Surface-modified Multiwalled Carbon Nanotubes Research Articles

Enhanced dielectric properties of PVDF polymer nanocomposites: A study on gold−decorated, surface−modified multiwalled carbon nanotubes

The integration of surface-modified multiwalled carbon nanotubes (fMWCNTs) into polymer nanocomposites has been extensively studied for their potential to enhance dielectric properties. This study, however, pioneers the use of a novel hybrid filler comprising fMWCNTs coated with metal nanoparticles, specifically aimed at augmenting the dielectric performance of polymers. In our research, poly(vinylidene fluoride) (PVDF) nanocomposite films were synthesized using fMWCNTs with a diameter of ∼6–9 nm and a length of 5 μm, adorned with gold nanoparticles (nAu) of ∼5.4 ± 0.9 nm via an adapted Turkevich method. Comprehensive analyses were conducted on nAu−fMWCNTs hybrid powder and their nanocomposites in PVDF with varying filler concentrations, confirming the formation of nAu−fMWCNTs with a weight ratio of 1.1 : 98.9. Three−phase percolative nanocomposites were produced by dispersing the hybrid filler in N,N−dimethylformamide, facilitated by interactions between the negative charge of nAu−fMWCNTs (zeta potential of ∼ −40.43 ± 0.46 mV) and polar phases of PVDF. This was verified through zeta potential and Fourier−transform infrared spectroscopy analyses. The dielectric permittivity (ε′) of the nanocomposites significantly increased from 17.8 to 524.8 (at 1 kHz) with filler loadings from 0.005 to 0.01 vol%, while the dielectric loss tangent (tanδ) showed a minor increase from 0.05 to 1.18. These enhancements are attributed to the elevated permittivity of nAu−fMWCNTs hybrid powder, PVDF's transition to the β−phase, and interfacial polarization effects. The restrained growth of nAu on fMWCNTs and the inhibition of conductive pathways in the polymer matrix contributed to the low tanδ values.

Reaching a near zero radiative heat transfer by the inclusion of modified multiwalled-carbon nanotubes (MWCNTs) in polyurethane-polyisocyanurate aerogels

This article studies the effect of adding different contents of surface-modified multiwalled carbon nanotubes (CNTs) on the structure and final properties of polyisocyanurate-polyurethane aerogels. The produced samples were characterized in terms of density, porosity, shrinkage, textural properties, mechanical behavior, ultrasonic behavior, and thermal conductivity. Low-weight aerogels were obtained with densities between 89 and 95 kg/m3. The inclusion of homogeneously dispersed carbon nanotubes protected the aerogel structure during supercritical drying decreasing the final shrinkage of these samples and, therefore, increasing their porosity. The porous structure of the aerogels containing CNTs was modified, and slightly larger pores were formed. The structural modifications contribute to decrease the stiffness of the samples while improving their resilience and elasticity. Finally, a significant enhancement on the insulating performance of the aerogels has been found when CNTs were added reaching values as low as 12 mW/mK. These fillers were proved to act as infrared opacifiers by absorbing and scattering the infrared radiation, a relevant contribution in these lightweight materials. In fact, the radiation contribution was strongly reduced when the content of CNTs reached 3 wt%, being this contribution near zero. Thus, this content was considered as the optimum for the final properties-balance in these aerogels.

Influence of conductive porous electrodes on the apparent electrode kinetics of fenitrothion

