Reduced Graphene Oxide-multiwalled Carbon Research Articles

Aspects of superior photocatalytic dye degradation and adsorption efficiency of reduced graphene oxide multiwalled carbon nanotubes with modified ZnO-Al2O3 nanocomposites

Due to the poor effectiveness of nanomaterials, the elimination of hazardous textile dyes from wastewater is quite challenging. A wide range of low-cost, hybrid, and highly effective nanomaterials have attracted much research for their potential in wastewater treatment. Herein, ZnO-Al2O3 nanoparticles were successfully grafted on reduced graphene oxide/multiwalled carbon nanotubes (ZnO-Al2O3-rGO/MWCNT) via the hydrothermal process. This nanohybrid material has been characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunner Emmet Teller (BET) analysis. ZnO-Al2O3-rGO/MWCNT has degraded 30 ppm Congo red dye to 90% within 1 h, while 20 ppm rose Bengal dye to 80% within 1.5 h. The kinetics of degradation for both these dyes is followed well by the pseudo-first-order model. Furthermore, ZnO-Al2O3-rGO/MWCNT was explored for the adsorption of Sudan III and displayed an outstanding removal capacity (220 mg g−1) compared with bare catalyst ZnO−Al2O3 (72 mg g−1). The sorption of Sudan III dye onto the adsorbent is spontaneous endothermic and follows pseudo−second−order kinetics and Langmuir isotherm models. Experiments using radical trapping have shown that hydroxyl radicals are the principal reactive intermediates in the photoexcitation process. The desorption and regeneration of as−prepared nanocomposite are also assessed.

Enhancing Polysulfide Confinement and Electrochemical Kinetics by Amorphous Cobalt Phosphide for Highly Efficient Lithium-Sulfur Batteries.

The application of lithium-sulfur (Li-S) batteries is severely hampered by the shuttle effect and sluggish redox kinetics. Herein, amorphous cobalt phosphide grown on a reduced graphene oxide-multiwalled carbon nanotube (rGO-CNT-CoP(A)) is designed as the sulfur host to conquer the above bottlenecks. The differences between amorphous cobalt phosphide (CoP) and crystalline CoP on the surface adsorption as well as conversion of lithium polysulfides (LiPSs) are investigated by systematical experiments and density-functional theory (DFT) calculations. Specifically, the amorphous CoP not only strengthens the chemical adsorption to LiPSs but also greatly accelerates liquid-phase conversions of LiPSs as well as the nucleation and growth of Li2S. DFT calculation reveals that the amorphous CoP possesses higher binding energies and lower diffusion energy barriers for LiPSs. In addition, the amorphous CoP features reduced energy gap and the increased electronic concentrations of adsorbed LiPSs near Fermi level. These characteristics contribute to the enhanced chemisorption ability and the accelerated redox kinetics. Simultaneously, the prepared S/rGO-CNT-CoP(A) electrode delivers an impressive initial capacity of 872 mAh g-1 at 2 C and 617 mAh g-1 can be obtained after 200 cycles, exhibiting excellent cycling stability. Especially, it achieves outstanding electrochemical performance even under high sulfur loading (5.3 mg cm-2) and lean electrolyte (E/S = 7 μLE mg-1S) conditions. This work exploits the application potential for amorphous materials and contributes to the development of highly efficient Li-S batteries.

Poly-L-Lysine functionalised MWCNT-rGO nanosheets based 3-d hybrid structure for femtomolar level cholesterol detection using cantilever based sensing platform

In this work we have developed a novel rGO-MWCNT (reduced graphene oxide-multiwalled carbon nanotube) nanocomposite material with Poly-L-Lysine functionalization which can be used for detection of biomolecules with enhanced sensitivity. The reduced GO sheets are found to play a major role as a connector and helps in the assembly of bundles of carbon nanotubes (CNTs) which may sometime play a role of upstanding nanostructures. The overall composite structure is further fully functionalized resulting in an overall high density of amino groups that can be used to capture biomolecules. The sensitivity of the as synthesized film is tested by the oxidation of cholesterol through cholesterol oxidase enzyme that is biochemically immobilized over these composite films. The test for the immobilization density of the novel films are carried out by mounting these films on sensitive thin section static micro/nano-cantilever platforms. The platforms have capability to measure cholesterol traces in blood upto an extent of 100 femto molar through deflection /bending of the cantilevers due to surface reaction. The films developed show a promise of high immobilization density which is further confirmed through fluorescence studies using FITC labeling of functionalized MWCNT-PLL and rGO-PLL films respectively.

