Deposition Of Carbon Nanotubes Research Articles

Influence of deposited CNTs on the surface of carbon fiber by ultrasonically assisted electrophoretic deposition

The surface property of carbon fiber directly affects the interface performance between carbon fiber and matrix. To improve the surface property of carbon fiber, we proposed a simple method to prepare carbon nanotubes /carbon fiber hybrid fiber via ultrasonically assisted electrophoretic deposition (EPD). Surface morphologies and surface functional group of carbon fibers were examined by atomic force microscopy (AFM), scanning electron microscopy (SEM) and fourier transform infrared spectrometer (FTIR), respectively. The results show that the deposition of carbon nanotubes changed the surface morphologies of carbon fibers and introduced polar groups (C=O and C-O) to carbon fiber surface. Comparing the results with EPD-only, ultrasonically assisted EPD increased the uniformity of carbon nanotubes coatings whereas only sparse and not uniformly deposition formed without ultrasonic.

(Invited) Spray Coating of Organic Semiconductors and Carbon Nanotube Electrodes for Solar Cells

The promise of solution processed organic solar cells lies in their low-cost high-throughput manufacturability. However, this low cost aspect can only be fully realized if all of the layers are deposited via in-line compatible methods. Spray coating is a high-rate, non-contact deposition technique characterized by the ability to deposit thin films over large areas by the superposition of small droplets. Here, we discuss our recent efforts in utilizing concurrently pumped ultrasonic spray coating, whereby two solutions are pumped to a vibrating nozzle and simultaneously atomized. With this technique, we are able to control solution concentration, donor:acceptor ratio, and multiple-solvent composition, giving us a method by which to optimize not only the smoothness and thickness of the dried film but also the active layer composition. Also, we will show our results with depositing patterned top and opaque electrodes composed of either metallic nanoparticles sintered upon deposition or multiwalled carbon nanotube (MWCNT)-based inks. Notably, despite the absorptive nature of a back MWCNT electrode, devices are able to exhibit ~85% of the photocurrent compared to an evaporated Ag top contact.

Inter-fiber stresses in composites with carbon nanotube grafted and coated fibers

Abstract Deposition of carbon nanotubes (CNT) on fiber surfaces is a promising technique to add functionalities to polymer composites. Upon deformation, these CNTs generate local stress heterogeneities which may affect properties of the interphase and the composite. The stress disturbance depends on the morphology of deposited CNT assemblies also linked to a deposition technique. In the present work, two types of morphologies are investigated: (1) CNTs grown on fibers; and (2) CNTs deposited in fiber coatings. The difference in the two cases is the orientation of CNTs near the fiber interface: radial for grown CNTs and tangent for CNTs in the coatings. Different parameters including CNT length, morphology of the grafting and density of the coating are evaluated. The analysis is performed using a recently developed two-scale model. Results show that CNT grafted and coated fibers produce distinctly different interface stresses.

High performance carbon nanotube based composite film from layer-by-layer deposition

So far, preparation of strong carbon nanotube (CNT)/polymer composites still faces big challenges mainly due to the limited controls of CNT dispersion and alignment in polymers. Here, a new “layer-by-layer deposition” method is put forward to prepare CNT/polyvinyl alcohol (PVA) composite films. This is based on intermittent deposition of aligned CNT and PVA layers on a paper tape substrate. The in situ deposition allows PVA to infiltrate into the CNT film efficiently, and, as a result, the mechanical property of CNT/PVA composite film has been improved remarkably. For example, the composite film possesses a tensile strength of 1.7GPa, which is almost one order of magnitude and 20 times higher than those of the pure CNT and PVA films, respectively. The high performance of the composite film could be ascribed to the role of PVA infiltration, which leads to not only the formation of strong interfacial bonding between CNTs and PVA matrix but also the reduction of film thickness. The novel process offers a new research direction for preparing CNT-based composites and future performance maximization.

