Reduced Graphene Oxide Nanosheets Research Articles

Enhanced Electromagnetic Wave Absorption Performance of Co0.5Zn0.5 ZIF-Derived Binary Co/ZnO and RGO Composites

Composites of porous Co0.5Zn0.5 zeolitic imidazolate framework (CZ-ZIF)-derived binary Co/ZnO with reduced graphene oxide (RGO) have been prepared by a wet chemical method and carbonization process. CZ-ZIF-derived Co/ZnO microframes with diameter of about 250 nm were dispersed onto the surface of RGO nanosheets. The impedance matching of the composite could be adjusted by controlling the weight ratio of RGO to Co/ZnO microframes. Due to its porous structure, excellent impedance matching, and dielectric loss characteristics, the Co/ZnO/RGO composite exhibited maximum reflection loss (RL) of − 52.2 dB at 10.96 GHz. Coatings with thickness of 2.0 mm to 4.0 mm showed bandwidth of 5.6 GHz (from 8.72 GHz to 14.32 GHz) for RL of − 10 dB (90% absorption). Additionally, the amount of composite added into paraffin matrix was only 8 wt.%, less than for most electromagnetic (EM) wave absorbers in previous reports. Therefore, such Co/ZnO/RGO composites may be promising candidate EM wave absorbing materials.

Highly sensitive electrochemiluminescence immunosensor based on ABEI/H2O2 system with PFO dots as enhancer for detection of kidney injury molecule-1

In this work, poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) dots is discovered to display an appealing dual enhancement effect for the electrochemiluminescence (ECL) system of N-(aminobutyl)-N-(ethylisoluminol)/hydrogen peroxide (ABEI/H2O2), which not only enhances the ECL intensity of ABEI but also catalyzes decomposition of H2O2 to further amplify the ECL signal of ABEI. Owing to the electronegative property of PFO dots, electropositive ABEI-PEI as ECL reagent could be adsorbed on their surface and thus form a novel luminescence emitter (ABEI-PEI-PFO dots) with high ECL efficiency based on electrostatic attraction. Meanwhile, the water solubility and stability of this emitter are improved in virtue of the amine-rich property of ECL reagent (ABEI-PEI), which could increase the luminous efficiency of ECL reaction in aqueous solution. To increase the electron transfer efficiency, Pt nanoparticles (PtNPs) supported on reduced graphene oxide nanosheets (RGOs) via a onepot synthetic strategy are chosen as immobilizing platform for the ECL emitter (ABEI-PEI-PFO dots). Herein, the obtained dual-amplifed ABEI-PEI-PFO dots-RGOs/PtNPs complex is served as an ideal nanocarrier to capture detection antibody (Ab2). According to sandwiched immunoreaction, a highly sensitive ECL immunosensor is constructed for the detection of kidney injury molecule-1 (KIM-1) with a linearity from 50 fg mL−1 to 1 ng mL−1 and a detection limit of 16.7 fg mL−1. The developed ECL emitter combining dual amplified property for signal enhancement purpose would provide new thought and potential for sensitive bioanalysis and clinical application.

Investigation of structural and thermal properties of distinct nanofillers-doped PVA composite films

Purpose of present study was to investigate the effect of different nanofillers doping on structural and thermal properties of poly(vinyl alcohol) (PVA)-based nanocomposite films. Herein, ZnO nanoparticles (NPs), CuO NPs, graphene oxide and reduced graphene oxide (RGO) nanosheets have been used as separate nanofillers in the formation of PVA nanocomposite films via solution casting approach. The prepared composite films were characterized using X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry and tensile strength testing. The results demonstrate the effect of various nanofillers on glass transition temperature (Tg), melting temperature (Tm), crystallization temperature (Tc), percentage crystallinity (%χc) and tensile strength of composite films. A doping with (0.02 wt%) RGO nanosheets caused significant influence on thermal properties and tensile strength of PVA composite films as compared to other test nanofillers. The doping with RGO nanosheets resulted in elevation of Tg (48.2 °C), Tm (218.3 °C), Tc (157.8 °C) and %χc (41.9%) as compared to that of pure PVA (Tg 38.4 °C, Tm 190.4 °C, Tc 115.1 °C and %χc 22.2%). Overall, the doping of PVA with graphene-based nanosheets exhibited better tensile strength and thermal stability of nanocomposite as compared with other tested nanofillers.

