Layer Of Multi-walled Carbon Nanotubes Research Articles

Sensitive MWCNT/P-Cys@MIP sensor for selective electrochemical detection of ceftizoxime

An electrochemical sensor based on molecular imprinted polymer (MIP) to detect ceftizoxime (CFX) with high sensitivity and selectivity is demonstrated. MIP was synthesized by electropolymerization of poly-cysteine (P-Cys) on a multi-walled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE). A targeted drug was used as a template molecule during the polymerization process. The bare GCE was coated with a layer of MWCNT before the synthesis of MIP to improve the sensor sensitivity. Experimental parameters such as polymerization conditions, the influence of pH, molar ratio of the template molecules and the monomer molecules were all optimized. The peak potential exhibited linearity with CFX concentration in the ranges of 1 $$\times 10^{ - 9}$$ –1× $$10^{ - 7}$$ molL−1 (R2 = 0.9904) and 2× $$10^{ - 7}$$ –1× $$10^{ - 4}$$ molL−1 (R2 = 0.9949). The LOD of the MIP sensor was found to be $$1 \times 10^{ - 10}$$ molL−1 under optimal conditions using a differential pulse voltammetry (DPV). The proposed sensor was tested on real samples, and good recovery results were obtained.

Calcium-enhanced retention of humic substances by carbon nanotube membranes: Mechanisms and implication

Efficient removal of humic substances (HS) in natural water is of importance to drinking water treatment. In this study, the adsorption and retention of HS by multi-walled carbon nanotube (MWCNT) membranes were systematically investigated by dynamic filtration of synthetic and natural surface water. In the absence of Ca(II), HS were dominated by small, dissolved species albeit the varying pH. Accordingly, HS retention by the MWCNT layers only ranged from 15%-65% at the end of the filtration. In contrast, the presence of Ca(II) in the feed water partially transformed HS molecules into colloidal aggregates as found by light scattering analyses. Furthermore, molecular dynamics (MD) simulation results reveal that Ca(II) complexation with -COO- on MWCNT and humic acid (HA) not only leads to HA aggregation in the feed solution, but also promotes HA adsorption onto carboxylated MWCNT. The modeling results are consistent with the high retention of HS by the carboxylated MWCNT membrane, i.e., >90% for the synthetic model water and >85% for the natural water, at a moderate calcium concentration range of 0.5–2.0 mM. Considering the widespread presence of calcium in natural water, these findings suggested that carboxylated MWCNT has a potential for effective adsorptive filtration of HS in drinking water.

Photoelectrochemical performance of MWCNT–Ag–ZnO ternary hybrid: a study of Ag loading and MWCNT garnishing

Herein, by using chemical methods such as successive ionic layer adsorption and reaction (SILAR) and spin coating we have demonstrated a novel strategy for the synthesis of ternary hybrid to study photoelectrochemical (PEC) performance. To the best of our knowledge, for the first time we have represented a case study of achieving optimum SILAR cycles for Ag nanoparticles decoration on ZnO nanorods and a discussion was made on a role of multi-walled carbon nanotube (MWCNT) as a top layer over Ag–ZnO nanostructures for better PEC performance. Firstly, Ag nanoparticles loading over SILAR grown ZnO nanorods was varied for different SILAR cycles to optimize better photocurrent. This Ag–ZnO hybrid showed higher photocurrent density of 0.45 mA/cm2 at 1 V bias (vs SCE) and photoconversion efficiency (PCE) of 0.21% (0.45 V vs SCE). Thereafter, MWCNTs were garnished by using spin coating as a top layer on Ag–ZnO hybrid leading to the formation of ternary hybrid of MWCNT–Ag–ZnO for further enhancement of PEC activity. We believe that top layer of MWCNT plays a vital role of electron and hole transfer and bridges Ag decorated ZnO nanorods together leading to well-connected conducting pathways for efficient charge collection and transport. The appropriate band bending of MWCNT–Ag–ZnO hybrid leads to the formation of active interface helping out in charge separation leading to excellent photocurrent density of 0.56 mA/cm2 at 1 V bias (vs SCE) and photoconversion efficiency of 0.26% (0.45 V vs SCE). Enhanced light harvesting, higher donor density, appropriate band bending, lowest charge transfer radius of C–Ag–ZnO hybrid signifies that efficient charge transfer and restriction to charge recombination leading to the enhanced PEC performance.

