Multiwalled Carbon Nanotube Thin Films Research Articles

Modified interdigitated arrays by novel poly(1,8-diaminonaphthalene)/carbon nanotubes composite for selective detection of mercury(II)

This study describes a novel type of interdigitated arrays (IDA), microfabricated by electropolymerizing structured Poly(1,8-diaminonaphthalene)/functionalized multi-walled carbon nanotubes (PDAN/CNT) thin film onto a silicon chip for square wave voltammetry (SWV) multi-element heavy metal ion detection. The structure of PDAN/CNT was characterized by Raman, FE-SEM and AFM techniques. Analysed experiments reveal that the uptake of Hg2+ by PDAN/CNT is quite specific and it can be used advantageously for electrochemical sensing of Hg2+ thanks to original feature of (Hg2+/Hg22+) redox potential with the respect to that of PDAN/CNT. As-developed IDA type electrode can extend its utility in other sensing applications.

TUNING THE OPTICAL PROPERTIES OF MULTIWALL CARBON NANOTUBE THIN FILMS BY N+ ION BEAMS IRRADIATION

Measurements of optical transmission in the visible spectral range of N+ irradiated thin films of multiwall carbon nanotubes (MWCNTs) at various doses prepared by a vacuum filtration method are reported. An increase in optical transmission was observed corresponding to increase in N+ ion doses. Changes in Raman spectra at different ions doses ranging from 5 × 1015 ions/cm2 to 1 × 1017 ions/cm2 indicate that the structure of graphene evolves from a highly ordered layer to a disordered domains. These structural changes result in a dramatic increase in the optical transmission. Additionally, the increase of optical transmission of irradiated MWCNTs thin film as a function of electrical conductivity at various doses is also discussed. The optical transmission increases in irradiated MWCNT thin films is found to be a function of defects density in MWCNTs.

Adhesion, proliferation and differentiation of pluripotent stem cells on multi-walled carbon nanotubes

This article studies the adhesion, growth and differentiation of stem cells on carbon nanotube matrices. Glass coverslips were coated with multi-walled carbon nanotube (MWNT) thin films using layer-by-layer self-assembling techniques. Pluripotent P19 mouse embryonal carcinoma stem cells were seeded onto uncoated or MWNT-coated glass coverslips and either maintained in an undifferentiated state or induced to differentiate by the addition of retinoic acid. The authors found that cell adhesion was increased on the MWNT-coated glass surfaces, and that the expression patterns of some differentiation markers were altered in cells grown on MWNTs. The results suggest that MWNTs will be useful in directing pluripotent stem cell differentiation for tissue engineering purposes.

MWCNT–polymer composites as highly sensitive and selective room temperature gassensors

Multi-walled carbon nanotubes (MWCNTs)–polymer composite-basedhybrid sensors were fabricated and integrated into a resistive sensor designfor gas sensing applications. Thin films of MWCNTs were grown ontoSi/SiO2 substrates via xylene pyrolysis using the chemical vapor deposition technique.Polymers like PEDOT:PSS and polyaniline (PANI) mixed with various solventslike DMSO, DMF, 2-propanol and ethylene glycol were used to synthesize thecomposite films. These sensors exhibited excellent response and selectivity at roomtemperature when exposed to low concentrations (100 ppm) of analyte gases likeNH3 andNO2. The effect of various solvents on the sensor response imparting selectivity toCNT–polymer nanocomposites was investigated extensively. Sensitivities as high as 28%were observed for an MWCNT–PEDOT:PSS composite sensor when exposed to 100 ppm ofNH3 and − 29.8% sensitivity for an MWCNT–PANI composite sensor to 100 ppm ofNO2 when DMSO was used as a solvent. Additionally, the sensors exhibited good reversibility.

Room temperature hydrogen gas sensor nanocomposite based on Pd-decorated multi-walled carbon nanotubes thin films

Multi-walled carbon nanotubes (MWCNTs) are successfully processed in the form of thin films (buckypapers), and their morphology and electrical behaviour are characterized. The MWCNTs are synthesized by the floating catalyst chemical vapour deposition process. The effects of a sequence of treatments applied for MWCNTs purification on the buckypapers electrical behaviour are also examined. Nanocomposite thin films constituted of pristine and purified MWCNTs and Pd nanoparticles are prepared in order to evaluate their viability as H 2 sensors at room temperature. For this purpose, the electrical resistance of the nanocomposite films in atmospheres with different H 2 concentrations, is determined. Scanning electron microscopy (SEM) images show that the buckypapers and the nanocomposite films are 2D structures constituted by randomly oriented MWCNTs. The buckypapers present a semiconductor-like electrical behaviour as determined by the standard four point method. Room temperature resistivity values of around 10 −3 Ω m are assessed. Nanocomposite films show different electrical behaviour depending on the purification treatment applied to the MWCNTs employed. Furthermore, the electrical resistance of the nanocomposite films is found to increase when the measurements are performed in H 2 atmosphere. Values of H 2 sensitivity at room temperature of the nanocomposite films up to 2.15% are determined for H 2 average concentration higher than 350 ppm with short recovery time.

