Multiwalled Carbon Nanotube Films Research Articles

Enhancement of CO gas sensing with ZnO nanostructures on MWCNTs films

CO gas sensing properties of 1-D ZnO nanostructures deposited on films of Multi-Wall carbon nanotubes were investigated using a vapor transport approach. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray, Raman spectroscopy, diffused reflectance spectroscopy, and photoluminescence, techniques were used to carry out the structural, morphological, and optical characterizations. The development of carbon-doped hybrid MWCNTs/ZnO nanostructures was demonstrated by the current results. The synthesized nanostructures were dense tapering belts and pedal-like crystalline structures as evidenced by their structural and morphological characteristics. Multiple networks of pure ZnO and hybrid MWCNTs-ZnO nanostructures were used to synthesize the gas sensors. Doped ZnO nanostructures sensing technique for CO gas detection was investigated in the present study. The combined impact of ZnO and MWCNTs was shown to be beneficial in boosting the response towards CO gas, as the response to CO gas at a concentration of 20 parts per million (ppm) was found to be five-times greater than that of ZnO sensors with good stability.

Electronic Skin as Human–Robot Interface for Human Grasp Recognition in Home-Care Robots: Introducing a Complete Set of Resources

Population aging has highlighted the significance of developing home-care robots to assist human life. However, traditional home-care robots work according to fixed procedures, which lack human–robot interaction to mimic human hand action. Human–robot interfaces provide an opportunity for interactions between robots and users, which play an important role in home-care robots. Traditional human–robot interfaces are based on rigid, cumbersome, and high-priced machines, which prevent their wide application in performing home-care tasks. An e-skin sensor with 11 stretchable resistors evenly distributed on the back of the human hand, which could be applied to monitor human finger motion and control robotic fingers to dexterously grasp diverse objects, is presented in this article. A 3D printer is employed to pattern high-performance wires into structurally soft and stretchable filamentary serpentines. The stretchable resistors are fabricated by a thin sensing film of mixed multiwalled carbon nanotubes (MWCNTs) and silicone elastomer. The e-skin sensor is applied in a hand-in-the-loop system for controlling a robotic hand to help grasp an object synchronously. A robot system is developed to connect the e-skin with the robotic hand to perform grasp actions with a success rate of more than 80%. By analyzing the experimental results of the e-skin sensor and robotic hand grasp, this work obtains insights showing that the skin sensor can help engineers design a home-care assistant plan for patients according to monitoring value or a human–robot interaction mode by robotic fingers mimicking human finger actions.

Structural optimization of ion storage layer for highly stable electrochromic devices based on polythiophene derivative films

Due to their rich color, fast switching speed and high coloration efficiency, polymer-based electrochromic devices (ECDs) have broad application prospects in various fields such as smart windows, anti-glare rearview mirrors, displays and adaptive camouflage. However, the preparation of highly stable polymer-based ECDs is still a great challenge. Herein, we present a simple and efficient strategy to construct the poly (3,4-ethylenedioxythiophene) (PEDOT)-multi-walled carbon nanotubes (MWCNTs) composite film or PEDOT/MWCNTs bilayer film, which serves as ion storage layer. The ECDs are assembled with poly (3-hexylthiophene) (P3HT) as EC layer due to its good EC behavior. The P3HT film was prepared by potentiostatic deposition, and the PEDOT, PEDOT-MWCNTs and PEDOT/MWCNTs films were obtained by spray-coating technology. We investigated the structure, morphology and electrochemical performance of P3HT, PEDOT, PEDOT-MWCNTs and PEDOT/MWCNTs films, and EC properties of devices. The results indicate that the rough and porous P3HT film consists of many nanoparticles. Compared with PEDOT-MWCNTs composite film, the PEDOT/MWCNTs film is more loose and porous, where PEDOT nanoparticles and some PEDOT nanosheets are coated on a three-dimensional skeleton film of MWCNTs. These films possess good electrochemical performance. The ECD based on P3HT and PEDOT/MWCNTs films achieves an optical contrast of 38 % and coloration efficiency of 375 cm2/C, exhibiting good cyclic stability (retaining 92 % of initial optical contrast after 2000 cycles). Its coloration time and bleaching time are 0.60 and 1.83 s, respectively. This study suggests that structural optimization of ion storage layer might be a facile strategy for fabricating highly stable polymer-based ECDs.

