Microwave Exfoliated Graphene Oxide Research Articles

Microwave Exfoliated Graphene Oxide for Sorption Concentration of Gold and Silver

A method has been reported for determining of Au and Ag in waters using preliminary sorption concentration of these analytes by microwave exfoliated graphene oxide (GO) and quantitative analysis by two-jet arc plasma atomic emission spectrometry (TJP-AES) and graphite furnace atomic absorption spectrometry (GFAAS). The parameters of sorption of analytes such as duration of sorption and pH were optimized for the preliminary concentration of Au and Ag on various carbon sorbents for subsequent TJP-AES and GFAAS analysis. The sorption properties of carbon nanotubes (CNTs), multilayer graphene (MLG) and GO such as sorption capacity and surface area were compared. The content of analytes in sorption materials was defined. The results demonstrated that GO provides the best sorption properties and the use of exfoliated GO for preconcentration decreaces the blank signal from nonselective absorption by 10 to 120 times. The limits of detection (LODs) for Au and Ag are 4·10−1 µg L−1 and 8·10−2 µg L−1 by GFAAS and 5 µg L−1 and 2·10−1 µg L−1 by TJP-AES.

High-range noise immune supersensitive graphene-electrolyte capacitive strain sensor for biomedical applications

This paper presents development and performance assessment of an innovative and a highly potent graphene-electrolyte capacitive sensor (GECS) based on the supercapacitor model. Although graphene has been widely researched and adapted in supercapacitors as electrode material, this combination has not been applied in sensor technology. A low base capacitance, generally the impeding factor in capacitive sensors, is addressed by incorporating electric double layer capacitance in GECS, and a million-fold increase in base capacitance is achieved. The high base capacitance (∼22.0 μF) promises to solve many inherent issues pertaining to capacitive sensors. GECS is fabricated by using thermally reduced microwave exfoliated graphene oxide material to form interdigitated electrodes coated with solid-state electrolyte which forms the double layer capacitance. The capacitance response of GECS on subjecting to strain is examined and an enormous operating range (∼300 nF) is seen, which is the salient feature of this sensor. The GECS showed an impressive device sensitivity of 11.24 nF kPa-1 and good immunity towards noise i.e. lead capacitance and stray capacitance. Two regimes of operation are identified based on the procedure of device fabrication. The device can be applied to varied applications and one such biomedical application of breath pattern monitoring is demonstrated.

Unsaturated edge-anchored Ni single atoms on porous microwave exfoliated graphene oxide for electrochemical CO2

Supported single atom catalysts (SACs), emerging as a new class of catalytic materials, have been attracting increasing interests. Here we developed a Ni SAC on microwave exfoliated graphene oxide (Ni-N-MEGO) to achieve single atom loading of ∼6.9 wt%, significantly higher than previously reported SACs. The atomically dispersed Ni atoms, stabilized by coordination with nitrogen, were found to be predominantly anchored along the edges of nanopores ( < 6 nm) using a combination of X-ray absorption spectroscopy (XAS) and aberration-corrected scanning transmission electron microscopy (AC-STEM). The Ni-N-MEGO exhibits an onset overpotential of 0.18 V, and a current density of 53.6 mA mg−1 at overpotential of 0.59 V for CO2 reduction reaction (CO2RR), representing one of the best non-precious metal SACs reported so far in the literature. Density functional theory (DFT) calculations suggest that the electrochemical CO2-to-CO conversion occurs more readily on the edge-anchored unsaturated nitrogen coordinated Ni single atoms that lead to enhanced activity toward CO2RR.

Fabrication of current collector using a composite of polylactic acid and carbon nano-material for metal-free supercapacitors with graphene oxide separators and microwave exfoliated graphite oxide electrodes

The method of fused deposition modelling has been applied for the preparation of a current collector from a composite of polylactic acid and carbon nano-material. The current collectors are investigated employing IR and Raman spectroscopy. A metal-free supercapacitor has been built on the base of microwave exfoliated graphene oxide electrodes, utilising a graphene oxide membrane as a separator and the current collectors from the polymer-nano-carbon composite. Electrochemical investigations (galvanostatic charge-discharge and cyclic voltammetry at various scan rates) have been performed on the supercapacitor.

