroscopy revealed the percentage of nanotube content improved after prolonged microwave treatment, as evidenced by the decrease in the ratio of the D (1328 cm−1) and G (1583 cm−1) bands. For the untreated MWCNTs, the ID/IG ratio was 0.56. After microwave treatment for 40 min, the value decreased to 0.29, indicating that the percentage of nanotube content improved. Dynamic mechanical analyses (DMAs) revealed that the storage moduli and the Tgs of the MWCNTs/PBZ nanocomposites were higher than that of the pristine PBZ. This is due to the nanometer‐scale MWCNTs restricting the motion of the macromolecular chains in the nanocomposites. Transmission electron microscopy (TEM) image revealed that the MWCNTs were well dispersed within the PBZ matrix on the nanoscale when the MWCNT content was less than 2.0 phr. The coefficient of thermal expansion (CTE) of the nanocomposites decreased on increasing the MWCNTs content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Enhanced capacitance in partially exfoliated multi-walled carbon nanotubes

We report for the first time the enhanced capacitance of multi-walled carbon nanotubes (MWCNTs) after exfoliation. Transmission electron microscopy studies confirmed that the MWCNTs were partially exfoliated with improved effective surface area. Carbon cloth electrode deposited with partially exfoliated carbon nanotubes (Ex-CNTs) yielded specific capacitances in a range of 130–165 F g −1 at charging/discharging current densities from 5 to 0.5 A g −1, with coulombic efficiencies of ∼98%. The specific capacitance of Ex-CNTs was an order of magnitude higher than untreated MWCNTs, and comparable to graphene at all charging/discharging current densities we studied. The enhanced capacitance can be attributed to improved effective surface area and increased defect density of the exfoliated tubular structure. The results declared that Ex-CNTs are promising electrode materials for high-capacitance supercapacitors.

Effect of functionalization on the thermo-mechanical and electrical behavior of multi-wall carbon nanotube/epoxy composites

The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, the mechanical and electrical properties of composites was investigated. Samples based on epoxy resin with different weight percentage of MWCNTs or COOH-functionalized carbon nanotubes (MWCNT–COOH) were prepared and characterized. Dynamic-mechanical thermal analysis shows that the storage modulus increases with the addition of MWCNTs, whereas a constant value or even a weak reduction was observed for functionalized nanotubes. Two phases were suggested in the composites with MWCNT–COOH, both by dynamic-mechanical properties and by water transport. Chemical functionalization of MWCNTs increases the compatibility with the epoxy matrix due to the formation of an interface with stronger interconnections. This, in turn, causes a significant decrease in the electrical conductivity of this type of composite with respect to the untreated MWCNTs which can be explained in terms of tunnelling resistance between interacting nanotubes.

Humidity Sensor Based on Multi-Walled Carbon Nanotube Thin Films

The properties of the humidity sensors made of chemically treated and untreated multi-walled carbon nanotube (MWCNT) thin films are investigated systematically. It shows that both the chemically treated and untreated MWCNT thin films demonstrate humidity sensitive properties, but the former have stronger sensitivity than the latter. In the range of 11%–98% relative humidity (RH), the resistances of the chemically treated and untreated MWCNT humidity sensors increase 120% and 28%, respectively. Moreover, the treated humidity sensors showed higher sensitivity and better stability. In addition, the response and recover properties, and stabilization of the humidity sensors are measured, and the humidity sensitive mechanisms of the sensors are analyzed. The humidity sensitivity of carbon nanotube thin films indicates it promise as a kind of humidity sensitive material.

대기압 화염 플라즈마 처리한 다중벽 탄소나노튜브 및 카본블랙 강화 고무복합재료의 기계적 특성 연구

다중벽 탄소나노튜브(MWCNT) 및 카본블랙(CB) 함유량, 대기압 화염 플라즈마(APFP) 처리 그리고 산처리를 함수로 한 고무복합재료의 기계적 특성에 대해 연구하였다. 고무복합재료의 인장강도 및 탄성률은 MWCNT의 함유량 증가에 따라 순수상태 그리고 동일량의 CB가 보강된 상태에 비해 증가하였다. APFP 처리한 MWCNT를 보강한 복합재료는 처리하지 않은 경우에 비해 강화효과(높은 강도, 높 은 탄성률 그리고 높은 연성)를 보였다. 반면에 APFP 처리한 CB를 함유한 복합재료는 처리하지 않은 경우에 비해 연화효과(높은 강도, 낮은 탄성률 그리고 높은 연성)를 보였다. 산처리 시간이 1시간에서 2시간으로 증가할수록, 그리고 황산의 농도가 60%에서 90%로 증가할수록 복합재료의 인장강도와 탄성률은 감소하였다. 전체적으로 MWCNT 함유량, CB 함유량, 대기압 화염 플라즈마 처리, 황산 농도 그리고 산처리 시간 등이 고무복합재료의 기계적 특성에 영향을 미치는 중요한 변수임을 확인하였다.