Self-assembled formation of conjugated 3D reduced graphene oxide-wrapped helical CNTs nanostructure and nitrogen-doped using photochemical doping for high-performance supercapacitor electrodes

Interconnected three-dimension (3D) networks of novel helical carbon nanotubes (HCNTs) wrapped with reduced graphene oxide nanosheets (HCNTs/rGO) are successfully fabricated via a facile solution of self-assembly method, as well as a robust process for the simultaneous reduction and high N-doping of HCNTs/rGO composites (N-HCNTs/rGO) by photoreduction under NH3 atmosphere. The as-prepared N-HCNTs/rGO are directly employed as binder-free supercapacitor electrodes, and exhibit a highly conductive 3D-interconnected structure (5.85 S cm−1), large surface area (528.9 m2 g−1), low internal resistance (0.5 Ω), and good wettability. As a result, N-HCNTs/rGO show high specific capacitance (368 F g−1), high energy density (12.8 Wh kg−1), and cycling stability (90.7% retention at 1 A g−1 for 5000 cycles) in two-electrode systems. Moreover, the 3D N-HCNTs/rGO hybrid networks exhibit enhanced electrochemical performance in supercapacitors, which combine the synergistic effects of the two carbon nanostructures, enhanced wettability, low internal resistance, and improved ion-diffusion ability, together with the large surface areas of 3D hybrid networks and high-level N-doping. The as-synthesized composite is a potential candidate for flexible and binder-free electrodes for high-performance supercapacitors.

Light-assisted recovery for a highly-sensitive NO2 sensor based on RGO-CeO2 hybrids

The poor sensing performance of reduced graphene oxide (RGO) and difficult recovery of RGO-based gas sensors have long been the challenging issues to overcome. In this work, the characteristic properties of cerium oxide (CeO2), including strong absorption in the ultraviolet (UV) range, polymorphism and mixed valence have been taken into consideration to construct RGO-CeO2 hybrid heterostructure for NO2 gas monitoring as well as recovery enhancement by UV light. Small CeO2 nanocrystals (∼3 nm) have been facile anchored onto RGO nanosheets by a controllable solvothermal method to obtain the RGO-CeO2 hybrids. Through the changing of the precipitant, the size of CeO2 nanocrystals on the RGO nanosheets can be adjusted. Especially, with the aid of 365 nm, 0.25 mW/cm2 UV-light illumination, the recovery process can be greatly accelerated to within 258 s. Otherwise the recovery process can typically take several hours to complete. In addition, our experimental results confirm that the as-fabricated sensor exhibits excellent selectivity and sensitivity (4.59–10 ppm NO2, ∼51 times enhancement). The sensor’s response has been demonstrated to maintain its stability after recycling for six times or stored non-encapsulated for one year at room temperature, indicating eminent stability of the fabricated RGO-CeO2 hybrids.

Nanocrystalline Cellulose-Functionalized Reduced Graphene Oxide Nanosheets and Their Composite Papers.

Aqueous-dispersed nanocrystalline cellulose functionalized-reduced graphene oxide (NCC-RGO) nanosheets (the precursor of the composite papers) were prepared via the reaction of graphene oxide (GO) nanosheets, NCC, and ascorbic acid. In this reaction, stiff rod-like NCC was attached to the surface of GO nanosheets via hydrogen bond interactions, which prevented the agglomeration of the nanosheets as the surface oxygen-containing functional groups were removed by ascorbic acid The NCC-RGO composite papers were fabricated using a flow-induced self-assembly strategy with vacuum filtration. NCC-RGO nanosheets underwent layer-by-layer self-assembly on the filter membrane as water permeated the membrane. The structures as well as the electrical and mechanical properties of the NCC-RGO nanosheets and the NCC-RGO composite papers were investigated. The results revealed that the aqueous dispersions of the NCC-RGO nanosheets exhibited long-term stability, consequently producing well-aligned, robust, electrically conductive NCC-RGO composite papers.