Hydrothermal synthesis of three dimensional reduced graphene oxide-multiwalled carbon nanotube hybrids anchored with palladium-cerium oxide nanoparticles for alcohol oxidation reaction

The synergistic effect of 3D carbon support on Pd-based catalyst and its performance toward direct alcohol oxidation reaction is reported here. The surface of 3DrGO-MWCNTs support was modified by loading different amounts (5–20 wt%) of cerium oxide (CeO2) by wet impregnation method. Further, Pd nanoparticles were dispersed over CeO2/3DrGO-MWCNTs nanocomposites by chemical reduction method. The synthesized nanocomposites were characterized by various techniques such as XRD, XRF, SEM, TEM, Raman, and XPS analysis. The electro-oxidation performance and long-term stability of the Pd/CeO2/3DrGO-MWCNTs electro-catalyst were measured by CV, LSV, and CA analysis. The modification of the catalyst's surface by cerium oxide Pd/10CeO2/3DrGO-MWCNTs leads to a higher anodic peak current of about138.43 mA/cm2 and 91.72 mA/cm2 when compared to the Pd/3DrGO-MWCNTs and Pd/C for ethanol and methanol electro-oxidation. In addition, the catalyst showed the highest electro chemical active surface area. The present work demonstrates a possible way to fabricate a nanostructure catalyst to improve the performance of electro-catalytic reactions.

Reduced graphene oxide-multiwalled carbon nanotubes hybrid film with low Pt loading as counter electrode for improved photovoltaic performance of dye-sensitised solar cells

In this work, the role of reduced graphene oxide (rGO) with hyperbranched surfactant and its hybridisation with multiwalled carbon nanotubes (MWCNTs) and platinum (Pt) nanoparticles (NPs) as counter electrode (CE) were investigated to determine the photovoltaic performance of dye-sensitised solar cells (DSSCs). Sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulphonate (TC14) surfactant was utilised as dispersing and stabilising agent in electrochemical exfoliation to synthesise graphene oxide (GO) as initial solution for rGO production prior to its further hybridisation and fabrication as thin film. A chemical reduction process utilising hydrazine hydrate was conducted to produce rGO due to the low temperature process and water-based GO solution. Subsequently, hybrid solution was prepared by mixing 1 wt% MWCNTs into the produced rGO solution. TC14-rGO and TC14-rGO_MWCNTs hybrid solution were transferred into fluorine-doped tin oxide substrate to fabricate thin film by spraying deposition method. Finally, the CE films were prepared by coating with thin Pt NPs. Photoanode film was prepared by a two-step process: hydrothermal growth method to synthesise titanium dioxide nanowires (TiO2 NWs) and subsequent squeegee method to apply TiO2 NPs. According to solar simulator measurement, the highest energy conversion efficiency (η) was achieved by using CE-based TC14-rGO_MWCNTs/Pt (1.553%), with the highest short current density of 4.424 mA/cm2. The highest η was due to the high conductivity of CE hybrid film and the morphology of fabricated TiO2 NWs/TiO2 NPs. Consequently, the dye adsorption was high, and the photovoltaic performance of DSSCs was increased. This result also showed that rGO and rGO_MWCNTs hybrid can be used as considerable potential candidate materials to replace Pt gradually.

Investigation of Electrical and Thermal Properties of Reduced Graphene Oxide–Multiwalled Carbon Nanotubes/PMMA Hybrid Nanocomposite

Electrical and thermal properties of the hybrid composites, prepared using reduced graphene oxide (rGO), multi‐walled carbon nanotubes (MWCNTs), and Poly (methyl methacrylate) (PMMA) have been investigated. In this hybrid composite, the effect of rGO wt.% in MWCNTs/PMMA composite has been investigated. The investigation demonstrates that the rGO–MWCNTs/PMMA hybrid composite achieved considerable improvements in electrical properties compared to the MWCNTs/PMMA and rGO/PMMA composites. The hybrid nanocomposite exhibits a percolation threshold of around 0.743 wt.% which is less than that of MWCNTs/PMMA () and rGO/PMMA () composites and has a maximum conductivity of 1.546 × 10−1 S cm−1 with a filler content of 6 wt.% rGO. The experimentally observed improved electrical and thermal properties as a result of increased rGO wt.% in MWCNTs/PMMA are attributed to a synergistic effect of MWCNTs and rGO. The experimentally observed physical properties of the rGO–MWNTs/PMMA nanocomposite suggest it as potential material for future applications.

