Multiwalled Carbon Nanotubes Samples Research Articles

Femtosecond pulsed laser microscopy: a new tool to assess the in vitro delivered dose of carbon nanotubes in cell culture experiments

BackgroundIn vitro models are widely used in nanotoxicology. In these assays, a careful documentation of the fraction of nanomaterials that reaches the cells, i.e. the in vitro delivered dose, is a critical element for the interpretation of the data. The in vitro delivered dose can be measured by quantifying the amount of material in contact with the cells, or can be estimated by applying particokinetic models. For carbon nanotubes (CNTs), the determination of the in vitro delivered dose is not evident because their quantification in biological matrices is difficult, and particokinetic models are not adapted to high aspect ratio materials. Here, we applied a rapid and direct approach, based on femtosecond pulsed laser microscopy (FPLM), to assess the in vitro delivered dose of multi-walled CNTs (MWCNTs).Methods and resultsWe incubated mouse lung fibroblasts (MLg) and differentiated human monocytic cells (THP-1) in 96-well plates for 24 h with a set of different MWCNTs. The cytotoxic response to the MWCNTs was evaluated using the WST-1 assay in both cell lines, and the pro-inflammatory response was determined by measuring the release of IL-1β by THP-1 cells. Contrasting cell responses were observed across the MWCNTs. The sedimentation rate of the different MWCNTs was assessed by monitoring turbidity decay with time in cell culture medium. These turbidity measurements revealed some differences among the MWCNT samples which, however, did not parallel the contrasting cell responses. FPLM measurements in cell culture wells revealed that the in vitro delivered MWCNT dose did not parallel sedimentation data, and suggested that cultured cells contributed to set up the delivered dose. The FPLM data allowed, for each MWCNT sample, an adjustment of the measured cytotoxicity and IL-1β responses to the delivered doses. This adjusted in vitro activity led to another toxicity ranking of the MWCNT samples as compared to the unadjusted activities. In macrophages, this adjusted ranking was consistent with existing knowledge on the impact of surface MWCNT functionalization on cytotoxicity, and might better reflect the intrinsic activity of the MWCNT samples.ConclusionThe present study further highlights the need to estimate the in vitro delivered dose in cell culture experiments with nanomaterials. The FPLM measurement of the in vitro delivered dose of MWCNTs can enrich experimental results, and may refine our understanding of their interactions with cells.

Improved CO2 adsorption properties through amine functionalization of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNT) with different functionalities (standard–; OH–; and COOH– functionalized) are chemically modified with N1-(3-trimethoxysilylpropyl)diethylenetriamine (DETASi) aiming to enhance their CO2 adsorption/separation properties. The grafting of the DETASi groups to the surface of the MWCNT samples is studied by X-ray photoelectron spectroscopy (XPS), operando thermogravimetric analysis - infrared spectroscopy (TGA-IR), –196 °C N2-sorption isotherms, and scanning electron microscopy (SEM). A comprehensive overview of the reaction mechanism and samples structure/composition is provided. It was found that the aforementioned functionalities highly influence the physical–chemical and the textural properties of the DETASi modified-MWCNT materials, impacting in the DETASi functionalization degree and its distribution on the sample. Amount (by TGA-IR) and homogeneity (by SEM) of the organosilicon group in the functionalized samples increases with the increase of the functionalities in the parent MWCNT materials. Standard-MWCNT and OH– functionalized MWCNT showed to be unable to adsorb CO2, while COOH– modified MWCNT adsorbed just 0.1% at 1 bar and 30 °C. At the same adsorption conditions, DETASi modification of the MWCNT materials enhanced the CO2 adsorption capacity, with the maximum CO2 uptake (2.11%) for COOH-MWCNT functionalized with DETASi. The selectivity for CO2/N2 separation was also improved after DETASi grafting reaction, with the highest value (1.89%) observed for the standard-MWCNT material modified with DETASi. In general, the increase of the DETASi amount and of the microporosity in the functionalized MWCNT sorbents is accompanied by an improvement of the CO2 adsorption-separation properties. The water vapor adsorption indicated that the standard-MWCNT sample modified with DETASi is resistant to the presence of water and its presence (water vapor of ~3.2 kPa) can improve the CO2 uptake.

