Few-layer Reduced Graphene Oxide Research Articles

Interface Modulation of CoNi Alloy Decorated with Few-Layer Reduced Graphene Oxide for High-Efficiency Microwave Absorption

Metal-organic frameworks (MOFs)-derived microwave absorbers with tunable components and microstructures show great potential in microwave absorption. Herein, we report a facile thermal reduction approach for synthesizing CoNi alloy/reduced graphene oxide (CoNi/rGO) composites from bimetallic CoNi-MOFs. By tuning the ratio of graphene oxide (GO) in the precursors, the resulting CoNi/rGO-2 composite demonstrates optimal microwave absorption performance with a minimum reflection loss (RLmin) of −66.2 dB at 7.6 GHz in the C band. Moreover, the CoNi/rGO-2 with 50 wt% filler loading achieves a maximum effective absorption bandwidth (EAB) of 6.8 GHz (10.6–17.4 GHz) at a thickness of 2.5 mm, almost spanning the entire Ku band and a portion of the X band. The outstanding performance of CoNi/rGO-2 is ascribed to the high magnetic loss from the CoNi alloy and the incorporation of rGO, which induces interfacial polarization to enhance the dielectric loss and improve the impedance matching of composite. These favorable findings highlight the considerable potential and superiority of the CoNi/rGO-2 composite as an electromagnetic wave absorption material. This work sets forth a viable strategy for designing high-efficiency alloy/rGO absorbers.

Large-scale Production of Few-Layer Reduced Graphene Oxide by the Rapid Thermal Reduction of Graphene Oxide and Its Structural Characterization

Graphene, a carbon allotrope, is a two-dimensional honeycomb of carbon atoms. Although graphene is a thin material, it is the strongest material known on Earth thanks to the strong carbon bonds in its structure. It is stated that the strength of these carbon bonds in graphene is about 100 times stronger than steel. In this study, graphite was first converted into graphene oxide (GO) by the Improved Hummers method, which is one of the methods suitable for large-scale production. Reduced graphene oxide (RGO) was obtained from the synthesized GOs by thermal reduction. TGA, FTIR, XRD, XPS, Raman, BET, and SEM analyses were used to characterize GO produced using the improved Hummers method and RGO reduced by thermal methods. TGA measurements show that RGO produced using the thermal approach had a lower mass loss than graphite oxidized using the improved Hummers process. This shows that the GO sample prepared using the improved Hummers approach contains a considerable number of distinct oxygen-containing groups. The novelty of the modified Hummers' method lies in its enhanced efficiency in producing graphene oxide through reduced thermal reaction times and improved scalability compared to the original approach in the literature. The C:O ratio of the GO and RGO samples was determined by XPS to be 1.88 and 11.17, respectively. The ID/IG ratio obtained by Raman analysis was 0.973. In addition, RGO's BET surface area was discovered to be 543.6 m2 g-1. These findings demonstrated that graphite was successfully oxidized by an improved Hummers method, and the resulting GO was thermally converted to few-layer RGO.

Synthesis and Characterization of Few-Layer Reduced Graphene Oxide Nanosheet by Modified Hummer's Method

Synthesis and Characterization of Few-Layer Reduced Graphene Oxide Nanosheet by Modified Hummer's Method

Synthesis of few-layered graphene sheets as support of cobalt nanoparticles and its influence on CO hydrogenation

We prepared few-layered reduced graphene oxide (rGO) as support in CO hydrogenation reaction. We investigated the graphene structure, mostly its electron donation effects to the cobalt particles, exploring the CO dissociation and the reaction results. Some modifications in the graphene synthesis method allowed the obtaining of a few-layered structure. No crystalline areas were detected. The prepared reduced graphene oxide was decorated with cobalt nanoparticles using the precipitation-deposition method (15% wt) in an alcoholic media. The catalyst was characterized before and after reaction by several techniques. XPS results revealed a higher concentration of Co2+ species at the surface and electrostatic interaction with the support. Diffuse Reflectance Infrared Fourier Transform Spectroscopy analysis (DRIFTS) suggested formate species formation on the catalyst surface and the absence of bridge-bonded adsorbed CO. The electronic interaction between cobalt nanoparticles and graphene affected carbon monoxide dissociation, preventing the electron backdonation from the active metal NPs to CO molecules.

