Single-walled Carbon Nanotube Composite Film Research Articles

High-performance g-C3N4 coated single-walled carbon nanotube composite films for flexible thermoelectric generators

Thermoelectric (TE) devices consisting of p-type and n-type single-walled carbon nanotubes (SWCNTs) based films, which can gather waste heat and turn it into electrical power, show potential application in supplying power for wearable electronic devices. In this study, graphitic carbon nitride (g-C3N4) has been prepared by high temperature pyrolysis of melamine and confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction pattern (XRD), respectively. Then the prepared g-C3N4 is composited with SWCNTs via mechanical mixing and vacuum-filtering method to obtain free-standing flexible g-C3N4/SWCNT thermoelectric composite films. The results demonstrate that g-C3N4 is efficiently covered on the surface of SWCNTs via interfacial π-π interaction, and g-C3N4 layer with several nanometers coated on SWCNTs simultaneously improves the electrical conductivity (σ) and the Seebeck coefficient (S) of g-C3N4/SWCNT. At a mass ratio of 2.5 % for g-C3N4/SWCNT, an optimal power factor value of 163.0 ± 1.0 μW m−1 K−2 is obtained for g-C3N4/SWCNT with the σ of 702.6 ± 1.6 S cm−1 and the S of 48.2 ± 0.2 μV K−1 at room temperature. Finally, a self-powering TE device composed of three pairs of p-n junctions is manufactured, and the actual output power is about 1.13 μW at the temperature difference of 50 K. As a result, this study offers a straightforward way to enhance the thermoelectric performance of single-walled carbon nanotubes, which can be utilized in flexible power generators.

A Supercapacitor Electrode Synthesis Strategy: Proton Acid‐Treated Ti3C2TX Film with Single‐walled Carbon Nanotubes as a Reinforcement

AbstractHigh‐performance electrode materials are the key to advances in the energy storage area. 2D transition metal carbide Ti3C2TX is the most widely studied MXene with a unique two‐dimensional structure, exhibiting excellent electrochemical properties and becoming a new choice electrode material for supercapacitors in many studies However, the poor mechanical properties of pure the Ti3C2TX film has become the bottlenecks for the application. Ti3C2TX with less Li+ was prepared by proton acid colloid treatment, and then the single‐walled carbon nanotubes (SWCNTs) were used as interlayer barriers in the films to prevent Ti3C2TX layers from restacking to prepare Ti3C2TX and SWCNTs composite films. The composite films were tested and analyzed by different electrochemical techniques. The results showed that the film formed by MXene colloidal filtration after proton acid treatment was denser and the electrical conductivity reached 608700 S/m, which was 3.2 times higher than that of the original Ti3C2TX film. The composite film was prepared by mixing MXene colloidal proton acid treatment and SWCNTs, followed by filtration showd good capacitive capacity, reaching 270.5 F/g by testing in the 1 m H2SO4 electrolyte with the CV cycle of 5 mV/s. And the specific capacitance retention reaches 97.6 % under 5000 CV cycles. The tensile test of composite film shows that the ultimate strength up to 50.3 MPa, which is about 2.3 times compared to original Ti3C2TX film.

Aniline-pyrrole Copolymer/SWCNT thermoelectric composites from electrochemical polymerization

Aniline-pyrrole copolymer (poly(ANi-co-Py)) electropolymerized on conductive glass was ultrasonically mixed with single-walled carbon nanotubes (SWCNTs) to prepare poly(ANi-co-Py)/SWCNT thermoelectric (TE) composites. Effects of SWCNTs contents and reaction parameters on morphology, structure, and TE properties of composites are investigated. In the as-prepared flexible poly(ANi-co-Py)/SWCNT composite films, SWCNTs and poly(ANi-co-Py) are fully entangled and tightly bonded. The highest electrical conductivity (σ) of 1035.3 ± 9.0 S cm−1 is obtained at 60 wt% of SWCNTs. The maximal Seebeck coefficient (S) of 33.0 ± 3.2 μV K−1 appears at 90 wt% SWCNTs. Thus, The peak room temperature power factor (PF) of the composites is 83.2 ± 3.3 μW m−1 K−2 at 60 wt% SWCNTs. Improved TE performance of the composites reflects increased chain ordering and enhanced interaction between SWCNTs and poly(ANi-co-Py).

