Reduced Graphene Oxide Powder Research Articles

Amplified sensing of nitrogen dioxide with a phosphate-doped reduced graphene oxide powder

Surface chemistry plays an essential role in gas-sensing applications, enabling significant improvements in the sensing performance. This study investigates the influence of the graphene oxide (GO) synthesis route on the sensitivity to NO2 gas at room temperature (25 °C) and 100 °C in a dry and humid atmosphere. GO powders were synthesized using both the classical Hummers' method (HGO), and an improved version of the Hummers' method (IGO) using a mixture of phosphoric and sulfuric acids. The subsequent reduction (resulting in rHGO and rIGO, respectively) aimed to enhance the electrical properties and procure nanomaterials sensitive to surface adsorbates. In contrast to the HGO, both IGO and rIGO samples exhibited a transient sensor response and an outstanding recovery performance, which was attributed to the existence of phosphate groups in the latter samples. Notably, the rIGO sample achieved a 23-fold increase in response to NO2 compared to rHGO. Additionally, the limit of detection (LOD) was calculated to be 0.98 ppb at 100 °C. Computational studies considering models of GO and of GO with phosphorus-containing species demonstrate that the presence of the latter, either at the surface or below the surface, leads to a four-fold increase in the NO2 adsorption energies, hence accounting for the significant enhancement in the sensing performance observed experimentally. This underscores the importance of tailoring the structure and chemical properties of GO/rGO materials for optimal performance in gas sensing applications.

Refining and Validating Thermogravimetric Analysis (TGA) for Robust Characterization and Quality Assurance of Graphene-Related Two-Dimensional Materials (GR2Ms)

Graphene-related two-dimensional materials available on the global market are manufactured using various production methods, with significant variations in properties and qualities causing serious concerns for the emerging multi-billion graphene industry. To address the limitations of conventional characterization methods probing the properties of individual graphene particles which may overlook the presence of non-graphene carbon impurities at a large (bulk) scale, this paper presents the refining thermogravimetric analysis as a complementary method for the reliable chemical characterization and quality control of graphene powders. A systematic parametric investigation of key experimental conditions such as sample mass and loading, heating rate, and gas environment and flow rate is performed to identify optimized settings for reliable thermal gravimetric measurements. These optimized conditions are evaluated through a series of comparative characterizations using industrially produced graphene, graphene oxide, and reduced graphene oxide powders, including their common carbon impurities. The ability of this method to provide both qualitative and quantitative analyses for characterizing graphene-related materials is confirmed. The optimized method is finally validated through an International Laboratory Comparison study and subsequently incorporated into a new standard. This low-cost, industry-affordable, and complementary characterization method is expected to enhance the quality control of manufactured graphene materials and make a valuable contribution to the growing graphene industry.

Investigations on material removal rate of reduced graphene oxide coated copper electrodes for electric discharge machining

ABSTRACT In the present work, the reduced graphene oxide (RGO) nanoparticles have been synthesised by modified Hummer’s technique. The RGO powder thus obtained was characterised by X-Ray diffraction analysis (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electront microscopy (TEM). Raman spectra showed the D-band at Raman shift of 1354 cm−1 and G-band at 1606 cm−1 of RGO. TEM analysis exhibited the RGO structure in nanometres. The prepared nanoparticles were mixed with alcohol to form a paste and was coated on standard Copper electrode for experimentation on Electric Discharge Machine (EDM). The influence of process parameters like current, pulse on and pulse-off on the material removal rate were studied using L9 Orthogonal Array of Taguchi Technique using Minitab18.0. Substantial improvement in material removal rate at current of 20 amperes, pulse on time of 90 microseconds and pulse off time of 1 microsecond. It was also found that current and pulse off were significant factors that influenced the material removal rate.

Effect of substrate temperature on electrical properties of RGO thin films deposited by atomized spray pyrolysis

Synthesis of reduced graphene oxide (RGO) by the modified Hummer's method is an excellent way for the bulk production of RGO powder. A novel atomized spray pyrolysis deposition (ASPD) method was used to deposit RGO thin films on borosilicate glass substrates. Deposition temperature was varied to optimize the electrical conductivity of RGO thin films. Turbostratic disorder and oxygen content of RGO powder decreased after depositing onto a thin film. Hall measurements and Raman analysis confirmed the deposition of p-type RGO thin films. Post-deposition annealing of the films decreased the oxygen content, recovering sp2 clusters. The conductivity of the RGO thin film was optimized at a substrate temperature of 150 °C at 16.8 × 102 S m−1.

