Effect of nitrile-functionalization and thermal cross-linking on the dielectric and mechanical properties of PEN/CNTs–CN composites

In this study, a novel series of composite films consisting of nitrile-functionalized carbon nanotubes (CNTs–CN) and poly(arylene ether nitriles) (PEN) were successfully fabricated by the tape-casting method. The –CN groups in PEN chains and the phthalonitrile groups on CNTs–CN formed the thermally stable triazine rings by thermal cross-linking reaction in the presence of diamino diphenyl sulfone, which was characterized by Fourier transform infrared spectroscopy. The result indicated that the chemical cross-linking reaction occurred accompanied by the emergence of a new absorption peak at 1,361 cm^?1. Besides, the effect of cross-linking on the morphology, thermal stability, mechanical and dielectric properties of the PEN/CNTs–CN was investigated. The SEM images showed that the phase interface between surface modified CNTs and PEN matrix was indistinct, and the surface modified CNTs presented a better dispersion behavior in PEN matrix. The mechanical properties of the processed films were improved substantially compared with the unprocessed films. Furthermore, the glass-transition temperature (T _g ) of composite films processed at 320 °C for 4 h (about 245 °C) was higher than that of composite films before thermal treatment (about 205 °C). The 5 % weight loss temperature of the composite films (processed at 320 °C for 4 h) increased by about 110 °C compared with the composite films (unprocessed). More importantly, by thermal cross-linking, the dielectric constant (ε) of composite films with 8 wt% CNTs–CN loading was increased from 31.8 to 33.9, and dielectric loss (tan δ) was decreased from 0.90 to 0.61 at 1 kHz.     

De novo growth of poly(amidoamine) dendrimers on the surface of multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are often used after modification. Poly(amidoamine) (PAMAM) dendrimers modified CNTs have attracted attentions due to their rich terminal amino groups. However, direct grafting of PAMAM dendrimers on CNTs’ surface is limited by the steric hindrance and its supply. De novo growth of PAMAM on multi-walled carbon nanotubes (MWCNTs), i.e., PAMAM@CNTs, is expected to eliminate the limits since the adopted reagents are readily available small molecular chemicals. It was realized using a divergent method and a “grafting from” technique by alternate amidization of terminal ester groups with ethylenediamine and Michael addition of methyl acrylate to the yielding amino groups. Spectral analysis, including Fourier transform infrared, Raman, hydrogen nuclear magnetic resonance, and X-ray photo-electron spectroscopy, verified that the functional groups were covalently grafted on the surface of MWCNTs, while thermogravimetric and elemental analysis showed that these groups were exponentially grown on MWCNTs, suggesting the formation of a dendritic PAMAM. Besides, high resolution transmission electron microscopy also confirmed that the spherical PAMAM was formed on the CNTs’ surface and an average particle size of 15–20 nm for G8.0-dendrimers was obtained.     

Densification behavior and mechanical properties of spark plasma-sintered ZrC–TiC and ZrC–TiC–CNT composites

Titanium carbide (TiC) and carbon nanotubes (CNTs) were introduced into zirconium carbide (ZrC) ceramics to improve the fracture toughness. ZrC–TiC and ZrC–TiC–CNT composites containing 0–30 vol.% TiC and 0.25–1 mass% CNT were prepared by spark plasma sintering at temperatures of 1750–1850 °C for 300 s under a pressure of 40 MPa. Densification behavior, microstructure, and mechanical properties of the ZrC-based composites were investigated. Fully dense ZrC–TiC and ZrC–TiC–CNT composites with a relative density of more than 98 % were obtained. Vickers hardness of ZrC-based composites increased with increasing TiC content and the highest hardness was achieved with the addition of 20 vol.% TiC. Addition of CNTs up to 0.5 wt% significantly increased the fracture toughness of ZrC-based composites, whereas the addition of TiC did not have this effect.     

