Layer Of Multi-walled Carbon Nanotubes Research Articles

A nanocellulose-based flexible multilayer sensor with high sensitivity to humidity and strain response for detecting human motion and respiration

Biomass-based flexible sensors with excellent mechanical and sensing properties have attracted significant attention. In this study, based on the excellent dispersibility and degradability of nanocellulose crystals, we designed a polyvinyl alcohol/nanocellulose crystals/phytic acid (PCP) composite film with good flexibility and high sensitivity to humidity. A layer of multiwalled carbon nanotubes (MWCNT) and nanocellulose crystals (CNC) was further sandwiched between two PCP layers as a flexible multifunctional sensor (PCPW) to detect human movement and respiration. Phytic acid contains abundant phosphate groups that enhance proton conduction, allowing the PCPW composite film to change its electrical resistance in a sensitive and repeatable manner when the relative humidity was varied between 35 %–93 %. Meanwhile, CNC derived from sisal fibers enhanced the PCPW sensor's conductivity (3.3 S/m) and mechanical properties (elongation at break: 99 %) by improving the dispersion and connectivity of MWCNT. The PCPW sensor displayed a high sensitivity to strain (gauge factor: 49.5) and could monitor both facial expressions (smiling and winking) and the bending of joints. The sensor also generated stable electrical responses during breathing and blowing due to the change in humidity. Therefore, this biodegradable and multifunctional sensor has good application prospects.

Analysis of coated samples containing hydroxyapatite/multiwalled carbon nanotubes on 2205 DSS substrate

For biomedical applications, hydroxyapatite and carbon nanotubes are currently being applied over duplex stainless steel (DSS) alone in order to increase corrosion resistance and biocompatibility. A composite of hydroxyapatite and multi-walled carbon nanotubes was used to improve biocompatibility, osseointegration, and corrosion resistance on 2205 DSS using electrophoretic deposition. The study investigates the effects of potential and time on the properties of the deposited layer in order to determine electrophoretic deposition factor values that are appropriate. The coating properties and effective groups of the phase resulting from this process are determined by Fourier transform infrared spectroscopy and X-ray diffraction. The antibacterial properties of E. coli bacterial strains are investigated for the coated layer. The adhesion between the hydroxyapatite and multi-walled carbon nanotube layers on the 2205 duplex stainless steel substrate was qualitatively evaluated using the adhesive tape test. It was found that the optimal suspension, which consists of 65 weight percent hydrogen acetate and 35 weight percent multi-walled carbon nanotubes, had a homogeneous morphology, a thick structure, and no cracks when coated at 50 V for two minutes.

Self-Assembly of Multiwalled Carbon Nanotubes on a Silicone Rubber Foam Skeleton for Durable Piezoresistive Sensors.

Conductive nanomaterial/flexible polymer composite foams are of great interest in the field of flexible and wearable piezoresistive pressure sensors. However, the existing composite foam sensors are faced with stability issues from conductive nanomaterials, which tends to decrease their long-term durability. Herein, we developed a solvent evaporation-induced self-assembly strategy, which could significantly improve the stability of multiwalled carbon nanotubes (MWCNTs) on a silicone rubber foam skeleton. The process for self-assembly of MWCNTs was straightforward. Aqueous MWCNT dispersion droplets were first hierarchically enclosed in silicone rubber via water-in-oil (W/O) Pickering high internal phase emulsions (HIPEs). Then, the high pressure generated by fast evaporation of the solvent from the droplets could break the thinnest pore walls to form interconnected pores. As a result, very dense and firm MWCNT layers were self-assembled on the pore wall surface. Due to the excellent stability of MWCNTs and tetramodal interconnected porosity, our MWCNTs/silicone rubber composite foam showed the following "super" properties: low density of 0.26 g/mL, high porosity of 76%, and excellent mechanical strength (the maximum stress loss of 8.3% at 80% strain after 100 compression cycles). In addition, excellent piezoresistive performance, including superior discernibility for different amplitudes of compressive strain (up to 80%), rapid response time (150 ms), and high sensitivity (gauge factor of 1.44), was demonstrated for such foams, together with prominent durability (39,000 compression cycles at 60% strain in air) and excellent stability of resistance response in water and organic solvents (5000 compression cycles at 30% strain in water and ethanol). Regarding its application, a wearable piezoresistive sensor, which was assembled from the as-prepared conductive silicone rubber composite foam, could capture various movements from tiptoeing and finger bending to small deformations resulting from human pulse.