Atmospheric pressure barrier discharge at high temperature: Diagnostics and carbon nanotubes deposition

Atmospheric pressure dielectric barrier discharge (DBD) in Ar/H2 gas feed with C2H2 or CH4 admixture was studied at room and high temperature of 680 °C by plasma diagnostics (electrical measurements, fast camera imaging, and optical emission spectroscopy). It was shown that filamentary DBD in pure Ar or Ar/H2 can be converted into homogeneous discharge by an acetylene admixture. Fast intensified charge-coupled device (ICCD) camera proved that this homogeneous discharge is an atmospheric pressure glow discharge (APGD) at room temperature whereas at high temperature the discharge mode switches at every half-period between APGD and atmospheric pressure Townsend discharge. The high temperature discharges (610–710 °C) in Ar/H2/C2H2 and Ar/H2/CH4 were also investigated with respect to a surface bound deposition of carbon nanotubes using 5 nm thick iron layer as a catalyst. CNTs were deposited without any dedicated catalyst pretreatment phase. The quality of CNTs, namely, their density, vertical alignment, and width of the diameter distribution, was better for the C2H2 gas feed and higher temperatures.

Electrophoretic deposition of multi-walled carbon nanotubes on porous anodic aluminum oxide using ionic liquid as a dispersing agent

Multi-wall carbon nanotubes (MW-CNTs) have been arranged in nanochannels of anodic aluminum oxide template (AAO) by electrophoretic deposition (EPD) to make a vertically-aligned carbon nanotube (VA-CNT) based electrode. Well ordered AAO templates were prepared by a two-step anodizing process by applying a constant voltage of 45V in oxalic acid solution. The stabilized CNTs in a water-soluble room temperature ionic liquid (1-methyl-3-octadecylimidazolium bromide), were deposited in the pores of AAO templates which were conductive by deposition of Ni nanoparticles in the bottom of pores. In order to obtain ideal results, different EPD parameters, such as concentration of MWCNTs and ionic liquid on stability of MWCNT suspensions, deposition time and voltage which are applied in EPD process and also optimal conditions for anodizing of template were investigated. The capacitive performance of prepared electrodes was analyzed by measuring the specific capacitance from cyclic voltammograms and the charge–discharge curves. A maximum value of 50Fg−1 at the scan rate of 20mVs−1was achieved for the specific capacitance.

Filtration properties of hierarchical carbon nanostructures deposited on carbon fibre fabrics

Hierarchical carbon nanostructures have been produced and examined for their use in liquid filtration experiments. The nanostructures are based on carbon nanotube growth and graphite oxide sponge deposition on the surface of commercially available carbon fibre fabrics. The hierarchical nanomaterial construction on the carbon fibre fabric is made possible due to the chemical vapour deposited carbon nanotubes which act as anchoring sites for the solution deposited sponge nanomaterial. The nanomaterials show a high capacity for Rhodamine B filtration, with the carbon fibre—carbon nanotube—graphite oxide sponge fabric showing filtering performance comparable to a commercial activated carbon filter. After 40 successive filtrations of 10 mg ml−1 Rhodamine B solution, the filtrate of dual modified fabrics returned an increase in transparency of 94% when measured at approx. 550 nm compared to 72% for the commercial carbon filter. When normalised with respect to the areal density of the commercial filter, the increase in optical transparency of the filtrate from the dual modified fabrics reduces to 65%. The Rhodamine B is found to deposit in the carbon nanomaterials via a nucleation, growth and saturation mechanism.