Physicochemical and antibacterial characterization of Aspergillus sp. filtrate-reduced graphene oxide

Graphene-based nanomaterials are rapidly emerging as antimicrobial agents against a range of pathogenic microorganisms. In the present study, we have demonstrated the synthesis of reduced graphene oxide (RGO) using Aspergillus sp. filtrate as a reducing agent. The obtained Aspergillus sp. filtrate-RGO (AF-RGO) was characterized by ultraviolet–visible absorption spectroscopy, dynamic light scattering, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force spectroscopy to obtain details about the size, composition, structure, and morphology. The characterization confirmed the reduction of graphene oxide, the restoration of sp2 conjugation, and the formation of few-layered RGO sheets. The surface charge and stability of the AF-RGO in aqueous media were examined by zeta potential measurements. The thermal stability of AF-RGO was increased significantly due to the restoration of the graphitic sp2 network. The antibacterial activity of AF-RGO was evaluated using the agar well diffusion method, broth microdilution method, and Live/Dead bacterial viability assay. AF-RGO exhibited good antibacterial activities against pathogenic Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 15 and 30 mg/ml, respectively. Therefore, fungal filtrate-mediated synthesis of RGO is a promising antibacterial carbon nanomaterial for a range of biomedical and nano(bio)technological applications.

Plant extract assisted synthesis of reduced graphene oxide sheet and the photocatalytic performances on cationic and anionic dyes to decontaminate wastewater

Green synthesis of reduced graphene oxide (RGO) has gained momentum over chemical methods due to its environmental compatibility. The present study deals with the green synthesis of the RGO sheet using the bark extract of Alstonia scholaris by the simple heating method in less time duration. Different characterizations such as x-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy confirm the formation of RGO and the transmission electron microscopy (TEM) study shows that the synthesized material is a few-layered RGO sheet. The result of the photoluminescence (PL) study explores the partial reduction of graphene oxide (GO). The photocatalytic activities of the synthesized product were investigated via photo-degradation of methylene blue (MB) and methyl orange (MO). The results show that the synthesized RGO is more fruitful in cationic dye (MB) degradation than that of anionic dye (MO) depending on the electrostatic interaction between RGO and the dyes. The rate of photocatalytic performance of the nanocomposite on MB dye is 40 times greater than that of MO dye.

Ultra-high capacity dual-ion batteries realized by few-layered reduced graphene oxide and cathode structure design

As the development of dual-ion batteries (DIBs) is limited by the capacity of anions intercalation, we put forward an innovative design idea of DIB. Compared with the traditional graphite cathodes, few-layered reduced graphene oxide (rGO) has a large specific surface area and can greatly improve the utilization ratio of carbon layers for fast redox reaction process. In addition, the carbon paper current collector with porous network structure facilitates the uniform distribution of active materials, rapid penetration of electrolyte and fast migration of ions, and also relieves the volume strain caused by PF6− intercalation/de-intercalation. Under the effects of the above two aspects, the lithium-rGO DIB demonstrates significantly enhanced electrochemical performance compared with conventional DIBs. It possesses an ultra-high discharge capacity of 405 mA h g−1 with a coulombic efficiency of > 98% after 1000 cycles at 1 A g−1 in the voltage range of 3.0–5.0 V. The detailed mechanism of electrochemical performance enhancement is also discussed.

Reduced graphene oxide membrane as supporting film for high-resolution cryo-EM.

Although single-particle cryogenic electron microscopy (cryo-EM) has been applied extensively for elucidating many crucial biological mechanisms at the molecular level, this technique still faces critical challenges, the major one of which is to prepare the high-quality cryo-EM specimen. Aiming to achieve a more reproducible and efficient cryo-EM specimen preparation, novel supporting films including graphene-based two-dimensional materials have been explored in recent years. Here we report a robust and simple method to fabricate EM grids coated with single- or few-layer reduced graphene oxide (RGO) membrane in large batch for high-resolution cryo-EM structural determination. The RGO membrane has decreased interlayer space and enhanced electrical conductivity in comparison to regular graphene oxide (GO) membrane. Moreover, we found that the RGO supporting film exhibited nice particle-absorption ability, thus avoiding the air-water interface problem. More importantly, we found that the RGO supporting film is particularly useful in cryo-EM reconstruction of sub-100-kDa biomolecules at near-atomic resolution, as exemplified by the study of RBD-ACE2 complex and other small protein molecules. We envision that the RGO membranes can be used as a robust graphene-based supporting film in cryo-EM specimen preparation.