Treatment of Multi-Walled Carbon Nanotubes with Dichromic Acid: Oxidation and Appearance of Intercalation.

This work is dedicated to the study of the treatment of multi-walled carbon nanotubes (MWCNTs) with dichromic acid. The dichromic acid was formed by dissolving different concentrations of CrO3 in water. The effect of the concentration of dichromic acid on the change in texture characteristics, elemental composition, defectiveness, graphitization degree, and surface chemistry of MWCNTs was investigated using various analytical techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Testing of MWCNTs as electrodes for supercapacitors in 3.5 M H2SO4 solution was carried out using cyclic voltammetry. A decrease in the average diameter of CNTs after treatment was found. The EDX and XPS showed that the oxygen content on the surface of MWCNTs increased after treatment with dichromic acid. The formation of Cr2O3 after treatment with dichromic acid was detected by XPS. High angle annular dark field scanning transmission electron microscopy was used to confirm the intercalation of the chromium-containing compound between graphene layers of MWCNTs after treatment with dichromic acid. It was found that two different types of MWCNTs showed diverse behavior after treatment. The highest specific capacitance of the MWCNTs after treatment was 141 F g-1 (at 2 mV s-1) compared to 0.3 F g-1 for the untreated sample.

Carbon nanotube-based double-layer microporous cathode for micro-direct methanol fuel cell

The micro-direct methanol fuel cell (μDMFC) has the advantages of high energy density, high conversion efficiency, and simple structure, which brought vast application prospects in portable devices. However, some shortcomings still exist, such as low catalyst utilization and power density. This paper proposes a new cathode electrode structure for the μDMFC. The structure consists of a multi-walled carbon nanotube layer and a cathode double microporous layer (CD-MPL) prepared from carbon powder. The outer microporous layer (OMPL) is composed of multi-walled carbon nanotubes (MWCNTs), Nafion solution, and carbon powder, and the inner microporous layer (IMPL) is composed of carbon powder and polytetrafluoroethylene (PTFE). The experimental results show that the maximum power density of the μDMFC with a CD-MPL (CD-μDMFC) is 42.8 mW/cm2, which is 31.6% higher than that of the μDMFC with a cathode single microporous layer (CS-μDMFC). The pore size distribution of the OMPL of the CNT is measured by the mercury intrusion method. It can be seen that the distribution of pore size is wider and there are more pores with larger pore sizes, which are more conducive to the utilization of catalysts. The discharge experiment of the cell shows that the CD-μDMFC shows high discharge performance and fuel utilization at different concentrations. The double microporous layer (MPL) structure increases the porosity and pore range, broadens the three-phase interface for the reaction, and allows the catalyst to have more attachment sites. The existence of MWCNTs improves the conductivity and mass transfer capacity of the cathode.

Thermally conductive MWCNTs/Fe3O4/Ti3C2T MXene multi-layer films for broadband electromagnetic interference shielding

• MWCNTs/Fe 3 O 4 /Ti 3 C 2 T x MXene composite film with multi-layer architecture was fabricated by a facile method. • The obtained composite film exhibited high comprehensive performance, including high thermal conduction property and broadband EMI shielding property. • The EMI shielding mechanism of the composite film was comprehensively disclosed. The Ti 3 C 2 T x MXene is thought to be a promising candidate for next-generation electromagnetic interference (EMI) shielding materials. However, its broadband shielding capability and thermal conduction performance are insufficient to meet the growing demands. Herein, we reported a layer-by-layer composite film composed of Ti 3 C 2 T x MXene, multi-walled carbon nanotubes (MWCNTs), and Fe 3 O 4 nanoparticles. Benefitting from the architecture and the synergistic effect of components, the obtained composite film exhibited high comprehensive performance. Specifically, the introduction of Fe 3 O 4 magnetic nanoparticles effectively reduced the impedance mismatch between the composite film and air and enhanced the magnetic loss of the composite film. The layered structure prolonged the transmission path of electromagnetic waves inside the composite film and constructed a rich conductive network, causing interfacial polarization and ohmic loss. The results indicated that the composite film (52 μm) delivered a high EMI shielding effectiveness of 49 dB in the frequency range from X-band to K u -band. Furthermore, the MWCNTs layers in the composite films provided numerous heat transfer channels, reducing phonon scattering during heat transfer and resulting in a maximum thermal conductivity of 8.241 W/(m K).