Controlled modification of carbon nanotubes and polyaniline on macroporous graphite felt for high-performance microbial fuel cell anode

Polyaniline (PANI) was electropolymerized on the surface of macroporous graphite felt (GF) followed by the electrophoretic deposition of carbon nanotubes (CNTs). The as-prepared macroporous material was characterized by scanning electron microscopy, water contact angle goniometry and electrochemical techniques. Upon the modification of PANI, a rough and nano-cilia containing film is coated on the surface of the graphite fibers, transforming the surface from hydrophobic to hydrophilic. The subsequent modification by CNTs increases the effective surface area and electrical conductivity of the resulting material. The power output of a mediator-free dual-chamber microbial fuel cell (MFC) constructed from the GF anode and an exoelectrogen Shewanella putrefaciens increases drastically with the CNT modification. The CNT/PANI/GF MFC attains an output voltage of 342 mV across an external resistor of 1.96 kΩ constant load, and a maximum power density of 257 mW m−2, increased by 343% and 186%, compared to that of the pristine GF MFC and the PANI/GF MFC, respectively. More bacteria are attached on the CNT/PANI/GF anode than on the PANI/GF anode during the working of the MFC. This strategy provides an easy scale-up, simple and controllable method for the preparation of high-performance and low-cost MFC anodes.

Polymer nanocomposite – fiber model interphases: Influence of processing and interface chemistry on mechanical performance

Electrophoretic deposition (EPD) has been established as a scalable and environmentally friendly approach for depositing carbon nanotubes (CNTs) from aqueous colloidal dispersions onto a variety of fibrous surfaces. EPD facilitates the micro/nano hybridization of CNTs and reinforcing fibers, enabling the controlled engineering of hierarchically-structured composites. Model studies have shown that the chemistry of the CNTs in the fiber/matrix interphase plays a critical role in the mechanical performance of the composite. Composite interphases were replicated on planar glass substrates to systematically study the influence of CNT functionalization, glass surface chemistry, and aqueous dispersion quality on the mechanical performance under shear loading. CNTs were functionalized using a novel ultrasonicated-ozonolysis (USO) and polyethyleneimine (PEI) process to prepare films on silane-treated glass surfaces. The epoxy-infused films exhibited a 50% improvement as compared to untreated glass/epoxy interfaces. Detailed surface analysis using X-ray photoelectron spectroscopy shows chemical bonds in the interphase, and computational modeling of the valence band spectra provides additional insight into the chemical nature of the bond. The formation of a PEI–CNT rich interphase facilitates a more homogeneous, ductile fracture zone relative to the brittle glass epoxy interface, and increases composite strength by shifting the fracture surface away from the glass surface. Intentional destabilization of the CNT dispersion resulted in re-agglomeration, diminishing any benefit of the PEI, thereby demonstrating the importance of a stable dispersion provided by the USO processing. The results replicate the trends observed previously in more complex composite systems and provide new insight into interfacial engineering of nanostructured composites.

Time-dependent subcellular distribution and effects of carbon nanotubes in lungs of mice.

Background and MethodsPulmonary deposited carbon nanotubes (CNTs) are cleared very slowly from the lung, but there is limited information on how CNTs interact with the lung tissue over time. To address this, three different multiwalled CNTs were intratracheally instilled into female C57BL/6 mice: one short (850 nm) and tangled, and two longer (4 μm and 5.7 μm) and thicker. We assessed the cellular interaction with these CNTs using transmission electron microscopy (TEM) 1, 3 and 28 days after instillation.ResultsTEM analysis revealed that the three CNTs followed the same overall progression pattern over time. Initially, CNTs were taken up either by a diffusion mechanism or via endocytosis. Then CNTs were agglomerated in vesicles in macrophages. Lastly, at 28 days post-exposure, evidence suggesting CNT escape from vesicle enclosures were found. The longer and thicker CNTs more often perturbed and escaped vesicular enclosures in macrophages compared to the smaller CNTs. Bronchoalveolar lavage (BAL) showed that the CNT exposure induced both an eosinophil influx and also eosinophilic crystalline pneumonia.ConclusionTwo very different types of multiwalled CNTs had very similar pattern of cellular interactions in lung tissue, with the longer and thicker CNTs resulting in more severe effects in terms of eosinophil influx and incidence of eosinophilic crystalline pneumonia (ECP).

Subchronic toxicity and cardiovascular responses in spontaneously hypertensive rats after exposure to multiwalled carbon nanotubes by intratracheal instillation.