Design, fabrication, and sensing applications of MWCNT/PET terahertz metasurface

In this paper, the periodic rectangular aperture arrays have been etched on a multi-walled carbon nanotube (MWCNT) film prepared by vacuum filtrating to fabricate a terahertz (THz) metasurface on a polyethylene terephthalate (PET) substrate. The transmission properties and the underlying resonance physical mechanism of the metasurface were investigated in detail. An obvious resonant peak located at 0.48 THz can be observed, the results of the scattering powers for various multipole moments show that the enhanced transmission peak is dominated by the radiation contribution of the electric dipole ultimately. To demonstrate the sensing capability, the fabricated metasurface was used to detect different concentrations of 2,4-dichlorophenoxyacetic acid (2,4 - D) solutions. The experimental results reveal that the transmission amplitude decreases linearly as the concentrations increase, and the amplitude sensitivity can achieve 1.69 × 10−2/ppm. This study demonstrates the MWCNT/PET metasurfaces can be applied for trace analytes sensing and improve the sensitivity and accuracy, while the processing technology can also be extended to the preparation and various applications of CNT-based metasurfaces, which provides a beneficial reference for the extended applications of carbon-based metamaterial devices in the THz band.

Photocatalytic active ZnO1−x S x @CNTs heteronanostructures

Herein, we report on the use of vertically aligned multiwall carbon nanotubes (CNTs) films as support for ZnO/ZnS photocatalytic active nanostructures. The CNTs were synthetized via a hot-filament chemical vapor deposition (HfCVD), using Fe catalyst on top of Al2O3 buffer layer. Controlled point defects in the CNTs outer walls were created by exposure to a low pressure nonthermal water vapors diffusive plasma and acted as seeds for subsequent pulsed-electrodeposition of Zn nanoparticles. This was to achieve a direct and improved contact between the nanoparticles and CNTs. To obtain ZnO, ZnS and mix phase of ZnO/ZnS spread on CNTs, the oxidation, sulfurization and 2 steps subsequent annealing in oxygen and sulfur rich atmospheres were applied. High resolution transmission electron microscopy with energy dispersive x-rays spectroscopy in scanning mode, provided the chemical mapping of the structures. X-ray diffraction (XRD) analyses proved the hexagonal phase of ZnO and ZnS, obtained after oxidation in H2O and S vapors, respectively. In the case of the samples obtained by the 2 steps subsequent annealing, XRD showed mainly the presence of ZnO and a small amount of ZnS. The benefit of the secondary annealing in S vapor was seen as an absorption enhancement of the ZnO1−x S x @CNTs sample having the absorption edge at 417 nm, whereas the absorption edge of ZnO@CNTs was 408 nm and of ZnS@CNTs 360 nm. For all the samples, compared to the bare ZnO and ZnS, the absorption red shift was observed which is attributed to the CNTs involvement. Therefore, this study showed the double sides benefit to induce the absorption of ZnO of the visible light, one from S doping and second of CNTs involvement. The absorption enhancement had a positive impact on photocatalytic degradation of methyl blue dye, showing that ZnO1−x Sx@CNTs heteronanostructure was the best photocatalyst among the studied samples.

Densification Induced Decoupling of Electrical and Thermal Properties in Free-Standing MWCNT Films for Ultrahigh p- and n-Type Power Factors and Enhanced ZT.

Generating sufficient power from waste heat is one of the most important things for thermoelectric (TE) techniques in numerous practical applications. The output power density of an organic thermoelectric generator (OTEG) is proportional to the power factors (PFs) and the electrical conductivities of organic materials. However, it is still challenging to have high PFs over 1mWm-1 K-2 in free-standing films together with high electrical conductivities over 1000Scm-1 . Herein, densifying multi-walled carbon nanotube (MWCNT) films would increase their electrical conductivity dramatically up to over 10000Scm-1 with maintained high Seebeck coefficients >60µVK-1 , thus leading to ultrahigh PFs of 7.25 and 4.34mWm-1 K-2 for p- and n-type MWCNT films, respectively. In addition, it is interesting to notice that the electrical properties increase faster than the thermal conductivities, resulting in enhanced ZT of 3.6 times in MWCNT films. An OTEG made of compressed MWCNT films is fabricated to demonstrate the heat-to-electricity conversion ability, which exhibits a high areal output power of ∼12 times higher than that made of pristine MWCNT films. This work demonstrates an effective way to high-performance nanowire/nanoparticle-based TE materials such as printable TE materials comprised of nanowires/nanoparticles.

