Graphene Multi-walled Carbon Nanotubes Research Articles

A novel electrochemical biosensor as an efficient electronic device for impedimetric and amperometric quantification of the pneumococcus

In this artice, we are going to report results of a study in which with the help of layer-by-layer modification of a glassy carbon electrode (GCE), a novel biosensor was fabricated whose impedimetric and amperometric responses were correlated with the number of pneumococcus (P). The GCE was modified by graphene-multiwalled carbon nanotubes (Gr-MWCNTs)/chitosan-1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (CS-IL)/gold‑lead nanoparticles (AuPb NPs)/DNA-[FAM]CGC AAT CTA GCA GAT GAA GCA GGA AAA AAA AAA [Thiol] (DNA-Q-S). All the modification layers were characterized by microscopic and electrochemical techniques which confirmed the successfulness of all of the modification steps. The charge transfer resistance of impedimetric response and current of amperometric response of the biosensor were correlated with the number of the Ps which helped us to develop a novel biosensing system for sensing the Ps whose performance was comparable with a reference method. Therefore, the biosensor can be suggested for clinical purposes as a fast, stable, simple, sensitive, selective, repeatable and reproducible electronic device.

Chloroaluminate Anion Intercalation in Graphene and Graphite: From Two-Dimensional Devices to Aluminum-Ion Batteries.

A rechargeable aluminum-ion battery based on chloroaluminate electrolytes has received intense attention due to the high abundance and chemical stability of aluminum. However, the fundamental intercalation processes and dynamics in these battery systems remain unresolved. Here, the energetics and dynamics of chloroaluminate ion intercalation in atomically thin single crystal graphite are investigated by fabricating mesoscopic devices for charge transport and operando optical microscopy. These mesoscopic measurements are compared to the high-performance rechargeable Al-based battery consisting of a few-layer graphene-multiwall carbon nanotube composite cathode. These composites exhibit a 60% capacity enhancement over pyrolytic graphite, while an ∼3-fold improvement in overall ion diffusivity is also obtained exhibiting ∼1% of those in atomically thin single crystals. Our results thus establish the distinction between intrinsic and ensemble electrochemical behavior in Al-based batteries and show that engineering ion transport in these devices can yet lead to vast improvements in battery performance.

Fabrication and Characterization of Physical and Mechanical Properties of Carbon Nanotubes-Graphene-Based Sandwich Composite Pressure Sensor.

In this work, piezoresistive properties of graphene-multiwalled carbon nanotubes (MWCNTs) composites are investigated, characterized, and compared. Sandwich-type composite piezoresistive pressure-sensitive sensors (Ag/Graphene-MWCNT/Ag) with the same diameters, but different fabrication pressures and thicknesses were fabricated using the mortar and pestle/hydraulic press technique. To produce low-electrical-resistance contacts, both sides of the composite sensors were painted with silver (Ag) paste. All the sensors showed reductions in the direct current (DC) resistance ‘R’ with an increment in external uniaxial applied pressure. However, it was observed that higher fabrication pressure led to a lower resistance value of the composite, while the thicker samples give lower electrical conductivity and higher resistance than the thinner samples. The experimental data for all composite pressure sensors were in excellent agreement with the simulated results.

Novel Zn‐Fe LDH/MWCNTs and Graphene/MWCNTs Nanocomposites Based Potentiometric Sensors for Benzydamine Determination in Biological Fluids and Real Water Samples

AbstractTwo sensitive and selective potentiometric sensors based on zinc‐iron layered double hydroxides/multiwalled carbon nanotubes (Zn−Fe LDH/MWCNTs) (sensor I) and graphene/multiwalled carbon nanotubes (Gr/MWCNTs) (sensor II) nanocomposites were developed for benzydamine hydrochloride (Benz) determination. The investigated sensors displayed excellent Nernstian slopes 58.5±0.7 and 59.5±0.5 mV decade−1, detection limits 8.3×10−7 and 1.9×10−7 mol L−1, long lifetimes, adequate selectivity, high chemical, and thermal stability within pH range of 2.4–8.5 for sensors І and ІІ, respectively. The surface morphology of sensors was analyzed using a Transmission Electron Microscope (TEM). The analytical method was efficiently implemented for Benz determination in biological fluids and surface water samples.