Thermoelectric properties of PEDOT: PSS and acid-treated SWCNT composite films

We investigated the thermoelectric properties of composite films that consist of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and single-walled carbon nanotubes (SWCNTs). Thin films with 5−10 μm thickness of PEDOT:PSS/SWCNT and PEDOT:PSS/acid-treated SWCNT (AC-SWCNT) were prepared by varying the CNT content to determine their power factor. Both PEDOT:PSS/SWCNT and PEDOT:PSS/AC-SWCNT films showed an increase in their power factors with CNT content. The power factor values of PEDOT:PSS/AC-SWCNT films were higher than those of PEDOT:PSS/SWCNT films over the entire experimental range, which was mainly attributed to the significantly increased electrical conductivity. Thus, a series of PEDOT:PSS/AC-SWCNT freestanding films with 100−250 μm thickness were synthesized, and the same sample was used to measure electrical conductivity, Seebeck coefficient, and thermal conductivity to calculate the in-plane figure-of-merit ZT values. The composite films exhibited lower ZT values than those of PEDOT:PSS and AC-SWCNT films because of the high in-plane thermal conductivity caused by the dimensional anisotropy of AC-SWCNTs.

Effects of oxidative doping on the thermoelectric performance of polyfluorene derivatives/carbon nanotube composite films

The thermoelectric properties of the composite films of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and single-walled carbon nanotube (SWCNT) were investigated with ferric chloride as oxidative dopant. Ferric chloride had a great influence on the enhancement of electrical conductivity and power factor of the composite films. It was found that the doped composite film with an SWCNT content of 50% (F8BT-FeCl3/50% SWCNT) exhibited a high electrical conductivity of 640.1 S cm−1 at room temperature, which increased fifteen times over the undoped composite film. The power factor of the F8BT-FeCl3/50% SWCNT composite film was 15.7 μW m−1 K−2, also higher than that of the undoped composite film. Additionally, in the temperature range of 20–120 °C, the electrical conductivity of the doped composite films decreased and the power factor increased with the increasing temperature, due to the increase of Seebeck coefficient. The carrier transport behavior was demonstrated to obey the fluctuation-induced tunneling model in the F8BT/SWCNT composite film, but was described by the variable range hopping model after doping, indicating the role of oxidative doping in alternating the electrical transport in the composites.

Vanadium oxide–carbon nanotube composite films characterized by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) is utilized to characterize the vanadium oxide (VOx)–single walled carbon nanotube (SWCNT) composite films prepared by sol–gel. Five Tauc–Lorentz oscillators model is employed to describe the dispersions in the optical responses of VOx and VOx–SWCNT thin films. Results reveal that if the SWCNT concentration in the composite film is increased, the refractive index is decreased, while the extinction coefficient is increased. Moreover, higher SWCNT content leads to lower optical band gap (Eg) but larger localized state (Ee). Interestingly, both Eg and Ee values reach saturated at a SWCNT content of ~8 wt%. Particularly, the peak transition energies of the 5 Tauc–Lorentz oscillators have been assigned to the specific transitions according to the band structures of VOx. This work reveals the feasibility of investigating the optical properties and microstructures of VOx–SWCNT composite films by SE. These experimental results will be helpful for better understanding the VOx–SWCNT composite films, and promoting future characterizations of other SWCNT-based composites by SE.