Simultaneous Enhancement of Energy and Power Density of Reduced Graphene Oxide by the Effect of Dispersed Metal Oxide Nanoparticles in the Electrolyte

Few-layered reduced graphene oxide (RGO) is prepared from graphite by chemical exfoliation method. In half cell, RGO electrode delivers a specific capacitance value of 41 mF cm−2 at 0.5 mA cm−2 in 1.0 M KOH. An attempt is made to improve the capacitance properties of RGO by widening the operating voltage window and improving the charge storage capability through the use of metal oxide nanoparticles as electrolyte additives. The specific capacitance of RGO increases to 62 mF cm−2 and 87 mF cm−2 when ZnO and SiOx nanoparticles were uniformly dispersed in the electrolyte, respectively, at 0.5 mA cm−2. For a power density of 1.5 mW cm−2, the symmetric supercapacitor assembled using ZnO and SiOx nanofluid electrolyte delivers an energy density of 2.6 μWh cm−2 and 3.03 μWh cm−2, respectively, which is 2.7 and 3.1 times the value of energy density obtained for symmetric supercapacitor assembled using KOH electrolyte. The nanofluid electrolytes show high stability even after 60 d and the electrochemical performance of RGO is reproducible in the aged nanofluid electrolytes. The RGO electrode shows stable cycling for the tested number of 10000 cycles in all the electrolytes.

Synthesis of graphene sheets from graphite flake mediated with extracts of various indigenous plants from Madagascar

Graphene, a single layer graphitic based material, is nowadays the most promising and studied material due to its unique physical and chemical properties [1]. The “top-down” method of synthesizing graphene from graphene oxide (GO) by chemical reduction is the most economical and efficient method. Oxygen based components of GO, such as epoxide, carbonyl, carboxyl and hydroxyl groups have to be eliminated, as much as possible to be more closed to a monomolecular layer of graphite. However, chemical reducing agents, such as hydrazine, are harsh and environmentally unfriendly to be used for large scale production [8].Madagascar has great varieties of indigenous plants, some of them have a power to heal illness and cancers [16], and used as herbal medicine by traditional health practitioners. This study will complete all reports done on bio-synthesis of graphene by green chemistry process [1]. Hence, physical and optical properties of the obtained graphene sheets mediated by Catharanthus roseus (CR), Phyllarthron madagascariense K. Schum (PM), Cinnamomum camphora cineoliferum (CCC), Cedrelopsis grevei Baill (CGB) and Artemisia annua (AA) natural extracts are reported on this work. Optical and physical properties of the obtained graphene sheets through Raman shift and X-Ray diffraction spectroscopy, confirmed the reduction and conversion of the bulk graphitic material to few-layered reduced graphene oxide. Hence, bio-active compounds extracted from Catharanthus roseus (CR), Phyllarthron madagascariense K. Schum (PM), Cinnamomum camphora cineoliferum (CCC), Cedrelopsis grevei Baill (CGB) and Artemisia annua (AA), can be used and are effective chelating agent for the synthesizing of graphene sheets.

“Green” Synthesis of Nanocarbons for Reduced Friction and Wear

In the following study, green carbon nanotubes and green few-layer reduced graphene oxide (rGO) were synthesized through simple, sustainable, and scalable processes starting from recycled plastic and charcoal, respectively, and with the highest number of steps involving non-harmful substances. After an extensive physicochemical characterization, which evidenced that both nano-carbons exhibit structures comparable with that of materials produced through more traditional methods and from pure sources, the samples were dispersed in two types of conventional base oils, in particular group I and group III, in order to carry out, for the first time on these green nanomaterials, an accurate study on their tribological performance. Tribological tests evidenced a remarkable reduction of coefficient of friction and wear scar diameter, especially for the green rGO dispersed at 0.1 wt% in the group III oil along with SDBS-Tween 80 surfactants mixture: 18% and 15% at ambient temperature, 12% and 13% at 80 °C, respectively. Furthermore, the tribological performance of the synthesized samples in both oils remained high for 160 min of investigation. A comparison with the same material obtained with a traditional synthesis revealed the absence of fouling phenomena in the lubrication chambers in our case, confirming the higher tribological performances of the green rGO sample, probably, as a consequence of its less ordered nature.

MoP supported on reduced graphene oxide for high performance electrochemical nitrogen reduction.

