Large-area Reduced Graphene Oxide Research Articles

Evolution of large-area reduced graphene oxide nanosheets from carbon dots via thermal treatment

Herein, we reveal a novel and facile pathway for the synthesis of reduced graphene oxide (rGO) from annealed carbon dots (CDs). The CDs (~ 2.5 nm) were synthesized from L-ascorbic acid via microwave synthesis at 180°C, after which formation of rGO nanosheets (≥ 40% yield) was achieved through 10 min annealing of CDs under N2 from 250-700°C. The TEM images showed that the CDs are initially transformed into an accreted sphere-like turbostratic carbon (d = 0.3390 nm) after annealing at 250°C, and finally to a layered ‘graphene-like’ nanomaterial (length ≈ 0.2-2.6 µm) at thermal treatment temperatures ≥ 500°C. The transformation into rGO was evidenced by the decrease in the oxygenated functional group content and removal of the oxygen functional groups facilitated the growth of rGO nanosheets through the interconnection of the C-C bonds at the defected CD edges. The FTIR, PL, PDF, and 13C NMR spectra confirmed the loss of functional groups after annealing at 700°C. Raman, and in particular PDF data, confirmed and rationalised the growth and evolution of the structured carbon domains with increasing annealing temperature. A mechanism to rationalize the data is proposed.

Assembly of large-area reduced graphene oxide films for the construction of Z-scheme over single-crystal porous Bi5O7I nanosheets

In this work, we have firstly achieved the construction of bismuth oxyiodide (Bi5O7I)/reduced graphene oxide (rGO)/ZnO Z-scheme photoelectrochemical (PEC) system without backward reactions through loading large-area ZnO quantum dots (QDs)/rGO films on Bi5O7I nanosheets. Single-crystal porous Bi5O7I nanosheets with numerous oxygen vacancies (OVs) were firstly fabricated through the calcination of BiOI in reductive glycols. The single-crystal facilitates charge transport, nanoporous structure promotes light absorption and OVs improves charge separation efficiency. As a result, single-crystal porous Bi5O7I nanosheets with OVs exhibited higher PEC performance than other morphologies reported before. Moreover, The PEC activity of Bi5O7I can be further enhanced through loading large-area ZnO QDs/rGO films to construct a pure Z-scheme charge transfer system, which not only achieves efficient separation of electron-hole pairs but also retains its excellent redox ability. To the best of our knowledge, the photocurrent density of Bi5O7I/rGO/ZnO heterostructures is the highest among Bi5O7I-based samples. For comparison, an opposite Z-scheme model has also been built up by replacing Bi5O7I with WO3, in which the photocurrent density decreased conversely. Therefore, it can be known that a pure Z-scheme system without backward reactions can be successfully prepared through loading ZnO QDs/rGO films on photoelectrodes.

In Situ Surface-Enhanced Infrared Absorption Spectroscopy of Aqueous Molecules with Facile-Prepared Large-Area Reduced Graphene Oxide Island Film.

Midinfrared plasmons in patterned graphene could advance the development of surface-enhanced infrared absorption spectroscopy (SEIRAS). However, limitation in measuring the extinction spectra with transmission and external reflection configurations greatly restricts the analyses of aqueous samples. In addition, complicated, time- and cost-consuming preparation of patterned graphene also limits its progress. Here we demonstrate a facile-prepared large-scale reduced graphene oxide island film on a total internal reflection silicon prism, which not only shows a prominent enhancement effect in mid-infrared region but also effectively eliminates the contribution of bulk solution by optical near-field effect. As a result, the entire vibrational fingerprints of methylene blue monolayer in aqueous solution can be acquired with high sensitivity in real time. Our work extends the application of graphene-based SEIRAS to aqueous environment, breaking through previously unattainable technology.