Flexible capacitive pressure sensor based on multi-walled carbon nanotubes microstructure electrodes

Flexible pressure sensors have been widely used in wearable devices, medical and health, smart services and other industries. However, the fabrication of sensor with high sensitivity, large sensing range and good stability is still a vital research topic. Herein, a flexible capacitive pressure sensor based on micro-structured electrode is developed, which uses a micro-structured polydimethylsiloxane (PDMS) film embedded with a layer of multi-walled carbon nanotubes as the micro-structured conductive electrode, and a smooth PDMS film as the dielectric layer. The results indicate that the sensor exhibits a strong linear pressure-capacitance relationship. The sensitivity of the sensor can reach 1.3 kPa−1 in the pressure range of 0–100 Pa by optimizing the size of the electrode microstructure. In addition, the sensor exhibits a good repeatability even after 4000 repeated pressing. In addition, we demonstrate that the pressure sensor can be applied to monitor arterial pulse waves and breathing. The sensor is assembled in the form of arrays, which can effectively detect the shape of the measured object, proving that the sensor can be applied in complicated scenarios such as service robot and wearable equipment.

A Functionalized Paper Strip‐Based Platform for Rapid Detection of Anticancer Drug Concentrations

This article presents a compact, low‐cost, robust, and flexible test platform for determining the concentration of drugs in fluids. This device is based on a PVC foil card containing copper conductive foils in which disposable paper test strips are inserted. The paper test strips are overlaid with deposition of multiwalled carbon nanotubes (MWCNTs) acting as a sensing layer. When a paper test strip is inserted into the test card, the conductive path between two copper lines is established. A drop of test fluid on the sensing MWCNT layer changes the conductivity in a concentration‐dependent manner, enabling calculation of the drug concentration after measurement of the electrical resistance at the copper terminals. An equivalent electrical circuit was also proposed to model the response of the fabricated sensor. It was shown that model parameters are dependent on the concentration of the cytostatic drug methotrexate. Additionally, the fabricated sensor demonstrated the ability to differentiate the same concentration of methotrexate and cyclophosphamide. The complete readout electronics and polynomial transfer function for calculating drug concentrations were also developed and are presented.

Feasibility study on microwave welding of thermoplastic using multiwalled carbon nanotubes as susceptor

Despite manufacturers’ goal of molding single component products from plastics, the structures of some of the products are far too complex to be molded as a single piece. Therefore, assembly of subcomponents into the final products is important for the manufacturing of many plastic-based products. To date, welding is the most efficient joining method for plastics. In this study, multiwalled carbon nanotubes were proposed as the susceptor for the microwave welding of high-density polyethylene considering multiwalled carbon nanotube is a good microwave absorber. multiwalled carbon nanotubes were first dispersed in ethanol in an ultrasonic bath to obtain a homogeneous dispersion. Multiwalled carbon nanotubes dispersion was dropped on the targeted area of the prepared dumbbell-shaped sample and dried in an oven at 45°C for 30 min. The sample was then subjected to 800 W microwave irradiation in the domestic microwave oven. The strength of the weld was tested by using tensile testing. Besides, the cross section of the welded joint was characterized by using scanning electron microscopy. The effect of microwave heating duration and the multiwalled carbon nanotube concentration in the dispersion were studied. It was found that the joint strength increased as the heating duration increase from 2 s to 8 s but decreased when the heating duration was further extended to 10 s. Scanning electron microscopic images showed that voids were formed at the joint interface when 10 s was used and resulted in the lowering of joint strength. In the study of the effect of the multiwalled carbon nanotube concentration in the dispersion, joint strength increased when the multiwalled carbon nanotubes concentration increased from 0.25 wt% to 0.75 wt%. However, the joint strength of sample with 1.00 wt% multiwalled carbon nanotube concentration decreased. The presence of a thick unwelded multiwalled carbon nanotubes layer at the joint interface for sample with 1.00 wt% multiwalled carbon nanotubes concentration as shown in scanning electron microscopic image was believed to cause the lowering of joint strength.

