Multilayer Reduced Graphene Oxide Research Articles

Hierarchically Structured Nitrogen-Doped Multilayer Reduced Graphene Oxide for Flexible Intercalated Supercapacitor Electrodes

Intercalated flexible electrodes for energy storage devices have drawn significant research interests as they can provide high energy densities for powering electronics without sacrificing the over...

Vitamin-C-enabled reduced graphene oxide chemistry for tuning biofilm phenotypes of methylotrophs on nickel electrodes in microbial fuel cells

This study reports the use of multi-layered reduced graphene oxide (rGO) coating on porous nickel foam (NF) electrodes for enhancing biofilm growth of Rhodobacter Sphaeroides spp fed with methanol in microbial fuel cells (CH3OH-MFCs). Electrochemical methods were used to assess the methylotrophic activity on rGO/NF electrodes. The power density and current density offered by rGO/NF (1200 mW m−2 and 680 mA m−2) were 220-fold and 540-fold higher compared to bare NF (5.50 mW m−2 and 1.26 mA m−2), respectively. Electrochemical impedance spectroscopy results show that rGO/NF suppresses charge transfer resistance to CH3OH oxidation by 40-fold compared to the control. This improved performance is due to the ability of rGO coatings to decrease the wetting contact angle (improve the hydrophilicity) of NF from 1280 to 00. A preliminary cost analysis was carried out to assess the viability of rGO/NF electrodes via vitamin-C-enabled graphene oxide chemistry for CH3OH-MFCs applications.

Reduced graphene oxide resistance in composites with polystyrene of different molecular masses

Multi-layered reduced graphene oxide after UV-perforation (RGOp) flakes of large areas, some of them up to 1 mm in diameter, have been produced on polystyrene surface during special precipitation method of RGOp/polystyrene composites from benzene solution. For this, composites on the base of polystyrenes of different molecular masses: 4500 Da; 6000 Da; 9000 Da; and 45,000 Da were synthesized. Very low resistances at the room temperature for some RGOp flakes deposited from benzene-petroleum ether solution of composite of 9000 Da molecular mass were obtained. The absolute values of measured resistances turned out to be almost 3 orders lower than copper resistance. This result can be related to formation a high conductive phase in the reduced graphene oxide bilayer inclusions. In the case of RGOp flakes produced from our highest molecular mass polystyrene composite (45,000 Da) resistance was high and varying from semiconducting values to non-conductive state.

Ternary Monolithic ZnS/CdS/rGO Photomembrane with Desirable Charge Separation/Transfer Routes for Effective Photocatalytic and Photoelectrochemical Hydrogen Generation.

Highly efficient and easy recyclable monolithic photocatalysts with ideal separation/transport route for photogenerated charge carriers are much desired. In this work, a ZnO seed-induced growth approach is developed to fabricate a ternary monolithic photomembrane, that is, ZnS/CdS heterojunction nanorods in situ grow into the interspaces of multilayer reduced graphene oxide (rGO) sheets (denoted as ZnS/CdS/rGO). The monolithic ZnS/CdS/rGO photomembrane can serve as an efficient visible-light photoactive membrane for photocatalytic (PC) or photoelectrochemical (PEC) hydrogen generation. The fast electron transport of 1D CdS nanorods, the excellent electronic conductivity of multilayer stacked rGO sheets, the intense visible-light absorption of CdS, the unique hierarchical structure, and double heterojunctions (ZnS/CdS and CdS/rGO) efficiently boost the photogenerated electron-hole pairs separation and transfer across the interfacial domain of the photomembrane under visible-light irradiation. Furthermore, the superior stability and reusability of the photomembrane is achieved by the ideal process of photogenerated electron-hole pair separation/transfer, i.e., holes transfer to ZnS and electrons transfer to rGO to inhibit CdS from photocorrosion.

N-doped graphene catalysts with high nitrogen concentration for the oxygen reduction reaction

Nitrogen doped reduced graphene oxide (NrGO) catalysts and composites of these with carbon nitride (CN) with nitrogen content as high as 19.8 wt% and 35.8 wt%, respectively, have been synthesized by thermal annealing of multilayer graphene oxide and urea at different temperatures. Nitrogen has been effectively introduced as a mix of pyridinic, pyrrolic, pyridonic and quaternary bonding configurations into the carbon lattice of graphene upon removal of CN phase over 650 °C. The electrocatalytic activity towards oxygen reduction reaction (ORR) in 0.1 M NaOH has been investigated. NrGO catalysts with less nitrogen content show better performance than composites. NrGO produced at 800 °C presents the best activity with half-wave potential of 0.76 V vs. RHE and a mean number of electrons of 3.7, which are close to a commercial Pt/C catalyst. This study concludes that a high concentration of nitrogen atoms in multilayer reduced graphene oxide does not necessarily produce a highly active electrocatalyst, suggesting that carbon in the neighbourhood of nitrogen atoms are the active sites for ORR in alkaline medium.

