Ammonia solution strengthened three-dimensional macro-porous graphene aerogel

Recently, many approaches were applied for assembling graphene sheets into a three-dimensional structure. However, it is still a great challenge to obtain a three-dimensional macroporous graphene network with high mechanical strength after drying. Herein, an ammonia strengthened three-dimensional graphene aerogel was prepared. Based on graphene chemistry and ice physics, the mechanical strength of graphene aerogel was improved greatly when the graphene hydrogel was treated by ammonia solution at an ambient temperature. The results demonstrated that the three-dimensional structure of graphene aerogels was destroyed thoroughly without ammonia solution treatment; conversely, the three-dimensional structure was maintained and the compressive strength was improved to 152 kPa at the static load after it was treated by ammonia solution at 90 degrees C for only 1 h. This phenomenon is due to two reasons: (1) the low freezing point of ammonia solution, which effectively retarded its freezing and then kept the porous structure undestroyed; (2) the reaction between ammonia and graphene hydrogel, which brought some covalent bonds among graphene sheets. We believe our efforts may pave the way for the development and application of three-dimensional graphene based materials.