Получение углеродных нанотрубок и их функционализация

In this work, the synthesis of carbon nanotubes was carried out on the sand surface with hydrophobic properties by chemical vapor deposition (CVD). The effective temperature for the synthesis of carbon nanotubes is 800 °C. Propane-butane gas mixture was used as a source of gaseous carbon. Argon gas (Ar) was used as an inert carrier gas. Nickel nitrate (Ni(NO3)2) was chosen as a catalyst for producing carbon nanotubes. Despite all the special properties of carbon nanomaterials, one of the problems with its use is its tendency to agglomerate and inert to the matrix of various substances. In order to solve this problem, the chemical functionalization of the surface layer of multiwall carbon nanotubes was carried out. To introduce carboxyl groups into the surface layer of carbon nanotubes, its surface was treated with a concentrated mixture of acids H2SO4/HNO3. It has been established that the main part of the functional groups in the surface layer of nanotubes are carboxyl, carbonyl and hydroxyl groups. Carbon nanotubes synthesized on the surface of hydrophobic sand were analyzed by the following research methods: scanning electron microscope, optical microscope, elemental analysis, Raman spectroscopy and a qualitative assessment of functionalized nanotubes using IR spectroscopy.

Alternative approach for efficient hole transporting electrode by depositing MWCNT layer on CZTS-MWCNT material for perovskite solar cell application

Abstract Metal electrode contact (i.e., Al, Ag, and Au) used for charge collection at perovskite solar cells (PSCs) needs an alternative replacement due to their expensive processing cost. Chemically reactive organic hole-transporting material (HTM) easily exposes corrosion threat to these metal electrode contacts at the Metal/organic-HTM junction. Including these two critical factors, PSC also faces a challenging issue of interface instability at perovskite/organic HTM junction. Therefore, in this work, metal contact has been replaced by Multi-wall Carbon Nanotube (MWCNT) with a simple drop-casting deposition process, and inorganic semiconductor material Cu2ZnSnS4 (CZTS) has been applied as HTM by spin coating technique. However, to improve the efficiency of PSC, CZTS-MWCNT composite has been used here as HTM due to its significant optoelectronics properties. These materials CZTS, MWCNT, and CZTS-MWCNT composites have been synthesized and characterized by XRD, FESEM, TEM, UV–Vis, and Raman spectroscopy, respectively. The fabrication process of the regular (n-i-p) structured PSCs has been described, and the photovoltaic performances have been investigated by their current-voltage characteristics. It has been observed that MWCNT embedded composite HTM (i.e., CZTS-MWCNT) has not only successfully delivered 7.60% PCE but also improved the stability of the PSC.

Resistance spot-welding of AISI-1008 steel joints with MWCNT coating interlayer

ABSTRACT Inclusion of multi-walled carbon nanotubes (MWCNTs) as an inter-layer sandwiched between the mating sides of AISI 1008 steel joints in resistance spot-welding and its impact on microstructure/mechanical behavior of the subsequent lap joint is discussed here. A thin layer of MWCNTs approximately 50 μm is incorporated as a coating at one of the mating surfaces of the lap joint. It was found that the MWCNTs get entrapped in weld-nugget during the spot-welding procedure, which subsequently leads to weld strengthening through various mechanisms. While the weld strength is reliant mainly on the welding current, time, and also on the nugget diameter, an improvement of ~45% in weld strength is attained in lap-shear tensile tests due to the MWCNT interlayer. A detailed microstructural and XRD studies corroborate the experimental observations. Peak shifts were observed in Raman spectroscopy which confirms the compressive stress associated with the weld nugget-entrapped MWCNTs. Transmission electron microscopic studies of the nugget region elucidate the prevailing strengthening mechanisms including dislocation pile up, interfacial stress transfer, and mechanical interlocking.

Optimized protocol for the preparation of multi-walled carbon nanotube:polystyrene transducers for electrochemical sensing

A practical method is presented to prepare films of a composite material constituted of multi-walled carbon nanotubes (MWCNTs) and polystyrene (PS) that are used for transduction applications. The method, which can be carried out by employing usual lab equipment, is simple, low-cost, rapid, and nonpolluting. Furthermore, it is compatible with microelectronic fabrication technology and is scalable for mass production. For designing this method, we studied how the number of drop-casted composite layers, the temperature used for curing the samples, and the duration of this thermal treatment influence on the electrochemical performance of a Si/SiO2/Au/MWCNT:PS electrode. The optimum electrochemical responses of the Si/SiO2/Au/MWCNT:PS electrode were obtained with films prepared with four layers of MWCNT:PS composite, each cured at 80 °C for 15 min. Under these conditions, the MWCNT walls are exposed and readily accessible for subsequent functionalization.