Microwave exfoliated graphene oxide/TiO2 nanowire hybrid for high performance lithium ion battery

Lithium ion battery (LIB) is a key solution to the demand of ever-improving, high energy density, clean-alternative energy systems. In LIB, graphite is the most commonly used anode material; however, lithium-ion intercalation in graphite is limited, hindering the battery charge rate and capacity. To date, one of the approaches in LIB performance improvement is by using porous carbon (PC) to replace graphite as anode material. PC's pore structure facilitates ion transport and has been proven to be an excellent anode material candidate in high power density LIBs. In addition, to overcome the limited lithium-ion intercalation obstacle, nanostructured anode assembly has been extensively studied to increase the lithium-ion diffusion rate. Among these approaches, high specific surface area metal oxide nanowires connecting nanostructured carbon materials accumulation have shown promising results for enhanced lithium-ion intercalation. Herein, we demonstrate a hydrothermal approach of growing TiO2 nanowires (TON) on microwave exfoliated graphene oxide (MEGO) to further improve LIB performance over PC. This MEGO-TON hybrid not only uses the high surface area of MEGO but also increases the specific surface area for electrode–electrolyte interaction. Therefore, this new nanowire/MEGO hybrid anode material enhances both the specific capacity and charge–discharge rate. Scanning electron microscopy and X-ray diffraction were used for materials characterization. Battery analyzer was used for measuring the electrical performance of the battery. The testing results have shown that MEGO-TON hybrid provides up to 80% increment of specific capacity compared to PC anode.

Synthesis of nanoporous graphene oxide adsorbents by freeze-drying or microwave radiation: Characterization and hydrogen storage properties

In the present work, we synthesized and systematically characterized two novel graphene-based nanomaterials, a chemically reduced graphene oxide (GO) sponge and a microwave-exfoliated GO. Textural properties were determined by N2 adsorption/desorption at 77 K, while additional characterization techniques were employed, such as Micro-Raman Spectroscopy, Field-Emission Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy, to elucidate further the structural and morphological features. Both nanomaterials were additionally evaluated for their H2 storage capacity and were critically compared to commercially available carbons (e.g. few-layer graphenes, carbon nanotubes) based on systematic H2 adsorption/desorption measurements at 77 K between 0 and 1 bar. Maximum H2 gravimetric capacities of ∼0.5 wt% and ∼0.7 wt% were recorded at 77 K and 1 bar for the reduced GO sponge and the microwave-exfoliated GO, respectively.

Polymer composites prepared by low-temperature post-irradiation polymerization of C2F4 in the presence of graphene-like material: synthesis and characterization

Study of PTFE–microwave exfoliated graphene oxide (MEGO) composites synthesized using a low temperature post-irradiation polymerization technique. SEM images of MEGO (left) and PTFE–MEGO composite (right).

High Electrochemical Performance of LiFePO4 Cathode Material via In-Situ Microwave Exfoliated Graphene Oxide

Compared with thermally exfoliated graphene oxide (TEGO) prepared at high temperature of 800°C and a long time of 12h, microwave exfoliated graphene oxide (MEGO) is successfully synthesized at 800W for 2min benefiting from “inert and instant heating” of microwave irradiation and employed to optimize electrochemical performance of LiFePO4. The as-obtained LiFePO4/MEGO exhibits overwhelming superiorities to LiFePO4/TEGO, particularly in high-rate performance. Although LiFePO4/MEGO delivers the similar specific capacity of 158.1 mAh·g−1 as well as the LiFePO4/TEGO at the rate of 0.1C, the LiFePO4/MEGO performs smaller polarization of 53.3mV resulting in better specific energy of 518.1 Wh·kg−1 and energy efficiency of 89.8%. Even at the high rate of 10C and 20C, the LiFePO4/MEGO delivers excellent specific energy of 300.3 Wh·kg−1 and 229.7 Wh·kg−1 (with corresponding specific capacity of 104.3 mAh·g−1 and 87.3 mAh·g−1 respectively), much better than those of the LiFePO4/TEGO. After 2000 cycles, the LiFePO4/MEGO still performs excellent rate capabilities with 91.2% and 83.8% retention respectively.