Improvement of photovoltaic performance of inverted hybrid solar cells by adding single-wall carbon nanotubes in poly(3-hexylthiophene)

Solution prepared hybrid solar cells show promising low cost technology for electricity generation from sun light, although their power conversion efficiency has to be improved. One of the approaches is to increase the absorbance or charge carrier mobility of organic semiconductors. In this work, pristine single walled carbon nanotubes (SWCNT) were added into poly(3-hexylthiophene) (P3HT) solution to form P3HT:SWCNT composite films with different weight percent (wt%) of SWCNT. It is observed that optical absorbance spectra as well as the morphology of the composite films were modified by the addition of SWCNTs. This phenomenon could be explained by the π-π interaction between the conjugated polymer and carbon nanotubes. Most importantly, the electrical conductivities of the composite films increased with the SWCNT wt%. When these films were used as hole conductor layers in inverted planar hybrid solar cell, with CdS thin films as electron acceptor layers, the fill factor (FF) and open-circuit voltage (Voc) of the corresponding cells were decreased with the increase of the wt% of SWCNT. However, the short-circuit current density (Jsc) and the power conversion efficiency (PCE) showed a maximum value at about 0.4wt% of SWCNT in P3HT. The transient photovoltage measurements (TPV) revealed that the presence of SWNCT promoted the charge recombination process at P3HT/CdS interface, and as a result, reduced the Voc. The photovoltaic performance of the hybrid solar cells could be optimized by choosing an adequate weight percentage of SWCNT in P3HT to balance the charge carrier transport and charge recombination processes at the donor-acceptor interface.

Bolometric Properties of Semiconducting and Metallic Single-Walled Carbon Nanotube Composite Films

Single-walled carbon nanotubes (SWNTs) have shown interesting bolometric properties, making them good candidates for the detection of infrared and terahertz radiation. However, little has been reported on the bolometric characteristics of SWNT as a function of their chirality or the possible influence of composite morphology on these properties. The separation of SWNTs based on chirality allows for almost purely semiconductive or metallic SWNTs to be studied. The current study focuses on the bolometric performance of self-assembled composite films of SWNTs. The dependence of these properties on the chirality of the SWNTs was evaluated. To this end, metallic, semiconducting, and a 1:1 mixture of metallic and semiconductive were studied. Also, a theoretical model based on the Wiedemann–Franz law is used to explain the resistance of the SWNT composite films as a function of temperature. Results show that the composite morphology has a significant impact on bolometer performance, with cracked composite films containing highly aligned SWNT arrays suspended over a silicon substrate showing superior responsivity values due to higher thermal isolation. Uncracked composite films showed superior thermal coefficient of resistance values (α = −6.5%/K), however, the responsivity was lower due to lower thermal isolation.

Амперометрические моноаминоксидазные биосенсоры на основе графитовых электродов и оксида графена как модификатора поверхности для определения некоторых антидепрессантов

Амперометрические моноаминоксидазные биосенсоры на основе графитовых электродов и оксида графена как модификатора поверхности для определения некоторых антидепрессантов

Increasing the thermoelectric power generated by composite films using chemically functionalized single-walled carbon nanotubes

We prepared and characterized flexible thermoelectric (TE) materials based on thin films of single-walled carbon nanotube (SWCNT) composites with polyvinylalcohol. While pristine SWCNTs incorporated in a polymer matrix generated a p-type TE material, chemical functionalization of SWCNTs by using polyethyleneimine produced an n-type TE material. TE modules made of both p- and n-type composite were fabricated to demonstrate TE voltage and power generation. A single p–n junction made of two composite strips containing 20wt.% of SWCNTs generated a high TE voltage of 92μV per 1K temperature gradient (ΔT). By combining five electrically connected p–n junctions an output voltage of 25mV was obtained upon the applying ΔT=50K. Furthermore, this module generated a power of 4.5nW when a load resistance matched the internal module resistance of 30kΩ. These promising results show the potential of TE energy conversion provided by the SWCNT composite films connected in scalable modules for applications that require light weight and mechanical flexibility.