Synergistic influence of multi-walled carbon nanotubes and graphene nanoparticles on the structural, thermal and mechanical characteristics of poly (3-hydroxybutyrate) films

Poly (3-hydroxybutyrate) (PHB) is a linear, semi-crystalline biopolymer that belongs to polyhydroxyalkanoates family. It is completely bio-based, biocompatible, and biodegradable in nature. However, due to its low melt processing window, PHB becomes unstable during high-temperature processing. Carbon-based materials such as graphene (Gr) and multi-walled carbon nanotubes (MWCNT) suffer from restacking /agglomeration problems when loaded into polymer matrix. Recent studies revealed that MWCNT could bridge the gap between Gr flakes and loading them together can solve the agglomeration problem. In the present study, tip sonication-assisted solution casting method was used to fabricate PHB-based nanocomposites loaded with 0.3 wt% Gr, 0.3 wt% MWCNT, and their combination (0.3 wt% Gr and 0.3 wt% MWCNT). The prepared films were characterized using Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and Field emission transmission electron microscope (FETEM). Furthermore, structural, mechanical and optical properties were measured. FTIR analysis evidenced that the nature of the interaction between PHB matrix and nanofillers was physical. In comparison with neat PHB, significant improvement in UV and visible light barrier was observed for PHB/0.3Gr/0.3MWCNT films. TGA revealed that reinforcement of dual nanofillers viz. 0.3 wt% Gr and 0.3 wt% MWCNT significantly improved thermal degradation temperature (over 8 ℃ compared to PHB) than single nanofiller-loaded films. Likewise, the tensile strength of PHB-based films increased from 19±1.32 to 29±4.53 MPa, and crystallinity increased from 38.15 to 47.34 % with dual nanofiller loading. Therefore, it can be concluded that the inclusion of two carbonaceous nanofillers had a positive synergistic effect on the thermal, mechanical and optical properties of PHB.

Growing Electrocatalytic Conjugated Microporous Polymers on Self-Standing Carbon Nanotube Films Promotes the Rate Capability of Li-S Batteries.

Lithium-sulfur (Li-S) batteries hold great promise for widespread application on account of their high theoretical energy density (2600Wh kg-1 ) and the advantages of sulfur. Practical use, however, is impeded by the shuttle effect of polysulfides along with sluggish cathode kinetics. it is reported that such deleterious issues can be overcome by using a composite film (denoted as V-CMP@MWNT) that consists of a conjugated microporous polymer (CMP) embedded with vanadium single-atom catalysts (V SACs) and a network of multi-walled carbon nanotubes (MWNTs). V-CMP@MWNT films are fabricated by first electropolymerizing a bidentate ligand designed to coordinate to V metals on self-standing MWNT films followed by treating the CMP with a solution containing V ions. Li-S cells containing a V-CMP@MWNT film as interlayer exhibit outstanding performance metrics including a high cycling stability (616mA h g-1 at 0.5 C after 1000 cycles) and rate capability (804mA h g-1 at 10 C). An extraordinary area-specific capacity of 13.2mA h cm-2 is also measured at a high sulfur loading of 12.2mg cm-2 . The underlying mechanism that enables the V SACs to promote cathode kinetics and suppress the shuttle effect is elucidated through a series of electrochemical and spectroscopic techniques.