Electronic properties of carbon nanotubes as detected by photoemission and inverse photoemission

The relation between morphology and energy level alignment in carbon nanotubes (CNT) is a crucial information for the optimization of applications in nanoelectronics, optics, mechanics and (bio)chemistry. Here we present a study of the relation between the electronic properties and the morphology of single wall CNT (SWCNT), aligned multi wall CNT (MWCNT) and unaligned MWCNT. The CNT were synthesized via catalytic chemical vapor deposition in ultra-high vacuum conditions. Combined ultraviolet photoemission and inverse photoemission (IPES) spectra reveal a high sensitivity to the nanotube morphology. In the case of unaligned SWCNT the distinctive unoccupied Van Hove singularities (vHs) features are observed in the high resolution IPES spectra. Those features are assigned to semiconducting and metallic SWCNT states, according to calculated vHs DOS. The two MWCNT samples are similar in the diameter of the tube (about 15 nm) and present similar filled and empty electronic states, although the measured features in the aligned MWCNT are more defined. Noteworthy, interlayer states are also revealed. Their intensities are directly related to the MWCNT alignment. Focussing and geometrical effects associated to the MWCNT alignment are discussed to account the spectral differences.

The vertically aligned carbon nanotubes arrays as biointerface for the E. Coli strain M-17

The biological interaction materials study is necessary when creating biocompatible implantable devices, including biosensors. Important criteria for their creation are the bactericidal properties of such materials. In this paper, we study the bacteria with vertically aligned carbon nanotubes interaction. In this work we examined the bioaffinity of multi-walled carbon nanotubes samples with E. Coli strain M17 bacteria. We synthesized carbon nanotubes with various structural features on the surface of silicon wafers. Then westudied of the wettability of the obtained samples and tested bioactivity of E. Coli bacteria using spectrometry and photometry methods. It was found that E. Coli bacteria of strain M-17 demonstrated the best vital signs when interacting with the surfaces of hydrophobic samples of vertically oriented carbon nanotubes.

Temperature‐dependent Battery Performance of a Na3V2(PO4)2F3@MWCNT Cathode and In‐situ Heat Generation on Cycling

Excellent structural stability, high operating voltage, and high capacity have made Na3 V2 (PO4 )2 F3 a promising cathode material for sodium-ion batteries. However, high-temperature battery performances and heat generation measurements have not been systematically reported yet. Carbon-coated Na3 V2 (PO4 )2 F3 @MWCNT (multi-walled carbon nanotube) samples are fabricated by a hydrothermal-assisted sol-gel method and the electrochemical performances are evaluated at three different temperatures (25, 45, and 55 °C). The well-crystallized Na3 V2 (PO4 )2 F3 @MWCNT samples exhibit good cycling stability at both low and high temperatures; they deliver an initial discharge capacity of 120-125 mAhg-1 at a 1 C rate with a retention of 53 % capacity after 1,400 cycles with 99 % columbic efficiency. The half-cell delivers a capacity of 100 mAhg-1 even at a high rate of 10 C at room temperature. Furthermore, the Na3 V2 (PO4 )2 F3 @MWCNT samples show good long-term durability; the capacity loss is an average of 0.05 % per cycle at a 1 C rate at 55 °C. Furthermore, ionic diffusivity and charge transfer resistance are evaluated as functions of state of charge, and they explain the high electrochemical performance of the Na3 V2 (PO4 )2 F3 @MWCNT samples. In-situ heat generation measurements reveal reversible results upon cycling owing to the high structural stability of the material. Excellent electrochemical performances are also demonstrated in the full-cell configuration with hard carbon as well as antimony Sb/C anodes.

Optimizing the conditions of multi-walled carbon nanotubes surface activation and loading metal nanoparticles for enhanced hydrogen storage

In this study, the effect of surface activation of multi-walled carbon nanotubes (MWCNTs) by KOH along with loading of cobalt and lithium nanoparticles on the surface of MWCNTs are investigated. In the first step, surface activation parameters, i.e. MWCNT/KOH weight ratio, activation temperature, and activation time are optimized to give the highest hydrogen uptake. According to obtained results, the optimum synthesis conditions are MWCNT/KOH weight ratio of 1:5, 800 °C, and 1 h of activation duration. Afterward, cobalt and lithium metal nanoparticles are doped discretely on the surface of activated nanotubes. It is demonstrated that amounts of loaded cobalt and lithium metals are 5.5 and 1.9% wt, respectively. In addition, it is revealed that the amount of hydrogen storage capacity for cobalt-loaded and lithium-loaded MWCNTs are 1.06% wt. and 1.33% wt., respectively (at 278 K) which are higher than the capacity of pristine and activated MWCNT samples.