• FT’s cyclic voltammetry response at planar and porous modified electrode is simulated. • Simulations reveal the occurrence of thin-layer effects at porous modified electrode. • Cyclic voltammetry experiment validates the simulation results. Planar bare electrodes fabricated with surface-modified multiwalled carbon nanotubes (MWCNT) are used to detect organophosphate (OP) compounds, which are used as herbicides and fungicides but are harmful to human health. Deposition of carbon nanotubes on the surfaces of bare electrodes enhances electrocatalysis, increasing the electrode to analyte current response and narrowing peak-to-peak potential separation during cyclic voltammetry (CV). We hypothesize that, as the thickness of the deposited MWCNT layer decreases, Fenitrothion (FT, an OP) mass transport between the layers of porous multiwalled carbon nanotubes changes from semi-infinite to thin-layer diffusion. This influences the electrode electrochemical response to the analyte. Using simulations and experiments, we show that when porous MWCNT are deposited on a conductive glassy carbon electrode the mass transport of FT changes from semi-infinite to thin-layer diffusion during CV. This alters the electrochemical response of the electrode and reduces peak-to-peak potential separation. To simulate CV response to multi-step and multi-electron electrochemical reactions of FT, both the semi-infinite and thin-layer diffusion models are employed for the planar bare and modified porous surface electrodes. The transition from thin layer to semi-infinite diffusion is clear when the nanotube layer thickness on the bare electrode increases. The model is applicable to other toxic chemicals, such as 4-nitrophenol, parathion, or methyl parathion that have similar electrode kinetics.

Transport of surface-modified multi-walled carbon nanotubes in saturated porous media.

Carbon nanotubes (CNTs) are widely used and may pose potential environmental risks to soil and groundwater systems. Therefore, it is important to improve current understanding of the fate and transport of CNTs in porous media. In this study, the transport behavior of multi-walled carbon nanotubes (MWCNTs) with different surface modifications were examined in water-saturated sand columns under different pH (5 and 7) and ionic strength (0.1, 1, and 5mM) conditions. COOH-MWCNTs have the strongest mobility among the five types of MWCNTs, followed by pristine MWCNTs. NH2-MWCNTs, Cu-MWCNTs, and Fe-MWCNTs have the weaker mobility. The transport of five types of MWCNTs decreased with the increase of ionic strength, while increased with the increase of pH value. The results suggested that the transport of MWCNTs can be affected by the electrostatic attraction between the functional groups on the surface of MWCNTs and quartz sand. Moreover, the pH and ionic strength of the solution also played an important role in enhancing the transport of MWCNTs, which have great significance for evaluating the transport and fate of MWCNTs in natural environment.

Functionalization of multi-walled carbon nanotube and its effect on shape memory behavior of nanocomposite based on thermoplastic polyurethane/polyvinyl chloride/multi-walled carbon nanotube (TPU/PVC/MWCNT)

Nanocomposites based on thermoplastic polyurethane/polyvinyl chloride/multi-walled carbon nanotubes were prepared by a solution method and their shape memory properties were studied. The blend ratios were 70/30, 60/40, and 50/50 (w/w) of thermoplastic elastomer polyurethane/polyvinyl chloride. To improve the dispersion of multi-walled carbon nanotubes, at 0.5% and 1% (wt), in polymer matrices, three-step chemical modifications were performed, including oxidation, chlorination and grafting of poly (ɛ-caprolactone) diol. The occurrence of surface modifications in MWCNTs was monitored using Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy and thermal gravimetric analysis techniques. SEM micrographs revealed a good dispersion of MWCNTs in the polymer matrix due to better matrix-filler interactions compared to filler–filler interactions. The results showed that the main indices of shape memory behavior (shape fixity and shape recovery) of nanocomposite samples were affected by the polymer blend ratio, nanoparticle concentration and surface modification. Increasing the content of polyvinyl chloride led to reduced shape fixity and shape recovery, which was attributed to the lack of rigid structural nature of polyvinyl chloride. The presence of nanoparticles contributed to enhanced shape fixity and weaker shape recovery. This can be explained by lower polymer chain mobility in the presence of multi-walled carbon nanotubes. The reduction in chain mobility in nanocomposites reinforced by surface-modified multi-walled carbon nanotubes was more significant due to higher distribution efficiency of nano-scale fillers in the polymer matrix.