Facile fabrication of ternary TiO2-gold nanoparticle-graphene oxide nanocomposites for recyclable surface enhanced Raman scattering

A bi-functional ternary nanocomposite was developed by decorating TiO2 and gold nanoparticles on the reduced graphene oxide nanosheets (TiO2-Au-rGO) for recyclable surface enhanced Raman scattering (SERS) detection. TiO2-Au-rGO nanocomposites have been shown to demonstrate the superior SERS performances, which can be used for highly sensitive detection of rhodamine 6 G with a limit of detection of 1.2 × 10−10 M. Subsequently, the surface can be cleaned automatically by the photocatalytic degradation of the adsorbed analytes into inorganic small molecules under visible light irradiation. This can be attributed to the excellent photocatalytic degradation ability, leading to a recyclable SERS application. After being used four times, their excellent SERS and catalytic performances can still be retained. These results suggest that the TiO2-Au-rGO nanocomposites can provide a new strategy for fabricating recyclable SERS substrates, which are highly desirable for SERS practical application.

Simultaneous extraction and determination of trace amounts of diclofenac from whole blood using supported liquid membrane microextraction and fast Fourier transform voltammetry.

A novel, simple, and inexpensive analytical technique based on flat sheet supported liquid membrane microextraction coupled with fast Fourier transform stripping cyclic voltammetry on a reduced graphene oxide carbon paste electrode was used for the extraction and online determination of diclofenac in whole blood. First, diclofenac was extracted from blood samples using a polytetrafluoroethylene membrane impregnated with 1-octanol and then into an acceptor solution, subsequently it was oxidized on a carbon paste electrode modified with reduced graphene oxide nanosheets. The optimal values of the key parameters influencing the method were as follows: scan rate,6V/s; stripping potential,200mV; stripping time, 5s; pH of the sample solution,5; pH of the acceptor solution,7; and extraction time, 240min. The calibration curves were plotted for the whole blood samples and the method was found to have a good linearity within the range of 1-25μg/mL with a determination coefficient of 0.99. The limits of detection and quantification were 0.1 and 1.0μg/mL, respectively. Using this coupled method, the extraction and determination were merged into one step. Accordingly, the speed of detection for sensitive determination of diclofenac in complex samples, such as blood, increased considerably.

Unilamellar Metallic MoS2/Graphene Superlattice for Efficient Sodium Storage and Hydrogen Evolution

Unilamellar metallic nanosheets possess superiority for electrochemical energy storage and conversion applications compared to the few-layered bulk and semiconducting counterparts. Here, we report the utilization of unilamellar metallic 1T phase MoS2 nanosheets for efficient sodium storage and hydrogen evolution through a MoS2/graphene superlattice. The superlattice-like assembly composed of alternately restacked unilamellar MoS2 and modified reduced graphene oxide nanosheets was prepared by a facile solution-phase direct restacking method. As an anode for sodium storage, the MoS2/graphene superlattice anode exhibited an excellent rate capability of ∼240 mA h g–1 at 51.2 A g–1 and a stable reversible capacity of ∼380 mA h g–1 after 1000 cycles at 10 A g–1. In addition, a low onset potential of ∼88 mV and a small Tafel slope of 48.7 mV decade–1 were attained for the hydrogen evolution reaction. Our findings are important for further developing the potential of 2D nanosheets for energy storage and conversion.