Efficient stacking of glucose/oxygen microfluidic biofuel cells using a single-streamflow channel

The stacking of microfluidic enzymatic biofuel cells (EBFCs) is a lucrative approach to achieve the targeted power requirements of microelectronic devices. Co-laminar flow based microfluidic EBFCs favour easy and cost-effective microfabrication owing to membrane-less architecture. However, stacking of these unit cells in large number is inefficient due to cross-mixing issues, especially in the cells located downstream of the stack. In this article, we present two-dimensional stacking of four single-streamflow-based EBFCs in a cascade-style serpentine-shaped microfluidic channel. A novel attribute of the device is the identical fuel utilisation in all cells due to mixed single electrolyte stream, which results in stable connection efficiencies. In addition, a novel composite material was used as an air-breathing biocathode implementing the cathodic enzyme covalently immobilised onto carboxyl multiwalled carbon nanotubes (MWCNTs). Negatively charged carboxyl MWCNTs were conformally attached to the highly porous structure of Toray carbon paper (TCP) using positively charged polyethyleneimine (PEI) by electrostatic layer-by-layer (LBL) deposition. At the bioanode, the enzyme and mediator were immobilised on the MWCNTs by a cross-linking method. The experimental results showed that enzyme immobilisation increased proportionally with the number of PEI/MWCNTs bilayers on TCP. When the bioelectrode was analysed individually with five layers of MWCNTs via cyclic voltammetry (CV), the catalytic performance was increased by 4.4-fold. Moreover, the unit cells in the microfluidic stacking device were connected in various configurations i.e., all in series, all in parallel, and series/parallel combined configuration. The connection efficiencies obtained for all the configurations were stable, thereby validating the potential of stacking single-stream microfluidic EBFCs in large number to satisfy the power requirements of small-scale electronic devices.

Assessment of commercialized nylon membranes integrated with thin layer of MWCNTs for potential use in desalination process

In this work, multi-walled carbon nanotubes (MWCNTs) will be implemented as a coating material on commercial membranes (nylon) using Trix as a surfactant. Four masses of MWCNTs (5, 15, 30, and 60 mg) were used in the coating process. Many parameters were measured for both nylon and the four coated membranes. These parameters include their electrical properties, wettability, mechanical properties, surface and textural properties, permeability and rejection of salt. The findings indicated that Elongation within the range of 2.7–18%, tensile strength within the range of 2.5–3.4 MPa, and Young's moduli in the range of 63–154 MPa were found in the fabricated membranes arising from MWCNTs and surfactants dispersions. The performance of membrane rejection was examined using NaCl or MgSO4 single salts. The fabricated membrane containing 60 mg of MWCNTs, on the other hand, can reject electrolytes with a very low rejection ratio of less than 14% for NaCl and 10% for MgSO4. This made as ultrafiltration (UF) membranes, and therefore they can be used as pre-treatment membranes in desalination processes. Future study is required to improve the rejection of these coated membranes by adding more additives such as polymers or biopolymers.

Binder-Free MnO2/MWCNT/Al Electrodes for Supercapacitors.

Recently, significant progress has been made in the performance of supercapacitors through the development of composite electrodes that combine various charge storage mechanisms. A new method for preparing composite binder-free MnO2/MWCNT/Al electrodes for supercapacitors is proposed. The method is based on the original technique of direct growth of layers of multi-walled carbon nanotubes (MWCNTs) on aluminum foil by the catalytic pyrolysis of ethanol vapor. Binder-free MnO2/MWCNT/Al electrodes for electrochemical supercapacitors were obtained by simply treating MWCNT/Al samples with an aqueous solution of KMnO4 under mild conditions. The optimal conditions for the preparation of MnO2/MWCNT/Al electrodes were found. The treatment of MWCNT/Al samples in a 1% KMnO4 aqueous solution for 40 min increased the specific capacitance of the active material of the samples by a factor of 3, up to 100–120 F/g. At the same time, excellent adhesion and electrical contact of the working material to the aluminum substrate were maintained. The properties of the MnO2/MWCNT/Al samples were studied by electron probe microanalysis (EPMA), Raman spectroscopy, cyclic voltammetry (CV), and impedance spectroscopy. Excellent charge/discharge characteristics of composite electrodes were demonstrated. The obtained MnO2/MWCNT/Al electrodes maintained excellent stability to multiple charge-discharge cycles. After 60,000 CVs, the capacitance loss was less than 20%. Thus, this work opens up new possibilities for using the MWCNT/Al material obtained by direct deposition of carbon nanotubes on aluminum foil for the fabrication of composite binder-free electrodes of supercapacitors.

