Exploring the Enhancement of Photocatalytic Performance in TiO2 Based Hollow Composites: Size Effect of the Adsorbed CeO2 Particles

AbstractThe photocatalytic (PC) behavior of CeO2–TiO2 hollow composites with different heterojunction structures are investigated. The composites are fabricated by combining TiO2 hollow spheres and CeO2 nanoparticles with changing the ratio between Ce and Ti. High‐resolution microscopic and spectroscopic analysis demonstrates that three types of cerium‐bearing structures form on the surface of the titania. The first involves Ce atoms adsorbed onto the surface of TiO2 particles. The second occurs with small CeO2 particles, ≈2 nm in size, resulting from the aggregation of the adsorbed Ce atoms, thus forming a CeO2–TiO2 heterojunction. The last type is obtained through the growth of the CeO2 particles up to 10 nm in size. All the CeO2–TiO2 composites exhibit enhanced photocatalytic degradation of methyl orange under visible light irradiation compared to mere CeO2 or TiO2 nanoparticles. The synergistic effect of these three structures leads to a competition between size effects and interface interactions, which affects the band alignment, the number of defects, and, consequently, the PC activity. The highest PC reaction rate constant under visible light reaches up to 0.017 min−1 and is achieved when the CeO2 nanoparticle size is smaller than its Debye length.