Li+-assisted treatment of graphene oxide for ultrahigh volumetric performance supercapacitors

Compact reduced graphene oxide powder was prepared via Li+-assisted treatment of graphene oxide and exhibited a high specific volume capacitance.

Electrode-Electrolyte Interactions in an Aqueous Aluminum-Carbon Rechargeable Battery System.

Being environmentally friendly, safe and easy to handle, aqueous electrolytes are of particular interest for next-generation electrochemical energy storage devices. When coupled with an abundant, recyclable and low-cost electrode material such as aluminum, the promise of a green and economically sustainable battery system has extraordinary appeal. In this work, we study the interaction of an aqueous electrolyte with an aluminum plate anode and various graphitic cathodes. Upon establishing the boundary conditions for optimal electrolyte performance, we find that a mesoporous reduced graphene oxide powder constitutes a better cathode material option than graphite flakes.

Synthesis, characterisation and thermo-physical properties of highly stable graphene oxide-based aqueous nanofluids for potential low-temperature direct absorption solar applications

Two types of highly stable 0.1% graphene oxide-based aqueous nanofluids were synthesised and investigated. The first nanofluid (GO) was prepared under the influence of ultrasonic irradiation without surfactant. The second nanofluid was treated with tetra ethyl ammonium hydroxide to reduce the graphene oxide to form reduced graphene oxide (RGO) during ultrasonic irradiation. The GO and RGO powders were characterised by various techniques such as field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman. Also UV–visible absorption spectroscopy was carried out and band gap energies were determined. Optical band gap energies for indirect transitions ranged from 3.4 to 4.4 eV and for direct transitions they ranged between 2.2 and 3.7 eV. Thermal conductivity measurements of the GO-based aqueous nanofluid revealed an enhancement of 9.5% at 40 °C compared to pure water, while the RGO-based aqueous nanofluid at 40 °C had a value 9.23% lower than pure water. Furthermore, the photothermal response of the RGO-based aqueous nanofluid had a temperature increase of 13.5 °C, (enhancement of 60.2%) compared to pure water, the GO-based aqueous nanofluid only displayed a temperature rise of 10.9 °C, (enhancement of 46.6%) after 20 min exposure to a solar irradiance of 1000 W m−2. Both nanofluid types displayed good long-term stability, with the GO-based aqueous nanofluid having a zeta potential of 30.3 mV and the RGO-based aqueous nanofluid having a value of 47.6 mV after 6 months. The good dispersion stability and photothermal performance makes both nanofluid types very promising working fluids for low-temperature direct absorption solar collectors.

Preservation stability of chemically synthesized graphite oxide slurry and reduced graphene oxide powder

Reduced graphene oxide (RGO) powder and graphite oxide slurry were stored under natural conditions for different times, and then they were characterized in the RGO powder state. The influences of preservation time on the physical and chemical performances of RGO were investigated by different analysis methods. The results indicate that they are relatively stable in X-ray diffraction and Raman activity, whereas changes are detectable in their scanning electron microscopy and transmission electron microscopy characterizations. Importantly, with the increase of preservation time, the specific capacitances at a current density of 1 A/g maintain around 150 F/g for those two groups of RGO samples, indicating that the electrochemical performance of RGO powder fabricated by chemical route is fairly stable. In contrast, there is an obvious decrease in electrical conductivity, and after being stored for 180 days, the electrical conductivities remain only 16.4% and 15.1% of their initial values, respectively. These test results can not only arouse some new research ideas about improving the stability of chemically derived RGO powder and graphite oxide slurry, but also provide important references to their practical applications for industrial production.