Synthesis of multi-walled carbon nanotubes via pyrolysis of plastic waste using a two-stage process

The pyrolysis of different plastic waste types such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) for producing multi-walled carbon nanotubes (MWCNTs) using a two-stage process has been investigated. Firstly, the cracking of plastic wastes was carried out at a temperature of 700°C to produce hydrocarbon gases. In the second stage, the produced hydrocarbon gases were decomposed at 650°C on the surface of the Ni-Mo/Al₂O₃ catalyst to form CNTs. Various analytical tools such as XRD, TPR, TGA, Raman spectroscopy and TEM were used to describe both the fresh catalyst and the obtained CNTs. The results showed that the amount of the hydrocarbon gases was related to the type of plastic waste and hence the CNT yield. Accordingly, LDPE or PP was decomposed to produce the largest gases yield of 72.5 or 70.7 wt%, respectively. As a result, a large CNTs yield of 5.8 and 5 g/g_cat can be achieved by pyrolysis of PP and LDPE waste, respectively. However, a small yield of CNTs with little quality and low purity was obtained by using PS or PET waste as the carbon feedstock.     

Growth and characterization of carbon nanotubes over CoFe2O4-MgO catalysts at different temperatures

Abstract

A novel approach for synthesizing carbon nanotubes (CNTs) via chemical vapor deposition (CVD) technique has been elucidated. CNTs are catalytically grown on the CoFe₂O₄-MgO nano-catalyst at various growth temperatures (700?°C, 800?°C, 900?°C) to clarify the effect of temperature and to achieve the optimum CNT growth temperature. The structural properties of the catalyst and CNTs were studied with thermal analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy (IR), Raman spectroscopy, and High Resolution Transmission Electron Microscope (HRTEM). X-ray diffraction is used to study changes in the crystal structure of the CoFe₂O₄+MgO nano-catalyst. The obtained data ratifies the formation of MWCNTs over the nanocatalyst. The intensity of the main peak of CNTs decreases as well as the yield with increasing the growth temperature. The two main Raman modes, G band and the D band, can be identified in the spectra multi-walled carbon nanotubes .The lowest I_D/I_G ratio is obtained at the highest growth temperature. HRTEM images show that the growth temperature has a significant parameter on CNT quality. The average diameters of grown CNTs are 42, 32 and 16?nm for growth temperatures of 700 ?C, 800 ?C and 900 ?C, respectively. The inner and outer diameters of MWCNTs become thinner and the quality of the tubes is enhanced with increasing the growth temperature. Additionally, it can be concluded from the temperature study that the balance between decomposition of acetylene gas and diffusion rate of manufactured carbon atoms in CoFe₂O₄-MgO catalyst nanoparticles occurs at the optimal growth temperature of 900?°C.     

Investigation of galvanic corrosion between AISI 1018 carbon steel and CFRPs modified with multi-walled carbon nanotubes

In this article, we investigate the effect of modified carbon fiber-reinforced polymer (CFRP) composites when galvanically coupled with AISI 1018 carbon steel. Two different resins were used to manufacture the CFRPs: neat epoxy resin, and epoxy resin modified with multi-walled carbon nanotubes (MWCNTs). The specimens of composite (the cathode of the galvanic cell) and metal (the anode of the galvanic cell) were paired and immersed in electrolyte (NaCl solution, 2 % by weight) at 40 °C, to simulate a corrosive environment and accelerate the electrochemical reaction. Results of corrosion rate (CR) and mass loss rate (MR) were obtained, and the electrical resistances of the CFRPs were also measured. This new study shows that the MWCNTs do not have a statistically significant impact on the corrosion and mass loss rate results, and that both types of CFRP composites have statistically the same electrical resistance. Therefore, common methods used in the engineering practice in conventional hybrid CFRP/steel joints and repairs may be sufficient to delay galvanic corrosion, as there is no increased liability.     

Preparation and characterization of carbon nanotube/polyetherimide nanocomposite films

Multi-walled carbon nanotube (MWCNT)/polyetherimide (PEI) nanocomposite films have been prepared by casting and imidization. A homogeneous dispersion of MWCNTs throughout the PEI matrix is observed by scanning electron microscopy of fracture surfaces, which shows not only a fine dispersion of MWCNTs but also strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTs) in the matrix and by the absence of debonding of CNTs from the matrix. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperature of PEI increases by about 10 °C by the addition of 1 wt% MWCNTs. Mechanical testing shows that for the addition of 1 wt% MWCNTs, the elastic moduli of the nanocomposites are significantly improved by about 250% while the tensile strength is comparable to that of the matrix. This improvement is due to the strong interfacial interaction between the MWCNTs and the PEI matrix which favors stress transfer from the polymer to the CNTs.     