Reduced Graphene Oxide Thin Films with Very Large Charge Carrier Mobility Using Pulsed Laser Deposition

Large area reduced graphene oxide (RGO) thin films have been grown using pulsed laser deposition (PLD) technique. A very large carrier mobility of 372 cm2 V-1s-1 has been observed in a PLD grown RGO thin film with a large sp2 carbon fraction of 87% along with narrow Raman 2D peak profile. The fraction of sp2 carbon and carbon/oxygen ratios are tuned through PLD growth parameters, and these are estimated from X-ray photoelectron spectroscopy (XPS) data. The electrical properties of the RGO thin films are comprehended by the intensity ratios between different optical phonon vibrational modes of Raman Spectra. The photoluminescence spectra also indicate a less intense and broader blue fluorescence spectrum detecting the presence of miniature sized sp2 domains in the near vicinity of π* electronic states which favor the variable range hopping transport phenomena. This study on large area RGO thin films with very large carrier mobility fabricated by PLD process will be very useful for high mobility electronic device applications and could open a roadmap for further extensive research in functionalized 2D materials.

Ultraviolet photosensor based on few layered reduced graphene oxide nanosheets

Reduced graphene oxide (RGO), a two-dimensional (2D) system, has attracted much interest in photonic applications owing to its ability to absorb light over a broad wavelength. This leads to several studies on RGO-based photosensors. In this paper, chemical oxidation of graphite was carried out at room temperature for the preparation of large area reduced graphene oxide using a modified Hummer’s method. The as-prepared reduced graphene oxide was characterized by XRD, Raman spectroscopy, FESEM, and TEM to confirm the absence of impurities and to ascertain their morphology. In addition, the as-prepared reduced graphene oxide for its possible application as UV photosensor is reported. The electric and optoelectronic properties of RGO based UV photosensor shows a fast response and recovery time of 1s and 3s; high photoresponsitivity (3.74AW−1) and quantum efficiency (1274%) indicating that the graphene oxide is an important material for high performance photosensor. This work demonstrates the ultrafast photoresponse with high photoresponsivity, proving its potential as a promising material for optoelectronic devices.

Highly conductive, monolayer and large-area reduced graphene oxide films fabricated by electrical connection at the two-dimensional boundaries between the tiled graphene oxide flakes

The demand to fabricate graphene film in large wafer-scale with minimum cost is crucial for device applications, and one of the promising techniques is the reduction of graphene oxide (GO) films. We have investigated morphological changes of large-area, monolayer GO films during methane (CH4)-assisted thermal annealing process and the role of CH4 in the restoration of their electrical conductivity. We have discovered that long reduction process in high CH4 flow rates can contribute to the partial reparation of lattice defects and formation of new multilayer graphene that are stacked at the boundary areas between the reduced GO (rGO) flakes. These multilayer graphene layers with graphitic domains operate as the electrical connection between the separated rGO flakes and create new conduction pathways across the entire films. This phenomenon is more important than the sole reduction process (elimination of oxygen functional groups) in the restoration of electrical conductivity of the continuous rGO films. We have achieved in the fabrication of highly conductive rGO films with a minimum sheet resistance value of 1.01kΩ/sq. This study exhibits a promising reduction method for the mass production of large-area, continuous rGO films for thin film device applications.

Binder-free combination of large area reduced graphene oxide nanosheets with Cu foil for lithium ion battery anode

Binder-free combination of large area reduced graphene oxide (RGO) nanosheets with Cu foil was designed and achieved via one-step facile electro-reduction reaction. The obtained composite RGO/Cu foil electrode were studied in terms of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman, galvanostatic charge/discharge, AC impedance and cyclic voltammetry (CV). As expected, large area RGO nanosheets with micron order of magnitude successfully formed and tightly combined with Cu foil without any additional polymer binders. Furthermore, RGO/Cu foil electrode delivered a reversible discharge capacity of 870.3mAh/g after 110cycles, indicating satisfactory cyclic stability and rate performance. High Li-storage activity, eminent conductivity and tight binder-free integration of RGO nanosheets with Cu foil current collector should be responsible for high electrochemical performances.

