Synthesis of anatase titanium dioxide nanocaps via hydrofluoric acid etching towards enhanced photocatalysis

Anatase titanium dioxide (TiO 2 ) nanocaps were created via a four-step process including the preparation of SiO 2 spheres, the deposition of a TiO 2 layer to fabricate SiO 2 @TiO 2 composite spheres, the calcination for obtaining the crystal structure of anatase phase, and hydrofluoric acid (HF) etching to dissolve SiO 2 cores. The SiO 2 @TiO 2 spheres calcined at 700   °C revealed fine photocatalytic activity. Interestingly, most of samples transformed into TiO 2 nanocaps via HF etching, and TiO 2 nanocaps prepared using optimal conditions exhibited quick degradation ( k is 0.052   min −1 ) compared with commercial P25 ( k is 0.030   min −1 ) and the TiO 2 nanostructures etched by a NaOH solution. The excellent photocatalytic performance is attributed to its unique hollow hemispherical nanocaps structure, which is in favor of making full use of incident light. The photocatalysis phenomenon in visible light was also observed after depositing Au nanoparticles on anantase TiO 2 nanocaps.