Mesoporous carbon nanomaterials with tunable geometries and porous structures fabricated by a surface-induced assembly strategy

Mesoporous carbon (MC) nanomaterials have received intensive investigation in the past decades. However, the synthesis of MC with controllable morphologies and porous structures still remains challenging. Herein, we report a surface-induced assembly strategy to construct MC with various geometries and porous structures, using one-dimensional (1D) surface-modified multiwalled carbon nanotubes and two-dimensional (2D) graphene oxide nanosheets as morphological inducers. Positively charged polyaniline (PANI) and silica (SiO2) nanoparticles that serve as carbon source and pore template, respectively, were used to produce SiO2@PANI aggregations in hydrochloric acid media via S+X−I+ assembly pathway, which nucleate and grow on the negatively charged inducer surfaces through electrostatic interaction. MC nanomaterials with precisely tunable dimensions (1D to 2D), diameters (35-210 nm), thicknesses (7-145 nm), and pore sizes (7-22 nm) are successfully fabricated. More importantly, this method can be extended to other morphological inducers that contain negatively charged surfaces, such as Ti3C2Tx. The electrodes based on the MC nanomaterials demonstrate excellent energy storage performance in flexible sulfur electrodes and supercapacitors. Our findings shed light on a new strategy to prepare various MC for energy storage.

Synthesis of magnetic nickel ferrites nanocomposites: An advanced remediation of electroplating wastewater

Nickel ferrite nanocomposites (NFNCs) were prepared and utilized to remove hexavalent chromium from the effluent of the electroplating industry. The nickel ferrite nanoparticles (NFNPs) were synthesized by the sol-gel auto combustion process, and they were doped ultrasonically onto the surface-modified multi-walled carbon nanotubes (SM-MWCNTs). Characterization results confirmed that the NFNPs with a cubic spinel structure were successfully impregnated onto the SM-MWCNTs. The synthesized NFNCs were tubular structures with an outer diameter in the range of 30–40 nm and had high crystal defect. The NFNCs with the surface area of 210.5 m2 g−1 offer high magnetic separability due to their paramagnetic behavior. Non-linear kinetic, thermodynamic, and isotherm models were used for interpretations, and high Cr(VI) uptake of 129.83 mg/g was obtained at 40 °C. The Cr(VI) uptake by NFNCs was dominated by electrostatic attractions at a low pH and ion exchange mechanism at a higher pH. Lastly, high efficient recyclability of the NFNCs and applicability in removing other heavy metals from electroplating effluent suggested them to be a promising material in wastewater treatment.

Fabrication of magnetic cobalt ferrite nanocomposites: an advanced method of removal of toxic dichromate ions from electroplating wastewater

Magnetic cobalt ferrites (CoFe2O4) were synthesized by sol-gel method. These nanoparticles were ultra-sonicated with surface modified multi-walled carbon nanotubes (SM-MWCNTs) to form CoFe2O4/SM-MWCNTs nanocomposites. The as-prepared materials were used as an adsorbent for the removal of hexavalent chromium (Cr(VI)) arising from the presence of dichromate ions (Cr2O72− ) in the electroplating effluent. The synthesized nanocomposites were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD), Fourier transmission infrared spectroscopy (FT-IR), raman spectroscopy, thermo-gravimetric analysis (TGA), and zeta analyzer. The effect of the environmental chemistry of the solution on the adsorption has been discussed. The adsorption isotherm of Cr(VI) adsorption onto the as-synthesized CoFe2O4/SM-MWCNTs best fitted the Langmuir Adsorption Isotherm model. The high adsorption capacity of 100mg/g was achieved at 40°C under optimized conditions. Besides, the magnetic properties of synthesized CoFe2O4/SM-MWCNTs nanocomposites allow them to separate from the aqueous solution by magnetization easily. Even after seven consecutive adsorption-desorption cycles, the CoFe2O4/SM-MWCNTs nanocomposites presented an efficiency loss of less than 20% for the removal of Cr(VI) ions. This study clearly shows that cobalt nanocomposites are promising candidates in environmental applications.