Strongly coupled sulfur nanoparticles on graphene-carbon nanotube hybrid electrode for multifunctional sodium and aluminium ion storage

The practical utility of multiwalled carbon nanotubes in sodium and aluminium ion batteries are limited due to its low interlayer spacing of 0.34 nm. Herein, we have developed a simple approach of enhancing the interlayer spacing of multiwalled carbon nanotubes by incorporating sulfur nanoparticles into graphene-multiwalled carbon nanotube (GCNT) structure. This proof of concept is realised from its excellent specific capacity and cyclic stability for the first time in sodium and aluminium ion batteries. GCNT/S as the anode in sodium ion battery exhibits a specific capacity of about 510 mA h g−1 at a current density of 50 mA g−1 with a cyclic stability of 2500 cycles which results in about 42% enhancement in specific capacity when compared to GCNT. GCNT/S as cathode in aluminium ion battery shows a specific capacity of 507 mA h g−1 at a current density of 50 mA g−1 and a stable cyclic stability for 600 cycles. This is about 7.2 times enhancement in specific capacity when compared to GCNT. The highly durable nature is due to the small sulfur particles which offer low volume expansion and the GCNT structure acts as a buffer matrix for controlling the volume expansion. Our study provides a new and a simple strategy to enhance the specific capacity and cyclic stability of multiwalled carbon nanotubes for sodium ion batteries and aluminium ion batteries which can be a promising approach for other cost-effective battery technologies as well.

Facile morphology controllable synthesis of PtPd nanorods on graphene-multiwalled carbon nanotube hybrid support as efficient electrocatalysts for oxygen reduction reaction

One-dimensional (1D) anisotropic platinum-based nanorods are particularly attractive electrocatalysts for oxygen reduction reaction (ORR) owing to the inherent structural advantages. In this work, we report the growth of ultrathin PtPd alloy nanorods (3–4 nm) on Graphene-Multiwalled carbon nanotube (G–M) hybrid support via a facile surfactant-free and template-free method as the efficient electrocatalyst for ORR. The as-synthesized PtPd NRs/G–M catalyst exhibits more excellent activity and better durability toward ORR than Pt NRs/G and Pt NRs/G–M catalysts. Noteworthily, it shows an outstanding half-wave potential of 0.810 V and mass activity of 49.5 mA mg–1 at 0.85 V, which are 30 mV and 2.1 times higher than those of commercial 40 wt% Pt/C (JM40) catalyst, respectively. After the accelerated durability tests (ADTs), it also maintains superior stability than JM40. The superior performance is attributed to the combination of the advantageous 1D morphological motif and the synergistic effect with G–M support.

Facile fabrication of 3D graphene–multi walled carbon nanotubes network and its use as a platform for natamycin detection

In this work, a three dimensional graphene-multiwalled carbon nanotubes (3DG-MWCNTs) network is successfully fabricated on the surface of glassy carbon electrode (GCE) using pulse potential method (PPM) in a graphene oxide-multi walled carbon nanotubes (GO-MWCNTs) homogeneous dispersion. Scanning electron microscopy (SEM) images and electrochemical experiments confirmed the 3D structure of interpenetrated graphene-MWCNTs network and excellent electrochemical performance. The 3DG-MWCNTs network was presented to develop a sensitive voltammetric sensor for detection of natamycin. Systematic electrochemical tests demonstrate that the 3DG-MWCNTs network modified electrode can effectively increase response to the oxidation of natamycin due to the large accessible surface area as well as its excellent conductivity. Under optimized conditions, the voltammetric sensor showed a linear relationship in the range of 5.0 × 10−8–2.5 × 10−6 mol L−1 and a low detection limit of 1.0 × 10−8 mol L−1. Moreover, the proposed method was also applied for detection of natamycin content in real samples (commercial red wine and beverage).

Facile preparation of molecularly imprinted polypyrrole-graphene-multiwalled carbon nanotubes composite film modified electrode for rutin sensing

In this paper, a novel molecularly imprinted composite film modified electrode was presented for rutin (RT) detection. The modified electrode was fabricated by electropolymerization of pyrrole on a graphene-multiwalled carbon nanotubes composite (G-MWCNTs) coated glassy carbon electrode in the presence of RT. The netlike G-MWCNTs composite, prepared by in situ hydrothermal process, had high conductivity and electrocatalytic activity. At the resulting MIP/G-MWCNTs/GCE electrode RT could produce a sensitive anodic peak in pH 1.87 Britton-Robinson buffer solution. The factors affecting the electrochemical behavior and response of RT on the modified electrode were carefully investigated and optimized. Under the selected conditions, the linear response range of RT was 0.01–1.0μmolL−1 and the detection limit (S/N=3) was 5.0nmolL−1. The electrode was successfully applied to the determination of RT in buckwheat tea and orange juice samples, and the recoveries for standards added were 93.4–105%.

