Preparation of hollow titania spheres and their photocatalytic activity under visible light.

Hollow titania spheres with different shell thicknesses were facilely prepared starting from TiCl4 and using ploystyrene methyl acrylic acid latexes as the sacrificial templates. The average diameters of the hollow titania spheres ranging from 294 to 340 nm were tuned by changing the weight ratios of TiO2 to ploystyrene methyl acrylic acid latex from 0.8:1 to 1.4:1. The hollow titania spheres were constructed by the small-sized anatase TiO2 nanoparticles with the average diameter of ca. 18 nm (SEM). In addition to UV light absorption caused by the primary anatase TiO2 nanoparticles, the hollow titania spheres also had visible light absorption performance. Photocatalytic results showed that all the hollow titania spheres had higher photocatalytic activity for the degradation of phenol under visible light irradiation than the commercial TiO2 nanoparticles (P25). The photocatalytic activity of the hollow titania spheres increased with the increase in sell thickness, being consistent with their visible light absorbance. The visible light photocatalytic activity was probably due to the presence of additional energy levels between valence and conduction bands, which were caused by the formation of oxygen bridging bonds between the primary TiO2 nanoparticles.