Paper Based Enzymatic Chemiresistor for POC Detection of Ethanol in Human Breath

A paper based chemiresistor has been fabricated to selectively sense ethanol in human breath. The chemiresistor was composed of a sensing mixture of multiwall-carbon-nano-tubes (MWCNTs), poly (diallyl-dimethyl-ammonium chloride) (PDDA), alcohol dehydrogenase (ADH), and coenzyme (NADH). The aluminum electrode was deposited on the paper surface, followed by drop-casting of the aforementioned sensing mixture. The resistance of the sensors was measured by exposing the same in gas-vapor mixture as well as the sample solution. The surface-modified MWCNTs specifically broke down ethanol present in the gas-vapor mixture or in a solution to generate a quantitative electronic response proportional to the ethanol concentration. Subsequently, the interference of other volatile organic materials was also tested to prove the selectivity and sensitivity of the sensor towards ethanol in the presence of different volatile organic compounds (VOCs). The variation of the resistance during the interaction between sensor and ethanol was also characterized by measuring the surface potential of the channel material under ethanol exposure using Kelvin probe force microscopy (KPFM). The sensor was integrated with a voltage divider circuit, a display, and a microcontroller unit to make a proof-of-concept prototype for the point-of-care (POC) detection of ethanol in human breath.

Enhanced sciatic nerve regeneration by poly-L-lactic acid/multi-wall carbon nanotube neural guidance conduit containing Schwann cells and curcumin encapsulated chitosan nanoparticles in rat.

The main aim of this study was to improve the efficacy of peripheral nerve regeneration by an artificial neural guidance conduit (NGC) as a carrier to transplant allogeneic Schwann cells (SCs) and curcumin encapsulated chitosan nanoparticles (nanocurcumin). The conduit was prepared by poly-L-lactic acid (PLLA) and surface-modified multi-wall carbon nanotubes (mMWCNT) and filled with SCs and nanocurcumin. SCs play an important role in the regeneration of injured peripheral nerve and controlled curcumin release can decrease SCs apoptosis, and enhance the regeneration and functional recovery of injured peripheral nerves. The mechanical properties, contact angle, and cell biocompatibility experiments showed that the optimized concentration of mMWCNT inside PLLA wall of conduits was 0.15wt%. The drug release experiments showed slower release of curcumin from nanocurcumin samples compared to nanocurcumin encapsulated inside NGC wrapped fibrin gel sample. It was found that simultaneous using of both SCs and curcumin inside NGC had a significant role in sciatic nerve regeneration in vivo. Histological examination revealed a significant increase in the number of axons in injured sciatic nerve following treatment by SCs and nanocurcumin compared to negative control group. Histological evaluation also revealed a significant decrease in the number of vessels in fibrin groups compared to positive control group. The results showed that there was no significant difference between the reaction time and sciatic functional index (SFI) values of rats with injured sciatic nerve treated by NGC/SCs/nanocurcumin sample and autograft sample. In conclusion, our results strongly showed that PLLA/mMWCNT nanofibrous conduit filled with fibrin gel containing SCs and nanocurcumin is a proper strategy for improving nerve regeneration after a nerve transaction in the rat.

