Multiwalled Carbon Nanotube Films Research Articles

Unidirectional Langmuir-Blodgett-Mediated Alignment of Polyaniline-Functionalized Multiwalled Carbon Nanotubes for NH3 Gas Sensor Applications.

Herein, we report the formation of well-aligned ultrathin films of polyaniline-functionalized multiwalled carbon nanotubes (PANI@MWCNTs) with a high orientational order over a macroscopic area by Langmuir-Blodgett (LB) technique and its enhanced ammonia gas sensing properties. During the interfacial assembly process, the PANI@MWCNTs gradually align to form small ordered blocks at the air-water interface, which further organize as a well-defined oriented monolayer. The orientation and alignment of PANI@MWCNTs in Langmuir films at the air-water interface were systematically studied as a function of interface temperature using transmission electron microscopic analysis. Surface functionalization of MWCNTs with polyaniline was found to overcome the 3D aggregation of CNTs leading to an oriented assembly of PANI@MWCNTs. The formation and stability of the compact monolayer/multilayer structures of PANI@MWCNTs-based LB films have been extensively studied using a π-A isotherm analysis and thermodynamic approach. For the first time, such highly oriented LB films of PANI-functionalized MWCNTs have been employed for ammonia gas sensing applications at room temperature. The sensor was found to exhibit outstanding sensitivity toward NH3 at room temperature compared to random networks, which is attributed to the directed electron transport through the aligned PANI@MWCNTs. The ultrathin LB film allows fast analyte diffusion due to the adequate molecular accommodation in the oriented assembly of the active sensing layer. The large-scale alignment of PANI@MWCNTs demonstrated in this investigation would enable the fabrication of high-density MEMS (micro-electromechanical system)-based nanoscale sensor arrays for high-performance NH3 gas sensor applications.

The Effect of Multi-walled Carbon Nanotubes and Reduced Graphene Oxide Doping on the Optical and Photovoltaic Performance of Ag2BiI5-Based Solar Cells

Due to the nontoxic and air-stable nature of bismuth-based photovoltaic materials, they are suitable materials to replace lead-based perovskite ones. In this research, the influence of doping with multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) on the structural, morphological, and optical properties of silver bismuth iodide (SBI) compounds was investigated. Structural characterizations revealed the formation of the hexagonal structure in SBI thin films, and also showed improvement in the surface morphology in the MWCNT and RGO-doped thin films. All absorber layers had a relatively high absorption coefficient above 104 cm−1 in the visible range, and the bandgap values varied between ∼ 1.83 eV and 2.04 eV. Also, we fabricated SBI-based solar cells, and their photovoltaic performance was studied. For the solar cell employing pure silver bismuth iodide, a photo conversion efficiency (PCE) of 0.44% was achieved. The inclusion of MWCNTs and RGO dopants in the SBI thin film PCE increased the device performance, and the highest PCE of 1.61% and 1.32% was obtained, respectively. The stability of the solar cells was also investigated under the environmental conditions. Results show that after 30 days, devices preserved about 90% of their efficiency.

Effect of nature of polymer as a binder in making photoanode layer and its influence on the efficiency of dye-sensitized solar cells

A simple method has been developed for the preparation of photoanode paste from hydrothermally synthesized nanocomposite, using different nature of polymers viz., synthetic: poly(vinyl alcohol) and polystyrene (PS) and natural: casein and sodium alginate (NaAlg) as binders. The titanium dioxide (TiO2)/multi-walled carbon nanotube (MWCNT) nanocomposite powder and film were characterized for analysis of their structure, crystallinity and morphology by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Dye-sensitized solar cells (DSSCs) were fabricated using TiO2/MWCNT composite paste made with different binders as photoanode, N719 dye, platinum as photocathode and Idolyte HI-30. The observed results of photocurrent density–voltage characteristics and electrochemical impedance spectroscopy suggested that the nature of the binder used in making photoanode film showed significant influence on the overall characteristics of DSSCs. Among the cells fabricated, the DSSC fabricated using TiO2/MWCNT-PS binder showed highest power conversion efficiency of 3.03%.

