Multiwalled Carbon Nanotubes Samples Research Articles

Effect of acid-treated multi-walled carbon nanotubes on thermo-oxidative stability and degradation behavior of silicone rubber

The effect of acid-treated multi-walled carbon nanotubes (MWCNTs) on thermo-oxidative stability and degradation behavior of silicone rubber (SR) was evaluated. Raman microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric (TG) analysis were performed to characterize the surface states of MWCNTs samples. The results demonstrated that after acid treatment the nanodefects and surface oxygen-containing groups (mainly hydroxyl and carboxyl groups) were formed and the number of them was gradually increased by increasing the treatment time. Then these MWCNTs were embedded into SR matrix. Furthermore, the thermo-oxidative stability and degradation behavior of MWCNTs/SR composites were studied using thermogravimetric/infrared spectrometry (TG-IR). Thermo-oxidative stability test in air revealed that the degradation of SR, at relatively low temperature, was mainly due to the oxidation of Si-CH3 side groups and the generation of free radicals. This behavior was hindered by the MWCNTs’ surface nanodefects and hydroxyl groups, as proved by TG-IR study which revealed that the amount of carbonyl compounds was reduced more than 60%, compared with that of neat SR. Therefore, acid treatment led a better thermo-oxidative stability of MWCNTs/SR. For 4hAT-MWCNTs/SR, with maximum hydroxyl groups on MWCNTs surface, the Ti (defined as the temperature for 5% mass loss) of it is increased by 34.8 °C compared to that of neat SR, and even increased by 18.5 °C compared with that of raw-MWCNTs/SR.

The electrocatalytic characterization and mechanism of carbon nanotubes with different numbers of walls for the VO2+/VO2+ redox couple

Carbon nanotubes (CNTs) have been applied as catalysts in the VO2+/VO2+ redox, whereas the mechanism of CNTs for the redox reaction is still unclear. In this work, the mechanism of the VO2+/VO2+ redox is investigated by comparing the electrocatalytic performance of CNTs with different distributions. For different CNTs, the peak current density of the VO2+/VO2+ redox increases with increasing content of oxygen-functional groups on the surface of CNTs, especially the carboxyl group which is proved as active sites for the redox reaction. Moreover, the reversibility of the VO2+/VO2+ redox decreases with increasing defects of CNTs, as the defects affect the charge transfer of the catalytic reaction. Nevertheless, when a multi-walled CNT sample is oxidized to achieve a high content of oxygen functional groups and defects, the peak current density of the redox reaction increases from 38.5 mA mg-1 to 45.4 mA mg-1 whilst the peak potential separation (ΔEp) also increases from 0.176 V to 0.209 V. Overall, a balance between the oxygen functional groups and the defects of CNTs affects the peak current and the reversibility for the VO2+/VO2+ redox.

Raman spectroscopy fingerprint of stainless steel-MWCNTs nanocomposite processed by ball-milling

Stainless steel 304L alloy powder and multiwalled carbon nanotubes were mixed by ball-milling under ambient atmosphere and in a broad range of milling times, which spans from 0 to 120 min. Here, we provided spectroscopic signatures for several distinct composites produced, to show that the Raman spectra present interesting splittings of the D-band feature into two main sub-bands, D-left and D-right, together with several other secondary features. The G-band feature also presents multiple splittings that are related to the outer and inner diameter distributions intrinsic to the multiwalled carbon nanotube samples. A discussion about the second order 2D-band (also known as G′-band) is also provided. The results reveal that the multiple spectral features observed in the D-band are related to an increased chemical functionalization. A lower content of amorphous carbon at 60 and 90 min of milling time is verified and the G-band frequencies associated to the tubes in the outer diameters distribution is upshifted, which suggests that doping induced by strain is taking place in the milled samples. The results indicate that Raman spectroscopy can be a powerful tool for a fast and non-destructive characterization of carbon nanocomposites used in powder metallurgy manufacturing processes.