Simple method for synthesis of carbon nanotubes over Ni-Mo/Al2O3 catalyst via pyrolysis of polyethylene waste using a two-stage process

Synthesis of valuable multi-walled carbon nanotubes (MWCNTs) by thermal pyrolysis of low-density polyethylene (LDPE) waste was investigated via a two-stage process. The first stage was the thermal pyrolysis of LDPE to gaseous hydrocarbons, and the second stage was the catalytic decomposition of the pyrolysis gases over Ni-Mo/Al₂O₃ catalysts. Two catalysts with the compositions of 5.2%Ni-10.96%Mo/Al₂O₃ and 10%Ni-9.5%Mo/Al₂O₃ were tested for carbon nanotubes (CNTs) formation. The catalyst containing 10%Ni showed better activity in terms of CNTs production. Accordingly, the impact of either pyrolysis or decomposition temperatures was investigated using the 10%Ni-9.5%Mo/Al₂O₃ catalyst. TEM, XRD, Raman spectroscopy, TGA, TPR, and BET analysis tools were used to characterize the fresh catalysts as well as the obtained carbon nanomaterials. TEM images proved that MWCNTs with various morphological structures were obtained at all pyrolysis and decomposition temperatures. Moreover, cup-stacked carbon nanotubes (CS-CNTs) were observed at the decomposition temperature of 600°C. MWCNTs with the best quality were produced at decomposition temperature of 750°C. The optimum pyrolysis and decomposition temperatures in terms of CNTs production were at 700 and 650°C, respectively.     

Alternative Synthesis Method for Carbon Nanotubes

It is demonstrated that carbon nanotubes (CNTs) can be synthetized on the surface of an example carbon background, activated carbon, using the thermal conversion of poly(furfuryl alcohol) (PFA). This newly discovered CNTs synthesis method is an alternative solution to previously known methods, e.g., chemical vapor deposition, arc discharge, and laser ablation. Scanning electron microscopy and high‐resolution transmission electron microscopy images deliver direct evidence of CNT formation through the thermal degradation of PFA in a temperature range of 500–700 °C. The discovered process consists of the free growth of CNTs from PFA without any mechanical patterning, casting, or molding. CNTs obtained in this manner resemble MWCNTs in size, though according to microscopic investigation the tubes do not possess the well‐developed layered structure of MWCNTs. Nonetheless, X‐ray photoelectron spectroscopy and Raman spectroscopy studies fully confirm that carbon (C) is the main elemental constituent of the tubes (C atomic content above 85%) and C atoms are structured in a manner typical of defected CNTs (D, G, and G' intensity ratios).     

Stability,viscosity, thermal conductivity,and electrical conductivity enhancement of multi-walled carbon nanotube nanofluid using gum arabic

This experimental investigation discussed on the stability and rheological behavior of multi-wall carbon nanotubes (MWCNTs) nanofluids with and without gum arabic (GA). The stability of MWCNT in the presence of GA dispersant in solar glycol is systematically investigated by taking into account the combined effect of different parameters, such as sonication time, temperature, dispersant and particle concentration. The concentrations of MWCNT and GA have been varied from 0.2 to 0.6% volume concentration and from 0.25 to 1.25 wt%, respectively, and the sonication time has been varied in between 30 and 120 min. The effect of sonication time on viscosity was discussed. It was perceived that the shear thinning behavior is exhibited by all the nanofluid samples. The stability of nanofluid is measured in terms of MWCNT concentration as a function of sediment time using UV-Vis spectrophotometer. Rheological behavior of MWCNT nanofluids is measured using Bohlin CVO Rheometer in the temperature range of 30–50°C, with step sizes of 5°C. Optimal GA concentration is obtained for the entire range of MWCNT concentration and 0.25–1.25 wt% of GA is found to be sufficient to steady all MWCNT range in solar glycol. Rapid sedimentation of MWCNTs is observed at higher GA concentration and sonication time. The presence of MWCNT and GA enhanced the thermal conductivity of the nanofluids by 30.59% at 0.6 vol.% particle concentration and 1.25 GA wt% at 50°C. The electrical conductivity is enhanced in a linear manner with respect to the loading of MWCNT and GA. Nevertheless, the electrical conductivity is increased linearly with increasing the temperature of the nanofluid. At particle concentration of 0.6 vol.% of MWCNT and 1.25 wt% of GA, the electrical conductivity of the nanofluid is improved by 190.57% at a temperature of 50°C.     

