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

Abstract

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.