Preparation of high performance Pd catalysts supported on untreated multi-walled carbon nanotubes for formic acid oxidation

Due to the inherent inertness of carbon nanotubes (CNTs), one of the most significant challenges in the preparation of CNT-supported catalysts is achieving a uniform deposition of nanoparticles on the surface of the nanotubes. In this paper, we report on the preparation and characterization of Pd nanoparticles supported on untreated multi-walled carbon nanotubes (MWCNTs), synthesized in the presence of glutamate. The results of Raman spectroscopy revealed that this synthetic procedure does not have a detrimental effect on the surface structure of MWCNTs. Transmission electron microscopy (TEM) measurements indicated that the dispersion of Pd nanoparticles on untreated-MWCNTs in the presence of glutamate were uniform, and a narrow particle size was observed. X-ray diffraction (XRD) patterns indicated that the Pd/MWCNT catalyst possessed a face-centered cubic crystal structure. Cyclic voltammetry and chronoamperometry tests demonstrated that the obtained Pd/MWCNT catalyst displayed superior electrocatalytic activity and stability in formic acid oxidation, as compared to both a Pd/MWCNT catalyst synthesized without glutamate and a Pd catalyst on acid-oxidized MWCNTs, under otherwise identical experimental conditions. These results indicate that the catalyst developed in this study is a superior candidate for direct formic acid fuel cells (DFAFCs).

Facile synthesis of solution-disposable carbon nanotube–TiO 2 hybrids in organic media

Oleic acid-capped TiO 2 nanoparticles (NPs) were directly grown on untreated multiwalled carbon nanotubes (MWCNTs) from a stable titanium carboxylate complex through a solvothermal aminolysis process in organic media. The shape of the TiO 2 NPs loaded on the MWCNTs can be controlled from nanodots (∼ 3 nm in diameter) to nanorods (∼ 5 nm in diameter, 30–40 nm in length) by changing solvent components and by Co 2+ doping. The resulting hybrids can be well dispersed in apolar organic solvents, which may provide possibilities for manipulating them in solutions for widespread applications.

One‐Step Preparation of Pt on Pretreated Multiwalled Carbon Nanotubes for Methanol Electrooxidation

AbstractFor the first time, intermittent microwave heating (IMH) is a one‐step technique applied to pretreat the multiwalled carbon nanotubes (MWCNTs) in H2O2 solution. The approach does not require washing and filtration of the sample, thus significantly reducing the loss of the material and treatment time. The IMH associated with H2O2 treatment, is optimised to fabricate efficient support for Pt electrocatalyst. Both as‐received and treated MWCNTs are used as Pt electrocatalyst supports, respectively. It demonstrates that the treated MWCNTs supported Pt has much better electrocatalytic performance than that of untreated MWCNTs supported Pt. The Pt on MWCNTs treated with an IMH irradiation mode in 10 s on and 20 s off for 5 times, shows the best performance for methanol oxidation. This work provides a novel approach to simply and economically fabricate an efficient MWCNT support at a large scale, for high performance Pt electrocatalysts.

Preparation and Mechanical Properties of Epoxy Resin Reinforced with Jeffamines-Grafted Carbon Nanotubes

The increasing proliferation and application of advanced polymer composites requires higher and broader performance resin matrices. Poly(oxypropylene) with –NH2 end-groups has been widely used to toughen epoxy resins, but the strength of resin matrix may be reduced due to the addition of flexible segments in the crosslinking network. Carbon nanotubes (CNTs) have been paid more and more attention in recent years because of their superior thermal and mechanical properties. In this paper, CNTs grafted with Jeffamines T403 were used to simultaneously improve the reinforcement and toughening of an epoxy resin. The untreated multi-walled carbon nanotubes (u-MWNTs) were functionalized with amine groups according to three steps: carboxylation, acylation, and amidation. The f-MWNTs were characterized by Fourier transform infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS). The experimental results indicated that the T403 was grafted to the surface of MWCNTs. The mechanical and thermal properties of epoxy with f-MWNTs were investigated. The tensile and flexural strength increased by 7.77 % and 7.03 % after adding 0.5wt% f-MWCNTs without sacrificing the impact toughness. At the same time, dynamic mechanical thermal analysis (DMTA) showed that the glass transition temperature (Tg) of epoxy with f-MWNTs were increased. The fracture surface of epoxy with f-MWNTs was observed by scanning electron microscopy (SEM) to understand the dispersion of f-MWNTs in epoxy matrix and interfacial adhesion between f-MWNTs and epoxy matrix, which can be attributed to the strong interfacial bonding between f-MWNTs and epoxy resin.