Effect of Preparation and Reduction on Specific Surface Electrical Resistance of Thin Films Obtained from Graphene Oxide Dispersion

The effect of reducing agents and reduction conditions on the electrophysical characteristics of thin transparent conductive films obtained from an alcohol dispersion of graphene oxide (GO) by spin coating at different rotation speeds of the substrate (from 5000 to 7000 rpm) is investigated. Surface morphology of the films, light transmittance, structure of chemical bonds in the films, specific surface electrical resistance, and thickness of the films are determined. Films of multilayer reduced graphene oxide (RGO) with a thickness of 10 to 60 nm and a specific surface electrical resistance of 7.7 to 26.77 kΩ/cm2 and light transmission of 74 to 88%, which can be widely used in photovoltaics and sensor electronics, are obtained. It is established that the treatment of the samples under study in saturated ammonia vapor most effectively contributes to the reduction of the specific surface electrical resistance of the films.

Enhanced mobility and controlled transparency in multilayered reduced graphene oxide quantum dots: a charge transport study

Reduced graphene oxide (rGO) layers are known to be significantly conductive along the basal plane throughout delocalized sp2 domains. Defects present in rGO implies in disordered systems with numerous localized sites, resulting in a charge transport governed mainly by a 2D variable range hopping (VRH) mechanism. These characteristics are observed even in multilayered rGO since the through-plane conduction is expected to be insubstantial. Here, we report on the multilayer assembly of functionalized rGO quantum dots (GQDs) presenting 3D VRH transport that endows elevated charge carrier mobility, ca ∼ 236 cm2 V−1 s−1. Polyelectrolyte-wrapped GQDs were assembled by layer-by-layer technique (LbL), ensuring molecular level thickness control for the formed nanostructures, along with the adjustment of the film transparency (up to 92% in the visible region). The small size and the random distribution of GQDs in the LbL structure are believed to overcome the translational disorder in multilayered films, contributing to a 3D interlayer conduction that enhances the electronic properties. Such high-mobility, transparency-tunable films assembled by a cost-effective method possess interesting features and wide applicability in optoelectronics.

Bio-inspired multilayered graphene-directed assembly of monolithic photo-membrane for full-visible light response and efficient charge separation

Highly efficient and easily recyclable monolithic photocatalysts with elaborate hierarchical heterostructure and functional components are desirable to tap solar energy and produce green hydrogen fuels for the sustainable future. Inspired by the natural leaves, here we have rationally designed and fabricated an efficient artificial leaf photocatalyst, i.e., the first monolithic photomembrane of CdS/ZnO nanocage arrays grown into the interspaces of multilayered reduced graphene oxide (rGO) nanosheets (denoted as CdS/ZnO/rGO). The CdS/ZnO/rGO have elaborate hierarchical porous heterostructure and multifunctional components, such as multilayer rGO nanosheets for visible light absorption/harvesting, rapid charge transport and collection, hollowed CdS/ZnO nanocage arrays for light harvesting and charge utilization, and multiple heterojunction interfaces for efficient charge separation. It can been used not only as a monolithic photocatalyst, but also directly as a freestanding photoanode in the photoelectrochemical (PEC) cell system, exhibits an enhanced performance of photocatalytic (PC) or PEC hydrogen generation under different monochrome light irradiation in full-visible light region. Moreover, the CdS/ZnO/rGO photo-membrane can macroscopically realize the separation of photogenerated hole elimination and hydrogen generation by adjusting co-catalysts loading position. Impressively, it still delivered a PC H2 generation activity (0.79 μmol cm−2 h-1) and a photocurrent response of 250 μA cm-2 even under near-infrared light (λ = 700 nm) irradiation, a striking feature rarely achieved in prior arts.

Laser-induced electrical signal filtering by multilayer reduced graphene oxide decorated with Au nanoparticles.