Poorly-/well-dispersed graphene: Abnormal influence on flammability and fire behavior of intumescent flame retardant

Surface feature of ammonium polyphosphate is modified by cation exchange reaction with piperazine, and then reduced graphene oxide nanosheets are attached to the surface of modified flame retardant via hydrogen bonding interactions. Good dispersion of graphene in the polypropylene matrix is observed. The dispersion state of graphene has an abnormal effect on the flammability results under small flame and fire behavior under forced flaming condition of intumescent flame retardant (IFR) composites. The well-dispersed graphene results in significantly deteriorated limiting oxygen index and UL-94 rating. The graphene with good dispersion is adverse to flammability results, which is in contrary to the widely-acknowledged flame retardant mechanisms. Low content of well-dispersed graphene exhibits higher reduction effect on heat release than that of poorly-dispersed counterpart. Novel flame retardant mechanism and model are proposed and new understanding of the role of graphene in the combustion of IFR is provided.

A green method to reduce graphene oxide with carbonyl groups residual for enhanced electrochemical performance

Reduced graphene oxide nanosheets modified with rich carbonyl groups (C=O) was obtained through a facile dehydration process by making use of the synergistic effect between phosphoric acid and monosodium phosphate. The product exhibited a high specific capacitance of 413 F g−1 at the current density of 0.25 A g−1 mainly owing to the high percentage of retained C=O groups which provided reversible pseudocapacitance and favored good dispersion. Additionally, the symmetric supercapacitors based on the modified graphene nanosheets showed high specific capacitance (314.2 F g−1 at 1 A g−1) and superior electrochemical stability with only 5.8% loss of its initial specific capacitance after 10000 cycle tests (at the current densities of 5 A g−1). The present work proposed an environmentally friendly way in controlling surface structure of reduced graphene oxide which promises great potential of graphene-based electrode materials for high performance energy-storage devices.

An effective approach to study the biocompatibility of Fe3O4 nanoparticles, graphene and their nanohybrid composite

The present manuscript describes a simple, facile and effective solvothermal route to synthesize Fe3O4 nanoparticles (Fe3O4 NPs), reduced graphene oxide nanosheets (rGO NSs) and Fe3O4/reduced graphene oxide nanohybrid composite (Fe3O4/rGO nanohybrid composite) and subsequently examines their comparative biocompatibilities. The as-obtained Fe3O4 NPs, rGO NSs and Fe3O4/rGO nanohybrid composite have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The XRD studies and scanning electron microscope confirmed the proper phase formation and the surface morphology of the as-synthesized products, respectively. The Raman spectra of Fe3O4 NPs show the strongest peak at 673 cm−1 which can be assigned to A1g peak of bare Fe3O4 NPs and it complements the XRD studies. Furthermore, the increment in the ID/IG ratio in the Fe3O4/rGO nanohybrid composite suggests the creation of defects in graphene sheets due to strain caused by Fe3O4 NPs. The biocompatibility of these samples has been tested using Lung cancer cell line H1299 through MTT assay. The MTT assay reveals that the nanohybrid composite endows more biocompatible and effectiveness than rGO NSs and Fe3O4 NPs individually, as anti-proliferative agent for cancer treatment.

Synthesis and application of NiMnO3-rGO nanocomposites as electrode materials for hybrid energy storage devices

Demand for more efficient and ecofriendly energy storage systems arouse research efforts in seeking to develop new energy materials with promising properties. In this regard, mixed transition metal oxides have recently attracted great attention due to their improved electrochemical and electrical properties in comparison with simple oxides. Herein, NiMnO3 and their composites with reduced graphene oxide (NiMnO3-rGO) were synthesized via a facile hydrothermal route, followed by a thermal treatment and their electrochemical properties have been evaluated as electrode materials for hybrid energy storage devices. The prepared samples were characterized by using X-ray diffraction (XRD), Raman spectroscopy, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and N2 adsorption measurements. The energy storage behavior of the samples was investigated using different electrochemical techniques including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Accordingly, a NiMnO3-rGO nanocomposite showed a high capacity of 91 mAh g−1 at a scan rate of 5 mV s−1, 48% higher than that of the pure NiMnO3 sample (47.7 mAh g−1). Furthermore, this nanocomposite was integrated as a positive electrode with reduced graphene oxide nanosheets as the negative electrode in an aqueous hybrid energy storage device. This system displayed a high specific energy of 23.5 Wh kg−1 and a maximum specific power of 7.64 kW kg−1.

