Solution-chemistry approach to graphene nanostructures

Abstract

Graphene has many novel optical and electrical properties desirable for applications in future electrooptical devices. Graphene nanostructures are especially attractive for their wide range of tunable properties. Here we describe the recent progress and challenges in the solution-chemistry approach to graphene nanostructures. This approach could not only lead to new materials with various well-defined properties, but also enable their production in large quantities.Graphene, containing a single layer of sp 2 -hybridized carbon atoms, has become an intensively studied topic because of its unique two-dimensional (2D) crystalline structure, extraordinary physical properties, 1-3 and potential applications in future optics and electronics. Even though graphene is the basic building block for graphite, carbon nanotubes, and fullerenes which have been studied for decades, not a lot of attention was paid to graphene until the first isolation of single-layer graphene from graphite by Geim and his co-workers 4 with a ''Scotch tape'' approach in 2004. Numerous follow-up investigations subsequently revealed a wide range of very attractive properties, such as extremely high carrier mobilities, 5-9 quantum hall effect, 10-16 and ambipolar field effect, 4,17 etc. These properties make graphene a very promising material for future devices, such as high-speed, high-frequency electronic devices, 6,7,18-21 single molecule sensors, 22,23 and ultrathin transparent electrodes. [24][25][26][27][28][29][30][31] Reliable production of graphene with high quality and in large quantities is still a challenge. 32 Although some proof-of-concept devices have been made from mechanically exfoliated graphene, the original layer-by-layer peel-off method cannot be used for large-scale production. In order to overcome this challenge, two distinct approaches have been taken by scientists: breaking down graphite into graphene (''top-down'' approach) and building up graphene from atomic or molecular building blocks (''bottom-up'' approach). The top-down approaches include mechanical exfoliation, 1,4,18 intercalation followed by solution-based exfoliation, 28,30,33-45 reduction of graphene oxide, 46-56 etc, (Fig. 1). The bottom-up approaches mostly include chemical vapor deposition (CVD) 31,57-66 and a solution-chemistry approach. 67,68 In this review we discuss the latest development in the emerging solution-chemistry approach to graphene nanostructures, especially quantum dots (QDs). 69 We refer readers to some recent reviews 70-72 for detailed descriptions of top-down approaches and CVD methods to make graphene.To make stable single-layer graphene it is essential to overcome inter-layer van der Waals attraction that favors formation of graphite. It is achieved in mechanical exfoliation with external forces, and in CVD methods with introduction of substrates to simultaneously immobilize graphene when they form.

New advances in nanographene chemistry

“…9 Such PAHs, consisting of sp 2 carbon frameworks extending over 1 nm, can be regarded as the smallest possible nanographenes, or graphene molecules. [18][19][20][21][22][23] One-dimensional extension of graphene molecules leads to ribbon-shaped nanographenes with high aspect ratios, which are called graphene nanoribbons (GNRs). [18][19][20][21][22][23] One-dimensional extension of graphene molecules leads to ribbon-shaped nanographenes with high aspect ratios, which are called graphene nanoribbons (GNRs).…”

Direct synthesis of graphene from adsorbed organic solvent molecules over copper

“…2,3 In another chemo-thermal approach graphene nanoribbons (GNRs) can also be formed through various heating steps from precursor monomers such as 10,100-dibromo-9,90-bianthryl monomers to first dehalogenate the monomers followed by Cyclodehydrogenation. 2,22 A drawback of this technique is that the reduced solubility of large polycyclic systems makes the formation of large graphene domains challenging. They include techniques in which small aromatic hydrocarbons are brought together to form a larger structure (graphene) through coupling reactions.…”

Zinc Phthalocyanine–Graphene Hybrid Material for Energy Conversion: Synthesis, Characterization, Photophysics, and Photoelectrochemical Cell Preparation

“…12--16 Recently, a variety of strategies became also available introducing organic addends cova--lently attached onto the surface of exfoliated graphene, thus yielding soluble graphene--based materials. 17 Moreo--ver, some novel graphene--based hybrid materials, in which the unique properties of graphene are combined with those of Eu, 18 Au 19 or CdS 20 nanoparticles as well as photoactive components such as porphyrins, 21--26 pyrenes 27-- 29 and recently electroactive exTTF, 30,31 have been pre--pared and shown that photoillumination induces intrahy--brid charge--separation. However, none of those materials have been tested so far in energy conversion schemes as active components (i.e.…”