Deposition Of Multi-walled Carbon Nanotubes Research Articles

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.

Continuous Determination of Glucose Using a Membraneless, Microfluidic Enzymatic Biofuel Cell.

In this article, we describe an enzyme-based, membraneless, microfluidic biofuel cell for the continuous determination of glucose using electrochemical power generation as a transducing signal. Enzymes were immobilized on multi-walled carbon nanotube (MWCNT) electrodes placed parallel to the co-laminar flow in a Y-shaped microchannel. The microchannel was produced with polydimethylsiloxane (PDMS) using soft lithography, while the MWCNT electrodes were replicated via a PDMS stencil on indium tin oxide (ITO) glass. Moreover, the electrodes were modified with glucose oxidase and laccase by direct covalent bonding. The device was studied at different MWCNT deposition amounts and electrolyte flow rates to achieve optimum settings. The experimental results demonstrated that glucose could be determined linearly up to a concentration of 4 mM at a sensitivity of 31 mV∙mM−1cm−2.

Facile deposition of multiwalled carbon nanotubes via electrophoretic deposition in an environmentally friendly suspension

The present work focuses on the application of electrophoretic deposition (EPD) as a facile process to generate homogeneous layers of multi walled carbon nanotubes (MWCNTs) using water as an environmentally friendly solvent. The EPD process requires a pretreatment of the commercially available MWCNT powder to create a surface charge on the surfaces of the MWCNTs as well as to realize stable suspensions. After pre-treatment, the electrophoretic mobility of the MWCNTs was approximately μ ≈ − 4.3 · 10−4cm2V−1s−1 and the resulting ζ-potential is in the range of ζ ≈ −55 mV. The suspension showed no sedimentation over 50 days. The EPD was carried out at an applied voltage of 50 V. The MWCNTs were successfully deposited as open porous layers on gold as well as on aluminum. The specific double layer capacitance of the MWCNT-layers on gold amounts to C ≈ 11.9 Fg−1.However, on aluminum as substrate, the EPD of the MWCNTs is associated with the formation of a thin barrier like oxide film. In this case a major part of the applied voltage drops down across the oxide film and only a minor part across the suspension. Consequently, the field strength in the suspension decreases. Moreover, the capacitance of the oxide film dominates the whole capacitance of the electrode. The specific capacitance amounts to C = 0.3 mFg−1 related to the deposited mass of MWCNTs.

Electrophoretic deposition of multiwalled carbon nanotubes onto porous silicon with enhanced NO2-sensing characteristics

The multiwalled carbon nanotubes were successfully electrophoresis deposited onto porous silicon to form a multiwalled carbon nanotubes/porous silicon composite and were then fabricated into chemiresistive gas sensors. The morphology, microstructure and NO2-sensing characteristics of the composite were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and gas-sensing test. The results indicated that all the carbon nanotubes/porous silicon sensors showed typical p-type semiconductor behavior at room temperature (∼25°C) of the optimal working temperature. The carbon nanotubes/porous silicon sensor under the electrophoresis time of 5 min yielded the best NO2-sensing characteristics, including a high sensor response (∼8.5), fast response-recovery time (∼37 s and ∼34 s), good repeatability and selectivity toward 1 ppm NO2. The heterostructure effect as well as the high specific surface area and the unblocked porous structure was considered essential for the gas-sensing performance.

Enhancing Electrical and Thermal Properties of Al6061 Parts by Electrophoresis Deposition of Multi-Walled Carbon Nanotubes

The present research work focuses on depositing multi-walled carbon nanotubes (MWCNTs) onto aluminum parts to modify their electrical and thermal properties by an electrodeposition process (EDP). This film coated over the sample surface creates a network of high conductive thin layer that promotes free electron flow and heat-loss reduction. Experimental measurements on the metallic surface part show an increment of the electrical conductivity of 9.6% for the sample coated with 0.05 mg/mL of MWCNTs with a heat dissipation increase of 36%.

