Porous TiO2 hollow spheres by liquid phase deposition on polystyrene latex-stabilised Pickering emulsions

Hollow TiO2-composite spheres in the size range of 50 - 150 mum were prepared by liquid phase deposition on template assemblies of self-organised PS latex particles. These assemblies spontaneously formed on the surface of octanol droplets in an oil-in-water emulsion, the overall process resembling the stages of natural biomineralisation. The TiO2-polymer composite capsules were converted into highly porous inorganic spheres by dissolution of the PS template particles and calcination at various temperatures. Removal of the organic template was monitored by DTA/TGA and He-pycnometry. The microstructure of the TiO2 films was characterised by nitrogen sorption and XRD measurements. The calcination temperature dependence of the photocatalytic activity of the hollow spheres was assessed by UV induced degradation of DCA. High photocatalytic activity was observed after calcination at 200 degreesC due to a high specific surface area of the film and the formation of micropores and mesopores in the size range <4 nm. Calcination at higher temperatures leads to the formation of larger mesopores and a drop in the photocatalytic activity due to a decrease in specific surface area and the disappearance of pores <4 nm. A major fraction of the deposited film consists of crystalline TiO2 in anatase modification. Further crystallisation and crystal growth at higher calcination temperatures has only minor influence on the photocatalytic activity.