Catalytic tailoring of large-area reduced graphene oxide by tunable arrays of Pt nanostructures synthesized from self-assembling diblock copolymers

In this study, the large-area tailoring of reduced graphene oxide (rGO) with tunable arrays of Pt nanostructures has been demonstrated. We synthesized arrays of catalytic Pt nanoparticles, nanowires, and their combined nanostructures from self-assembled thin films of polystyrene-block-poly(4-vinylpyridine) copolymers and their micelles. Then, rGO was transferred onto these Pt nanostructures, which were capable of catalyzing the oxidative elimination of carbon atoms from the rGO nanoregions in contact with the Pt, resulting in successful pattern transfer from the Pt nanoarrays onto the rGO, forming various nanostructures, such as nanoholes, nanoribbons, and perforated nanoribbons. Moreover, we transferred the tailored rGO onto a transparent and flexible polymeric substrate. The size and periodicity of the rGO nanostructures were controlled on the nanometer scale by adjusting those of the Pt nanostructures, which were strongly dependent on the molecular weights of the copolymers. In addition, arrayed Pt nanowires were aligned in a topographically patterned substrate by the directed self-assembly of the copolymers, enabling the fabrication of well-aligned rGO nanoribbon and nanosquare arrays.

Size-controllable synthesis of Fe3O4 nanospheres decorated graphene for electromagnetic wave absorber

A large-area reduced graphene oxide (RGO)/Fe3O4 nanocomposite has been synthesized for electromagnetic wave absorber by a simple hydrothermal method. A series of characterization methods including transmission electron microscopy, X-ray diffraction, Raman spectroscopy and vibrating sample magnetometer indicate that masses of Fe3O4 nanospheres are well decorated on the thin RGO sheets and the nanocomposite exhibit ferromagnetic behavior at room temperature. Moreover, the size of Fe3O4 nanospheres which are decorated on RGO surface can be controlled by adjusting the concentration of FeCl3·6H2O in ethylene glycol/diethylene glycol binary solvent mixtures. Electromagnetic wave absorption properties of the as-synthesized nanocomposite have been investigated by a vector network analyzer between 2 and 18 GHz at room temperature. The electromagnetic data demonstrate that the Fe3O4/RGO nanocomposite can be a powerful candidate in the field of electromagnetic wave absorption, which probably originates from the proper electromagnetic match and strong electromagnetic wave attenuation in the materials. A possible formation mechanism of Fe3O4/RGO nanocomposite based on the hydrothermal method has also been proposed.

Large-area reduced graphene oxide thin film with excellent thermal conductivity and electromagnetic interference shielding effectiveness

In this work, we fabricated reduced large-area graphene oxide (rLGO) with maximum surface area of 1592μm2 through a cost-effective chemical reduction process at low temperature. The product revealed large electrical conductivity of 243±12Scm−1 and thermal conductivity of 1390±65Wm−1K−1, values much superior to those of a conventional reduced small-area graphene oxide (with electrical conductivity of 152±7.5Scm−1 and thermal conductivity of 900±45Wm−1K−1). The rLGO thin film also exhibited not only excellent stiffness and flexibility with Young’s modulus of 6.3GPa and tensile strength of 77.7MPa, but also an efficient electromagnetic interference (EMI) shielding effectiveness of ∼20dB at 1GHz. The excellent performance of rLGO is attributed to the fact that the larger area LGO sheets include much fewer defects that are mostly caused by the damage of graphene sp2 structure around edge boundaries, resulting in large electrical conductivity. The manufacturing process of rLGO is an economical and facile approach for the large scale production of highly thermally conducting graphene thin films with efficient EMI shielding properties, greatly desirable for future portable electronic devices.

Reduced Graphene Oxide Micromesh Electrodes for Large Area, Flexible, Organic Photovoltaic Devices

A laser‐based patterning technique—compatible with flexible, temperature‐sensitive substrates—for the production of large area reduced graphene oxide micromesh (rGOMM) electrodes is presented. The mesh patterning can be accurately controlled in order to significantly enhance the electrode transparency, with a subsequent slight increase in the sheet resistance, and therefore improve the tradeoff between transparency and conductivity of reduced graphene oxide (rGO) layers. In particular, rGO films with an initial transparency of ≈20% are patterned, resulting in rGOMMs films with a ≈59% transmittance and a sheet resistance of ≈565 Ω sq−1, that is significantly lower than the resistance of ≈780 Ω sq−1, exhibited by the pristine rGO films at the same transparency. As a proof‐of‐concept application, rGOMMs are used as the transparent electrodes in flexible organic photovoltaic (OPV) devices, achieving power conversion efficiency of 3.05%, the highest ever reported for flexible OPV devices incorporating solution‐processed graphene‐based electrodes. The controllable and highly reproducible laser‐induced patterning of rGO hold enormous promise for both rigid and flexible large‐scale organic electronic devices, eliminating the lag between graphene‐based and indium–tin oxide electrodes, while providing conductivity and transparency tunability for next generation flexible electronics.