Potential of electrical discharge treatment incorporating MWCNTs to enhance the corrosion performance of the β-titanium alloy

The study presents the surface modification of β-titanium alloy by the electrical discharge chemical treatment (EDCT) to achieve a corrosion-resistant surface. This technique incorporated multi-walled carbon nanotubes (MWCNTs) in the dielectric medium to alter the surface properties of the substrate. Herein, the MWCNTs act as potential candidates due to its chemical inertness and physical as well as electrical properties for achieving desired surface properties. For the sake of comparison, the μ-hydroxyapatite (μHAp) powder was also utilized in the dielectric medium. Surface morphology, topography, and elemental composition of the treated surfaces were investigated by FE-SEM, EDS, and XRD techniques, respectively. The electrochemical potentiodynamic test was carried out to investigate the corrosion resistance of untreated and treated surfaces. The treated surfaces were also evaluated in terms of change in surface morphology, wettability, and surface free energy. The outcome revealed that the alloy treated with MWCNTs favors the synthesis of the chemically stable corrosion-resistant surface. The existence of TiO2, ZrO2, Nb2O5, TaO, ZrO2, TiC2, and NbC phases detected from XRD examination affirmed that the corrosion resistance of the substrate is significantly affected by multi-walled carbon nanotube deposition. The MWCNT-treated surface presented the improved wettability and surface free energy which are twofold higher than the untreated surface.

Enhancing tribological performance of β-titanium alloy using electrical discharge process

In this study, medical-grade β-titanium (Ti–35Nb–7Ta–5Zr) alloy was treated using the electrical discharge machining process. Biofavorable substances, such as multiwalled carbon (C) nanotubes and μ-hydroxyapatite powder, were selected for possible deposition during the production of spark between electrodes. The L18 array was used to conduct the experiments considering polarities, peak current, pulse on time, pulse off time, dielectric medium and tool electrode material as machining variables. The treated surfaces were evaluated in terms of change in surface microhardness, recast layer morphology and wear behavior. The outcome revealed that the alloy treated at high spark energy using a tungsten (W) tool electrode incorporating multiwalled carbon nanotubes in the dielectric medium favored the synthesis of a high-quality wear-resistant substrate. The presence of titanium carbide (TiC), niobium carbide (NbC) and tungsten carbide (WC) phases detected from X-ray diffraction examination confirmed that the microhardness of the recast layer, as well as wear resistance of the substrate, was significantly affected by multiwalled carbon nanotube deposition.

28-Day inhalation toxicity study with evaluation of lung deposition and retention of tangled multi-walled carbon nanotubes

Lung deposition and retention measurements are now required by the newly revised OECD inhalation toxicity testing guidelines 412 and 413 when evaluating the clearance and biopersistence of poorly soluble nanomaterials, such as multi-walled carbon nanotubes (MWCNTs). However, evaluating the lung deposition concentration is challenging with certain nanomaterials, such as carbon-based and iron-based nanomaterials, as it is difficult to differentiate them from endogenous elements. Therefore, the current 28-day inhalation toxicity study investigated the lung retention kinetics of tangled MWCNTs. Male Sprague Dawley rats were exposed to MWCNTs at 0, 0.257, 1.439, and 4.253 mg/m3 for 28 days (6 h/day, 5 days/week, 4 weeks). Thereafter, the rats were sacrificed at day 1, 7, and 28 post-exposure and the pulmonary inflammatory response evaluated by analyzing the bronchoalveolar lavage fluid. Plus, the blood biochemistry, hematology, and histopathology of the lungs were also examined. The lung deposition and retention of MWCNTs were determined based on the elemental carbon content in the lungs after tissue digestion. The number of polymorphonuclear cells and LDH concentration were both found to be significantly higher with the medium and high concentrations (1.439 and 4.253 mg/m3) and dose dependent. The estimated retention half-life for the high concentration (4.253 mg/m3) was about 35 days. The results of this study indicate that tangled MWCNTs seem to have a relatively shorter retention half-life when compared to previous reports on rigid MWCNTs, and the no-observed adverse effect level (NOAEL) for the tested tangled MWCNTs was 0.257 mg/m3 in a previous rat 28-day subacute inhalation toxicity study.

