One-step fabrication of platelet-shaped Janus supraparticles via spray-drying

Supraparticles, i.e. assemblies of nanoparticles, can be classified as Janus supraparticles if they comprise two different types of nanoparticles that are asymmetrically distributed within the supraparticles. Due to their anisotropic character, they exhibit a high potential for various applications. However, the development of a scalable and material-wise flexible method to fabricate Janus supraparticles is still a challenge. In this work, a one-step synthesis of Janus supraparticles via spray-drying is reported. The segregation of binary particle dispersions during droplet evaporation, the tunable hollowness of supraparticles, and their fragmentation due to mechanical forces in the cyclone are exploited to fabricate platelet-shaped Janus supraparticles. By varying cyclone types, weight and diameter ratio between large and small nanoparticles of binary dispersions, their solid content and ionic strength, an optimized parameter setting is achieved. The obtained understanding of how to fabricate Janus supraparticles from binary silica model dispersions is transferred to mixed silica, iron oxide, titania and alumina supraparticles. This work opens a door for fabricating platelet-shaped Janus supraparticles in a fast and scalable manner.