Modifications of Graphite and Multiwall Carbon Nanotubes in the Presence of Urea

The effect of high-energy ball milling on two carbon allotropes, graphite and multiwall carbon nanotubes (MWCNT) in the presence of urea has been studied. Samples were investigated using Raman spectroscopy, x-ray diffraction, scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS). Nitrogen-doped graphene has been successfully synthesized via a simple scalable mechanochemistry method using urea and graphite powder precursors. XPS results revealed the existence of the different nitrogen atoms configurations including pyridine, pyrrodic and graphitic N. SEM observations showed that the graphene nanosheets morphology become more wrinkles folded and crumbled as the milling time increased. The ID/IG ratio also increased as the milling time rose. The presence of both D′ and G + D bands at 1621 cm−1 and 2940 cm−1, respectively, demonstrated the nitrogen incorporation in the graphene lattice Two factors contribute to the used urea: first it helps to exfoliate graphite into graphene, and second it preserves the graphitic structure from damage during the milling process as well as acting as a solid-state nitrogen source. Based on the phase analysis, the d-spacing of MWCNT samples in the presence of urea decreased due to the mechanical force in the milling process as the milling time increased. On the other hand, in the graphite case, due to its open flat surface, the graphite (002) peak shifts toward lower two theta as the milling time increase. Such findings are important and could be used for large-scale production of N-doped graphene, diminishing the use of either dangerous chemicals or sophisticated equipment.

Ion irradiation-induced, localized sp 2 to sp 3 hybridized carbon transformation in walls of multiwalled carbon nanotubes

Abstract In this report, ion irradiation-induced localized sp2 to sp3 hybridized carbon transformation in multiwalled carbon nanotubes (MWCNTs) was observed after irradiating MWCNTs with high-energy Au+8 ions (100 MeV). The used MWCNTs were grown using cobaltocene and benzene as catalyst and carbon source, respectively by the thermal CVD technique and consist of both unfilled and Co-filled tubes. Prior to irradiation, the MWCNT sample was characterized using scanning electron microscope and micro-Raman and photoluminescence spectrometers. The effect of ion fluence on MWCNT walls and transformation of sp2 to sp3 sites was analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. We found that as the fluence increased, the localized transformation from sp2 to sp3 sites occurred in the walls of MWCNTs, which was evident by the emergence of peak at approximately 1543 cm−1 associated with the G peak in tetrahedral amorphous carbon (ta-C) and the vanishing of 2D band (2700 cm−1). Furthermore, we observed broadening in D and G, with slight shift in their positions and consistent decrease in 2D band intensity, as fluence increased.

Synthesis of novel microporous nanocomposites of ZIF-8 on multiwalled carbon nanotubes for adsorptive removing benzoic acid from water

This study reports a controlled route for straightforward synthesizing novel microporous nanocomposites of ZIF-8 type metal–organic frameworks material incorporated with multiwalled carbon nanotubes (MWNTs). The prepared ZIF-8/MWNTs samples were characterized by XPS, XRD, SEM, TEM, N2 adsorption and TGA experiments to investigate the effects of synthesis methods on the formation of the hybrid composite structure of ZIF-8 nanocystals growing on MWNTs. The ZIF-8/MWNTs nanocomposites were successfully synthesized by the method of adding MWNTs into a zinc nitrate solution prior to react with a 2-methylimidazole solution and the microporous structures of the ZIF-8/MWNTs nanocomposites were controlled by the MWNTs content. As an adsorbent for adsorptive removing benzoic acid (BA) from water, the prepared ZIF-8/MWNTs-25 (B) nanocomposite exhibits the best adsorption capacity of 303mg/g, about 65mg/g higher than the ZIF-8. The improvement in the BA adsorption is due to the pore/size-selective BA adsorption of the effective micropores yielded by the ZIF-8/MWNTs hybrid composite structure, in addition to the basic-acid, coordination, and π–π stacking interactions between ZIF-8 and BA. The high adsorption capacity and good reusability of the ZIF-8/MWNTs-25 (B) nanocomposite suggests that it can be applied as novel adsorbents showing attractive potential.

