Formation of Na_0.44MnO₂ Nanowires via Stress-Induced Splitting of Birnessite Nanosheets

High aspect ratio Na_0.44MnO₂ nanowires with a complex one-dimensional (1-D) tunnel structure have been synthesized. We found that the reaction went through layered birnessite nanosheet intermediates, and that their conversion to the final product involved splitting of the nanosheets into nanowires. Based on our observations, a stress-induced splitting mechanism for conversion of birnessite nanosheets to Na_0.44MnO₂ nanowires is proposed. The final and intermediate phases show topotaxy with 〈001〉_f//〈020〉_b or 〈110〉_b where f represents the final Na_0.44MnO₂ phase and b the intermediate birnessite phase. As a result of their high surface areas, the nanowires are efficient catalysts for the oxidation of pinacyanol chloride dye.