Spatially confined growth of Bi2O4 into hierarchical TiO2 spheres for improved visible light photocatalytic activity

Bi2O4 is a promising visible light responsive photocatalyst but its application is limited by the large particle size and fast recombination rate of charge carriers. Herein, the flower-like hierarchical TiO2 sphere with rich mesorpores and macropores was used as the framework for the space-confined growth of nanosized Bi2O4, creating enormous Bi2O4/TiO2 type II heterojunctions and enlarging the interfacial contract areas between Bi2O4 and TiO2. Benefitting from these outstanding features, the photocatalytic activity of Bi2O4/TiO2 heterojunction for the degradation of methyl orange is much higher than that of pure Bi2O4 under visible light. The greatly improved separation efficiency of charge carriers that derived from the heterojunction and the shortened transfer distance of photogenerated charges from interior to surface of nanoscaled Bi2O4 are responsible for the enhanced photocatalytic performance. In addition, radical capture experimental results imply that hole is the dominant reactive species for the degradation of methyl orange.