Influence of preparation methods on the activity of macro-structured ball-milled MWCNT catalysts in the ozonation of organic pollutants

A series of macro-structured catalysts consisting of nanostructured layers of mechanically processed multiwalled carbon nanotubes (MWCNT) coated onto cordierite monoliths were prepared using a novel methodology and assessed as catalysts in the ozonation of a model organic pollutant. The often used chemical vapor deposition method for formation of nanostructured layers of carbon materials is, by nature, incompatible with ball-milling or other methods for mechanical or mechano-chemical modification of MWCNT. The preparation method here described was designed to translate the positive effect observed in the performance of ball-milled MWCNT as ozonation catalysts when compared with unmodified MWCNT to macro-structured catalytic systems. The performance of such macro-structured catalysts in the ozonation of organic pollutants is reported and analyzed for the first time. The effect of the preparation methodology, which includes physical functionalization of the MWCNT with a non-ionic surfactant (Triton X-100®), in the performance of the powder catalysts was evaluated. It was found that, for the coated nanostructured layers, the decrease in the expected activity is related to the packing of the materials. Nevertheless, the catalytic nanostructured coated layers were found to compare favorably with a reference sample. Thus, the beneficial effect of ball-milling MWCNT is still retained upon coating, even with a decrease in the intrinsic activity of the powder material. The increase in MWCNT mass in the coated samples introduces diffusion limitations, suggesting that creating a macroporous system in the MWCNT layers might be desirable. The introduction of oxygen-containing surface functionalities improved the long-term stability of the nanostructured catalytic layers.

Mechanical Characterization of Multiwalled Carbon Nanotubes: Numerical Simulation Study.

The elastic properties of armchair and zigzag multiwalled carbon nanotubes were investigated under tensile, bending, and torsion loading conditions. A simplified finite element model of the multiwalled carbon nanotubes, without taking into account the van der Waals interactions between layers, was used to assess their tensile, bending, and torsional rigidities and, subsequently, Young’s and shear moduli. Relationships between the tensile rigidity and the squares of the diameters of the outer and inner layers in multiwalled carbon nanotubes, and between the bending and torsional rigidities with the fourth powers of the diameters of the outer and inner layers, were established. These relationships result in two consistent methods, one for assessment to the Young’s modulus of armchair and zigzag multiwalled carbon nanotubes, based on tensile and bending rigidities, and the other to evaluate shear modulus using tensile, bending, and torsional rigidities. This study provides a benchmark regarding the determination of the mechanical properties of nonchiral multiwalled carbon nanotubes by nanoscale continuum modeling approach.

Improved hydrogen adsorption of ZnO doped multi-walled carbon nanotubes

Hydrogen storage is still one of the most important problems to improve hydrogen energy usage widespread. New materials capable of storing hydrogen with high efficiency must be introduced to overcome this problem. In recent years, addition of metals or inorganic compounds to multiwalled carbon nanotubes (MWCNTs) has been generally used for hydrogen uptake studies to enhance adsorption property of the nanotubes. In this study, Zinc oxide (ZnO) nanoparticles doped MWCNTs (ZnO-MWCNTs) have been produced as new reversible hydrogen storage materials, and we have investigated characterization of ZnO-MWCNTs by XRD, SEM, TGA, TEM and BET analyses. The functionalized MWCNTs and ZnO doped MWCNTs were subjected to hydrogenation step by dynamic gas sorption analyser under pressure of 5–50 bar. The hydrogen uptake capacities of the materials under different pressures were measured gravimetrically. It was indicated that by controlling the pressures for hydrogenation of ZnO-MWCNTs induces the spillover of ZnO nanoparticles in the layer of MWCNTs which in return with high hydrogen adsorption capacity. Consequently, the hydrogen adsorption of the functionalized MWCNTs (f-MWCNTs) and the ZnO-MWCNTs were achieved to be 1.05 wt% and 2.7091 wt% under pressure of 50 bar as maximum.