Preparation of flexible reduced graphene oxide/poly(vinyl alcohol) film with superior microwave absorption properties

In this study, a large-area reduced graphene oxide (rGO)/poly(vinyl alcohol) (PVA) film with excellent microwave absorption properties in the range of 2–18 GHz has been prepared by a simple solution processing method.

Porous conducting polymer and reduced graphene oxide: preparation, characterization and electrochemical performance

We demonstrated direct deposition a porous conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructure on reduced graphene oxide (RGO) as high performance electrochemical electrode. The large area RGO film was constructed on substrate through a Langmuir–Blodgett deposition of graphene oxide and a following reductive treatment. The porous PEDOT nanostructure was successively constructed on RGO through an in situ solution polymerization and simple thermal treatment. This porous PEDOT/RGO nanocomposites contained large and highly opened surface area with superior electrochemical activity. A specific capacitance as high as 267 F/g at a current density of 0.5 A/g was achieved. The compared conductive performance between RGO and porous PEDOT resulted in better EIS performance of composite electrode. The stable covering of porous PEDOT on RGO also improved the capacitance retention performance of PEDOT, and the nanocomposites showed excellent capacitance retention rate after 4,000 charge/discharge cycles. The research data revealed that high specific capacitance and good cycling stability can be achieved either by coupling the advantages of carbon materials and conducting polymer.

Deterministic growth of AgTCNQ and CuTCNQ nanowires on large-area reduced graphene oxide films for flexible optoelectronics

We describe a synchronous reduction and assembly procedure to directly produce large-area reduced graphene oxide (rGO) films sandwiched by a high density of metal nanoparticles (silver and copper). Further, by using the sandwiched metal NPs as sources, networks consisting of AgTCNQ and CuTCNQ nanowires were deterministically grown from the rGO films, forming structurally and functionally integrated rGO/metal-TCNQ hybrid films with outstanding flexibility, bending endurance, and electrical stability. Interestingly, due to the p-type nature of the rGO film and the n-type nature of the metal-TCNQ NWs, the hybrid films are essentially thin-film p–n junctions which are useful in ubiquitous electronics and optoelectronics. Measurements of the optoelectronic properties demonstrate that the rGO/metal-TCNQ hybrid films exhibit substantial photoconductivity and highly reproducible photoswitching behaviours. The present approach may open the door to the versatile and deterministic integration of functional nanostructures into flexible conducting substrates and provide an important step towards producing low-cost and high-performance soft electronic and optoelectronic devices.

The preparation of the poly(vinyl alcohol)/graphene nanocomposites with low percolation threshold and high electrical conductivity by using the large-area reduced graphene oxide sheets

We report a method to prepare the poly(vinyl alcohol)/reduced graphene oxide (PVA/rGO) nanocomposites with low percolation threshold and high electrical conductivity by using the large-area reduced graphene oxide (LrGO) sheets. The large-area graphene oxide (LGO) sheets are expected to overlap better with each other and form the continuous GO network in PVA matrix than small-area graphene oxide (SGO). During the thermal reduction process, the LGO sheets are easily restored and improve the electrical conductivity of nanocomposites due to their low damage level of conjugate-struc- ture. As a result, the percolation threshold of PVA/LrGO nanocomposites is ~0.189 wt% lower than present reports (0.5~0.7 wt%). At the LrGO content of 0.7 wt%, the electrical conductivity of PVA/LrGO nanocomposites reaches 6.3·10 -3 S/m. Besides that, this method only takes 15~30 min to reduce the PVA/GO nanocomposites effectively.

Position dependent photodetector from large area reduced graphene oxide thin films

We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases, or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemical synthesis and interconnecting sheets.

Photo-assisted preparation and patterning of large-area reduced graphene oxide–TiO2 conductive thin film

A mild photo-assisted reduction method was developed to fabricate large-area, uniform reduced graphene oxide-TiO(2) films and micropatterns on various substrates in air at room temperature from a composite insulating film of graphene oxide sheets and TiO(2) nanoparticles, with a conductivity (0.5-2 Omega cm) comparable to chemically reduced graphene.