Electrochemical Determination of Bisphenol A on a Glassy Carbon Electrode Modified with Gold Nanoparticles Loaded on Reduced Graphene Oxide-multi Walled Carbon Nanotubes Composite

Abstract A glassy carbon electrode (GCE) modified with gold nanoparticles loading on the reduced graphene oxide (rGO)-multi-walled carbon nanotubes (MWCNTs) composite film was fabricated by a two-step procedure. Firstly, rGO-MWCNTs composite were prepared by in-situ chemical reduction with hydrazine as a reducing agent. Then, gold nanoparticles (AuNPs) were deposited on the surface of rGO-MWCNTs using simple cyclic voltammetry. This modified electrode was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electrochemical methods. Furthermore, the electrochemical behavior of bisphenol A (BPA) was also investigated using this modified electrode. The results showed that the modified electrode had high electrochemical activity for the oxidation of BPA. In 0.10 M phosphate buffer (PBS, pH 7.0), the linear range for the determination of BPA with differential pulse voltammetry (DPV) was in the range of 5.0 × 10−9−1.0 × 10−7 M and 1.0 × 10−7−2.0 × 10−5 M. The detection limit was 1.0 × 10−9 M (S/N = 3). The as-prepared modified electrode was successfully used to determine BPA in river water and the shopping receipt samples with recoveries range of 97%–110% and 98%–104%, respectively.

Reduced graphene oxide–multiwalled carbon nanotubes composites as sensing membrane electrodes for DNA detection

Thin films of reduced graphene oxide–multiwalled carbon nanotube (rGO–MWCNT) composites were demonstrated as sensing membrane electrodes for single-stranded DNA (ssDNA) detection. The morphology of the rGO–MWCNT composite thin films was observed via field emission scanning electron microscopy. The GO sheet and MWCNTs were clearly obtained, and the MWCNTs were uniformly distributed on the surface of the GO. The chemical bonding of the rGO–MWCNTs was examined using Fourier transform infrared spectroscopy. The element compositions of carbon, silicon, and oxygen were confirmed via energy-dispersive X-ray spectroscopy and X-ray powder diffraction analysis. The biosensor demonstrated high sensitivity to the ssDNA target with a linear range from 500 to 100 pM. Furthermore, the biosensor demonstrated good selectivity, reproducibility, and long-term stability for DNA detection. Since, the biosensor responded very-well and demonstrated excellent detection capabilities, it is highly recommended to be used in detecting specific biomarkers and other targeted proteins.

Synthesis of nitrogen-doped reduced graphene oxide-multiwalled carbon nanotube composite on nickel foam as electrode for high-performance supercapacitor

An electrode with nitrogen-doped reduced graphene oxide/multiwall carbon nanotubes deposited on nickel foam (N-rGO/MWCNTs/NF) was successfully prepared using a simple one-pot hydrothermal method. The N-rGO/MWCNTs/NF composite was fabricated as an electrode for supercapacitor application. The supercapacitive performance of the N-rGO/MWCNTs/NF electrode was studied using electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge in a 6M KOH electrolyte solution. The N-rGO/MWCNTs/NF electrode showed an enhanced capacitance compared to rGO/MWCNTs/NF, N-rGO/NF, N-MWCNTs/NF, and bare NF electrodes because of nitrogen atom doping and more accessibility of the electrolyte after the incorporation of MWCNTs between the graphene sheets. The N-rGO/MWCNTs/NF electrode showed a specific capacitance of 142.08Fg−1 at a current density of 1Ag−1 and cycling stability with 76.2% of its initial capacitance after 1000 charge/discharge cycles.

Electrochemical Determination of Nitrite Using a Reduced Graphene Oxide–Multiwalled Carbon Nanotube-Modified Glassy Carbon Electrode

ABSTRACTGraphene oxide nanosheets were encapsulated with multiwalled carbon nanotubes by direct reduction on glassy carbon to obtain a reduced graphene oxide/multiwalled carbon nanotube-modified electrode. The encapsulated multiwalled carbon nanotubes facilitated the reduction of graphene oxide with characterization by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The reduced graphene oxide–multiwalled carbon nanotube-modified electrode exhibited high catalytic activity for the oxidation of nitrite. Under the optimized conditions, the modified electrode had a linear dynamic range from 0.2 to 640 µM with a detection limit of 0.07 µM. This device was used to determine nitrite in water samples and satisfactory results were obtained.