Synthesis of reduced graphene oxide nanosheets using nanofibers from methane and biogas thermal decomposition with various catalysts

Reduced graphene oxide and graphene oxide (rGO, GO) were synthesised from carbon nanofibers, which were formed in catalytic thermal decomposition of methane (CDM) and biogas with different catalysts used in the process. The aim of the work was valorization of CDM carbon nanofiber products. The samples were characterized using Raman spectra, a scanning electron microscope and a transmission electron microscope. As a result, we observe exfoliation and the sample surface to obtain the best samples of rGO and GO. These valuable products will be useful in improving the methane/biogas thermal decomposition process. The samples have been compared and a single layer of reduced graphene oxide can be seen on images. In addition, the influence of various catalysts (especially for Fe/Al2O3 and Ni/Al2O3) used in CDM on quality of samples was compared.Graphical

Electrochemically reduced graphene oxide nanosheet coatings as solid lubricants in humid air

A facile, low cost and green approach to fabricating graphene nanosheet coatings is reported. It is composed of spraying graphene oxide (GO) suspension to form GO nanosheet coatings followed by a low voltage electrochemical reduction process. The tribological performance of the as-prepared electrochemically reduced graphene oxide (ERGO) nanosheet coatings on copper disk are evaluated by sliding against steel ball in humid air. The friction coefficient of copper is reduced to 1/6 its value, and its specific wear rate is reduced more than two orders of magnitude when copper disk is coated with ERGO nanosheet coatings. These improved tribological performance are attributed to the presence of ERGO nanosheets in the sliding interface of steel vs. copper friction pair. They not only provide easy shearing, reducing the friction coefficient, but also effectively suppress abrasive wear and adhesive wear, decreasing the wear rate of copper disk.

SnS2 /Sb2 S3 Heterostructures Anchored on Reduced Graphene Oxide Nanosheets with Superior Rate Capability for Sodium-Ion Batteries.

Tin disulfide, as a promising high-capacity anode material for sodium-ion batteries, exhibits high theoretical capacity but poor practical electrochemical properties due to its low electrical conductivity. Constructing heterostructures has been considered to be an effective approach to enhance charge transfer and ion-diffusion kinetics. In this work, composites of SnS2 /Sb2 S3 heterostructures with reduced graphene oxide nanosheets were synthesized by a facile one-pot hydrothermal method. When applied as anode material in sodium-ion batteries, the composite showed a high reversible capacity of 642 mA h g-1 at a current density of 0.2 A g-1 and good cyclic stability without capacity loss in 100 cycles. In particular, SnS2 /Sb2 S3 heterostructures exhibited outstanding rate performance with capacities of 593 and 567 mA h g-1 at high current densities of 2 and 4 A g-1 , respectively, which could be ascribed to the dramatically improved Na+ diffusion kinetics and electrical conductivity.

Enzymatic biosensing by covalent conjugation of enzymes to 3D-networks of graphene nanosheets on arrays of vertically aligned gold nanorods: Application to voltammetric glucose sensing.

The authors demonstrate efficient direct electron transfer from the enzyme glucose oxidase to vertically aligned gold nanorods with a diameter of ~160nm and a length of ~2μm that are covalently linkage to a 3-dimensional network of reduced graphene oxide nanosheets. The assembly can be prepared by a 2-step electrochemical procedure. This hybrid structure holds the enzyme in a favorable position while retaining its functionality that ultimately provides enhanced performance for enzymatic sensing of glucose without utilizing mediators. The nanorod assembly was applied to the voltammetric detection of glucose. Figures of merit include an electrochemical sensitivity of 12μA·mM-1·cm-2 (obtained from cathodic peak current at a voltage of -0.45V vs. Ag/AgCl), a 3μM detection limit (at signal/noise = 3), and a wide linear range (0.01-7mM). The hybrid nanostructure has a heterogeneous electron transfer rate constant (ks) of 2.9s-1. The high electrochemical activity is attributed to the synergistic effect of a large active surface and an enhanced electron transfer efficiency due to covalent amide linkage. Graphical Abstract Schematic of the procedure utilized for the fabrication of an electrochemical biosensor based on gold nanorods (AuNRs) modified with a reduced graphene oxide (rGO)/glucose oxidase (GOx) conjugate. The enzyme electrode was employed to the determination of glucose by differential pulse voltammetry.

