Reduced Graphene Sheets Research Articles

Novel and green synthesis of chemically reduced graphene sheets using Phyllanthus emblica (Indian Gooseberry) and its photovoltaic activity

The study presents a novel and environment friendly procedure for obtaining chemically reduced graphene sheets (CRGs). Graphene Oxide as precursor material and Phyllanthus Emblica fruit extract as reductant. This procedure is suitable for mass production of graphene. Characterization of graphene flakes has subsequently been done using Raman spectroscopy, DLS, Fourier transform infrared spectroscopy (FTIR), x-ray-diffraction (XRD) and UV–vis spectroscopy. A reduction was observed in the oxygen containing functionalities of graphene oxide. Presence of Graphene layers was also confirmed by morphological studies like SEM and TEM. Further thermal strength of precursor material and its product was investigated by TGA. The strategy is successful in obtaining graphene which subsequently may be utilized in supercapacitors, sensors, and electronic devices. Its photovoltaic performance has also been compared with GO.

The reactivity of reduced graphene depends on solvation

The reactivity of reduced graphene sheets (graphenide), obtained by dissolution of graphite intercalation compounds, in particular KC8, was systemically studied by covalent functionalization with 4-fluorobenzenediazonium tetrafluoroborate and 4-iodoaniline in different solvents (5 pure and 7 solvents with addition of K+ chelating agents). Interestingly, proper solvation of the potassium cations was beneficial to the covalent functionalization, while excessive solvation led to destabilization and flocculation, with decreased reactivity of graphenide. The results were confirmed by scanning Raman spectroscopy (SRS) and x-ray photoelectron spectroscopy (XPS).

Sparsely Pillared Graphene Materials for High-Performance Supercapacitors: Improving Ion Transport and Storage Capacity.

Graphene-based materials are extensively studied as promising candidates for supercapacitors (SCs) owing to the high surface area, electrical conductivity, and mechanical flexibility of graphene. Reduced graphene oxide (RGO), a close graphene-like material studied for SCs, offers limited specific capacitances (100 F·g–1) as the reduced graphene sheets partially restack through π–π interactions. This paper presents pillared graphene materials designed to minimize such graphitic restacking by cross-linking the graphene sheets with a bifunctional pillar molecule. Solid-state NMR, X-ray diffraction, and electrochemical analyses reveal that the synthesized materials possess covalently cross-linked graphene galleries that offer additional sites for ion sorption in SCs. Indeed, high specific capacitances in SCs are observed for the graphene materials synthesized with an optimized number of pillars. Specifically, the straightforward synthesis of a graphene hydrogel containing pillared structures and an interconnected porous network delivered a material with gravimetric capacitances two times greater than that of RGO (200 F·g–1vs 107 F·g–1) and volumetric capacitances that are nearly four times larger (210 F·cm–3vs 54 F·cm–3). Additionally, despite the presence of pillars inside the graphene galleries, the optimized materials show efficient ion transport characteristics. This work therefore brings perspectives for the next generation of high-performance SCs.

Determination of the antioxidant propyl gallate in meat by using a screen-printed electrode modified with CoSe2 nanoparticles and reduced graphene oxide.

A voltammetric sensor is described for the quantitation of propyl gallate (PG). A screen-printed carbon electrode (SPCE) was modified with reduced graphene sheets that were decorated with cobalt diselenide nanoparticles (CoSe2@rGO). The material was hydrothermally prepared and characterized by several spectroscopic techniques. The modified SPCE displays excellent electrocatalytic ability towards PG. Differential pulse voltammetry, with a peak voltage at 0.34V (vs. Ag/AgCl) has a sensitivity of 12.84μA·μM-1·cm-2 and a detection limit as low as 16nM. The method is reproducible, selective, and practical. This method was applied to the determination of PG in spiked meat samples, and the result showed an adequate recovery. Graphical abstract Schematic of a new method for fast and sensitive electrochemical determination of the food additive propyl gallate in meat.