Hydrogen-acetylene gas ratio and catalyst thickness effect on the growth of uniform layer of carbon nanotubes

ABSTRACTEffect of catalyst thickness (2, 4, and 6 nm) and acetylene-hydrogen gas ratio (1/4, 2/4, and 3/4) on the synthesis of carbon nanotubes is reported in this article. Synthesized nanotubes are characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and Raman effect. From SEM results, nanotubes growth is less for higher thickness, as at higher thickness catalyst nanoparticles agglomerate which suppress the growth of nanotubes. Raman spectroscopy results reveal that at higher thickness defects density increases. Nanotube of better crystallinity and graphitic outer walls grows for lower acetylene-hydrogen gas ratio and at smaller thickness of catalyst layer. The sheet resistance of carbon nanotube thin film is measured by using Hall effect measurement systems. Smallest sheet resistance among synthesized multi-walled carbon nanotubes sample is obtained for nanotubes grown on 2 nm thick catalyst film and is 0.9 kΩ/square.

He ion irradiation effects on multiwalled carbon nanotubes structure

Samples of multi-walled carbon nanotubes (MWNTs) were irradiated with 80 keV He ions. Scanning electron microscopy (SEM) inspection showed that the average outer diameters of the tube decreased as a result of ion irradiation. The samples were also characterized using Raman spectrometry by analysis of the intensity of main bands in the spectra of virgin and irradiated MWNT samples. Modifications of the disorder mode (D-band) and the tangential mode (G-band) were studied as a function of irradiation fluences. Raman spectra showed that as the fluence increases, the MWNTs first show disorder due to the produced defects, and then amorphization under still higher fluence of ion irradiation. Thermal and athermal mechanisms of the radiation induced MWNTs modifications are discussed.

Utilizing Fullerenols as Surfactant for Carbon Nanotubes Dispersions Preparation

Dispersions of individual carbon nanotubes (CNTs) are crucial for nanodevices and polymer/CNTs nanocomposites. In this paper, stable and homogenous dispersions of individual multiwalled carbon nanotubes (MWCNTs) have been synthesized. The factors influencing the dispersibility mechanism, including the surfactant concentration and the pH value, have been investigated. SEM images display the impurities sticking on MWCNTs which have been removed. The oxygen-containing groups on the surface of MWCNTs sample have been detected through FT-IR and Raman spectra. All experimental results illustrate that using fullerenols as surfactant can greatly improve the dispersibility of MWCNTs. Moreover, the prepared dispersions exhibit good stability that the sediment percentage of fullerenols-MWCNTs is only 5.2% after 5 days.

Investigation of Different Pre-Treated Multi-Walled Carbon Nanotubes by Raman Spectroscopy

Raman spectroscopy is a common method of studying carbon-based materials such as multi-walled carbon nanotubes (MWCNT). However, the analysis of this technique is non-trivial since recorded spectra may be a convolution of both molecular vibrations and phonon resonances. The energies of these physical processes may occur in the same energy regime, and hence several analytical approaches can be necessary for a full analysis. Due to the negligible quantities of non-graphitic carbon in MWCNT, the present fitting procedure focuses on understanding phonon resonances to elucidate how varying modifications of MWCNT ultimately influence their graphitic bulk structure. We have found this approach to provide greater insight into the structure of MWCNT when low quantities of amorphous carbon are present, when compared with methods which try to interpret both phonon scattering and molecular vibrations simultaneously. Different pre-treatments for the modification of the graphitic structure of MWCNT are compared, including aqueous acidic and gas phase methods, and statistically evaluated. Focusing on phonon resonances enables one to analyze the reaction process of nitrosulfuric acid pre-treatment at different temperatures. Thereby, it is possible to control the ratio between defects and graphitic structures in MWCNT samples and prepare samples with reproducible D/G ratios.

