The molecular level control of three-dimensional graphene oxide hydrogel structure by using various diamines

The well-controlled and covalently cross-linked three-dimensional networks of graphene oxide hydrogels (GOH5) are realized by using two different diamines, such as o-phenylene diamine (oPDA) and p-phenylene diamine (pPDA). Amide linkages are formed between two graphene oxide (GO) sheets due to the condensation reaction between diamines and carboxylic acids on the GO sheets. The surface area and pore volume of pPDA-GOH are twice the size of those of oPDA-GOH due to the longer amineto-amine distance. Aromatic amine-based hydrogels exhibit enhanced mechanical strength compared to that of aliphatic amine due to the presence of an aromatic ring between amide linkages. Highly-developed 3D networks of GOH fabricated by using pPDA facilitate the removal of organic dye such as methylene blue in aqueous solutions at various pH conditions. It also shows improved regeneration ability in repeated adsorption tests. (C) 2014 Elsevier B.V. All rights reserved.