Macroscopic Graphene Structures: Preparation, Properties, and Applications

Abstract

Since its discovery by Geim and coworkers in 2004 [1], graphene has attracted increasing attention because of its unique structure and properties . Graphene is a monolayer of carbon atoms with close-packed conjugated hexagonal lattices, in which the carbon bonds are sp 2 hybridized [30]. This unique structure endows graphene with remarkable physical properties. In graphene, electron-phonon scattering is so weak that the mobility of charge carriers can be improved significantly, even up to 200 000 cm 2 V −1 s −1 under ambient conditions, if the extrinsic disorder is eliminated [31]. This value exceeds the intrinsic mobility of any other semiconductor [31,32]. In addition, graphene possesses large theoretical specific surface area (2630 m 2 g −1 ) [33], high Young's modulus (∼1.0 TPa) [34], as well as good thermal (∼5000 W m −1 K −1 ) [35] and electrical conductivity [36].In order to fully understand and utilize the excellent physical and chemical properties of individual graphene sheets at a macroscopic level, it is desirable to fabricate various macroscopic graphene-based materials. As a fundamental twodimensional (2D) carbon structure, graphene sheets can be considered as basic building blocks to construct 3D graphene-based materials. A critical challenge in building graphene-based macroscale structures is to effect the transfer of the exceptional properties of graphene nanosheets to the macroscale structures by controlling the orientation and organization of the building blocks at the nanoscale. For example, the strong π-π stacking and van der Waals force between the planar basal planes of graphene sheets result in self-agglomeration of graphene, creating particulate graphite platelets which lose the unique ultrahigh surface area of graphene sheets. This adversely affects the potential applications of graphenebased macroscale structures in the fields of supercapacitors and batteries. To prevent self-aggregation, currently a number of strategies have been developed for fabricating porous macroscale structures, including the addition of ''spacers'' (i.e., surfactants, nanoparticles (NPs), polymers) [37][38][39][40][41][42][43][44][45][46], template-assisted growth [47], crumpling of graphene sheets [48,49], and so on. While the specific surface area of these graphene macroscopic structures is still lower than the theoretical specific

Waltzing with the Versatile Platform of Graphene to Synthesize Composite Photocatalysts

“…In view of the fact that the graphene-driven “gold rush” has been flourishing in various areas since the isolation of a single-layer pristine graphene sheet in 2004, the term “graphene” seems very popular and familiar to the scientific and technological communities. However, it has been used loosely in the literature. − The oversimplified and vague naming of “graphene” with regard to graphene-based materials under the umbrella of “graphene” inevitably results in the misunderstanding of differences in physicochemical properties for different kinds of graphene among researchers, particularly who are not intimately involved in graphene-related research.…”

“…The issue becomes more prominent in the community of graphene-based photocatalysis, for which most of the graphene is derived from the reduction of graphene oxide (GO) that is a widely used precursor of graphene in the synthesis of graphene-based composite photocatalysts. − Notably, the abundance of oxygenated functional groups endows GO with the flexible, easily accessible wet-chemistry processability . However, the oxygenated moieties inevitably cause considerable disruption of the electronic structure of graphene via breaking the 2D π-conjugation of the original graphene sheet.…”

“…However, in the literature, researchers are inclined to simply attribute the activity enhancement of graphene-based composite photocatalysts to “the unique properties of graphene, particularly its outstanding electrical conductivity”. − Clearly, this vague but “panacea” expression does not benefit the readership (i) with an objective and rational viewpoint on the role of graphene in promoting the activity of graphene-based composite photocatalysts, and (ii) with focusing on how to better transform the power of different kinds of graphene into the graphene-based composite photocatalysts. It is worth noting that the properties of graphene in the composites can change dramatically when it interacts with the surrounding environment or its structure and morphology are changed. ,, …”

“…As such, we think it is the ripe and right time to present a comprehensive, systematic, and up-to-date review on graphene-based photocatalysis from a whole scenario of viewpoint, considering the fast growth of literature reports in this field and that the development of this field is likely confronted with a bottleneck period. Although there have been some reviews and book chapters on this topic, − they only focus on summarizing the preparation methods and/or some selected photocatalytic reactions of graphene-based composites. None of the previous reviews and book chapters − have covered all the reported photoredox types over the graphene-based composite photocatalysts, the elaborate understanding of the fundamental roles of graphene in promoting the photocatalytic performance and, particularly, charge carrier dynamics in the graphene-based composites, the comparison between graphene-based and other carbon allotropes-based composite photocatalysts, the existing problems and challenges in this field, and how and what we should rationally consider for applying the graphene-based composite photocatalysts to practical applications in solar energy conversion.…”

“…It can be seen from Figure S1 (Supporting Information) that, thus far, the photocatalytic degradation of pollutants and bacteria and photocatalytic water splitting have received the majority of the research interest in graphene-based composite photocatalysts (accounting for 78.6% and 15.5% of all the photocatalytic applications of graphene-based composites, respectively), whereas the photocatalytic reduction of CO 2 and photocatalytic selective organic transformations have been paid less attention, whose proportions are 4.2% and 1.7%, respectively. The previous reviews and book chapters often neglect or give little attention to the latter two types of important photocatalytic applications, − which are of great significance for widening the application scope of graphene-based composites in solar energy conversion. − …”