Gecko foot-inspired reduced graphene oxide surface with multi-resistant, nonpolar/polar separation and reliable adhesion utility

Nature offers intriguing examples for adhesive surface with superhydrophobicity, like gecko foot hair and red rose petals. The superhydrophobic adhesion surface mainly depends on its ingenious hierarchical structure and chemical composition. Utilizing biomimetic strategy, we synthesized a fluorosulfurized reduced graphene oxide powder with a hierarchical structure by post-processing of graphene oxide. The adhesive fluorine-sulfurized reduced graphene cotton (AFC) was successfully prepared by ultrasonic soaking, self-assembly and drying. The water contact angle of AFC was 154° ± 1.4°, and its maximum adhesion force was about 102.9 ± 4.9 μN. The AFC exhibited excellent high superhydrophobic adhesive because it possessed not only the C–F bond and microscopic morphology of wrinkles and protrusions but also the inherent roughness of cotton fabrics. Importantly, the high superhydrophobic adhesive properties of AFC were not attenuated by sonication for 200 mins or UV exposure for 30 hours. Interestingly, AFC had prominent oleophobic properties for certain organic solvents (e.g., glycerol, ethylene glycol, etc.) with surface tensions greater than 30 mN/m. Finally, AFC was successfully used to nonpolar/polar separation and transfer droplets to various accepted surfaces (e.g., copper sheets, stainless steel mesh, plastics, etc.), demonstrating its great potential in liquid mixture separation and microdroplet transport.

Arc spectra of different solid reduced graphene oxide samples under microwave irradiation

It is often accompanied by an intense arc when solid-state graphene samples are irradiated by microwaves (MWs); however, arc spectra have not been studied. In this study, the arc spectra of reduced graphene oxide (RGO) powder, three-dimensional (3D) porous RGO, and RGO paper under MW irradiation were measured; these spectra exhibited diverse features. For the same reaction conditions and the same initial sample, the arc spectra should be the same if the reaction process and mechanisms are the same. Further analyses showed that the obtained RGO paper with an evident 2D band, a smaller D band, lower sheet resistance, and lower oxygen content was of higher quality than the RGO powder and 3D porous RGO obtained after MW irradiation. Based on these results, the diverse spectra may suggest different reaction processes and mechanisms. Overall, these findings provide novel insights into the preparation of graphene via MW reduction.

Synthesis and analysis of Mg–3%Al alloy nanocomposites reinforced by RGO

ABSTRACT Graphene and its derivatives, due to their extraordinary mechanical, thermal, and tribological properties, are extensively used to fabricate bulk graphene-based nanocomposites. On the other hand, magnesium alloys are lightweight and manifest excellent mechanical properties. In the present study, the hardness and compressive responses of Mg–3 wt%Al/xRGO (x = 0.1 wt% and 0.3 wt.%) nanocomposites at ambient temperature were investigated. Further, the coefficient of thermal expansion of Mg–3 wt%Al/xRGO (x = 0.1 wt% and 0.3 wt.%) nanocomposites at elevated temperatures were estimated and compared with those of pure Mg and Mg–3 wt%Al alloy. Reduced graphene oxide (RGO) synthesized through the improved Hummer’s Method followed by the thermal reduction method was used as the reinforcement material. The bulk samples of pure Mg, Mg–3%Al alloy, and nanocomposites were synthesized by blending of Mg, Al and RGO powder followed by cold compaction, microwave sintering and hot extrusion. Nanocomposite samples displayed significant changes in microstructures and substantial improvements in both Vickers hardness and ultimate compressive strength. The lower thermal expansion coefficients of Mg–3%Al/xRGO (x = 0.1 wt% and 0.3 wt.%) nanocomposites demonstrated better thermal and dimensional stability with respect to temperature. The obtained results would be conducive to design lightweight structural materials.

Zirconia Reduced Graphene Oxide Nano-Hybrid Structure Fabricated by the Hydrothermal Reaction Method.

In this work, we report an available technique for the effective reduction of graphene oxide (GO) and the fabrication of nanostructured zirconia reduced graphene oxide powder via a hydrothermal method. Characterization of the obtained nano-hybrid structure materials was carried out using a scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The confirmation that GO was reduced and the uniform distribution of zirconia nanoparticles on graphene oxide sheets during synthesis was obtained due to these techniques. This has presented new opportunities and prospects to use this uncomplicated and inexpensive technique for the development of zirconia/graphene nanocomposite powders.

Electrical Measurements of Thermally Reduced Graphene Oxide Powders under Pressure.

