Competitive binding of natural amphiphiles with graphene derivatives

Understanding the transformation of graphene derivatives by natural amphiphiles is essential for elucidating the biological and environmental implications of this emerging class of engineered nanomaterials. Using rapid discrete-molecular-dynamics simulations, we examined the binding of graphene and graphene oxide with peptides, fatty acids, and cellulose, and complemented our simulations by experimental studies of Raman spectroscopy, FTIR, and UV-Vis spectrophotometry. Specifically, we established a connection between the differential binding and the conformational flexibility, molecular geometry, and hydrocarbon content of the amphiphiles. Importantly, our dynamics simulations revealed a Vroman-like competitive binding of the amphiphiles for the graphene oxide substrate. This study provides a mechanistic basis for addressing the transformation, evolution, transport, biocompatibility, and toxicity of graphene derivatives in living systems and the natural environment.

Graphene oxide sheath on Ag nanoparticle/graphene hybrid films as an antioxidative coating and enhancer of surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) has been extensively investigated since its discovery on rough Ag surface because of high sensitivity and resolution. Ag nanostructures are considered highly active for SERS but their liability to oxidization impedes their practical applications as a SERS-based sensing platform. Here, we show that graphene oxide (GO) coating on the polyallylamine hydrochloride (PAA) functionalized Ag nanoparticles (PAA-AgNP) immobilized on PAA-functionalized reduced GO (PAA-RGO) films (GO/PAA-AgNP/PAA-RGO, sandwich structure) protect AgNPs from oxidation under ambient condition for prolonged time up to 72 days with increased and reproducible SERS signals and fast adsorption kinetics of rhodamine 6G, a model Raman probe molecule. The present strategy for GO coating on top of the immobilized AgNPs will be useful for the development of an efficient SERS-based chemical and biosensor because of its simplicity, cost-effectiveness, long-term stability, and high reproducibility.

Graphene-based electrodes

Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene-based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field-effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene-based electrodes, their fabrication techniques, and application areas.

Three-dimensional assemblies of graphene prepared by a novel chemical reduction-induced self-assembly method

In this study, three-dimensional (3D) graphene assemblies are prepared from graphene oxide (GO) by a facile in situ reduction-assembly method, using a novel, low-cost, and environment-friendly reducing medium which is a combination of oxalic acid (OA) and sodium iodide (NaI). It is demonstrated that the combination of a reducing acid, OA, and NaI is indispensable for effective reduction of GO in the current study and this unique combination (1) allows for tunable control over the volume of the thus-prepared graphene assemblies and (2) enables 3D graphene assemblies to be prepared from the GO suspension with a wide range of concentrations (0.1 to 4.5 mg mL(-1)). To the best of our knowledge, the GO concentration of 0.1 mg mL(-1) is the lowest GO concentration ever reported for preparation of 3D graphene assemblies. The thus-prepared 3D graphene assemblies exhibit low density, highly porous structures, and electrically conducting properties. As a proof of concept, we show that by infiltrating a responsive polymer of polydimethylsiloxane (PDMS) into the as-resulted 3D conducting network of graphene, a conducting composite is obtained, which can be used as a sensing device for differentiating organic solvents with different polarity.

Fabrication of flexible MoS2 thin-film transistor arrays for practical gas-sensing applications

By combining two kinds of solution-processable two-dimensional materials, a flexible transistor array is fabricated in which MoS(2) thin film is used as the active channel and reduced graphene oxide (rGO) film is used as the drain and source electrodes. The simple device configuration and the 1.5 mm-long MoS(2) channel ensure highly reproducible device fabrication and operation. This flexible transistor array can be used as a highly sensitive gas sensor with excellent reproducibility. Compared to using rGO thin film as the active channel, this new gas sensor exhibits much higher sensitivity. Moreover, functionalization of the MoS(2) thin film with Pt nanoparticles further increases the sensitivity by up to ∼3 times. The successful incorporation of a MoS(2) thin-film into the electronic sensor promises its potential application in various electronic devices.

Recent progress on graphene-based photocatalysts: current status and future perspectives

Graphene (GR) has become a sparkling rising star on the horizon of material science. Due to its unique planar structure, excellent transparency, superior electron conductivity and mobility, high specific surface area, and high chemical stability, GR is regarded as an ideal high performance candidate to prepare GR-based nanocomposites for energy storage and conversion. During the past few years, GR-based photocatalysts have been attracting ever-increasing research attention. In this tutorial review, the applications of GR-based nanocomposites in photocatalysis, including nonselective processes for degradation of pollutants, selective transformations for organic synthesis and water splitting to clean hydrogen energy, are summarized systematically. In particular, in addition to discussing opportunities offered by GR, we will also describe the existing challenges for future exploitation and development of GR-based nanocomposites, which we hope would significantly advance us to rationally and efficiently harness the outstanding structural and electronic properties of GR to design smarter and more efficient GR-based photocatalysts instead of joining the graphene "gold rush".

OWL-based nanomasks for preparing graphene ribbons with sub-10 nm gaps

We report a simple and highly efficient method for creating graphene nanostructures with gaps that can be controlled on the sub-10 nm length scale by utilizing etch masks comprised of electrochemically synthesized multisegmented metal nanowires. This method involves depositing striped nanowires with Au and Ni segments on a graphene-coated substrate, chemically etching the Ni segments, and using a reactive ion etch to remove the graphene not protected by the remaining Au segments. Graphene nanoribbons with gaps as small as 6 nm are fabricated and characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The high level of control afforded by electrochemical synthesis of the nanowires allows us to specify the dimensions of the nanoribbon, as well as the number, location, and size of nanogaps within the nanoribbon. In addition, the generality of this technique is demonstrated by creating silicon nanostructures with nanogaps.

Biomolecule-assisted, environmentally friendly, one-pot synthesis of CuS/reduced graphene oxide nanocomposites with enhanced photocatalytic performance

In this work, we develop a novel environmentally friendly strategy toward one-pot synthesis of CuS nanoparticle-decorated reduced graphene oxide (CuS/rGO) nanocomposites with the use of L-cysteine, an amino acid, as a reducing agent, sulfur donor, and linker to anchor CuS nanoparticles onto the surface of rGO sheets. Upon visible light illumination (λ > 400 nm), the CuS/rGO nanocomposites show pronounced enhanced photocurrent response and improved photocatalytic activity in the degradation of methylene blue (MB) compared to pure CuS. This could be attributed to the efficient charge transport of rGO sheets and hence reduced recombination rate of excited carriers.