Photosystem I-Modified Multi-Walled Carbon Nanotube Anodes for Enhanced Solar Energy Conversion

As renewable energy sources strive to match growing energy demands, new materials and designs constantly push the performance of preexisting solar cells to new levels. However complex patterning techniques or use of environmentally toxic materials limit the extent to which state-of-the-art designs can transition from research scale devices into commercially applicable devices. Biohybrid solar cells address this limitation by employing naturally occurring dyes or light harvesting protein complexes, such as photosystem I (PSI) in their design. In this work, multi-walled carbon nanotube (MWCNT)-coated electrodes have been modified with PSI to serve as high surface area anodes in an effort to enhance generated photocurrent. The chemical treatment of MWCNTs prior to deposition on conductive substrates resulted in uniform films and lead to a 7-fold enhancement in observed photocurrent compared to PSI-based devices assembled on unmodified, planar gold electrodes. This facile treatment and deposition of MWCNTs promotes their use in electrochemical devices as an inexpensive, robust, and high surface area alternative to other carbon allotropes.

Chemical Vapour Deposition of MWCNT on Silica Coated Fe3O4 and Use of Response Surface Methodology for Optimizing the Extraction of Organophosphorus Pesticides from Water.

Multiwalled carbon nanotube (MWCNT) was fixed onto the surface of a magnetic silica (Fe3O4@SiO2) substrate via chemical vapour deposition (CVD). Acetylene gas was used as the carbon source and cobalt oxide as the catalyst. The chemical and physical characteristics of the materials were investigated by transmission electron microscopy (TEM), Raman spectroscopy (RS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and nitrogen adsorption/desorption isotherm. The synthesized Fe3O4@SiO2-MWCNT nanocomposite was used as a magnetic solid phase extraction (MSPE) adsorbent for the preconcentration of organophosphorus pesticides (OPPs), specifically, azinphos methyl, chlorpyrifos, parathion, and malathion. The factors influencing the extraction efficiency such as pH, contact time, and adsorbent dosage were investigated and optimized by response surface methodology (RSM) and desirability function. Linear response was obtained in the concentration range of 10–200 μg/L for the analytes with determination coefficients ranging between 0.9955 and 0.9977. The limits of detection (LODs) and quantification (LOQs) were in the range of 0.004-0.150 μg/L and 0.013-0.499 μg/L, respectively. Fe3O4@SiO2-MWCNT was applied in the extraction and subsequent determination of OPPs in water samples from Vaal River and Vaal Dam with recoveries ranging from 84.0 to 101.4% (RSDs = 3.8–9.6%, n = 3) in Vaal River and 86.2 to 93.8% (RSDs = 2.9–10.4%, n = 3) in Vaal Dam. The obtained results showed that the newly synthesized Fe3O4@SiO2-MWCNT nanocomposite can be an efficient adsorbent with good potential for the preconcentration and extraction of selected OPPs from aqueous media.

Layer-by-Layer modification of graphite felt with MWCNT for vanadium redox flow battery

Layer-by-Layer (LbL) deposition of multi-walled carbon nanotubes (MWCNT) was used to modify porous electrodes for vanadium redox flow batteries. Preliminary studies performed over glassy carbon (GC) electrodes showed that assemblies obtained with MWCNT displayed better mechanical stability than those prepared with other carbon nanoforms. The LbL process involved successive deposition of the polyethylenimine (PEI) and carbon nanotubes dispersed with poly(acrylic acid) (PAA). The thickness of the MWCNT assembly deposited onto a GC strongly influenced the electrochemistry of VO2+/VO2+ species. The thicker the film, the better the electrochemical reversibility resulted. An apparent electron transfer rate constant kapp of 5 × 10−4 cm s−1 was determined for a glassy carbon electrode modified with one hundred bi-layers and treated at 650 °C in inert atmosphere. The LbL technique was applied to the modification of graphite felt (GF) electrodes. GF electrodes modified with ten bilayers of PEI-PAA(MWCNT) were tested in a vanadium redox flow battery, showing a net decrease in the charge and discharge overpotentials with respect to the unmodified graphite felt. Lower overpotentials for charge-discharge resulted in higher energy and voltage efficiencies for the battery with modified GF electrodes. Furthermore, cyclability of the system was tested and no fading was observed in the battery performance after one hundred cycles.