Characterization of microwave absorption in carbon nanotubes using resonance aperture transmission method

A new method to characterize microwave electromagnetic (EM) absorption of a bulk carbon nanotube (CNT) material is proposed and experimentally evaluated in this paper. The method is based on the measurement of microwave transmission through a capacitive-resonator aperture (CRA) in a conductive screen loaded with a CNT sample under test. This method allows us to measure microwave permittivity and absorption of thin samples (∼0.1 μm–10 μm thick) with linear dimensions much smaller than the wavelength of radiation in free space. This “minimal” sample requirement restricts the application of conventional microwave characterization methods such as free-space or waveguide permittivity characterization. It is demonstrated that the resonance E-field enhancement inside the CRA leads to strong EM interaction of the microwave E-field with the CNT sample under test, thus enabling high sensitivity and dynamic range (∼5 dB) of the measurement procedure. Another advantage of the proposed technique over conventional non-resonance characterization methods is that in the resonance transmission band, the CRA operation is reflection-less, which leads to a relatively simple qualitative algebraic de-embedding procedure of the material parameters based on the principle of energy conservation. The experimental microwave absorption data of the multiwall CNT samples are presented in the S frequency band (2–4 GHz), demonstrating microwave absorption properties of the multiwall CNT ribbons.

Analysis on DI Diesel Engine with Combined Multi-walled Carbon Nanotubes and Vegetable Oil Refinery Waste as Biodiesel

The need of alternate fuel for the reason is demand of fossil fuel and environmental degradation in all over the world. Biodiesel plays an important role because of its potential and availability in the environmental degradation and present energy crisis. The main objective of this experimental work is to reduce the emission without affecting the engine performance with alternate fuel. In this paper, the experimental analysis engine was run by B20EEGAO (20% ethyl ester of ground nut acid oil) with multi-walled carbon nanotubes (MWCNT) in the proportions of 10, 20, 30, 40 and 50 ppm. Five samples of MWCNT with B20EEGAO blend are prepared with the help of ultrasonicator. The important results smoke density of MWCNT30ppmB20EEGAO blend was 50 HSU at maximum load. The CO emission of MWCNT30ppmB20EEGAO blend is reduced in 20%, and HC emission is reduced for 15% compared to diesel. The observed results were that the brake thermal efficiency was higher in MWCNT30ppmB20EEGAO compared to biodiesel, and emission was also reduced except oxides of nitrogen. The best blend selected is MWCNT30ppmB20EEGAO compared to other blends.

Stacked-cup multiwall carbon nanotubes as components of energy-intensive suspension jet fuels

Objectives. The addition of high-density carbon materials to jet fuels can lead to a significant increase in the volumetric energy of the fuel combustion. The purpose of the current study was to thermodynamically analyze the possibility of obtaining model hydrocarbon fuels from toluene and T-1 using stacked-cup multiwall carbon nanotubes (MWCNTs). Methods. Bomb combustion calorimetry was used to define the combustion energy of the MWCNTs in the crystalline state. The temperature dependence of the MWCNTs’ heat capacity in the range 5–370 K and the fusion parameters were estimated using low-temperature adiabatic calorimetry. The physical density of MWCNTs was measured using the pycnometric method. The sedimentation stability of the mixtures of MWCNTs with liquids was determined using centrifugation at 7000 g. The calculations were carried out in MS Excel. Results. The energy and enthalpy of combustion of a technical sample of MWCNTs in the crystalline state were determined. Based on the smoothed heat capacity values, the standard thermodynamic functions (enthalpy, entropy, and Gibbs reduced energy) of MWCNTs in the crystalline state were obtained in a temperature range of 0–2000 K. The extrapolation of the MWCNTs’ heat capacity was carried out at a temperature of up to 2000 K using the heat capacity of crystalline graphite. It has been established that mixtures of MWCNTs with liquids containing more than 33 mass % of MWCNTs are stable during centrifugal sedimentation at 7000 g. For the toluene–MWCNTs and fuel T-1–MWCNTs model systems, the specific and volumetric combustion energies, the adiabatic combustion temperatures, and the conditional final maximum speed of the model rockets with fuel of various compositions were also calculated. Conclusions. The thermodynamic analysis showed that the addition of MWCNTs can significantly increase the volumetric energy intensity of traditional jet fuels, which can in turn improve the operational characteristics of drones and rockets.

