Surface‐Initiated Redox Route to Hollow MnO₂ Nanostructures

Abstract Nanostructured MnO₂ are gaining great research interest because of their wide applications ranging from optical and electronic devices to energy storage and catalysis. However, the formation of a well‐defined MnO₂ coating on the surface of various colloidal objects has been challenging due to surface incompatibility. Here, we report a unique and robust surface‐initiated redox route to the controlled deposition of MnO₂ on colloidal particles, which can be employed to produce high‐quality hollow MnO₂ nanoshells and a variety of MnO₂ coated nanocomposites. Colloidal resorcinol formaldehyde (RF) resin spheres serve as both reducing agents and sacrificial templates to initiate the controlled deposition of MnO₂ on their surfaces. Further, the RF resin can also be coated on the surface of other colloidal nanostructures to allow overcoating of MnO₂ through the redox reaction and produce nanocomposites such as SiO₂@MnO₂ and Au@MnO₂. The size and thickness of the MnO₂ nanoshells can be tuned precisely to induce resonant Mie scattering, leading to bright colorations that can shift reversibly in response to the changes in the refractive index of the surroundings.