Reduced Graphene Oxide Films Research Articles

Single-layer graphene oxide films on a silicon surface

A method is proposed to produce large-area single-layer graphene oxide films on the surface of semiconductor silicon wafers by precipitation from aqueous suspensions. Graphene oxide is synthesized from natural crystalline graphite during chemical oxidation and represents a wide-gap insulator. Single-layer graphene with a homogeneous-fragment size up to 50 μm can be formed by the reduction of graphene oxide films, and this size is significantly larger than those achieved to date.

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.

Flexible NO2 sensors fabricated by layer-by-layer covalent anchoring and in situ reduction of graphene oxide

Novel flexible NO2 gas sensors were fabricated by covalently bonding graphene oxide (GO) to a gold electrode on a plastic substrate using a peptide chemical protocol and then reducing in situ GO film to a reduced GO (RGO) film. A pair of comb-like Au electrodes on a polyethylene terephthalate (PET) substrate were pretreated with cysteamine hydrochloride (CH) and then reacted with GO using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) as the peptide coupling reagent, before undergoing a final reduction by sodium borohydride (NaBH4). The anchored RGO film was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR). The gas sensing properties, including sensitivity, sensing linearity, reproducibility, response time, recovery time, cross-sensitivity effects and long-term stability, were investigated. Interfering gas NH3 affected the limit of detection (LOD) of a target NO2 gas in a real-world binary gas mixture. The flexible NO2 gas sensor exhibited a strong response and good flexibility that exceeded that of sensors that were made from graphene film grown by chemical vapor deposition method (CVD-graphene) at room temperature. Its use is practical because it is so easy to fabricate.

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.

Simultaneous synthesis and patterning of graphene electrodes by reactive inkjet printing

Reactive inkjet printing (RIP), a single-step process for micro-chemical reactions and arbitrary patterning, was applied to fabricate reduced graphene oxide (RGO) films. Graphene oxide was successfully reduced to RGO through the RIP process. The printed RGO films showed moderate conductivity and transmittance. LED operation with reactive inkjet-printed RGO electrodes was also demonstrated. By utilizing this printing method, we can drop additional reducing steps and obtain directly patterned RGO instead, which suggests that reactive inkjet-printed RGO would be feasible for use as transparent electrodes to replace indium tin oxide in displays and photovoltaic devices.

π‐Conjugated Molecules Crosslinked Graphene‐Based Ultrathin Films and Their Tunable Performances in Organic Nanoelectronics

Graphene‐based ultrathin films with tunable performances, controlled thickness, and high stability are crucial for their uses. The currently existing protocols, however, could hardly simultaneously meet these requirements. Using amino‐substituted π‐conjugated compounds, including 1,4‐diaminobenzene (DABNH2), benzidine (BZDNH2), and 5,10,15,20‐tetrakis (4‐aminophenyl)‐21H,23H‐porphine (TPPNH2), as cross‐linkages, a new protocol through which graphene oxide (GO) nanosheets can be anchored on solid supports with a high stability and controlled thickness via a layer‐by‐layer method is presented. A thermal annealing leads to the reduction of the films, and the qualities of the samples can be inherited by the as‐produced reduced GO films (RGO). When RGO films are integrated as source/drain electrodes in OFETs, tunable performances can be realized. The devices based on the BZDNH2‐crosslinked RGO electrodes exhibit similar electrical behaviors as those based on the non‐π‐conjugated compound crosslinked electrodes, while improved performances can be gained when those crosslinked by DABNH2 are used. The performances can be further improved when RGO films crosslinked by TPPNH2 are employed. This work likely paves a new avenue for graphene‐based films of tunable performances, controlled thickness, and high stability.

Hybrid film of chemically modified graphene and vapor-phase-polymerized PEDOT for electronic nose applications

A hybrid of graphene and conducting polymer holds great potential as the active materials for high performance chemical sensor application. In this work, a thin hybrid film of reduced graphene oxide (RG-O) and poly(3,4-ethylenedioxythiophene) (PEDOT) was fabricated by means of vapor phase polymerization and explored as active material for chemical sensors. The chemical sensors based on hybrid film of RG-O and PEDOT are capable of detecting electrical signals caused by the absorption of trace levels of different analyte vapors with high sensitivity, selectivity and fast response.