Dielectric and thermal properties of novel three-component CCTO/MWCNTs/polyarylene ether nitrile composite films

In this paper, a series of calcium copper titanate/multi-walled carbon nanotubes (MWCNTs)/polyarylene ether nitriles composite films were obtained by ultrasonic shocking under the condition of constant temperature water bath (80 °C). The composite films were characterized by scanning electron microscope, differential scanning calorimetry (DSC), thermogravimetric analysis. It is confirmed that the MWCNTs were combined with the matrix well and the composite films possess excellent thermal stability. The glass transition temperatures of the composite films obtained from DSC curves were in a range of 224–230 °C. The initial decomposition temperatures and the maximum decomposition rate temperatures were all above 480 °C. Besides, the dielectric and mechanical characterizations showed that the composite films possess excellent dielectric properties and flexibility. When the content of MWCNTs reached 6 wt%, the dielectric constant of the composite film increased to 35 (1 kHz), yet the dielectric loss is just 0.38 (1 kHz). Moreover, the composite films cannot break even though they were cured into columns of several layers, indicating the outstanding flexibility.     

Improved the electrochemical property of multiwall carbon nanotubes by mesophase pitch fluoride coating

The surfaces of two types of multiple wall carbon nanotubes (MWCNTs), namely, straight and distorted tubes, were modified by mesophase pitch fluoride coating (PFC). Brunauer–Emmett–Teller analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to compare the specific surface area (SSA), functional groups, and micrograph of the MWCNTs with and without modified coating. Results show that PFC can improve the SSA of the straight tube (55 %) more significantly than that of the distorted tube (7.27 %). However, surface coating is more easily implemented on the latter (F/C = 0.48) than on the former (F/C = 0.44) because of self-structure features. Electrochemical measurements indicate that PFC may enhance the specific surface capacitance and energy density of the two MWCNTs because of the effect of functional groups on the modified surface.     

Low temperature synthesis of multiwalled carbon nanotubes and incorporation into an organic solar cell

ABSTRACT

Metal nanoparticle (MNP) catalysts used for the synthesis of multiwalled carbon nanotubes (MWCNTs) consisted of single metals (Fe, Ni or Co) and bimetallic mixture (CoFe, NiFe or NiCo). MWCNTs were successfully synthesised at 200 °C in 10 min using liquefied petroleum gas as carbon source with non-equilibrium plasma enhanced chemical vapour deposition (PECVD) method. The nanostructures and the morphology of the MNPs and the MWCNTs film were characterised using relevant microscopic and spectroscopic methods. The synthesised MWCNTs were used as part of the electrode material in organic solar cell (OSC) set-up. Poly (3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) was used as an electron transporter and poly-3-hexyl thiophene (P3HT) as an electron donor. The performance of OSC devices was tested using standard electrical measurements and solar simulator operating at 100 mW/cm². The measured power conversion efficiencies was found to be dependent on the metal catalyst used during synthesis. Among all the catalysts employed in this investigation, the best device performance was found from the synthesis of MWCNTs using Fe as a catalyst followed by Co and then Ni, respectively.     