A Facile UV-Curing Method for the Preparation of Transparent and Conductive Carbon Nanotube Hybrid Films

A new method for preparing flexible, transparent, and conductive multiwalled carbon nanotube (MWCNT) hybrid films with scratch resistance through a facile UV-curing method is described herein. UV-curable urethane oligomers were used as the binder between the MWCNTs and the plastic substrates. The transparency and sheet resistance of MWCNT thin films can be easily tailored by controlling the number of bar coaters. Composite films with different binder ratios were prepared to evaluate and optimize the surface abrasion resistance and adhesion parameter. Two types of MWCNT films, those with a 56% (with a 586 komega/sq sheet resistance) and a 78% transmittance (with a 22 Momega/sq sheet resistance) were obtained using the UV-curable resin, and the conductive films showed distinguished abrasion resistance and good adhesion.

Humidity Sensor Based on Multi-Walled Carbon Nanotube Thin Films

The properties of the humidity sensors made of chemically treated and untreated multi-walled carbon nanotube (MWCNT) thin films are investigated systematically. It shows that both the chemically treated and untreated MWCNT thin films demonstrate humidity sensitive properties, but the former have stronger sensitivity than the latter. In the range of 11%–98% relative humidity (RH), the resistances of the chemically treated and untreated MWCNT humidity sensors increase 120% and 28%, respectively. Moreover, the treated humidity sensors showed higher sensitivity and better stability. In addition, the response and recover properties, and stabilization of the humidity sensors are measured, and the humidity sensitive mechanisms of the sensors are analyzed. The humidity sensitivity of carbon nanotube thin films indicates it promise as a kind of humidity sensitive material.

Effect of fluorination of carbon nanotubes on superhydrophobic properties of fluoro-based films

In this work, we prepared multi-walled carbon nanotubes (MWCNTs) thin films on glass substrates with transparent, conductive, and superhydrophobic properties. MWCNTs were dispersed in fluoropolymer (FP) solutions for modification of their surface by grafting FP. A dip-coating process was used to prepare the films at a continuous speed and different numbers of coatings. The chemical compositions and microstructures of the prepared film surface were also investigated by using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The film showed 83.5% transmittance and a sheet resistance of 1.38 × 10 4 Ω sq −1, and a high contact angle of 160.2°. The 3D MWCNTs networks and the low surface energy of the FP play important roles in creating the superhydrophobic surface of the MWCNTs film.

The effect of oxidation treatment on the properties of multi-walled carbon nanotube thin films

Carbon nanotube thin sheets – buckypapers – were prepared from multi-walled carbon nanotubes oxidised with different oxidation agents. Prepared buckypapers were characterized by mechanical testing, surface conductivity and mercury porosimetry. It was found that their mechanical properties were increased by increasing the power of oxidation agents. Nitric acid-treated buckypapers showed the highest structural integrity and surface conductivity.

Gas-sensing properties of tin oxide doped with metal oxides and carbon nanotubes: A competitive sensor for ethanol and liquid petroleum gas

SnO 2 doped with metal oxides such as PtO 2, PdO, La 2O 3 CuO, and Fe 2O 3 and multi-walled carbon nanotubes (MWCNTs) thin films were prepared by the sol–gel method. Thin film gas sensors were fabricated by spin-coating the sol onto interdigitated microelectrodes. The microstructure and morphology of the materials were characterized by XRD, FE-SEM, and TEM. The results reveal that their SnO 2 particle size is lower than 10 nm, and the MWCNTs doping is well embedded in the SnO 2 matrix. The response of all the sensors was studied for different concentrations of ethanol and liquid petroleum gases (LPG) and at different operating temperatures. Comparative results reveal that the (1 wt%) PtO 2-doped SnO 2 sensor exhibits higher sensitivity to ethanol gas and LPG than the sensors doped with the other dopants. Especially, the (1 wt%) PtO 2-doped SnO 2 sensor shows higher selectivity to ethanol gas over LPG, while the (0.1 wt%, 20 < d < 40 nm)-doped SnO 2 shows higher selectivity to LPG over ethanol gas in the same testing conditions.

