Urchin-like AlOOH nanostructures on Al microspheres grown via in-situ oxide template

• We present a simple, scalable method to grow urchin-like AlOOH on Al microspheres.
• Al2O3 nanoparticles from the native oxide films and self-assemble to form templates.
• Urchin-like nanostructures spontaneously form and growth on the Al2O3 templates.

Three dimensional (3D) metal oxide hydroxide nanostructures are highly desirable for numerous applications. Here, we present a simple, scalable method to grow urchin-like AlOOH nanostructures on the surface of Al microspheres. Al nanoparticles with native oxide film were melted in molten salts, forming an immiscible materials system. During ultrasonic processing of the mixture, emulsion of micro Al droplets occurs and Al2O3 nanoparticles form from the native oxide films and self-assemble to form in-situ nanostructured templates on the surfaces of Al microspheres. When the solidified mixture of Al spheres and salt is exposed to water, urchin-like nanostructures spontaneously form on the Al microspheres due to a heterogeneous nucleation and growth of γ-AlOOH on the Al2O3 templates. This work could be readily extended to other metals, providing a novel and scalable method for the fabrication of urchin-like metal oxide hydroxide nanostructures on metal microspheres.