Fabrication and characterization study of ultrathin multi‐walled carbon nanotubes/polydimethylsiloxane composite membranes for strain sensing application

AbstractConductive polymer composite membranes such as multi‐walled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) membranes are important for flexible strain sensors. However, ultra‐thin MWCNTs/PDMS films (<20 μm) have rarely been studied, mainly due to inherent difficulties in fabricating processes such as the peeling and transferring. In this work, the filtration‐from‐suspension (FFS) method was used to fabricate ultra‐thin layer of MWCNTs (buckypapers, BPs). Subsequently, spin‐coating PDMS on the BPs was carried out, and the penetration of PDMS into BPs was promoted under vacuum conditions to obtain the MWCNTs/PDMS composite films. The elastic nature of PDMS assisted in peeling the composite films off the filter papers. Compared with the other methods, the fabrication method of MWCNTs/PDMS membranes in this paper is more time‐efficient and reliable. A comprehensive study on the fabricated MWCNTs/PDMS membranes with different compositions was carried to understand the mechanical and electrical performance under static and cyclic loading conditions. The obtained stress–strain and resistance‐strain curves show that the modulus of the MWCNTs/PDMS membrane can be significantly increased over 8–10 times compared with pure PDMS membranes. The near exponential relationship between the resistance change versus the strain implies the MWCNTs/PDMS membranes are suitable for strain sensors. Moreover, we find there is a stability transition point in thickness at which the MWCNTs/PDMS composite membrane exhibits the best overall integrated performance. At this point, the changes before and after cyclic loading/unloading on composite membranes is almost negligible, implying the good reliability of the sensing membranes. This study has demonstrated the feasibility of fabricating ultrathin MWCNTs/PDMS membranes for wearable sensors.

Erosion resistance of ethylene propylene diene monomer insulations reinforced with precoated multi-walled carbon nanotubes

Condensed particles in the internal flow field of a solid rocket motor can cause serious erosion to thermal insulations under overload flight condition. Multi-walled carbon nanotubes (MWCNTs) can improve erosion resistance of insulations but at the cost of reduced thermal insulation performance. In this study, MWCNTs were precoated with pyrolytic carbon via chemical vapor deposition to reduce their thermal conductivity. Further, ethylene propylene diene monomer insulations reinforced with different contents of MWCNTs and precoated MWCNTs were prepared. Moreover, their ablation performances under simulated overload ablation conditions were tested and compared. Experimental results show that precoated MWCNTs can not only improve thermal insulation performance but also significantly increase particle erosion resistance of ethylene propylene diene monomer insulation materials. Charring ablation rate of the formula with 10phr precoated MWCNTs is 44.3% lower than that of basic formula and 41.6% lower than that of the formula with 3phr MWCNTs which has the same pure MWCNTs content. The char layers of MWCNTs reinforced formulas are more complete than basic formula, indicating that MWCNTs can improve char layer structure under particle erosion condition. The precoated MWCNTs can also promote the CVD reaction of pyrolysis gas in char layers during ablation, decreasing the porosity of char layers, which can increase the particle erosion resistance of insulation.

TEMPO-Functionalized Carbon Nanotubes for Solid-Contact Ion-Selective Electrodes with Largely Improved Potential Reproducibility and Stability.