The effect of heat treatment temperature and time on the microstructure and mechanical properties of PAN-based carbon fibers

The influence of heat treatment temperature from 1400 to 2840 °C and time from 1.2 to 12.0 min on the structure and mechanical properties of polyacrylonitrile carbon fibers was studied. It was observed that the Young’s modulus increased with increasing temperature and time, but the tensile strength exhibited different variation trends with the different processing methods. For a fixed time of 1.2 min, the strength dropped from 4.6 GPa at 1400 °C to 2.6 GPa at 2840 °C, (~43.5 %) as opposed to a 63.9 % increase in Young’s modulus. However, when the treatment time was increased to 6.0 min at 2500 °C, the tensile strength decreased only by 1.9 %, from 3.71 to 3.64 GPa, versus a nearly 20.0 % increase in Young’s modulus. The same situation was found for treatment at 2000 and 2700 °C. Raman spectroscopy and uniform stress model analysis show that the degree of covalent cross-linking between the graphene planes decreased as temperature increased, while it remained almost constant as treatment time was increased. It is believed that during heat treatment of a carbon fiber, the cross-linking collapses at the beginning but the crystalline size keeps growing with prolonging time, so the tensile strength decreases little with further heat treatment while tensile modulus keeps increasing.     

Estimation of agglomerate size of multi-walled carbon nanotubes in fluidized beds

The objective of this study was to determine hydrodynamic characteristics of multi-walled carbon nanotubes (MWCNTs) agglomerates and examine their sizes. The bed collapsing process of MWCNTs agglomerates was found to be closer to that of Geldart group C particles than group A particles. Median diameters of MWCNTs agglomerates determined by sedimentation method at initial superficial gas velocity of 0.120 and 0.190 m/s were 157 and 221 μm, respectively. The size of these MWCNTs agglomerates in fluidization state was measured by image analysis using a high speed camera. Median diameters of these MWCNTs agglomerates in freeboard were increased from 138 to 189 μm as superficial gas velocity was increased from 0.088 to 0.190 m/s at static bed height of 0.16 m. Median diameter and size distribution determined by sedimentation method fitted well with those measured using image analysis. Results were reasonable at superficial gas velocity up to 0.190 m/s.     

Synthesis of multiwalled carbon nanotubes from polyethylene waste to enhance the rheological behavior of lubricating grease

Abstract

Carbon nanotubes (CNTs) are attracting great interest in enhancing rheological behavior and thermal performance of lubricating grease. In this study, CNTs were synthesized by catalytic chemical vapor deposition (CCVD) method using low-density polyethylene (LDPE) waste as a cheap carbon source and Co/MgO as an effective catalyst. The effect of temperature on the catalytic pyrolysis of LDPE to produce CNTs has been studied. Catalytic pyrolysis of LDPE waste was conducted in a temperature range of 350–600?°C using the H-ZSM-5 catalyst. The structure and quality of CNTs were fully characterized using HR-TEM, XRD, and Raman spectroscopy. On the other hand, various concentrations of CNTs (0.2, 0.4, 0.6, 0.8, and 1.0?wt%) were mixed with pure lithium grease to determine the optimum percentage that improves the properties of nano-grease. The results showed that a high yield of multiwalled carbon nanotubes (MWCNTs) was obtained with high quality at temperatures ranging from 400 to 550?°C. Also, the addition of CNTs enhanced the rheological behavior of lithium grease, and the optimum percentage of CNTs was 0.8?wt%. Furthermore, the apparent viscosity and shear stress of lithium nano-grease increased by increasing the concentration of CNTs up to 0.8%. At this concentration, the penetration value of lithium nano-grease was greater than pure grease, and the dropping point increased by 12.5%. These results suggested that CNTs prepared from LDPE waste were an excellent additive to enhance the physicochemical properties of lithium grease.     

Low-temperature preparation of transparent conductive Al-doped ZnO thin films by a novel sol–gel method

