Preparation And Characterization Of Three Dimensional Graphene By Self-assembly

Graphenes provide numerous possibilities for applications due to their unique and superior mechanical, electrical and physical properties. However, realizing their potential versatility requires assembling graphenes into various macroscale architectures. On the basis of the bulk-quantity production of graphene-based sheets through chemical oxidation of graphite, paper-like graphene oxide (GO) or reduced GO (rGO) films have been prepared and exploited for multipurpose applications in energy storages, transparent electrodes, mechanical actuators and so forth. Then the sheets adhere together by surface interaction of Van der Waals and residualπ-πstacking between the faces of each sheet, as well as the cross-linking of the hydrogen bonds formed among the oxygen functional groups on GO and the interlamellar water molecules. The chemical cross-linking between GO sheets could be elevated by adding divalent ions such as Mg2+ and Ca2+, leading to significant enhancement in mechanical properties of the GO films. Since water molecules could be intercalated into the galleries between the layers, the volume of the GO films would swell by more than 70% with increasing humidity level to 100%. In addition to these two-dimensional films, very recently, three-dimensional (3D) graphene-based structures have been successfully prepared at a higher temperature of 180℃without any additive as well as at a lower temperature of 120℃using noble-metal nanocrystals as linker and glucose derived polymers as strengthening agent. The freshly-made 3D rGO structure is a type of hydrogel filled with a large amount of water, which could be dried unchangeably by freeze-drying when linker and reinforcer were used. To meet the demands of broad applications such as tissue engineering and molecular storage, it is worthwhile to explore another route to assemble 3D architecture of graphene-based materials, especially without using noble-metal nanocrystals as linkers. Herein, we report divalent-ion (Ca2+, Ni2+ or Co2+) driven self-assembly of rGO into gel-like 3D architecture at 120℃. After strengthening by polyvinyl alcohol (PVA) intercalation and the following freeze-drying, solid 3D architecture of microporous rGO was obtained, suggesting that divalent-ion linked 3D rGO architecture will be a versatile host for the incorporation of guest materials.Graphene and carbon nanotubes (CNTs) have many similarities both in structure and in properties, where their superior mechanical, electrical and thermal properties as well as large surface area make them potential for wide and analogous applications such as field-effect transistors, flexible and transparent electrodes, actuator and polymer composites. To realize their potential versatility, especially in energy storage and conversion, it is required to assemble graphene and CNTs into various macroscopic architectures for controllable processing. When introducing CNTs into graphene-based films by the assistance of GO dispersion, the interlamellar distance between the graphene sheets is believed to increased some how while the electrical conductivity of the hybrid film is significantly enhanced. In addition to prepare macroscale graphene materials by external-force direction, three-dimensional (3D) graphene-based structures with highly separated graphene sheets could be obtained by self-assembly under hydrothermal treatment, which have shown excellent performance in catalysis and supercapacitor. According to the merits owned by CNT/graphene hybrid films, it is highly desirable to prepare 3D carbon structure composed of 2D graphene sheets and 1D CNTs.