The tremendous demand of the market for carbon nanotubes has led to their massive production that presents an increasing risk through occupational exposure. Lung deposition of carbon nanotubes is known to cause acute localized pulmonary adverse effects. However, systemic cardiovascular damages associated with acute pulmonary lesion have not been thoroughly addressed. Four kinds of multiwalled carbon nanotubes (MWCNTs) with different lengths and/or iron contents were used to explore the potential subchronic toxicological effects in spontaneously hypertensive (SH) rats and normotensive control Wistar-Kyoto (WKY) rats after intratracheal instillation. MWCNTs penetrated the lung blood-gas barrier and accumulated in the liver, kidneys, and spleen but not in the heart and aorta of SH rats. The pulmonary toxicity and cardiovascular effects were assessed at 7 and 30 days postexposure. Compared to the WKY rats, transient influences on blood pressure and up to 30 days persistent decrease in the heart rate of SH rats were found by electrocardiogram monitoring. The subchronic toxicity, especially the sustained inflammation of the pulmonary and cardiovascular system, was revealed at days 7 and 30 in both SH and WKY rat models. Histopathological results showed obvious morphological lesions in abdominal arteries of SH rats 30 days after exposure. Our results suggest that more attention should be paid to the long-term toxic effects of MWCNTs, and particularly, occupationally exposed workers with preexisting cardiovascular diseases should be monitored more thoroughly.

Direct decomposition of methane over SBA-15 supported Ni, Co and Fe based bimetallic catalysts

Thermocatalytic decomposition of methane is an alternative route for the production of COx-free hydrogen and carbon nanomaterials. In this work, a set of novel Ni, Co and Fe based bimetallic catalysts supported over mesoporous SBA-15 was synthesized by a facile wet impregnation route, characterized for their structural, textural and reduction properties and were successfully used for the methane decomposition. The fine dispersion of metal oxide particles on the surface of SBA-15, without affecting its mesoporous texture was clearly shown in the low angle X-ray diffraction patterns and the transmission electron microscopy (TEM) images. The nitrogen sorption analysis showed the reduced specific surface area and pore volume of SBA-15, after metal loading due to the partial filling of hexagonal mesopores by metal species. The results of methane decomposition experiments indicated that all of the bimetallic catalysts were highly active and stable for the reaction at 700°C even after 300min of time on stream (TOS). However, a maximum hydrogen yield of ∼56% was observed for the NiCo/SBA-15 catalyst within 30min of TOS. A high catalytic stability was shown by the CoFe/SBA-15 catalyst with 51% of hydrogen yield during the course of reaction. The catalytic stability of the bimetallic catalysts was attributed to the formation of bimetallic alloys. Moreover, the deposited carbons were found to be in the form of a new set of hollow multi-walled nanotubes with open tips, indicating a base growth mechanism, which confirm the selectivity of SBA-15 supported bimetallic catalysts for the formation of open tip carbon nanotubes. The Raman spectroscopic and thermogravimetric analysis of the deposited carbon nanotubes over the bimetallic catalysts indicated their higher graphitization degree and oxidation stability.

Surface modification of plastic substrates via corona-pretreatment and its effects on the properties of carbon nanotubes for use of flexible transparent electrodes

In this study, the surface of polyethylene terephthalate (PET) substrates was modified via corona treatment before the deposition of carbon nanotubes (CNTs), and the effects of such surface modification on the properties of the CNTs for flexible transparent electrodes were investigated. The changes in the surface roughness, contact angle, and surface energy of the PET substrates due to the corona treatment were characterized in terms of the applied corona energies, PET feeding directions, and treatment times. The higher corona energies, the more frequent treatment times, and the bi-directional treatment produced the larger surface roughness of the PET substrates. The results of the contact angles and the surface energies indicated that the surfaces of the PET substrates became hydrophilic from hydrophobic after the corona treatment. The analysis using X-ray photoelectron spectroscopy confirmed that oxygen polar groups appeared when the PET substrates were corona-treated. In addition, the increase in the CNTs' sheet resistance values due to their repeated outer and inner bending (up to 16,000 times) was found to have been significantly alleviated when the CNTs were deposited on the corona-treated PET substrates. This confirmed that the adhesion of the CNTs was improved after the corona pretreatment of the PET substrates.

