Graphene Oxide “Surfactant”‐Directed Tunable Concentration of Graphene Dispersion

Abstract

Homogeneous graphene dispersions with tunable concentrations are fundamental prerequisites for the preparation of graphene‐based materials. Here, a strategy for effectively dispersing graphene using graphene oxide (GO) to produce homogeneous, tunable, and ultrahigh concentration graphene dispersions (>150 mg mL−1) is proposed. The structure of GO with abundant edge‐bound hydrophilic carboxyl groups and in‐plane hydrophobic π‐conjugated domains allows it to function as a special “surfactant” that enables graphene dispersion. In acidic solutions, GO sheets tend to form edge‐to‐edge hydrogen bonds and expose the π‐conjugated regions which interact with graphene, thereby promoting graphene dispersion. While in alkaline solutions, GO sheets tend to stack in a surface‐to‐surface manner, thereby blocking the π‐conjugated regions and impeding graphene dispersion. As the concentration of GO‐dispersed graphene dispersion (GO/G) increases, a continuous transition between four states is obtained, including a dilute dispersion, a thick paste, a free‐standing gel, and a kneadable, playdough‐like material. Furthermore, GO/G can be applied to create desirable structures including highly conductive graphene films with excellent flexibility, thereby demonstrating an immense potential in flexible composite materials.

Roles of Graphene Oxide in Heterogeneous Photocatalysis

“…Compositing semiconductors with graphene (GR) is considered as a viable strategy to boost the performance of semiconductors because the superior conductivity of GR enables it to efficiently accept and conduct photoinduced electrons from semiconductors. − Therefore, the more effective separation of photogenerated electron–hole pairs is beneficial to improve the photocatalytic activity of semiconductors. − Regarding the synthesis of GR-based semiconductor hybrid, graphene oxide (GO), on account of its high yield, abundant surface functional groups, and flexible solution processability, has been frequently used as the precursor of GR. − Because of the unique structure and surface chemistry features, the roles of GO played in heterogeneous photocatalysis are found to be diverse. , For example, except for the role as precursor to synthesize GR, GO can also act as “macromolecular surfactants” to promote the dispersion of insoluble materials. − The two-dimensional (2D) structure allows GO to serve as a growth template to induce the synthesis of composite materials with special morphology. − In addition, GO can also be used as a building block for the preparation of three-dimensional (3D) GR aerogel-supported photocatalysts. − Furthermore, GO with appropriate degree of oxidation can be directly used as a photocatalyst for various redox reactions. , There have been some excellent reviews on preparation and applications of GR-based composite photocatalysts. − However, to the best of our knowledge, an integral overview that focuses on synthesis, properties, and multifarious roles of GO in heterogeneous photocatalysis has been still unavailable. Therefore, it is imperative to compile a general review from the widely dispersed literature to provide useful information and stimulate further development in this significant field.…”

An efficient cooling solution with 3D interconnected graphene architectures for passive heat dissipation

“…26 In particular, aromatic CQC vibrations seen around 1643 cm À1 were attributed to the conjugated honeycomb carbon in rGO and benzene structure of AR. 20,27,28 In addition, the peaks centred at 1461-1389 cm À1 and 1055 cm À1 were assigned to the C-H bending vibrations and C-O stretching vibrations, respectively. With the addition of AR, some new peaks appeared, including the bands at 3743 cm À1 (stretching vibrations of -N-H), and those at 1732 and 1554 cm À1 corresponding to the CQO and CQC stretching vibrations in a mononuclear aromatic ring, respectively.…”

Water-Mediated Attractive Interaction between Negatively Charged GO Nanosheets at the Air–Water Interface

“…In an aqueous solution, the enhanced ionization of GO could be obtained through the acid/base reaction of carboxyl groups on the edge of GO with hydroxyl ions, ,− in which the base (NaOH) is generally added and the stable homogenous dispersion of GOs is achieved. Although the ionized GO nanosheets can be transferred to the air–water interface, ,,, the counterion Na + has been found to be depleted at the interface region. − Thus, in our simulation systems, because of the limitation of cell size, it is not appropriate to directly and explicitly insert the counterions in the interface system.…”