High performance room temperature NO2 sensors based on reduced graphene oxide-multiwalled carbon nanotubes-tin oxide nanoparticles hybrids

A facile and effective strategy has been successfully developed to synthesize reduced graphene oxide-multiwalled carbon nanotubes-tin oxide nanoparticles (rGO-CNT-SnO2) hybrids by hydrothermal method. The combined characterizations of X-ray diffraction, Raman spectrum and Transmission electron microscopy were used to characterize the samples thus obtained, indicating the successful preparation of rGO-CNT-SnO2 hybrids. A room temperature NO2 sensor was fabricated by dropping the dispersion of rGO-CNT-SnO2 hybrids on the surface of ceramic substrate previously printed Au electrodes. Most importantly, the sensor based on rGO-CNT-SnO2 hybrids shows high response, fast response and recovery rate, high selectivity and good stability, which are much better than NO2 sensors based on pure rGO and rGO-SnO2 hybrids.

A label-free voltammetric immunoassay based on 3D-structured rGO–MWCNT–Pd for detection of human immunoglobulin G

In this work, a 3D-structured reduced graphene oxide–multiwalled carbon nanotube–palladium nanoparticles (NPs) nanocomposite (rGO–MWCNT–Pd) was prepared by a facile and green way and used as substrate material for the development of a label-free electrochemical immunoassay for human immunoglobulin G (HIgG) detection. The network structure of rGO–MWCNT nanocomposite provides more active sites for Pd nucleation. And the synergistic effect of rGO, MWCNTs and Pd NPs significantly improved the electrochemical performance of the modified electrode. Pd particles can combine HIgG antibodies and enhance the conductivity of electrode. The structure of rGO–MWCNT–Pd nanocomposite was characterized by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The HRTEM of Pd NPs and energy dispersive X-ray spectroscopy (EDS) of rGO–MWCNT–Pd nanocomposite confirmed the composition of the as-synthesized nanocomposite. K3[Fe(CN)6] was used as a redox probe. HIgG antibodies are immobilized onto the nanocomposite via PdNH2 bonds. Cyclic voltammetry and square wave voltammetry were used to characterize the recognizability of HIgG. Under optimum experimental conditions, the proposed immunoassay exhibited a low detection limit (3.3pg/mL), a wide linear range (from 0.01 to 25ng/mL) as well as good stability, reproducibility and selectivity.

One-step synthesis of Ag–reduced graphene oxide–multiwalled carbon nanotubes for enhanced antibacterial activities

A silver nanoparticles decorated reduced graphene oxide–multiwalled carbon nanotubes (Ag–rGO–MWCNTs) hybrid exhibits an excellent antibacterial activity against Escherichia coli (E. coli).

Efficient synthesis of graphene–multiwalled carbon nanotubes nanocomposite and its application in electrochemical sensing of diethylstilbestrol

Herein, a sensitive voltammetric method for the determination of diethylstilbestrol (DES), illegally used as a growth promoter in animal husbandry, was developed using electrochemically reduced graphene oxide–multiwalled carbon nanotubes (ERGO–MWCNTs) modified electrode. The incorporated multiwalled carbon nanotubes (MWCNTs) served as electrical conducting wires, which could facilitate the electrochemical reduction of graphene oxide (GO). Compared to either electrochemically reduced graphene oxide (ERGO) or MWCNTs, integrating these nanostructures resulted in a strong synergistic effect between the two materials consequently leading to a superior hybrid material with higher activity for the electro-oxidation of DES. The electron transfer coefficient (α), the standard rate constant (ks), electrochemically effective surface area (A) and the saturating absorption capacity (Гs) were calculated. Under the optimized conditions, ERGO–MWCNTs modified electrode exhibited better linearity than either ERGO or MWCNTs over ranges from 0.01 to 40μM with the detection limit of 3nM (S/N=3). Moreover, the proposed method was successfully applied to determine DES in real sample and satisfactory results were obtained. The results showed that the modified electrode exhibits an excellent catalytic activity, good sensitivity and reproducibility.

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.