A simple, fast, portable and selective system using carbon nanotubes films and a 3D-printed device for monitoring hydroxychloroquine in environmental samples

In this work, an electrochemical method was developed for rapid and sensitive detection of hydroxychloroquine (HCQ), an ineffective candidate drug for COVID-19 treatment however widely consumed during the pandemic, in aqueous samples using a multi-walled carbon nanotubes (MWCNT) film produced through the interfacial method on the indium tin oxide electrode (ITO). According to Raman spectroscopy, X-ray diffraction, UV–vis spectroscopy, Energy-dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy, the interfacial method produces homogeneous thin films of carbon nanotubes on the substrate surface, which keep connected to the surface forming a three-dimensional microporous structure. The electrochemical behavior and oxidation kinetics of HCQ were also investigated in the MWCNT film. The sensor showed a 7 times higher oxidation current for (69.88 μA) for HCQ than the ITO electrode (9.33 μA) due to the electrocatalytic properties MWCNTs. The ITO-modified electrode was assembled on a portable 3D-printed batch-injection cell for the amperometric detection of HCQ. The oxidation peak current of HCQ is linearly proportional to the concentrations of HCQ ranging from 1.0 to 100.0 μmol L−1, with a limit of detection of 0.27 μmol L−1. Water samples (river and tap water) were spiked with HCQ, without the need for dispendious pretreatment (except filtration), and analyzed by the portable system, revealing the detection of HCQ with the recovery of 92.0%–99.8%, which suggested the great potential for real environmental monitoring application.

Highly efficient and wearable thermoelectric composites based on carbon nanotube film/polyaniline

Polyaniline (PANI) was prepared by in-situ polymerization and compounded on the two-dimensional network structural multi-walled carbon nanotube film (CNTF). Compared with the CNT/PANI composites fabricated by using CNT powders or dispersions, the compact and continuous network structure of CNTF/PANI is beneficial to both the thermoelectric and mechanical properties of the composites. The resultant CNTF/PANI composites with PANI polymerization time of 5 h obtain an electrical conductivity of 1 338.4 S/cm and Seebeck coefficient of 63.3 μV/K at 360 K, which are 168.7% and 5.7% higher than those of the CNTF (498.1 S/cm and 59.9 μV/K at 360 K). Consequently, a maximum power factor of 536.8 μW·m−1·K−2 at 360 K is acquired, which is about 2 times higher than that of CNTF (181.7 μW·m−1·K−2 at 360 K). The electrical conductivity of the composites could maintain 93.3% after being bent for 500 times, indicating the excellent flexibility. The tensile strength, Young's Modulus and toughness of CNTF/PANI composites (232.3 MPa, 3.6 GPa and 20.1 MJ/m3, respectively) are 3.5, 2.6 and 2.1 times of those of the CNTF. The flexible, free-standing, lightweight and high-strength CNTF/PANI composites reveal the excellent thermoelectric performance, which are promising in the applications in wearable thermoelectric devices.

Nickel Oxy-Hydroxy/Multi-Wall Carbon Nanotubes Film Coupled with a 3D-Printed Device as a Nonenzymatic Glucose Sensor.

A rapid and simple method for the amperometric determination of glucose using a nanocomposite film of nickel oxyhydroxide and multi-walled carbon nanotube (MWCNTs) was evaluated. The NiHCF)/MWCNT electrode film was fabricated using the liquid-liquid interface method, and it was used as a precursor for the electrochemical synthesis of nickel oxy-hydroxy (Ni(OH)2/NiOOH/MWCNT). The interaction between nickel oxy-hydroxy and the MWCNTs provided a film that is stable over the electrode surface, with high surface area and excellent conductivity. The nanocomposite presented an excellent electrocatalytic activity for the oxidation of glucose in an alkaline medium. The sensitivity of the sensor was found to be 0.0561 μA μmol L-1, and a linear range from 0.1 to 150 μmol L-1 was obtained, with a good limit of detection (0.030 μmol L-1). The electrode exhibits a fast response (150 injections h-1) and a sensitive catalytic performance, which may be due to the high conductivity of MWCNT and the increased active surface area of the electrode. Additionally, a minimal difference in the slopes for ascending (0.0561 µA µmol L-1) and descending (0.0531 µA µmol L-1) was observed. Moreover, the sensor was applied to the detection of glucose in artificial plasma blood samples, achieving values of 89 to 98% of recovery.

Glucose Electrocatalysis of Multi-walled Carbon Nanotubes/Polyvinyl Alcohol Conducting Hydrogel Composite Platinum Electrode

A porous conductive hydrogel electrode film of multi-walled carbon nanotubes (MWCNTs)/polyvinyl alcohol (PVA) was prepared by electrophoretic deposition technology, and the selective catalytic ability of MWCNTs/PVA on glucose was verified by cyclic voltammetry and open-circuit voltage. The electrochemical and physicochemical properties of MWCNTs/PVA porous conductive hydrogel electrode films were also characterized. The synergistic catalytic effects of MWCNTs/PVA porous conductive hydrogel electrode films and platinum electrode on the electrochemical oxidation of glucose in different PH solutions were studied.