Nanoscale plasmonic particles represent a crucial transformation on optical and electronic properties exhibited by advanced materials. Herein are reported remarkable interferometric optical effects with dependence on polarization for filtering or modulating electronic signals in multilayer nanostructures. Metallic nanoparticles were incorporated in randomly distributed networks of reduced graphene oxide by an in-situ vapor-phase deposition method. The polarization-selectable nonlinear optical absorption contribution on the photoconductivity of reduced graphene oxide decorated with gold nanoparticles was analyzed. Nanosecond pulses at 532 nm wavelength were employed in a two-wave mixing experiment to study photoconduction and nonlinear optical absorption in this nanohybrid material. The ablation threshold of the sample was measured in 0.4 J/cm2. Electrochemical impedance spectroscopy measurements revealed a capacitive response that can be enhanced by gold decoration in carbon nanostructures. A strong two-photon absorption process characterized by 5 × 10-7 m/W was identified as a physical mechanism responsible for the nonlinear photoconductive behavior of the nanostructures. Experimental shift of 1 MHz for the cutoff frequency associated with an electrical filter function performed by the sample in film form was demonstrated. Moreover, amplitude modulation of electronic signals controlled by the polarization of a two-wave mixing experiment was proposed. All-optical and optoelectronic nanosystems controlled by multi-photonic interactions in carbon-based materials were discussed. The key role of the vectorial nature of light in two-wave mixing experiments is a fascinating tool for the exploration of low-dimensional systems.

Simultaneous Encapsulation of Nano-Si in Redox Assembled rGO Film as Binder-Free Anode for Flexible/Bendable Lithium-Ion Batteries.

The emerging ubiquitous flexible/wearable electronics are in high demand for compatible flexible/high-energy rechargeable batteries, which set a collaborative goal to promote the electrochemical performance and the mechanical strength of the fundamental flexible electrodes involved. Herein, freestanding flexible electrode of Si/graphene films is proposed, which is fabricated through a scalable, zinc-driven redox layer-by-layer assembly process. In the hybrid films, silicon nanoparticles are intimately encapsulated and confined in multilayered reduced graphene oxide (rGO) nanosheet films. The designed monolithic rGO/Si film possesses several structural benefits such as high mechanical integrity and three-dimensional conductive framework for accessible charge transport and Li+ diffusion upon cycling. When adopted as binder-free electrode in half-cells, the optimized hybrid rGO/Si film delivers high gravimetric capacity (981 mA h g-1 at 200 mA g-1 with respect to the total weight of the electrode) and exceptional cycling stability (0.057% decay per cycle over 1000 cycles at 1000 mA g-1). Besides, the binder-free rGO/Si film anode is further combined with a commercial LiCoO2 foil cathode for completely flexible full cell/battery, which exhibits excellent cycling performance and a high capacity retention of over 95% after 30 cycles under continuous bending. This solution-processable, elaborately engineered, and robust Si/graphene films will further harness the potential of silicon-carbon composites for advanced flexible/wearable energy storage.

A Pt-free graphenaceous composite as an electro-catalyst for efficient oxygen reduction reaction.

Use of Pt-based electro-catalysts for the oxygen reduction reaction (ORR) is a major hindrance in large-scale application of proton exchange membrane fuel cells (PEMFCs). Hence, new, cost-effective and high performance electro-catalysts are required for the commercial success of PEMFCs. In this work, a Pt-free magnesium oxide (MgO) decorated multi-layered reduced graphene oxide (MLGO) composite is tested as an electro-catalyst for the ORR. The ORR activity of MgO/MLGO in terms of diffusion-controlled current density is found to be superior (6.63 mA per cm2-geo) than that of in-house prepared Pt/rGO (5.96 mA per cm2-geo) and commercial Pt/C (5.02 mA per cm2-geo). The applicability of less expensive MgO/MLGO not only provides a new electro-catalyst but also provides a new direction in exploring metal oxide-based electro-catalysts for the ORR.

Platinum nanoparticles homogenously decorating multilayered reduced graphene oxide for electrical nanobiosensor applications

Multilayered reduced graphene oxide decorated homogenously with Platinum nanoparticles (rGO/Pt) was confirmed by Transmission Electron Microscopy and X-ray diffraction. It was found that the rGO/Pt flakes were suitable for adsorbing biomolecules in one step with the use of carbon disulfide (CS2) based compound. In this context, the adsorption-interaction of CS2 and Human Serum Albumin biomolecules on rGO/Pt (forming Platinum dithiocarbamate complexes) was confirmed by X-ray photoelectron spectroscopy and cyclic voltammetry techniques in neutral conditions. As a proof of concept, this nanocomposite was used as a transducer in Back-gated Field Effect Transistor (GFET) based nanobiosensors. The fabrication of GFET devices, at the level of 2-inch wafer, was conducted by conventional photolithography. The CS2, rGO/Pt and protein G that detects IgG, were locally deposited by using a commercial microplotter instrument. The experiments demonstrated that the homogenous decoration with Platinum nanoparticles as surface could permit the detection of biomolecules by using non-uniform graphene flakes functionalized with CS2, for rapid elaboration of electrochemical and electrical-nanobiosensors.