Electrochemical determination of carbamazepin in the presence of paracetamol using a carbon ionic liquid paste electrode modified with a three-dimensional graphene/MWCNT hybrid composite film

In this research work, a carbon ionic liquid paste electrode (CILPE) based on butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([bmim] NTF2) was fabricated and further modified with graphene/multiwall carbon nanotube (GR/MWCNT) hybrid composite. The modified electrode (GR/MWCNT/CILPE) was used for measurement of carbamazepine (CBZ) in the presence of paracetamol (PA) with an excellent electrochemical catalytic behavior. The application of the electrode was investigated by cyclic voltammetry and differential pulse voltammetry. The oxidation peak currents of CBZ and PA were linear at the ranges of 1–60μM and 2–80μM, respectively. Also, the detection limits for CBZ and PA were 0.233μM and 0.262μM, respectively. The proposed sensor was successfully applied for the determination of CBZ and PA in tablet and urine samples.

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L−1 for uric acid and 10.0 to 400.0 µmol L−1 for dopamine in the presence of 500 µmol L−1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L−1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.

Graphene-Multiwalled Carbon Nanotube Hybrids Synthesized by Gamma Radiations: Application as a Glucose Sensor

Three-dimensional hybrid nanomaterial of graphene-multiwalled carbon nanotubes (G-MWCNTs) was synthesized using gamma rays emitted by a60Co source with a dose rate of 3.95 Gy min−1. The products were characterized by fourier transform infrared (FTIR), ultraviolet-visible (UV-Vis), photoluminescence (PL), and micro-Raman spectroscopy, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). FTIR and UV-Vis analysis reveals the formation of hybrid nanomaterial which is confirmed by XRD, micro-Raman analysis, and PL. SEM micrograph depicts the composite structure of graphene layers and MWCNTs, while the TEM micrograph exhibits graphene layers covered by MWCNTs. The G-MWCNTs hybrid used as electrode for electrochemical studies in K3Fe(CN)6shows enhancement in electrocatalytic behavior, compared to each individual starting material, therefore, has been applied for amperometric sensing of glucose in alkaline solution and exhibits sensitivity of 12.5 μAmM-1 cm−2and low detection limit 1.45 μM (S/N=3) in a linear range of 0.1 to 14 mM (R2=0.985).

Platinum-decorated chemically modified reduced graphene oxide–multiwalled carbon nanotube sandwich composite as cathode catalyst for a proton exchange membrane fuel cell

Graphite oxide (GO) was chemically altered using polyethylene glycol (PEG) to produce functionalized GO (f-GO). An ensemble of reduced f-GO sheets and multiwalled carbon nanotubes (MWNTs), referred to as few-layer graphene–MWNT sandwiches (GCSs), were synthesized by a catalysis-assisted chemical vapor deposition (CCVD) method and explored as the electrocatalyst support material for oxygen reduction reaction (ORR) in a proton exchange membrane fuel cell (PEMFC). Platinum nanoparticles were decorated on the carbon supports by a modified glycol reduction technique. As-prepared electrocatalysts were characterized by Raman spectroscopy, X-ray diffraction and transmission electron microscopy. Electrocatalytic performance was evaluated by cyclic voltammetry and PEMFC fuel cell measurements and compared with a commercially available Pt/C electrocatalyst. The Pt/GCS electrocatalyst gave a maximum PEMFC performance of 495 mW cm−2 at 60 °C temperature. The improvement in the ORR activity was ascribed to the uniform dispersion of Pt nanoparticles with an optimal particle size (∼3.5 nm) over a well-organized conducting catalyst support.

Iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite-modified glassy carbon electrode for the sensitive determination of nitrite

In the present work, we described the preparation of iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite (GR-MWCNTs/FeNPs) modified glassy carbon electrode (GCE) and its application for the sensitive determination of nitrite. First, GR-MWCNTs/FeNPs nanocomposite has been prepared by a simple solution-based approach via chemical reduction and then it was characterized. Afterwards, GR-MWCNTs/FeNPs/GCE was prepared and employed for the electrocatalysis of nitrite. Electrocatalytic oxidation of nitrite at the GR-MWCNTs/FeNPs/GCE has been significantly improved in terms of both reduction in overpotential and increase in peak current. Therefore, the modified electrode was employed for amperometric determination of nitrite which exhibited excellent analytical parameters with wide linear range of 1 × 10−7 M to 1.68 × 10−3 M and very low detection limit of 75.6 (±1.3) nM. The proposed sensor selectively detects nitrite even in the presence of high concentration of common ions and biological interferrants. Good recoveries achieved for the determination of nitrite in various water samples reveal the promising practicality of the sensor. In addition, the sensor displays an acceptable repeatability and reproducibility along with appreciable storage and excellent operational stabilities.