The stability, viscosity and thermal conductivity of carbon nanotubes nanofluids with high particle concentration: A surface modification approach

This study demonstrated a novel approach to formulating nanofluids with high mass concentration, good colloidal stability, enhanced thermal conductivity and moderate viscosity increase from the β-Cyclodextrin (β-CD) modified carbon nanotubes. This method could be applied to a variety of functional nanomaterials and make use of the liquid properties and functions of dispersed nanoparticles to make nanofluids become more efficient heat transfer fluids and industrial application media. A scalable improved two-step method based on mechanical milling technique for the preparation of nanofluids was demonstrated. Highly stable nanofluids with up to 5 wt% of surface-modified multiwalled carbon nanotubes (CD-CNTs) in deionized water were successfully obtained. It was demonstrated that the preparation method could effectively disperse the carbon nanotube aggregates, providing relatively small increases in viscosity (the viscosity of 5 wt% nanofluids was 31 mPa·s averagely). The thermal values of CD-CNTs/water nanofluids reached to their maximum values (1.013 W/(m·K) and 69.68%, respectively) at 5 wt%. Heat was more easily transferred along the carbon nanotubes, which was more efficient than thermal conduction through solid-liquid-solid paths. This study has demonstrated that the proposed surface modification technique and preparation method could together ensure the requirements for achieving MWCNTs nanofluids with high mass concentration and desired properties.

Effect of Surface-Modified Carbon Nanotubes on Intrinsic Properties and Microstructures of Cement Composites.

Multi-walled carbon nanotubes (MWCNTs) modified by gum arabic (GA) were incorporated into cement matrix composites to investigate their effect on intrinsic properties. Their ability to disperse the surface-modified MWCNTs uniformly in the cement matrix was also assessed using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The intrinsic mechanical properties of the cement composites were investigated using Nano Indenter. Results showed that the addition of treated nanotubes significantly improved the intrinsic properties of cement matrix composites. The porosity and pore size distribution of the composites were measured using mercury intrusion porosimetry (MIP), and the results indicated that cement paste containing MWCNTs had lower porosity and a more uniform pore size distribution. The morphological structure of samples was investigated using field emission scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and X ray diffraction analysis (XRD), which showed that the MWCNTs acted as bridges across cracks and voided and formed a network that transferred the load in tension.

Preparation and Mechanical Properties of Polypropylene Composite for Seats

This paper describes the effects of the Multiwalled Carbon Nanotubes (MCNs)of different masses on the mechanical properties of polypropylene/calcium sulfate whisker composites for seats. With a twin roller open mill, a kind of composite PP-g-MAH/CSW/NWNTS may be made from surface-modified MCNs and modified calcium sulfate whiskers, polypropylene (PP), maleic anhydride grafted polypropylene (PP-g-MAH) using melt blending method, thereby to compare which effects the modified MCN of different doses plays on the mechanical properties of the PP/PP-g-MAH/CSW/NWNTS composites for sports seats. This study shows that the MCNs that have a mix-acid treatment on the surface uniformly disperse in the composite material, and well bond with the interface of the polymer matrix, thus playing a function for toughening and strengthening composite material. But worse, when the mass fraction of carbon nanotubes is higher, there is a phenomenon of agglomeration occurred, which in turn worsens the mechanical properties of the composite material. The carbon nanotubes at approx. 0.5%make the mechanical properties of the composite the best.

Surface modification-based three-phase nanocomposites with low percolation threshold for optimized dielectric constant and loss

Integration of the excellent attributes of high dielectric constant and low dielectric loss in flexible polymer-based nanocomposites has attracted increased research attention because of their extensive applications in modern electronic and electric industry. In this study, to obtain the optimized dielectric constant and loss, the fabrication and properties of a three-phase nanocomposites, including poly(vinylidene fluoride) (PVDF) and two nanofillers, namely, surface-modified multi-wall carbon nanotubes (mCNTs) and barium titanate nanoparticles (mBTs), are investigated in detail. The mCNTs and mBTs were obtained via the hydrolysis of 3-aminopropyltriethoxysilane (AMEO) and condensation reactions between the AMEO and nanofillers. The three-phase nanocomposites are fabricated by a phase-separation and hot-pressing process. The mCNTs and mBTs can be uniformly dispersed within the PVDF polymer matrix because of the enhanced hydrogen bonding interaction and compatibility with the polymer matrix. The percolation threshold (as low as 0.50vol%) of the two-phase mCNTs/PVDF nanocomposites is adopted to optimize the dielectric properties of the three-phase mCNTs/mBTs/PVDF nanocomposites. At the frequency of 102Hz, a high dielectric constant of 109 and low loss of 0.06 are obtained for the three-phase nanocomposites with only 0.41vol% mCNTs and 2.8vol% mBTs, respectively. Meanwhile, owing to the low percolation threshold and enhanced surface compatibility between the nanofillers and PVDF, the tensile strength of the three-phase nanocomposites is greater than that of PVDF by a factor of greater than 1.5. Owing to their high dielectric constant, low dielectric loss and good mechanical properties, these PVDF-based ternary nanocomposites show potential for applications in electronic devices and energy storage systems.