Improving the oxidation resistance and stability of Ag nanoparticles by coating with multilayered reduced graphene oxide

A kind of coating nanostructure, Ag nanoparticles coated with multilayered reduced graphene oxide (RGO), is fabricated by employing a three-step reduction method in an orderly manner, which is significantly different from the conventional structures that are simply depositing or doping with Ag nanoparticles on RGO via chemical reduction. The as-prepared nanostructure is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electronic diffraction (SEAD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results show that the obtained Ag/RGO nanostructure is observed to be a perfect coating structure with well dispersed Ag particles, which is responsible for the remarkable oxidation resistance. The results of XPS spectra indicate the content of metallic Ag is far greater than that of Ag oxides despite of prolonged exposure to the air, which fully demonstrate the excellent stability of thus coating nanostructure.

Fabrication of sensitive enzymatic biosensor based on multi-layered reduced graphene oxide added PtAu nanoparticles-modified hybrid electrode.

A highly sensitive amperometric glucose sensor was developed by immobilization of glucose oxidase (GOx) onto multi-layer reduced graphene oxide (MRGO) sheets decorated with platinum and gold flower-like nanoparticles (PtAuNPs) modified Au substrate electrode. The fabricated MRGO/PtAuNPs modified hybrid electrode demonstrated high electrocatalytic activities toward oxidation of H2O2, to which it had a wide linear response that ranged from 0.5 to 8 mM (R2 = 0.997), and high sensitivity of 506.25 μA/mMcm2. Furthermore, glucose oxidase-chitosan composite and cationic polydiallyldimethylammonium chloride (PDDA) were assembled by a casting method on the surface of MRGO/PtAuNPs modified electrode. This as-fabricated hybrid biosensor electrode exhibited high electrocatalytic activity for the detection of glucose in PBS. It demonstrated good analytical properties in terms of a low detection limit of 1 μM (signal-to-noise ratio of 3), short response time (3 s), high sensitivity (17.85 μA/mMcm2), and a wide linear range (0.01–8 mM) for glucose sensing. These results reveal that the newly developed sensing electrode offers great promise for new type enzymatic biosensor applications.

Fabrication of reduced graphene oxide-graphite paste electrode for H2O2 formation and its implication for ciprofloxacin degradation

A multilayer reduced graphene oxide (rGO)-impregnated graphite electrode was fabricated to improve the production efficiency of H2O2. Graphene oxide was prepared using the improved Hummer's method and, it was then reduced to multilayer rGO using hydrazine hydrate. The XRD peak at 2θ = 24.1° and, the Raman shift with D, G and low-intensity 2D bands at 1333, 1591 and 2641 cm−1, respectively, confirmed the formation of multilayered rGO structure. The performance of the electrode was tested through cyclic voltammetry and H2O2 generation studies at different pH. H2O2 generation was about 22.41mg/L in 60min of electrolysis using the graphite/rGO-graphite (anode/cathode combination) system. The cell current efficiency was 15.54% more using the rGO-modified electrode as compared to the graphite cathode. The degradation potential of electro-generated H2O2 was tested for ciprofloxacin, an antibiotic drug, during electro-Fenton and UVA/H2O2 oxidation processes in an undivided cell.

Supercapacitive characteristics of carbon-based graphene composites

Graphene, also referred as reduced graphene oxide (RGO) is prepared by chemical exfoliation method, which delivers specific capacitance of 77 and 40Fg−1 at 0.1 and 1.0Ag−1, respectively in aqueous electrolyte. In order to improve the specific capacitance and high power performance of RGO, composites of RGO are prepared with various carbonaceous ‘spacer’ materials such as acetylene black (AB), activated carbon (AC), multi-walled carbon nanotube (CNT) and carbon derived from polyaniline (C-PANI). Composites of RGO with spacer materials such as AB, AC and CNT is prepared by mechanically mixing RGO with the spacer materials; whereas, RGO composite with C-PANI is prepared by in situ method. These two different preparation methodologies are adopted to realise its effect on the physical and electrochemical characteristics of the composites. Morphological, X-ray diffraction and Raman data confirm the formation of mixture of few and multi-layered RGO stacks. Surface area analysis and morphological data show that the composite prepared by in situ method is beneficial in achieving higher specific surface area and improved mesoporosity. Specific capacitance of RGO and its composites obtained at 0.1Ag−1 decreased in the order: RGO/C-PANI (165Fg−1)>RGO/AC (121Fg−1)>RGO/AB (107Fg−1)>RGO/CNT (95Fg−1)>pristine RGO (77Fg−1). Capacitance retention of RGO and its composite electrodes (in percentage) at 1.0Ag−1, in comparison with the value obtained at 0.1Ag−1 decreased in the order: RGO/AB (84%)>RGO/CNT (75%)>RGO/AC (71%)>RGO/C-PANI (64%)>pristine RGO (52%).

