Christopher W. Bielawski

From conception to realization: an historial account of graphene and some perspectives for its future.

There has been an intense surge in interest in graphene during recent years. However, graphene-like materials derived from graphite oxide were reported in 1962, and related chemical modifications of graphite were described as early as 1840. In this detailed account of the fascinating development of the synthesis and characterization of graphene, we hope to demonstrate that the rich history of graphene chemistry laid the foundation for the exciting research that continues to this day. Important challenges remain, however; many with great technological relevance.

High-performance supercapacitors based on poly(ionic liquid)-modified graphene electrodes.

We report a high-performance supercapacitor incorporating a poly(ionic liquid)-modified reduced graphene oxide (PIL:RG-O) electrode and an ionic liquid (IL) electrolyte (specifically, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide or EMIM-NTf(2)). PIL:RG-O provides enhanced compatibility with the IL electrolyte, thereby increasing the effective electrode surface area accessible to electrolyte ions. The supercapacitor assembled with PIL:RG-O electrode and EMIM-NTf(2) electrolyte showed a stable electrochemical response up to 3.5 V operating voltage and was capable of yielding a maximum energy density of 6.5 W·h/kg with a power density of 2.4 kW/kg. These results demonstrate the potential of the PIL:RG-O material as an electrode in high-performance supercapacitors.

Elucidating the structure of poly(dopamine)

Herein we propose a new structure for poly(dopamine), a synthetic eumelanin that has found broad utility as an antifouling agent. Commercially available 3-hydroxytyramine hydrochloride (dopamine HCl) was polymerized under aerobic, aqueous conditions using tris(hydroxymethyl)aminomethane (TRIS) as a basic polymerization initiator, affording a darkly colored powder product upon isolation. The polymer was analyzed using a variety of solid state spectroscopic and crystallographic techniques. Collectively, the data showed that in contrast to previously proposed models, poly(dopamine) is not a covalent polymer but instead a supramolecular aggregate of monomers (consisting primarily of 5,6-dihydroxyindoline and its dione derivative) that are held together through a combination of charge transfer, π-stacking, and hydrogen bonding interactions.

Three‐Dimensional Self‐Assembly of Graphene Oxide Platelets into Mechanically Flexible Macroporous Carbon Films

Graphene is an atom-thick, two-dimensional material comprised of a monolayer hexagonal sp-hybridized carbons. It is flexible, has a large specific surface area, and exhibits excellent electrical and thermal conductivities and also good mechanical properties. Moreover, given the low cost of natural graphite, the potential for obtaining large quantities of graphene by a low-cost production process is high. As such, graphene and its chemically modified forms are promising building blocks for accessing highly ordered assemblies that are suitable for nanoelectronics, energy storage/conversion, catalysis, composites, and other applications. Although previous efforts have demonstrated that graphene-based platelets may be assembled into papers, thin films, or other two-dimensional constructs, the ability to control the assembly such platelets into three-dimensional (3D) structures could result in the carbon materials that exhibit very large surface areas, unusual or novel physical and electronic properties, unsurpassed chemical functionality, and other attractive features that are necessary for the aforementioned applications. Herein we demonstrate the self-assembly of graphene oxide (GO) platelets into mechanically flexible, macroporous 3D carbon films with tunable porous morphologies. Selfassembly is the spontaneous bottom-up organization of preexisting components into patterned structures. The intrinsic parallelism and scalability inherent to self-assembly can, in principle, enable low-cost, large-scale syntheses of highly ordered nanostructures. Indeed, as will be described below, the self-assembly of chemically modified graphene platelets into a complex 3D morphology was achieved by the “breath-figure” method, which is a straightforward procedure for synthesizing large-area porous polymer films. The breath-figure method as employed herein is illustrated in Figure 1A. Briefly, polymer-grafted GO platelets were synthesized and dispersed in an organic solvent. The dispersion was then cast onto a suitable substrate and exposed to a stream of humid air. Endothermic evaporation of the volatile organic solvent resulted in the spontaneous conden-

Reduction of graphite oxide using alcohols

A method for reducing graphite oxide using a variety of commercially available alcohols is described. The carbon products were found to exhibit high C : O ratios (up to 30 : 1, as determined by elemental combustion analysis), high conductivities (up to 4600 S m−1), and good specific capacitances (up to 35 F g−1) when tested as electrode materials in ultracapacitors.

Polymer Brushes via Controlled, Surface‐Initiated Atom Transfer Radical Polymerization (ATRP) from Graphene Oxide

A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface-grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.

Carbocatalysis: Heterogeneous carbons finding utility in synthetic chemistry

In this minireview, we discuss the utility of heterogeneous carbons as catalysts for facilitating a broad range of synthetic transformations. While such materials are commonly used as supports for transition metals that are catalytically active, carbons that are free of metals are also capable of enabling useful chemical reactions. Carbon catalysts hold promise in the development of sustainable alternatives to existing metal-dependent processes, as well as the discovery of mechanisms and transformations that are altogether new. Spanning from the 1930s to the present day, we provide a broad overview of the utility of carbon to facilitate various oxidation, reduction, and bond forming processes. Lastly, we will present some challenges for the future of the field.

Unclicking the Click: Mechanically Facilitated 1,3-Dipolar Cycloreversions

Application of ultrasound can cleanly reverse a widely used chemical coupling reaction. The specific targeting of covalent bonds in a local, anisotropic fashion using mechanical methods offers useful opportunities to direct chemical reactivity down otherwise prohibitive pathways. Here, we report that embedding the highly inert 1,2,3-triazole moiety (which is often prepared using the canonical “click” coupling of azides and alkynes) within a poly(methyl acrylate) chain renders it susceptible to ultrasound-induced cycloreversion, as confirmed by comprehensive spectroscopic and chemical analyses. Such reactivity offers the opportunity to develop triazoles as mechanically labile protecting groups or for use in readily accessible materials that respond to mechanical force.

A Benzobisimidazolium-Based Fluorescent and Colorimetric Chemosensor for CO2

A new sensor for the fluorescent and colorimetric detection of CO(2) is described. The system utilizes fluoride to activate a tetrapropyl benzobisimidazolium salt and operates in the absence of an exogenous base. On the basis of spectroscopic and theoretical analyses, the mode of action of the present system is ascribed to the fluoride-induced formation of an N-heterocyclic carbene intermediate that reacts with CO(2) to form an imidazolium carboxylate.

Towards electrically conductive, self-healing materials

A novel class of organometallic polymers comprising N-heterocyclic carbenes and transition metals was shown to have potential as an electrically conductive, self-healing material. These polymers were found to exhibit conductivities of the order of 10−3 S cm−1 and showed structurally dynamic characteristics in the solid-state. Thin films of these materials were cast onto silicon wafers, then scored and imaged using a scanning electron microscopy (SEM). The scored films were subsequently healed via thermal treatment, which enabled the material to flow via a unique depolymerization process, as determined by SEM and surface profilometry. A method for incorporating these features into a device that exhibits electrically driven, self-healing functions is proposed.