Improved NO2 sensing properties at low temperature using reduced graphene oxide nanosheet–In2O3 heterojunction nanofibers

Pure In2O3 and reduced graphene oxide (rGO)–In2O3 composite nanofibers are prepared by a facile electrospinning technique. Low-temperature gas-sensing properties to NO2 of the produced nanofibers are evaluated. Our results indicate that in comparison with pure In2O3 nanofibers, the rGO–In2O3 heterojunction nanofibers display much better sensing properties in response, selectivity and detection limit to NO2. Moreover, the weight ratios of rGO to In2O3 are used as a parameter to estimate the best gas-sensing properties of rGO–In2O3 nanofibers. Consequently, the heterojunction nanofibers with an optimized amount of rGO (2.2 wt%) exhibit the highest response of 42 to 5 ppm NO2 at the low operating temperature of 50 °C, which is 4.4 times higher than that of pristine In2O3. From our perspective, the enhanced sensing properties of the composite nanofibers can be mainly attributed to the formation of p–n heterojunctions between rGO and In2O3, and ultrahigh specific surface area as well as strong gas adsorption capacity of rGO nanosheets. These excellent gas-sensing properties make the rGO–In2O3 heterojunction nanofibers attractive to application for low-temperature NO2 gas sensors.

Reduced graphene oxide functionalized with a CoS2/ionic liquid composite and decorated with gold nanoparticles for voltammetric sensing of dopamine.

A nanohybrid electrode was prepared by functionalizing reduced graphene oxide nanosheets (GNs) with gold nanoparticles (AuNP), CoS2, and an ionic liquid. It is shown to enable voltammetric determination of dopamine (DA). The AuNPs were electrodeposited onto the electrode that was first modified with CoS2 and the IL-GNs to obtain a well-defined 3-dimensional and porous structure. The nanohybrid material displays high catalytic activity and an ultrasensitive cyclic voltammetric response to DA. The peak current (best measured at a working voltage of 0.17V vs. Ag/AgCl) increases linearly in the 0.1 to 400μM DA concentration range, with a 40nM detection limit (at S/N = 3). The electrode was successfully applied to the determination of DA in spiked serum samples. Graphical abstract Schematic of the preparation of a nanohybrid electrode odified withgraphene oxide nanosheets functionalized with gold nanoparticles/CoS2/ionic liquid by electrodeposition. The electrodeexhibits excellent electrocatalytic performance with respect to the electrochemical detection of dopamine. The determination of the DPV curves provides satisfactory results which can be characterized by a linear response for DA concentrations ranging from 0.1 to 400.0μM with a 40nM detection limit (at S/N = 3).

Synthesis, characterization and enhanced electromagnetic properties of BaTiO3/NiFe2O4-decorated reduced graphene oxide nanosheets

A novel kind of ternary nanocomposites, BaTiO3 and NiFe2O4 nanoparticles deposited on reduced graphene oxide nanosheets, was prepared via a three-step method. The phase structure, morphology, chemical composition, and magnetic properties were analyzed by powder X-ray diffraction (XRD) technique, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Raman spectroscopy and vibrating sample magnetometry (VSM) while the microwave absorption performance was investigated by vector network analyzer (VNA). The results showed the sample with 30 wt% reduced graphene oxide exhibits the most remarkable microwave absorption properties. The optimal reflection loss can reach −51.1 dB at 9.52 GHz with a coating layer thickness of only 2.9 mm and a broad bandwidth (RL < −10 dB) of 3.12 GHz.