Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

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Graphene-based composites

Isolated graphene, a nanometer-thick two-dimensional analog of fullerenes and carbon nanotubes, has recently sparked great excitement in the scientific community given its excellent mechanical and electronic properties. Particularly attractive is the availability of bulk quantities of graphene as both colloidal dispersions and powders, which enables the facile fabrication of many carbon-based materials. The fact that such large amounts of graphene are most easily produced via the reduction of graphene oxide--oxygenated graphene sheets covered with epoxy, hydroxyl, and carboxyl groups--offers tremendous opportunities for access to functionalized graphene-based materials. Both graphene oxide and graphene can be processed into a wide variety of novel materials with distinctly different morphological features, where the carbonaceous nanosheets can serve as either the sole component, as in papers and thin films, or as fillers in polymer and/or inorganic nanocomposites. This Review summarizes techniques for preparing such advanced materials via stable graphene oxide, highly reduced graphene oxide, and graphene dispersions in aqueous and organic media. The excellent mechanical and electronic properties of the resulting materials are highlighted with a forward outlook on their applications.

Graphene oxide, highly reduced graphene oxide, and graphene: versatile building blocks for carbon-based materials.

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Magnetite−graphene hybrids have been synthesized via a chemical reaction with a magnetite particle size of ∼10 nm. The composites are superparamagnetic at room temperature and can be separated by an external magnetic field. As compared to bare magnetite particles, the hybrids show a high binding capacity for As(III) and As(V), whose presence in the drinking water in wide areas of South Asia has been a huge problem. Their high binding capacity is due to the increased adsorption sites in the M−RGO composite which occurs by reducing the aggregation of bare magnetite. Since the composites show near complete (over 99.9%) arsenic removal within 1 ppb, they are practically usable for arsenic separation from water.

Water-Dispersible Magnetite-Reduced Graphene Oxide Composites for Arsenic Removal

Graphene, a one-atom layer of graphite, possesses a unique two-dimensional (2D) structure, high conductivity and charge carrier mobility, huge specific surface area, high transparency and great mechanical strength. Thus, it is expected to be an ideal material for energy storage and conversion. During the past several years, a variety of graphene based materials (GBMs) have been successfully prepared and applied in supercapacitors, lithium ion batteries, water splitting, electrocatalysts for fuel cells, and solar cells. In this review, we will summarize the recent advances in the synthesis and applications of GBMs in these energy related systems. The challenges and prospects of graphene based new energy materials are also discussed.

Graphene based new energy materials

Pd2+-exchanged graphite oxide and chemically derived graphenes therefrom were employed as supports for Pd nanoparticles. The influence of catalyst preparation, carbon functionalization, and catalyst morphology on the catalytic activity in the Suzuki−Miyaura coupling reactions was investigated. The catalysts were characterized by means of spectroscopy (FT-IR, solid-state 13C NMR, AAS, XPS), X-ray scattering (WAXS), surface area analysis (BET, methylene blue adsorption), and electron microscopy (TEM, ESEM). In contrast to the conventional Pd/C catalyst, graphite oxide and graphene-based catalysts gave much higher activities with turnover frequencies exceeding 39 000 h−1, accompanied by very low palladium leaching (<1 ppm).

Palladium Nanoparticles on Graphite Oxide and Its Functionalized Graphene Derivatives as Highly Active Catalysts for the Suzuki−Miyaura Coupling Reaction

Pd2+-Exchanged graphite oxide (GO) serves as a precatalyst for the formation of Pd-nanoparticles which are then deposited on the highly functionalized carbonaceous support This versatile, air-stable, and ligand-free system was applied successfully to SuzukiMiyaura couplings of some aryl chlorides and to the MizorokiHeck as well as the Sonogashira reaction showing relatively high activities and good selectivities Like with other ligand-free supported systems, the reaction proceeded dominantly by a homogeneous mechanism, but attack of an aryl iodide to Pd-nanoparticles can be excluded as substantial contribution to the entire catalytic process Beside its straightforward preparation and its stability in air, the system combines the advantages of both homogeneous and heterogeneous catalysis

Palladium Nanoparticles on Graphite Oxide as Catalyst for SuzukiMiyaura, MizorokiHeck, and Sonogashira Reactions

Palladium Nanoparticles on Graphite Oxide and Its Functionalized Graphene Derivatives as Highly Active Catalysts for the Suzuki—Miyaura Coupling Reaction.

Spherical Pd nanoparticles (2–8 nm) were immobilized on the nanometer-scaled platelets of montmorillonite (MMT) by means of cation exchange of Pd2+ for Na+ followed by chemical reduction. The resulting Pd catalysts were readily dispersible in water and polar solvents. Polarity design and thus, variation of the dispersion behavior was achieved by subsequent organophilic MMT modification involving cation exchange with N-alkyl and N-perfluoroalkylethyl pyridinium cations. This allowed for easy catalyst dispersion in a wide range of organic solvents. According to characterization by TEM, EDXS, AAS and WAXS the nanoparticle formation did not destroy the superstructure of unmodified and organophilic MMT. Catalysts were applied to hydrogenation, Suzuki–Miyaura C–C coupling and fluorous biphase catalysis. The tunable dispersion behavior of MMT catalysts was successfully employed to guarantee easy catalyst recovery and recycling.

Catalysts Based Upon Organoclay with Tunable Polarity and Dispersion Behavior: New Catalysts for Hydrogenation, C–C Coupling Reactions and Fluorous Biphase Catalysis

The reaction of a variety of aryl bromides with ester (II) affords the products with moderate to good high yields.

Gil M. Scheuermann

Papers

Palladium Nanoparticles on Graphite Oxide and Its Functionalized Graphene Derivatives as Highly Active Catalysts for the Suzuki−Miyaura Coupling Reaction

Palladium Nanoparticles on Graphite Oxide as Catalyst for SuzukiMiyaura, MizorokiHeck, and Sonogashira Reactions

Palladium Nanoparticles on Graphite Oxide and Its Functionalized Graphene Derivatives as Highly Active Catalysts for the Suzuki—Miyaura Coupling Reaction.

Catalysts Based Upon Organoclay with Tunable Polarity and Dispersion Behavior: New Catalysts for Hydrogenation, C–C Coupling Reactions and Fluorous Biphase Catalysis

Palladium Nanoparticles on Graphite Oxide as Catalyst for Suzuki—Miyaura, Mizoroki—Heck, and Sonogashira Reactions.