Fabrication of graphene/single wall carbon nanotubes/polyaniline composite gels as binder‐free electrode materials

ABSTRACTA three‐dimensional (3D) graphene‐based hydrogels system containing one‐dimensional (1D) carbon material‐single wall carbon nanotubes (SWCNTs) and pseudocapacitor material‐polyaniline (PANI) was prepared by combination of cross‐linking, reduced and in situ polymerization. The polyaniline nanoparticles were combined with the reduced graphene sheet by π‐π conjugation. The as‐perpared composite gels could be directly used as electrode materials without binders. Due to the synergistic effect between SWCNTs, graphene sheet and PANI, the graphene/single wall carbon nanotubes/polyaniline (GH/SWCNTs/PANI) composite gel shows the enhanced electrochemical performances. The resultant GH/SWCNTs/PANI gel electroactive material shows a gravimetric specific capacitance of 145.4 F/g at 0.5 A/g and has improved 45% compared with initial graphene hydrogel (GH) at the same current density. And it keeps high retention of 98.8% of the initial capacity after 10,00 charge/discharge cycles at high current density of 10 A/g. The great cycle stability achieved is fundamentally attributed to the support of graphene sheet and single wall carbon nanotubes, which favors stress distribution and charge transfer during the longtime charge/discharge process. The graphene‐based hydrogels could be a potential applicant for high rate charge/discharge applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46948.

N-S co-doped C@SnS nanoflakes/graphene composite as advanced anode for sodium-ion batteries

Tin sulfides have attracted great attentions as sodium-batteries anode materials due to the remarkable high theoretical capacity, but their application is vastly limited by the poor rate capability and cycle stability. In this report, we constructed a double carbon-coated structure of carbon-coated tin (II) sulfide nanoflakes anchored on reduced graphene sheets (C@SnS-rGO) by a one-pot solvothermal synthesis with a subsequent annealing process. The carbon layer deposited on the surface of nanoflakes and the rGO sheet substrate combined into a framework which can enhance the electric conductivity and structural stability. Moreover, the carbon skeleton is doped with nitrogen and sulfur atoms which can increase the active sites and surface-capacitive effect of the as-prepared composite. As anode materials for sodium-ion batteries, the C@SnS-rGO composite electrode exhibits high capacity, good rate capability and cycling stability. The superior electrochemical performances are attributed to the improved electronic conductivity and good structural stability of the composite electrode.

Highly sensitive luminol electrochemiluminescence immunosensor based on platinum-gold alloy hybrid functionalized zinc oxide nanocomposites for catalytic amplification

A highly sensitive sandwiched luminol electrochemiluminescence (ECL) immunosensor has been constructed based on the double catalysis effect and multiamplification strategy of platinum-gold alloy hybrid functionalized zinc oxide nanocomposites (Pt-Au@ZnONPs). First, the improved surface area and excellent biocompatibility of Pt-Au@ZnONPs were used for binding the secondary antibody (Ab2) and glucose oxidase (GOD) to obtain the novel bioconjugate Pt-Au@ZnONPs-GOD-Ab2. Pt-Au@ZnONPs and the loaded GOD amplified luminol ECL signals and promoted the luminol ECL response by efficiently catalyzing glucose to produce hydrogen peroxide (H2O2) in situ as a coreactant of luminol. Then, Pt-Au@ZnONPs catalyzed H2O2 to generate various reactive oxygen species (ROSs) that accelerated the ECL reaction of luminol, thus enhanced the ECL intensity of luminol and improved the sensitivity of the immunosensor. Second, gold nanoparticles decorated reduced graphene sheets (AuNPs@GS) with large specific surface area, good biocompatibility, high conductivity, and high catalytic activity were prepared and used as substrate of the immunosensor to capture the primary antibody (Ab1). Experimental results demonstrated that the proposed ECL immunosensor showed a sensitive response for the detection of α-1-fetoprotein (AFP) from 0.1 pg mL−1 to 200 ng mL−1 with detection limit of 0.03 pg mL−1 (S/N = 3). The as-proposed luminol ECL immunosensor has excellent sensitivity, stability, and specificity, which makes it very promising for clinical applications.