Morphological and structural modifications of multiwalled carbon nanotubes by electron beam irradiation

Effects of electron beam irradiation on a morphology and structure of multiwalled carbon nanotubes sample in a normal imaging regime of a scanning electron microscope (SEM) were investigated. Direct SEM observations give evidence that irradiation by electron beam in SEM eliminates morphological unevenness, in the form of round spots of white contrast, on the surface of carbon nanotubes (CNTs) and makes the tubes thinner. Electron dispersive analysis and Raman spectroscopy are used to explore the origin and nature of these spots. From this analysis we found that e-beam irradiation improves the CNTs graphitization. The synergy of thermal heating and ionization produced by the irradiation are discussed as possible mechanisms of the observed effects.

Tuning Work Function of Multi-Walled Carbon Nanotubes By Defects Creation

Carbon nanotube(CNT) is a very attractive material to various electronic devices and optoelectronic applications owing to its promising structural and electronic properties comparing with other carbon materials.1CNT has been successfully applied on field emission displays, light emitting diodes, solar cells, etc. To these electronic or optoelectronic devices which require modification of the junction interface to achieve a well-defined electronic energy level leading to a desired performance, work function is a critical parameter. It is of importance to develop a systematic methodology to manipulate CNT’s work function to match diverse energy structures. Impacts of multi-walled carbon nanotube(MWCNT) surface functional groups on its work function has been poposed,2 which provides a potential strategy of tailoring an appropriate work function for different applications. In our previous study,3we found that creating defects on MWCNT benefits planting abundant functional groups on it, this would contribute to control work function in a wide range. In this work, a surface functional group decoration methods associated with coating, defects creation, surface functional groups decoration and doping on MWCNT for tuning work function has been designed and carried out. Inductively coupled plasma mass spectrometry(ICP-MS) are employed to distinguish the impact of impure metal elements, since the raw CNT always contains some metal impurities which may have negative effect on investigating the origin of work function changes. Annealing MWCNT samples in different temperatures to remove certain functional group is conducted to identify which certain functional group responsible for the work function tuning. Photo-electron spectroscopy in air (PESA)* and ultraviolet photoelectron spectroscopy (UPS) are conducted to measure modified CNT’s work function directly and also provide information of density of state (DOS) near Femi level. Temperature programed desorption(TPD) and X-ray photoelectron spectroscopy(XPS) analysis provides estimation of different functional group amount and compelling evidence of doping and coating. Field emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM) are adopted to observe the morphology of modified MWCNTs. Structure disorder information is supplied by Raman spectroscopy. It has been revealed that a 0.55 eV work function difference between different modified WMCNTs is achieved at current stage (Figure 1). The further modification parameters will be presented on the conference. PESA*: It is an instrument for Photoelectron Spectroscopy at atmospheric pressure. UV photons emitted from a deuterium lamp are monochromated by a grating spectrometer and focused on a sample. Then, photoelectrons emitted from the sample are counted by an open counter. In terms of metal, when the photon energy is smaller than work function, there is no electron reach counter. If the photon energy is larger than work function, the electron from sample starts to be counted by open counter which indicates the exact value of work function. After plotting data in a graph, the crossing point of the back ground and the yield line is a photoemission threshold energy, also called the work function or the ionization potential. Acknowledgement: This work partially was supported by COI STREAM from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Shin-Etsu Chemical Co., Ltd. Japan. and Riken Keiki Co., Ltd. Their contribution is greatly appreciated. Reference: 1 S. Iijima, Nature, 1991, 354, 561–58. 2 H. Ago, T. Kugler, F. Cacialli, W. R. Salaneck, M. Shaffer, A. H. Windle and R. H. Friend, J. Mater. Chem. B, 1999, 103, 8116–8121. 3 K, Waki, R. A. Wong, H. S. Oktaviano, T. Fujio, T. Nagai, K. Kimoto and K. Yamada, Energy Environ. Sci., 2014,7, 1950-1958 Figure 1

Divergent surface properties of multidimensional sp2 carbon allotropes: the effect of aging phenomena