Raman spectroscopic characterization of acid refluxed and surfactant‐assisted dispersed multiwalled carbon nanotubes on surface functionalized substrates

AbstractThis communication focuses on the Raman spectroscopic characterization of a voltage‐controlled electrospray deposition (VCED) of multiwalled carbon nanotubes (MWCNTs) dispersed from acid refluxed and SDBS (sodium dodecyl benzene sulfonate) assisted carbon nanotube (CNT) dispersion techniques. This versatile method resulted in the direct deposition of CNT films on the surface functionalized target substrates, that is—APTES (3‐aminopropyl‐triethoxysilane) treated metal (aluminum foil), semiconducting (bare Si), and insulators (microscopy grade glass, silicon dioxide, and polymethyl methacrylate or PMMA)—used in this study. During the voltage‐controlled deposition process itself, the spray area and thickness of the MWCNT films on a substrate can be easily manipulated. In this work, CNT thin films of 40‐70 nm to 3‐7 μm were produced as a function of deposition time, with excellent packing density and surface coverage. The precise thickness control of the CNT deposits on each target substrate was achieved by meticulously calibrating the mechanics of the voltage‐controlled spray system, for example, inter‐electrode distance between the target surface and the nozzle, electric field, and flow rate of the CNT solution feed, in addition to the concentration of the CNT solution and the deposition time. These overall experimental results bode well for use of this technique in a wider range of applications where CNTs films with controlled thicknesses are required.

Side-Polished Optical Fiber Structure for Sodium Nitrate Sensor

Side-polished optical fiber has long been used to build fiber sensors in a range of applications. In this work, we demonstrate a biochemical sensor application leading to sodium nitrate solutions enhanced by the interaction of multi-walled carbon nanotubes (MWCNTs) with evanescent field of propagating light in a side-polished optical fiber. Insertion loss of this sensor was estimated to be around 5 dB, which is quite high and close to the core index of the polished fiber. The influence of MWCNTs film, particularly on its sensitivity to sodium nitrate, was investigated by coating single drop of MWCNTs on a side-polished single mode fiber. It is observed the improvement of sensitivity with MWCNTs coated side-polished optical fiber has reached 0.125 dBm/°C near the resonant wavelength of 1550 nm. The experimental results clearly verify the present of MWCNTs on side-polished optical fiber has slightly influence the performance of the fiber. The output power values and shifting of the spectral positions were observed during the sensor tests by exposure of the sodium nitrate solutions with increasing concentration from 1 to 7%.

Self-healing flexible sensor based on metal-ligand coordination

Self-healing is an indispensable property of the next generation wearable electronic devices. However, it is a hugely difficult problem to achieve good self-healing abilities and good elastic properties at different conditions. Herein, we report a self-healing substrate from commercially available methyl vinyl silicone rubber (MVQ) that has been cross-linked through metal-ligand coordinate bonds. The strain sensor was then assembled by coating nanostructured conductive layer (Multiwall carbon nanotubes (CNTs) film and silver film) onto the self-healing elastomeric substrate. The resulting flexible sensors show a desirable healing efficiency under both high temperatures and underwater conditions. Notably, the healed strain sensors can still precisely capture diverse human activities, such as large limb movements and minute physiological activities. The self-healing strain sensors demonstrated in this study will push forward the design and application of stretchable and flexible electronic devices.

Multiwall Carbon Nanotube / Polyvinyl Alcohol Nanofibers Film, Electrical Conductivity Improvement

Conductive polymer films were prepared of polyvinyl alcohol (PVA) with (0, 2, 4, 6, 8, and 10) wt. % multiwalled carbon nanotubes (MWCNTs) by electrospinning technique. The morphologies of the synthesized films were tested by scanning electron microscopy (SEM). Average fiber diameters gauged statically was (115nm) for (PVA/10 wt. % MWCNT film) while (170nm) for pure PVA electro spun film. Electrical conductivity (EC) of Polymeric nanofiber films improve by increasing MWCNT addition concentration from (3.69 × 10-7 S/ cm) for the pure (PVA) film to (1.24 ×10-2 S/cm) for the film with 10 wt. % MWCNT. The maximum stress of PVA film were increased by adding MWCNTs concentration, the modulus of elasticity was enhanced from 12.87 MPa for pure PVA to 49.89 MPa for PVA/8wt% MWCNT.