Solid-contact ion-selective electrodes (SCISEs) can overcome essential limitations of their counterparts based on liquid contacts. However, attaining a highly reproducible and predictable E0, especially between different fabrication batches, turned out to be difficult even with the most established solid-contact materials, i.e., conducting polymers and large-surface-area conducting materials (e.g., carbon nanotubes), that otherwise possess excellent potential stability. An appropriate batch-to-batch E0 reproducibility of SCISEs besides aiding the rapid quality control of the electrode manufacturing process is at the core of their “calibration-free” application, which is perhaps the last major challenge for their routine use as single-use “disposable” or wearable potentiometric sensors. Therefore, here, we propose a new class of solid-contact material based on the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with a chemically stable redox molecule, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This material combines the advantages of (i) the large double-layer capacitance of MWCNT layers, (ii) the adjustable redox couple ratio provided by the TEMPO moiety, (iii) the covalent confinement of the redox couple, and (iv) the hydrophobicity of the components to achieve the potential reproducibility and stability for demanding applications. The TEMPO-MWCNT-based SC potassium ion-selective electrodes (K+-SCISEs) showed excellent analytical performance and potential stability with no sign of an aqueous layer formation beneath the ion-selective membrane nor sensitivity toward O2, CO2, and light. A major convenience of the fabrication procedure is the E0 adjustment of the K+-SCISEs by the polarization of the TEMPO-MWCNT suspension prior to its use as solid contact. While most E0 reproducibility studies are limited to a single fabrication batch of SCISEs, the use of prepolarized TEMPO-MWCNT resulted also in an outstanding batch-to-batch potential reproducibility. We were also able to overcome the hydration-related potential drifts for the use of SCISEs without prior conditioning and to feature application for accurate K+ measurements in undiluted blood serum.

All-Solid-State Potentiometric Platforms Modified with a Multi-Walled Carbon Nanotubes for Fluoxetine Determination.

Novel cost-effective screen-printed potentiometric platforms for simple, fast, and accurate assessment of Fluoxetine (FLX) were designed and characterized. The potentiometric platforms integrate both the FLX sensor and the reference Ag/AgCl electrode. The sensors were based on the use of 4′-nitrobenzo-15-crown-5 (ionophore I), dibenzo-18-crown-6 (ionophore II), and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) (ionophore III) as neutral carriers within a plasticized PVC matrix. Multiwalled carbon nanotubes (MWCNTs) were used as a lipophilic ion-to-electron transducing material and sodium tetrakis [3,5-bis(trifluoromethyl)phenyl] borate (NaTFPB) was used as an anionic excluder. The presented platforms revealed near-Nernstian potentiometric response with slopes of 56.2 ± 0.8, 56.3 ± 1.7 and 64.4 ± 0.2 mV/decade and detection limits of 5.2 × 10−6, 4.7 × 10−6 and 2.0 × 10−7 M in 10 mM Tris buffer solution, pH 7 for sensors based on ionophore I, II, and III, respectively. All measurements were carried out in 10 mM tris buffer solution at pH 7.0. The interfacial capacitance before and after insertion of the MWCNTs layer was evaluated for the presented sensors using the reverse-current chronopotentiometry. The sensors were introduced for successful determination of FLX drug in different pharmaceutical dosage forms. The results were compared with those obtained by the standard HPLC method. Recovery values were calculated after spiking fixed concentrations of FLX in different serum samples. The presented platforms can be potentially manufacturable at large scales and provide a portable, rapid, disposable, and cost-effective analytical tool for measuring FLX.

Influence of conductive porous electrodes on the apparent electrode kinetics of fenitrothion

• FT’s cyclic voltammetry response at planar and porous modified electrode is simulated. • Simulations reveal the occurrence of thin-layer effects at porous modified electrode. • Cyclic voltammetry experiment validates the simulation results. Planar bare electrodes fabricated with surface-modified multiwalled carbon nanotubes (MWCNT) are used to detect organophosphate (OP) compounds, which are used as herbicides and fungicides but are harmful to human health. Deposition of carbon nanotubes on the surfaces of bare electrodes enhances electrocatalysis, increasing the electrode to analyte current response and narrowing peak-to-peak potential separation during cyclic voltammetry (CV). We hypothesize that, as the thickness of the deposited MWCNT layer decreases, Fenitrothion (FT, an OP) mass transport between the layers of porous multiwalled carbon nanotubes changes from semi-infinite to thin-layer diffusion. This influences the electrode electrochemical response to the analyte. Using simulations and experiments, we show that when porous MWCNT are deposited on a conductive glassy carbon electrode the mass transport of FT changes from semi-infinite to thin-layer diffusion during CV. This alters the electrochemical response of the electrode and reduces peak-to-peak potential separation. To simulate CV response to multi-step and multi-electron electrochemical reactions of FT, both the semi-infinite and thin-layer diffusion models are employed for the planar bare and modified porous surface electrodes. The transition from thin layer to semi-infinite diffusion is clear when the nanotube layer thickness on the bare electrode increases. The model is applicable to other toxic chemicals, such as 4-nitrophenol, parathion, or methyl parathion that have similar electrode kinetics.