Integrated Damage Sensing in Fibre‐Reinforced Composites with Extremely Low Carbon Nanotube Loadings

A nanoengineered hybrid composite system has been developed, with integrated damage sensing capabilities at extremely low carbon nanotube (CNT) contents. The employed simple spray coating technique offers good spatial control and the possibility of localized CNT deposition, especially near the fibre/matrix interface, solving traditional problems associated with the incorporation of nanofillers in fibre‐reinforced composite laminates such as increased resin viscosity and filtering effects. Moreover, the employed spraying technology has good potential for industrial scale‐up. In situ damage sensing based on standard composite tests has been demonstrated for the first time on hybrid glass fibre/CNT composites using extremely low CNT loadings (below 0.1 wt.%) and shows great potential for localized structural health monitoring by controlled CNT deposition into damage prone zones.

MOCVD of a Nanocomposite Film of Fe, Fe3O4 and Carbon Nanotubes from Ferric Acetylacetonate: Novel Thermodynamic Modeling to Reconcile with Experiment

ABSTRACTThermodynamic modeling of the MOCVD process, using the standard free energy minimization algorithm, cannot always explain the deposition of hybrid films that occurs. The present investigation explores a modification of the procedure to account for the observed simultaneous deposition of metallic iron, Fe3O4, and carbon nanotubes from a single precursor. Such composite films have potential application in various device architectures and sensors, and are being studied as electrode material in energy storage devices such as lithium ion batteries and supercapacitors.With ferric acetylacetonate [Fe(acac)3] as the precursor, MOCVD in argon ambient results in a nanocomposite of CNT, Fe, and Fe3O4 (characterized by XRD and Raman spectroscopy) when growth temperature T and total reactor pressure P are in the range from 600°C-800°C and 5-30 torr, respectively. No previous report could be found on the single-step formation of a CNT-metal-metal oxide composite. Equilibrium thermodynamic modeling using available software predicts the deposition of only Fe3C and carbon, without any co-deposition of Fe and Fe3O4, in contrast with experimental observations. To reconcile this contradiction, the modeling of the process was approached by taking the molecular structure of the precursor into account, whereas “standard” thermodynamic simulations are restricted to the total number of atoms of each element in the reactant(s) as the input. When Ocon (statistical average of the oxygen atom(s) taken up by each metal atom during CVD) is restricted to lie between 0 and 1, thermodynamic computations predict simultaneous deposition of FeO1-x, Fe3C, Fe3O4 and C in the inert ambient. At high temperature and in a carbon-rich atmosphere, iron carbide decomposes to iron and carbon. Furthermore, FeO1-x yields Fe and Fe3O4 when cooled below 567°C. Therefore, the resulting film would be composed of Fe3O4, Fe and C, in agreement with experiment. The weight percentage of carbon (∼40%) calculated from thermodynamic analysis matches well with experimental data from TG-DTA.

Fabrication of Counter Electrode of Electrochemical CO Gas Sensor by Electrophoretic Deposition of MWCNT

In the present study, we aim to report on the applicability of electrophoretic deposition (EPD) technique for the deposition of Multi-Walled Carbon Nanotube (MWCNT) on Polytetrafluoroethylene (PTFE) membrane in non-aqueous media to fabricate the counter electrodes of electrochemical gas sensors. We also tried to compare the results with similar applicable electrodes shaped by the Doctor Blade technique. The morphology of the particles and the deposition pattern were investigated by scanning electron microscope (SEM). The stability of the prepared carbon based suspension was altered by pH changes and controlled by turbidity method. The sensitivity of both kinds of sensors was examined and confirmed by the linear sweep voltammetry analysis. Shorter processing time, monotonic layers and using less CNTs compared with other methods are among the advantages of employing EPD in our study. Our results suggest the application of the EPD technique for the fabrication of electrochemical gas sensor electrodes.