Electrocatalytic nitrogen fixation under ambient temperature and pressure has always been considered crucial in the ammonia industry. In this study, MoP nanoparticles were evenly grown on few-layered reduced graphene oxide (MoP@rGO) and served as an efficient electrocatalyst for NRR. The MoP@rGO electrocatalyst showed an excellent NRR activity with a high average NH3 yield of 7.5 μg h-1 mg-1cat (at -0.6 V vs. RHE) and high faradaic efficiency of 9.1% (at -0.5 V vs. RHE). The excellent catalytic activity and stability of MoP@rGO originated from the increased rate of electron transfer between MoP and rGO, enlarged active surface area, synergetic effect between MoP and rGO, and excellent chemical stability. This study thus opens an alternative route towards NRR electrocatalysis.

Intercorrelated Relationship Between the Thermoelectric Performance and Mechanical Reliability of Mg2Si-Reduced Graphene Oxide Nanocomposites

We fabricated Mg2Si-based thermoelectric nanocomposites with reduced graphene oxide using ultrasonic-based wet chemical pulverizing-mixing and spark plasma sintering to improve the trade-off relationship between thermoelectric properties and mechanical reliability. The dependence of thermoelectric properties and mechanical reliability on the nanophase morphologies has been systemically investigated, demonstrating the fracture toughness of the nanocomposite with thin reduced graphene oxide significantly increased. Moreover, the introduction of the few-layered reduced graphene oxide with high interface density was more effective in improving the trade-off relationship. This result suggests that an in-depth research on the dependence of the thermoelectric properties and mechanical reliability on the intrinsic properties of the nanophases is required to prepare efficient thermoelectric nanocomposites.

Working with Minions: Assisted Scalable Bio-nanomanufacturing of Functional Materials

The fictional “Minions” from film are single-focused workers, useful for accomplishing a specific task en masse. Here, minion-like bacteria is presented as a useful intermediary craftsman for functionalizing biomaterials, enabling a generic process for integrating desired chemical additives and/or nanoparticles.

Green, fast, and scalable production of reduced graphene oxide via Taylor vortex flow

Developing a cost-effective and bulk-scale process for graphene synthesis is essential for its commercialization in a wide range of industrial applications. In this study, for the first time, we used a Couette–Taylor fluid structure with axial flow as a green, rapid, and scalable protocol to synthesize reduced graphene oxide (RGO) flakes. We have determined five different flow characteristics in the laminar, transitional, and turbulent regimes and systematically investigated the effect of flow structure on RGO production. The toroidal vortices ensure the reactants are efficiently mixed, shortening the reduction time of graphene oxide (GO) from several hours to minutes. The results showed that the degree of RGO reduction significantly increased in the Taylor vortex flow (TVF) structure, and decreased in the wavy vortex flow (WVF) regime, because of the secondary instability of the fluid structure. More importantly, the TVF regime results in the synthesis of highly exfoliated and readily water-dispersible RGO products. Finally, the resulting RGO exhibited higher electrical conductivity and mechanical strength than conventional RGO synthesized under circular Couette flow (CCF). Thus, the proposed fluid dynamic protocol may open an effective, potentially cost-competitive, and industrially accessible pathway for producing few-layered RGO flakes for various applications.

A double-shelled structure confining sulfur for lithium-sulfur batteries

Lithium-sulfur battery has attracted notable attention because of its high special capacity (1675 mAh g−1). However, polysulfide dissolution and low electronic conductivity of sulfur cathode usually cause significant capacity fading during cycling. In this paper, we introduce a double-shelled structure of reduced graphene oxide@polyaniline@sulfur (rGO@PANI@S) composite, which not only can prevent volume expansion at sulfur charge/discharge process, inhibit lithium polysulfides dissolution and shuttle in the electrolyte, and also ensure a good electro-conductibility for sulfur cathode materials. The microstructure and electrochemical performance of the rGO@PANI@S cathode are investigated systematically. The results show that polyaniline inner shell with thickness of about 27.5 nm is coated uniformly on the surface of S submicron particles and few-layered reduced graphene oxide sheets are chemically bonded at the outer surface with a high sulfur content (74 wt%). When used as cathode for lithium-sulfur battery, the rGO@PANI@S composite shows an initial capacity of 1482.7 mAh g−1 at a rate of 100 mA g−1 and retains reversible capacity of 812.1 mAh g−1 over 100 cycles. This all-solution-based process is scalable and the double-shell wrapping structure has promising candidate in designing rechargeable sulfur cathode for application.