Carbon nanotube films embedded with Cu@C nanocubes for electromagnetic interference shielding

AbstractFlexible carbon tube films for electromagnetic interference (EMI) shielding are assembled by mixing the well‐aligned Cu@C core‐shell nanocubes with multi‐walled carbon nanotubes (MWCNTs). The Cu@C core‐shell nanocubes are achieved by the thermal pyrolysis of polyvinylpyrrolidone (PVP) coating on Cu2O nanocubes. With the optimal PVP concentration of 1.5 mg/mL, the Cu@C/MWCNTs composite film with ultra‐thin thickness (52.2 μm) displays good conductivity of 12.5 S cm−1 and excellent specific EMI shielding value of 510.73 dB mm−1, which is higher than the pure MWCNTs film (439.50 dB mm−1) under the same weight condition. Moreover, the 1.5 mg/mL‐Cu@C/MWCNTs composite film exhibits highly mechanical repeatability after being bended for 10,000 cycles. The carbon layers protecting metal nanoparticles can partly replace precious carbon nanotubes to construction highly flexible composite film with anticipated electrical conductivity, which have a good application prospect for thin, lightweight and flexible EMI shielding fields.

Improving the performance of perovskite solar cells with carbon nanotubes as a hole transport layer

There are several types of organometallic halide perovskite solar cells (OHPSCs), but the carbon-based PSC has the lowest materials/fabrication cost and the longest-term stability, making it the most promising for practical application. In this study, we used multi—walled carbon nanotubes (MWCNTs) as the hole transport layer in the PSC architecture. We experimentally achieved an optimized efficiency of 13.7% for a MWCNTs-based device. Besides, this research describes a simulation-guided optimization process to fabricate high-performance MWCNT-based photovoltaics. We have thoroughly investigated the effect of different parameters, such as the total defect density of the absorber, the thickness of the MWCNTs film, the thickness of the absorber, shunt resistance, series resistance, and temperature, utilizing numerical simulations. By using the thin film photovoltaic program SCAPS-1D, we were able to simulate defect states and interfaces between layers to get as close as possible to a realistic PSC in our simulations and analysis. An optimized PSC of F-doped tin oxide (FTO)/titanium dioxide (TiO2)/MAPbI3/MWCNTs/gold (Au) is designed here with a voltage-open circuit (VOC) of 1.100 V, a short-current density (JSC) of 19.192 mA/cm2, and efficiency of 18.3% with a high fill factor (FF) of 86.62%, which is among the best for carbon-based OHPSCs.

Spatially Resolved Photo-Response of a Carbon Nanotube/Si Photodetector

Photodetectors based on vertical multi-walled carbon nanotube (MWCNT) film-Si heterojunctions are realized by growing MWCNTs on n-type Si substrates with a top surface covered by Si3N4 layers. Spatially resolved photocurrent measurements reveal that higher photo detection is achieved in regions with thinner MWCNT film, where nearly 100% external quantum efficiency is achieved. Hence, we propose a simple method based on the use of scotch tape with which to tune the thickness and density of as-grown MWCNT film and enhance device photo-response.

Binder-Free Supercapacitors Based on Thin Films of MWCNT/GO Nanohybrids: Computational and Experimental Analysis

