Hierarchical nanosheet-assembled yolk–shell TiO2 microspheres with improved photocatalytic activity

Nanosheet-assembled yolk–shell anatase TiO2 microspheres were synthesized utilizing the slow hydrolysis of K2TiO(C2O4)2 in a mixed solution of H2O2 and HNO3. Under a temperature near to the ambient one, microspheres assembled with nanoparticles were firstly obtained at the early reaction stage. Prolonging the reaction duration led to the formation of urchin-like microspheres, which further developed into nanosheet-assembled yolk–shell microspheres through a dissolution–precipitation procedure. The intermediate acid washing and final calcination transformed the microspheres to phase-pure anatase TiO2. The yolk–shell anatase microspheres exhibited a photocatalytic activity twice that of the urchin-like microspheres when utilized to assist the photodegradation of both rhodamine B and phenol in water under the illumination of UV light.