Atomic layer deposition on gram quantities of multi-walled carbon nanotubes

Atomic layer deposition (ALD) was employed to grow coaxial thin films ofAl2O3 andAl2O3 /W bilayers on multi-walled carbon nanotubes (MWCNTs). Although the MWCNTs havean extremely high surface area, a rotary ALD reactor was successfully employed to performALD on gram quantities of MWCNTs. The uncoated and ALD-coated MWCNTs werecharacterized with transmission electron microscopy and x-ray photoelectron spectroscopy.Al2O3 ALDon untreated MWCNTs was characterized by nucleation difficulties that resulted in the growth ofisolated Al2O3 nanospheres on the MWCNT surface. The formation of a physisorbedNO2 monolayer provided an adhesion layer for the nucleation and growth ofAl2O3 ALDfilms. The NO2 monolayer facilitated the growth of extremely conformal coaxialAl2O3 ALD coatings on the MWCNTs. Cracks were also observed in the coaxialAl2O3 ALD films on the MWCNTs. After cracking, the coaxialAl2O3 ALDfilms were observed to slide on the surface of the MWCNTs and expose regions of bare MWCNTs.The Al2O3 ALD film also served as a seed layer for the growth of W ALD on theMWCNTs. The W ALD films can significantly reduce the resistance of theW/Al2O3/MWCNT wire. The results demonstrate the potential for ALD films to tune the properties of gramquantities of very high surface area MWCNTs.

Wear behavior of Carbon Nanotube/High Density Polyethylene composites

Carbon Nanotube/High Density Polyethylene (CNT/HDPE) composites were manufactured and tested to determine their wear behavior. The nanocomposites were made from untreated multi-walled carbon nanotubes and HDPE pellets. Thin films of the precursor materials were created with varying weight percentages of nanotubes (1%, 3% and 5%), through a process of mixing and extruding. The precursor composites were then molded and machined to create test specimens for mechanical and wear tests. These included small punch testing to compare stiffness, maximum load and work-to-failure and block-on-ring testing to determine wear behavior. Each of the tests was conducted for the different weight percentages of composite as well as pure HDPE as the baseline. The measured mechanical properties and wear resistance of the composite materials increased with increasing nanotube content in the range studied.

Effects of mechanical strain on the electric conductivity of multiwalled carbon nanotube (MWCNT)/polyurethane (PU) composites

Conducting polymers have been under development for more than thirty years as replacements for metals in various applications, such as fuel cells, solar cells, actuators, etc. In this study, we investigate conducting polymer composites and attempt to fabricate composite polyurethane/multiwalled carbon nanotubes. The multiwalled carbon nanotubes (MWCNTs) were acid-treated to add functional groups such as -OH or -COOH so they could then be chemically bonded to diisocyanate to form a urethane linkage. Because they have fewer impurities and reduced surface roughness (as confirmed by TEM micrographs), acid-treated MWCNTs can be better dispersed in a polyurethane (PU) matrix than untreated MWCNTs, and acid-treated MWCNTs exhibit better adhesion with the PU matrix, as well. In addition, the conductance test of MWCNT/PU films as a function of elongation showed that the conductance of the acid-treated MWCNT/PU increased up to a certain % elongation, while that of the untreated MWCNT/PU decreased monotonically with % elongation.

Dispersion of carbon nanotubes in low pH aqueous solutions by means of alumina-coated silica nanoparticles

A novel noncovalent and inorganic method was used to disperse multiwalled carbon nanotubes (MWCNTs) in aqueous solutions through alumina-coated silica (ACS) nanoparticle halos. MWCNTs were directly dispersed into a highly charged ACS nanoparticle aqueous solution without functionalization of their surfaces. The dispersed MWCNTs were characterized by transmission electron microscopy and atomic force microscopy. Raman spectroscopy of MWCNTs prepared from dispersion in the ACS solution revealed reduced bundling compared to the corresponding untreated MWCNTs. The characteristic Raman peak at about 1570 cm −1, corresponding to the G band, shifted to a higher wavenumber with a narrower peak. It was possible to disperse up to 20 mg/mL of MWCNTs in a 1 wt% ACS nanoparticle aqueous solution at pH 2. This homogeneous MWCNT–ACS aqueous solution was stable for weeks after ultrasonication.

Electrochemical Reduction of Oxygen on Multiwalled Carbon Nanotube Modified Glassy Carbon Electrodes in Acid Media

The electrocatalytic reduction of oxygen has been studied on multiwalled carbon nanotube (MWCNT) modified glassy carbon (GC) electrodes in 0.5 M H 2 SO 4 solution using the rotating disk electrode technique. The oxygen reduction behavior of oxidatively pretreated and untreated MWCNT modified GC electrodes was compared. The results obtained indicate that the electrocatalytic properties of untreated MWCNTs toward O 2 reduction in acid media are noticeably better than that of pretreated MWCNTs. This effect is caused by catalyst impurities which remain in the nanotubes prepared by chemical vapor deposition and can be largely removed by treatment in acids.