Solution-based Graphene Research Articles

Air-stable, long-length, solution-based graphene nanoribbons.

Within the context of nanoelectronics, general strategies for the development of electronically tunable and air stable graphene nanoribbons are crucial. Previous studies towards the goal of processable nanoribbons have been complicated by ambient condition instability, insolubility arising from aggregation, or poor cyclization yield due to electron deficiency. Herein, we present a general strategy for the elongation of smaller graphene nanoribbon fragments into air-stable, easily processed, and electronically tunable nanoribbons. This strategy is facilitated by the incorporation of electron-rich donor units between electron-poor acceptor perylene diimide oligomeric units. The ribbons are processed in solution via a visible-light flow photocyclization using LEDs. The resulting long nanoribbons can be solution-cast and imaged, which are necessary characteristics for device fabrication. The ribbons become conductive after thermolysis of the pendent side-chains. The electron-accepting character of these nanoribbons in solution is reversible, and the conductivity of the thermolyzed species as a solid remains stable. This work highlights our general strategy for the mild and reliable fabrication of tunable and ambient-stable graphene nanoribbons, and charts a straightforward route for facile device incorporation.

Highly sensitive and portable gas sensing system based on reduced graphene oxide

Graphene has been widely used in gas-sensing applications due to its large specific surface area and strong adsorption ability. Among different forms of graphene used as gas-sensing materials, reduced graphene oxide is one of the most convenient and economical materials to integrate with Si-based electronics, which is very important to graphene-based gas sensors. In addition, the stacking structure of graphene oxide flakes facilitates absorption and detection of gas molecules. Based on reduced graphene oxide, a highly sensitive and portable gas-sensing system was demonstrated here. Solution-based graphene oxide was cast on a chip like a TF memory card and then reduced thermally. A signal acquisition system was designed to monitor resistance variation as a sign of gas concentration. This miniature graphene-based gas sensor array demonstrates a new path for the use of graphene in gas-detection technologies. And the creation of a sensitive and portable graphene gas sensor also shows great potential in fields such as medicine and environmental science.

New insights into the thermal reduction of graphene oxide: Impact of oxygen clustering

Graphene has attracted interest for a number of applications ranging from electronics, optoelectronics to membrane-based technologies. The thermal reduction of chemically exfoliated graphene oxide (GO) sheets represents an important step for large-scale, solution-based graphene synthesis. Therefore, understanding the reduction process and being able to provide new handles to control the resulting sheet properties is highly desirable. Using atomistic calculations combined with experiments, we study and demonstrate the impact of one such new handle – oxygen clustering on the graphene basal plane – on the structural and electrical properties of reduced GO (rGO) structures. Our calculations reveal that the number of oxygen and carbon atoms removed from the graphene plane during reduction can be tuned depending on the degree of oxygen clustering, without altering the reduction temperature. Further, we demonstrate that rGO thin films with improved sheet resistance (up to 2-fold smaller) can be obtained by facilitating oxygen clustering prior to reduction. Overall, our results highlight that oxygen clustering serves as a useful handle in controlling the structural and electrical properties of the resulting rGO structures, and could be potentially useful toward the synthesis of electrodes, graphene quantum dots and for different graphene-based thin film applications.

Large-scale production of high-quality reduced graphene oxide

Large-scale (2kg/day) solution-based graphene was fabricated in a continuous pilot process. It was found that controlling the heat of solution, ΔHsoln, rather than that of the oxidation reaction, ΔHrxn, was crucial for safe operation because the heat-release rate of the dissolution of the oxidizer to sulfuric acid was higher than that of the oxidation of graphite to graphite oxide (GO). A small amount of water can also suppress the formation of the peroxide form that can cause an explosion. Three continuous stirred tank reactors (CSTRs) in series were used to feed the graphite and oxidizer step by step with slightly diluted sulfuric acid solution. The main oxidation reaction requires more than 2h at 50°C for adequate oxidation when the Hummers method is used. Reduced graphene oxide (RGO) prepared using the continuous thermal reduction equipment shows electrical conductivity of 600S/m and a BET surface area of 400–600m2/g, which were comparable to the values for RGOs fabricated using well-controlled laboratory scale procedures.

Thiourea Dioxide as a Green Reductant for the Mass Production of Solution-Based Graphene

Abstract Mass production of solution-based graphene derived from the precursor graphene oxide is a challenging step toward achieving industrialization of graphene. Inspired by a classical reducing method performed in the textile and paper making industries, we report here a rapid, cost-effective, and safer approach to the facile production of graphene that employs thiourea dioxide (TDO) as the green reductant. Graphene oxide was converted into high quality graphene within 30 min with TDO as the reductant under moderate reaction conditions. The C/O ratio of the TDO reduced graphene was ca. 5.9 with the yield of graphene from graphene oxide >99%. This is better than the reduction efficiency under the identical experimental conditions by using l-ascorbic acid as the reductant which required a reaction time of about 48 h. This simple and effective procedure should offer an alternative route to the mass production of solution-based graphene for practical applications.

Flexible Gigahertz Transistors Derived from Solution-Based Single-Layer Graphene

Flexible electronics mostly relies on organic semiconductors but the limited carrier velocity in polymers and molecular films prevents their use at frequencies above a few megahertz. Conversely, the high potential of graphene for high-frequency electronics on rigid substrates was recently demonstrated. We conducted the first study of solution-based graphene transistors at gigahertz frequencies, and we show that solution-based single-layer graphene ideally combines the required properties to achieve high speed flexible electronics on plastic substrates. Our graphene flexible transistors have current gain cutoff frequencies of 2.2 GHz and power gain cutoff frequencies of 550 MHz. Radio frequency measurements directly performed on bent samples show remarkable mechanical stability of these devices and demonstrate the advantages of solution-based graphene field-effect transistors over other types of flexible transistors based on organic materials.

Spin coated graphene films as the transparent electrode in organic photovoltaic devices

Many research efforts have been devoted to the replacement of the traditional indium–tin-oxide (ITO) electrode in organic photovoltaics. Solution-based graphene has been identified as a potential replacement, since it has less than two percent absorption per layer, relative high carrier mobility, and it offers the possibility of deposition on large area and flexible substrates, compatible with roll to roll manufacturing methods. In this work, soluble reduced graphene films with high electrical conductivity and transparency were fabricated and incorporated in poly(3-hexylthiophene) [6,6]-phenyl-C 61-butyric acid methyl ester photovoltaic devices, as the transparent electrode. The graphene films were spin coated on glass from an aqueous dispersion of functionalized graphene, followed by a reduction process combining hydrazine vapor and annealing under argon, in order to reduce the sheet resistance. The photovoltaic devices obtained from the graphene films showed lower performance than the reference devices with ITO, due to the higher sheet resistance (2 kΩ/sq) and the poor hydrophilicity of the spin coated graphene films.