Hybrid Nanocomposites of Multi-walled Carbon Nanotubes (MWCNTs) and CuO as Electrode Materials for Energy Storage Devices

The search for electrode materials as a potential candidate for Li-ion based batteries is important to achieve high-performance devices. This work constitutes the experimental and theoretical investigation of structural stability and electrochemical behavior of cupric oxide and multi-walled carbon nanotubes (CuO/MWNNTs) nanocomposites. The electrochemical performance of nanocomposites was gauged employing charge/discharge and cyclic voltammetry studies. It is shown that electrochemical properties of pure materials, due to the synergistic effect, are considerably enhanced in CuO/MWNNTs composites. As a result, high rate capability and better cycling stability is observed in CuO-5%MWCNTs samples. In addition, this composite possesses better specific capacity 810 mAh g−1 and a high columbic efficiency of 80.86%. The DFT calculations also confirmed the improved electrochemical properties of MWCNTs in the presence of CuO nanoparticles.

Modification of Carbon-Nanotube Wettability by Ion Irradiation

The results of investigating the wettability of commercial multi-walled carbon nanotubes (MWCNTs) Taunit-MD under irradiation with 120-keV Ar+ ions with various fluences are presented. The structure of the irradiated MWCNTs is investigated using Raman spectroscopy, scanning electron microscopy, and X-ray microanalysis of the samples. The dependences of the average diameter of the MWCNTs, the O2 concentration, and defects in the MWCNT samples on the irradiation fluence, as well as their effect on the wettability with distilled water, ethylene glycol, and cyclohexane are considered. The possibility and prospects of using ion-beam modification methods for controlled variation of the wettability with the aim of creating a MWCNT coating, which is hydrophobic or hydrophilic to various types of liquids, are discussed.

The influences of functionalized carbon nanotubes as lubricating additives: Length and diameter

The super high strength, ductility and one-dimensional system of multi-walled carbon nanotubes (MWCNTs) make them become ideal additives for liquid lubricants. Although the MWCNTs have been added in kinds of lubricants, the influences of the length and diameter of the MWCNTs have not been studied systemically when they are used as lubricant additives. In this study, a series of MWCNTs with different diameter and length are modified by oxygen functional group and long-chain alkyl, and applied as additives of water and liquid paraffin (LP) respectively to investigate how the length and diameter of the MWCNTs influence their tribological properties. The results indicate that the short length MWCNTs samples showed better tribological properties than the long length MWCNTs samples, and the middle-diameter (10–20 nm) MWCNTs sample presented the best antiwear performance either in water or in LP. The established mechanisms are that the appropriate diameter (10–20 nm) and length (0.5–2 μm) make the MWCNTs-5 easier to enter the clearance of the friction pairs, play the role of rolling bearing between friction pairs, and fill in the cracks to mend surface damage of the friction pairs.

Electric characteristics of multi-walled carbon nanotubes irradiated with highly charged ions

The electric characteristics of individual multi-wall carbon nanotubes (MWNTs) irradiated with highly charged ions were evaluated. Each MWNT was located on a highly doped Si substrate with a source/drain contact, forming a back-gate FET configuration. We used highly charged Ar ions (Ar8+, Ar11+, and Ar14+) extracted from an electron beam ion source. We measured the current–voltage curves of the MWNTs irradiated at fluences in the 1011–1013 cm−2 range. The Ar8+ irradiation caused a 10% increase in the resistivity at room temperature at a fluence of 6 × 1011 cm−2. The resistivity at room temperature for the MWNT samples with a high fluence of 1013 cm−2 reached values higher than five times the original values. The current–voltage characteristics at low temperature became nonlinear and Coulomb oscillations were observed in the gate voltage dependence of the drain current. One of the samples exhibited Coulomb diamond characteristics particular to single quantum dot at 1.6 K.