Study on the effect of graphene and glycerol plasticizer on the properties of chitosan-graphene nanocomposites via in situ green chemical reduction of graphene oxide

Unplasticized and glycerol plasticized chitosan/graphene (CS/GS) nanocomposites were synthesized via in situ chemical reduction of graphene oxide sheets (GO) with l-ascorbic acid (L-AA) as reductant by solution casting. The reduction of GO with L-AA was investigated to establish the optimal amount of reductant required to produce chemically reduced graphene sheets (GS). The combine effect of both nanofiller and glycerol on the structure, thermal, mechanical, and electrical properties of CS/GS nanocomposite films was evaluated. Materials were characterized by FT-IR, NMR, UV–Vis, XPS, XRD, Raman, SEM, TEM, and TGA. The results showed that GS sheets were homogeneously dispersed throughout the CS matrix, and that interactions between CS and the surface of GS took place. When compared with neat CS, nanocomposites showed a decrease in the crystallinity, better thermal stability under oxidative atmosphere, and improved mechanical properties, while maintained the thermal properties of CS under inert conditions. Combined use of glycerol and GS led to substantially enhanced mechanical properties. The electrical conductivity was increased with increasing GS loading in nanocomposite. This study demonstrates how CS/GS nanocomposites performance properties can be tailored by controlling GsS and plasticizer content.

Scalable production of water-dispersible reduced graphene oxide and its integration in a field effect transistor

The development of environmentally benign, low-processing and low-cost approaches to the large-scale preparation of advanced nanomaterials based on the use of biological materials is currently attracting great interest. Here, we report the discovery that aqueous honey solutions reduce graphene oxide in a low-cost and an eco-friendly manner, yielding highly water dispersive functionalized reduced graphene sheets. The roles of honey in the reduction of graphene oxide of as-prepared graphene are demonstrated. The possible mechanism for the de-epoxidation of graphene oxide is elucidated. The fabricated a honey-reduced graphene oxide-based field-effect transistor exhibited ambipolar transfer characteristics, thereby demonstrating that the developed material may therefore have applications in electronic devices and sensors.

Synthesis of Pseudocapacitive Polymer Chain Anode and Subnanoscale Metal Oxide Cathode for Aqueous Hybrid Capacitors Enabling High Energy and Power Densities along with Long Cycle Life

AbstractAqueous electrochemical energy storages are of enormous attention due to their high safety and being environmentally friendly, but they must satisfy very challenging standards in energy and power densities over long repeated charging/discharging cycles. Herein, a strategy to realize high‐performance aqueous hybrid capacitors (AHCs) using pseudocapacitive negative and positive electrodes is reported. Polymer chains, which are synthesized by in situ polymerization of polyaniline on reduced graphene sheets, show fiber‐like morphologies and the redox‐reactive surface area allowing high capacitance as anode materials even at a high current density of 20 A g−1 and a high loading of ≈6 mg cm−2. Additionally, subnanoscale metal oxide particles on graphene are utilized as pseudocapacitive cathode materials and they show the approximately threefold higher capacitance than nanocrystals of ≈10 nm. Assembling these polymer chain anode and subnanoscale metal oxide cathode in full‐cell AHCs is shown to give the high energy density exceeding those of aqueous batteries along with the ≈100% capacity retention over 100 000 redox cycles. Additionally, AHCs exhibit the high power density allowing ultrafast charging, so that the switching wearable display kit with two AHCs in series can be charged within several seconds by the flexible photovoltaic module and USB switching charger.