Performance enhancement of single-walled nanotube–microwave exfoliated graphene oxide composite electrodes using a stacked electrode configuration

Optimised SWNTs/MW-rGO supercapacitor in a stacked electrode configuration, leading to an enhancement of energy density.

3D Honeycomb‐Like Structured Graphene and Its High Efficiency as a Counter‐Electrode Catalyst for Dye‐Sensitized Solar Cells

Graphene, a two-dimensional carbon sheet, has attracted great interest due to its unique properties. To explore its practical applications, large-scale synthesis with controllable integration of individual graphene sheets is essential. To date, numerous approaches have been developed for graphene synthesis, including mechanical cleavage, epitaxial growth, and chemical vapor deposition. All of those techniques are used to prepare flat graphene sheets on a substrate. Chemical exfoliation of graphite has been applied to prepare graphene oxide solutions and graphene-based composite materials. Recently, tuning graphene shapes is attracting much attention. Cheng and co-workers synthesized graphene foam using porous Ni foam as a template for the CVD growth of graphene, followed by etching away the Ni skeleton. The graphene foam consists of an interconnected flexible network of graphene as the fast transport channel of charge carriers for high electrical conductivity. Ruoff et al. prepared porous graphene paper from microwave exfoliated graphene oxide by KOH activation. The porous graphene, which has an ultra-high surface area and a high electrical conductivity, was exploited for supercapacitor cells, leading to high values of gravimetric capacitance and energy density. Feng, M llen, and co-workers synthesized hierarchical macroand mesoporous graphene frameworks (GFs). The GFs exhibited excellent performance for electrochemical capacitive energy storage. Yu et al. and Qu et al. fabricated graphene tubes that could be selectively functionalized for desirable applications. Choi et al. synthesized macroporous graphene using polystyrene colloidal particles as sacrificial templates in graphene oxide suspension, and the pore sizes can be tuned by controlling template particle size. These important results represent a significant topic—tuning the properties of graphene sheets by controlling their shapes. However, it is still a challenge to synthesize three-dimensional graphene (3D) with a desirable shape. Herein, we develop a novel strategy for the synthesis of a new type of graphene sheet with a 3D honeycomb-like structure by a simple reaction between Li2O and CO. Furthermore, these graphene sheets exhibited excellent catalytic performance as a counter electrode for dye-sensitized solar cells (DSSCs) with an energy conversion efficiency as high as 7.8%, which is comparable to that of an expensive platinum electrode. Li2O is widely exploited as a promoter in catalysts to inhibit carbon formation. However, this general principle is challenged by this work, in which Li2O is used to react with CO to form graphene-structured carbon [Eq. (1)]

Manganosite–microwave exfoliated graphene oxide composites for asymmetric supercapacitor device applications

Graphene based materials coupled with transition metal oxides are promising electrode materials in asymmetric supercapacitors owing to their unique properties which include high surface area, good chemical stability, electrical conductivity, abundance, and lower cost profile over time. In this paper a composite material consisting of graphene oxide exfoliated with microwave radiation (mw rGO), and manganosite (MnO) is synthesised in order to explore their potential as an electrode material. The composite material was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to explore the process occurring at the electrode/electrolyte interface. Long term cyclability and stability were investigated using galvanostatic charge/discharge testing. From the resulting analysis, an asymmetric supercapacitor was constructed with the best composite containing 90% MnO–10% mw rGO (w/w). The device exhibited a capacitance of 0.11F/cm2 (51.5F/g by mass) and excellent capacity retention of 82% after 15,000 cycles at a current density of 0.5A/g.