Graphene Oxide Sheets Chemically Cross-Linked by Polyallylamine

We report that a homogeneous aqueous colloidal suspension of chemically cross-linked graphene oxide sheets was generated by addition of polyallylamine to an aqueous suspension of graphene oxide sheets followed by sonication of the mixture. This is the first example for producing a homogeneous colloidal suspension of cross-linked graphene sheets. As a demonstration of the utility of such a colloidal suspension, "paper" material samples made by simple filtration from such a suspension of cross-linked graphene oxide sheets showed excellent mechanical stiffness and strength.