Plasma polishing of multi-walled carbon nanotubes towards single-walled limit

This article reports that plasma exposure decreases the wall thickness of multi-walled carbon nanotubes (MWCNTs), which can be one of the promising techniques for mass production of single-walled carbon nanotubes (SWCNTs) in the future. This technique is attractive because MWCNTs have a significant advantage in the production rate. In this article, we first observed the reduction of the wall thickness with a transmission electron microscope (TEM) to investigate CNT morphology after plasma exposure. Then, we randomly selected more than 500 nanotubes from the TEM pictures to measure the wall thickness. Our histogram of the wall thickness showed that plasma exposure reduced a few layers of MWCNTs. We then confirmed the plasma-exposed CNTs with Raman spectroscopy, which again shows the reduction of the wall thickness of MWCNTs by observing the ratio of the two characteristic intensities, as known as G/D ratio. In conclusion, our observations were consistent so that plasma exposure can apply to future mass production from MWCNTs to SWCNTs after decent optimization.

Graphite Sheet as Flexible Electrode for Construction of a Super-Stable Tin Oxide Anode

A novel type of graphite sheet (GS) flexible electrode was obtained from high-temperature carbonized polyimide film. The GS establishes an excellent conductive network and promotes the transfer of electrons. In order to ensure the carrying capacity of tin oxide, the surface of the GS was coated with a layer of multi-walled carbon nanotube (MWCNT) slurry, and then coated with tin oxide. The fluffy porosity of MWCNT coating is an excellent carrier of tin oxide, which inhibits the volume expansion of tin oxide to a certain extent. Through repeated tests, the electrochemical performance of the electrode is best when the coating thickness is 0.3 mm.

Gold nanoparticles mixed multiwall carbon nanotubes, supported on graphene nano-ribbons (Au-NT-G) as an efficient reduction electrode for Polymer Electrolyte Membrane fuel cells (PEMFC)

This research reports fabrication of three Polymer Electrolyte Membrane fuel cells (PEMFC) using composite of gold nanoparticles and nanotube graphene by varying concentration of Gold nanoparticles. The outer most layer of multiwall carbon nanotubes is un-zipped and nano ribbons of graphene are developed to attain a durable electrode. Moreover, the addition of gold nanoparticles adds benefit of better conductance over usual platinum electrodes. The effect of changing gold concentration on properties of composite material as well as fuel cell performance is investigated. The presence of gold nanoparticles and graphene nano-ribbons attached to carbon nanotubes are identified using SEM, TEM, and Raman analysis. Cyclic voltammetry analysis has showed that increase in concentration of gold nano particles improves the performance of fuel cell. EIS analysis reveled that the polarization resistance decreased by increasing the Au concentration. Thermal Gravimetric Analysis proved the thermal stability of composite material. Maximum power density of 242.29 mWcm−2 is achieved for the highest concentration of Gold nanoparticles.

Sensitive biosensing of neurotransmitter: 2D material wrapped nanotubes and MnO2 composites for the detection of acetylcholine

Acetylcholine (ACh) is a neurotransmitter which plays central role in transmitting information between nerve - skeletal intersection and neurons present in the spinal cord. Presently, there are few conventional techniques for the detection of ACh however they have certain limitations including requirement of trained technicians, time consumption and low sensitivity. Therefore, it is necessary to develop new methods based on emerging nanotechnology for detecting ACh in real samples. The ACh biosensor was fabricated with the co-immobilization of acetylcholinesterase (AChE) and choline oxidase (ChO) over the Au-electrode coated with nanocomposite layer of multi-walled carbon nanotubes (MWCNT)-manganese oxide (MnO2)- reduced graphene oxide (rGO). Characterizations of the nanocomposites were accomplished by Scanning Electron Microscopy (SEM). The cyclic voltammetry (CV) technique was adopted for the testing and optimization of the developed biosensor. The observation for current in proportion to various ACh concentrations show a linear relation ranging between 0.1–100 μM. The detection limit (LOD) of the biosensor was obtained up to 0.1 μM.