Chemically Reduced Graphene Oxide for Ammonia Detection at Room Temperature

Chemically reduced graphene oxide (RGO) has recently attracted growing interest in the area of chemical sensors because of its high electrical conductivity and chemically active defect sites. This paper reports the synthesis of chemically reduced GO using NaBH4 and its performance for ammonia detection at room temperature. The sensing layer was synthesized on a ceramic substrate containing platinum electrodes. The effect of the reduction time of graphene oxide (GO) was explored to optimize the response, recovery, and response time. The RGO film was characterized electrically and also with atomic force microscopy and X-ray photoelectron spectroscopy. The sensor response was found to lie between 5.5% at 200 ppm (parts per million) and 23% at 2800 ppm of ammonia, and also resistance recovered quickly without any application of heat (for lower concentrations of ammonia). The sensor was exposed to different vapors and found to be selective toward ammonia. We believe such chemically reduced GO could potentially be used to manufacture a new generation of low-power portable ammonia sensors.

Reduction of graphene oxide films on Al foil for hybrid transparent conductive film applications

We report the reduction of graphene oxide (G-O) films on Al foil using hydrogen as a reducing agent generated during the etching of Al foil in an aqueous solution of hydrochloric acid (HCl). Complete etching of the Al substrate results in simultaneous reduction and a free standing film composed of stacked and overlapped reduced graphene oxide (RG-O) platelets. Generation of hydrogen at the G-O/Al interface increases the reduction efficiency of this method that is demonstrated in better electrical conductivity of the obtained films compared to the RG-O films reduced by the similar method but using remote Al foil in HCl solution and hydrazine reduced RG-O films. By transferring the free standing RG-O films onto Ag NW films, hybrid transparent conductive films (TCFs) with opto-electrical properties comparable to that of ITO films were obtained.

Ultrathin Reduced Graphene Oxide Films as Transparent Top‐Contacts for Light Switchable Solid‐State Molecular Junctions

A new type of solid-state molecular junction is introduced, which employs reduced graphene oxide as a transparent top contact that permits a self-assembled molecular monolayer to be photoswitched in situ, while simultaneously enabling charge-transport measurements across the molecules. The electrical switching behavior of a less-studied molecular switch, dihydroazulene/vinylheptafulvene, is described, which is used as a test case.

Reduced graphene oxide film as a shuttle-inhibiting interlayer in a lithium–sulfur battery

A reduced graphene oxide (rGO) based film is sandwiched between a sulfur cathode and the separator, acting as a shuttle inhibitor to the sulfur and polysulfides. The lithium–sulfur cell with such a configuration shows an initial discharge capacity of 1260 mAh g−1 and the capacity remains at 895 mAh g−1 after 100 cycles. The excellent electrochemical performance of the cell is attributed to both the functional groups on the rGO sheets that anchor the sulfur and polysulfides and the carbon additive that helps to produce channels for the electrolyte and polysulfide to enter.

Terahertz, optical, and Raman signatures of monolayer graphene behavior in thermally reduced graphene oxide films

We report on our joint spectroscopic study of the thermal reduction process of quasi-monolayer graphene oxide films grown on fused silica substrates by spin-coating. We estimate that about 65% of our film area consists of monolayer platelets of reduced graphene oxide, based on our quantitative analysis of the local atomic force microscopy topography. With thermal annealing under suitable conditions, clear signatures of monolayer graphene behavior were identified in the resonant excitonic absorption at 4.55 eV, the overall decrease in the visible-range transmission, the re-emergence of the Raman 2D band, the red-shift of the Raman G band toward the monolayer position, and the decrease in the optical sheet resistance in the terahertz range.