Graphene powders obtained via the reduction of graphene oxide flakes have been widely used in various applications as they can be synthesized in large quantities with outstanding properties. The electrical conductivity of graphene powders is critical for their uses in fabricating high-performance devices or materials. Here, we investigated the bulk electrical conductivity of reduced graphene oxide (rGO) powders depending on the applied pressure and additional thermal annealing. The electrical conductivity of the rGO powders was correlated with the change in the carbon-to-oxygen ratio via additional thermal reduction. Furthermore, the effect of the morphology of the rGO powders was studied through electromechanical measurements. This study provides a reliable method for the electromechanical characterization of rGO powders and a better understanding of the electrical conductivity of graphene-based materials.

Effects of various vitamin C amounts on the green synthesis of reduced graphene oxide

Abstract In this study, a simple and green chemistry approach is described for the preparation of reduced graphene oxide (RGO). To this aim, we used a novel reducing agent (vitamin C) for the synthesis of RGO. The GO was reduced at different weight ratios of vitamin C:GO (1:1, 1.5:1 and 2:1). The XRD, FTIR and EDS results showed the deoxygenation of GO due to the loss of hydroxyl, carbonyl, and epoxy groups. The thermal stability of the GO was lower than those of all the RGO powders, and the BET surface area of the GO was much lower than those of all the RGO powders. The results showed that the structural and thermal properties of RGO powders depend on the ratio of vitamin C:GO. When the ratio is 1:1, the RGO powder has the best thermal stability, and the highest BET surface area (m2g−1) was found to be a 2:1 ratio.

Dysbiosis of gut microbiota by dietary exposure of three graphene-family materials in zebrafish (Danio rerio)

The increasing application and subsequent mass production of graphene-family materials (GFMs) will lead to greater possibilities for their release into the environment. Although GFMs exhibit toxicity toward various aquatic organisms, little information is available on their influence on gut microbiota of aquatic organism. In this study, zebrafish were fed diets containing three GFMs, namely, monolayer graphene powder (GR), graphene oxide nanosheet (GO) and reduced graphene oxide powder (rGO), or appropriate control for 21 days. The gut bacterial communities were then characterized for comparison of the exposure effects of each GFM. Alterations of the intestinal morphology and oxidative stress indicators were also examined. The results showed GFMs led to different inflammatory responses and significantly altered the relative composition of the gut bacterial species by increasing the relative abundance of Fusobacteria and the genus Cetobacterium and Lactobacillus and decreasing the abundance of Firmicutes and the genus Pseudomonas; GR caused marked shifts in the diversity of the gut microbiota. The GFMs also altered the intestinal morphology and antioxidant enzyme activities by inducing more vacuolation and generating more goblet cells. Our findings demonstrate that GFM exposure poses potential health risks to aquatic organisms through alteration of the gut microbiota.

Hierarchical Petal-on-Petal MnO2/Vertical Graphene Foam for Postplasma Catalytic Decomposition of Toluene with High Efficiency and Ultralow Pressure Drop

A hierarchical petal-on-petal MnO2/vertical graphene (VG) foam catalyst for high-performance toluene decomposition with low pressure drop in postplasma catalysis is demonstrated in this work. The as-fabricated hierarchical structure exhibits high toluene decomposition of ∼93% and ozone conversion of nearly 100% at a high flow rate of 500 mL min–1, significantly higher than those of MnO2 deposited on conventional activated carbon and reduced graphene oxide powders with pressure drop of 2–3 orders of magnitude higher than that of VG foam. The three-dimensional macroporous structure of VG foam is beneficial for gas permeability and thus significantly decreases the pressure drop. The nonagglomerated morphology, large surface area, and sharp exposed edges of VG foam could provide abundant sites for anchoring catalysts without obvious agglomeration. Besides, the unique petal-like structure and open channels of MnO2 prominently enlarge the accessible surface area exposed to gas, leading to enhanced decomposition efficiency.

Electrical and electrochemical properties of reduced graphene oxide film for secondary battery electrode

We prepared thin layer of reduced graphene oxide (rGO) from reduced graphene oxide powder that dispersed in deionized water and dimethylformamide (DMF) using drop-casting technique. We used carboxymethyl cellulose (CMC) as a binder in order to obtain better surface of rGO film with varied concentration of rGO. We obtained that rGO film prepared using rGO dispersed in deionized water has better surface compare to the ones dispersed in DMF. An addition of CMC into rGO has improved its film surface and increasing amount of rGO resulted higher conductivity of the sample. The cyclic voltammogram (CV) of the rGO film has shown a hysteresis curve that correspond to charging and discharging process. From CV measurement we obtain that rGO-CMC film that prepared using 3 mg/ml rGO dispersed in DI water and blend with CMC has higher specific capacitance of 400 mF/g.

