There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

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The chemistry of graphene oxide

The reduction of graphene oxide

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene: The New Two-Dimensional Nanomaterial

Graphene – a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice – is the basal building block in all graphitic materials. Since it was first reported in 2004, graphene has attracted great interest because of the unique electronic, thermal, and mechanical properties arising from its strictly 2D structure, and to its potential technical applications. However, producing graphene on a large scale using existing mechanical methods is still unfeasible. Searching for alternative chemical approaches is an urgent matter. However, the hydrophobic nature of graphene and its strong tendency to agglomerate in solvents present a great challenge to the development of fabrication methods, and severely restrict its promising applications. Although the mechanism involved remains unproven, the chemical reduction of readily available exfoliated graphite oxide (GO) with reducing agents such as hydrazine and dimethylhydrazine is a promising strategy in the large-scale production of graphene. Unfortunately, the reducing agents involved are very hazardous, and the graphene obtained presents irreversibly agglomerated features in solvents that do not contain polymer surfactants. Here, we report a new green route for the synthesis of processable graphene on a large scale. We observed that a stable graphene suspension could be quickly prepared by simply heating an exfoliated-GO suspension under strongly alkaline conditions at moderate temperatures (50–90 8C) (Figure 1a). Our initial purpose was to introduce functional groups to exfoliated GO by free-radical addition. Surprisingly, the addition of NaOH to the GO suspension – to improve the solubility of the alkyl free-radical initiator, which is carboxyl-terminated – was accompanied by a fast, unexpected color change (from yellow-brown to homogeneous black). Careful experiments revealed that exfoliated GO can undergo fast deoxygenation in strongly alkaline solutions, resulting in stable aqueous graphene suspensions

Deoxygenation of Exfoliated Graphite Oxide under Alkaline Conditions: A Green Route to Graphene Preparation

Nanoporous nickel hydroxide (Ni(OH)2) thin film was grown on the surface of ultrathin-graphite foam (UGF) via a hydrothermal reaction. The resulting free-standing Ni(OH)2/UGF composite was used as the electrode in a supercapacitor without the need for addition of either binder or metal-based current collector. The highly conductive 3D UGF network facilitates electron transport and the porous Ni(OH)2 thin film structure shortens ion diffusion paths and facilitates the rapid migration of electrolyte ions. An asymmetric supercapacitor was also made and studied with Ni(OH)2/UGF as the positive electrode and activated microwave exfoliated graphite oxide (‘a-MEGO’) as the negative electrode. The highest power density of the fully packaged asymmetric cell (44.0 kW/kg) was much higher (2–27 times higher), while the energy density was comparable to or higher, than high-end commercially available supercapacitors. This asymmetric supercapacitor had a capacitance retention of 63.2% after 10 000 cycles.

Nanoporous Ni(OH)2 thin film on 3D Ultrathin-graphite foam for asymmetric supercapacitor.

A Si/graphene composite is drop-casted on an ultrathin-graphite foam (UGF) with three dimensional conductive network. The Si/graphene/UGF composite presents excellent stability and relatively high overall capacity when tested as an anode for rechargeable lithium ion batteries.

Graphene-Encapsulated Si on Ultrathin-Graphite Foam as Anode for High Capacity Lithium-Ion Batteries

Scientific interest in graphene as a catalyst and as a catalyst support in heterogeneous catalytic reactions has grown dramatically over the past several years. The present critical review summarizes the multiple roles of graphene in heterogeneous catalysis and highlights the influence of defects, heteroatom-containing functionalities, and graphene's two-dimensional structure on catalytic performance. We first discuss the role and advantages of graphene as a catalyst support, with emphasis on its interactions with the catalytic phases and the influence of mass transfer processes. We then clarify the origin of the intrinsic catalytic activity of graphene in heterogeneous catalytic reactions. Finally we suggest challenges and potential practical applications for graphene in industrial processes.

Multiple roles of graphene in heterogeneous catalysis

Graphene has been successfully modified with palladium nanoparticles in a facile manner by reducing palladium acetate [Pd(OAc)2] in the present of sodium dodecyl sulfate (SDS), which is used as both surfactant and the reducing agent. The palladium nanoparticle–graphene hybrids (Pd–graphene hybrids) are characterized by highresolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. We demonstrate that the Pd–graphene hybrids can act as an efficient catalyst for the Suzuki reaction under aqueous and aerobic conditions, with the reaction reaching completion in as little as 5 min. The influence of the preparation conditions on the catalytic activities of the hybrids is also investigated.

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Fengbao Zhang

Papers

Deoxygenation of Exfoliated Graphite Oxide under Alkaline Conditions: A Green Route to Graphene Preparation

Nanoporous Ni(OH)2 thin film on 3D Ultrathin-graphite foam for asymmetric supercapacitor.

Graphene-Encapsulated Si on Ultrathin-Graphite Foam as Anode for High Capacity Lithium-Ion Batteries

Multiple roles of graphene in heterogeneous catalysis

Palladium Nanoparticle-Graphene Hybrids as Active Catalysts for the Suzuki Reaction