This work reports an innovative approach to the fabrication of free-standing thin films of multiwalled carbon nanotubes (MWCNTs)/graphene oxide (GO) nanohybrids by using dimethyl formamide (DMF) and n-hexane as a solvent–antisolvent system for the growth of thin films of MWCNTs/GO nanohybrids. The synthesis of the GO was carried out by using the modified Hummers method, while the synthesis of MWCNTs/GO nanohybrids was done by the intermixing of the carboxylic acid functionalized MWCNT and GO using the solution-mixing method. The growth of the thin film of MWCNTs/GO nanohybrids was done by obeying the surface-tension-driven phenomena which occur mainly due to the coalescence of bubbles due to the solvent–antisolvent interfacial tension. Furthermore, density functional theory (DFT)-based first-principles simulations were performed to understand the structural, electronic, and capacitive aspects of MWCNT/GO nanohybrids. The computational results demonstrated excellent quantum capacitance in the MWCNT/GO nanohybrid electrodes. Inspired by the computational results, the same process elaborated above has also been employed to develop binder-free supercapacitor devices utilizing the MWCNT/GO nanohybrid as an electrode material. The electrochemical performance of this electrode in 1 M aqueous H2SO4 demonstrates a good energy density of 21.63 WhKg−1 at a current density of 0.5 Ag−1, with a high specific capacitance of 369.01 F/g at the scan rate of 2 mVs−1 and excellent cyclic stability of 97% for 5000 charge–discharge cycles.

Netted C-Doped TiO2 Mesoporous Nanostructure Decorated by Cu Nanoparticles for Photocatalytic CO2 Reduction

Acquiring an anatase TiO2 catalyst with tiny size and high crystallinity for excellent photocatalytic performance still remains a huge challenge. Herein, a mesoporous C-doped TiO2 netted nanostructure is successfully synthesized by a vacuum dipping and calcination method, where the thin film of multiwalled carbon nanotubes is skillfully utilized as the confinement template to suppress the grain growth and phase transfer. In addition, small Cu nanoparticles are deposited on the surfaces of the TiO2 by an electronic beam evaporation way. The obtained C–TiO2–Cu photocatalyst exhibits high CH4 and CO production rates of 8.8 and 60.3 μmol/g/h, respectively, which are excellent among the TiO2-based photocatalysts. This high performance originates from the following synergistic effects. This good crystalline and small size can facilitate the charge separation, while this unique netted mesoporous structure will provide sufficient sites for the reaction. Moreover, the C doping can enhance light absorption and the plasmonic Cu can inject hot electrons into TiO2, which will increase the amounts of electrons and promote their transfer.

Vertically Aligned Conductive Polymeric Nanotubes Grown on Percolated Multiwalled Carbon Nanotube Films for Supercapacitor Electrodes

Vertically Aligned Conductive Polymeric Nanotubes Grown on Percolated Multiwalled Carbon Nanotube Films for Supercapacitor Electrodes

Terahertz and infrared transmission properties of super-thin periodic multi-walled carbon nanotube gratings

Super-aligned multi-walled carbon nanotube arrays on Si wafer were synthesized by low press chemical vapor deposition. The super-thin multi-walled carbon nanotube films were obtained by a drawing process on the side of the vertically aligned carbon nanotubes. The as-synthesized samples were characterized by scanning electron microscopy and optical microscopy. Terahertz time-domain measurements showed that anisotropic transmission properties were observed. The multi-walled carbon nanotube films with various two-dimensional periods and thicknesses displayed remarkably enhanced transmission at the terahertz range. Comparing experimental results with theoretical calculations revealed that the excitation of surface plasmon polaritons on the carbon nanotubes/Si interface was the key mechanism responsible for the enhanced transmission. The resonance peaks were red shifted with increasing period. In the infrared region, no obvious resonance peaks were observed.

High-performance p-hexafluoroisopropanol phenyl functionalized multi-walled carbon nanotube film on surface acoustic wave device for organophosphorus vapor detection

A delay line-type surface acoustic wave (SAW) gas sensor based on p-hexafluoroisopropanol phenyl (HFIPPH) functionalized multi-walled carbon nanotube (MWCNT) film is developed to detect organophosphorus dimethyl methylphosphonate (DMMP) vapor (a simulant of chemical nerve agent sarin). Inspired by the transfer process of Cu-based graphene, a uniform and size-controllable HFIPPH-MWCNT film is successfully prepared on the SAW device via a wet-etching transfer method. For the first time, we use the method of measuring the change of the sensor’s insertion loss to achieve the detection of ultra-low concentration DMMP vapor. The designed sensor exhibits a fast response/recovery time about 3 s/50 s, and a low detection limit of 0.1 ppm. Additionally, the stability and selectivity of the sensor and the influence of humidity on its response are evaluated through experiments. The acoustoelectric effect is proved to be the sensing mechanism of the sensor insertion loss response.