Free-standing, layered graphene monoliths for long-life supercapacitor

Fabricating free-standing film/paper or 3D material without additive binder is of great importance to maintain its original architectures and properties. Here, we for the first time introduce a simple, facile approach to fabricate a free-standing, layered N-doping reduced graphene oxide (NRGO) monolith for supercapacitor, firstly mixing graphene oxide (GO) with urea, and lastly taking a short-term flame bath. It is found that urea is a key sacrificial grasper, which can effectively prevent reduced GO (RGO) sheets from being peeled off in flame bath. Moreover, 3.5–7.0 at.% of N elements are successfully introduced into RGO skeleton. These structural characteristics are translated into high specific capacitance (323.7 F g−1 at 1 A g−1, higher than RGO powder (252.1 F g−1)), ultra-high coulombic efficiency (125% at 1 A g−1) and superior cycle performance with a 9.2% improvement in specific capacitance after 50,000 cycles at 30 A g−1. Relatively, only 69.3% of the specific capacitance for RGO powder remains after 10,000 cycles at 30 A g−1. Compared with RGO powder, NRGO shows obviously improvement in coulombic efficiency, energy efficiency, and especially in cycle stability. Thus, this layered NRGO not only shows a high energy storage capacity, but also successfully solves the stability problem in the long-term charge/discharge cycle. This provides a novel clue for designing long-life graphene-based electrode materials for supercapacitor.

Effect of Embedding Cu-Graphene Hybrid Powder into 2-Phase In-Cu Solders on Its Suitability as Metallic Thermal Interface Material

The effect of embedding Cu-graphene hybrid powder, namely “graphene nano-sheet Cu” (GNS-Cu) powder, into In-40 vol.% Cu solder alloy on the electrical and mechanical properties of In-Cu solder is investigated. GNS-Cu hybrid powders were prepared by mixing reduced graphene oxide powders and CuSO4·5H2O, followed by reduction of the mixture with hydrazine. Subsequently, In-Cu solders with GNS-Cu powders were prepared using a 2-step process, comprising liquid phase sintering (LPS) of In and Cu powders followed by accumulative roll bonding (ARB). During ARB, the GNS-Cu powders were embedded as distinct layers into In-Cu composite solders. Electrical conductivity of the GNS-Cu embedded solders increased by > 20% as compared to pure In-Cu solders processed through the same combination of LPS–ARB steps. The yield strength of In-Cu solder increased by only 10% with the addition of GNS-Cu powders and thus retained the moderate strength often associated with pure In-Cu composite solders. Moreover, the thermal conductivity of GNS-Cu-embedded solders was estimated theoretically to increase by > 60%. These promising findings suggest that GNS-Cu-embedded In-Cu solders can be suitable for next-generation metallic thermal interface material and package-level interconnect applications.

Platinum–Iron nanoparticles supported on reduced graphene oxide as an improved catalyst for methanol electro oxidation

Platinum–Iron nanoparticles supported on reduced graphene oxide powder are synthesized by chemical reduction method as an anode catalyst for the methanol electro oxidation. The characterization of the catalyst has been investigated using physical and electrochemical methods. Prepared catalyst was characterized by scanning electron microscopy (SEM), TEM (Transmission electron microscopy), FT-IR (Fourier-transform infrared spectroscopy), Raman spectroscopy and, X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDX). Pt and Pt-Fe nanoparticles are uniformly dispersed on the surface of reduced graphene oxide (rGO) powder nanocomposite support. The catalytic properties of the catalyst for methanol electro-oxidation were thoroughly studied by electrochemical methods that involved in the cyclic voltammetry, linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Pt-Fe/rGo exhibits high electrocatalytic activity, catalyst tolerance for the CO poisoning and catalyst durability for electro-oxidation of methanol compared to the Pt/rGo and commercial Pt/C catalyst. Therefore, the Pt-Fe/rGo catalyst is a good choice for application in direct methanol fuel cells.