Highly Efficient Synthesis of Neat Graphene Nanoscrolls from Graphene Oxide by Well-Controlled Lyophilization

Graphene nanoscroll (GNS) is an important one-dimensional tubular form of graphitic carbon with characteristic open topology. It has been predicted to possess extraordinary properties that are significantly different from the analogical multiwalled carbon nanotubes. However, comprehensive experimental investigations on its properties and applications are still hindered by the lack of its reliable synthesis in high yield. To efficiently transform the scalable graphene oxide sheets into GNSs, here, we proposed a well-controlled lyophilization that comprises four sequential steps: chemical reduction of giant GO, freezing isolation of reduced graphene sheets, freeze-drying, and thermal annealing. The combined method has an extremely high efficiency, up to the record 92%. Systemic control experiments and cryo-SEM inspections revealed that the topological transformation from 2D sheet to 1D scroll is the sublimation-induced scrolling of individually confined graphene sheets in ice, which was controlled by chemical reduction, feed concentration, and freezing rate. GNSs exhibited high structural integration and were solution-processed into macroscopic forms. We also revealed the spontaneous swelling behavior of GNS in a reversible manner for the first time, verifying the featured open topology of GNS. Through this combined protocol, GNS can be scalably synthesized from massive graphene oxide with high efficiency, which should promote comprehensive research and massive applications in the real world.