Macroscopic Graphene Oxide Hollow Spheres

Inspired by soap bubbles, millimeter-sized graphene oxide (GO)-stabilized bubbles are produced by blowing air into an aqueous suspension containing GO and surfactants. The bubbles are air-dried to form self-supporting hollow spheres with an exceptional diameter-to-wall thickness ratio of 65,000, corresponding to the ratio between the macroscopic diameter and microscopic wall thickness, and an ultralow density of 0.16 mg/cm³. During drying, the GO suspension self-assembles into lamellar, nanometer-thin GO walls, which prevent bubbles from bursting due to gravity drainage. In the hydrated state, bubbles can be pierced and loaded with particles that remain encapsulated in the hollow spheres upon drying. After thermal treatment, the resulting reduced GO (rGO) hollow spheres can be coated with a multilayer poly(ethylenimine)/GO shell that inhibits gas transport. Macroscopic GO and rGO hollow spheres are appealing for many potential applications and exemplify the unique self-assembly properties of 2D materials.