X-ray Absorption and Magnetic Circular Dichroism in CVD Grown Carbon Nanotubes.

Nowadays, a deep knowledge of procedures of synthesis of nanostructured materials plays an important role in achieving nano-materials with accurate and wanted properties and performances. Carbon-based nanostructured materials continue to attract a huge amount of research efforts, because of their wide-ranging properties. Using X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy in the soft X-ray regime, by the synchrotron radiation, we studied the L3,2 absorption edges of iron (Fe) nanoparticles, when they are embedded in oriented Multi Wall Carbon Nanotube (MWCNTs) layers grown by thermal Chemical Vapor Deposition (CVD) technique catalyzed by this transition metal. This could allow us to understand the valence state and role of catalysts and thus their electronic and magnetic structures. It is important to note that the control of the size of these tethered nanoparticles is of primary importance for the purpose of tailoring the physical and chemical properties of these hierarchical materials. The MWCNTs samples used in XAS and XMCD measurements were synthesized by the CVD technique. The actual measurements were carried out by the group NEXT of the INFN- LNF with the logistic experimental support of the INFM-CNR and the Synchrotron Elettra Trieste.

Titanium dioxide protection against Al4C3 formation during fabrication of aluminum-TiO2 coated MWCNT composite

Aluminum and aluminum alloys have been very useful in the industry, mainly in the transport sector. So, is important to improve their mechanical properties to increase their applications. Carbon nanotubes (CNTs) could be an excellent reinforcing phase for metal matrix composites, specifically for composites with aluminum or aluminum alloy matrix. However, CNTs dispersion, wettability, and interaction with the matrix must be improved, without damaging their structure. In this work, multi-walled CNTs (MWCNTs) were coated by the sol-gel process with a titanium oxide (TiO2) layer with three different thickness and calcined at two different temperatures: 500 °C and 750 °C. The resultant powder was mixed by electrostatic adsorption method with aluminum powder and cold compacted. To simulate high temperature processing, the compacted disks were pressureless heated at 850 °C, aiming to check the effect of TiO2 in protecting the MWCNT when in contact with melted Al. The TiO2 coated MWCNT samples were characterized by a range of analytical techniques including Field-Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction (XRD), Z-Potential, Brunauer–Emmett–Teller (BET), Energy Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy (RS). The effect of the TiO2 layer as a protective barrier on the MWCNT against the Al4C3 formation during the heating process and the hardness of the Al/MWCNT (coated and uncoated) composite were studied. The results show that the MWCNT were successful coverage by a uniform amorphous TiO2 layer. After calcination at 500 °C and 750 °C, the layer was completely crystallized into a TiO2 film, with reduced surface area and pore volume. Electrostatic adsorption between TiO2 covered MWCNT and Al powders in aqueous suspension was found to disperse the reinforcing phase prior to consolidation. On the heat-treated discs, the formation of Al4C3 phase was observed to occur only for uncoated MWCNT samples, showing that the TiO2 layer effectively protected the nanotubes in presence of melted Al. The microhardness of the heated samples was increased up to 26% when reinforced with MWCNT and up to 46% when reinforced with TiO2 coated MWCNT, compared with pure aluminum.

Wall Thickness of Industrial Multi-Walled Carbon Nanotubes Is Not a Crucial Factor for Their Degradation by Sodium Hypochlorite

The propensity of multi-walled carbon nanotubes (MWCNTs) for biodegradation is important for their safe use in medical and technological applications. Here, we compared the oxidative degradation of two samples of industrial-grade MWCNTs—we called them MWCNT-d and MWCNT-t—upon their treatment with sodium hypochlorite (NaOCl). The MWCNTs had a similar inner diameter but they differed about 2-fold in the outer diameter. Electron microscopy combined with morphometric analysis revealed the different degradation of the two types of MWCNTs after their incubation with NaOCl—the thicker MWCNT-d were damaged more significantly than the thinner MWCNT-t. The both types of MWCNTs degraded at the inner side, but only MWCNT-d lost a significant number of the outer graphitic layers. Raman spectroscopy demonstrated that both MWCNTs had a similar high defectiveness. Using energy-dispersive X-ray spectroscopy, we have shown that the more degradable MWCNT-d contained the same level of oxygen as MWCNT-t, but more metal impurities. The obtained results suggest that the biodegradability of MWCNTs depends not only on the wall thickness but also on the defects and impurities. Thus, the biodegradability can be regulated by the synthesis conditions or the post-synthesis modifications. Such degradation flexibility may be important for both medical and industrial applications.

