Novel inkjet droplet method generating monodisperse hollow metal oxide micro-spheres

• Inkjet system was used to generate hollow metal oxide particles.
• PSL particles as template material were evaporated by heating.
• Hollow particles have 41–85 nm sized pores on the surface.
• Hollow particle size can be controlled by adjusting droplet size.
• Hollow TiO2 was demonstrated as a photoelectrochemical cell.

A novel method to synthesize monodisperse hollow TiO2, SnO2 and ZnO microspheres was developed. Water droplets generated from an inkjet nozzle contain clusters of polystyrene latex (PSL) particles covered with metal oxide nanoparticles were continuously dried up forming PSL clusters decorated with metal oxide nanoparticles. By heating the clusters up to 400 °C, the PSL particles are evaporated forming hollow spheres. Monodisperse hollow TiO2, SnO2 and ZnO spheres in the size range of 5.1–8.6 μm were consequently generated with a narrow particle size distribution. And the hollow TiO2, SnO2 and ZnO spheres have 41.0 nm, 30.0 nm, and 85.3 nm sized pores, respectively. The method enables us to have simpler and faster process to generate hollow TiO2, SnO2 and ZnO spheres and to control the diameter of hollow spheres easily by adjusting waveform applied to a nozzle compared to other processes. A potential applicability to photoelectrochemical cells was demonstrated for the prepared hollow TiO2 grown a Si substrate.