Direct deposition of multi-walled carbon nanotubes onto stainless steel and YEF foils using a simple electrophoretic deposition for electrochemical capacitor electrode

Metals including metal alloys have been widely used as current collector in energy storage devices. Many papers reported the direct deposition of carbon materials like multi-walled carbon nanotube (MWCNT) onto aluminum or copper or stainless steel foils. However, it is important to note that the study of YEF 50, an engineering iron alloy and high performance stainless steel SUS 310S as current collector is very limited. This manuscript discusses the usage of electrophoretic deposition technique using the MWCNT colloids in isopropyl alcohol electrolyte during the direct deposition. Other than CNT characterization using several analytical techniques, electrochemical analyses confirmed the excellent capacitive performance of MWCNT electrode with the evidence of small internal resistance. From cyclic voltammetry measurement at 1 mV s−1, a relatively high specific gravimetric capacitance of 124 F g−1 and 89 F g−1 for YEF 50 and SUS 310S, respectively were obtained. Other than the intrinsic properties of the CNTs, the excellent capacitance is attributed to the polyvinyl alcohol react as adhesive material between MWCNT and the surface of conductive substrate.

Study on interfacial and mechanical improvement of carbon fiber/epoxy composites by depositing multi-walled carbon nanotubes on fibers

To improve the interfacial properties between carbon fiber (CF) and epoxy resin (EP), T300 carbon fibers were coated with multi-walled carbon nanotubes (MWCNTs) using aqueous suspension deposition method. The carbon fiber/epoxy laminated composites were prepared by molding process. The wettability and interfacial properties between MWCNTs deposited carbon fibers (MWCNTs-T300) and EP were studied. The mechanical properties of carbon fiber/epoxy laminated composites were tested, and the mechanism of the interface strengthening was discussed. The results show that the surface energy of T300 carbon fiber is obviously increased after MWCNT deposition. The contact angle between MWCNTs-T300 and EP is reduced, and the interfacial energy and adhesion work are greatly improved. The MWCNTs-T300/EP laminated composites have excellent mechanical properties, the flexural strength is 822 MPa, the tensile strength is 841 MPa, and the interlaminar shear strength (ILSS) is 25.68 MPa, which are increased by 15.1%, 17.6% and 12.6% compared with those of the original carbon fiber/EP laminated composites (original T300/EP) respectively. The MWCNTs-T300/EP composites have good interface bonding performance, low porosity and uniform fiber distribution. Interfacial friction and resin toughening are the main mechanisms for the interface enhancement of MWCNTs-T300/EP composites.

Voltage-Controlled Spray Deposition of Multiwalled Carbon Nanotubes on Semiconducting and Insulating Substrates

A facile, cost-effective, voltage-controlled, “single-step” method for spray deposition of surfactant-assisted dispersed carbon nanotube (CNT) thin films on semiconducting and insulating substrates has been developed. The fabrication strategy enables direct deposition and adhesion of CNT films on target samples, eliminating the need for substrate surface functionalization with organosilane binder agents or metal layer coatings. Spray coating experiments on four types of sample [bare silicon (Si), microscopy-grade glass samples, silicon dioxide (SiO2), and polymethyl methacrylate (PMMA)] under optimized control parameters produced films with thickness ranging from 40 nm to 6 μm with substantial surface coverage and packing density. These unique deposition results on both semiconducting and insulator target samples suggest potential applications of this technique in CNT thin-film transistors with different gate dielectrics, bendable electronics, and novel CNT-based sensing devices, and bodes well for further investigation into thin-film coatings of various inorganic, organic, and hybrid nanomaterials on different types of substrate.

