Synthesis of functional graphenes for high-performance nanopapers

Functional graphenes were synthesized from graphene oxide, which was obtained from low-cost graphite via oxidation. In order to prevent the precipitation of graphene during the reduction process, graphene oxide was partially reduced using sodium borohydride and then treated with diazonium salts having -SO ₃H groups, followed by complete reduction with hydrazine. Functional graphenes were prepared in such a way that they could be well dispersed in water, and as a result, nanopapers could be obtained by flow-directed assembly of individual graphene nanosheets via simple filtration. The resulting nanopapers have high electrical conductivity with excellent mechanical properties close to those of steel. The structure of nanopapers was characterized by X-ray diffraction pattern and Raman spectroscopy. These functional graphenes are also promising for the applications in water purifications, ultracapacitors, lithium batteries, and electronic materials.