Nano graphene based sensor for antiarrhythmic agent quinidine in solubilized system

An ultrasensitive electrochemical sensor based on the electrocatalytic properties of nano graphene (nGN) and multiwalled carbon nanotubes (MWCNTs) for the detection of quinidine (QD) in solubilized systems has been developed. This nano graphene-multiwalled carbon nanotube (nGN-MWCNT) composite film modified sensor shows the higher stability and stronger catalytic activity towards oxidation of quinidine and the over-potential decreased significantly compared with the bare glassy carbon electrode (GCE). The electrochemical characterization of the sensor was done by scanning electron microscopy (SEM) and cyclic voltammetry (CV) with working electrode surface area 0.56cm2 and diffusion coefficient 2.15×10−3cm2s−1. Under the optimized conditions, the oxidation peak current of QD is found to be proportional to its concentration in the range of 60ng–50μg with a detection limit of 0.186ng. The sensor was successfully employed for the detection of quinidine in bulk drugs and in its commercial pharmaceutical formulation.

Electrochemical sensor using neomycin-imprinted film as recognition element based on chitosan-silver nanoparticles/graphene-multiwalled carbon nanotubes composites modified electrode

A novel imprinted electrochemical sensor for neomycin recognition was developed based on chitosan-silver nanoparticles (CS-SNP)/graphene-multiwalled carbon nanotubes (GR-MWCNTs) composites decorated gold electrode. Molecularly imprinted polymers (MIPs) were synthesized by electropolymerization using neomycin as the template, and pyrrole as the monomer. The mechanism of the fabrication process and a number of factors affecting the activity of the imprinted sensor have been discussed and optimized. The characterization of imprinted sensor has been carried out by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The performance of the proposed imprinted sensor has been investigated using cyclic voltammetry (CV) and amperometry. Under the optimized conditions, the linear range of the sensor was from 9×10−9mol/L to 7×10−6mol/L, with the limit of detection (LOD) of 7.63×10−9mol/L (S/N=3). The film exhibited high binding affinity and selectivity towards the template neomycin, as well as good reproducibility and stability. Furthermore, the proposed sensor was applied to determine the neomycin in milk and honey samples based on its good reproducibility and stability, and the acceptable recovery implied its feasibility for practical application.

Graphene–multiwalled carbon nanotube-based nanofluids for improved heat dissipation

A solution-free green method using focused solar electromagnetic radiation is used to synthesize graphene and graphene–multiwalled carbon nanotube (MWNT) composite. Stable nanofluids are prepared by dispersing the nanomaterials in polar base fluids. Thermal conductivity of the nanofluids improves with graphene–MWNT nanocomposites as additives, which could be due to prevention of restacking of graphene sheets by MWNT along with a synergistic effect of intrinsic high thermal conductivity of graphene and MWNT. The advantage of the present synthesis method in particular to nanofluids application is that the presence of oxygen functional groups resulting from pre-functionalized MWNT rules out the need for functionalizing the hybrid composite again, thereby preserving the high thermal properties of graphene. Thermal conductivity enhancement of 9.2% and 10.5% is obtained with graphene and graphene–MWNT nanofluids in de-ionized water at room temperature for 0.04% volume fraction. The high thermal transport characteristics of graphene–MWNT composite nanofluids is ascribed to the high aspect ratio of MWNT and graphene, which in turn can form tightly bonded clusters and, by suppressing the interface resistance, can become excellent additives to attain high thermal conductivity. Further, an enhancement in heat-transfer coefficient of 193% at Reynolds number 2000 for 0.02% volume fraction of aqueous graphene–MWNT nanofluids suggests the potential application of the present hybrid material-based nanofluids in cooling circuits.