Advanced multifunctional graphene aerogel – Poly (methyl methacrylate) composites: Experiments and modeling

In this work, graphene aerogel (GA)–poly (methyl methacrylate) (PMMA) composites are first developed by backfilling PMMA into the pores of the GAs, providing uniform distribution of multi-layer reduced graphene oxide (m-rGO) sheets in the PMMA matrix. Electrical, mechanical and thermal properties of the as-prepared GA–PMMA composites are investigated by two-probe, microindentation and comparative infrared techniques respectively. As graphene loadings increase from 0.67 to 2.50vol.%, the composites exhibit significant increases in electrical conductivity (0.160–0.859S/m), microhardness (303.6–462.5MPa) and thermal conductivity (0.35–0.70W/mK) from that of pure PMMA as well as graphene–PMMA composites prepared by traditional dispersion methods. Thermal boundary resistance between graphene and PMMA is estimated to be 1.906×10−8m2K/W by an off-lattice Monte Carlo algorithm that takes into account the complex morphology, size distribution and dispersion of m-rGO sheets.

Design of multicomponent aerogels and their performance in photocatalytic hydrogen production

Multicomponent aerogels were prepared from the preformed components (i) crystalline TiO2 nanoparticles, (ii) Pt nanoparticles as well as (iii) multilayer reduced graphene oxide (m-rGO) and were subsequently tested for photocatalytic H2 evolution. The multicomponent photocatalysts showed a 3D architecture consisting of crosslinked TiO2 nanoparticles which are decorated with (1–2nm) platinum nanoparticles with embedded m-rGO. The three-component materials retained the mesoporosity and high surface area of pure TiO2 aerogels, as illustrated by transmission electron microscopy and nitrogen sorption experiments. This architecture is responsible for the enhancement of the photocatalytic activity, which reached a maximum hydrogen production rate of 11.61mmolH2g−1h−1 for the TiO2 aerogel with a cocatalyst content of 0.4wt% Pt. In comparison, a Pt/TiO2 reference powder produced only about 3.28mmolH2g−1h−1. In this way, the aerogel architecture enables the design of compositions other than Pt/TiO2 or even the co-assembly of further active materials such as conducting components into the aerogel matrix as shown by the addition of m-rGO to the Pt/TiO2 aerogels.

Advanced Charge Utilization from NaTaO3 Photocatalysts by Multilayer Reduced Graphene Oxide

NaTaO3 compound prepared by (i) a solid state reaction (SSR) with crystallite sizes between 1–5 μm and (ii) by an exotemplate method (EM) with crystallite sizes of about 25 nm was tested as photocatalyst in light-driven water splitting. NaTaO3(EM) showed an 18 times higher photocatalytic hydrogen evolution rate than NaTaO3(SSR). A further improvement by a factor of 28 was achieved by mixing the EM derived material with multilayer reduced graphene oxide (m-rGO). Moreover, by depositing 0.2 wt % Au on the surface of NaTaO3(EM), the hydrogen production efficiency has been increased by a factor of 41. Surprisingly, the hydrogen production rate could not be significantly improved with NaTaO3(SSR) under the same conditions. By using in situ EPR spectroscopy, the electronic interactions between semiconductor, cocatalyst, and m-rGO have been investigated in detail. Plausible electron separation and transfer mechanisms from NaTaO3(SSR) or NaTaO3(EM), respectively, to m-rGO are discussed and compared to the catalyt...

Study of nanotribological properties of multilayer graphene by calibrated atomic force microscopy

The nanotribological properties of multilayer graphene oxide (MGO), multilayer reduced graphene oxide (MRGO), and mechanically exfoliated multilayer graphene (MEMG) deposited on SiO2 substrate were comparatively investigated via calibrated atomic force microscopy in ambient conditions. Friction as a function of the applied normal load and sliding velocity was studied. Results show that all three types of multilayer graphene films exhibit good adhesion and friction reduction properties. MEMG exhibits the lowest friction and adhesive force because of its perfect planar lattice. A logarithmic increase in friction was observed at low sliding velocities for all measured graphene films. Friction decreases on MGO and bare SiO2 substrate, whereas it remains approximately constant on MEMG and MRGO, when the sliding velocity exceeds their critical velocities. The possible mechanisms for the experimental results were discussed. Our studies provide a good opportunity to use different types of multilayer graphene films for promising lubricant applications in nanodevices.