Thermoelectric properties of single walled carbon nanotube networks in polycarbonate matrix

AbstractWe report on single walled carbon nanotubes (SWCNTs) used as a filler material for polycarbonate (PC) composites in this paper. Thin flexible composite films were prepared by solvent casting with a viscous dispersion of SWCNTs in a polymer matrix. The interaction of SWCNTs with PC was studied by Raman spectroscopy. Our investigations focus on the electrical conductivity and thermopower of the carbon nanotube network formed within the matrix. In this paper, we demonstrate that the incorporation of carbon nanotubes in the polymer composite profoundly modifies the electrical properties of the polymer composite in proportion with the SWCNT concentration. Although, the electrical conductivity of the composite increases by 16 orders of magnitude upon adding 1 wt% of SWCNTs, the Seebeck coefficient, which characterizes the thermoelectric properties, appears to be dominated by the type of polymer matrix and decreased slightly throughout the tested filler loading. A reasonable Seebeck coefficient of 65 µV K−1 was determined for these SWCNT composite films and, thus, suggests that thermoelectric power generation would be a good application for them. We also demonstrated that both the electrical conductivity and the Seebeck coefficient of SWCNTs embedded in a polymer can be efficiently modified by means of chemical treatments. In this way, flexible composite films exhibiting positive and negative Seebeck coefficients were fabricated. Assembling these films into a sandwich structure with alternating p/n junctions should produce a higher potential difference when a temperature gradient is applied across a multilayer thermoelectric device.

Humidity sensing properties of different single-walled carbon nanotube composite films fabricated by layer-by-layer self-assembly technique

Poly(diallyldimethylammonium chloride)/single-walled carbon nanotube (PDDA/SWNT) multilayered thin films were prepared on quartz crystal microbalance by layer-by-layer self-assembly technique, and their sensing properties to humidity were studied. The SWNTs were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The composite films were observed by field-emission scanning electron microscope. Two types of SWNT humidity sensors were fabricated using SWNTs and carboxyl (COOH) modified SWNTs as sensitive material, respectively. The results showed that the sensitivity of the PDDA/SWNT–COOH humidity sensor was 20.23 % higher than that of the PDDA/SWNT sensor. In contrast, the latter had a much superior hysteresis property, and the reason to cause this phenomenon was discussed.

Highly sensitive amperometric sensor for carbamazepine determination based on electrochemically reduced graphene oxide–single-walled carbon nanotube composite film

Abstract We report a highly sensitive amperometric sensor for the determination of carbamazepine (CBZ) at an electrochemically reduced graphene oxide (ERGO) and single walled carbon nanotube (SWCNT) composite film modified glassy carbon electrode (GCE). The π – π stacking interactions between ERGO and SWCNT add good stability to the composite film which was confirmed by UV–visible and FTIR spectroscopy. Compared with SWCNT modified electrode, ERGO–SWCNT composite film modified electrode exhibits a 3.2 fold enhancement in peak current for CBZ oxidation. The proposed sensor detects CBZ as low as 29 nM and has a sensitivity of 5.1076 μA μM −1 cm −2 in the linear range of 50 nM to 3 μM. The practicality of this sensor has been evaluated by the determination of CBZ from Tegratol tablets showing good sensitivity and linearity.

Al 3+-directed self-assembly and their electrochemistry properties of three-dimensional dendriform horseradish peroxidase/polyacrylamide/platinum/single-walled carbon nanotube composite film

A novel general methodology for protein immobilization and third-generation biosensor construction is demonstrated, which involves Al 3+-directed polyacrylamide (PAM) self-assembly into an ordered dendriform structure, easily immobilizing enzymes and nanoparticles. Platinum/single-walled carbon nanotube (Pt/SWCNT) heterojunction nanomaterials were for the first time fabricated via an EDTA-directed synthesis strategy. The Pt/SWCNTs were employed as a supporting matrix to explore a novel immobilization and biosensing platform of redox proteins through cooperating Al 3+-directed PAM self-assembly. Compared with the almost single-layer horseradish peroxidase (HRP)/PAM film electrode, multilayer HRP/PAM/Pt/SWCNT film electrode exhibited a pair of much stronger redox peaks at −0.22 V (vs. Ag/AgCl). Moreover, with advantages of the ordered multilayer HRP/PAM/Pt/SWCNT film, facilitated direct electron transfer of the metalloenzymes with an apparent heterogeneous electron transfer rate constant ( k s) of 14.94 ± 1.36 s −1 and smaller peak-to-peak separation (Δ E p) of about 37 mV was acquired on the PAM/Pt/SWCNT-based enzyme electrode. The PAM/Pt/SWCNT-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with a small apparent Michaelis–Menten constant (87 μM), wide linear range (1–270 μM), very low detection limit (0.08 μM, S/ N = 3), and high sensitivity (372 mA cm −2 M −1). Together, these indicated that the Al 3+-directed HRP/PAM/Pt/SWCNT film was one of ideal candidate materials for direct electrochemistry of redox proteins and the construction of the related enzyme biosensors, and may find potential applications in biomedical, food, and environmental analysis and detection.

