Morphological Evolution of Two-Dimensional MnO<sub>2</sub> Nanosheets and Their Shape Transformation to One-Dimensional Ultralong MnO<sub>2</sub> Nanowires for Robust Catalytic Activity

This paper reports the nucleation and growth of 2D δ-MnO<sub>2</sub> nanosheets from a simple wet chemical reaction at low temperature. The reaction between aqueous KMnO<sub>4</sub> and pure ethyl acetate constitutes a new a biphasic platform for product evolution. Then the synthesized δ-MnO<sub>2</sub> nanosheets undergo shape transformation to 1D α-MnO<sub>2</sub> nanowires in the same pot via a dissolution–recrystallization mechanism. The detailed growth mechanism of nanosheet formation and the morphology transformation are described in this paper. Moreover, this low temperature technique can be used to produce ultralong α-MnO<sub>2</sub> nanowires in industrial amounts which are difficult to synthesize by conventional high temperature methods. In this method, we have prepared 25.00 g of α-MnO<sub>2</sub> nanowires in our nanomaterial laboratory from 18 batches. Lastly, solvent-free catalytic activity of α-MnO<sub>2</sub> nanowires is investigated for the hydrolysis of benzonitrile to benzamide in one step.