We developed a novel sol–gel method to prepare transparent conductive Al-doped ZnO (AZO) thin film at low temperature. The AZO nanocrystals were prepared by a solvothermal method and then they were dispersed in the monoethanolamine and methanol to form AZO colloids. A (002)-oriented ZnO thin film was used as a nucleation layer to induce the (002)-oriented growth of AZO thin films. The AZO thin films were prepared on Si(100) and fused quartz glass substrates with the (002)-oriented ZnO nucleation layer and annealed at 400 °C for 60 min. All AZO thin films showed (002) orientation. For electrical and optical measurements, the films deposited on glass substrates were post-annealed at 400 °C for 30 min in forming gas (100 % H₂) to improve their conductivity. These samples had high transparency in the visible wavelength range, and also showed good conductivity. A 0.2 mol L^?1 AZO solution with 3 at.% Al content was heated in a Teflon autoclave at 160 °C for 30 min to form AZO nanocrystals, and then the AZO nanocrystals were suspended in the MEA and methanol to obtain the stable AZO colloid. The Al content in the AZO nanocrystals was 2.7 at.%, and the high Al doping coefficient was mainly attributed to the formation of AZO nanocrystals in the autoclave. The AZO thin film using this colloid had the lowest resistivity of 3.89 × 10^?3 Ω cm due to its high carrier concentration of 3.29 × 10²⁰ cm^?3.     

Annealing effects on structural and optical properties of ZnMgO films grown by RF magnetron sputtering

Two sets of ZnMgO thin films have been fabricated on Si (111) substrates by RF magnetron sputtering, and were annealed at air atmosphere afterwards. The effects of annealing temperature and time on structural and optical properties were also characterized by X-ray diffraction, scanning electron microscopy and photoluminescence (PL) spectra. For samples fabricated at a lower temperature (200 °C, defined as samples I), the experimental results revealed that only hexagonal phase was observed for the films annealed at the temperature range from 180 to 420 °C, and the best crystal quality for the films was found at 240 °C. For samples synthesized at 220 °C (defined as samples II), the crystal structures exhibited anneal-time dependent. The experimental results revealed coexistence of hexagonal and cubic phase when they were annealed at a set temperature of 220 °C with the different annealing time, and the best one can be observed when the anneal time was 30 min. PL spectra showed blue shift for UV peak with the increase of annealing temperature for samples I, and the UV emission occurred red shift and then blue shift when the anneal time increased from 20 to 30 min for samples II.     

Photocatalytic degradation mechanisms of dimethyl phthalate esters by MWCNTs-anatase TiO2 nanocomposites using the UHPLC/Orbitrap/MS technique

Dimethyl phthalate esters (DMPEs) have been identified as endocrine disrupting plastisizers and emerging contaminants which can be released readily upon exposure to the environment. In this study, MWCNTs/TiO₂ nanocomposites, which possess the potential application for the photocatalytic degradation of DMPEs under UV irradiation, were prepared via simple one-pot sol-gel reaction using titanium isopropoxide (TTIP) as titania precursor and multiwalled carbon nanotubes (MWCNTs). The MWCNTs/TiO₂ nanocomposites was calcined in air for 2 h at the temperatures ranging from 350 to 750 °C. As a result, the MWCNTs/TiO₂ nanocomposites synthesized at calcination temperature of 450 °C demonstrated the highest photodegradation efficiency of 97% after 180 min UV irradiation and its degraded products were evaluated using the ultra high performance liquid chromatography (UHPLC) coupled with a high resolution (HR) Orbitrap mass spectrometry (MS). A primary degradation mechanism was proposed and it was noteworthy that some new intermediates were discovered and reported. This work has developed a simple method for qualitative determination of DMPEs based on HPLC with UV detection.     

Preparation and characterization of rice-shaped MnO2/CNTs composite and superior catalytic activity on thermal decomposition of ammonium perchlorate

Manganese dioxides (MnO₂) were successfully deposited on carbon nanotubes (CNTs) surface by redox reaction between potassium permanganate and CNTs. The characterization results showed that the MnO₂ exhibited the rice-shaped nanostructure with about 5～10 nm in width and 10～30 nm in the length on CNTs. The solvothermal temperature of composite can greatly affected its morphology and structure to improve the thermal catalytic on ammonium perchlorate (AP) decomposition. Compared with other samples, the prepared composite at 120°C exhibited superior catalytic performance, as 3wt% of composite added in AP, the second exothermic peak temperature decreased by 160.2°C and the apparent release heat of the thermal decomposition of AP which is four times of that of pure AP. A possible mechanism for formation the rice shaped MnO₂/CNTs composite is also presented.