Despite the current interest in the scientific community in exploiting divergent surface properties of graphitic carbon allotropes, conclusive differentiation remains elusive even when dealing with parameters as fundamental as adhesion. Here, we set out to provide conclusive experimental evidence on the time evolution of the surface properties of highly oriented pyrolytic graphite (HOPG), graphene monolayer (GML) and multiwalled carbon nanotubes (MWCNTs) as we expose these materials to airborne contaminants, by providing (1) statistically significant results based on large datasets consisting of thousands of force measurements, and (2) errors sufficiently self-consistent to treat the comparison between datasets in atomic force microscopy (AFM) measurements. We first consider HOPG as a model system and then employ our results to draw conclusions from the GML and MWCNT samples. We find that the surface properties of aged HOPG are indistinguishable from those of aged GML and MWCNT, while being distinct from those of cleaved HOPG. Herein, we provide a sufficient body of evidence to disregard any divergence in surface properties for multidimensional sp2 carbon allotropes that undergo similar aging processes.

Fabrication and evaluation of thin layer PVDF composites using MWCNT reinforcement: Mechanical, electrical and enhanced electromagnetic interference shielding properties

Radar X-band electromagnetic interference shielding (EMS) is one of the prime requirements for any air vehicle coating; with limitations on the balance between strength and thickness of the EMS material. Nanocomposite of multiwalled-carbon-nanotubes (MWCNT) has been homogeneously integrated (0 – 9 wt%) with polymer, poly (vinylidene fluoride, PVDF) to yield 300 micron film. The PVDF + 9 wt% MWCNT sample of density 1.41 g/cm3 show specific shielding effectiveness (SSE) of 17.7 dB/(g/cm3) (99.6% EMS), with maintained hardness and improved conductivity. With multilayer stacking (900 microns) of these films of density 1.37 g/cm3, the sample showed increase in SSE to 23.3 dB/(g/cm3) (99.93% EMS). Uniform dispersion of MWCNTs in the PVDF matrix gives rise to increased conductivity in the sample beyond 5 wt% MWCNT reinforcement. The results are correlated to the hardness, reflection loss, absorption loss, percolation threshold, permittivity and the conductivity data. An extremely thin film with maximum EMS property is hence proposed.

Investigation of polycarbonate/acrylonitrile butadiene styrene/multiwall carbon nanotube nanocomposites under impact loading

In this study, the effect of polycarbonate (PC)/acrylonitrile butadiene styrene (ABS)‐reinforced multiwall carbon nanotube (MWCNT) nanocomposites under a high‐velocity impact was investigated. PC/ABS (70/30 w/w)/MWCNT nanocomposites containing 1, 2, and 4 wt% were used to manufacture samples for this study. The samples were fabricated in sheet form with 100 × 100 mm dimensions and tested by gas gun for high‐velocity impact tests. The experimental results indicate that the energy absorption, limit velocity, and tensile modulus of the nanocomposite samples increased by approximately 121%, 52%, and 103% for the PC/ABS (70/30 w/w)/2 wt% MWCNT samples respectively. These results were confirmed by a transmission electron microscopy analysis test that was conducted for the state of dispersion of MWCNTs in the nanocomposite samples. The transmission electron microscopy results show that the best morphological structure of carbon nanotube at the interface of PC and ABS is that for the nanocomposite containing 2 wt% MWCNTs, which led to improved interface of the nanocomposites and higher mechanical properties. Copyright © 2016 John Wiley & Sons, Ltd.