Reduced graphene oxide and CuInS2 co-decorated TiO2 nanotube arrays for efficient removal of herbicide 2,4-dichlorophenoxyacetic acid from water

Refractory herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) can be efficiently removed by photocatalytic degradation when using reduced graphene oxide (RGO) and CuInS2 nanoparticles (NPs) co-decorated TiO2 nanotube arrays (NTs) (RGO/CuInS2–TiO2 NTs) as a photocatalyst prepared by successive pulse electrodeposition of CuInS2 and RGO film onto the top surface of TiO2 NTs. The new catalyst exhibits significant photocatalytic activity and good removal efficiency of 2,4-D. The photodegradation rate toward 2,4-D over RGO/CuInS2–TiO2 NTs under simulated solar light (or visible light) irradiation is 96.2% (or 87.7%), much higher than 68.0% (or 58.4%) over CuInS2–TiO2 NTs, 50.1% (or 38.1%) over RGO–TiO2 NTs and 36.0% (or 26.3%) over bare TiO2 NTs, respectively, meaning that the photocatalytic performance of TiO2 NTs could be greatly enhanced by the synergetic effect of RGO and CuInS2. This work could provide new insights into the design and fabrication of advanced photocatalysts.

Study of Pt catalyst on graphene and its application to fuel cell

In this work Pt nanoparticles on graphene (PtNPs/GN) were formed from graphite oxide by two routes (one-step and two-step routes). For one-step route, a fixed weight of graphene oxide (GO) and a variable weight of H2PtCl6·6H2O were put in ethylene glycol for a reflux at 120 and 150°C for 3, 6, 12 and 24h, respectively. For the two-step route, the first step is reduction of GO films by sodium tetrahydridoborate to obtain graphene. Then, the graphene deposited with Pt particles was put in ethylene glycol for a reflux at 120, 150 and 180°C for 3, 6, 12 and 24h.The results show that the electrode catalyst Pt particles have a smaller size and a better distribution on the surface of graphene under the following reducing condition: two-step reduction, reaction time of 12h, reaction temperature of 150°C and the 1g/L of H2PtCl6. These PtNPs/GN composites exhibit superior electrochemically active surface area and high poison tolerance toward methanol oxidation compared to Vulcan XC-72-Pt with the same Pt content. This revealed that the PtNPs/GN can be used as promising electrocatalyst support for direct methanol fuel cells.

Wafer‐Scale Patterning of Reduced Graphene Oxide Electrodes by Transfer‐and‐Reverse Stamping for High Performance OFETs

A wafer-scale patterning method for solution-processed graphene electrodes, named the transfer-and-reverse stamping method, is universally applicable for fabricating source/drain electrodes of n- and p-type organic field-effect transistors with excellent performance. The patterning method begins with transferring a highly uniform reduced graphene oxide thin film, which is pre-prepared on a glass substrate, onto hydrophobic silanized (rigid/flexible) substrates. Patterns of the as-prepared reduced graphene oxide films are then formed by modulating the surface energy of the films and selectively delaminating the films using an oxygen-plasma-treated elastomeric stamp with patterns. Reduced graphene oxide patterns with various sizes and shapes can be readily formed onto an entire wafer. Also, they can serve as the source/drain electrodes for benchmark n- and p-type organic field-effect transistors with enhanced performance, compared to those using conventional metal electrodes. These results demonstrate the general utility of this technique. Furthermore, this simple, inexpensive, and scalable electrode-patterning-technique leads to assembling organic complementary circuits onto a flexible substrate successfully.

Terahertz conductivity of reduced graphene oxide films

We performed time-domain terahertz (THz) spectroscopy on reduced graphene oxide (rGO) network films coated on quartz substrates from dispersion solutions by spraying method. The rGO network films demonstrate high conductivity of about 900 S/cm in the THz frequency range after a high temperature reduction process. The frequency-dependent conductivities and the refractive indexes of the rGO films have been obtained and analyzed with respect to the Drude free-electron model, which is characterized by large scattering rate. Finally, we demonstrate that the THz conductivities can be manipulated by controlling the reduction process, which correlates well with the DC conductivity above the percolation limit.