Flexible and Highly Efficient Bilayer Photothermal Paper for Water Desalination and Purification: Self-Floating, Rapid Water Transport, and Localized Heat.

In view of the sustainable and environmentally friendly characteristics of solar energy, solar water evaporation has been identified as a promising approach to mitigate the global water crises. However, it is still a great challenge to develop a portable, flexible, scalable, and high-performance solar water evaporation material. Herein, a bilayer-structured solar water evaporation material consisting of a top multiwalled carbon nanotube (MWCNT) layer and a bottom polyphenylene sulfide/fibrillated cellulose (PPS/FC) paper was fabricated via a simple vacuum filtration technology for efficient solar water evaporation. The MWCNT layer performs as a light absorber with a high solar absorptance (∼93%) in the wavelength range from 400 to 1200 nm and good light-to-heat conversion capability, while the bottom layer (porous network-structured PPS/FC paper) exhibits excellent water transporting ability, high temperature stability, and good thermal insulating capability (0.0467 W m-1 K-1). Benefiting from the above advantages, an attractive water evaporation rate of 1.34 kg m-2 h-1 was achieved with near ∼95% efficiency under 1 sun irradiation (1 kW m-2). Moreover, the MWCNTs@PPS/FC paper maintains high solar evaporation efficiency after several cycles, indicating long-term durability and good reusability. Moreover, the collected clean water using the MWCNTs@PPS/FC paper from seawater of different salinities, simulated wastewater samples with different pH values or containing heavy metal ions, as well as industrial dyes, satisfy the drinkable water standard (defined by WHO), demonstrating excellent seawater desalination and wastewater purification capability. The advanced performances of the MWCNTs@PPS/FC paper could inspire novel paradigms of solar-driven water evaporation technologies in drinkable water collection.

Mechanical and thermal properties of polyoxymethylene-matrix composites filled with multi-walled carbon nanotubes-coated milled glass fiber

The advanced multifunctional filler has become one of the main challenges in developing high-performance polymer composites. In this study, the acid-treated multiwall carbon nanotubes (MWCNTs) were adhered to the surface of milled glass fiber under the combined effect of 3-aminopropyltriethyloxy silane and tetraethyl orthosilicate to fabricate a hierarchical fiber (MWCNTs-MGF). The morphologies of the hierarchical fibers were characterized using field-emission scanning electron microscope and transmission electron microscope, which showed evidence of a coating layer of MWCNTs on each fiber surface. The MWCNTs-MGF was employed as a multifunctional filler to prepare polyoxymethylene-based composites using a twin-screw extruder by melt blending. The obtained composites exhibited improved mechanical and thermal properties. The composite tensile strength and notched impact strength and Young's modulus increased by 10%, 32%, and 32%, respectively, as the MWCNTs-MGF content varies from 0 to 10 wt.%. Meanwhile, the reinforcing and toughing mechanisms of MWCNTs-MGF were also elaborated by analyzing the interfacial adhesion and fracture morphologies of the composites. Moreover, the study on thermal stability and crystallization behavior indicated that the polyoxymethylene/MWCNTs-MGF composites had higher thermal stability, crystallization temperature, and crystallinity as compared to the polymer matrix. The improvement of thermal stability originates from the unique surface structure of MWCNTs-MGF, while the increase in crystallization temperature and crystallinity is due to the strong heterogeneous nucleation ability of the hierarchical fibers.

Surface-Modified Carbon Nanotubes for Enhanced Ammonia Gas Sensitivity at Room Temperature.

By electron beam evaporation, noble metals (Au, Co, Pt, and Ag) with 2 and 4 nm nominal thicknesses were coated onto multi-walled carbon nanotube layers. The metals were in the form of nanoparticles mounted onto the side walls of carbon nanotubes (CNTs) to create a metal/CNT junction. The CNTs were directly grown on patterned Pt-electrode alumina substrates through chemical vapor deposition to produce a resistivity-based ammonia gas sensor. The metallic surface-modified CNT-based sensors were found sensitive to NH₃ gas at room temperature. Compared with pristine CNT sensor, the response of Au/CNTs sensor increased slightly, whereas the responses of the Pt/CNTs, Co/CNTs, and Ag/CNTs increased by two, three, and more than four times, respectively.