(Invited) The Influence of the Carbon Support and Platinum Particles Size on Degradation of Cathode for Low Platinum Loading Catalyst Layer

The Reactive Spray Deposition Technology (RSDT) is a thin-film deposition process that overcomes many of the shortcomings of traditional vapor deposition techniques while yielding equal or better quality coatings at a lower cost [1, 2]. The RSDT process bypasses traditional wet chemical routes by simultaneously nucleating the catalyst on a support and sequential deposition of catalytic layers via gas-phase. The process does not require intensive electrical power and harnesses the energy stored in a liquid fuel to decompose the metal organic precursor into the desired metallic or bi-metallic product. The process can be tailored to favor both alloying and core-shell formation. This has allowed our team to reduce the cathode Pt loading below 0.1 mg/cm2 with enhanced performance. The Pt/Ketjen Black system surpassed the 2017 DOE target with a mass activity of 0.51 A mg-1at 0.9V and oxygen pressure of 180kPa [2]. In the present work mass transport overpotential is investigated with ultra-low Pt loading (0.1 and 0.05 mg cm-2 on cathode and anode; catalyst with average particle size of 2 nm and 3 nm, respectively) deposited directly by RSDT onto two supports: Ketjen Black (KB) and multi-walled carbon nanotube (MWCNT). We conduct fundamental studies of the ORR on low Pt loading C supports to address the durability issues. The focus is to strengthen the support-Pt anchoring and also lower the total Pt loading in the cathode to 0.05 mg/cm2, an enhancement in electro-catalytic activity, mass activity @900 mV iR-free of 0.44 A/mg PGM and durability testing at 30,000 voltage cycles. Long-term compatibility with other cell components in real-world environments, including Accelerated Stress Test (AST) cycling will be demonstrated in MEAs (≥25cm2). We performed polarization curves in pure Oxygen RH 100%, 80°C, stoich. 9.5/2, for KB and MWCNT with the same catalyst loading but different particle sizes. We noticed that there were no significant differences in the absolute performances due to the variation of particle size for Ketjen-Black samples while MWCNT samples show improvement in performances by increasing the diameter of Pt particles from 2 to 3 nm. We performed polarization curves in Air with constant flows: 1 L/min Air and 0.5 L/min Hydrogen. Figure 1, shows initial performance and after 30,000 of cycles for both supports and Pt particles size of 3 nm, see figure 1a. The Ketjen-Black sample shows better performance in constant-flow polarizations than the MWCNT sample, as we presume it suffers to a lesser extent from cathode charge transfer limitations. Differences between the two samples seem not to vary during AST. A microscopy study on post-durability electrodes showed an agglomeration in the cathode layer for KB and MWCNT particles size from 2-15 nm and 2-12, respectively, after 30K cycles, Figure 1b and c. The evolution during the AST of specific activity and platinum oxide coverage is also investigated showing results in accordance with particle growth mechanisms.

Rapid adsorption of toxic Pb(II) ions from aqueous solution using multiwall carbon nanotubes synthesized by microwave chemical vapor deposition technique

Multiwall carbon nanotubes (MWCNTs) were synthesized using a tubular microwave chemical vapor deposition technique, using acetylene and hydrogen as the precursor gases and ferrocene as catalyst. The novel MWCNT samples were tested for their performance in terms of Pb(II) binding. The synthesized MWCNT samples were characterized using Fourier Transform Infrared (FT-IR), Brunauer, Emmett and Teller (BET), Field Emission Scanning Electron Microscopy (FESEM) analysis, and the adsorption of Pb(II) was studied as a function of pH, initial Pb(II) concentration, MWCNT dosage, agitation speed, and adsorption time, and process parameters were optimized. The adsorption data followed both Freundlich and Langmuir isotherms. On the basis of the Langmuir model, Qmax was calculated to be 104.2mg/g for the microwave-synthesized MWCNTs. In order to investigate the dynamic behavior of MWCNTs as an adsorbent, the kinetic data were modeled using pseudo first-order and pseudo second-order equations. Different thermodynamic parameters, viz., ∆H0, ∆S0 and ∆G0 were evaluated and it was found that the adsorption was feasible, spontaneous and endothermic in nature. The statistical analysis revealed that the optimum conditions for the highest removal (99.9%) of Pb(II) are at pH5, MWCNT dosage 0.1g, agitation speed 160r/min and time of 22.5min with the initial concentration of 10mg/L. Our results proved that microwave-synthesized MWCNTs can be used as an effective Pb(II) adsorbent due to their high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.