Multi-walled carbon nanotubes growth by chemical vapour deposition: Effect of precursor flowing path and catalyst size

Carbon nanomaterials have been found to have promising performance in various applications. However, the complexity and high operation cost during the fabrication still limit the mass production. In this study, multi-walled carbon nanotubes (MWCNTs) were grown on nickel oxide (NiO) via chemical vapour deposition (CVD) with ethanol as the carbon precursor. The NiO catalyst was fabricated from a nickel nitrate – ethanol mixture. The particle size of NiO was altered through high-energy ball milling for 0, 4, and 7 h. The influence of precursor flowing path (D) and NiO catalyst size during the MWCNTs growth have been investigated. The Raman spectra showed that the crystallite size of MWCNTs (L a ) increased from 16.97 to 18.00 nm as the NiO milling time increased. Furthermore, NiO-catalysed MWCNTs at D = 12 cm achieved the highest carbon yield (80.54%), with an I D /I G ratio of 1.134. Also, SEM and TEM revealed that the larger size of NiO catalyst produced fewer layers of MWCNTs. These findings are significant to aid researchers and manufacturers in optimising the CVD process towards large-scale MWCNTs fabrication.

Vanadium telluride nanoparticles on MWCNTs prepared by successive ionic layer adsorption and reaction for solid-state supercapacitor

Anchoring of vanadium telluride (VxTey) nanoparticles onto the exterior layer of multi-walled carbon nanotubes (MWCNTs) has been successfully employed at room temperature (300 K) as first report by using successive ionic layer adsorption and reaction (SILAR) to yield VxTey/MWCNTs surface architecture. Mutualistic contribution from ion insertion/extraction introduced non-stoichiometric vanadium telluride with electric double-layer involved MWCNTs have been unified to enrich excellent electrochemical performance. Three-electrode system configured VxTey/MWCNTs electrode yields 16-fold enhancement in specific capacitance compared to the bare MWCNTs electrode. Achieved performance forced us to construct flexible solid-state supercapacitor device (FSS-SC). Symmetric electrode embedded with PVA-LiClO4 gel mediator harvests remarkable 2 V voltage window to gain 34.5 Wh/kg energy density and 0.7 kW/kg power density. Cycling over 10000 replications confirms the pronounced (82.5 %) stability of designed device and growing LED enables practical evidence; demonstrating its capacity as efficient energy storage device. Correlated density functional theory (DFT) has been manifested to confirm synergistic interactions between the VxTey and MWCNTs, and a corresponding enhancement in the electron density at the Fermi level of VxTey/MWCNTs describes the insight origin for enhanced supercapacitance.

Simple technique of multiwalled carbon nanotubes growth on aluminum foil for supercapacitors

A promising method for the direct growth of multiwalled carbon nanotubes (MWCNTs) on aluminum foil for supercapacitor electrodes has been developed. Mild oxidation of aluminum foil in a nickel nitrate solution was used to give catalytic properties to aluminum. After the treatment, the detected concentration of nickel in the surface layer of the aluminum foil was 20 wt%. Low-temperature deposition of MWCNTs was carried out by catalytic pyrolysis of ethanol vapor using liquid ethanol as the only precursor. The resulting MWCNTs layers had excellent adhesion to aluminum foil. A symmetrical two-electrode cell as well as a classical three-electrode cell, were used for electrochemical testing of the obtained materials. The cell with MWCNTs/Al foil electrodes exhibits the behavior of an electric double layer capacitor (EDLC). The specific capacity of the MWCNTs reaches 60F/g. This result is comparable to the characteristics of similar materials obtained by other methods. Excellent resistance to multiple charge–discharge cycles is also shown.

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.

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.