Fig. 7.

a Schematic of formation of networks during hydrothermal reduction in microscale, optical photographs of GO suspension and GHs formed by hydrothermal reduction and the scanning electron microscope (SEM) image of the graphene network [123]. b Optical photographs of GO suspension and GHs formed by chemical reduction and the SEM image of the graphene network [124]. c–e Schematics of the microscopic mechanism of the formation of graphene 3D networks induced by adding multivalent metal ions and water-soluble polymers and optical photographs of the graphene foams formed after post-treatment [125–127]