Preparation and capacitance of graphene/multiwall carbon nanotubes/MnO2 hybrid material for high-performance asymmetrical electrochemical capacitor

Graphene/multiwall carbon nanotubes/MnO2 (GR/MCNTs/MnO2) hybrid material with a specific capacitance of 126Fg−1 within a potential window of 0–1.1V vs. saturated calomel electrode has been synthesized by a simple redox reaction between graphene/multiwall carbon nanotubes (GR/MCNTs) and KMnO4 at room temperature. The morphology and structure of the obtained material are examined by XRD, SEM and TEM. The electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The mass percentage of MnO2 with layered structure is 37% in the hybrid material. An asymmetrical electrochemical capacitor (EC) is assembled using GR/MCNT/MnO2 hybrid material as positive electrode and GR/MCNT material as negative electrode, respectively. The electrochemical properties of the two electrodes and the asymmetrical EC are investigated in 1molL−1 Na2SO4 aqueous electrolyte. The asymmetrical EC can cycle reversibly in a cell potential of 0–2.0V and gives a high energy density of 28.33Whkg−1, which is much higher than those of symmetrical ECs based on GR/MCNT/MnO2 (6.20Whkg−1) and GR/MCNT (3.92Whkg−1). Moreover, the asymmetrical EC presents a high power density (5kWkg−1 at 13.33Whkg−1) and excellent cycling performance of 83% retention after 2500 cycles.

Concise route to prepared graphene-CNTs nanocomposite supported Pt nanoparticles and used as new electrode material for electrochemical sensing

The sandwich lamination structure of graphene-multi-walled carbon nanotubes (Gr-CNTs) nanocomposite has been fabricated through in situ facile and green method. Then Pt nanoparticles are fabricated on Gr-CNTs via a simple one-step chemical reduction method in ethylene glycol (EG) and water system. The Gr-CNTs nanocomposite increased the solubility of carbon nanotubes in water, and CNTs could effectively prevent the irreversible aggregation of graphene. The Pt/Gr-CNTs were further characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), which indicated that the as-synthesized Pt nanoparticles were successfully dispersed on the surface of Gr-CNTs nanocomposite. Electrochemical study has proved that the Pt/Gr-CNTs nanocomposite has higher catalytic activity in neutral medium for methanol oxidation, which is hopefully used in various types of cells and biosensors in physiological medium.

Layer-by-layer assembly of chemical reduced graphene and carbon nanotubes for sensitive electrochemical immunoassay

In this work, uniform and stable multi-walled carbon nanotubes (MWCT) and chemically reduced graphene (GR) composite electrode interface was fabricated by using layer-by-layer assembly method. The performances of these GR–MWCT assembled electrode interfaces were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It was demonstrated that the assembled composite film significantly improved the interfacial electron transfer rate compared with that of GR or MWCT modified electrode. Based on the GR–MWCT assembled interface, a sandwich-type electrochemical immunosensor was constructed using human IgG as a model target. In this assay, human IgG was fixed as the target antigen, the HRP-conjugated IgG as the probing antibody and hydroquinone as the electron mediator. The detection limit of the immunosensor was 0.2ngmL−1 (signal-to-noise ratio of 3). A good linear relationship between the current signals and the concentrations of Human IgG was achieved from 1ngmL−1 to 500ngmL−1. Moreover, this electrochemical immunosensor exhibited excellent selectivity, stability and reproducibility, and can be used to accurately detect IgG concentration in human serum samples. The results suggest that the electrochemical immunosensor based on GR–MWCT assembled composite will be promising in the point-of-care diagnostics application of clinical screening of multiple diseases.

Synthesis of graphene-multiwalled carbon nanotubes hybrid nanostructure by strengthened electrostatic interaction and its lithium ion battery application

We report a novel way of synthesizing graphene-carbon nanotube hybrid nanostructure as an anode for lithium (Li) ion batteries. For this, graphene was prepared by the solar exfoliation of graphite oxide, while multiwalled carbon nanotubes (MWNTs) were prepared by the chemical vapor deposition method. The graphene–MWNT hybrid nanostructure was synthesized by first modifying graphene surface using a cationic polyelectrolyte and MWNT surface with acid functionalization. The hybrid structure was obtained by homogeneous mixing of chemically modified graphene and MWNT constituents. This hybrid nanostructure exhibits higher specific capacity and cyclic stability. The strengthened electrostatic interaction between the positively charged surface of graphene sheets and the negatively charged surface of MWNTs prevents the restacking of graphene sheets that provides a highly accessible area and short diffusion path length for Li-ions. The higher electrical conductivity of MWNTs promotes an easier movement of the electrons within the electrode. The present synthesis scheme recommends a new pathway for large-scale production of novel hybrid carbon nanomaterials for energy storage applications and underlines the importance of preparation routes followed for synthesizing nanomaterials.