Controllable location of Au nanoparticles as cocatalyst onto TiO2@CeO2 nanocomposite hollow spheres for enhancing photocatalytic activity

Visible-light-driven photocatalysis as a green technology has attracted a lot of attention due to its potential applications in environmental remediation. Although TiO2 is the most popular photocatalyst, the lack of visible light utilization and a low efficiency of electron-hole separation should be overcome. Therefore, Au nanoparticles (NPs) as cocatalyst were controllably loaded between the double-shell or into CeO2 shell (as photocatalyst and oxygen buffer) and then a novel visible-light-driven TiO2@CeO2 nanocomposite was prepared, using functionalized polystyrene spheres, sol-gel, hydrothermal reaction, and calcination. The presence of TiO2 shell, Au NPs and CeO2 shell were confirmed by EDX and electron energy loss mapping analysis. Under visible-light irradiation, the photo-degradation rate constant k (min(-1)) was in the order of TiO2@Au@CeO2 (0.026) > TiO2@CeO2/Au (0.021) > TiO2@CeO2 (0.014) > CeO2 (0.0091) > TiO2 (0.0046) > P25 (0.0034). Compared with P25, TiO2@CeO2, and TiO2@CeO2/Au, the visible-light photocatalytic activity of TiO2@Au@CeO2 for the photo-degradation of organic pollutant and photo-reduction of Cr(VI) were the highest. This result was attributed to the combination of TiO2 and CeO2, the double shelled and sandwiched nanostructure and the addition of Au NPs as electron trap site and surface plasmon resonance-sensitizer, which could reduce the recombination of the electron-hole and induce the visible light absorption. The major obstacle of heterogeneous photocatalysis could be resolved. The photo-degradation rate of 95% was achieved by TiO2@Au@CeO2, which exhibited an increase of 63% compared to Degussa P25 TiO2. The photo-degradation activity of TiO2@CeO2/Au was improved by Au NPs loaded on outer shell of TiO2@CeO2/Au but limited by their stability. This work confirmed the importance of controllable location of the noble metals as cocatalysts. (C) 2016 Elsevier B.V. All rights reserved.