Self-standing MWCNTs based gas sensor for detection of environmental limit of CO2

In this work, we have demonstrated multi walled carbon nanotubes (MWCNTs) based CO2 gas sensor using a reliable and low cost gel-cast method with MWCNT concentration of 0.6, 1.0, 1.5, 2.0 and 3.0 by wt% in alumina Al2O3 sol which acts as a host matrix for the composite. Sensing response of the as prepared highly uniform self-standing MWCNTs film was measured at room temperature by exposure to different CO2 concentrations, ranging from 50 ppm to 450 ppm. The adsorption effect of CO2 on the varying concentration of CNTs was investigated by measuring a significant change in the resistance. Upon exposure to CO2 molecules, the device shows a drastic increase in resistance attributed to the charge transfer between CNTs and CO2 molecules. High sensor response of 7.3% with a response time of 53.7 s exhibited by sensor S3 (1.5 wt% of MWCNTs) is reported when the concentration of CO2 is 450 ppm in ambient conditions. In addition, different recovery modes were examined and the results reveal that there is a significant decrease in the recovery time of sensor upon UV light exposure and heat application. Besides being fast recoverable with heat energy, the fabricated gas sensor shows favorable stability in response over multiple exposure of analyte gas.

Synthesis, optical, thermal, electric properties and impedance spectroscopy studies on P(VC-MMA) of optimized thickness and reinforced with MWCNTs

The synthesis of polymeric blends and nanocomposites with improved physical properties has attracted increasing attention worldwide, for its practical and technological applications. The present study aims to tune the physical properties of thermoplastic polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) blends by adjusting the film thickness and loading with multiwall carbon nanotubes (MWCNTs). To this end, P(VC/MMA) films of thickness in the range 36.4–204 µm and P(VC/MMA)/MWCNTs films were prepared using solution casting. A scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to investigate the films morphology and cross-sectional area and the vibrational properties, respectively. UV–vis measurements demonstrated that the transmittance spectra and absorption index were significantly affected by the film thickness and fillers content ratio. Moreover, both the direct and indirect optical bandgap increased with increasing thickness and decreased with increasing MWCNTs content inside P(VC/MMA) films. Further, thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) showed that the films exhibit thermal stability in the temperature range of 179–230 °C, and the melting temperature and degree of crystallinity increased with increasing thickness and decreased after doping with MWCNTs. The influences of film thickness and MWCNTs on the refractive index, dielectric constant, dielectric modulus, ac conductivity, impedance, and Nyquist plots have been discussed, along with the induced capacitance nature of the samples. Consequently, it was ascertained that the observed improvement in the optical properties and ac conductivity make these blends and nanocomposites suitable for optical devices and dielectric applications.

Highly stretchable, transparent and room-temperature self-healable polydimethylsiloxane elastomer for bending sensor

Highly stretchable and self-healable elastomers are attractive for a variety of applications in the fields of electrical skin and wearable devices. Herein, we proposed a simple one-pot two-step approach to synthesize room-temperature self-healable polydimethylsiloxane (PDMS) elastomers. Excess aminopropyl terminated polydimethylsiloxane was firstly reacted with isophorone diisocyanate to synthesize amino-terminated PDMS with incorporated ureido groups, followed by further reaction with terephthalaldehyde as chain extender to yield self-healing PDMS elastomers. The obtained elastomer exhibited high stretchability of 1670% and transmittance of 92%. Owing to the dynamic intermolecular hydrogen bonds, reversible imine bonds and highly flexible SiO chains, the elastomer showed excellent self-healing capability with a healing efficiency of 95% after healing at room temperature for 24 h. Even in water and artificial sweat, the healing efficiencies also reached 89% and 78%, respectively. In addition, the elastomer supported triple-layer bending sensor was fabricated with a sandwiched hydroxylated multiwalled carbon nanotubes (MWCNTs-OH) film and successfully applied for detecting human motions. Interestingly, the cut sensor was able to be recovered for working after being irradiated under sunlight for only 10 min. Our method to synthesize highly stretchable, transparent and self-healing elastomers is simple and the reaction can be carried out at room temperature, which is beneficial for the large-scale production and the further practical application in functional electronics.