A novel design for mass production of multi-walled carbon nanotubes using Co-Mo/MgO catalyst via pyrolysis of polypropylene waste: effect of operating conditions

A two-stage process was employed for high yield production of multi-walled carbon nanotubes (MWCNTs) via pyrolysis of polypropylene (PP) waste. In the first stage, a new design was used for the pyrolysis of PP waste at 500 °C to form a mixture of condensable hydrocarbons (≥C6) and non-condensable gases (C1–C5) inside a vertical reactor closed from the bottom and connected directly to a vertical condenser at the top. This pyrolysis technique permitted to form a large amount of non-condensable hydrocarbon gases, which were used in the second stage as a carbon source for the production of MWCNTs over Co-Mo/MgO catalyst. The influences of growth temperature (700–850 °C) and carrier gas flow rate of N2 (50–110 sccm) on the yield and morphology of as-deposited MWCNTs have been investigated. The fresh Co-Mo/MgO catalyst and the as-deposited carbon were characterized by XRD, FTIR, TPR, BET surface properties, TEM, Raman spectroscopy and TGA. The results demonstrated that the adjustment of growth temperature and N2 flow-rate caused a marked impact on the yield, type and quality of as-grown MWCNTs. The optimum MWCNTs yields of 32.6 and 38.3 g/gcatalyst have been achieved at the growth temperature of 800 °C and the carrier gas flow rate of 90 sccm, respectively. TEM images illustrated the formation of pure MWCNTs at the growth temperature range of 700–800 °C, whereas mixed materials of MWCNTs and graphene nanosheets (GNSs) were obtained at the growth temperature of 850 °C. Raman spectroscopy illustrated that highly graphitized and crystalline MWCNTs were produced at all operating conditions. TGA proved that all MWCNTs samples exhibited higher thermal stability.

Growth of Wall-controlled MWCNTs by Magnetic Field Assisted Arc Discharge Plasma

Carbon nanotubes have long attracted great scientific interest because of their simplicity, ease of synthesis and unique properties. The novel properties of nanostructured carbon nanotubes including its high surface area, stiffness, tensile strength, thermal and electrical properties which become suitable for the application in the fields of energy storage, hydrogen storage, electrochemical supercapacitor, field-emitting devices, transistors, nanoprobes and sensors, composite material, templates, etc. In this study, carbon nanotubes were synthesized through arc discharge plasma with two different configurations, transverse and axial field, applied across arc plasma synthesis process to enable a much rapid rate growing of tubular carbon multi-walled carbon nanotubes (MWCNTs). TEM, FESEM, RAMAN, FTIR and XRD were used to investigate the morphology and structural evolution of the MWCNT samples produced with different synthesis environment. Introduction of magnetic field during the MWCNTs synthesized through arc discharge plasma technique has also been found to enhance the carbon nanotube growth, increase the high aspect ratio and its chemical stability, and shows potential for regulating the number of walls formed.

Structural and thermal characterization of multiwall carbon nanotubes (MWCNTs) / aluminum (Al) nanocomposites

Abstract The present study aims to assess the influence of multiwall carbon nanotubes (MWCNTs) as a filler in an Aluminum (Al) matrix in terms of structural and thermal performance. Al + 1% MWCNTs nanocomposites were prepared, and their structural behavior was characterized using dilatometry, X-ray diffraction (XRD), infrared (FT-IR) and Raman spectroscopy as compared to Al + 0% MWCNTs samples. The dilatometry measurements confirmed an important reduction of the thermal dilatation coefficient, while Raman spectroscopy allowed to report an increase of defects. The thermal stability of the composites were then assessed using differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA). The obtained results confirmed the impact of the MWCNTs on the physico-chemical characteristics of Al-MWCNTs nanocomposites, and in particular on the improvement of the thermal properties (increased thermal resistance) as compared to pure aluminum, indicating potential applications in the aeronautical, transport and construction sectors.

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.