Scalable synthesis of smooth PS@TiO2 core-shell and TiO2 hollow spheres in the (sub) micron size range: understanding synthesis and calcination parameters

Abstract

Hollow spheres made from titanium dioxide (TiO2) are interesting structures because of their high surface area and low density, combined with semiconducting properties of the TiO2. However, the synthesis is still challenging because of the high reactivity of the titania precursors. Here, we present a simple, reproducible, and scalable way to synthesize TiO2 hollow spheres in the micrometer/sub-micrometer size range comprising three steps: synthesis of polystyrene template particles, growth of TiO2 shells, and calcination to hollow spheres. We investigate the importance of adjusting the seed particle surface functionalization via the appropriate choice of comonomer during the dispersion polymerization. An aging step and a calcination process at low temperatures are mandatory to retain the particle integrity during the seed particle removal. We provide a detailed characterization of each step of this process including electron microscopy, small angle X-ray scattering, and simultaneous thermal analysis. [Figure not available: see fulltext.].