The effects of liquid-phase oxidation of multiwall carbon nanotubes on their surface characteristics

The development of new sorbents based on nanostructured carbon materials recently became a perspective field of research. Main topic of current study is to investigate the effect of different regimes of multiwall carbon nanotubes (MWCNT) surface modification process on their structural characteristics. MWCNT samples were treated with nitric acid at high temperature. Structural properties were studied using low temperature nitrogen adsorption and acid-base back titration methods. The study showed that diluted nitric acid does not affect MWCNT structure. Concentrated nitric acid treatment leads to formation of 2.8 carboxylic groups per 1 nm2 of the sample surface.

High-performance LiMn0.8Fe0.2PO4 with hybrid conductive additives based on functionalized and etched multi-walled carbon nanotubes by self-destruction during the lithiation process

High-performance LiMn0.8Fe0.2PO4 (LMFP) was prepared with both etched and functionalized multi-walled carbon nanotubes (MWNTs) and ketjen blacks (KBs). The MWNTs functionalized with carboxylic groups exhibited better affinity toward cathode materials than did pristine nanotubes. The electrochemical performance of the LMFP cathode materials was also improved by using MWNTs shortened by vigorous mechanical mixing, compared with pristine long MWNT samples. Moreover, the use of MWNTs together with KB provided better electrochemical performance than when KBs or MWNTs were used separately. The modified LMFP (m-LMFP) had an excellent rate capability, with discharge capacities of 162 mAh g−1 at 0.1 C and 147 mAh g−1 at 1 C, the highest values reported to date for this type of electrode. The capacity retention of the m-LMFP was 94% after 50 cycles, whereas that of the pristine sample was only 82%. Transmission electron microscopy and AC impedance results confirmed that the addition of MWNTs to the cathode materials improved their networking and electrical properties. However, excessive substitution of MWNTs for KB was not favorable for maximizing electrochemical performance because of increased internal resistance.

Polyvinylchloride intercalated poly(ethylene glycol)-modified-multi-walled carbon nanotube buckypaper composites via resin-infiltration technique

In this paper, synthesis and characterization of polymer intercalated carbon nanotube buckypaper for improved structural, morphological, electrical, and thermal properties have been discussed. Resin-infiltration technique was opted for the preparation of polyvinylchloride intercalated poly(ethylene glycol) -modified-multi-walled carbon nanotube buckypaper. The effect of increasing purified nanotube (purified multi-walled carbon nanotube) and functional nanotube (functional multi-walled carbon nanotube) content on the properties of BP-polyvinylchloride/poly(ethylene glycol)/purified multi-walled carbon nanotube and BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube buckypaper composites was investigated, while using same amount of polymer. Results indicated better interaction between polyvinylchloride and functional multi-walled carbon nanotube due to hydrogen bonding relative to polyvinylchloride and purified multi-walled carbon nanotube where no chemical link was present between the two. Fourier transform infrared spectroscopy results confirmed the modification of functional multi-walled carbon nanotube, and formation of buckypaper composite. Scanning electron microscopy micrographs showed better network formation in BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube samples and intercalation of polymer can be seen forming polymer-coated functional multi-walled carbon nanotube network. Thermal stability was found to be improved by the increment of multi-walled carbon nanotube and the difference between the thermal stability of functional multi-walled carbon nanotube and purified multi-walled carbon nanotube buckypaper was also prominent. The maximum degradation temperature (Tmax) of functional composite BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 (469℃) was higher relative to non-functional BP-polyvinylchloride/poly(ethylene glycol)/purified multi-walled carbon nanotube 0.05 (461℃). The glass transition temperature of BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 was found as 249℃, while BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 depicted higher Tg of 271℃. Amorphous character of polymer/carbon nanotube -buckypaper composite showed a trend towards crystallinity according to X-ray diffraction results. Purified multi-walled carbon nanotube-based buckypaper presented conductivity up to 1.91 × 10−1 S cm−1, while BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.01–0.08 had increased conductivity up to 9.88 × 10−1 S cm−1.