The Effect of the Gaseous Environment on the Electrical Conductivity of Multi-Walled Carbon Nanotube Films over a Wide Temperature Range.

The surrounding gas atmosphere can have a significant influence on the electrical properties of multi-walled carbon nanotube (CNT) ensembles. In this study, we subjected CNT films to various gaseous environments or vacuum to observe how such factors alter the electrical resistance of networks at high temperatures. We showed that the removal of adsorbed water and other contaminants from the surface under reduced pressure significantly affects the electrical conductivity of the material. We also demonstrated that exposing the CNT films to the hydrogen atmosphere (as compared to a selection of gases of inert and oxidizing character) at elevated temperatures results in a notable reduction of electrical resistance. We believe that the observed sensitivity of the electrical properties of the CNT films to hydrogen or vacuum at elevated temperatures could be of practical importance.

Wearable Strain Sensors Using Light Transmittance Change of Carbon Nanotube-Embedded Elastomers with Microcracks.

A number of flexible and stretchable strain sensors based on piezoresistive and capacitive principles have been recently developed. However, piezoresistive sensors suffer from poor long-term stability and considerable hysteresis of signals. On the other hand, capacitive sensors exhibit limited sensitivity and strong electromagnetic interference from the neighboring environment. In order to resolve these problems, a novel stretchable strain sensor based on the modulation of optical transmittance of carbon nanotube (CNT)-embedded Ecoflex is introduced in this paper. Within the film of multiwalled CNTs embedded in the Ecoflex substrate, the microcracks are propagated under tensile strain, changing the optical transmittance of the film. The proposed sensor exhibits good stretchability (ε ≈ 400%), high linearity (R2 > 0.98) in the strain range of ε = 0-100%, excellent stability, high sensitivity (gauge factor ≈ 30), and small hysteresis (∼1.8%). The sensor was utilized to detect the bending of the finger and wrist for the control of a robot arm. Furthermore, the applications of this sensor to the real-time posture monitoring of the neck and to the detection of subtle human motions were demonstrated.

Functionalized Multi-Walled Carbon Nanotubes and Micro Cellulose Reinforced Poly (Vinyl Alcohol) Hybrid Composite Films: Characterization and Reprocessing Performance

The aim of this research paper was to investigate the synergetic effect of micro cellulose and multi-walled carbon nanotubes (MWCNTs) combination on physicochemical, mechanical and reprocessing performance of Poly (Vinyl Alcohol) hybrid composite films. The hybrid composite films production was carried out by the solution casting method, and the reprocessed films were produced using defective (torn, faulty) films from primary production by the same method. The combined use of MWCNTs and micro cellulose improved the hydrophobicity approximately 85% in ratio. After the reprocessing, decreased intensities of the peaks in the FTIR and Raman results confirmed the reduced molecular interaction between all components of the hybrid composite film, moreover, SEM and TEM revealed the negative defects such as agglomeration which caused mechanical strength decrease. The tensile strength of PVA hybrid composite films loaded cellulose/MWCNTs, reached 97 MPa strength value and elongation at break decreased to 33% according to the neat PVA film. The study results revealed that hybridization had a remarkable impact on improving characteristic properties of composite films and reprocessing process might have been compatible with solution casting method.

Facile fabrication of a novel disposable pencil graphite electrode for simultaneous determination of promising immunosuppressant drugs mycophenolate mofetil and tacrolimus in human biological fluids.

