Daniel R. Dreyer

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.

Biocompatible, robust free-standing paper composed of a TWEEN/graphene composite.

Nonspecific binding (NSB), a random adsorption of biocomponents such as proteins and bacteria on noncomplementary materials,isoneofthebiggestproblemsinbiological applications including biosensors, protein chips, surgical instruments, drug delivery, and biomedicine. Polyoxyethylene sorbitan laurate (TWEEN), a commercially available chemical with aliphatic ester chains, has shown promise as a medical material and in overcomingproblems associated withNSB. [1‐4] However,stability during solution-based processing and uniformity of the materials that have TWEEN coating on flat substrates or nanomaterials using the selfassembled-monolayer (SAM) method has been an important issue. Further, biocompatible materials with high strength are important for several medical applications including stents, nail implants, and strong invasive instruments. Here, we present the production of a free-standing ‘‘paperlike’’ material composed of TWEEN and reduced graphene oxide (RGO) platelets and obtained by simple filtration of a homogeneous aqueous colloidal suspension of TWEEN/RGO hybrid. The ‘‘TWEEN paper’’ was highly stable in water without leakage of TWEEN and is compliant and sufficiently robust to be handled by hand without breaking. Furthermore, the TWEEN paper was noncytotoxic to three mammalian cell lines and biocompatible, inhibiting nonspecific binding of Gram-positive bacteria. [5] In contrast, RGO paper without TWEEN showed nonspecific bacterial binding. TWEEN is composed ofthree chemical parts (Fig. 1a): aliphatic esterchains that can prevent NSB ofbiomolecules, three-terminal hydroxyl groups that are hydrophilic and can be chemically modified for further applications, and an aliphatic chain that can easily be adsorbed on a hydrophobic surface by noncovalent interaction. Protein microarrays on flat substrates with SAM of TWEEN [4] and highly sensitive biosensors, [1‐3] built using field-effect transistor (FET) behavior of individual carbon nanotube (CNT) strands coated with TWEEN, have demonstrated that TWEEN can be effectively used to overcome NSB.

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.

Perspectives on poly(dopamine)

Poly(dopamine) has emerged in recent years as a readily accessible synthetic analogue of the naturally occurring melanins. However, the polymers structure has proved difficult to unambiguously elucidate and a variety of models have been proposed. Despite these challenges, poly(dopamine) has found extraordinary utility in a range of applications including surface coatings, biotechnology and biomedicine, and water purification membranes. Most of these applications take advantage of the robust polymer films that deposit onto a wide range of surfaces, as well as its inertness to harsh chemical environments. In view of the expansion of interest in poly(dopamine), we provide perspective on this material, focusing on its history, chemical relationship to melanins, recent applications, and potential areas for future study.

A Computational Investigation of the Catalytic Properties of Graphene Oxide: Exploring Mechanisms by using DFT Methods

Herein we describe a computational study undertaken in an effort to elucidate the reaction mechanisms behind the experimentally observed oxidations and hydrations catalyzed by graphene oxide (GO). We used the oxidation of benzyl alcohol to benzaldehyde as a model reaction and DFT calculations revealed that the reaction occurred via the transfer of hydrogen atoms from the organic molecule to the GO surface. In particular, neighboring epoxide groups that decorate the GO basal plane were ring‐opened, which resulted in the formation of diols, followed by dehydration. Our calculations were consistent with the experimentally observed dependence of this chemistry on molecular oxygen, and revealed that the partially reduced catalyst was able to be recharged by molecular oxygen, which allows for catalyst turnover. Functional group‐free carbon materials, such as graphite, were calculated as having substantially higher reaction barriers, which indicates that the high chemical potential and rich functionality of GO are necessary for the observed reactivity.

Surface Modification of Water Purification Membranes

Polymeric membranes are an energy-efficient means of purifying water, but they suffer from fouling during filtration. Modification of the membrane surface is one route to mitigating membrane fouling, as it helps to maintain high levels of water productivity. Here, a series of common techniques for modification of the membrane surface are reviewed, including surface coating, grafting, and various treatment techniques such as chemical treatment, UV irradiation, and plasma treatment. Historical background on membrane development and surface modification is also provided. Finally, polydopamine, an emerging material that can be easily deposited onto a wide variety of substrates, is discussed within the context of membrane modification. A brief summary of the chemistry of polydopamine, particularly as it may pertain to membrane development, is also described.