Nanoparticles of magnetite anchored onto few-layer graphene: A highly efficient Fenton-like nanocomposite catalyst

Developing a catalyst with high efficiency and recyclability is an important issue for the heterogeneous Fenton-like systems. In this study, magnetic Fe3O4 and reduced graphene oxide (RGO) nanocomposites were prepared by a facile alkaline-thermal precipitation method and employed as a highly effective heterogeneous Fenton-like catalyst for methyl orange (MO) degradation. Characterization of these nanocomposites by XRD, FTIR, Raman, FESEM and TEM revealed that nanoparticles (NPs) of Fe3O4 were tightly anchored on the few-layer RGO sheets. The anchoring of Fe3O4 NPs and the reduction of GO were achieved in one pot without adding any other reducing agents. Based on the measurements of GO surface Zeta potentials, a possible anchoring mechanism of Fe3O4 NPs onto RGO sheets was given. The Fe3O4/RGO nanocomposites exhibited much higher Fenton-like catalytic efficiency for MO degradation than pure Fe3O4 NPs. This degradation process followed the first-order kinetics model, where k1 and T complied with the Arrhenius equation with Ea of 12.79 kJ/mol and A of 8.20 s−1. Magnetic measurements revealed that Fe3O4/RGO nanocomposites were ferromagnetic as indicated by the presence of magnetic hysteresis loops. The Fe3O4/RGO nanocomposites showed good stability and recyclability. Hydroxyl radicals, OH were determined as the dominant oxidative species in Fe3O4/RGO-H2O2 system and the Fenton-like mechanism for MO degradation in water was proposed and discussed.

Step-by-step self-assembly of 2D few-layer reduced graphene oxide into 3D architecture of bacterial cellulose for a robust, ultralight, and recyclable all-carbon absorbent

Development of high performance absorbents is of particular importance in environmental protection. Herein, we report a mechanically robust, ultralight, and recyclable absorbent with highly dispersed two-dimensional (2D) few-layer reduced graphene oxide (FrGO) in a three-dimensional (3D) carbonized bacterial cellulose (CBC) monolith via a novel step-by-step in situ biosynthesis (SBSB) method followed by carbonization. The step-by-step self-assembly produces a mechanically entangled nanostructure between FrGO and CBC nanofibers. The self-assembled CBC/FrGO nanocomposite absorbent possesses multi-scaled pores and large specific area. When used as absorbents, the monolithic CBC/FrGO aerogel exhibits excellent recyclability and high absorption capacities toward numerous oils and organic solvents. These properties, together with the green, cost-effective and scalable production process, make it very promising as a superior all-carbon absorbent for environmental protection.

Process optimization on methyl orange discoloration in Fe3O4/RGO-H2O2 Fenton-like system.

The development of a catalyst with high catalytic activity was one of the most important issues for the heterogeneous Fenton-like process. In this study, nanocomposites of Fe3O4 anchored onto reduced graphene oxide (RGO) were prepared by a moderate alkaline-thermal precipitation method and developed as highly efficient heterogeneous Fenton-like catalysts. The characterization results indicated that Fe3O4 nanoparticles (NPs) were tightly anchored onto few-layer RGO sheets via a strong interaction. Contrast experiments showed that Fe3O4/RGO nanocomposites had much better Fenton-like catalytic activity than Fe3O4 NPs. The process optimization of methyl orange (MO) discoloration in Fe3O4/RGO-H2O2 system was accomplished by central composite design under response surface methodology. A second-order polynomial model was established to predict the optimal values of MO discoloration and its significance was evaluated by analysis of variance. Three-dimensional response surfaces for the interaction between two variables were constructed. Based on the model prediction, the optimum conditions for MO discoloration in Fe3O4/RGO-H2O2 system were 2.9 for solution pH, 16.5 mM H2O2 concentration, 2.5 g/L catalyst dosage and 33.5 min of reaction time, with the maximum predicted value for MO discoloration ratio of 99.98%.

Facile synthesis of graphene via reduction of graphene oxide by artemisinin in ethanol

The preparation of reduced graphene oxide (RGO) by chemical reduction of graphene oxide (GO) usually involves highly toxic reducing agents which are harmful to the environment and human health. In this paper, a mediated facile and relative green approach for the preparation of RGO in ethanol using artemisinin as a reducing agent is reported for the first time. The morphology and de-oxidation efficiency of the obtained RGO were characterized by transmission electron microscope (TEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed that artemisinin can effectively reduce GO into few-layered RGO with a high carbon to oxygen ratio (11.7). The mechanism for elimination of oxygen-containing functional groups decorated on GO nanosheets by artemisinin was proposed. The important features of relatively environmentally friendly and facile operation procedures endow this approach with great promise in the mass production of RGO and various graphene-based materials, especially for biomaterials.