A novel hybrid supercapacitor with a carbon nanotube cathode and an iron oxide/carbon nanotube composite anode

A scalable spray deposition technique has been adopted to the fabrication of a flexible nanostructured hybrid supercapacitor based on thin film multi-walled carbon nanotube (MWNT) cathodes and hematite (α-Fe2O3)/MWNT composite anodes. On the basis of the total weight of the binder-free MWNT and α-Fe2O3/MWNT thin film composite electrodes, the hybrid supercapacitor provided a very high specific energy density of 50 Wh kg−1 at a specific power density of 1000 W kg−1 over the potential range 0–2.8 V, which was an energy density 8 times that of identically prepared symmetric supercapacitors with MWNT only electrodes under the same conditions. The superior electrochemical performance of the hybrid supercapacitor arrangement can be attributed to the incorporation of MWNTs into the α-Fe2O3 anodes, which leads to a decrease of internal resistance and an improvement in both the ion diffusion behaviour and the integrity of the α-Fe2O3 containing films.

Layer-by-Layer Assembly of All Carbon Nanotube Ultrathin Films for Electrochemical Applications

All multiwall carbon nanotube (MWNT) thin films are created by layer-by-layer (LBL) assembly of surface functionalized MWNTs. Negatively and positively charged MWNTs were prepared by surface functionalization, allowing the incorporation of MWNTs into highly tunable thin films via the LBL technique. The pH dependent surface charge on the MWNTs gives this system the unique characteristics of LBL assembly of weak polyelectrolytes, controlling thickness and morphology with assembly pH conditions. We demonstrate that these MWNT thin films have randomly oriented interpenetrating network structure with well developed nanopores using AFM and SEM, which is an ideal structure of functional materials for various applications. In particular, electrochemical measurements of these all-MWNT thin film electrodes show high electronic conductivity in comparison with polymer composites with single wall nanotubes, and high capacitive behavior with precise control of capacity.

Preparation and characterization of low- and high-adherent transparent multi-walled carbon nanotube thin films

Thin films of multi-walled carbon nanotubes (MWNTs) were prepared by spin coating on borosilicate substrates. The precursor solution was a dispersion of MWNTs in water containing hexadecyl-trimethyl-ammonium-chloride (HDTAC), a cationic surfactant. In order to enhance the adhesion of the films to the substrate, different concentrations of an adhesion promoter were added to the precursor dispersion. Parameters such as the optimum concentration of MWNTs in the networks, temperature of heat treatment, transparency in the visible range, hardness and adherence of the films were investigated. The structural, optical, electrical and mechanical characterization of the thin films is demonstrated in this work.

Fabrication and characterization of carbon nanotube based high sensitive gas sensors operable at room temperature

Multi-walled carbon nanotubes (MWCNTs) were prepared using both dc sputtering method and thermal CVD method. Single-walled carbon nanotubes (SWCNTs) were prepared by pulsed laser ablation (PLA) method. CNT based NO x gas sensors which can operate at low temperature were fabricated. Both MWCNT thin films and SWCNT thin films were grown on Al 2O 3 substrate with interdigitated Pt-electrodes to make a gas sensor. Gas sensing properties to NO and NO 2 gases were measured. Resistance of the prepared CNT-based gas sensor decreased with increase of NO and NO 2 gas concentration. The SWCNT-based gas sensor showed higher sensitivity and rapid-response to the test gas.

Pulsed laser deposition of multiwalled carbon nanotubes thin films

The physical/chemical properties of multiwalled carbon nanotubes have attracted much interest for applications in different fields, from micro-electronic to coating technology due, in particular, to their peculiar conductivity properties, to their hardness and high resistance to thermal stress. The technology to produce carbon nanotubes thin films with the desired properties, however, is still under development. In this work, we report on multiwalled carbon nanotubes thin films deposited by pulsed laser deposition techniques ablating commercially polystyrene-nanotubes pellets on alumina substrates. MicroRaman spectroscopy and high resolution Transmission Electron Microscopy provide the experimental confirmation that carbon nanotubes-like structures are present on the alumina surface with both minimal morphological damage of the tubes and structural changes induced by laser beam.

FLOW SENSING CHARACTERISTICS OF THIN FILM BASED ON MULTI-WALL CARBON NANOTUBES

Multi-wall carbon nanotubes (MWNTs) thin film was synthesized and its sensing for different flowing solutions was investigated in this paper. The voltage generated from MWNTs thin film was in sublinear fashion and a new discovery in this paper is that the charge-to-mass ratio (q/m) of the ions is an important factor. The results were inconsistent with the conventional idea that a streaming potential is the efficient factor. New mechanism has been discussed about their effects on the charge of MWNTs and the sublinear response based on a pulsating ratchet model. This result would be indicative in nanoscale sensors, detectors and power cells.