Surface Modification of Carbon Nanotubes with an Enhanced Antifungal Activity for the Control of Plant Fungal Pathogen.

The addition of surface functional groups to multi-walled carbon nanotubes (MWCNTs) expands their application in engineering, materials, and life science. In the study, we explored the antifungal activities of MWCNTs with different surface groups against an important plant pathogenic fungi Fusarium graminearum. All of the OH-, COOH-, and NH2-modified MWCNTs showed enhanced inhibition in spore elongation and germination than the pristine MWCNTs. The length of spores decreased by almost a half from 54.5 μm to 28.3, 27.4, and 29.5 μm, after being treated with 500 μg·mL−1 MWCNTs-COOH, MWCNTs-OH, and MWCNTs-NH2 separately. Furthermore, the spore germination was remarkably inhibited by surface-modified MWCNTs, and the germination rate was only about 18.2%, three times lower than pristine MWCNTs. The possible antifungal mechanism of MWCNTs is also discussed. Given the superior antifungal activity of surface modified MWCNTs and the fact that MWCNTs can be mass-produced with facile surface modification at low cost, it is expected that this carbon nanomaterial may find important applications in plant protection.

Characteristics of hydrogen plasma treated carbon nanotubes and their influence on the mechanical properties of polyetherimide-based nanocomposites

The structural phase transformation and etching of the sidewalls of multi-walled carbon nanotubes (MWCNTs) by hydrogen plasma and the effect on the dispersion and mechanical properties of polyetherimide (PEI) composites was investigated. Surface-modified MWCNTs with various plasma treatment times were characterized using FESEM, HRTEM, Raman spectroscopy, FT-IR, and XPS. The results showed that plasma treatment facilitates the attachment of functional groups while damaging and detaching the sidewalls of the MWCNTs and modifying the crystallinity of the graphene layer. The mechanical properties of the PEI composites with the modified MWCNTs depended on the degree of damage to the surface and crystallinity modification of the MWCNTs. Hydrogen plasma treatment led to a significant improvement in the dispersion and mechanical properties of PEI/MWCNT composites due to the surface modification of the MWCNTs.

Covalent Functionalization of Multi-Walled Carbon Nanotubes Surface via Chemical Treatment

Due to the strong hydrophobic and van der Waals interactions between individual carbon nanotubes (CNTs), these particles easily aggregate with themselves. When CNTs were introduced into a polymer matrix as a filler, aggregations formed that can adversely affect the mechanical and thermal properties of polymer/CNTs composites. To prevent aggregation, covalent functionalizations via chemical treatments using H₂SO₄/HNO₃, H₂O₂/H₂O and a silane coupling agent(STX)-glycidoxypropyltrimethoxysilane, GPTMS) on the CNTs were chosen in this study. Moreover, the effect of the functional groups on the solubility of CNTs in tetrahydrofuran (THF) was investigated. The surface-modified multi-walled carbon nanotubes (MWCNTs) were also characterized and compared with pristine MWCNTs using several techniques. Morphology changes in surfacemodified MWCNTs were observed by Raman spectroscopy and Field-Emission Scanning Electron Microscopy (FE-SEM) images. Qualitative analyses of the functional groups on the surface-modified MWCNTs were performed by Fourier Transform Infrared Spectroscopy (FT-IR). Additionally, quantitative analyses were performed by X-Ray Photoelectron Spectroscopy (XPS), Energy Dispersive Spectroscopy (EDS), a titration method and Thermogravimetric analysis (TGA).

