Preparation of fracture-free, uniform, crystallized titania hollow nanospheres by spray pyrolyzing core–shell seeds

Crystalline hollow nanospheres that are potentially applicable for optical, catalytic, and electronic devices have been generally synthesized by wet chemical approaches with multiple steps. Colloidal aerosol pyrolysis is a valuable approach producing crystallized hollow nanospheres with mass-production, minimum manufacturing steps, and less chemical usage than conventional wet chemical methods. However, conventional gas phase pyrolysis strategy has unsolved critical issues when synthesizing uniform shell-type nanoparticles including uncontrollable fracturing by sharp thermal shocks and material shrinking during crystallization. In this manuscript, the shell fracture in the gas phase continuous process is eliminated utilizing two stage pyrolysis which removes significant stresses from thermal treatment and gas emission. Advantages of solution chemistry and gas phase continuous process are combined by exploiting colloidal spray pyrolysis with two stages, therefore enabling continuous synthesis of uniform hollow spheres accompanying with organic core burning and nanoshell crystallization without fracture.