Humidity Sensitivity of Carbon Nanotube and Poly (Dimethyldiallylammonium Chloride) Composite Films

This paper demonstrates a highly sensitive humidity sensor based on carbon nanotube and poly(dimethyldiallylammonium chloride) composite films. The composite film is deposited between interdigitated electrodes on a Si/SiO2 substrate through layer-by-layer self-assembly technique. The resistance stability of the composite film is effectively improved through thermal annealing, and I-V characteristic of the film exhibits a very good linear behavior. The resistance increases exponentially with relative humidity from 20% to 98%, and a much higher sensitivity in comparison with pure carbon nanotube networks is achieved. With temperature increased, the water vapor density versus RH shifts upwards, while the resistance is reduced downwards. The resistance is dependent on temperatures with a negative coefficient. The composite films with multiwalled carbon nanotubes show an adjacent sensitivity, compared with the single-walled carbon nanotube composite films. The experimental results show that the humidity sensors have a fast response and a short recovery time, and their response is reversible. A simple model is proposed to explain the change of composite film resistance with humidity. The carbon nanotubes junctions may play a more important role in the overall resistance change for water molecule absorption.

Inkjet Printing of Transparent, Electrically Conducting Single‐Walled Carbon‐Nanotube Composites

Clearly superior resistance: Flexible, conductive, transparent single-walled carbon nanotube composite films (see picture) have been prepared by inkjet printing of nanotube dispersions. A single printed layer exhibited sheet resistance of 100 kΩ per square at 85 % optical transparency. The films display sensitivity to alcohol vapors.

Evidence of temperature dependent charge migration on conjugated segments in poly-p-phenylene vinylene and single-walled carbon nanotubes composite films

We present new results of temperature dependence of photoluminescence spectra carried out on poly-p-phenylene vinylene (PPV) and on PPV composite films with single-walled carbon nanotubes. By performing studies at different temperatures (87 and 300 K), we show that a distribution of conjugated PPV segments is needed to interpret experimental data. At the microscopic scale, such a distribution corresponds to the morphological picture of poorly packed short chain segments and well-packed ordered long chain segments. Within this scheme, a new interpretation emerges for explaining the specific behavior of the photoluminescence bands. In particular, the two most intense components of the photoluminescence spectra of PPV thermally converted at 300 degrees C (2.23 and 2.43 eV at 300 K) change drastically their relative intensity when the observation temperature decreases. This effect is interpreted as due to the inhibition of charge migration to longer segments and to radiative recombination occurring mainly on n = 5 conjugated segments.

Electrical and optical properties of PPV and single-walled carbon nanotubes composite films

We present a study of the evolution of the structural and electrical properties of poly(paraphenylene vinylene) (PPV) and single-walled carbon nanotubes (SWNT) composites as a function of the concentration of carbon nanotubes. We used essentially scanning electron microscopy (SEM), resonant Raman scattering and X-ray diffraction measurements to investigate the spectroscopic characteristics of the composites. When the SWNT concentration increases, the optical properties exhibit modifications which are discussed in relation with the shortening of conjugated segments lengths and the increase of disorder in PPV. Electrical conductivity measurements show that conductivity of the resulting films increases by eight orders of magnitude as the carbon nanotubes mass fraction increases from 0% to 64%. This result can be explained by using a simple percolation path theory, resulting in an estimated percolation threshold around 2%.