An innovative electrochemical sensor was proposed for simultaneous determination of mycophenolate mofetil (Mph) and tacrolimus (TAC) for the first time. A novel sensor based on electro-polymerization of multi-walled carbon nanotubes (MWCNTs) and a novel Cu-1N-allyl-2-(2,5-dimethoxyphenyl)-4,5-diphenyl-1H-imidazole metal organic framework (Cu-ADPPI MOF) on disposable pencil graphite electrode (dPGE). Many techniques were used to characterize the electrochemical activity and surface structure of the fabricated sensor. The proposed sensor exhibited good catalytic performance towards Mph and TAC oxidation due to the synergistic effect. Under optimal conditions, the proposed sensor has achieved a linear range of 0.85-155 × 10-8 M and 1.1-170.0 × 10-8 M with LODs of 0.28 × 10-8 M and 0.36 × 10-8 M for Mph and TAC, respectively. The designated sensor showed good reproducibility, repeatability, stability, and selectivity for the determination of Mph and TAC. Moreover, the simultaneous determination of Mph and TAC in different human biological fluids was carried out with acceptable results. As a result, the proposed sensor opens a new venue for the use of electro-polymerized MOFs in combination with other conductive materials such as MWCNTs for electrochemical sensing of different analytes with the desired sensitivity and selectivity. Graphical abstract Construction of disposable graphite electrode, based on electro-deposition of multilayer films of multi-walled carbon nanotubes and a new generation of Cu-MOFs, for simultaneous analysis of tacrolimus and mycophenolate mofetil for the first time.

Bias Tunable Photocurrent in Metal-Insulator-Semiconductor Heterostructures with Photoresponse Enhanced by Carbon Nanotubes.

Metal-insulator-semiconductor-insulator-metal (MISIM) heterostructures, with rectifying current-voltage characteristics and photosensitivity in the visible and near-infrared spectra, are fabricated and studied. It is shown that the photocurrent can be enhanced by adding a multi-walled carbon nanotube film in the contact region to achieve a responsivity higher than under incandescent light of . The optoelectrical characteristics of the MISIM heterostructures are investigated at lower and higher biases and are explained by a band model based on two asymmetric back-to-back Schottky barriers. The forward current of the heterojunctions is due to majority-carrier injection over the lower barrier, while the reverse current exhibits two different conduction regimes corresponding to the diffusion of thermal/photo generated carriers and majority-carrier tunneling through the higher Schottky barrier. The two conduction regimes in reverse bias generate two plateaus, over which the photocurrent increases linearly with the light intensity that endows the detector with bias-controlled photocurrent.

Durable and Robust Self-Healing Superhydrophobic Co-PDMS@ZIF-8-Coated MWCNT Films for Extremely Efficient Emulsion Separation.

The discharge of large amounts of sewage has caused enormous damage to the environment and human health. There is an urgent need for efficient and environmentally friendly materials to deal with such troubles. Materials with emulsion separation have attracted everyone's attention. In this study, zeolitic imidazolate framework (ZIF)-8- and Co-polydimethylsiloxane (PDMS)-modified multiwalled carbon nanotube films were fabricated. First, the surface of the nanotube films was modified with ZIF-8 by in situ growth, and then a Co-PDMS layer was added by dip coating. The membrane has excellent wettability, and it is superhydrophobic and superoleophilic in air. The separation efficiency of water-in-oil emulsions reaches more than 99.9%, and it has an outstanding separation ability for corrosive emulsions. Moreover, the membrane has an excellent self-healing ability, and it can rapidly heal at normal temperature after being damaged. This makes the film more suitable for practical oily wastewater treatment. We performed related research and propose a possible self-healing mechanism.

Gold Plate Electrodes Functionalized by Multiwall Carbon Nanotube Film for Potentiometric Thallium(I) Detection.