ZnO/rGO/C composites derived from metal–organic framework as advanced anode materials for Li-ion and Na-ion batteries

A novel ZnO/reduced graphene oxide/carbon (ZnO/rGO/C) composite is synthesized by pyrolysis of Zn-based metal–organic framework where graphene oxide and the glucose are imported as carbon sources. As a result, ZnO nanoparticles dispersing on a uniform reduced graphene sheet with a thin carbon layer construct a unique structure, which can prevent the aggregation of ZnO, enhance the electronic conductivity, and offer a robust scaffold during electrochemical processes. Compared to the bare ZnO and ZnO/rGO, the obtained ZnO/rGO/C composite can exhibit a high reversible capacity (~ 830 mA h g−1 after 100 cycles, approximately 85% of theoretical capacity), and superior rate capability as anodes for Li-ion battery. Additionally, the electrochemical property of ZnO-based materials for Na-ion batteries is also proposed for the first time. It demonstrates that the as-synthesized ZnO/rGO/C composite also delivers an outperformance cyclic stability and considerable reversible capacity (~ 300 mA h g−1 after 100 cycles). This simple methodology can be further extended to other energy storage applications.

Preparation and electrochemical properties of polyaniline/reduced graphene oxide composites

ABSTRACTPolyaniline (PANI)/reduced graphene oxide (rGO) composites were synthesized by in situ oxidative polymerization of aniline on reduced graphene sheets. Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, transmission electron microscopy, and scanning electron microscopy were used to characterize the composites. The results indicated PANI/rGO composites were produced and contained covalent bonds between the functional groups of PANI and rGO. A uniform coating of PANI on the rGO sheets had a synergistic effect on the properties of the composites. The electrochemical properties of the PANI/rGO composites produced using different feed ratios of aniline to rGO were studied. The results showed that the composites exhibited a maximum specific capacitance of 797.5 F/g at 0.5 A/g and minimum charge transfer resistance of 0.98 Ω when the feed ratio of aniline to rGO was 2:1. These values were superior to those of pure PANI and rGO. The composites also displayed excellent cycling stability, with specific capacitance retention of 92.43% after 1000 cycles. These stable structural composites show promise for the development of new supercapacitor applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46103.

Simultaneous Electrospinning and Electrospraying: Fabrication of a Carbon Nanofibre/MnO/Reduced Graphene Oxide Thin Film as a High‐Performance Anode for Lithium‐Ion Batteries

AbstractRational fabrication of flexible thin‐film electrodes with superior electrochemical performance is challenging now in consumer electronics miniaturization. In this work, we combine electrospinning with electrospraying in a simultaneous process to achieve the CNFs/MnO/rGO composite film electrodes (CNFs=carbon nanofibres; rGO=reduced graphene oxide) for lithium‐ion batteries. For the as‐obtained thin‐film electrode, the 2D reduced graphene sheets are dispersed on each of the 1D CNFs/MnO composite filaments, in which the nanofibres and rGO nanosheets can form interconnected morphologies simultaneously. The thin‐film electrodes with enhanced electrical conductivity and flexibility could efficiently accommodate the volume changes of MnO particles by the very elastic buffer space. As expected, the composite electrode exhibits a high discharge capacity of 1118 mAh g−1 at 0.1 A g−1, and then back to 0.1 A g−1 after 80 cycles, the capacity retention is still up to 98 %; at high rates (e. g. 5 A g−1), the composite is still able to maintain a high reversible capacity of 574 mAh g−1 after 3000 cycles with a significant Coulombic efficiency of 99 %. This is the best specific capacity at 5 A g−1 and longest cycling life reported for MnO thin‐film anodes. In addition, the technique provides a facile path to combine 1D fibres/2D nanosheets layer‐by‐layer in a composite film with tunable fibre diameter. This is the first time that the fabrication of 1D CNFs/MnO fibres and 2D rGO sheet network film electrodes via simultaneous electrospinning and electrospraying methods has been reported.