Enhanced interfacial, electrical, and flexural properties of polyphenylene sulfide composites filled with carbon fibers modified by electrophoretic surface deposition of multi-walled carbon nanotubes

Electrophoresis can be an effective approach for depositing carbon nanotubes (CNTs) on the surface of carbon fiber (CF). Nevertheless, it has been rarely reported on polyphenylene sulfide (PPS) composites filled with CFs surface-modified by CNTs based on electrophoresis. In this study, we investigated the electrophoresis process conditions that can completely coat CF with multi-walled CNTs (MWCNTs) using self-manufactured electrophoresis equipment, and the enhancement of interfacial, electrical and flexural properties of PPS composites by introducing CFs coated with MWCNTs based on electrophoresis. In particular, interfacial shear strength (IFSS) of the PPS composites was measured by microbond tests and improved by about 41.7% due to the MWCNTs introduced on the surface of CFs. These enhancements were theoretically explained by an interface-modified CF-based micromechanical model. Introducing MWCNTs on the CF surface based on electrophoresis was demonstrated to be an effective method for improving the interfacial, electrical and flexural properties of PPS composites.

Formation of Multiwall Carbon Nanotubes on Cylindrical Substrates in Synthesis by Metal-Organic Chemical Vapor Deposition

Processes of deposition of multiwall carbon nanotubes in the synthesis by metal-organic chemical vapor deposition on hollow cylindrical substrates and the effect of the substrate area on the yield of the target product were studied. Making larger the tubular deposition reactor and the area of the cylindrical substrate enabled a substantial increase in the yield of carbon nanotubes. The technological synthesis parameters of the carbon material were optimized. Methods were developed for purification of carbon nanotubes by annealing in air, and materials were obtained with purity of no less than 98%. Physicochemical analysis methods were used to examine the structure and properties of the materials.

Ultrasound-spray deposition of multi-walled carbon nanotubes on NiO nanoparticles-embedded perovskite layers for high-performance carbon-based perovskite solar cells

Carbon-based perovskite solar cells (C-PSCs) are prized for their simple device structure, high cost-efficiency and good stability. However, the absolute efficiency of C-PSCs is still low due to inappropriate C/perovskite interfaces. Herein, we report a simple ultrasound spray method to deposit pure multi-walled carbon nanotubes (MWCNT) films. When directly deposited on perovskite films, MWCNT could form a seamless contact at the perovskite/carbon interface, thus boosting the power-conversion efficiency (PCE) of C-PSCs to 14.07% as compared to drop cast MWCNT electrodes. In addition, when the perovskite surface was embedded with a sub-monolayer of nickel oxide nanoparticles (NiO NPs) prior to the MWCNT deposition, we achieved a champion efficiency as high as 15.80%, which is among the highest C-PSCs efficiencies reported to date. Detailed characterizations revealed that by planting NiO NPs into the surface region of CH3NH3PbI3 crystals, the hole extraction efficiency was effectively enhanced and interfacial recombination was reduced. With silicon dioxide (SiO2 NPs) as a control, the NiO NPs layer was found to favorably bend the energy levels at the interface for selective hole extraction, thereby enhancing the overall photovoltaic performance. The combination of ultrasound spray and nanoparticle embedment technologies opens the way to cost-efficient and scalable production of C-PSCs.