Solid-contact potentiometric ion-selective electrodes (SC-ISEs) for thallium determination have been designed using multiwall carbon nanotubes (MWCNTs) as the ion-to-electron transducer. Dispersed MWCNTs were drop-casted over a gold plate electrode. Two different crown ethers were used in the sensing membrane for the recognition of thallium (I). Sensorsbased on dibenzo-18-crown-6 (DB18C6) as a neutral carrier and NaTPB as an anionic additive exhibited a near Nernstian response of 57.3 mV/decade towards Tl+ ions over the activity range 4.5 × 10−6–7.0 × 10−4 M, with a limit of detection of 3.2 × 10−7 M. The time required to achieve 95% of the steadyequilibrium potential was <10 s. The complex formation constant (log βML) between dibenzo-18-crown-6 and thallium (I) (i.e., 5.99) was measured using the sandwich membrane technique. The potential response was pH independent over the range 3.0–9.5. The introduction of MWCNTs as an electron-ion-transducer layer between gold plate and the sensing membrane lead to a smaller membrane resistance and a large double layer capacitance, which was proven using impedance spectra and chronopotentiometry (i.e., 114.9 ± 12 kΩ, 52.1 ± 3.3 pF, 200 ± 13.2 kΩ, and 50 ± 4.2 µF). Additionally, reduction ofthe water layer between the sensing membrane and the underlying conductor wastested. Thus, it is clear that MWCNTs can be used as a transducing layer in SC-ISEs. The proposed sensor was introduced as an indicator electrode for potentiometric titration of single and ternary mixtures of I−, Br−, and S2− anions.

Amperometric detection of diclofenac at a nano-structured multi-wall carbon nanotubes sensing films

COOH-functionalized multi-walled carbon nanotubes (f-MWCNTs) film coated on glassy carbon electrode (GCE) were prepared, and the detection of diclofenac (DCF) was investigated by cyclic voltammetry and amperometry. The results showed that the nano-structured electrodes exhibit good analytical performances towards the electrochemical oxidation of DCF with a detection limit of 0.1 μM and a sensitivity of 0.06 μA. μM−1 within a dynamic concentration range varying from 2 μM to 15 μM.

A novel highly sensitive thebaine sensor based on MWCNT and dandelion-like Co3O4 nanoflowers fabricated via solvothermal synthesis

For this study, the synthesis of dandelion-like Co3O4 nanoflowers is presented via the straightforward solvothermal approach and specified by various analytical methods. Furthermore, electrochemical activity of dandelion-like Co3O4 nanoflowers and multiwall carbon nanotubes (MWCNT) concerning thebaine detection. Papaver somniferum is the most important alkaloid bearing species of family Papaveraceae. Major opium alkaloids such as thebaine are often used in medicine for pain relief. Therefore, a method that allows for the accurate and rapid determination of opiate compounds is a necessity. According to our research, there are no other reviews on thebaine sensing characteristics of MWCNT and Co3O4 films. By implementing CV, it was evident that the fabricated modified electrode (DNF-Co3O4/MWCNTs/GCE) exhibited prompt electron transfer in comparison with unmodified electrodes and also clear electrocatalytic behavior in regard to thebaine electro-oxidation. At an optimal state, the adjusted electrode exhibited linearity between the concentrations and peak current of thebaine across a 0.01–900.0 μM range and 2.4 nM (3Sb/m) detection limit. Finally, thebaine was also detected in real samples using our introduced approach as a selective, simple and precise electrochemical sensor.

Unzipped carbon nanotubes for aluminum battery

As low-cost commercial materials, the application of carbon nanotubes (CNTs) in the aluminum battery is limited by the lack of active intercalation sites. Herein, a flexible unzipped multi-walled carbon nanotubes (UCNTs) film consisting of graphene nanoribbons and a carbon nanotube backbone is prepared via a simple, low-cost and scalable method for high-performance aluminum battery positive electrode. In the nanostructure, the neonatal graphene nanoribbons provide numerous active intercalation sites to store AlCl4− anions, while the internal core CNTs are responsible for the rapid transportation of electrons to the active sites. Fast transportation of electrons and anions in UCNT film are simultaneously achieved, promoting the kinetics in the aluminum battery. Thus the UCNT-Al battery exhibits a high storage performance with a capacity as high as 100 mA h g−1 (current density: 2000 mA g−1) and a long cycle life of 5600 cycles with a capacity of 75 mA h g−1 (Coulombic efficiency: 98%) at 5000 mA g−1. Furthermore, the excellent flexibility and fast charging and variable discharging performance are beneficial for the development of portable devices. This work effectively tackles bottleneck caused by the lack of active sites for CNT-based aluminum batteries and accelerates the development of aluminum batteries.