The Effect of Varying Ultrafast Pulse Laser Energies on the Electrical Properties of Reduced Graphene Oxide Sheets in Solution

Laser treatment of graphene oxide solution among other techniques is a well-established technique for producing reduced graphene sheets. However, production of high-quality ultra-low sheet resistance reduced graphene oxide (rGO) sheets in solution has been a challenge due to their high degree of randomness, defect-rich medium, and lack of controlability. Recent studies lack an in-depth analytic comparison of laser treatment parameters that yield the highest quality rGO sheets with a low defect ratio. Hence, in this study, we implement a comprehensive comparison of laser treatment parameters and their effect on the yielded rGO sheets from an electronic and physical standpoint. Ultra-low sheet resistance graphene oxide sheets were fabricated using ultrafast laser irradiation with different laser pulse energies in the range of 0.25–2 mJ. Laser treatment for 10 min using a pulse energy of 1 mJ resulted in an increase in the defect spacing, accompanied by a large red shift in the optical absorption of the C=C bond, indicating significant restoration of the sp 2 carbon bonds. These enhancements resulted in a significant reduction in the electrical resistance of the rGO flakes (up to 2 orders of magnitude), raising the electron mobility of the films produced using the irradiated graphene oxide a step closer to that of pristine graphene films. From this study, we can also deduce which exposure regimes result in the fabrication of quantum dots and continuous defect-free films.

Facile fabrication of graphene-based aerogel with rare earth metal oxide for water purification

We report a one-step facile fabrication of macroscopic multifunctional graphene-based aerogel with three-dimensional interconnected networks under the synergistic effects of the reduction of graphene oxide sheets by L-ascorbic acid and in situ simultaneous deposition of nanoparticles on graphene sheets. The functional components, Nd2O3 nanoparticles, can be easily incorporated with graphene sheets to assemble bulk macroscopic graphene materials under mild conditions. The reduced graphene oxide/neodymium oxide (rGO/Nd2O3) aerogel showed remarkable adsorption capacity towards different types of dyes, especially for anionic dyes, with the adsorption capacity for indigo disulphonate (ID) being more than 220mgg−1 within one hour while the adsorption capacity at equilibrium is as high as 397mgg−1. The method proposed is proven to be universal to induce macroscopic assembly of reduced graphene sheets with rare earth metal oxides and thus facilitates to accessing various graphene-based multifunctional nanocomposites in the form of macroscopic aerogels.

Preparation of nanoporous graphene sheets via free radical oxidation of graphene oxide and their application in lithium ion battery

Graphene is an attractive candidate for use as an electrode material in electrochemical energy storage due to its unique structure and excellent properties. Compared with graphene, nanoporous graphene is a superior electrode material, owing to the porous structure of its graphene sheets, which facilitates cross-plane lithium ion transportation and provides more binding sites for the lithium ions during the lithiation/delithiation process. In this work, we demonstrate a simple and efficient strategy for obtaining nanoporous graphene on a large scale. Nanoporous graphene can be generated through the oxidation of graphene oxide by H2O2 under high-power UV irradiation with a subsequent reduction process. The morphology, chemical composition and defects of the as-generated nanoporous graphene were studied. The electrochemical evaluation of the nanoporous graphene sheets showed that it delivered higher specific capacity and better charge/discharge rate capability compared with chemically reduced graphene sheets for use as an anode material in lithium ion batteries.

One-step solvothermal synthesis of TiO2-reduced graphene oxide nanocomposites with enhanced visible light photoreduction of Cr(VI)

Hexavalent chromium, Cr(VI), is a mutagenic and carcinogenic heavy metal environmental pollutant. Photoreduction is one of the remediation methods of the hexavalent chromium Cr(VI), which necessitates design of an efficient catalyst for visible light performance. Here, we report a one-step solvothermal synthesis of TiO2-reduced graphene oxide (TiO2-xRGO) composite catalysts using a mild reducing agent, dimethylformamide (DMF). Nanoscale TiO2 particles in the size range of 4–9 nm were formed on the reduced graphene sheets. The formation of the composite catalysts was accompanied by the appearance of a large fluorescence quenching, which indicates an efficient separation of photogenerated electrons and holes. The composites displayed excellent photoreduction of Cr(VI) in the visible light, which was found to be a function of the weight percentage of RGO in the composite. At the optimum composition of TiO2-xRGO, a maximum removal rate of 96% was recorded, which was higher than that of the pristine TiO2, which showed no appreciable catalytic activity under the same condition. The performance degraded with increasing RGO content in the composite, which can be attributed to the higher electron-hole recombination on the RGO surface. The Cr(VI) photoreduction also exhibited a pH dependence. The highest removal rate was observed in the acidic medium.