Improved fracture toughness and integrated damage sensing capability by spray coated CNTs on carbon fibre prepreg

The development of a hierarchically engineered micro-nano hybrid composite system is described. A spray coating technique has been utilized as an effective way to deposit carbon nanotubes (CNTs) onto carbon fibre prepregs with good control of network formation and the potential for localization. Compared to more traditional approaches of introducing CNTs into epoxy matrices for enhancing composite properties, this technique has benefits in terms of its simplicity and versatility, as well as the potential for industrial scale-up. The effectiveness of the technique is demonstrated by the extremely low CNT loading (0.047wt.%) needed to significantly increase the Mode-I fracture toughness of the carbon fibre laminates by about 50%, which is so far the largest reported improvement for such extremely low concentrations of non-functionalized CNTs. In-situ damage sensing has also been presented for the monitoring of structural health of these nano-engineered composite laminates upon loading, and a systematic analysis of sensing signals is performed.

Wet deposition of carbon nanotube black coatings for stray light reduction in optical systems

Stray light, also known as optical noise, affects the performance of many optical devices. It can be reduced to a tolerable level by well-designed and well-baffled system or/and by using functional black coatings that are fabricated in a complex and costly process. Carbon nanotubes (CNTs) absorb light strongly, making them an ideal candidate for realizing a super black coating. CNT coatings were formed by spraying formulations composed of a silicon binder and low cost multiwalled CNTs on a pre-heated aluminum plate. The diffuse reflectance of the coatings in the VIS range (350–800nm) was in the range of 2.6–5.11%, depending on the MWCNT concentration in the coating. In the NIR range (850–2400nm), the reflectance values were in the range of 4–6.5%, however the dependence on MWCNT concentration was not very significant. Excellent adhesion to the aluminum substrates was achieved, for coatings with CNT concentration below 15%, while still having very low reflectance, even at temperature cycling between 200°C and −196°C. The proposed coating formulations enable simple and low cost approach for producing high light-absorbing coating of complex 3D structures within a very short time by wet deposition of CNTs.

Photodetectors based on carbon nanotubes deposited by using a spray technique on semi-insulating gallium arsenide.

In this paper, a spray technique is used to perform low temperature deposition of multi-wall carbon nanotubes on semi-insulating gallium arsenide in order to obtain photodectors. A dispersion of nanotube powder in non-polar 1,2-dichloroethane is used as starting material. The morphological properties of the deposited films has been analysed by means of electron microscopy, in scanning and transmission mode. Detectors with different layouts have been prepared and current–voltage characteristics have been recorded in the dark and under irradiation with light in the range from ultraviolet to near infrared. The device spectral efficiency obtained from the electrical characterization is finally reported and an improvement of the photodetector behavior due to the nanotubes is presented and discussed.

Estimation of carbon nanotubes deposition in a human respiratory tract replica

Investigation of the deposition of airborne carbon nanotubes (CNTs) in the human respiratory tract is essential from the occupational health perspective. Due to the dimension of CNTs, it is very difficult to apply traditional deposition experimental methods to CNTs for conducting a deposition study using human airway replicas. In this research, an innovative experimental approach was adopted to estimate the deposition of CNTs in the human respiratory tract. Two types of CNT materials were used as the challenge CNT materials. The deposition experiments were carried out by delivering size classified CNT aerosols into a human airway replica (from the oral cavity down to part of the 4th lung generation). The CNT deposition fractions and efficiencies in the airways were estimated based on the air flow rates, as well as the CNT concentrations measured in associated lung airways. Experimental results acquired showed that CNT deposition fractions in different sections of the airway replica were all smaller than 5%. The CNT deposition efficiency in the tracheobronchial airways was generally less than 0.1. This result implies that the CNTs inhaled into the human respiratory tract could easily penetrate through the upper airways and transit down to the lower airways to cause potential health effects.