Simple and scalable synthesis of urchin-like ZnO nanoparticles via a microwave-assisted drying process

The urchin-like nanoparticles of semiconducting oxides have been attracting considerable attention as they can significantly improve reactivity owing to their enlarged surface areas. Herein, we report a simple and scalable synthesis method of ZnO nanomaterials via a microwave-assisted drying process. Commercial ZnO powders (~300 nm) and expanded graphite were used as starting materials to prepare urchin-like ZnO nanoparticles with nanoscale legs (diameter ~20 nm) by triggering the rapid phase transformation, which was induced by a repeated microwave irradiation in an alumina crucible for a few minutes. The possible mechanisms to trigger this morphological and dimensional change are described in detail. The high-yield production and superior reproducibility completed in shortened processing times enable this synthetic route to be widely applicable for the massive production of nanostructured oxide particles.