Direct electrochemistry of myoglobin at reduced graphene oxide-multiwalled carbon nanotubes-platinum nanoparticles nanocomposite and biosensing towards hydrogen peroxide and nitrite

We described the preparation of a novel nanobiocomposite, reduced graphene oxide- multiwalled carbon nanotubes-platinum nanoparticles/myoglobin (RGO-MWCNT-Pt/Mb) for the direct electrochemistry of myoglobin and its application towards determination of hydrogen peroxide (H2O2) and nitrite (NO2−). RGO-MWCNT-Pt nanocomposite has been prepared by simple solution based approach and its structure was characterized. RGO-MWCNT-Pt/Mb nanobiocomposite was prepared and attained the direct electrochemistry of Mb with pair of well-defined redox peaks with the formal potential of −0.33V and peak to peak separation of 22mV. Amount of electroactive protein (Г) and heterogeneous electron transfer rate constant (ks) were calculated to be 1.04×10−9molcm−2 and 9.47s−1. The sensor displayed lowest detection limit (LOD) of 6pM which is the lowest LOD ever achieved for the detection of H2O2. Two linear ranges were observed for the detection of H2O2: (1) 10pM–0.19nM with sensitivity of 1.99 (±0.058)µApM−1cm−2 and (2) 0.25nM–2.24µM with sensitivity of 0.037 (±0.081)µAnM−1cm−2. In addition, the biosensor offered good analytical parameters towards determination of NO2− with wide linear range of 1µM to 12mM and high sensitivity of 0.1651 (±0.026)µAµM−1cm−2. The sensor acquires good selectivity, repeatability, reproducibility and stability. The practical feasibility of the sensor has been addressed.

Platinum–TM (TM = Fe, Co) alloy nanoparticles dispersed nitrogen doped (reduced graphene oxide-multiwalled carbon nanotube) hybrid structure cathode electrocatalysts for high performance PEMFC applications

The efforts to push proton exchange membrane fuel cells (PEMFC) for commercial applications are being undertaken globally. In PEMFC, the sluggish kinetics of oxygen reduction reactions (ORR) at the cathode can be improved by the alloying of platinum with 3d-transition metals (TM = Fe, Co, etc.) and with nitrogen doping, and in the present work we have combined both of these aspects. We describe a facile method for the synthesis of a nitrogen doped (reduced graphene oxide (rGO)-multiwalled carbon nanotubes (MWNTs)) hybrid structure (N-(G-MWNTs)) by the uniform coating of a nitrogen containing polymer over the surface of the hybrid structure (positively surface charged rGO-negatively surface charged MWNTs) followed by the pyrolysis of these (rGO-MWNTs) hybrid structure-polymer composites. The N-(G-MWNTs) hybrid structure is used as a catalyst support for the dispersion of platinum (Pt), platinum-iron (Pt3Fe) and platinum-cobalt (Pt3Co) alloy nanoparticles. The PEMFC performances of Pt-TM alloy nanoparticle dispersed N-(G-MWNTs) hybrid structure electrocatalysts are 5.0 times higher than that of commercial Pt-C electrocatalysts along with very good stability under acidic environment conditions. This work demonstrates a considerable improvement in performance compared to existing cathode electrocatalysts being used in PEMFC and can be extended to the synthesis of metal, metal oxides or metal alloy nanoparticle decorated nitrogen doped carbon nanostructures for various electrochemical energy applications.

Direct electrochemistry of glucose oxidase at electrochemically reduced graphene oxide-multiwalled carbon nanotubes hybrid material modified electrode for glucose biosensor

Direct electrochemistry of glucose oxidase (GOx) at an electrochemically reduced graphene oxide–multiwalled carbon nanotubes hybrid (ERGO–MWCNT) modified glassy carbon electrode (GCE) has been reported. The π–π stacking interaction operating between the MWCNT and graphene oxide (GO) has been revealed by UV–Vis absorption spectroscopy. GOx was well immobilized onto the ERGO–MWCNT hybrid film, as a result direct electrochemistry of GOx has been achieved. Compared with pristine MWCNT, 2.1 fold higher peak current and very low peak to peak separation (ΔEp) of 26mV were observed at the hybrid film, demonstrating faster electron transfer between GOx and the modified electrode surface. Moreover, the modified film exhibited high electrocatalytic activity towards glucose via reductive detection of oxygen consumption and in the presence of mediator. The proposed biosensor exhibits low detection limit of 4.7μM with wide linear range of 0.01–6.5mM and acquires excellent storage and operational stabilities. The accurate glucose determination in human blood serum and good recoveries achieved in spiked urine samples revealed their great potential in the practical applications.