Breathable, water-repellent γ-MnOOH nest production by vapor-assisted conversion

Abstract

Bird nests, formed by slender, semi-flexible twigs, are lightweight, freestanding porous frameworks with excellent permeability to gases and liquids. Translating this concept to microscale inorganic materials promises a broad impact on engineering and biomedical applications. However, constructing freestanding porous architectures from rigid one-dimensional (1D) particles remains challenging due to the directional processing and sparse interparticle contacts. To overcome these limitations, an in situ route for growing high-aspect-ratio 1D crystals within powder compacts is developed, yielding abundant, randomly oriented interparticle contacts. Exposing MnCO₃ to H₂O₂/H₂O vapor at 200 °C drives vapor-assisted oxidative conversion to γ-MnOOH, producing hierarchical, nest-like porous frameworks. The resulting γ-MnOOH bodies exhibit high water permeability (≈140 L m⁻² h⁻¹) and rapid evaporation (0.45–0.56 L m⁻² h⁻¹ at 40 °C), and simple postsynthetic surface modification imparts water repellency (contact angle of 169°). Because oxyhydroxides are versatile precursors for ceramic oxides, this approach provides a platform for entangled, binder-free inorganic architectures. This establishes a scalable and straightforward route to breathable porous materials, guided by the design logic of nature.