Graphene nanowires anchored to 3D graphene foam via self-assembly for high performance Li and Na ion storage

Graphene has been extensively investigated as anode material for Li and Na ion batteries due to its excellent physical and chemical performance. Herein, we report a new member of ‘graphene family’, a reduced graphene nanowire on three-dimensional graphene foam (3DGNW). The novel graphene nanowires were synthesized via a template strategy involving reduction and assembly process of nanosized graphene oxides (nGO), pyrolysis of polystyrene spheres (PS) template and catalytic reaction between GO and PS decomposition products. When evaluated as anodes material for Li and Na ion batteries, the 3DGNW exhibits relatively low discharge-voltage plateau, excellent reversible capacity, rate capability, and durable tolerance. For anode of Na ion batteries, a reversible capacity of more than 301mAhg−1 without capacity fading after 1000 cycles at rate of 1C were achieved. Even at rate of 20C, a high reversible capacity of 200mAhg−1 can be retained. The superior electrochemical performance is ascribed to hierarchical multidimensional graphene architecture, high graphene crystallinity, expansile graphene interlayer distance, and extensively lateral exposed edges/pores, which can promote the electron and ion transport. The realization of assembling reduced graphene sheets to graphene nanowire offers new opportunities for energy storage application of graphene based assembly in future.

Synthesis of Graphene on Conducting Substrate by Electrochemical Deposition Method

Investigation to optimize the synthesis process of graphene on conducting substrate is essential for many applications. In this investigation suitable approach to extract graphene thin film on a conductive ITO substrate is optimized. This optimization is carried out by electrochemical Reduction of Graphene Oxide (RGO) solution utilizing a repetitive cyclic potential against reference electrode. To do this, Silver chloride reference electrode is employed within a three electrode system at a potential range of (0 to -1.5) V. A number of four consecutive cycles is used to obtain a negative reduction peak. Yet more importantly the material’s electrochemical properties were studied by Cyclic Voltammetry (CV) operation. From CV, it is clear that, the surface area with electrodeposition from ITO to RGO/ITO and RGO/RGO/ITO rates in a potential window of (2V) for (-1 to 1) V is improved. Moreover, Electrochemical Impedance Spectroscopy (EIS) showed reduced electrode surface internal resistance of the modified electrode that dramatic decreased in comparison from 96.33kΩ of RGO/ITO to 32Ω of RGO/RGO/ITO. In addition, Charge/Discharge Cycle (CDC) is obtained that showed relatively symmetrical charging property along with its corresponding discharge equivalents viewing rapid charging/discharging process that favors redox process for increased mobility and thus conductivity improvement. Moreover the modified electrode was studied for its physical characteristics using Scanning Electron Microscopy (SEM) that showed uniform reduced graphene sheets deposition with particles diameter ranging from 1.65µm to 635nm. Atomic Force Microscopy (AFM) was used in contact mode for a square area of 5µm showing increased surface roughness from ITO of 2.773nm in comparison to Reduced Graphene Oxide/RGO/ITO 34.93nm. Results also proved that deposition of multiple layers of Graphene could strongly improve energy storage applications if implemented by allowing the material to hold greater charge in smaller area. This will lead to enhance the power densities far beyond existing electrochemical capacitors in a cost effective eco-friendly manner.

Intercalated reduced graphene oxide and its content effect on the supercapacitance performance of the three dimensional flower-like β-Ni(OH)2 architecture

Anchoring of three dimensional (3D) metal oxides with a controlled morphology on a reduced graphene sheet (rGO) is a promising and challenging route towards the development of highly efficient electrode materials for supercapacitor applications.