Fabrication and characterisation of novel ZnO/MWCNT duplex coating deposited on Mg alloy by PVD coupled with dip-coating techniques

Zinc oxide (ZnO)/multi-walled carbon nanotube (MWCNT) duplex coating was synthesized on Mg-0.8Ca-3Zn alloy by physical vapour deposition (PVD) combined with dip coating. The ZnO inner layer was 1.1 μm thick and consisted of spherical nanoparticles. The outer layer of the MWCNTs was 10.2 μm thick, the diameter of the raw MWCNTs was approximately 42 nm, and their lengths were around a few microns. The ZnO/MWCNT duplex coating showed higher compressive strength than the single-layer coated ZnO and bare Mg alloy after immersion in simulated body fluid (SBF) solution. Polarisation and electrochemical impedance spectroscopy tests revealed that the ZnO/MWCNT duplex coating has lower corrosion current (icorr = 7.2 μA/cm2) and higher charge transfer resistance (Rt = 5250 Ω cm2) than the ZnO single-layer coated (Rt = 3420 Ω cm2; icorr = 42.3 μA/cm2) and bare Mg alloy (Rt = 1720 Ω cm2; icorr = 205.4 μA/cm2). In the immersion test, the ZnO/MWCNT duplex coating protected the substrate effectively in the SBF solution, while moderate to serious damage in this electrolyte was observed on the surface of the ZnO-coated and bare samples, respectively. The results indicated that the deposition of MWCNTs as the outer layer and ZnO as the inner layer on the surface of bare Mg alloy sample is a promising technique to enhance its corrosion resistance.

Performance of Platinum Nanoparticles / Multiwalled Carbon Nanotubes / Bacterial Cellulose Composite as Anode Catalyst for Proton Exchange Membrane Fuel Cells

Highly dispersed platinum (Pt) nanoparticles / multiwalled carbon nanotubes (MWCNTs) on bacterial cellulose (BC) as anode catalysts for proton exchange membrane fuel cells (PEMFC) were prepared with various precursors and their electro-catalytic activities towards hydrogen oxidation at 70 oC under non-humidified conditions. The composite was prepared by deposition of Pt nanoparticles and MWCNTs on BC gel by impregnation method using a water solution of metal precursors and MWCNTs followed by reducing reaction using a hydrogen gas. The composite was characterized by using TEM (transmission electron microscopy), EDS (energy dispersive spectroscopy), and XRD (X-ray diffractometry) techniques. TEM images and XRD patterns both lead to the observation of spherical metallic Pt nanoparticles with mean diameter of 3-11 nm well impregnated into the BC fibrils. Preliminary tests on a single cell indicate that renewable BC is a good prospect to be explored as a membrane in fuel cell field.

Transport of multi-walled carbon nanotubes stabilized by carboxymethyl cellulose and starch in saturated porous media: Influences of electrolyte, clay and humic acid

This study investigated the transport behaviors of carboxymethyl cellulose (CMC) and starch stabilized multi-walled carbon nanotubes (MWNTs) through a saturated quartz sand column in the presence of electrolytes, model clays, and natural organic matter (humic acid) through column breakthrough experiments and model simulations. Both stabilizers, CMC and starch, greatly enhanced the breakthrough of MWNTs, with a full breakthrough plateau (C/C0) ranging from 0.69 to 0.90 at ionic strength from 0.3 to 10mM. Between the two stabilizers, CMC was more effective in resisting particle deposition, and thus CMC-stabilized MWNTs were more transportable through the medium. While non-stabilized MWNTs were much less transportable and were vulnerable to electrolyte effects (especially Ca2+), the stabilized counterparts were much more resistant to the coagulation effects of electrolytes. The presence of colloidal clay particles showed contrasting effects on the transport of bare and stabilized MWNTs. The full breakthrough C/C0 of bare MWNTs was suppressed by kaolinite and montmorillonite particles from 0.33 to <0.15 with 5mg/L clay, indicating that the presence of both clays enhanced the aggregation and deposition of MWNTs. However, kaolinite particles facilitated the transport of stabilized-MWNTs, while montmorillonite weakened the breakthrough of stabilized MWNTs. Humic acid had less effect on the mobility of stabilized-MWNTs than that of bare MWNTs. The advection-dispersion transport model incorporated with the filtration theory was able to simulate the breakthrough curves and quantitatively interpret the particle deposition. The results can facilitate our understanding of fate and transport of stabilized carbon nanotubes in the environment.