Effect of temperature on the electron field emission from aligned carbon nanofibers and multiwalled carbon nanotubes

Effect of temperature and aspect ratio on the field emission properties of vertically aligned carbon nanofiber and multiwalled carbon nanotube thin films were studied in detail. Carbon nanofibers and multiwalled carbon nanotube have been synthesized on Si substrates via direct current plasma enhanced chemical vapor deposition technique. Surface morphologies of the films have been studied by a scanning electron microscope, transmission electron microscope and an atomic force microscope. It is found that the threshold field and the emission current density are dependent on the ambient temperature as well as on the aspect ratio of the carbon nanostructure. The threshold field for carbon nanofibers was found to decrease from 5.1 to 2.6 V/μm when the temperature was raised from 300 to 650 K, whereas for MWCNTs it was found to decrease from 4.0 to 1.4 V/μm. This dependence was due to the change in work function of the nanofibers and nanotubes with temperature. The field enhancement factor, current density and the dependence of the effective work function with temperature and with aspect ratio were calculated and we have tried to explain the emission mechanism.

Thin Films Composed of Multiwalled Carbon Nanotubes, Gold Nanoparticles and Myoglobin for Humidity Detection at Room Temperature

Optically transparent and electrically conductive nanocomposite thin films consisting of multiwalled carbon nanotubes (MWCNTs), gold nanoparticles (GNPs) and myoglobin molecules that glue GNPs and MWCNTs together are fabricated for the first time on glass substrates from aqueous solution. The nanocomposite thin film is capable of varying its resistance, impedance or optical transmittance at room temperature in response to changes in ambient humidity. The conductometric sensitivity to relative humidity (RH) of the nanocomposite thin film is compared with those of the pure and Mb-functionalized MWCNT layers. The pure MWCNT layer shows a small increase in its resistance with increasing RH due to the effect of p-type semiconducting nanotubes present in the film. In contrast, a four times higher sensitivity to RH is observed for both the nanocomposite and Mb-functionalized MWCNT thin films. The sensitivity enhancement is attributable to swelling of the thin films induced by water absorption in the presence of Mb molecules, which increases the inter-nanotube spacing and thereby causes a further increase of the film resistance. A humidity change as low as DeltaRH=0.3 % has been readily detected by conductometry using the nanocomposite thin film.

Palladium dispersed multiwalled carbon nanotube based hydrogen sensor for fuel cell applications

Palladium nanocatalysts supported on surface-oxidized multiwalled carbon nanotubes (MWNT) were prepared by the aqueous solution reduction of PdCl 2 . MWNT have been synthesized by catalytic chemical vapor deposition (CCVD) technique. Pyrolysis of acetylene using a fixed-bed catalytic reactor over rare earth (RE) based AB 2 alloy hydride catalyst, obtained through hydrogen decrepitation technique, has been performed to synthesize MWNT. Structural, morphological and vibrational characterizations have been carried out using XRD, SEM, TEM and Raman spectroscopy, respectively. In situ electrical resistance measurements for thin films of MWNT obtained by spin coating samples were carried out by two-probe technique in a chamber with provision to introduce known concentration of hydrogen in constant air flow. Investigations of hydrogen sensing properties of Pd–MWNT ensembles have been carried out. The stability of Pd–MWNT thin films after several cycles of adsorption and desorption was studied. The change in electrical resistance due to hydrogen adsorption is reversible, with increase to saturation on exposure to hydrogen gas. The results demonstrate that chemically treated MWNT functionalized with nanostructured Pd show good H 2 sensing response at room temperature.

Supercapacitors using carbon nanotubes films by electrophoretic deposition

Multi-walled carbon nanotube (MWNT) thin films have been fabricated by electrophoretic deposition technique in this study. The supercapacitors built from such thin film electrodes have exhibited near-ideal rectangular cyclic voltammograms even at a scan rate as high as 1000 mV s −1 and a high specific power density over 20 kW kg −1. More importantly, the supercapacitors showed superior frequency response, with a frequency ‘knee’ at about 7560 Hz, which is more than 70 times higher than the highest ‘knee’ frequency (100 Hz) so far reported for such supercapacitors. Our study also demonstrated that these carbon nanotube thin films can serve as a coating layer over ordinary current collectors to drastically enhance the electrode performance, indicating the huge potential in supercapacitor and battery manufacturing. Finally, it is clear that electrophoretic deposition is a promising technique for massive fabrication of carbon nanotube electrodes for various electronic devices.