Inflating Strategy To Form Ultrathin Hollow MnO<sub>2</sub> Nanoballoons

Ultrathin MnO<sub>2</sub> hollow nanoballoons (UMHNBs) have a large ratio of interfacial to total atoms, corresponding to expected improved performance. However, their synthesis is a challenge due to difficulty in controlling the concentration of the unit cells. Herein, we describe a strategy to synthesize dry intact UMHNBs through a one-step synthesis by inflating MnO<sub>2</sub> (reduced from KMnO<sub>4</sub>) with CO<sub>2</sub> (oxidized from single-layer graphene oxide nanosheets) followed by instant freeze-drying. UMHNBs are 30–500 nm in diameter with a shell thickness of 3.7 nm, packing with laminar [MnO<sub>6</sub>] unit cells in the form of δ-MnO<sub>2</sub>. UMHNBs show efficient catalytic activity for decomposing the organic dye methylene blue (MB), 15 times the biggest reported value, and have long-term catalytic efficacy and durability. The described strategy in this paper makes use of graphene nanosheets to assemble durable ultrathin hollow nanoballoons.