Reduced graphene oxide and PbS nanoparticles co-modified TiO2 nanotube arrays as a recyclable and stable photocatalyst for efficient degradation of pentachlorophenol

TiO2 nanotube arrays (TiO2 NTs) were simultaneously modified by reduced graphene oxide (RGO) and PbS nonoparticles (NPs) through a simple one-step electrodeposition process. RGO film is formed on the top surface of TiO2 NTs and PbS NPs showing size less than 20nm are intercalated within the RGO sheets and also dispersed inside/outside walls the TiO2 NTs. Resulting from the synergetic effect of RGO and PbS, the photocatalytic activity of the ternary RGO/PbS-TiO2 NTs photocatalyst far exceeds those of bare TiO2 NTs, the binary RGO-TiO2 NTs and PbS-TiO2 NTs photocatalysts in the degradation of pentachlorophenol (PCP) under simulated solar light. After 120-min irradiation, almost 100% PCP removal is obtained on the RGO/PbS-TiO2 NTs, compared to 61% on bare TiO2 NTs, 76% on RGO-TiO2 NTs, and 86% on PbS-TiO2 NTs. Because the PbS NPs were covered by the RGO sheets, to a certain extent the photocorrosion of PbS was suppressed, and therefore the RGO/PbS-TiO2 NTs photocatalyst shows a good stability relative to the PbS-TiO2 NTs without RGO. This study will inspire better design of advanced photocatalysts with high visible-light photocatalytic activity, easy recovery, and good stability.

A low-temperature method to produce highly reduced graphene oxide

Chemical reduction of graphene oxide can be used to produce large quantities of reduced graphene oxide for potential application in electronics, optoelectronics, composite materials and energy-storage devices. Here we report a highly efficient one-pot reduction of graphene oxide using a sodium-ammonia solution as the reducing agent. The solvated electrons in sodium-ammonia solution can effectively facilitate the de-oxygenation of graphene oxide and the restoration of π-conjugation to produce reduced graphene oxide samples with an oxygen content of 5.6 wt%. Electrical characterization of single reduced graphene oxide flakes demonstrates a high hole mobility of 123 cm(2) Vs(-1). In addition, we show that the pre-formed graphene oxide thin film can be directly reduced to form reduced graphene oxide film with a combined low sheet resistance (~350 Ω per square with ~80% transmittance). Our study demonstrates a new, low-temperature solution processing approach to high-quality graphene materials with lowest sheet resistance and highest carrier mobility.

Towards full repair of defects in reduced graphene oxide films by two-step graphitization

The complete restoration of a perfect carbon lattice has been a central issue in the research on graphene derived from graphite oxide since this preparation route was first proposed several years ago, but such a goal has so far remained elusive. Here, we demonstrate that the highly defective structure of reduced graphene oxide sheets assembled into free-standing, paper-like films can be fully repaired by means of high temperature annealing (graphitization). Characterization of the films by X-ray photoelectron and Raman spectroscopy, X-ray diffraction and scanning tunneling microscopy indicated that the main stages in the transformation of the films were (i) complete removal of oxygen functional groups and generation of atomic vacancies (up to 1,500 °C), and (ii) vacancy annihilation and coalescence of adjacent overlapping sheets to yield continuous polycrystalline layers (1,800–2,700 °C) similar to those of highly oriented graphites. The prevailing type of defect in the polycrystalline layers were the grain boundaries separating neighboring domains, which were typically a few hundred nanometers in lateral size, exhibited long-range graphitic order and were virtually free of even atomic-sized defects. The electrical conductivity of the annealed films was as high as 577,000 S·m−1, which is by far the largest value reported to date for any material derived from graphene oxide, and strategies for further improvement without the need to resort to higher annealing temperatures are suggested. Overall, this work opens the prospect of truly achieving a complete restoration of the carbon lattice in graphene oxide materials.

Fabrication of Electrochemically Reduced Graphene Oxide Films on Glassy Carbon Electrode by Self-Assembly Method and Their Electrocatalytic Application

We report a simple, facile, and reproducible method for the fabrication of electrochemically reduced graphene oxide (ERGO) films on glassy carbon electrode (GCE) by the self-assembly method. The graphene precursor, graphene oxide (GO), was self-assembled on GCE through a diamine linker which was preassembled on GCE by electrostatic interaction between the positively charged amine and the negatively charged layers of graphene oxide (GO). The oxygen functional groups present on the surface of GO were electrochemically reduced to retain the aromatic backbone of graphene. The attachment of GO followed by its electrochemical reduction was confirmed by ATR-FT-IR spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Raman spectra show that the intensity ratio of D and G bands was increased after the electrochemical reduction of GO. XPS results reveal that the carbon-to-oxygen ratio was increased af...