Influence of sp(3)-sp(2) Carbon Nanodomains on Metal/Support Interaction, Catalyst Durability, and Catalytic Activity for the Oxygen Reduction Reaction.

In this work, platinum nanoparticles were impregnated by two different techniques, namely the carbonyl chemical route and photodeposition, onto systematically surface-modified multiwalled carbon nanotubes. The different interactions between platinum nanoparticles with sp(2)-sp(3) carbon nanodomains were investigated. The oxidation of an adsorbed monolayer of carbon monoxide, used to probe electronic catalytic modification, suggests a selective nucleation of platinum nanoparticles onto sp(2) carbon nanodomains when photodeposition synthesis is carried out. XPS attests the catalytic center electronic modification obtained by photodeposition. DFT calculations were used to determine the interaction energy of a Pt cluster with sp(2) and sp(3) carbon surfaces as well as with oxidized ones. The interaction energy and electronic structure of the platinum cluster presents dramatic changes as a function of the support surface chemistry, which also modifies its catalytic properties evaluated by the interaction with CO. The interaction energy was calculated to be 8-fold higher on sp(3) and oxidized surfaces in comparison to sp(2) domains. Accelerated Stability Test (AST) was applied only on the electronic-modified materials to evaluate the active phase degradation and their activity toward oxygen reduction reaction (ORR). The stability of photodeposited materials is correlated with the surface chemical nature of supports indicating that platinum nanoparticles supported onto multiwalled carbon nanotubes with the highest sp(2) character show the higher stability and activity toward ORR.

Facile-low temperature route towards development of SiC-based coating on carbon nanotubes for improved oxidation resistance

Coating with silicon carbide is a preferred avenue for improving the oxidation resistance of carbon nanotubes. However, expensive and non-scalable techniques like vapor deposition are commonly used to develop such coatings. Against this backdrop, reported here is a facile, cost-effective and low temperature route, based on wet-chemical synthesis, for obtaining SiC-based coating on multi-walled carbon nanotubes (MWCNTs). The coating was achieved by dispersing surface-modified MWCNTs in silica sol (having optimized viscosity), followed by simultaneous reduction and ‘carburization’ of the silica (wetting MWCNTs) in the presence of Mg at 600 °C. X-ray diffraction and RAMAN spectroscopy confirmed the presence of β-SiC, while TEM observations revealed the development of uniform and thin coating (~3 nm thick) on undamaged MWCNTs. Thermo-gravimetric and differential thermal analyses up to 1500 °C in air confirmed significant improvement in oxidation resistance for the MWCNTs with SiC-based coating (just ~15 % mass loss; as against rapid mass loss of ~100 % for uncoated MWCNTs due to oxidation). Additionally, undamaged MWCNTs (with SiC-based coating) could be imaged in TEM after exposure in air at 1200 °C for longer duration.

Microwave-induced chemical functionalization of carboxylated multi-walled nanotubes with p-aminophenol: Towards the synthesis of MWCNT–poly(amide-imide) hybrids

Covalent functionalization of multi-walled carbon nanotubes (MWCNT) with p-aminophenol was conducted to give enhanced solubility and dispersability by rapidly and efficiently generating of an appreciable amount of hydrophilic functional groups using microwave radiation. The functionalized MWCNTs were analyzed by means of field emission and transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. The surface-modified MWCNTs showed better chemical stability in common solvents. The functionalized MWCNT/poly(amide-imide) hybrid films prepared by solution blending method showed a good thermal stability and an increase in the elastic modulus with increasing of functionalized MWCNT content.